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Engine Operation and System|
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Operations;
Content
Fuel Management; ......10 Reasons Engine Failures Occur;
The Engine; ...Rethinking
Engine Operation; ...Squared
Power Settings; ...Getting
Old.; ...Engine Systems;
In an
Hour;
Use
of Aluminum; ..Engine History; ...Pilot
Training; ...Preflight
Neglect;
Fuel Problems;
Fueling;
Fuel
Weight;
Engine TBO; ...Engine Operation;
Constant
Speed Propellers;
Constant
Speed Cruise Operations;
Propeller
Revisited;
Turning the Propeller
by Hand;
Primer;
Engine
Maintenance;
Trend Monitoring;
Engine
Savers;
Engine Operations to
Avoid; ...Using
the Engine; ...Ground Running;
...Cold Weather Operations; ...Power-Off Descents;
Ways
of Losing Power;
Engine Warnings;
Top Overhaul; ...Factors
Reducing Engine Power; ...Valves; ...Breaking in an Engine; ...Exhaust
System;
Drag and cooling;
...Shock Cooling; ...Engine
Heat;
Engine Cooling;
...Magnetos; ...Opinion
on Magneto Check; ...Engine Won't
Stop; ...Magneto Revisited;
...P-Lead; ...Distributor;
...Spark Plugs; ...Ignition
Problems ; ...Carburetors; ...Carburetor Revisited; ...Fuel
Injection;
Carburetor Heat;
...Air Intake; ...Vacuum
Pump; ...Engine Monitor; ...Oil
by Grade; ...Oil;
Oil
by Exxon; ...Oil Filter;
Oil
Analysis; ...Oil
Pressure Gauge; ...Oil Temperature Gauge;
Lubrication; ...Cylinder
Head Temp Gauge;. ...Carburetor Temperature
Gauge; ... Tachometer;
RPM;
...Engine Isolators;
Lycoming
Shut Down;
Fuel Efficiency;
Tire History; ...Basics
of Tire Construction;...Tire Classification;
..Tire Care;
Flying
with Pressure;
Altitude Standards;
Altimeter Accuracy;
Altimeter Readings;
...Pressure Altitude;
Rusting
Out;
Aviation Workplace Hazardous
Materials;
Turn Coordinator;
Knowing the Systems;
AVgas vs
MOgas; ...Water in Fuel; ...Filling a Knowledge
Vacuum; ...Accelerator Pump; ... Oil
Revisited; ...Dripping Fuel; ...Detonation;
...Preignition; ...Engine
Monitors; ...On Condition; ...Re-Engine
or Not; ... Operational
Procedures for Making an Oil Change; ...
Fuel Management
The 3 -F’s
Fly - Find - Fix
Contamination Most likely water…always sump tanks
Exhaustion…don’t run tanks dry
Starvation…Fly by time
10
Reasons Engine Failures Occur
1, Fuel starvation i.e. pilot neglect or error
2. Induction system i.e. maintenance or preflight neglect
3. Ignition system i.e. plugs or magnetos
4. Miscellaneous maintenance i.e. nut missing
5. Cylinder valve failure i.e. improper leaning
6. Fuel system operation i.e. selector to off
7. Carburetor ice i.e. failure to apply until late
8. Fuel contamination i.e. water and such
9. Inadequate lubrication i.e. pilot neglect or error.
10. Major internal failure i.e. metal fatigue.
The Engine
The four-stroke/cycle engine was invented by N.A. Otto in
1876. His engine operated by having a piston sliding in a cylinder.
The piston has a connecting rod fastened inside the piston and
extending to a crankshaft which in an airplane has the propeller
on one end. The reciprocating motion of the piston is changed
into the rotation of the propeller. The aircraft engine develops
full power for 90% of 2000 hours during which the comparable
life of an automobile engine is developing 20% power for slightly
over 100,000 miles. Most propellers have from 50 to 87% effective
thrust.
The four cycles of the piston are timed to the opening and closing of valves with the spark to a sparkplug. The first stroke draws fuel through the open intake valve, the second stroke closes the valve and compresses the fuel to make it volatile. The explosion of the fuel on the piston head gives the engine its power. The fourth stroke gets rid of the residue of the explosion and is called the exhaust stroke.
All the letters and numbers of an aircraft engine tell the
significant things about the engine. An "I" in its
title shows that the engine has a fuel injection instead of a
carburetor fuel system. O says that the engine is a horizontal
opposed with the cylinders flat and in pairs opposite to each
other. The number following the 0 is the total piston displacement
volume in cubic inches. Different aircraft engine manufacturers
have different lettering and numbering systems.
Single-engine planes have two to five degrees of downward tilt
to the engine from the horizontal. This is the reason the rudder
is the first positive control during takeoff. This also keeps
the propwash away from the horizontal-tail and reduces the pitch
changes that occur from power changes. This also serves to reduce
the noise of singles when compared to twins.
There are several ways to learn about how engines operate. There are videos, reading, and actual taking apart a small engine. Visit a maintenance show where the engine is opened up so you can see the parts and get an idea of what the insides look like. Los Banos has such a shop.
Lycoming Model Codes for Reciprocating Engines
Each engine designation is made up of a prefix of a series of
letters, a three-digit number and a suffix, which combines letters,
and numbers. Some examples:
TO 360 C1A6D
IO 540 AA1A5
IO 360 A3B6D
PREFIX DISPLACEMENT SUFFIX
L - Left-hand rotation Cubic-Inches A - Power Section & Rating
crankshaft or
AA
T - Turbocharged
(exhaust gas driven) 3 - Nose Section
I - Fuel Injected B - Accessory Section
G - Geared (reduction gear) 6 - Counterweight
Application
S - Supercharged (mechanical)
D - Dual Magneto
V - Vertical Helicopter
A - Aerobatic
AE - Aerobatic Engine
O - Opposed Cylinders
Rethinking Engine Operation
BFC-Brake Specific Fuel Consumption a measure of fuel economy
CHT Cylinder Head Temperature hottest to the rich side of peak.
ICP Internal Cylinder Pressure highest pressure near CHT peak. Sets engine temperatures.
EGT Exhaust Gas Temperature gauge is rich-peak-lean as fuel/air
proportions set.
POH Pilots Operating Handbook is a frequently not a consumer oriented
source of engine operation.
--Common EGT setting 50-degrees on rich side of peak (ROP) is a compromise of efficiency and power.
--Best power occurs 125 degrees on rich side of peak. Excess fuel cools engine. Uses more fuel.
--Lean Side of Peak (LOP) flown with a cooler engine and no damage, less
fuel, less power and fly further.
–It will cost you money to get the exact leaning numbers for your engine
Squared Power Settings
---25 inches at 25000 rpm is a fallacy in power management
---Radial engines can be damaged at high manifold pressures and low rpm
---Lindbergh taught WWII pilots how to fly manifold pressures and rpm in the
P-38 which had inline engines.
Range was increased from 500 to 950 miles. That’s how we shot down Yamamoto.
---Unable to get a security clearance due to his forecasting a German victory
before WWII, Lindbergh flew 50
combat missions in the Pacific as a manufacturer’s representative.
---Use the POH numbers and you will find the may over-square settings are
acceptable.
---Over-square has FAA approval as written in Accident Prevention Publication
87-40-28
---FAA says set power for smooth running and low noise.
---General rule is that low rpm causes less vibration, noise, heat, and wear.
---Longer engine life is sure to follow.
---Best operation will vary from aircraft and engines
---Exception apply to takeoff, engine break-in with high rpm required.
Getting Old
Engines deteriorate slowly and deceptively. The trouble will
be structural due to excessive temperature or operational in
one of the four operational systems; ignition, lubrication, carburetor,
or cooling. 22% of aircraft accidents are the result of engine
failure. Only 10% are due to mechanical failures. Of these 4%
is only a partial loss of power. 12% are the result of running
out of fuel to the engine and carburetor ice.
--Know what normal is.
--Is something not right?
--How is control response?
--Can the malfunction be corrected from the cockpit?
Engine
Systems
Ignition
Carburation
Fuel
Lubrication
At 2400 rpm
piston up/down 40 times second
valves open/close 20 time second
sparkplug fires 20 times second
In
an hour
Crankshaft 144,000 revolutions
Pistons reverse direction 288,000 times
In 1800 hours (engine life) propeller will turn 259,200,000 times
Use
of Aluminum:
Lighter than steel
Changes with heat more than steel
Good ability to transfer heat
Parts of uneven thickness heat and cool unevenly causing stress.
This stress will weaken and eventually crack given enough time.
This stress can be reduced by slowly heating and cooling engine
Engine
History
(AC No: 20-105B 6/15/98)
The history of engine operation reveals that there has been little
change in the causes of small single and multi-engine aircraft
engine failures over the past forty years. 51% of all engine
failures are directly related to pilot error related to preflight,
inspection, or use of controls. Training programs could have
prevented 70% of all engine failure accidents for pilots, mechanics,
and trend monitoring.
The J-3 Cub, and an Aeronca Champ, had the same Continental engine.,. This engine was later modified from 65HP to 100 HP and became the O-200 found in Cessna 150's. the O-200 is a carbureted engine with the carburetor below the engine in front of the oil tank. This keeps the induction system cool and allows a little more power because of the cooler air in the cylinders. It also makes carburetor icing more likely. Flying behind a small Continental requires the application of full carburetor heat before throttle reduction.
In the sixties, Piper came out with a trainer modified from the Tri-Pacer series. This "Colt" had a Lycoming four cylinder engine. Lycoming engines had the camshaft above the crankshaft instead of beneath it like the Continental. This allowed a large oil pan on the bottom of the engine. By running the induction system right through the middle of the hot oil in the pan it let the engine to run a little cooler. An additional benefit was that it heated the air/fuel mixture. With Lycoming engines, you don't need use carburetor heat overtime.. The POHs said to add carb heat only if there was some sign of icing. The Lycomings are in all later Piper models. Piper pilots were occasionally surprised by icing when they failed to add carb heat on downwind.
All modern training aircraft use the Lycoming engine. The Cessna 150 was changed to the Cessna 152 to note the engine change. The early C-172's used the Continental O-300 which is a spin off of the O-200 in the C-150 with two more cylinders. It also has the ice problem of the O-200. The Lycoming C-172's do not have ice problems.
Pilot Training
--Use of operating manuals with emphasis on fuel management,
power settings, carburetor heat and systems design, location
and controls.
--Adherence to operational instructions, placards and limitations
--Use of checklists during normal and emergency situations.
---Recurrent training related to replacement parts, airworthiness
directives and technical publications.
--The correct use of the primer must be a part of all checkouts
and instruction. The primer pumps fuel to one or more cylinders
in un-vaporized liquid. Failure to set and lock the primer is
a frequent cause of a rough engine and engine damage. A cracked
primer O-ring can have the same effect even with the primer locked.
--The correct care of tires and oleo struts must be a part of
all checkouts and instruction. The oleo strut is a combined cylinder
of oil and air. The air is compressible while the oil is not.
Both of these are sealed at the top by an air valve and filler
cap and from below by a rubber O-ring. If the exposed part of
the oleo strut is not cleaned prior to every flight the accumulation
of dirt and grit will be ground into the O-ring. In a relative
short time the O-ring will be unable to seal either the air or
the oil and the strut will deliver any landing or taxiing shock
directly to the aircraft structure. No maintenance program can
overcome the destructive expenses of a poor checkout or pilot
training programs. Raising the costs of rentals can never keep
up with the costs of poor piloting.
Preflight
Neglect
1. Know total usable fuel aboard. Ignore unusable fuel.
2. Check and sump drain tank for proper color, debris, feel and
liquidity.
3. Check vents especially fuel cap vents.
4. Confirm operation of fuel selector in off position as well
as for fuel flow for selected tanks (Four minutes run time).
Fuel
problems
1. Water due to condensation, filler caps, rain, and
service personnel.
2. Wrong type or octane fuel.
3. Bladder tanks with defects.
Item:
A dead battery will show that you are out of fuel.
Fueling
1. Know exactly how much fuel you have prior to departure.
2. Know exact consumption rate
3. Know time in tanks
4. Develop fuel performance chart
5. Always plan to land with at least minimum reserves.
Grounding is a procedure to prevent the flow of electricity that is capable of producing sparks capable of igniting fuel. By grounding at least three minutes prior to refueling you give electricity time to balance the charge between the aircraft and the fuel service be it truck or pump makes no difference.. Once the balance is achieved the flow of fuel will not change the electrical equilibrium. When fueling over the wing be sure to touch the nozzle to an unpainted part of the fuel cap PRIOR to opening the cap.
Difficulties are simple and easy to understand. Prevention
of occurrence is not so easy. Running out of fuel is not an expected
event. The pilot is usually very much aware of the situation
but lacks the mental discipline to choose a safe option.
1. Misinformation
POH numbers for capacity, consumption, fueling
2. Mismanagement
Tank selection errors, fuel caps, sump leaks,
3. Mechanical difficulty
Fuel pump, leak in pump, selector, electric pump, bladder problem
or gauge problem.
Survival rate after engine failure is 94%.
Maintenance related accidents are only 20% of total.
Two planes a week run out of fuel.
Not refueling when the opportunity exists is viewed by the FAA
as careless operation.
Fuel
Weight:
--At 32-degrees F gasoline weighs5.93 pounds per gallon.
--At 97s-degrees F gasoline weights 5.7 pounds per gallon
--Buy your fuel when it's cold.
--Prime as hard as you can to vaporize cold fuel into the manifold
system.
