Page 3.14 ( 5698)
Use
of Flaps
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Contents
…Flaps; …Flap effects;
...Pitching Moments; ...Putting
on Flaps; ...Taking off Flaps; ...Flaps
and Descent Angle; ...Short Approach with Full Flaps;
...Flaps in a Crosswind Landing; ...No
Flap Landing; ...Partial Flaps; …A
Partial Flaps Answer to a Question; …Flap
Emergency; …Opinion on Asymmetrical Flap
Extension; …Flaps Indicators; ...Slips
with Full Flaps; …The Why of Slips with Flaps;
…Use and Non-use of Flaps; ...Irreversible
Split Flap Emergency; ...Dialogue about
Flaps; ...
Flaps
The total weight of air displaced by an airplane must equal or exceed the
weight of the aircraft for it to remain airborne. This air weight is obtained
by the velocity of the relative wind over the lifting surfaces. An aircraft on
approach and using flaps has most of the airflow over the top of the wing and
horizontal tail. Flaps change the wing lift capability by changing camber and
wing area.
Where the G-limits of a light aircraft are 3.8 positive and 1.5 negative the use of flaps make a significant change in these figures. The flap positive load falls to 2.0 and the negative approaches 1.0. What is means is that flaps should not be used during turbulence or high stress maneuvers. Flaps should be removed in a spin since the recovery from the spin can result in a high G-load pull out.
Flaps are not used as brakes. Flaps are used to increase and maintain lift at slower speeds. During the flare the flaps change horizontal energy to vertical energy that is used to decrease the sink rate prior to touchdown. Fowler type flaps, as on Cessnas, deflect air downward and the gap created on flap deployment helps increase airflow over the wing's trailing edge. In the flare the flaps allow an energy conversion from horizontal to vertical. The air is reflected downward into the ground effect region. This allows the aircraft to be slow, nose high and controlled as it floats to touchdown.
Flaps contribute primarily to the landing approach angle by increasing the 'braking effect' of drag. The drag is used initially to increase the approach angle without a corresponding increase in speed. There is no appreciable (required or created) change in approach speed as distinguished from no-flap speeds. When the approach slope is changed into the roundout and flare, speed is quickly decreased. It is this decrease in speed, the horizontal slowness of possible ground contact that protects the aircraft structure. The more flaps available and used, the slower the speed, the slower the touchdown and shorter the rollout.
Flaps can change the camber or curve of the wing airfoil by adding 1/4 of the wing cord without changing the critical angle of attack. The efficiency of the wing at different speeds can be changes as required. When flaps are added the zero lift line changes, as does the angle of attack. Exceeding this angle with or without flaps will cause a stall. As flaps change the trailing edge of the wing the chord line (zero lift line parallel to the relative wind) between the leading edge and trailing edge of the wing is changed.
With each additional degree of flaps both lift and drag are added but in different proportion. Initially the gain in the coefficient of lift exceeds the increase in drag and reduces the stall speed. What is means is that the stall angle of attack changes with every change in flaps. Every addition of flaps increases the stalling angle of attack and reduces the maneuvering speed (energy) margin. The first 15-degrees of flap will increase the lift and shift it toward the rear of the wing. This gives a corresponding pitch down movement of the nose. Over 15 degrees of flap the amount of drag begins to exceed the amount effective lift and there is a significant increase of wing induced downwash on the horizontal tail surfaces which causes a corresponding pitch up of the nose. The excess drag provides superior glide path control and approach aim. Flaps replaced the slip as a descent device for landing accuracy. Spoilers are a still better means of giving the drag effect. Gliders, with spoilers, habitually hit between 10' aiming markers.
Full flaps function best at a range between 1.3 and 1.6 of stall speed. Any slower, the stall angle of attack and narrow maneuvering speed (energy) margin makes actual constant level flight close to the ground in this configuration very difficult. Flaps increase the lift factor but decrease the angle of attack prior to stall. The critical angle of attack to flying attitude range of the wing is much less with than without flaps. This is one of the reason stalls with flaps are a 'surprise'.
Depending on the manufacturer, the aerodynamic geometry of the flaps will
affect trim. Except for the C-152 all Cessnas with 40-degrees of flap
extension appear to have a one full turn
of trim TO ten degrees of flap relationship if power is 1500 RPM.
