B- 52 Fowler flap
Slotted flap
C- 17 flap
C- 17 leading edge
reduction is a function of the original airfoil shape and
the type of flap used, but decreases of 5 to 10 degrees of
AOA are not uncommon. This is also why your instructor
told you not to use aileron to correct roll near stall. If you
deflect the aileron to counteract a roll, the down-going
aileron will increase the effective AOA of that piece of
the wing. This may push the airfoil beyond its stall AOA,
which will induce an immediate stall on that portion of
the wing. This will then cause the wing to drop, increasing the AOA for the entire downward-moving wing, and a
classic stall spin results. The rudder on the other hand will
be at nearly zero AOA and will have full authority.
Flap History
The most basic flap is the plain flap. It is typically used
for elevator, rudder, and aileron control and is even used
for “flaps.” These flaps are usually hinged at or near the
chord line of the wing (the vertical center of the airfoil
shape) and at or near the leading edge of the flapped
surface. Some have diamond-shaped leading edges with
the point of the diamond falling on the hinge line. Other
designs have the hinge on the top or bottom surface with
a triangular cut to clear the flap when actuated toward
the interfering side. These flaps are seen most commonly
on fabric-covered aircraft or composite aircraft where this
arrangement simplifies covering the surfaces and securing
the hinges. Metal aircraft more commonly have the hinge
near the centerline with just enough setback to form a nice
radius so the gap between the wing and the control surface
stays constant.
As aircraft go faster, the force necessary to deflect
plain flaps, especially on larger aircraft, becomes more