Engine
TBO (Time Before Overhaul )
An aircraft engine that is flown non-commercially can be operated
beyond the TBO recommended by the manufacturer. Once the choice
is made a program of regular oil analysis should be in place.
Oil analysis will give trend indication on engine wear and type
of wear. The bottom end of the engine, consisting of crankshaft,
camshaft, bearings and gears can be monitored by oil analysis.
The top end, consisting of cylinders and their components are
monitored by both oil analysis and compression checks.
1. Exceeding TBO will accelerate wear.
2. Part 121 and 135 operations cannot exceed TBO
Engine Operation
Thermal shock damage is caused by failure to warm up engine
prior to takeoff. Shock cooling damage is caused by failure to
prevent rapid cooling. Hot or cold temperature damages engines.
A normally aspirated engine can be throttled from idle to full
power without damage. Detonation is impossible if proper fuel
is used. Don't expect to hear or feel detonation. Aircraft should
be climbed at full power and maximum rpm. Engine temperature
is the controlling factor. At high power settings overly rich
fuel flows are unnecessary and wasteful. Injected engines do
not always distribute fuel evenly.
Excessive leaning may cause a cylinder operating so poorly that full power will not be produced.. The vibration dampers will not function properly unless occasional full power is used. You will not be able to feel or hear uneven piston operation. A six-cylinder engine may run smoothly even on five working pistons.
Engine operation is a fire triad made up of air, fuel and
ignition. Without all three in appropriate amounts the engine
will not function either at all or appropriately. To stop the
engine we eliminate one of the three. Icing of the air intake
may unintentionally cut off air. Fuel is commonly cut off by
filling the tanks with air. Turning of the magneto key
to off shorts out the P-lead of the magneto thus grounding out
the current that triggers the spark plugs.
Air is controlled by a butterfly valve in the carburetor. This
is valve is moved open and shut by the throttle control. A special
form of air is made available to the carburetor by the carburetor
heat control. Many aircraft have an additional alternate air
source for the engine. The durability and life expectancy of
an engine is build into the engine. How well it reaches these
levels is keyed into the suggested operating parameters, fuels,
lubricants, and maintenance recommendations.
Fuel flows through a collection of pipes and valves from the
tanks to the carburetor. Contamination is one of the causes of
a fuel failure. Water is a common contaminant. The fuel selector
and cut-off valve allows fuel to flow, change directions and
cut-off. I have been 'surprised' on the ground by discovering
that an occasional cut-off setting does not cut-off. Low-wing
aircraft have an auxiliary electric pump while high-wing aircraft
may rely just on gravity feed. For ease in starting a primer
pump is available to spray fuel into the induction system.
There are two ways engine operation makes a critical difference
in flying. There is little that can be done about the 70% of
engine wear that occurs in the first 30 seconds of after start
operation. You must avoid operation over 800 rpm. Proper operation
allows us to get the published performance and it prevents damage
caused by overheating, shock cooling and stress. Smooth power
changes is the first requirement. With fixed propellers we enrich
before power increases and reduce power before leaning. The POH
has a cruise performance table that covers a variety of settings
of RPM, pressure altitudes, temperatures and RPMs to be used
for selected TAS and fuel consumption expressed for a percentage
of horsepower.
Proper leaning can set engine power parameters for best range,
maximum endurance, best economy, best speed, or anything in between.
Best economy runs the engine at peak power. This is the top of
the EGT scale. The best power is slightly richer by about 100
degrees EGT temperature. This uses more fuel with a slight improvement
in airspeed. Modern engines can be operated with manifold pressures
of square or even over square (manifold pressure higher than
RPM) without harm. Cruise power settings lower than 75% can be
flown at peak EGT.
The standard leaning procedure is to lean by pulling the mixture
until the engine runs rough, and then turn it in until it smooths
out. If using an EGT, pull the mixture until the EGT gauge read
as high as it will go. You may need to reposition the EGT needle
if it goes all the way to the top. Once it has stabilized at
a high point that the engine has gone rough, enrich the mixture
to get at least a fifty-degree drop. Proper leaning will coincide
With a throttle back to full idle, fuel flow is set
by the idle adjust screw. Full idle is usually about 600 RPM
in light aircraft engines. At idle you cannot taxi nor keep the
engine running if the weather is cold.
Typically, 800-1200 RPM are the ground operating speeds. At these
power settings leaning has noticeable effect. You should lean
regardless of the fuel used. At these powers leaning can be done
until the engine coughs; then enrich a bit. An engine that dies
when you add power is a good indicator of correct low power leaning.
You cannot damage the engine by leaning It is possible to foul
the plugs if you do not lean enough, regardless of the fuel used.
By operating an engine at low temperatures with a rich mixture you are sure to reap a harvest of carbon deposits. With leaded fuel you will harvest lead deposits. Proper leaning will solve the carbon-fouling problem but will not prevent lead fouling. Only by keeping the engine temperatures high enough to keep all the lead vaporized can you prevent lead fouling. The leaner the mixture the hotter the engine and the less fuel to supply lead needing vaporization.
One of the most common operating problems is on starting. The throttle is in so far as to cause the engine to operate at relatively high power before the oil has had a chance to circulate. A surging engine start will cause excessive wear throughout the engine. Abusive operation may involve taxiing at high power and holding the brakes on to keep the speed down. This can use 50 hours of steel off the camshaft and scuff the pistons against cylinders. Keep the starting rpm low and let the oil work before moving. If it is cold the oil will be so thick that some oil passages will be plugged, you will get squirts instead of sprays and there won't be much splash for the splash-lubricated parts. High starting oil pressure is indicative of plugged passages.
If you have ever taken an air filter and cowling off and observed the action and location of the throttle (accelerator) pump vs the prime (look where the primer activated fuel goes in) you will see the wisdom of NOT pumping the throttle to prime. Also it is important to prime and then IMMEDIATELY turn the starter, as even he primer fuel will drain down to the carb and intake box. The intake box is where you DO NOT want the fuel to be. I am talking about typical Lycoming carb on the bottom trainers and the like.
Abusive engine operation creates thermal shock to the engine
and its parts. Ideally every engine would be preheated. 110V
preheat systems now exist. Pre-oilers are in existence. Every
cold engine start has metal to metal parts scraping each other
without oil film separation. Abrupt throttle operation, cowl
flaps, and rpm adjustments cause variations in heat and cooling
sufficient to damage even the most rugged of engines. Do what
it takes to keep the engine warm within its operating temperatures
and avoid extremes of heat and cooling.
Keeping an engine log can prevent some failures. Keep a record
of fuel flow, oil pressure, temperatures, and electrical readings.
Record oil consumption and changes. Have the oil lab checked
for metal to determine what and how much wear is occurring. Some
is normal but too much of one kind is significant. Poor lubrication
causes excessive wear.
You can take better care of your engine if you avoid those throttle
changes that cause sudden heat changes. Abrupt throttle movements
cause cylinder head, exhaust header and turbo cracks. A sudden
power application or sudden shut down (As when stopping) can
cause bearings to coke up, overheat and seize. Counterweights
can be de-tuned by sudden throttle movement.
Under certain conditions an engine may be unable to obtain fuel
to the carburetor due to vapor lock. If the fuel lines have curves
that allow the formation of hot air pockets the fuel may be unable
to force its way through the blockage. A hot engine compartment
may make it impossible to start the engine and under certain
conditions the blockage may exceed the ability of a pump or gravity
to move the fuel. A dent or a crimp in a fuel line can decrease
fuel flow ability. A dent in a fuel injector line is particularly
dangerous where takeoff performance is required.
A pilot who has predetermined power and configuration to be used
in a journey is reducing his piloting workload. He knows ahead
of time the Vy/Vy speeds to be used in climb. He has picked an
altitude for winds and fuel efficiency, he pre-plans his descent
to make the best use of altitude for airspeed, and arrives at
the pattern for an efficient arrival. Additionally, he knows
the trim, mixture and power changes before the needs occur.
The bible of engine operation is the POH but each aircraft model
year varies so only a POH specific to the aircraft and year should
be used. When an aircraft is a mixed breed such as having a later
engine different than that of the aircraft year, you must develop
your own POH.
Lycoming has some very specific suggestions for high performance
aircraft. Don't lean below 5000' when using climb power. Don't
reduce manifold pressure over five inches at one instance. Better
to do one-inch every one-minute. Maintain 15 inches during descent
with rpm set to lowest cruise to prevent piston flutter. Fixed
propeller operations should be limited to 400-rpm reductions
at a time. Descents faster than high cruise and more than 1000
fpm are not recommended.
Leaning is performed to get the maximum power with the best air to fuel mix. Excess fuel will cool the engine, but too much can dilute the oil needed to lubricate the cylinder wall. This causes excessive engine wear. An excessively rich mixture tends to foul plugs in smaller engines. A lean mixture will gives better power, but excessive leaning will cause higher temperatures in the combustion chamber.. Excessive leaning over a period of time can cause serious engine problems and lack of power. Aircraft with an exhaust gas temp gauge, (EGT) gives positive indicators in the leaning needed to attain best operation. Without the EGT lean by incrementally pulling the mixture until the engine noticeably loses power and then put the mixture in until you get the max rpm back. This setting is correct for a specific altitude for that time. Any other altitude or time requires new settings.
Partial power takeoffs are worse for engine than the use of
full power. Full throttle opens up a fuel jet that allows extra
(cooling and not used) fuel to enter the cylinders. This can
be demonstrated if you have a cylinder head temperature gauge.
Constant
Speed Propellers
The knob at the front of a constant speed propeller (inside
the spinner) is an oil piston that is controlled by the operation
of the propeller knob (blue). This knob controls the amount of
oil allowed into the piston. The piston sets the blade pitch
according to the amount of oil allowed into the piston.
The twisting moment of the blade resulting from centrifugal forced tends to decrease blade angle. This effect is offset by the oil pressure from the prop control governor which acts against the linkage to the blades.
Adjacent to the piston is a type of flywheel which is a combination of weights and springs. This flyball is rotated by engine crankshaft gears that also drive the governor. Should the propeller change speed for some reason the flyball will open or close oil passage accordingly to the piston. This will change the blade angle to reestablish desired speed. One of the best ways to see this in action is do face at right angles to a stiff wind. The propeller will cycle repeatedly in this situation. It also shows during run-up that you did not face into the wind for best cooling.
Propeller is always increased in rpm prior to addition of
power as when beginning a climb. Power is reduced before the
propeller when setting cruise. With constant speed propellers
we enrich and bring up the RPM before adding power. Reduction
of power reverses the process, power back, set the RPM and then
lean.
Propeller Governor
–Gear driven shaft that pumps oil and spins weights to control
opening according to engine speed.
--Oil flow is about 45 quarts per hour to control blades in a given position.
--Prop rpm control affects tension of spring.
--Is an oil pressure control on piston that moves blades.
--Pitch of propeller controlled by oil pressure on piston moving against a
spring.
--Oil flow stops when spring load on weights and oil pressure are in balance.
--Any change in pitch causes propeller speed to change and oil pressure adjust
pitch to maintain rpm.
--Unwanted lag or cycling. of propeller can be indicative of needed
maintenance.
--Maintenance is expensive primarily because of removal and installation
costs.
--Propeller of singles go to flat pitch with loss of pressure, twins + go to
feather.
--Made by Hamilton Standard, Hartzell, McCauley, Woodward and Garwin
Constant
Speed Cruise Operations
--Most efficient cruise is obtained by having a low RPM and
a lean mixture
--Use full throttle and use rpm to adjust power
--Greatest efficiency of fuel is 25-50 degrees to lean side of
EGT peak
--Climb with best power for less time in the climb while avoiding
overheating
--The greatest range efficiency for time is obtained at the altitude
where throttle is all the way forward.
--By reducing fuel burn by 20 percent you can increase range
by increasing time in flight by 40 percent.
Propeller
Revisited
--Almost all propeller failures are result of ignorance caused
neglect
--A propeller strike requires a non-destructive inspection
--Strike may damage crankshaft, propeller, counterweights, bearing
caps and more.
--Failure to tear-down is a dangerous option
--All aircraft types and models have had records of fatigue-crack
causes prop failures
--Always assume that the magnetos are hot when touching a propeller.
--Perform a magneto grounding check prior to shutdown.
--Propellers have limited life and should be given NDI (non-destructive
inspection)
--as required by manufacturer's specifications
Propeller deicing boots extend only part way up because any
longer would affect propeller efficiency. Outer part
of blade throws ice pretty well and stays warmer due to compression
of air.
Turning
the Propeller by Hand (Opinion_
Rule # 1: Always assume the mags are HOT! An ungrounded p-lead
will make it hot and you need to always treat
the prop as such.
Primer
Primer is a hand operated fuel injection system. It injects
fuel into the engine while bypassing the carburetor. The plunger
has a pin that is keyed to hold the primer in place during engine
operations. If the key is not properly locked in place the engine
will draw fuel through the primer and run excessively rich. I
know of a situation were the pilot failed to lock the primer
and several hours of mechanic time was spent trying to find the
problem.
Engine Maintenance
--Reliability is related to maintenance of oil/filter changes,
air/fuel filters, magneto timing, spark plugs, ignition harness,
baffling and seals.
--Any control cable housing should be clamped every 12 inches
to prevent and repeated flexing that will ultimately cause a
break. Pilot should be taught not to force any control into making
such a flexing pattern.
--Propeller ground strikes will not only damage the propeller
but the internal engine parts connected to the crankshaft. Taxiing
across a shallow drainage ditch while taking the runway can easily
flex the shock absorbers sufficiently to cause a propeller strike.