The manufacturer's recommended landing is using full flaps. Full flap landings
provide the best aim to the runway. Side benefits are to reduce wear and tear
on the aircraft by slower ground contact, less tire wear, and less required
braking. Once you have acquired reasonable mastery of full flap landings you
should include periodic landings with no flaps and partial flaps. The no-flap
landing is the best one to use when practicing slips to a landing.
Less than full flap landings will flatten the glide angle and make touchdown
point accuracy more difficult. The approach speeds are the same with or
without flaps for the C-150, 60-kts. In the roundout with less than full flaps
the pilot must be aware that the lower drag will mean greater lift during
flare. Using the same yoke movement as with full flaps will cause a balloon.
This is especially true if the flare is close to the ground. For every three
full flap landings you would be well advised to make at least one partial flap
landing to maintain the correct 'touch'.
The discussion about flaps is directly related to the nose-wheel shimmy
discussion. I see this as an instructor problem, though most instructors
resist assuming any accountability. It is much easier to teach students to
make partial flap landings because less precise airspeed and attitude is
required. The partial flap landings are far more apt to result in nose-wheel
first landings at a much higher ground-contact speed. A few such landings will
lead to nose-wheel shimmy.
There is another side to the partial-flap coin. The pilot who first learns to do such landings is more likely to use them as an option. Cessna, in a 'commercial' decision reduced the degree of flaps available in order to increase the useful load of its aircraft. This gave us the C-152 and later models of the larger Cessna with only 30 degrees of flap. Only those who learned on earlier Cessnas can appreciate the difference in landing precision that was lost.
The learning 'Law of Primacy' says that under sufficient stress you will resort to the way a process is first learned. A student who is taught the 'easy' way to fly without trim is entering a world of hurt in flying high performance aircraft. A student who has never learned how to use and anticipate power effect will find transition to a twin a carnival experience. Poor initial instruction from the very beginning is the most insidious because the student has no prior reference on which to base an opinion.
The student concept of a good landing is often based on the 'landing' learned while playing with toy airplanes. The 'greaser' is not the good landing you should be seeking. The landing should be a surprise. You should not land the airplane. The airplane should land you.
I really wonder how many of the pilots in the shimmy/flap discussion have been taught to do touch-and-goes without ever touching the nose wheel? Try it; do it. Once you make a full-yoke-back and Up landing you should never be satisfied with any other. If you can't do it, find an instructor who will help you correct any problem. Nose wheels are for taxiing and not for takeoffs or landings.
How many react to initial ground contact with a forward yoke and full sight
of the runway. (bad) How many hold the yoke back and UP after ground contact
in an effort to see how long nose-wheel contact can be delayed. (good) The
more flaps you use the more difficult it is, but it should be done.
One last rant. I fly in a flying club where the C-150 and C-172 have had a
long history of nose-strut problems. In past years I have offered to take
various instructors up and demonstrate how to prevent damage with me paying
the way. I have never had any takers. At the club meetings the damage is
always blamed on the pilots and students, never on the instructors. I feel
that the cause and responsibility rests with the instructors. They refuse to
admit any accountability. Sad.
Flap Effects
The good/bad effects of flaps on an aircraft are multiple
--Increase lift
--Increase drag
--More abrupt stall
--Lower stall speed
--Decrease climb rates
--Change pitch attitude
--Increase approach angle
--Change trim requirements
--Decrease distance to lift-off
--Far narrower aerodynamic stall range.
--The use/misuse of flaps is a judgment situation
Pitching Moments
Pitching moments makes the aircraft rotate around its center of gravity
either nose up or nose down. Any single change in configuration usually
requires an offsetting adjustment of trim. The use of flaps is a change in
aircraft configuration as is the landing gear. In a C-182RG the simultaneous
retraction of landing gear and 10-degrees; of flaps have offsetting pitch
changes so that no trim adjustment is required. A nice piece of engineering as
is the 1:1 relationship that exists between notches of flaps and a full turn
of trim in many Cessnas.
