LATERAL AND DIRECTIONAL STABILITY AND CONTROL IN AIR-TO-AIR REFUELING

Application of a wake roll-up method coupled with the vortex lattice m ethod and approximate expressions for the receiver fuselage effect hav e been used to determine the induced loads on a Hercules receiver airc raft behind a KC10 tanker. The induced lends depend strongly on the ve rtical position of the receiver wing and fin relative to the tanker wi ng wake. In the case of steady sideslip there is a large decrease in t he directional stability of the receiver as quantified by the gradient of the rudder angle versus sideslip. This is due mainly to the combin ed effects of the yawing moments due to bank, yaw and side displacemen ts. Minimum directional stability corresponds to the tip of the receiv er fin intersecting the tanker wing wake. The associated aileron angle is two to three times the value in free air in agreement with flight test data. Solution of the linearized equations of motion gives three lateral characteristic oscillations for the air-to-air refuelling case . These include the usual Dutch roll oscillation; a highly damped roll ing oscillation and a divergent oscillation involving mainly bank and side displacements.