Altitude stability in supersonic cruising flight

The importance of maintaining a fixed altitude is increased for aircraft cruising at supersonic speed. The difficulties of altitude control are enhanced by the small flight-path angle required to cause large vertical rates and by the time scale and basic instability of the longperiod motion. The causes of altitude deviation, the magnitude of their effects, and the stability of the motion are defined for a wide range of altitudes and Mach numbers and for aircraft of varying lift-drag ratio, wing loading, thrust law, and pitch dynamics. In addition to suggesting necessary and favorable control laws, the effects of horizontal and vertical wind, atmospheric state variation, and engine “unstarts” are treated.