Just adding flaps will cause an aircraft to pitch up or down depending on how
the change in lift and drag created is positioned around the center of
gravity. Flaps lowered on high-wing usually cause a nose-up pitching moment as
the camber changes the lift around the center of pressure. The resulting drag
also causes a nose-up pitch. Low-wing aircraft flaps causes drag that pitches
the nose down. Only the aggregate of pressures of lift and drag determines the
direction of pitch change.
Flap extension also affects the airflow over the horizontal tail surfaces and
thereby affects its lift. This lift is normally a downward force and the flow
from the flaps can have a greater effect than either the camber or drag. The
extension of the gear can, at various points of the extension cause either up
or down pitch changes. This gear effect tends to be more marked in low-wing
aircraft than in high-wing. The last configuration changes that can have
effects are in power or propeller changes.
Putting on Flaps
The use of flaps is the most practical way to lower the liftoff speed and
touchdown speed and thereby shorten the takeoff and landing distances. Flaps
increase drag, shift the lift/angle of attack relationship, reduce lateral
control and the maneuvering load factor. The flap can increase the angle of
climb or descent and reduce float. Flaps make it possible for the pilot to
improve his landing approach judgment and aim. Along with this improvement
comes a slower ground contact speed but not necessarily a slower approach
speed.
Vary your use of flaps to improve your mastery of the aircraft. Every
extension of flaps through various settings will give a predictable change in
flight and performance characteristics. Rate of climb is always less
with use of flaps during climb.This is a requirement by the FAR's.
You should cycle the flaps through various settings of power and trim during
your training until you can both predict and anticipate what will happen. In
Cessnas the addition of flaps while maintaining the same speed by trim
corrections will improve over-the-nose visibility. Flaps without trim
adjustments will generally cause low-wing aircraft to pitch down. In level
flight, adding power will cause pitch up and reducing power will lower the
nose somewhat in proportion to the amount of flaps extended. Good operating
practice calls for the maximum application of flaps as crosswind conditions allow.
The student should practice using a count to apply Cessna flaps where an
indent is not installed. Too many things can go wrong with aircraft control if
the attention (eye) is focused on the relatively slow movement of the flap
indicator to a desired position. Different models (years) of Cessna have flap
switches that operate differently and even opposite. Practice use of the flap
switch to determine in which position it must be held, will neutralize, or
stick. The most common switch must be held down to lower flaps, will center
when released from down, and will bring the flaps all the way up when set (but
not held) in the up position. Thus, in order to milk up the flaps in small
increments the switch must be held between the fingers and moved accordingly.
Taking off Flaps
Milking the flaps is a required skill in certain slow flight and go-around situations. At these times full power should first be applied, throttle
and then C. H. and a minimum level attitude attained before removing any flaps
at all. Any time the go-around airspeed is less than 60-kts the aircraft
should be held in level flight and the flaps should be milked up. Milking
requires that the flap handle is held throughout as brief spurts of movement
with the handle raise the flaps a bit at a time. As more
airspeed is acquired the flaps may be brought off more quickly. When climb
speed is attained the flap switch may be placed in the up position and a climb
attitude established. The flaps motor cuts off when flaps are full up or
down.
The danger of teaching the dumping of flaps to a student lies in the law of
primacy causing a future retractable pilot using the gear lever instead of the
flap lever on the post landing rollout. There is some argument as to the best
operation of flaps after landing. Because of a proclivity for gear retraction
accidents to occur to those pilots who practice bringing up flaps on landing.
(They use the gear lever instead of the flap lever). Recommendations have been
made that flaps be left down until clear of the runway and stopped. In line
with the learning law of primacy such a practice has much to recommend it.
I strong wind conditions the flap
rollers may jump from their tracks. The flap motor and gears are capable
of seriously bending and twisting the flaps when the rollers are off track.
However, there are wind conditions when the ground control of the aircraft
necessitates getting the flaps up as soon as possible. Also there is a
tendency for many pilots to apply brakes with the flaps down in such a manner
as to lock the tires or to skid. The aerodynamic lifting of flaps, even under
a light wind, is such that tire damage can result. The practicality of
economics says to bring up the flaps on touchdown. If the landing shock causes
the pilot to allow the yoke to move forward, the flaps can cause a condition
known as 'wheel-barrowing'. This means that the lift from the flaps when added
to the yoke position is sufficient to lift the main wheels off the pavement.
