Flight Instructors Training Procedures _revised AIC_x

9. PITCHING MOVEMENT
i. Aerodynamic:
a. Positive longitudinal static stability .................................................. Anti-Spin.
b. Effect of the tailplane....................................................................... Anti-Spin.
c. Autorotation ..................................................................................... Pro-Spin.
d. Elevator ........................................................................................... Pro-Spin.
ii. Inertial pitching moments:
a. C-gyro plus roll ................................................................................ Pro-Spin.
b. A-gyro plus yaw............................................................................... Anti-Spin.
The C-gyro, having the greatest mass distribution about its axis, is normally the largest.
iii. Centrifugal flattening moment:
This may be demonstrated with a pointer held at an angle of 45˚ to the ground and
spun rapidly in the horizontal plane – the pointer will tend to spin flat. This moment is
pro-spin.
10. ROLLING MOMENTS
i. Aerodynamic:
ii. Inertia:
a. Autorotation .................................................................................... Pro-Spin.
b. Angle of attack difference............................................................... Pro-Spin.
c. Speed of wings ............................................................................... Pro-Spin.
d. Sweepback and sideslip ................................................................. Pro-Spin.
a. C-gyro plus pitch.............................................................................. Anti-Spin.
b. B-gyro plus yaw............................................................................... Pro-Spin.
C-gyro normally stronger, therefore anti-spin.
11. BALANCE OF THE MOMENTS:
The rate of rotation, wing tilt, incidence, rate of descent, sideslip and the radius of a spinning
aircraft is determined by the balance achieved by the forces in the spin and the effect of the
aerodynamic and inertial moments.
i. Yawing moments.
In aircraft types where the B ratio is larger than A, the inertial moment will be anti-spin.
However, the aerodynamic yawing moment is usually very strong due to the applied
rudder. This moment is pro-spin and is normally necessary to keep the aircraft in a
steady spin.
ii. Pitching moments.
The aerodynamic moments are anti-spin, but with the elevator deflected upwards they
become pro-spin. The resultant of the inertial moments is also pro-spin.
The balance between these two moments gives the incidence at which the aircraft
spins.
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