Automatic Spin Recovery
The problem of recovery from oscillatory spins, where the pilot can be completely disoriented and unable to apply the proper recovery technique, suggests using suitable automatic controls once a spin is recognized. A candidate technique (Lee and Nagati, 2000) suggests applying controls in a direction to cancel the vehicle’s total angular momentum vector. The angular momentum vector is usually close to the angular velocity vector, differing because of unequal moments and products of inertia about body axes.
The Lee-Nagati approach is in two parts. First, the angular momentum vector is calculated several times per second during the spin. Then, at each interval, a minimization problem is solved, finding the control surface angles that minimize a cost function. The cost function is the difference between the vehicle’s momentum vector and the negative of a calculated aerodynamic control moment vector. Although not fundamental to the concept, in the Lee – Nagati paper a sophisticated regression parameter identification scheme is used to model the aerodynamic control moments used to form the control vector. One striking example of the power of this automatic control approach was a calculated recovery from a flat spin of the Grumman/American AA-1B in which a spin chute was actually used in flight.