There are those who make a living on poor pilot techniques.
--Muffler internal failure can be abrupt or extremely gradual.
The former is easy to detect. The latter can be so insidious
as to evade any detection until aircraft performance degrades
as much as 30%. Adequate inspections every 100 hours should resolve
this problem.
--Within limits most propeller damage can be repaired. A qualified
mechanic or shop should do all repairs of even the most minor
dressing out of nicks and scratches. Limit any pushing or pulling
of the aircraft by holding as close to the spinner as possible.
Pulling from further out on a blade can give sufficient leverage
to create a stress riser (crack).
--A hard starting or 2-minutes rough engine usually indicates
a sticking valve. This is a major repair problem that if neglected
will lead to a total stoppage.
--The consistent fouling of spark plugs may indicate worn rings,
improper plug heat range, a shorted ignition harness, a cracked
cigarette (connects to top of plug), wrong fuel, or incorrect
timing. More likely it will be improper leaning during low power
operations and idle. Typically such fouling can occur during
full rich gliding descents where excessive cooling occurs.
--Unfiltered air ingested into the engine will cause severe damage
to the cylinder walls. The proper fit of the air filter is essential.
Use of carburetor heat on the ground should be limited to removal
or ice and heat checks
--Cylinder compression checks require replacement if readings
are below 60/80 psi. The ideal is 80/80. An experienced mechanic
either through the exhaust or at the air cleaner can hear air
leaks.
--Induction filter in good condition will screen out 98% of impurities.
--Mixed with dirt, oil becomes a powerful abrasive.
--Induction filters are best changed or cleaned every 25 hours.
--Some aircraft have alternate air doors that open if the filter
becomes clogged. Enter unfiltered air.
--As engine cools water vapors will condense and mix with the
oil in the crankcase.
--Corrosive exhaust products become acidic when mixed with water.
--Oil additives are blended into the oil to inhibit and neutralize
these acids.
Trend Monitoring
1. A trend monitoring can predict a failure mode before it
happens.
2. Internal engine deterioration can be determined by oil analysis.
3. Keeping a record of compression checks will track cylinder
condition.
4. Accessories such as magnetos, harness, spark plugs, exhaust,
alternator, belts, hoses, pumps should be removed for inspection
and testing.
5. A trend is only as valid as the RPM, oil pressure, oil temperature,
cylinder head temperature, EGT, fuel gauges and manifold gauge
are in giving accurate measurement.
Engine Savers
Starting a cold engine is just about the worst think you
can do to it. The colder it is the more damaging the start. The
culprit is lack of lubrication. Very little oil gets to the cylinder
walls during the first few critical revolutions. The cause is
lack of lubrication so that metal to metal contact results in
excessive bearing and ring wear, oil burning, and piston slap.
An engine seldom flown with long non-operation periods between
is subject to corrosion. Lycoming recommends over haul after
12 years regardless of use factors..
1. Use cylinder head temperature gauge. Gradual power reductions
2. Use slight power reductions for cruise descents
3. Avoid touch and goes on cold days
4. Carry power throughout landing approach
5. Be as slow and smooth on the throttle while doing airwork
as possible.
6. Keep mixture leaned until leveling off in pattern
7. What is good for the cylinders is good for the engine.
8. Use power only as required.
9. Minimize full power operations
10. Use oil analysis program
11.Follow manufacturers recommendations
Engine
Operations to Avoid:
--Rapid throttle movement
--Wide differences between manifold pressure and engine speed
--Excessive RPM and power
--Sudden cycling of the propeller
--Sudden stoppage
--Avoid inactivity over one week.
--Use low quality oil.
--Not keeping the air filter clean.
--Minimize ground running.
--Climb at speeds sufficient to cool engine.
--Avoid high speed descents.
--Practice good leaning procedures for all operations.
--The older the engine, to more it shows wear.
--Running past TBO increases wear rate.
Using
the Engine
--Aircraft engines are reliable but expensive to repair and
replace
--Improper care and poor operational practices keep aircraft
engines from making it to TBO.
--Engines wear out more from lack of use than from frequent and
heavy use.
--Rust and corrosion damage bare metal surfaces that do not get
the lubrication of frequent use.
--Oil, over time, will drain away from high to low and eventually
into the crankcase.
--After seven days of non-use the moving components will make
their first moves without oil.
--After fourteen days of non-use rust and corrosion occur.
--Rubber parts lose resiliency and become permanently deformed
when not flexed often
--Many non-metal parts require oil to 'wet' them to prevent drying
out.
--The engine has openings that allow hot gases to escape and
allow moisture into the unused engine.
--A minimum of 30-minutes at full cruise every seven days is
required.
--Ground run-ups do more harm than good. The engine never gets
hot enough to purge moisture.
Ground Running
--Air cooling takes place by way of the pressure cooling of the
relative wind.. Propeller is a poor second.
--The lack of cooling by ground operations is damaging the more
it is done.
--Facing the wind, minimize runup, no high power runups, low
idle before shutdown
--Propeller at fine pitch for all ground operations except when
cycling.
--Always open cowl flaps on the ground.
--Never run engines at high power with the cowling removed.
--Engine accessories are damaged by excessive ground running.
Cold
Weather Operation
--Aviation fuel is not blended for seasons. Excess priming
will wash cylinder walls of oil.
--Maintain idle speeds until engine warms.
Power-off
Descents
--High speed descents with rich mixtures can and will damage
cylinders.
--A windmilling propeller will drive the engine and detune the
counterweights or create internal flutter.
--Maintain enough power in descents to maintain temperature at
least to the bottom of the green.
--Lean mixture gradually during descent
Ways of Losing Power
Magnetos cause fewer that one accident a month. Most magneto
failures are due to neglected maintenance and servicing. As much
as 15% of engine power is lost through the application of carburetor
heat. The heat enriches the mixture thus causing the loss. For
every 10 degrees of heat above standard (59F) there is a one-percent
power loss. Application of preventative carburetor heat during
conditions conducive to carburetor ice requires leaning the mixture.
A dead or weakened magneto costs at least 3 percent of your available
power. Electrical leaks from the sparkplug harness will cause
a loss of power. This type of loss is more likely at altitude.
Plugs are connected to the harness by a "cigarette' like
connector. A dirty "cigarette" or plug barrel can cost
you two percent of your power. Never touch a clean "cigarette".
Loose intake manifolds let in air and lean the mixture when richness
is required as during takeoff and climb. If the carb heat flapper
valve in the air box does not make the proper seal it will cost
you power.
Engine Warnings
30% of single engine aircraft accidents involved a loss of
engine power. As an engine ages it loses compression. All cylinders
do not lose compression equally. When piston rings, cylinder
walls and exhaust valves fail to perform within design limits,
it is time for an overhaul. Any one of the above failings is
not going to cause an accident. Carburetors wear out and require
overhaul. Fuel pumps have an average life expectancy. Oil pumps
have a limited pressure adjustment. Cylinders operate at widely
varied temperatures due to uneven fuel flow. You have no way
of knowing about this without instrumentation.
Compression checks can be used to determine if the valves, and
rings, are producing adequate sealing. Excessive pressure escaping
reduces available power. The compression check is done with the
engine at operating temperature with readings made of all cylinders
using the starter to turn the engine. A 15-pound variation in
cylinder pressures is the maximum limit. Valve leakage is the
most common weakness. In addition to the compression check the
condition of the spark plugs are indicative of problems. See
spark plugs.
Low oil pressure is symptomatic of problems. If a bearing moves
from its proper position, more than the required oil will pass
by it and reduce the amount of oil for other parts. High-tech
oils may be too slippery for an older worn engine. Difficulty
in starting may be due to sticking valves that have warped due
to heat.
The sounds of the engine or its accessories from clanks to grinds
to whines are like cries of pain. A change in sound not caused
by throttle movement warns of greater problems to come later.
Get on the ground. You ability, as a pilot, to detect subtle
changes in performance, sound, or feel will give you time to
get down successfully. When the aircraft has engine-monitoring
gauges, learn what is normal. Any change from normal is a warning.
A change in an exhaust gas temperature gauge (EGT) or a cylinder
head temperature (CHT) gauge is indicative of combustion problems
in the cylinder.
One way to check the condition of an engine is by several different
compression checks. Applying 80 pounds of pressure to the cylinder
while measuring the pressure retained makes a differential compression
check. A 60/80 reading means that 60 pounds of pressure is retained
for the 80 pounds applied. The leakage can located by listening
at the exhaust pipe, induction air intake, breather tube or oil-filler.
A 20/80 reading or worse signifies a probability of a real problem.
A dynamic compression check has the plugs removed to allow starter
to attain a maximum speed. If one cylinder checks 15 pounds below
another there is a problem. Engine power is the result of good
maintenance. Total time on engine is not necessarily, indicative
of engine capability. Frequent oil changes are essential to engine
life.
Top
Overhaul
Top overhaul does not include rocker arms, pushrods and tubes
plus everything in the bottom of the engine-bearing, cams, gears,
bushing, and crankshaft. The top does not include the alternator,
starter, and other accessories. Top overhaul costs less than
half of a major overhaul. Lack of use is the most damaging factor
in engines. Without use engines die from corrosion and dry starting.
Excessive leaning is likewise bad on engines, since the engines
run hotter and heat is damaging to engines. Signs of needing
a top may be seeping oil, low cylinder pressure, oil consumption
or poor performance. The FAA does not consider a top as affecting
the TBO.
TBOs are best case and more often than not never reached. Engines
worked hardest seem to last longest. Optimum use is about 500
hours per year. Heat ruins engines so running too lean can cause
a heat problem. Break-in should be conducted at highest allowable
power setting with minimum at 75%.
Factors Reducing Engine Power
1. Carburetor heat/alternate air (-10%)
2. Temperature 1% loss for every 10 degrees above standard.
3. Rich mixture
4. Altitude (For each 1000' a 25% increase in takeoff distance.)
5. Single magneto operation causes 3% power loss.
6. Wet air merits additional 10% required takeoff distance.
Valves
The exhaust valves are most likely to give notice to the
pilot that there has been a heat, corrosion or stress problem.
Even though such values are made from nichrome, silchrome or
cobalt-chromium steel, pilot abuse can cause a failure of the
designed lubrication and resulting sticking or bending/breaking.
The valve face and seat are made from stellite for increased
resistance to the factors just mentioned while the valve stem
is likewise hardened. The valve is lifted and allowed to re-seat
by a cam on the engine driven camshaft and a return spring.
It is most likely that piloting practice has caused a valve problem.
Oil quality/quantity, leaning practices, and climb/descent procedures
affect engine cooling. Try to start an engine as slowly as possible.
This allows time for lubrication to build up pressure and penetrate
into the valve guides. Climb power uses excess fuel for cooling
but other flight regimes should be leaned so that excess fuel
does not put lead-sludge into the oil. Cylinder fins, fuel, baffles,
and throttle usage.
Valves usually stick in the valve guide. This shows to the pilot
by an engine hesitation or miss. Something is making it so the
valve cannot move freely. These may be bits of carbon or cooked
oil. Early detection and correction of sticky valves is important.
Breaking in an Engine
An engine or a piston that is new should not be run at low
power.
The proper seating of the piston rings requires sufficient
pressure to seat into the cylinders. The cylinder walls need
to be given a sheen that will allow the oil film to separate
the wall from the ring's surface. Any area that is not separated,
lubricated and cooled by oil will become hot. Heat is required
for engine operation, excessive heat is the greatest enemy of
continuous and successful operation. A proper break-in is essential
if an engine is to reach its design time before overhaul (TBO).
If the break-in allows lacquer and varnish to accumulate on the
surfaces of moving parts, you will have problems of oil consumption
and engine temperatures. Multi-viscosity mineral-based oils are
less likely to form lacquer and varnish deposits.
The way an engine is broken in has much to do with its ability
to reach its TBO. Many engines were run to failure to determine
a mean time before failure. (MTBF) This time was cut by 50% to
set an initial TBO time. TBO could be extended if experience
proved it safe. Most important factor in reaching or exceeding
TBO has to do with use and maintenance. Unused engines will accumulate
water, which mixes with the acids of combustion to cause corrosion
to the engines internal parts. Normal flight use will clean the
engine and allow the oil to carry off the corrosive acids and
will evaporate the moisture. The less an airplane is flown the
more frequently the oil should be changed. TBO is an average
that many well used engines can be expected to exceed. The principle
reason for changing oil is to remove oil containing suspended
impurities. An engine can be run past the TBO, but only in 100-hour
increments. This could result in a more expensive overhaul since
wear increases with age.
Given enough time heat, friction and load will wear even the
best-maintained engine down. The manufacturers estimate of engine
life is just that, an estimate of expected service life. An engine
that has regular changes of oil and filters may live an extended
life if flown regularly. Keeping records and track of the oil
condition helps. Baffles are essential to proper engine cooling.
Check their condition at every opportunity.
Well-maintained engines will start promptly. I quit cranking
if after six-blades the engine is not running. Cranking time
is the most trying time for an engine. Keep the engine filter
tight and in good condition and minimize C.H. on the ground.
Lean for taxi, and whenever you can to prevent excessive rich
mixture dilution of the oil. Don't force the engine to takeoff
power before it has a chance to warm up.
Throttle changes should be smooth and gentle. Avoid disuse that
can cause corrosion.
Exhaust System
The system is made as light as possible and formed to minimize
space at the lowest possible cost. Exhaust systems are subjected
to extreme temperatures, temperature changes, and vibration.