This means the only ground contact is the nose wheel. Such a 'wheelbarrow'
condition results in instant loss of control and a ground loop (very sharp
turn). There are many landing situations where the yoke is held still or moved
back and up. There are none where the yoke should be moved forward after
touchdown.
Flaps and Descent Angle
The installation of flaps on aircraft makes possible a controlled steep
approach. This has improved the ability of pilots to judge their arrival at
the runway. There is an additional safety factor in using flaps. In the event
of engine failure, the removal of flaps will make a significant increase in
glide distance. (See flap emergency) A C-150 with full flaps has a glide angle
of about 11 degrees in a no wind condition. VASI lights are usually at 3
degrees. Under most conditions a White over White VASI is acceptable in a
Cessna until short final. Any head wind can increase the glide angle
proportionate to the wind velocity. The untrained eye is able to detect
angular differences when they exceed 5 degrees. A diagram of the runway
showing a steep approach with a 5 degree angle of error will show how much
more accurate the steep approach is. Compare this to the aiming error likely
if the 5 degrees is drawn to the runway from a shallow approach. You must draw
it to see it. _\_____________
Short Approach with Full Flaps
For pure simplicity and accuracy, the short approach wins. Downwind do the
prelanding check. Abeam the numbers pull Carb Heat, reduce throttle to 1500
RPM. Hold altitude just long enough (5 seconds) to have airspeed reach the
white arc. Apply full flaps. Fly 60 kts. No trim will be necessary. Turn base.
Turn final. Roundout. Flare. Back on yoke and throttle. Rollout. Cleanup. If
this were the only landing taught solo in five hours is possible. 10-degrees
of flaps selected on downwind will not create a problem unless the crosswind
is at 90-degrees and over 15-knots. Between 5 and 15-kt crosswinds limit flaps
to 20-degrees. Above 15-kts no flaps should be used. The addition of airspeed
and power can increase rudder effectiveness. It is rudder power that
determines ability to maintain the nose parallel to the runway centerline.
There is no crab wind correction on final. The wind is compensated for by a
wing low, opposite rudder, half Dutchroll correction as required to keep the
aircraft course aligned with the runway and the nose straight (parallel) to
the runway. The wind velocity will change as you descend so will your aileron
and rudder applications. Proficiency in the Dutch roll makes these changes
reflexive.
If you are unable to maintain the nose parallel to the runway heading with
full rudder, increase the speed to gain more rudder authority. The increased
speed and rudder power let you bring the nose into a parallel line with the
runway. If such a lowering of the nose for speed causes a descent below the
desired glide path, apply full power and then back off as required to maintain
approach speed. The 'Dutch roll' skill is required to keep such changes and
adjustments smooth.
Flaps in a Crosswind
Landing (Instructor)
Flaps provide a surface area for a crosswind to act upon; the more flap
the more surface. The upwind flap is more affected than the downwind flap. In
the wing low, slip approach the lowered wing partially shields the flap and
helps keeps the flight path aligned with the runway. The more flap used the
less it is shielded and the more rudder required for lateral control. This
lateral control difficulty increases as the flap extension reaches 40 degrees
and the crosswind component reaches 90 degrees. Better rudder power can only
be attained by an increase in airspeed. The crab-kick crosswind landing is
another way of accomplishing a successful landing even at slow speeds.
However, timing of the touchdown 'kick' is very critical to prevent
damaging side loads to the landing gear and gear box..
The stronger gustier and more nearly 90 degrees the wind is to the runway the
fewer degrees of flaps should be used. Under certain gusty strong wind
conditions it is possible for the flaps to blank out the elevator and
horizontal stabilizer from its normal flow of air. When the elevator/
horizontal stabilizer stalls the nose goes straight down--NOW. Many Cessna
manuals say that slips are not to be made with flaps. A slip can blank out the
tail surfaces. However, this restriction does not apply to the wing low slip
used to maintain runway alignment during cross wind landings.
The selection of flaps in crosswind conditions can be delayed until on final.
