block 62 is for the purpose of permitting the fuel to fill the manifold between the fuel shut off valve and fuel injectors before ignition thus the output signal from schedule block 52 on signal line 74 initially calls for a reduced fuel flow the precised value being a function of altitude p amb and after a time determined as a function of altitude is increased to a maximum fuel flow the output signal on line 74 is fed as one input to a least select circuit 76 immediately after ramjet ignition has occurred it is desirable to modulate fuel flow to provide the maximum ramjet thrust available at the particular flight condition in general at low mach numbers the maximum thrust is limited by the air inlet operating conditions some inlets may permit operations in the slightly sub critical region while other inlets may require only supercritical operation to avoid unsatisfactory or unstable inlet performance the fuel control must operate so as to maintain the desired inlet operatiing condition over the complete range of vehicle mach numbers and angles of attack the point at which the inlet will actually operate is affected by inlet and ram burner performance characteristics exhaust nozzle effective area fuel heating value and fuel control metering accuracy and the schedule must be determined empirically for the open loop mode of control fuel flow is scheduled to maintain desired inlet margin as shown in block 78 in which the parameter equ1 is scheduled as a bivariant function of mach number m n on line 46 and vehicle angle of attack u03b1 on line 48 where u03b8 2 x is a temperature.