The exhaust takes away hot engine gases to prevent damage to
engine components and provide maximum breathing capability for
the engine. The aircraft manufacturer makes some systems while
the engine manufacturer makes others.
For smaller aircraft engines the system is made of 321 stainless
alloy. The average life of a system is about 1000 hours. Reparability
goes down with age. Important inspection areas require removal
of shields. Damage directly related to condition of engine isolators
(rubber doughnuts on engine mounts) and out of balance propellers.
Baffles of interior are weak spot. Best repaired by specialist
shop. White stains at cylinder heads indicate leaks. Critical
inspection is around the heater muff. Cracks in the muff can
cause carbon monoxide to enter the cabin via the heater. Internal
parts of the muffler baffle can break lose and plug the exhaust
breathing capability. Only a pressure check can determine if
a muffler is internally o.k.
Where the exhaust meets the cylinder is a flange that requires
a gasket to keep gases from escaping. This is an area requiring
frequent visual inspection. Problems are cause by bolts not being
tightened correctly. Certain parts of the system have slip joints
that are lose only when the engine is cold. Age is the determining
factor. The older the system the more internal erosion, fatigue,
and stress will lead to ultimate failure. Just like people.
Cockpit heating is done via a heat exchanger welded around the
exhaust manifold. Engine heat is transferred to the ducted air
from outside and this heated air is again ducted into the cabin.
Any obstruction of this system is likely to reduce engine power.
If every, you sense unexplained power loss and greatly reduced
fuel consumption with smooth engine operation while leaned, suspect
that the baffles of the muffler have come apart inside. In some
aircraft it is possible to inspect this condition with a flashlight.
Once made long cross-country with all the above indicators. Found out
that the failed exhaust baffling had reduced the exhaust flow into a pencil
sized hole.
Drag
and Cooling
Cooling created by the aircraft engine baffles and deflectors
make up as much as 30% of an airplane's total drag. This cooling
is required because of climbs in hot conditions. Cooling is predicated
on worst case conditions. If the cooling system fails, the lubrication
system will fail. Air is the most common cooling method because
it is so available and so inexpensive. There is no need for a
recovery system and it adds no weight. Air can cool simply by
its velocity over the engine or can be 'pressurized' by the design
of the air intakes, baffles, and low-pressure escape routes. If the cooling system fails, the lubrication system will
fail
The design of the cylinders with cooling fins allows easier heat
transfer. Additional cowl flaps can be used for additional cooling
during climb. The fuel air mixture can be used for additional
cooling. Pointing the aircraft into the wind during runup is
a good operational practice. Care should be taken not to cool
the engine too fast by rapid descents with the power off. Shock
cooling can be avoided by reducing the throttle in stages every
thirty seconds or so.
Shock Cooling
An aircraft engine spends much more time developing near
full power than does an automobile engine. The wear on an aircraft
engine is made shorter through negligent operation, non-operation,
corrosion, and the shocking effect of hot and cold cycles. Shock
heating cycles the metals of an engine just as much as does shock
cooling.
Heat shock can be reduced by starting the engine at idle leaning
to reduce oil dilution by excess fuel and then allowing the oil
pressure to rise before aggressive leaning. The start of an engine
its most damaging cycle of operation. A sudden reduction of engine
power after a period of increased power causes a rapid reduction
of engine heat being generated. This heat change inside the cylinders
is reflected in the heat released by the cooling fins and increased
cooling airflow through the engine plenum. The result is called
shock cooling. Lycoming says that shock cooling results in worn
piston grooves, broken rings, warped exhaust valves, bent pushrods,
and plug fouling. Recommended cooling rate is no greater than
50-degrees per minute.
Shock cooling occurs when the pilot reduces power to off and
goes into a descent. The effect of this is to suddenly reduce
the internal heat of the engine and greatly increasing the cooling
effect of the air over the cooling fins of the engine. This may
be a damaging shock to the bimetallic cylinder blocks. The principal
effects of shock cooling are cylinder-head cracking, valve seat
to valve seat, plug to plug. Anywhere inside the engine where
tool marks, sharp edges and other stress points are liable to
damage. Any engine operation that makes it possible for the valve
guide to shrink faster than the valve will cause sticking. Valves
stick open and the pushrod bends. A raised valve hits the piston
dome, breaks and is redistributed throughout the engine and turbo
if any. This situation often occurs when poor navigational planning
causes the pilot to arrive over his destination at several thousand
feet too high. Never make descents that will shock cool the engine.
It may not fail on your but it will on some pilot down the road.
To prevent all these bad things from happening to your engine
keep some power on the engine, re-lean during altitude changes
to keep the EGT near cruise values. If you have CHT on all cylinders
maintain a controlled (slow) decrease rate. Use of factory CHT
on one cylinder is a very poor second. Regardless, always reduce
power in increments so that engine temperature changes will be
gradual. Retard the throttle during descents. Do not enter a
descent that will both give a throttle reduction and an increase
in engine cooling air. Use landing gear and flaps to keep the
speed down. control the thermal changes of the engine to limit
temperature and cooling related damage.
When on the ground, take advantage of any cooling wind, lean
the mixture, open cowl flaps on the ground and during climb.
All engines should be run for at least two or three minutes on
the ground after a long flight to allow the oil to carry heat
away from the engine. In hot weather or with a turbo engine allow
more time. Before killing the engine run it up to 1200 and lean
to but not into roughness for 20 seconds. This will clean the
plugs from any residue of lead or carbon.
Engine Heat
Heat makes an engine work. An engine burning ten gallons
of gasoline an hour gives off as much head as would be required
to boil 750 gallons of water. Less than 40% of this engine heat
produces work. Over 60% is wasted and must be taken away. Controlled
heat makes it work better and longer. If removal fails to take
place the engine will fail in short order. Allowing oil to come
up to operating temperatures removes trapped moisture and insures
oil coating of the engine parts.
Nearly 50% of the energy of an aircraft engine is wasted out
the exhaust stacks. 30% of the fuel is used in cooling, pumping
and friction factors. Only 27% of the fuel's chemical energy
turns into horsepower.
Most of the working heat is removed through the exhaust system.
The rest remains in the metal of the engine waiting to be removed
by circulating oil and cooling air. The engine has numerous well-placed
holes, sprays, and reservoirs to facilitate the flow of oil.
Oil lubricates but cooling is a big part of its function. The
engineering of the engine and the aircraft controls the airflow
over the engine. The engineering of an engine has cylinder fins
and baffles placed to dissipate the engines operational heat
continuously and evenly. Even the propeller spinner is a factor
in cooling. Cowl flaps, air intakes, cowling openings and baffles
are designed so that aircraft and engine are mated to provide
the cooling the engine requires.
Recent aircraft/engine combinations have used exhaust augmenters
to provide a pressurized flow of air over the engine. This eliminates
flaps and allows a more streamlined aircraft with smaller cowl
openings. The latest propellers have a cooling projection near
the hub
To achieve maximum service life, Lycoming recommends limiting
power to 65% instead of the more common 75%. Cylinder head temperature
should be below 400-degrees and oil temperature between 165 and
200-degrees. Recommendation is to lean to 100-degrees F rich
for best power; peak EGT for best economy. Engine roughness is
caused by EGT or traditional leaning that causes one cylinder
to fail first. Always enrich for smooth operation. Below 5000'
density altitudes takeoffs require full rich mixture. Whenever
mixture is adjusted, rich or lean, it should be slowly in increments
with pauses between. Do not increase power settings without slowly
setting mixture to full rich. To reduce shock cooling, avoid
power/mixture changes that cause greater than 50-degrees;F changes
per minute. Watch temperature instruments.
Engine
Cooling
ALL engines are cooled by air. Just run your water-cooled car
for a while with no circulation through the
radiator! However, the heat transfer to the ambient air occurs
through several methods. The majority of the waste heat in your
aircraft engine is carried away in the exhaust. The waste heat
that causes us problems is the heat that is conducted into the
cylinder head, the valves, and the piston. Usually the center
top of the piston is the most critical "hot spot" in
the engine because the heat transfer path to remove the heat
from the piston top is quite convoluted.
Of the heat carried away from the hot parts of your engine, other
than the exhaust, the oil carries away about two thirds as much
as it carried away by direct transfer to the air. The oil is
especially important for cooling of the piston and the valves/valve
stems, and guides.
Of course the fins are important. Thermal transfer is merely
a function of area exposed and the temperature difference. Air
is a pretty good insulator if it is allowed to just sit there.
It warms up easily, but doesn't conduct heat well. For the air
to carry away the heat it has to be kept moving. Until we learned
how to get enough fin area on a cylinder head we had to keep
the cylinders moving to get sufficient airflow. That is why the
only successful air-cooled aircraft engines in WWI were "rotary"
engines where the whole engine turned with the propeller
Highflyer
Magnetos
The magneto is a self-contained voltage amplifier designed
for constant rpm. It provides its own electrical energy. Magnets
on the rotor shaft set up a magnetic field in the coil. through
timing the right spark is distributed at the right time. Three
internal circuits are involved. The primary is of relatively
heavy wire and few turns. This primary coil has 1-200 turns.
Combined with a condenser and a powerful magnet this circuit
produces a high current (amperage). At a precise moment in the
cycle the primary circuit is broken and the electro-magnetic
flux field collapses and cuts through the thousands of thin wire
coils in the secondary system. The secondary coil induces voltage
into the 15,000 turn secondary coil. This sends a 20,000-volt
surge toward the spark plug. This produces a critically timed
high voltage but low current surge, which arcs across the points
of the spark plug. It uses a mechanical spark advance, is independent
of the electrical system, and is driven by the engine.
The faster you pass a magnet past a wire the higher the current.
The magneto secondary coil is used to create a current that cuts
across the primary coil of numerous fine wires. The secondary
coil greatly multiplies the voltage and it is delivered to the
spark plugs. The timing of the voltage to the plugs is done by
a rotating magnet, which makes a brief contact that allows the
high-voltage to leave the coil and reach the spark plug.
Starting the engine with the starter causes the magneto to initially
retard the spark and activate a spring loading device called
an impulse coupling that supercharges the initial starting spark
to the plugs. The magneto generates the electricity needed by
the spark plugs and engine operation. For ease of starting, two
different systems exist. The impulse coupling would allow the
magneto to rotate faster than the engine. This increased the
voltage and thereby the size of the spark to the plugs. The timing
is adjusted (retarded) to provide maximum starting opportunity.
The second method used a vibrating relay to create a rapid series
of sparks to the plug during the start. This extended the ignition
spark exposure time to the fuel.
Bendix and Slick are the major manufacturers. A mechanic can
repair Bendix. The latest Slicks are sealed units not for local
repair. Many ADs and SBs on magnetos exist. Points and gap inspections
required at 100 and 500 respectively. Bendix recommends dissembling
and inspection every 500 hours. Lack of use causes interior deterioration.
A special non-arcing bearing lubricant is required for magnetos.
Change magneto and harness at engine TBO cycle. Magnetos are
usually only checked for operation at 100 hour and annual inspections.
Never, never hand turn a magneto to watch the spark during overhaul
and avoid shocks that will degrade the magnets. Since 1985, magnetos
are cited as cause/factor in 92 accidents. 130 reports of deficiencies
(cracks, arcing, leaking) in magneto ignition coils have been
filed since 1993.
The magneto uses a permanent magnet coil, a condenser, and timed-gapped
points to generate a high voltage (25-30,000 volts)/low amperage
spark. This spark is sent through a rotor to the spark plugs.
The arc of the spark across the tip of the spark plug ignites
the fuel/air mixture. The timing of the ignition of air/fuel
is, when once set, an effective and simple method of running
an engine. Failure of a magneto is gradual over a period of time.
Failure of an electronic magneto is instantaneous.
This mechanical system does not age in the manner of electronic
systems. The latest electronic systems are piggybacked on the
magnetos and give 10% greater fuel efficiency because the timing
and spark can be varied by engine requirements. The electronic
microprocessor can detect a fault or electrical failure and allow
the magneto system to take over engine operation.
Early magnetos were unreliable so aircraft were equipped with
two parallel systems. Now dual magnetos are used for better fuel
combustion. When properly functioning, the dual system gives
better fuel efficiency. The slight drop in rpm when switching
between the dual systems is due to loss of this combustion efficiency.
One spur gear running both magnetos reduces reliability (PA32,
C-182RG, and Mooney 201). Gearing rotates the magneto at engine
speed (1.5 x for 6 cylinders).
Dual magnetos produce prolonged ignition (microseconds) that
starts two flame fronts when the piston is well advance of top-dead
center. A single system retards the combustion and prolongs the
burning. The magneto points and rotor cap send the voltage to
the plugs in the correct sequence. 12 sparks per second in 6-cylinder
engine) Prolonged burning causes higher combustion temperature
and detonation. Not a problem at 75% power but under takeoff
and climb can cause engine damage. A frequently flown aircraft
will be less likely to have a magneto problem.
One of the hindrances to improved ignition systems is that such
a development might suggest to the legal profession that the
existing system is less than safe. Magnetos are quite wasteful
in their operation. Only during full power operations are magnetos
operating at top efficiency. The timing of the magnetos remains
the same even at low power operations such as taxiing. The magneto
and engine operation, once started, is completely independent
from the aircraft electrical system.
The electronic systems of automobiles are designed for variable
operations not as important to aircraft. The relatively low rpm
of aircraft engines do not require electronic ignition or multi-barrel
carburation. The spark advance of the magneto is not set to optimum,
it is fixed, and it decreases power and fuel economy. Starting
is made easier if the aircraft has an impulse coupling which
can vary the speed of the magneto. Magneto timing is adjusted
by varying its mounted position.
