Stalls -Cont. - P-330_wch50036

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CHAPTER TWO
T-34C CONTACT
steady turn still develops lift greater than weight, but experiences increased stall speeds due to
load factor increases. However, no appreciable change in load factor or stall speed occurs at
bank angles less than 30º.
Angle of Bank
(º)
15º
30º
45º
60º
75.5º
Level flight
(G's)
1.00
1.035
1.154
1.414
2.00
4.00
Notice that above 45º angle of bank, the increase in load factor and therefore, stall speed, is quite
rapid. This fact emphasizes the need to avoid steep turns at low airspeeds - a flight condition
common to stall/spin accidents. (Refer also to NATOPS Vn Diagram.)
It must be reemphasized here that low speed is not necessary to produce a stall. The wing can be
brought into an excessive angle of attack at any speed. For example, take the case of an airplane
which is in a dive with an airspeed of 200 KIAS, when suddenly the pilot pulls back sharply on
the elevator control.  Because of gravity and centrifugal force, the airplane could not
immediately alter its flight path, but would merely change its angle of attack abruptly from quite
low to very high. Since the flight path of the airplane, in relation to the oncoming air, determines
the direction of the relative wind, the angle of attack is suddenly increased, and the airplane will
quickly reach the stalling angle at a speed much greater than normal stall speed.
The primary purpose of high lift devices (i.e., flaps, slats, and slots) is to increase the coefficient
of lift and reduce the stall speed for an airplane. Therefore, flap extension increases the total lift
available and reduces the angle of attack for any given lift coefficient. Full flap extension on a
T-34C produces approximately a 20% reduction in stall speed.
At this point we should examine the action of the airplane during a stall.  In our earlier
discussion of pitching (longitudinal) stability, we learned that to balance the airplane
aerodynamically, the center of lift is normally located aft of the center of gravity. It was also
pointed out that, although this made the airplane inherently "nose heavy," downwash on the
horizontal stabilizer counteracted this condition. It can be seen then, that at the point of stall
when the upward force of the wing's lift and the downward tail force cease, an unbalanced
condition exists. This allows the airplane to pitch down abruptly, rotating about its center of
gravity. During this nose down attitude, the angle of attack decreases and the airspeed again
increases; hence, the smooth flow of air over the wing begins again, lift returns, and the airplane
is again flying. However, considerable altitude may be lost before this cycle is complete.
The associated loss of altitude and control response in the stalled configuration has meant the
lives of both students and seasoned naval aviators. A stall never checks anyone's logbook or
qualifications before it decides to happen. Therefore, it is important to remember that the stall is
not merely a precision maneuver, but an actual situation into which you may inadvertently fly
while concentrating on some other aspect of your flying.
2-10 INTRODUCTION TO T-34C AERODYNAMICS

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