Set the jitter parameters. Set everything to 0 to stop jittering. Vehicle ignores jitter parameters when on ground
self SetJitterParams( (0,0,20), 0.5, 1.5 ); // Jitter up or down randomly within 20 units, switching every 0.5 to 1.5 seconds
For player helicopters, the jitter params are used for jittering the pitch and roll of the helicopter