Around flight Mach number I strong normal shocks are generated These arc very sensitive to small changes of the flow field and tend to oscillations.
Control flaps have to produce aerodynamic forces by pressure differences between the flap sales and adjacent wing area. Usually they generate a pressure rise on one side and a pressure drop on the other. Near Mach I the pressure rise at the hinge line provokes a strong shock with strong boundary layer interference This easily results in vibrating loads (buffet) and weakens the flap’s control forces. During transonic acceleration, therefore, the aircraft should not require strong control forces Suited control flaps have swept hinge lines, hinge lines in less ent –
ical regions (for instance close to the trailing edge of the wing), or moving tails.
Engine efficiency is critical at low supersonic speeds. Especially the inlets have to cope with rapidly varying conditions due to sensitive Mach angle variations. The shock system, designed for supersonic cruise, cannot yet establish; an inlet control mechanism, designed only for supersonic cruise shocks, does not work. Measures arc required, therefore, to allow for sufficient inlet efficiency, like special inlet doors.
At high subsonic cruise optimize L/D:
• avoid separation.
• minimize induced drag.
For transonic acceleration:
• minimi/.*’ wave drag which is dominated by interference effects.
• provide control of the aircraft.
• provide control of engine inlet and nozzle.