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decent, the forward slip in usually unnecessary. Some aircraft manufacturers state that forward slips
should not be made with flaps deployed.
Stalls and Spins
The angle of attack which produces maximum lift is a function of the wing design, and is called the
CRITICAL ANGLE OF ATTACK. A stall occurs when the Critical Angle of Attack is exceeded.
Smooth air flow across the upper surface of the wing begins to separate and turbulence is created along
Aerodynamics
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the wing surface. Lift is lost and the wing quits “flying”. THE STALL IS A FUNCTION OF
EXCEEDING THE CRITICAL ANGLE OF ATTACK, AND CAN OCCUR AT ANY AIRSPEED ,
ANY ATTITUDE, AND ANY POWER SETTING.
On most aircraft, the stall starts at the wing root, and progresses outward to the wing-tip. The wings are
designed in this manner so that the ailerons are the last wing elements to loose lift. Flap and gear
extension affect the stall characteristics. In general, flap extension creates more lift, thus lowering the
airspeed at which the aircraft stalls.
Recovery from a stall requires that the angle of attack be DECREASED to again achieve adequate lift.
This means that the back pressure on the elevators must be reduced. If one wing has stalled more than the
other, the first priority is to recover from the stall, then correct any turning that may have developed.
A CG that is too far rearward can significantly affect the ease of stall recovery. The aft CG may inhibit
the natural tendency of the nose to fall during the stall. It may be necessary to force a “nose down”
attitude to recover.
Although weight does not have a direct bearing on the stall, an overloaded aircraft will have to be flown
at an unusually higher angle of attack to generate sufficient lift for level flight. Therefore the closer
proximity to the critical angle of attack can make an inadvertent stall due to pilot inattention more likely.
Snow, ice or frost on the wings can drastically affect lift of the wing. Even a small accumulation can
significantly inhibit lift and increase drag. Due to the reduced lift, the aircraft can stall at a higher-thannormal
airspeed. Takeoff with ice, snow or frost on the wings should never be attempted.
Stall recognition can come several ways. Modern aircraft are equipped with stall warning devices
(usually an audible signal) to warn of proximity to the critical angle of attack. The aircraft may vibrate,
control pressures are probably "mushy", the "seat of the pants" sensation that the aircraft is on the verge
of loosing lift, and other sensations can tip off the pilot of an impending stall. Practice of slow flight and
stalls at altitude is invaluable training in stall recognition.
A spin is a stall that has continued, with one wing more stalled than the other. The aircraft will begin
rotation around the more stalled wing. The spin may become progressively faster and tighter until the
stalled condition is "broken" (stopped).
Usually spin recovery procedures are covered in the Pilot Operating Handbook (POH) for the given type
of aircraft. If one is not available, the following is the suggested spin recovery technique.
a. Close the throttle. Power usually aggravate the spin. b. Stop the rotation by applying opposite rudder.
c. Break the stall with positive forward elevator pressure. d. Neutralize the rudder when rotation has
stopped. e. Return to level flight.
Secondary Controls
Aerodynamics
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Trim
There are some secondary "pilot-controlled" functions which can "trim" the elevators, rudder and
ailerons for improved straight and level flight, thus freeing the pilot from constant attention and control
of the major control surfaces. Most small aircraft have only Elevator Trim. As the sophistication of an
aircraft design increases, Rudder Trim and Aileron Trim are added. In most cases, the elevator trim is an
additional moveable surface on one of the elevator assemblies which causes a “nose up”, “level”, or
“nose Down” trimmed attitude.
In some aircraft, rudder trim and aileron trim can also be accomplished by pilot from the cockpit.. The
purpose of the trim action is to compensate for variations in aircraft loading or other minor factors which
may tend to cause deviation from straight and level flight.
Flaps
Flaps are moveable surfaces on the trailing edge of the wing similar in shape to the ailerons. they are
usually larger in surface area. They are located on inboard end if the wing next to the fuselage. Both
sides are activated together so they do not produce a rolling action like the ailerons.
　
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