FURTHER INVESTIGATION OF ELASTIC MODE EFFECTS ON CLOSED-LOOP STABILITY OF A WINGED BOOSTER.
Final rept. for Dec 62-Mar 63,
AIR FORCE FLIGHT DYNAMICS LAB WRIGHT-PATTERSON AFB OHIO
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This report is devoted to a closed-loop analysis of the dynamic interaction of elastic and rigid body modes for a large booster in the ORION class. A variety of possible first and second elastic mode shapes is assumed along with three different sensor locations. Closed-loop dynamics are determined for all combinations of these conditions and for a wide variation in autopilot, actuator, and rate gyro gains. The interaction is shown to be very severe on both the shortperiod and elastic modes. For all cases considered, regardless of the gains used, the real roots corresponding to the first-order actuator and rate gyro time constants were positive, indicating instabilities. It is also shown analytically that there is no combination of actuator, autopilot, and gyro gains which would stabilize the stated system. In addition, the short-period characteristics are very insensitive to orders-of-magnitude variations in system gains. These surprising results mean that conventional sensing and feedback control with single actuation would not be suitable for this vehicle. Author