No flaps should be added within 200' of the runway because of the possibility
of airspeed control problems. Using less than full flaps in crosswinds should
not change the approach speed but may increase the touchdown speed to the
benefit of rudder control required for keeping the nose parallel. The approach
attitude of a no flap landing is closer to the actual landing attitude than is
the flap landing. No flap landings will take longer to decelerate so the flare
to landing attitude will take longer with greater margins of error possible.
Have plenty of runway for no flap landings because you are much more likely to
make a judgment error as to where touchdown will occur. Any flaps used in a
crosswind should be removed immediately on ground contact to prevent a
weathervane turn from occurring
No Flap Landing (Instructor)
A no-flap landing uses more runway, requires more braking, and lacks
obstacle clearance capability without requiring slips. You can determine a no
flap approach speed by using the no flap calibrated stall speed and
multiplying by 1.3. Refer to the POH to get the IAS. POH speeds are always
based on gross weights unless otherwise stated. The requirement of more
runway is due to a shift in the touchdown point caused by a shallow glide
angle. An obstruction will require a slip to allow adequate runway in most
situations.
The no flap landing is best practiced in all conditions but best used in gusty
conditions. Such a landing may never be needed but should always be available.
Flap landings occur close to aerodynamic stall and compromise control
effectiveness. No flap landings retain a desirable crispness of control with
some sacrifice of stall speed. This control may be required with the higher
speed of touchdown and greater leverage of any swerve.
The no flap landing lacks the accuracy of flap landings due to the shallower
glide angle. Downwind do the prelanding check. Abeam the numbers pull Carb
Heat, reduce throttle to 1500 RPM. Hold altitude and heading. Trim down three
full turns for 60 kts. Since no flaps will be used the downwind will need to
be extended. This is a judgment call and affects accuracy. Turn base and fly
60 kts. Turn final and fly 60 kts. The reduction of power is now the only
desirable accuracy adjustment. Full power may be added. (See
"Decelerating approach") Once power is off a slip is an acceptable
adjustment. (See slips) Roundout. Flare. Touchdown. Cleanup.
The power off no flap landing is not recommended as a continual practice
because it can shock cool the engine. The procedure is as above except that
there is an apparent rapid descent. This causes the pilot to attempt to slow
the descent by raising the nose. Don't! You will lose airspeed and lose the
flaring capacity that goes with the proper airspeed.
Partial flaps (Instructor)
Using partial flaps is sometimes used as an easier way to teach landings.
Partial flaps allow the nose to lift higher in flare without full yoke
movement. The partial flap go-around does not require such radical control
pressures. Any stalls are going to be gentler than with full flaps.. Any power changes are going to
give a more pronounced change in speed and/or pitch. Cessna took an
inadvertent step in that direction when reducing flap extension to 30-degrees.
I believe that all degrees of flap extension from 0 to maximum should be
taught and expected of a pilot.
Twenty degrees of flaps will lower the nose, and make the descent steeper.
Either one or two notches will lower the nose and allow an easier flare than
would no flaps. Thirty or forty degrees of flaps will lower the nose still
more and will make the descent steeper. Any flaps mean that any climb will
require more power. A climb with flaps will require considered speed control.
The flaps you use should be sufficient to create a controlled descent
depending on wind conditions. Twenty degrees of flaps are mostly lift with an
element of drag. Any additional flaps beyond twenty degrees will be mostly
drag. On the other side of the coin, the sight angle of a partial flap landing
is not as precise as is the full flap sight angle. The touchdown speed is
going to be somewhat faster and ground contact correspondingly more firm. The
additional speed and float inherent to the partial flap landing means that
there is an increased likelihood of running out of runway. This possibility
means that the inexperienced pilot may delay the go-around and attempt to
'force' and 'hold' the plane on the runway. When this happens the weight is
transferred to the nose wheel. All of these conditions give the greatest
potential of a subsequent directional control problem. A wheel-barrowing ground
loop becomes the most likely outcome.
I teach the standard landing as using maximum flaps for wind conditions. In
normal wind down the runway conditions I teach the use of full flap landings.
This approach minimizes the speed and float over the runway. It does require
precise airspeed control and careful use of power reduction and yoke movement.
Any go-around will require considered anticipation of yoke pressure, rudder
and power application.
