Fighter Combat

APPENDIX 413this condition occurs, a roll will commence, accelerate to a maximumvalue, and then stabilize at that rate. A stabilized roll rate is attained whena balancing, or "damping," moment is generated which offsets the torqueof the roll controls. This damping moment is produced primarily by liftdifferences between the two wings caused by one wing moving upward andthe other downward, and is proportional to the roll stability of the aircraft.In general, the more stable a fighter is about the roll axis, the slower its rollrate will be.Figure A-20 graphically illustrates the effects of speed on steady rollperformance. The charts in the figure discount both compressibility,which may reduce the effectiveness of roll controls or even cause rollsopposite to the intended direction (called "roll reversal"), and "aeroelasticeffects," which may cause similar problems as a result of the wings twistingunder the torque of the roll-control deflections. Note that as speedincreases, the force (F r ) required from the pilot to maintain full controldeflection (8 r ) increases until reaching the limits of his physical ability,after which further speed increases result in reduced control deflection. Inthe range of maximum-control deflection, roll rate increases almost linearlywith speed, reaching a maximum at the highest speed at which fullcontrol deflection (8 rMAX ) can be maintained. Roll-rate capability thendecreases with further speed increase, possibly to very low values at highspeeds. To maintain roll performance at high speeds, power-boosted orfully powered controls are often employed to enable the pilot to attain fullcontrol deflection. With powered controls the pilot's control inputsusually position valves that allow hydraulic fluid pressure to move thecontrol surfaces. The effects of such systems are shown by the dashedlines. For supersonic fighters it is also desirable to make these controlsirreversible, so that variations in airloads on the control surfaces are nottransmitted back to the pilot. Shock waves moving around on these surfacescan lead to some very distracting and misleading feel cues, makingaircraft control difficult. With such controls, artificial-feel systems areusually provided so that control forces vary as the pilot would expect.Figure A-19. Load Factor versus Radial G in Vertical Maneuvering