Stalls -Cont. - P-330

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 30.

Angle of Bank

()

75.5

Level flight

Load factor

(G's)

1.00

1.035

1.154

1.414

2.00

4.00

Notice that above 45 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