I also expose my student to those situations where only partial flaps may be
appropriate. I suggest that additional flaps within 200 feet AGL may require
attitude adjustments beyond the beginning student capability. Even though the
partial or no flap approach may be flown at the same indicated speed as the
full flap approach, the float will be considerably more and the touch down
speed higher in the full back yoke condition. The best landing is made as slow
as possible.
A Partial Flaps Answer
to a Question
There is no 'wrong' in most landings where the available runway is adequate.
Most POHs allow less flaps under certain conditions but generally recommend
full flaps since they allow a slower touchdown speed, a steeper approach for
better 'aim' and a shorter roll-out.
Later models of Cessna have gone from 40-degrees to 30-degrees. They did this
to raise the useful load. This load is determined by the climb capability with
full flaps at gross. This was a sales gimmick by Cessna that sacrificed some
very useful performance qualities in older aircraft. Cessna did very much the
same thing when they cuffed the leading edge of their wings.
When you use less than full flaps when not advised due to crosswinds, you are
essentially duplicating to another degree what Cessna has already done by
going to 30-degree flaps. I own a C-172M which has a 150 h.p. engine and
40-degrees of flaps available. I can make it an N-model by changing the
cylinders to give 160 h.p. and limiting the flaps to 30-degrees. By doing this
I get 100 pounds more useful load. Instead I have gone to a 180 h.p
engine and a Power-Flow tuned exhaust (Read under C-172 Techniques) so I may
get over 200 h.p.With a longer propeller and greater pitch to prevent red-lining the rpm I will
have a 1000 fpm
climb rate but only about five knots increase in cruise. It would take
about a 600hp engine to make a C-172 go 250 knots. As it is the
P-factor is so great as to nearly overpower the rudder input unless power is
added slowly.
Since I value my aircraft I always land with maximum flaps except in
crosswinds. I try to make full stall landings with a smigin of power to cover
my mis-judgments. I avoid using brakes where practical.
Whenever you use less that full-available flaps in doing maximum performance
landings you are giving up some of the aircraft capability. The only time this
might be 'wrong' would be when maximum capability determines survival. With
this in mind, you should at least practice some full flap maneuvers.
I get the impression that you have concerns about the full flap go-around. The
most common error during such a go-around is by not holding the aircraft level while
getting in full power. Do not climb or attempt to climb until you have removed
your flaps incrementally and allowed the aircraft to at least Vx. As you climb
then you continue to remove flaps incrementally so long as you continue to
climb. This procedure requires that you are focused outside the aircraft and
do the inside-the-cockpit items by feel.
Flap Emergency (Instructor)
A simulated emergency-landing situation that deserves instructional
attention is that of engine-failure on short final. Create the following
situation on a 5000' or more runway. Arrive at short final with full flaps, at
least 1500 RPM and the slowest approved approach speed. At 400' take off the
power. The student should immediately remove all flaps and use the yoke to
maintain the same approach speed. The initial reduction of power should make it
obvious that the aircraft will be unable to reach the runway in its full flap
configuration. The immediate removal of flaps will cause a sink of nearly
200'. These negatives are soon seen to be offset by the flatter glide and
extended glide path made possible by the absence of the flaps. When done
smoothly, touchdown should occur about 2000' down the runway. Introduce this
procedure shortly before solo. In 35 years this knowledge has prevented
at least two off-airport landings by my soloing students at Concord CA..
One of the greatest procedure rules for an emergency is: "Undo what you
just did. This applies directly to flaps. If you put in flaps and something
untoward happens, take them off NOW. The effect in a split-flap application
can be reduced by applying flaps incrementally.
Opinion on
Asymmetrical Flap Extension (Emergency)
I would climb to a safe elevation AGL, watching closely for any sign of a
rolling moment that I couldn't
counteract. Put the nose down if you get close to full aileron deflection
staying level and get a little more
speed.
Then I would slow down until I reached 3/4's deflection on the ailerons and
note that airspeed. Then I would proceed to a suitable airport, preferably one
without a crosswind if possible, and, keeping the airspeed above the speed
noted, proceed to land.
On the occasions when I did find myself with a "split flap"
condition, I found that I could maintain wings level down to my usual landing
speed, so I went ahead and landed. The minimum control speed for the split
flap condition may vary between different airplanes, as well as with the
actual amount of flap extended.