Magnetos are designed to last as long as the engine. Magneto
maintenance is normally only done when a failure occurs. Points
out of adjustment on spark plugs and fouling are factors that
place heavy loads on magnetos for which they are not designed.
When the magneto has difficulty firing the plugs, the voltages
try to find another way. This other way is usually inside the
magneto itself through the insulation of the secondary coil.
Inline noise filters on magneto leads will create an electrical
imbalance resulting in advanced timing, points burning and subsequent
weakening of the magneto.
Magneto maintenance should at least consist of setting the spark
plug gaps every hundred hours. The wrong gap can cause the magneto's
high voltage seeking other routes through the wiring insulation.
It is well every 500 hours to clean the inside of the magneto
case and check the breaker point gap. Internal corrosion can
occur if the inside of the case is not vented for fresh air and
the removal of moisture.
Leaning for taxi and low power operations helps keep the plugs
clean. Check the P-lead for its ability to shut down the engine
every few shutdowns. Do this by turning the switch to off to
confirm that the engine will actually stop running. Switch the
engine on before it dies completely. If it dies, let it remain
dead and make a normal restart. A damaging backfire is possible
if the magnetos are turned on too late.
When the key is in the off position the expectation is that the
magnetos are shorted out electrically so that any turning of
the engine or propeller will not start the engine. A digital
tachometer can detect the failure of a magneto and let you know
which one has failed.
Opinion
on Magneto Check
From the Sky Ranch Engineering Manual by John Schwaner: "To
check for a hot magneto, reduce RPM ti idle and turn switch to
OFF to see if engine dies. If it keeps running, beware of a hot
magneto."
The "Top End" volume of Light Plane Maintenance's "Firewall
Forward" library has a long discussion of checking for hot
mags...too long to quote, but it goes along with the "turn
it to OFF" procedure.
The thing to remember is that if the engine quits when the key
is turned OFF, it should be left there, not turned back to either
L or R, and the airplane towed back to the shop. If that is not
feasible, use the normal starting procedure and get it to a mechanic
as soon as possible.
Bob Gardner
Actually a short in the p-lead will keep the engine
from running. It's an open p-lead that you have to be
careful about. However, more often than not, it's the cheezy
ignition switch NOT the p-leads that is bogus. The mags on my
plane were found to be intermittently hot, even though the preflight
mag checked always shows a drop in the L and R position. It turns
out (and this IS common) that you can turn the key to off and
remove it in such a way that leaves one of the mags hot.
Ron Natalie
Engine
Won't Stop
If you happen to switch the mags into the off position while
doing the mag check, its best to let the engine quit and then
restart. What you might get if you switch it back is an after
fire. A backfire comes out the intake and an after fire comes
out the exhaust. What happens is that the exhaust gets filled
up with gas and air when the mags get turned off. When you turn
the mags back on, you might set off that air/fuel charge and
get a bang.
Coe
Detonation is caused by exceeding the temp and pressure limits
of the fuel/air mixture. It usually occurs after the spark plug
fires and the flame front is burning normally, but the pressure
and temp in the cylinder eventually exceeds the limits of the
fuel/air mixture and the rest of that mixture explodes. As you
mentioned it can be attributed to a timing problem. If the timing
is advanced to far, the CHT's are too high, the mixture is too
lean, the MP is too high, or any combination of these can lead
to detonation. Happy flying:)
Coe
Magneto
Revisited
The magnetos are timed to give near-perfect ignition at cruise.
This timing is too advanced to allow the engine to start; the
plug fires too early (if it fires at all) and the prop kicks
back instead of forward. The impulse coupling retards the spark
on one or both mags when the starter is engaged. The most common
setup is for the left mag to have an impulse coupling. If the
aircraft has a keyed starter, the ignition switch selects only
the left mag when the starter is engaged. If the aircraft has
a starter button, the pilot selects the left mag before engaging
the starter.
An impulse coupling is between the gear driven by the engine and the magneto shaft. It has 2 swinging weights and a large clock spring in it. At very low speed (when the engine is being cranked) the weights dangle and get caught on a pin, so stopping the rotation of the magneto shaft. Of course the engine gear is still turning so what it does is to wind up that big spring. After a few degrees of rotation the weight that is caught by the pin is mechanically released by another part of the coupling. The spring unwinds with great enthusiasm, momentarily spinning the magneto shaft very fast, so producing a nice fat spark. That's the first benefit.
The second benefit is that because the magneto shaft has been held stationary for a moment, when the spark does occur it is retarded from the usual running position, thus helping the engine to start smoothly - i.e., the spark timing is retarded for starting by the impulse coupling. The second benefit is the reason for starting on only one magneto, if only one is fitted with the coupling. If you start on both magnetos in that case, the one without the coupling (and so not retarded) will spark first, frequently causing a backfire and in any case giving the starter motor a hard time. If impulse couplings are fitted you can hear the "clack" as they release when pulling the prop through. (Author unknown)
P-Lead
The P-lead is part of the primary coil of the magneto. If
the magneto will not stop the engine it means that the P-lead
is not grounding out the magneto. Voltage can go to the secondary
coils of the magneto and thence to the spark plugs only through
induction from the primary coil. If the P-lead is unable to ground
through the starter switch 'off' position the engine will continue
to run as long as fuel is provided. Occasionally make a magneto
check for a defective contact or broken P-lead. When the magneto
switch is to OFF the system is supposed to be grounded so any
turning of the propeller will not activate the magneto voltage
and start the engine.
Distributor
The harness of the engine consists of multi-layered insulated
wiring from the distributor to the spark plugs. The positioning
of the harness protects it from engine heat and weather. The
construction of the harness reduces electrical radio interference
and other magnetic effects.
Spark Plugs
The spark plug is made up of a ceramic insulator, which protects
the electrode and acts as a heat sink to cool the plug. the outer
casing of the plug is made of machined steel threaded to fit
into the cylinders. A copper washer completed the pressure seal.
The electrode carries the voltage from the harness to the gap
sized to produce the maximum arc size and heat.
The spark plug gets the burst of high voltage produced by the
magneto via the distributor and harness at a timed moment to
produce an arc of flame that will ignite the fuel air mixture
in the cylinder. A propeller approaches 2500 rpm nearly 20 arcs
at 30,000-degrees F cross every plugs electrode every second.
The cylinder gas pressures will exceed 2000 pounds per square
inch.
Spark plugs must be matched to the engine according to the desired
and required heat range. It is a violation of the FARs to use
a plug other than specified for aircraft engines. A hot plug
may be used if your engine runs cool. A cold plug is used if
the engine runs hot. A colder plug is subject to combustion deposits
of carbon and lead. It is only at temperatures below 800 degrees
F that these deposits are likely to form. The burning off of
these deposits during runup occurs when a rise of just 100 F
degrees by leaning will vaporize the deposits. It is always best
to taxi with a leaned mixture. Fouled or burned plugs make an
engine hard to start. Iridium tipped plugs cost twice as much
but give three times the life. Greater care is required in cleaning
iridium plugs.
The best way to avoid lead fouling is by using one ounce of Alcor
TCP per gallon of fuel. TCP is known as a lead scavenger. By
avoiding rich mixtures and sudden full movements of the throttle
you give the spark plug temperature to increase with the increase
in power. Lead fouling may not be removed by leaning when the
plug temperature is above 1300 degrees. Removal may be the only
solution. Carbon fouling is most likely to occur at low power
settings with the plug temperatures below 800-degrees as when
first starting or taxiing. Added power during runup or shutdown
can be used to raise the plug temperature to burn off the carbon.
The best preventative is to lean the mixture at every opportunity
to keep the plug in the proper heat range that will keep carbon
fouling away. When all top plugs show wet oil it means excessive
wear on all cylinders and guides.
Ignition Problems
Improper engine operation will cause lead fouling of the
plugs. This results in a rough engine and low power. High voltages
will seek out the weakest insulating point of the harness resulting
from wear or moisture. Every time a spark plug fires the electrode
erodes slightly. At some point the erosion affects engine operation,
efficiency and starting. Coils can burn out, condensers short
out and points burn and wear.
Carburetors
Carburetors allow the pilot to meter fuel into the engine.
A part of this system is the idle system, which is rich, low
power but separate in operation and adjustment from the other
systems. Its richness cools the engine when airflow is least
over the engine. Extensive operation at idle will foul the plugs
unless leaning is an operational practice.
The accelerating system of the carburetor provides extra fuel
when the throttle is moved . If this system is not properly adjusted
the engine will hesitate with quick throttle movement. Overly
abrupt movement can still cause the engine to hesitate. This
system can be used to prime the engine during mild weather by
giving the throttle a couple of rapid pumps. Any pumps beyond
two can cause excess fuel to flow into the air intake. This is
hazardous because the exhaust can ignite the fuel and create
a fire in the engine compartment.
Putting Out a Start Fire
The existence of an engine start fire requires the pilot to immediately
apply full throttle and pull the mixture This will allow the
propeller to extinguish the fire and the engine to use all carburetor
fuel very quickly. If the fire exists and the engine has not
started the mixture should be pulled and the engine cranked to
suck any fire up into the exhaust and air intake. Shut off the
fuel selector, evacuate the cockpit and locate a fire extinguisher
on one of the light poles. Part of your preflight should be to
locate the nearest fire extinguisher.
The fuel-air proportions are adjusted by the mixture control.
This adjustment is done based on temperature and altitude, both
of which affect atmospheric density. Carburetors use either mechanical
or back-suction methods to control fuel flow. The mechanical
method restricts fuel flow. The back suction allows a low pressure
to enter the carburetor, which reduces the pressure differential
and draw caused by piston movement. Run the throttle to full power at
the same time to use up as much fuel in the carburetor bowl as possible.
Using the ignition key is faster but it leaves fuel available for burning in
the carburetor.
A full extension of the mixture control activates the idle cutoff. The idle cutoff stops all fuel flow and is used to stop the engine
and reduce the probability of a propeller accident. The mechanical
control shuts off the fuel while the back suction cuts off fuel
by reducing the pressure differential to zero.
In most operations some fuel is used to cool the engine. This
additional fuel is added by the economizer system which applies
more to the engine than to fuel savings. The economizer system
operates by increasing or decreasing supplementary fuel flow
in conjunction with movement of the throttle. The last half-inch of the
throttle movement opens the economizer jet.
Liquid aviation fuel will not burn in its pure condition. The
carburetor's functions to put air and fuel to the engine any
where from an 8:1 through 16:1 parts of air to one part of fuel,
by weight. 12:1 gives best power. The mixture is richest at idle
and goes from there through a range of leanness until it becomes
rich again at full power. The rich mixtures use some of the fuel
for cooling. Lean mixtures burn slower but hotter. Lean mixtures
can make an engine backfire when the fuel is still burning as
the intake valve lets the next draw of fuel to enter. Rich mixtures
cause an after-fire when unburned fuel is ignited in the exhaust
system.
The fuel mixture is pulled into the engine by the intake stroke
of the pistons. This stroke creates a low pressure in the carburetor,
which sucks fuel and air through the carburetor venturi. The
carburetor has a constricted tube (venturi throat) for the air
intake from either outside air filter or from the heater muff
around the exhaust system. The constriction is a high airspeed/low
pressure area that draws fuel from the carburetor fuel tank.
The proportion of the fuel is maintained as proportional to the
air by a "butterfly" valve in the air intake throat
of the carburetor. The "butterfly" is directly linked
to the throttle. The less the "butterfly " blocks the
air by moving toward a knife-edge the more air, fuel and power
to the engine. Lycomings have an intake system which benefits from engine
heat, This makes them less susceptible to carburetor
icing.
The carburetor flows from the bottom to the engine. Water in
the fuel will settle to the bottom. Two ounces of water are enough
to make your engine quit. Contaminated fuel causes more accidents
that bad magnetos, blocked air filters and mechanical failures combined. One test for water in the fuel
requires two people.
One person should hold the tail down while the other drains the
sumps. I did this after a plane had been flown all day and was
able to get water in the sump cup. The larger the aircraft the
more likely it is to occur. Try it with C-182.
The fact that airplanes normally operate at relatively high and
constant revolutions per minute (RPM), are not subject to rapid
throttle changes and power smoothness requirements means the
carburetor does not need automotive vacuum advances and throttle
pumps. Aircraft carburetors are single barrel. The spark from
a magneto or an added vibrator (shower of sparks) does the job
in an airplane. Having a variable mixture in an aircraft also
helps the starting. The intake manifold still makes certain cylinders
to run richer than others do. The system, for aircraft, is simple
and reliable and still in use in a fuel injection age.
During WWII the Germans used fuel injection in aircraft. This
gave them superiority during many aerobatic situations over carburetor
equipped aircraft. Today, fuel-injection systems are aimed at
fuel efficiency (5%). A mechanical pump parcels out the fuel
evenly to each cylinder. Timing is still by an "old-fashioned"
magneto. Fuel pump operations with fuel-injection engines must
be according to POH since, in some instances, the pump can kill
the engine with too much fuel. Fuel injection engines are subject
to choking caused by impact icing. This can be corrected by application
of alternate air before ice can freeze door shut. Automotive
electronic ignitions and injection systems are primarily for
emissions control. The operation of this system does not, at
present, hold advantages for aircraft.
