Saturday, February 7, 2009

Fundamentals Of Stall Recovery

During the practice of intentional stalls, the real
objective is not to learn how to stall an airplane, but to
learn how to recognize an approaching stall and take
prompt corrective action. Stall recognition and recovery.
Though the
recovery actions must be taken in a coordinated
manner, they are broken down into three actions here
for explanation purposes.

First, at the indication of a stall, the pitch attitude and
angle of attack must be decreased positively and

immediately. Since the basic cause of a stall is always
an excessive angle of attack, the cause must first be
eliminated by releasing the back-elevator pressure that
was necessary to attain that angle of attack or by
moving the elevator control forward. This lowers the
nose and returns the wing to an effective angle of
attack. The amount of elevator control pressure or
movement used depends on the design of the airplane,
the severity of the stall, and the proximity of the
ground. In some airplanes, a moderate movement of
the elevator control—perhaps slightly forward of
neutral—is enough, while in others a forcible push to
the full forward position may be required. An
excessive negative load on the wings caused by
excessive forward movement of the elevator may
impede, rather than hasten, the stall recovery. The
object is to reduce the angle of attack but only enough
to allow the wing to regain lift.

Second, the maximum allowable power should be
applied to increase the airplane's airspeed and assist in
reducing the wing's angle of attack. The throttle
should be promptly, but smoothly, advanced to the
maximum allowable power. The flight instructor

should emphasize, however, that power is not essential
for a safe stall recovery if sufficient altitude is
available. Reducing the angle of attack is the only way
of recovering from a stall regardless of the amount of
power used.

Although stall recoveries should be practiced without,
as well as with the use of power, in most actual stalls
the application of more power, if available, is an
integral part of the stall recovery. Usually, the greater
the power applied, the less the loss of altitude.

Maximum allowable power applied at the instant of a
stall will usually not cause overspeeding of an engine
equipped with a fixed-pitch propeller, due to the heavy
air load imposed on the propeller at slow airspeeds.
However, it will be necessary to reduce the power as
airspeed is gained after the stall recovery so the
airspeed will not become excessive. When performing
intentional stalls, the tachometer indication should
never be allowed to exceed the red line (maximum
allowable r.p.m.) marked on the instrument.

Third, straight-and-level flight should be regained with
coordinated use of all controls.

Practice in both power-on and power-off stalls is
important because it simulates stall conditions that
could occur during normal flight maneuvers. For
example, the power-on stalls are practiced to show
what could happen if the airplane were climbing at an
excessively nose-high attitude immediately after
takeoff or during a climbing turn. The power-off
turning stalls are practiced to show what could happen
if the controls are improperly used during a turn from
the base leg to the final approach. The power-off
straight-ahead stall simulates the attitude and flight
characteristics of a particular airplane during the final
approach and landing.

Usually, the first few practices should include only
approaches to stalls, with recovery initiated as soon as
the first buffeting or partial loss of control is noted. In

this way, the pilot can become familiar with the
indications of an approaching stall without actually
stalling the airplane. Once the pilot becomes
comfortable with this procedure, the airplane should
be slowed in such a manner that it stalls in as near a
level pitch attitude as is possible. The student pilot
must not be allowed to form the impression that in all
circumstances, a high pitch attitude is necessary to
exceed the critical angle of attack, or that in all
circumstances, a level or near level pitch attitude is
indicative of a low angle of attack. Recovery should be
practiced first without the addition of power, by merely
relieving enough back-elevator pressure that the stall
is broken and the airplane assumes a normal glide
attitude. The instructor should also introduce the
student to a secondary stall at this point. Stall
recoveries should then be practiced with the addition
of power to determine how effective power will be in
executing a safe recovery and minimizing altitude loss.

Stall accidents usually result from an inadvertent stall
at a low altitude in which a recovery was not
accomplished prior to contact with the surface. As a
preventive measure, stalls should be practiced at an
altitude which will allow recovery no lower than 1,500
feet AGL. To recover with a minimum loss of altitude
requires a reduction in the angle of attack (lowering
the airplane's pitch attitude), application of power, and
termination of the descent without entering another
(secondary) stall.

No comments:

Post a Comment