Variable-Structure Control of a Model Glider Airplane

A variable-structure control system designed to enable a fuselage-heavy airplane to recover from spin has been demonstrated in a hand-launched, instrumented model glider airplane (see figure). It has long been known that the most effective spin recovery technique for fuselage- heavy aircraft involves the use of ailerons to roll the airplane into the spin. This technique might be considered counter-intuitive because the pro-spin aileron deflection tends to initially increase the roll-rate component of the angular momentum of the airplane. However, it restores some controllability, enabling the pilot to perform subsequent maneuvers to pull out of the spin. The design of the present model-airplane control system was inspired in part by recognition that the aforementioned (and conventional) spin-recovery technique mimics a variable-structure control law.