Carburetor Revisited:
A float type carburetor uses the vacuum produced by the
air drawn in through the venturi of the carburetor to lift fuel
into the engine. This vacuum sucks the fuel through a jet with
a metering pin in it (adjust with the mixture knob) and into
the air stream created by the intake stroke of the piston. A throttle
plate (butterfly valve) which is down stream from the fuel intake
port meters the airflow. When you open the throttle plate you
momentarily reduce the level of vacuum and thereby fuel flow
until the RPMs pick up to bring the vacuum back up which will
suck the proper amount of fuel to maintain that power level.
The carburetor has a plunger pump in it connected to the throttle
cable so when you push on the throttle it literally pumps in
a metered amount of fuel in the air stream to make up for what
isn't being sucked up by the vacuum. This is the accelerator
pump. Being too quick in pushing in the throttle can cause the
engine to sputter and then pick up. Smooth movements of the throttle
work better. Additionally, when the throttle is in the last half
inch of movement as for takeoff and climb, a separate fuel jet
allows excess fuel to flow, the sole purpose of this jet is to
provide additional cooling for the engine. .Airplanes have updraft
carburetors where the carburetor sits on the bottom of the engine.
To get fuel to the cylinders, you are advised to use the primer
pump. The primer which pumps fuel through a set of lines to some
fittings which are screwed into some holes which lead directly
into the intake manifold of the cylinders where it can go into
the cylinder where it is used to prime the engine. Using this
primer reduces the likelihood of an engine start fire. Using
the accelerator pump with the throttle can cause a fire by overfilling
the carburetor.
Some pilots push the throttle in past its initial stop. It may go a bit further but in the process the wire that is doing the pushing lis required to bend a bit. Just where it binds is an unknown but eventually the bending will cause the wire to break. This is essentially the same process you use to break a wire when unable to cut it. The throttle arm has a spring that will allow you a bit of power but usually not enough to keep flying very fast. This means that you may have difficulty landing due to excess airspeed. The engine can be controlled somewhat by use of the ignition key and stopped with either the mixture or the key..
Fuel
Injection
With fuel injection, the throttle cable is connected to a
throttle body, which meters the air with a plate much as with
a carburetor. This mechanism is connected with a rod to a unit
known as a fuel controller. The fuel controller meters fuel through
a valve that is controlled both by the throttle body link and
the mixture control. This fuel is then pumped up to what is known
as the spider which is the round thing you see sitting on top
of the engine with all the metal lines coming out of it going
to the cylinders. The spider distributes the fuel to the injector
nozzles, which are screwed into the intake ports in the cylinder
heads.
The fuel is sprayed into the air stream for use in the cylinder.
The fuel pump pumps more fuel than will be pumped through the
nozzle at any given pressure and more than the engine can use.
For this reason there is a return line at the nozzle which returns
excess fuel to the tank. To maintain the pressure where it needs
to be, the return is metered through a jet sometimes called "The
Pill". For starting you prime the engine with the fuel pump, while
controlling the amount of the prime you use the throttle and
mixture controls along with the pump.
Carburetor
Heat
Both the throttle via the butterfly valve and the mixture
controls the ratio of air to fuel in the carburetor. Carburetor
icing when it clings to the butterfly valve, which will decrease
the airflow and decrease the venturi effect drawing fuel from
the carburetor fuel jet. On the application of carburetor heat
the warmer air will cause the mixture to become richer. It is
possible that with a Carburetor Heat Temperature gauge that some
leaning could be done to offset the effect of the warm air on
the fuel/air ratio.
Leaning the mixture can reduce some of the additional roughness
caused by the use of carburetor heat. This leaning will also
increase the operating temperature of the engine and thereby
increase the amount of carburetor heat available. One of the unintended
consequences of a well leaned carburetor is that while the engine runs hotter,
it may be so hot that pulling the carburetor heat on will not cause the usual
drop in RPM. This is normal and can be confirmed by a bit of enrichment.
A rough engine during run-up means that one cylinder is not firing.
Plug fouling is the problem. With the 100LL fuel now being used
in engines designed for 87 octane this is a common problem caused
by failing to lean during taxi. Fouling can be 'cured' by leaning
the mixture. First increase the RPM to 2000+ and then slowly
pull the mixture. This will increase the cylinder internal temperature
sufficient to vaporize the lead/carbon deposits. Reduce power
to 1700 after a minute and check magnetos again. It is proper
to lean an aircraft engine any time the power is 75% or less.
Air Intake
The air intake below the propeller has a filter that is much
smaller and less effective than that used on automobiles. Accidents
occur every year when the air filter is installed backwards and
parts of it are ingested into the carburetor system. A stationary
aircraft with the engine running has a propeller vortex that
is putting dirty air into the air intake. For this reason you
want to minimize operations where such dust is possible. Dust
is like sandpaper once it gets into the engine and oil.
The cowl flaps allow an escape route for engine intake air while
allowing a directed flow over the hotter (upper) engine parts
during low speed operations. This is called downdraft cooling.
Small changes in the flexible baffling material can have large
effect on cooling efficiency. Airflow is supposed to make the rubber baffles flex into a tight seal, thus redirecting airflow to where
it is needed most.
Vacuum Pump
Poor life expectancy of dry type pumps is characterized by instantaneous
failure. The wet (oiled) pump functions better but is uncommon.
They slowly fail over a period of time. Contamination of air
in system is the greatest cause of failure. Low pressure should be corrected by increasing pump setting. Replace or find
cause for decrease. Pump must work harder at altitude. Such operations
increase wear and frequency of failure. Tight cowlings and dirty
filters are next causes of limited life. Pumps that last 20 hours
usually last a thousand. Average life is 400-500 hours. Vacuum
pump manufactures say that turning the propeller backwards also
causes the vacuum pump to work backwards and is damaging. It
is for this reason that it is best not to turn a propeller backwards. (C-150) There is some question about this.
An additional question related to vacuum is how much will be
available in the event of engine failure. A windmilling propeller
may not turn fast enough to make the vacuum pump keep the gyros
of the HI and AI functioning. In IFR conditions you might be
well advised to cover both the HI and AI for this reason.
Engine Monitor
The effective use of an engine monitor depends first on being
able to set the normal operational parameters. Secondly, you
need to pick up abnormalities as they occur in your flight and
ground operations.
The engine preflight with the magnetos confirmed off and the
P-lead shorting out the magneto says that you pull the propeller
through to listen for air leaks. The intake valves leak if the
air sound comes from the air intake. Sounds coming from the exhaust
indicate exhaust valve leakage. Hissing from the engine casing
says you have a piston ring problem.
If on startup or even later, the engine backfires or is rough
this should be interpreted as it's not being warm enough for
full power operations. If the oil is too cold to allow a rise
in oil pressure the engine can be damaged.
Oil
by Grade
The "100" in AeroShell Oil W100 and similar grades
is an indication of the oil's viscosity. It relates to an old
imperial method of measuring kinematic viscosity known as Saybolt
Universal Seconds (SUS or SSU).
If you are interested, SUS is the time, in seconds, for 60 ml of fluid to flow through a capillary tube in a Saybolt Universal viscosimeter at a temperature of 212°F. This term has generally been replaced by the metric centistoke, cSt, which leads to the more common SAE (Society of Automotive Engineers) classification system of viscosity measurement i.e. SAE 40, SAE 50 etc.
As far as the aviation piston engine oil grades are concerned,
the SAE viscosity grade should be marked on the bottle, but the
product name still carries on with the old system as this naming
system is what the
market is used to.
The correlation between the two is as follows:
"SUS" Grade
SAE Grade
AeroShell Oil W65
SAE 30
AeroShell Oil W80
SAE 40
AeroShell Oil W100
SAE 50
AeroShell Oil W120
SAE 60
Just to confuse things further, you will have probably noticed
that the multigrade oils used in aviation have adopted the SAE
system of classification in their naming (to wit AeroShell Oil
W 15W-50 behaves like a SAE 15 grade oil at -15degrees;C, and
like a SAE 50 oil at 100degrees C).
General Aviation and Military Technical Support
Shell Aviation
Oil
Oil seals, cools, lubricates and cleans. The viscosity of
a multi-grade oil allows these activities to be accomplished
with lighter molecules with much less of the lacquers and varnishes
that cause deposits.
All oils seem to lubricate equally well. An ashless-dispersant
(AD) oil will prevent carbon build up by suspending wear particles
for removal in the oil filter. AD oils give you a cleaner engine
with unclogged oil passages. Price or additives are not good
measures of oil. Oils are about equal although some are different.
Any additive that is supposed to do a particular job will be
wasted money unless present in sufficient quantity to do the
job. You have no way of knowing if the job is being done.
You can learn what is going on inside your engine by reading
what oil can tell you. You will need to use your senses of sight,
sound, smell and feel.
--How soon oil gets black indicates the amount of blowby past
the rings.
--The acidic mixture of oil residue and water can only be removed
by oil changes.
--Black oil will lubricate but must be heated to 180 degrees
to boil off moisture.
--Hot oil that smells like exhaust indicates engine problems
unless over 25 hours old.
--Listening for air sounds at the dipstick or breather tube while
turning propeller by hand checks rings blow-by.
--Oil dripping from breather outlet is blow-by indicator
--Oil leaks must be bad before they are serious.
--Max oil burn: (.006 x HP x 4)/7.4
A 200 H.P engine can
burn .65 qt. per hr.
--Track oil consumption rate.
--Cut open oil filter to study metal in oil.
--Shell recommends aircraft with cartridge filter be changed
every 50 hour or every 4 months.
Oil
by Exxon
--Called Elite
--Ashless dispersant additives
--better wear and corrosion factors
--works in combination with other oils
--suspends carbon, dirt, etc better so gets darker sooner.
Oil
Filter
Best filtering has most restriction, which causes greater
pressure drop. Filter may have an adjacent valve to open when
pressure difference reaching a certain point of about eight pounds
differential. Any time idle oil pressure drops by 10 psi
check
the filter. Some of these valves have an associated cockpit light.
Oil is another area of change. Pilots and mechanics have rejected
the use of multigrade oils. There are now aviation grade multiviscosity
oils that retain viscosity at 250 degrees as do single grade
oils and become thicker at 300 degrees. Multigrade oils do not
wear out nor do they drain off engine parts sooner than 100 weight
oils. Single grade oils will be out performed by the multigrade
oils.
Oil
Analysis
The purpose of oil analysis is to use the history of an engine's
oil to detect small problems before they become large ones. Oil
analysis uses a spectrometer to measure the particular colors
and their proportions when a specimen is burned. The history
of the colors (different substances) and a change can be indicative
of a change in engine wear. By asking the right questions about
oil analysis you can avoid unexpected large expenses by accepting
smaller expenses earlier.
Oil Pressure Gauge
This is the most important instrument of engine operation.
In normal conditions oil pressure will be indicated within 30
seconds of starting. the gauge measures engine resistance to
the flow of oil. Oil pressure indications can be quite variable
and unreliable in cold conditions. Get the engine plenty warm
when taking off in cold weather.
In trainers the oil gauge is mechanical. Gauge has small line
to engine. Interior of gauge has Bourdon tube, which unwinds
under pressure. Attached needle give reading of oil pressure.
A reducer lets a limited amount of oil into a watch-spring shaped
Bourdon tube. Oil pressure unwinds the tube and moves the oil
pressure indicator needle. Pricy aircraft use an electric system.
The oil pressure line is very small so that it will read zero
after a break long before the engine oil is lost. This allows
you time to note the reading and still more time to get down
before the engine quits.
If the oil temperature goes beyond the red line but the oil pressure
remains in the green the problem may be in the temperature gauge
and not the engine. High temperature and low oil pressure calls
for an immediate engine shut down. If you smell hot oil, shut
down the engine. Too high pressures are indicative of too heavy
oil grade or oil not warmed enough for high power operation.
Oil Temperature Gauge
Any sudden rise in temperature along with engine roughness
is good cause to get on the ground.
Rise in temperature without
roughness is sign of low oil level. Good pressure and high temperature
is sign of gauge error. Any internal engine cooling that takes
place is done by oil. The size of your oil supply is the determining
factor. No oil, no cooling.
The oil temperature gauge is a pressure gauge that uses a Bourdon
tube. Inside the tube is liquid methyl chloride that expands
when heated. This allows the Bourdon tube to wind and unwind
with changes of oil temperature. Gauge is usually electric and
usually accurate. High temperature readings can be confirmed
by hot oil smell.
The gauge on a Cessna is a dc meter movement connected to a variable-resistance
sender mounted in the crankcase near the varitherm. Its resistance
decreases as the temperature rises, causing more current to flow,
and thereby causing the meter reading to increase.
The wire between the meter and the sender were to fail, the meter
reads cold. If a short occurs then the meter would read to the
highest temperature. Meter movements do not become more sensitive
on their own. So its much more likely that when an oil temp gauge
shows hot, it is hot.
Lubrication
Anything that moves on an airplane requires lubrication.
Even rubber. Aircraft owners can perform most lubrication tasks
if no disassembly is required beyond cover plates, fairings and
the cowling. It is contrary to the FARs to perform any lubrication
without having reference access to appropriate manuals. When
the use of a lubricant is a part of preventative, a maintenance
record entry must be made in the maintenance log according to
FAR 43.5 and 43.9(a) (1 through 4). The log entry must contain
a description of the work, the date completed, the name and signature
of the person along with the certificate number and kind of certificate.
Major problem with pilot/owner maintenance is that they do not
have the proper tools, current data, or the training to do the
job properly. Pilot/owners rarely made a maintenance entry in
the logbooks even though required.