First, fly the airplane. Then figure out what your new limits may be. Then
find a suitable place and land it.
HighFlyer
Flaps Indicators (Instructor)
The most practical way to lower flaps without indent stops is to use the
indicator only as a check. A 1-2-3-4- count on the flaps switch can be timed
to give 10 degree flap application. Every individual will need to perfect
their own count for a particular aircraft because of individual variations of
speech.
The application of flaps will depend on the situation with variations from the
normal 10 degrees before turning base, 20 degrees on base, and full flaps on
final. If you plan to do slips it is best not to use any flaps. If there is a
crosswind the stronger it is the fewer degrees of flaps the better. Flaps in
cross winds will vary also according to pilot capability.
During a closed traffic practice session the amount of flaps may be varied.
Going around and around repeating the same procedure with the same mistakes is
not the way to improve. It is vital that the pilot keep track of the trim
position as it relates to flap position. Any unanticipated yoke pressure is a
warning about flap position or trim position.
Flaps are a source of drag that permits a steeper approach and greater landing
accuracy for a given approach speed. Flaps reduce the aerodynamic stall speed.
This reduction effectively reduces touchdown speed, shortens landing roll
distance, improves forward visibility, and improves landing accuracy.
Extending flaps increases the effective angle of attack of the horizontal
tail.
Cessna in its original designs used 40 degrees of flap but this was reduced
to 30 degrees where gross weights were
increased. This was to meet both go-around requirements and potential accident
liability. The flare control required
for different flap settings will vary so landings should be practiced at each
setting.
Slips with full flaps
If the landing approach is so high that even after full flaps, power off,
and 55 kts IAS a slip is required this is indicative of poor planning and
procedures. The use of slips in a flap-equipped aircraft is indicative of
misjudgment. In addition, the POH (Pilot's Operating Handbook) for Cessna 150
and 172 expressly recommends against the use of flaps when slipping the
aircraft. With flaps down, it is possible for the airflow that normally flows
over the wing back to the horizontal stabilizer to be interrupted. The flaps
"blank out" the stabilizer and elevator. It stalls.
This causes an abrupt, straight down nose attitude. I have experienced this
condition when I had a total of four hours of private pilot time. It happened
during a wind shear with gusts to 22 knots. I had been taught to land only
with full flaps. The shear caused the flaps to blank out the airflow to the
stabilizer/elevators. At 400' I was going straight down.
The Why of "Slips
with Flaps"
Over the years of Cessna aircraft production the Pilot Operating Handbook
has grown more and more extensive in advising on allowable flight procedures.
This has been a direct result of lawsuits and insurance settlements. One of
these additions to the POH has been regarding the use of flaps.
Prior to the invention of flaps, all aircraft would control their descent,
along with the use of power and airspeed, through the use of slips. A slip is
a cross-controlled right-left or left-right application of rudder and aileron
that through its lack of coordination uses the side of the aircraft as an air
brake. As the slip decreases forward motion, the aircraft's rate of descent
can be increased dramatically. A slip is most often applied without flaps, but
not necessarily so.
It was discovered that an occasional abrupt application of a slip when a
high-wing Cessna had full flaps would cause a bobble or wavering of the nose.
There has never been, as far as I can discover, an accident from this event.
Never the less, Cessna Corporation in an effort to reduce the potential
financial impact of an accident, appended to their POH a remark to the effect,
"Slips with flaps not recommended."
Over the years a broad series of interpretations of this mild warning have led
to exaggerated statements and even prohibitions. These have been spread by the
uninformed, misinformed, deluded, and imaginative until it has become a matter
of aviation folklore. The misconceptions arising from this folklore has led to
a failure of many pilots to learn and use what can be a very useful aspect of
aircraft control. The "Slips with Flaps' T-shirt is a small effort at
facing up to the teaching and learning problem derived from the lawyer
instigated statement. The number of my aircraft as it appears on the shirt is
in recognition of my contribution to the teaching and learning of flying.
Use and Non-use of
Flaps
--Flaps are usually certified only to 2-Gs.
--Aircraft can be slipped with and without flaps.
--Normal landings use the maximum flap extension.
--When on the ground in windy conditions remove your flaps asap
--Severe misjudgment of a situation will require both flaps and a slip.
