Flight Mechanics of Ram-Scram Transition

Abstract

Among known air-breathing propulsion systems, the system that can be operated over the widest range of flight Mach numbers is the dual-mode ramjet-scramjet. In such an engine, either subsonic combustion or supersonic combustion can occur in a shared flowpath, and the mode of operation is determined by the flight condition and control inputs. Recent research has indicated that the steadystate thrust of such an engine is discontinuous across the transition from one mode to the other. This work discusses evidence for that discontinuity and discuss conditions and strategies required to maintain control through ram-scram transition. Nomenclature a = acceleration A = duct area c p = specific heat at constant pressure C L = lift coefficient C D = drag coefficient I = impulse function K = drag polar coefficient m f = cumulative fuel consumptioṅ m = mass floẇ m f = fuel mass flow rate M = Mach number p = pressure q ∞ = freestream dynamic pressure Q f = specific fuel heat release R = normalized gas constant S = reference area t = time T = temperature u = total flow speed u = vector of control variables V = velocity of vehicle x = vector of state variables γ = ratio of specific heats, flight path angle η c = combustion efficiency ρ = density τ = temporal integration variable