The engine problems that may be expected when pilots consistently
make fast letdowns with little or no power....
1. Excessively worn ring grooves accompanied by broken rings.
2. Cracked cylinder heads.
3. Warped exhaust valves.
4. Bent pushrods.
5. Spark plug fouling.
Cylinder Head Temp
Gauge
This is installed after flight testing on the hottest cylinder
unless it
is installed on all. This gauge gives a faster more accurate
indication of
engine temperatures. Detonation and preignition produce a rapid
rise in CHT to be followed by rising oil temperature. The engine
may be damaged in this situation very quickly.
Carburetor Temperature
Gauge
This device uses a temperature probe to determine if the
carburetor is subject to icing. A color-coded scale of green,
yellow, and red indicates probability of ice. Adjust heat to
keep needle in the green.
Tachometer
Green is normal operating; red is never exceed limit. Gauge is usually
mechanical and prone to low readings. Numbers are usually high
at low speeds and low at cruise speeds. False tachometer readings
are major cause of inaccurate fuel calculations. The tachometer
should be used to avoid exceeding the redline operational limit.
Forces on the engine parts increase greatly as engine speed rises.
The tachometer is used to check magneto operation and adjustment during
runup. The tachometer shows when plug fouling has occurred and when
it has been corrected. A falling tachometer is the first visual
indication of carburetor ice except in constant speed propeller
aircraft.
A flexible shaft geared to the engine drive system mechanically
drives trainer tachometers. The drive cable has a rotating magnet
on the end that drives the tachometer dial. Tachometers are relatively
inaccurate and read too high at the low rpm and too low at the
high rpm settings. This inaccuracy makes it wise to plan fuel
consumption on the safe side. Age affects the tachometer accuracy
and may cause a pilot to operate at the very speeds he should
be avoiding. Only AC Type ST-640 grease should be used on Cessnas.
This is a G.M. product.
RPM
Because tachometers are so inaccurate, the only way you can fly
with any assurance that you are using the same rpm over two given
same courses is by flying at full power. Your tachometer usually
reads low.
Engine Isolators
These are thick rubber pads that go between the firewall
and the engine mount. There are used to reduce the engine/propeller
vibration transmitted to the aircraft frame.
Manufactured of rubber compounds and have limited service life.
Rarely last 10 years or to TBO of engine. Harden with age and
do not provide protection. 100-hour inspections are a good time
to rotate to even wear. Isolators are subject to damage from
oils and fluids, which cause swelling and loss of elasticity.
Heat will age and crack. They should be checked by finger to
see if hard or spongy. They have limited shelf life and are dated
at manufacture. Don't use undated isolators.
Any time the nose wheel shock system is not functioning properly
every jar from the ground is transmitted to the rubber engine
isolators. As these in turn lose flexibility the ground shocks
are sent direct to the engine where cumulative damage occurs.
Engine
Shutdown by Lycoming
"Prior to engine shut-down the engine speed should be
maintained between 1000 and 1200 RPM until the operating temperatures
have stabilized. At this time the engine speed should be increased
to approximately 1800 RPM for 15 to 20 seconds, then reduced
to 1000 to 1200 RPM and shut-down immediately using the mixture
control."
Fuel
Efficiency
You can reduce fuel consumption just by slowing down. Vz
is the speed of lowest consumption. At 7500' you are close to
the optimum altitude at which an engine can develop 75% power
for the highest true airspeed.
In a C-172 operating at Vz +5% you are at 50% power with at TAS
of 97 knots getting 16 nautical miles per gallon and operational
costs are about 10% less than normal cruise. Slowing down saves
you $12 per hour on a flight that takes a half-hour longer. The
only aircraft more efficient are the two seat Cessnas and the
next level of efficiency is all the Mooneys. If you want to fly
for maximum endurance select the speed that is halfway between
Vx and Vy.
Leaning for maximum efficiency requires that you fly at altitude
where the engine is capable of developing no more than 75% power.
You lean as far as will keep a smooth running engine and still
maintain EGT and CHT in limits. A new engine should be run rich
to seat rings.
Aggressive leaning can only cause detonation in higher-powered
engines, turbos or fuel injection systems where one injector
is plugged. The lower the power the less likely is detonation
or damage. Learning to lean both in climb and descent can save
considerable fuel. The wear of an engine occurs from the relative
speed of the moving parts. Temperature, material and lubrication
are the determining wear factors. The piston/cylinder fit on
aircraft is much looser than for automobiles. This is done deliberately
to give better reliability though at the cost of greater oil
consumption. Low power operations can cause the cylinders and
pistons to glaze. Using full power on takeoff should be enough
to remove and keep removed this problem.
By flying lighter you do the most for fuel economy most remarkably
when flying slow. You can fly higher and slower more easily when
light. The faster you fly the less difference weight makes. For
every 10% your weight is below gross you can reduce Vz by 5%.
With the advent of LORAN and GPS we have made available a major
reduction in fuel consumption. Flying a straight line is becoming
an easier way to save gas.
A conservative number for ALL piston engines burning gasoline
is about one gallon per hour for every twelve horsepower actually
being produced.
Tire
History
Goodyear made the first airplane tires in 1909. These tires
were mounted on bolted rims. The tires had implanted wire into
the rubber to better secure the tire to the rim. Internal reinforcement
to the tire used leather strips. B.F. Goodrich built a Palmer
Aircraft Tire as a four ply continuous cord embedded in rubber.
This tire was used by Glenn Curtiss to set his early speed records.
Military airplane tires were developed in 1911. In the 1920 Goodyear
made a streamlined tire to reduce drag.
During the 1920's tires caused numerous accidents. A balloon
tire to give softer landings was developed by Goodyear called
the Airwheel in 1928. It has a pressure between 10 and 15 psi.
Landing shock was greatly reduced by this tire.
In the 1930s diamond tread and the deep ribs still in use today
took over. Today aircraft tires are tested and retested to meet
the safety, quality and reliability required by the FAA. Any
new tire must meet or surpass the 200 dynamic load, speed, and
time requirements of the FAA test. Then an eight-day endurance
test on a flywheel must be matched with a specific aircraft's
performance requirements.
Basics
of Tire Construction
Materials have a dozen different components each made from
up to fifteen ingredients. Rubber is the largest single element.
Specialties are softeners, reinforcing agents, tackifiers, plasticizers,
anti weather materials, anti-oxidants and vulcanizing agents.
Each of these is specially blended to make the nine distinct
parts of an aircraft tire.
The main part of the tire is called the CARCASS. The carcass
includes the rubber, fabric and bead wire. The
UNDERTREAD is a layer of rubber that lies between the
tread and the top of the carcass. Tubeless tires have a
LINER that is a layer of dense rubber that acts an air
sealant like an inter tube. The SIDEWALL is a layer of
rubber that extends over the outside of the tire from tread to
the bead. The foundation of a tire is called the BEAD.
The bead gives the tire strength and bead is a number of cotton
or other fiber cords that are wound parallel and diagonally to
the circumference and centerline of the tire. The fabric provides
the tire stability, bruise resistance, flexibility and weight
carrying ability. Nylon is now used instead of cotton or rayon.
Because of nylons characteristics two plies of nylon are given
a 4-ply rating. Remember this the next time you see cord showing
through the rubber. The CHAFER is added as a layer of fabric and rubber about
the beads of the tire where it holds to the wheel. The
APEX STRIP is a triangular insert to shape the tire from
the bead to the sidewall. The FLIPPER is a fabric addition
that circles the bead and apex strip and holds them for ease
of manufacture and to give the tire a more rigid structure.
Tire
Classification
Tire types are either III, VII or VIII that still exist at
the present from the eight that existed over time. Type II is
low
pressure and high volume. Type Vii is extra-high pressure for
military and civil jets and prop jets. Type VIII is a low
profile, high pressure for very high takeoff speeds.
Tire
Care
Proper inflation extends tire life. Only an accurate
needle gauge should be used at least once a week. Under-inflation
causes a tire to overheat on landing, taxiing and takeoff. Over-
inflation
causes a tire to wear unevenly and excessively. Sharp turns should
always have the inside tire rolling. The more a tire flexes the
hotter it gets. Touchdown speeds should be as slow as the aircraft
performance will allow. The tire goes from dead still to full
speed in an instant on landing touchdown. This transition should
be done as slow as possible. Excessive braking speed is a sure
way to tire failure. The tire tread is essential to give the tire stability and resistance
to sideloads and hydroplaning. Move your tires every
few days to distribute the weight and weathering that takes place
naturally.
Avoid:
---Excessive inflation that causes the tread center to wear excessively.
---One sided tire wear is caused by excessive camber of the tire
out or in.
---Weather checking is acceptable unless the chord is exposed.
---Tires can be re-treaded if wear is stopped soon enough.
---Any cut through 50% of a rib is cause for removal.
---Braking hard will damage the bead making removal necessary.
---Rough runways cause excessive tire wear.
---Severe braking can and will cause flat spots on tires.
---The use of improper tire tools during installation will damage
tires.
---Tire abuse of many kinds can cause tread separation.
---Running on a flat tire can and will cause irreparable tire
damage.
Flying
with Pressure
---Absolute pressure, such as manifold pressure, is pressure
relative to a total vacuum.
--Gauge pressure is the difference between atmospheric pressure
and the measured pressure. An example would be differential cabin
pressure measured as the difference between static pressure (outside
pressure) and inside cabin pressure.
---Differential pressure is measured between two separate pressures
as that sealed inside an altimeter bellows and the atmospheric
pressure.
Airplanes have several possible fluid pressures such as hydraulic,
oil and cooling (rare). Non-fluid pressures such as vacuum, manifold,
pitot and static are part of most every aircraft. Hydraulic pressure
operates brakes, struts, shimmy dampers and some flaps. Oil pressure
keeps moving metal parts apart and inline engines are liquid
cooled. Vacuum pressure drives most HI and AI. This pressure
can be obtained from a venturi or a suction pump. The difference
between pitot and static air pressure gives us our airspeed reading.
A coiled Bourdon tube is used to measure the hot-oil pressure
of engines. The tube is like the coiled tail of a monkey that
unwinds to move the indicator needle. The manifold, altimeter,
VSI and airspeed are relatively low pressures, which use a bellows
to move the indicator needles over a carefully calibrated scale.
Higher temperatures are usually measured electrically such as
by means of a dissimilar metal thermocouple. Cabin and outside
temperatures can be measured by mercury or spring calibrated
thermometers
Converting raw pressure in. Hg. to millibars.
29.92 inches of mercury = 1013.2 millibars
1 inch of mercury = 33.86 millibars
Calculating station pressure (Psta) when I have the raw pressure
in. Hg,
Thermometer reading and the correction (in. Hg.).
Calculating sea level pressure (Pslp) when I am given raw pressure
(in.
Hg.) and station altitudes above sea level.
Pressure decreases at about 1 in. Hg per 1,000 increase in altitude.
Altitude
Standards
IFR and VFR separation is primarily dependent upon altimeter
settings. All airspace is sliced into layers above 3000' except
where it reaches ground under different designations. Historic
and current navigational standards until just recently were so
inaccurate or misleading that reliance of position was relatively
uncertain and grew more so with distance from navaids. Only a
common altimeter setting among aircraft in the same area provided
the requisite separation and safety. The allowable altimeter
errors provide adequate vertical clearance only between IFR aircraft.
VFR to IFR clearance is marginal vertically. With the advent
of ADS-B the use of GPS clearances are sure to replace barometric
altimeter settings for vertical separation. Aircraft at the flight
levels (above 29,000) will soon have (RVSM) reduced vertical
separation minimum radar calibrated altimeters. Technologically
we can maintain both lateral and vertical separation with far
greater accuracy than is now required for the present parameters
of error. Why not?
Altimeter
Accuracy
The 75-foot requirement has to do with whether overhaul is
required or replacement. 14 CFR Appendix E or Part 43 requires
that an altimeter off by 30-feet at sea level fails a FAR Part
91.411 check.
Item:
Only if temperatures are standard is the sea level altimeter
setting accurate.
Altimeter
Readings
Flying over a mass of air as our reference and the altimeter
is reading correctly. We weigh the air mass and then heat it
and it expands. The density decreases and the mass decreases.
Colder temperatures increase the air density. The higher density
air will give the same pressure/altimeter reading at a lower
altitude. By flying into colder air you are probably lower than
your altimeter indicates. Look out below,
Heated every cubic foot of air now weighs less. The heated air no
longer fits in the same space. Air does have mass. The altimeter
is a pressure device, not a density device. When gravity is the
force applied to mass, it produces weight, which in turn produces
pressure. So the altimeter provides pressure change data.
In warm air the pressure change with altitude is less than in
cold air. You must climb higher to see the same drop in pressure.
The air expands when it is warm, and the pressure lines are separated
farther apart. You will be higher than what your altimeter tells
you. This has nothing to do with density being lower in warm
temperatures. Altimeter is a pressure instrument, not a density
instrument. Hot to cold, High to low... Look out below"
Pressure Altitude
Set 29.92 in the Kollsman window of your altimeter and read the
altitude directly.
Get the altimeter setting from ATIS. Take the difference between
that and 29.92. If the altimeter setting is lower than 29.92
add to the airport elevation 100' for every 1/10 difference.
For a setting is above 29.92, the pressure altitude is lower
than the airport elevation.