--The flap motor is capable of bending the flaps if it is off its guide
tracks.
--You should practice no-flap landings to maintain that region of your skills.
--The greater the crosswind component the less flap extension based upon your
skills.
--The use of flaps allows a pilot to maintain altitude in the pattern while
close to the airport.
--Abide by the white-arc flap use limitations of the airspeed indicator to
avoid eventual flap failure.
--Flaps are to allow a steeper angle of decent and better touch down aim
without an increase in airspeed.
--On engine failure in the pattern, consider removing any flaps to extend
gliding range. at approach airspeed.
--If you are into turbulence sufficient to slow below the yellow zone of the
airspeed indicator, don't use flaps.
Irreversible Split Flap
Emergency
--Reduce power to get lowest controllable airspeed.
--Make initial turns shallow into jammed control.
Dialogue about Flaps
>Mike White wrote:
> Gene,
>> Your web site has a lot of good information and insight. However, I
must take exception to some of your statements in the Flaps section:
> You say, "The total weight of air displaced by an airplane must equal or > exceed the weight of the aircraft for it to remain airborne.". This > erroneously appears to state that an airplane floats on air. In reality, an > airplane flies by accelerating air downward producing an upward reaction
In my opinion your use of the term accelerating air downward is just another way of my saying displaced perhaps with more precision.GW
> Later you state, "Flaps are not used as brakes.". In the next paragraph, > you state, "Flaps contribute primarily to the landing approach angle by > increasing the 'braking effect' of drag.". You really should clearly state that flaps produce both lift and drag.
More interesting is the fact that the final approach speed of most aircraft with and without flaps is exactly the same. The flaps improve the aim of the approach by changing the landing approach angle. Every flying surface produces both lift and drag. My intent was to point out the specialized effect of the flaps. GW
>I came across your site by Googling on "Cessna Flaps", hoping to find out > when Cessna decided to restrict full flaps, on high wing singles, to 30 degrees. I see that you state, "Cessna, in a commercial' decision reduced the degree of flaps available in order to increase the useful load of its
> aircraft. This gave us the C-152 and later models of the larger Cessna with only 30 degrees of flap.". Can you tell me the source of this information,
The C-150 into C152 occurred about late 1976. Compare POH’s. There is a Cessna book giving all the changes by year and models somewhere out there…. and, perhaps, when this occurred, and how would it increase the useful load/ I find 40 degrees, with the extra drag, to be very helpful to get me down, Ш over obstacles, onto short fields.
I presently own a C-172M with 40-degrees of flaps but it also has a180 h.p
Lycoming and a Power-flow exhaust which gives it nearly 200 h.p. Only five
knots faster but climbs well. My preference, too, is 40-degrees.
I am presently instructing in a C-150, a Grumman AA-5B, and will soon be
teaching in a Sport Light aircraft. Over 11,000 total hours and the C-150 is
still the most fun to fly. By FAR related to aircraft performance the useful
load of an aircraft is determined on the go-around capability of an aircraft
at gross in a full flap configuration. I can’t quote the exact FAR but its
somewhere in the regulations.
The go-around and even flight capability of the 40-degree flap Cessnas was
very marginal until the removal of some flaps. The Cessna was in competition
with the other manufacturers to improve performance. The easiest, quickest,
cheapest, least obvious way to get useful load was to lower the full flap
position of a given aircraft.
Were you to look at the performance figures of the C-172 M and C-172N you will
(should) find that the N model has about 100 pounds more useful load. The only
differences in the structures was in the reduction of flap extension making
the N with 100 pounds more useful load.
The C-152 is a very poor redesign of the C-150 brought about by a ‘threat’
of the U.S. government that 87-octane would become unavailable. Cessna tried
to jump the gun by putting a different voltage battery and engine using
100-octane into a C-150. This meant that weight and balance shifts could be
‘adjusted’ by several changes one of which was limiting the flap extension
to 30-degrees. The engine has had plug fouling problems and many other
difficulties making it a relatively expensive aircraft to have.
Should you read my site about the engineered balance of power, trim and
flaps of the C-150 when compared with what they got in the C-152 we lost a
great deal. I hope I have answered your concerns. Thanks for reading my site.
Gene Whitt
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