Figure 1-9 Causes of Autorotation

CHAPTER ONE

T-34C OUT-OF-CONTROL FLIGHT

Figure 1-9 Causes of Autorotation

As the AOA increases in normal flight, both lift and drag increase; but as the aircraft stalls, lift

drops sharply while drag continues to rise. During the initiation of the spin, as rudder is applied

at the stall in the direction of desired spin, the yawing motion increases the speed of the outside

wing. The increase in local airflow shallows the relative airflow vector, which in turn, creates a

reduction of AOA, an increase in lift, and reduction of drag. These forces result in a rolling

motion in the direction of initial yaw input. The inside wing experiences a corresponding

reduction in airspeed and lift, an increase in AOA and drag, which adds to the rolling motion.

Although the outside wing is still in a stalled condition, it is less stalled than the inside wing

(Figure 1-9). Because of the greater lift on the outside wing, the aircraft will roll in the direction

of rudder deflection and will generally go slightly inverted or make a barrel roll type maneuver

during the spin entry. In Figure 1-9, the inside or downgoing wing has a greater AOA, less lift,

and more drag than the outside wing. Figure 1-10 shows how the slightly greater and more

forward tilt of the resultant lift-drag vector of the outside wing drives that wing forward and up

in a self-sustaining rolling and yawing motion known as autorotation. Therefore, the T-34C spin

is described as a nose-low autorotation. In the OCF syllabus, the control release spin is

performed to demonstrate this phenomenon.

Figure 1-10 Self-Sustaining Autorotation

INTRODUCTIONS AND SPINS 1-7