From ATIS:
Current Pressure = 29.98 inches
Current temp at 4500 feet = 18 degrees C
Cruise Altitude = 4500 feet
--To get PRESSURE ALTITUDE:
(Current Pressure) -29.92 (Standard Pressure)
= FEET (Intended Indicated Altitude) + (Actual altitude
adjustment; add/subtract pressure
(PRESSURE ALTITUDE) Altimeter set to 29.92
--To get DENSITY ALTITUDE:
Temp (degrees C)
Standard Sea Level Temp)
(Standard lapse for intended altitude = 2 degree per 1000ft =
2C x )
(Standard at intended altitude)
(Current at intended altitude)
(Actual temperature at altitude)
Use pressure altitude and temperature with E6b to get density
altitude.
Density altitude is the effect of air pressure, temperature and
humidity on performance. Each one affects the engine's power,
the propeller's thrust and the wing's lift. Density altitude
charts use pressure altitude and temperature to get performance
factor. Performance factor is the total change in performance
due to loss of engine power, propeller thrust, and wing lift.
These losses affect ground roll distance on takeoff, climb performance
after takeoff and ground roll on landing.
Rusting Out
Most pilots rust out before they wear out. You never forget flying
skills but they do get rusty. The same is true
of aircraft engines. The more the engine is used the more
likely it is to avoid the various ailments that come from inactivity.
Most important is the used engine will have frequent oil changes
and hence clean oil. Only oil changes remove the acid residue
resulting from moisture and oxidized oil. The active engine will
be at the higher temperatures required to evaporate out the moisture
and inhibit the formation of acids. Regardless of operation,
oil should be changed every four months.
Preservation of an inactive engine is a complex procedure that
may or may not work. Special spark plugs can reduce moisture.
Plugging all orifices will help. Do not move the propeller during
storage. Ground running is not a substitute for flying. It takes
30 minutes of 180-degree temperatures to remove all moisture.
Shell oil has developed a special type of oil that acts as a
preservative.
Aviation
Workplace Hazardous Materials
--Acetone used as solvent
--Ammonia used as cleaning agent
--Asbestos used as insulator and friction agent
--Carbon Monoxide poisonous gas from combustion
--Chlorofluorcarbon used as cleaning agent
--Ethylene Glycol uses as deicer and cooling agent
--Methylene Chloride used as solvent and degreaser
--Methylethyl Ketone used as solvent in paint and glue
--Cadium, chromium, cyanide, lead, mercury, phenol, phosphoric
acid, trichioroethylene, TCP, sulfuric acid, etc.
Turn
Coordinator
--The most reliable instrument for determiming spin direction
--The turn coordinator lies. It shows standard rate turns
and level flight before it occurs.
--The quality of damping requires that they be calibrated in
the air.
--Turn coordinators read backwards from attitude indicators.
--The gyro is tilted and spring-loaded. The amount of deflection is
proportional to the rate of yaw (ie turn) and the tilt (not present in a
'needle') makes it respond to rate of roll, making it easier to fly partial
panel.
Knowing
the Systems
You will best learn just how the panel of your aircraft is
related to the various systems of your aircraft by learning to
draw the panel and the dial indications. A brief series of questions
may help awaken your interest. Answers may vary with type,
model and aircraft manufacture.
1. What systems have no gauges aboard for measuring operation
or condition?
2. What electrical component is activated by the initial use
of the battery side of the master switch?
3. Which, if any, of your aircraft circuit breakers can be pulled?
4. What is the minimum oil level at which your aircraft engine
can be operated?
5. What is the effect on the VSI if the static port is completely
plugged?
6. What is the half-life of your aircraft battery with only the
transponder on?
7. If you smell fuel in the cockpit, what is the most likely
cause?
8. What is the difference in air pressure used in the mains and
the nose wheel or tailwheel?
9. What instruments work just as well when removed from the airplane?
10. What is the lowest VHF frequency available on your nav radios?
11. What will you notice during runup if you lean your mixture
to the lean side of peak power?
12. What will you notice if you do not face into a strong wind
during runup with a constant speed propeller?
13. What system is checked without a gauge or instrument?
14. What is the least accurate system on your aircraft?
15. What is the most accurate system on your aircraft?
16. Where are lead weights used on your aircraft?
17. Where does an aircraft have cigarettes?
18. How are aircraft tire valve caps different than those for
automobiles?
19. How are the cylinders of your aircraft numbered?
20. What is the primary cause of every existing FAR?
21. Where is the fuel pump on your aircraft?
AVgas vs MOgas
AVgas: 112.500 Btu (British thermal units) per gallon w/ 1-2 percent
variation
MOgas:--108,00 to 118,000 Btu per gallon w/up to 8 percent variation
AVgas: Consistent octane rating
MOgas: --87 to 94 octant with seasonal and altitude variations
AVgas: Formulated to minimize vapor lock problems (Vapor lock is caused by
'bubble' in lines stopping fuel flow.
MOgas: --Formulated to give easy start in winter and minimize vapor lock in
summer
AVgas: Formulated to be useable down to -72F
MOgas:--Unknown Z-level
AVgas: Can be stored for a year without change.
MOgas: --Gums and additives settle out and will damage system
AVgas: Will not damage fuel system metals or compounds
MOgas: --May contain alcohol or ether with harmful effects on aircraft fuel
systems.
Water in Fuel
--All fuel contains some water
--It takes seven gallons of water to make a gallon of gasoline. (Refineries
are all near water)
--Filling fuel tanks before the air in the tanks can collect moisture is a
step toward reducing water in fuel.
--Unless replaced with fuel, the water accumulating in the air precipitates on
the cooler metal of the tank
--In colder climates EGMME is an additive that prevents ice crystals from
precipitating into water. (Prist)
--Prist is toxic to the skin and lungs.
Filling a knowledge
Vacuum
--Be prepared to spend money.
--Pump life is 500 hours or six years
--Precession involves condition of filter.
--Initial change in air supply is first indication
--Vacuum system is subject to unpredictable failure.
-AI or system failure will show as drift or tumblings.
--Erratic operation involves oil or other fluids in system.
--No gauge indication means open line or defective gauge.
--Leaks are not to be prevented by Teflon tape or thread lube.
--A vacuum back up system covers only the pump and little else.
--Low gauge indication is caused by filter, hoses, regulator or gauge.
--Pressure at full power means leak, stuck regulator, or pump problem.
--A slow death of the system is more likely than catastrophic pump failure.
--Failure to replace entire system along with pump may be poor judgment.
--Regular inspection of components and pre-emptive maintenance is way to go.
--Low pressure requires check of lines, leaks and the last resort pressure
adjustment.
--Proper operation is shown by how the gyros 'park' in a tilted pitch and roll
after shutdown.
--The AI's 'rotation dance' is a visual show of proper operation. A change
shows a problem.
--Failures derive from hoses, fittings, regulators, gauges, couplings, valves,
filters, lights and instruments.
Accelerator Pump
Engage the starter using the ignition switch and advance the throttle. This
way the accelerator pump takes fuel from the carb and "shoots" it
directly into the intake manifold. The accelerator pump is built into the
carburetor, which feeds fuel into the intake manifolds when the throttle is
advanced.
To check the accelerator pump's operation you could have a mechanic remove the engine cowling. With the ignition key out. Place yourself in front of the carb air box and have the mechanic advance the throttle from idle-cutoff to full forward with the mixture full rich. You should hear fuel being shot into the intake manifold, and then see excess fuel draining back down onto the carb air box. When the engine is not running, excess fuel can not be drawn into the cylinders and will drain back into the intake manifolds and gravity will eventually have fuel at the carburetor. Inspect and clean the carburetor fuel screen and fuel strain. Give these screens some attention and verify that your carburetor is receiving a sufficient amount of fuel.
Oil Revisited
--Ways of measuring viscosity, Saybold Second Universal (SSU)/ Society of
Automotive Engineers (SAE).
--SSU of 100 is the same as the SAE of 50
--Use multiweight oils of the lowest viscosity oil allowed for the temperature
in your airplane.
--You don’t need to worry about the lubrication or the oil flow.
--You are more likely to seize a piston by over-revving the engine on startup
on a hot day than a cold day.
--Let the engine warm up at low rpm before raising the power.
--Initial valve clatter due to the hydraulic valve lifters is not a problem if
you use the proper oil.
--Heating the crankcase oil at temperatures below 20-F will keep the main
bearings from pinching.
--Aircraft that fly less than 50-hours a year need oil changes by time not
use.
--Thick oil provides better lubrication than thin oil.
--Rule of Thumb: Preheat oil until it comes off the dipstick in drops instead
of a string.
Dripping Fuel
The dripping from the fuel vent tube after topping off the tanks is
very common. The routing of the vent line from the tank is down hill and once
the fuel expands and starts flowing out bleed hole in the check valve, it will
continue until the siphon action is broken. Compounding this problem is the
fuel from the right tank flowing into the left tank through the inner connect
vent line so if the airplane is parked at a location where the left wing is
low, you can lose several gallons out the vent tube.
Solutions involve not topping off tanks if aircraft is not level. At
annual having
line checked for routing. Parking or using small ramps to level
parked aircraft.
Detonation
Exists when uncontrolled burning of the fuel and air mixture takes place
after the spark pugs have fired. Detonation is un-timed and untamed cylinder
explosions that greatly increase internal cylinder temperatures.
Cylinder pressures are half-again higher during detonation. than normal. Internal parts of the cylinders can melt when detonation extends in time. Unlike automobiles, you cannot hear detonation in aircraft. The internal high temperatures can be caused by low octane fuel, high internal temperatures and excessive power.
Preignition
This second kind of uncontrolled and un-times internal explosion caused by
hot foreign matter inside the cylinder. When internal temperatures are high,
this material can cause the fuel and aix mixture to explode before the piston
and spark plug is ready. Most common cause is related to spark plug failure that
results in higher pressure and temperatures than during detonation. Next cause
in frequency is cross-firing of magnetoes. A helicoil used to improve the fit of
a spark plug can leave a tang sticking into the piston space. Under pressure
alone the helicoil tang can cause preignition. Preignition
cause rise in CHT and drop in EGT
Engine Monitors
---Probes tend to fail open with a zero reading.|
---A full rich mixture and boost pump will help cool both preignition and
detonation.
---You can download the monitor’s data for comparison and analysis to set
norms and variations.
---Power Flow tuned-exhaust system increase power and lower noise levels.
"On Condition"
Is a term used for a for-sale aircraft. It means that it
has passed its recommended overhaul time. This is usually hours air time, but
can also be calendar months since last major.
Example: a typical small Lycoming is gived a TBO (time before overhaul) of 2000
hours air time. So if you are looking at an aircraft that has flown 2100 hours
since its last overhbaul it is "On Condition" As Majoring the engine
is probably the most expensive thing most of us will do with our aircraft, you
should expect to be paying at the low end of the scale for an on condition
aircraft.
Tony Roberts
Re-Engine or Not
---Original equipment is a mass of compromises
---FA STC is a way of removing different compromises
---Common STCs provide power, speed and climb
---Life cycle situation of aircraft is primary motivation
---Issues are cost, possibility and sensibility of making change
---FAA Order 8130.2E is where you must go.
---AB/DAR is amateur-built/designated Airworthiness Representative knows answers
---Factory-built and certificated is not eligible for experimental or anateur-built
status.
---To be a home-built you must do 51%
---AC 20-139 Fabrication/assembly Operation Checklist requires plan agreement of
FAA/DE
---There is no way to beat the system, comply or else
---It is possible with proper planning and outlook
Operational
Procedures for Making an Oil Change
What you need
Sterile area
Rubber gloves
Clean five gallon bucket with lid and large funnel
Have a clamp and piece of screen to catch larger particles
Diagonal. cutters or shears, bread knife, water-pump pliers
Drain hose
Champion filter cutter
Clean work surface to lay out pleats of filter
Clean rages, coffee filters
Dow Corning DC-4 gasket lubricant
Lyle filter wrench and torque wrench with 1" socket
If using a strap wrench have some sandpaper to help it grip
Safety wire and twisting tool
Procedures
Take sample of oil near mid-drain point
Never mix this oil with any other oil
Cutter must press so as to give clean removal of filter top
Filter should drain completely and oil saved in clean container
Use diagonals to cut holder holding pleats together
Run clean magnet down each pleat
A fuzzy magnet pulled from the oil is sign of trouble
Rinse the pleated element in clean solvent in open area
Drain solvent through a clean shop rag or coffee filter
Safety wire should have 6 to 12 turns per inch
Out of specification safety wiring should be redone
You will never know what was done unless you are there
Analysis
Upper limit that requires further study is a pencil tip size in a
spoonful of oil
What happens of this change has direct influence on next and future analysis
http://www.blackstone-labs
---Use only aviation specialized labs
---Ask to see the results and verify your markings on metal filter housing
---Keep your debris separated so results can be verified and re-tested
---Have particles identified as type and source
---Keep as much evidence of samples as you can keep track of in permanent
storage
Re-installation Procedure
---Use longest filter that will fit
---Slip safety wire through tank before mounting the filter
---Your engine may require quick replacement by new filter to keep oil prime
---Confirm filter’s ‘use by date’ information
---Examine engine adapter
---Examine new filter base and gasket
---With new filter upside down whack it to make sure nothing is inside
---Lube new gasket with a bit of DC-(Cartridge-type filters use clean engine
oil)
---Fill filter with new oil before installation to prevent air blockage
---Always make sure twist of safety wire tightens the filter down
---Pre-decide safety wire attachment point criteria
---Safety-wire before leak check
---Do not safety wire to engine mount
Engine Check
---Run engine and check for leaks
Flight check
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Related to Material on Pages 2.25, 2.20, 5.74
Continued on Page 5.73 Electrical
System