Advanced Pilot Training: Brakes

General

Using flaps increases the lift of a wing by changing its effective camber, or increasing its area, or both; and also reduces length of roll upon landing by providing a resisting surface to the passing air.

The increase in lift is accompanied by a large increase in drag and by an increase in virtual angle of attack. If the airplane remains in the same attitude when flaps are used, it will approach dangerously near to the stall.

Use

Correct use of flaps in flight is to steepen the gliding angle and not to decrease the gliding speed.

A depressed flap increases the wing diving moment, generally neutralized by increased downwash on the tail. Simultaneous use of elevator trim tabs may be necessary to maintain longitudinal balance.

Take-Off

Using flaps for take-off increases drag, tending to increase the run, while the increase in lift tends to reduce the run. These two effects combine to give a minimum take-off distance for a definite flap setting.

A split or bent type flap may be lowered from one-fourth to one-half (usually 10 to 20 degrees) to improve take-off. Within these limits the exactsetting will vary with the individual type of air. plane and can be obtained by experiment.

In general, an airplane with flaps in take-off posi. tion will clear an obstacle by a greater margin than it will if flaps are not used. The take-off run itself may be increased. There is no general rule which can be applied. Information determined by test will be in the operation instructions for each type of airplane.

In event of engine failure following take-off in a maximum performance climb using flaps, the danger of stalling is greater than when flaps are not used due to more abrupt stalling characteristics.

CAUTION

If engine fails when flaps are down, keep flaps down. Sudden raising may result in an excessive loss of lift.

Forced Landings

In the event of a forced landing made from an altitude which permits maneuvering and where there is insufficient or unsuitable terrain for rolling to a stop, have landing gear retracted and flaps extended.

Flaps will provide normal drag and lift with which you are familiar in normal landing routine. Don't worry about the damage caused by landing with flaps extended, since it will be relatively slight compared to what might ensue if they were not used.

Landing

Split or bent type flaps limit maneuverability of the airplane and eventually stall it more abruptly. The following recommendations are made for landing:

1. With flaps down, glide at a speed not less than 10 to 15%, above the stalling or landing speed listed in the operation instructions of the airplane to provide sufficient margin of safety against inadvertent stalls and to provide sufficient kinetic energy to force the tail into position for landing.

2. Be sure to maintain gliding speed to the point of leveling off for landing. Using flaps causes an airplane to stall rapidly when leveled off. Consequently you must level off at a lower altitude than when flaps are not used.

3. The effect of a cross wind on a landing airplane is to apply a yawing force which tends to swing the nose into the wind. This effect is greater when using flaps. The resultant effect upon the airplane is to increase lift on the up-wind wing and to decrease it on the down-wind wing. This tends to tip the airplane over in a down-wind direction. Since both wings stall rapidly, the tipping force, though strong, is of short duration. This effect is especially critical in a short coupled airplane.

Unless extreme caution is used, you may overcontrol and lose control. Use caution and sufficient excess speed to insure adequate control. In crosswinds of appreciable velocities, use no more flap than is necessary.

Precautions

1. Don't raise flaps immediately after take-off or at other times when near the stalling speed. An appreciable interval of time may be required for speed and angle of attack to become adjusted to the new condition.

2. Raise flaps gradually to avoid a sudden loss of lift.

3. When controllable pitch propellers are installed, use the maximum cruising rpm position whenever the flaps are depressed. This makes available the maximum thrust under the resulting low speed and high drag condition.

4. Don't lower flaps at an indicated air speed higher than the limiting air speed for flaps posted in the cockpit.

5. After flaps have been lowered, keep air speed below the limiting speed to avoid overstressing the structure.

6. Avoid rapid or otherwise violent maneuvers, including steep banks, when flaps are extended.

7. Use flaps only for normal maneuvers necessary for landing or take-off.

8. Avoid long flight or glides with flaps lowered.

9. Be cautious when using flaps on low winged airplanes on rough ground or on fields that are covered with mud, water puddles, or slush. Don't taxi such airplanes with flaps down because of the limited ground clearance and the possibility of damage to the flaps by objects being thrown against them by the wheels and propeller.

10. Avoid water puddles and slush wherever possible when making landings or take-offs with flaps extended. If water or slush may be encountered on the ground when landing, extend flaps only partially if landing conditions permit.

REFERENCE: Technical Order 01-1-60.