Mach airspeed indicator

Abstract

A mach airspeed indicator capable of internally determining mach number and VMO from measured altitude and airspeed information directly. An internal microprocessor, capable of storing a plurality of selectable VMO curves and a table of mach number versus q.sub.c /P.sub.s, receives the measured altitude and airspeed information, determines VMO and mach number therefrom, and directly drives the VMO and mach number displays where q.sub.c represents the impact pressure and P.sub.s represents the static pressure. The measured altitude and airspeed signals are analog synchro signals. In order to drive the VMO display, the received analog altitude synchro signals are digitized in a synchro-to-digital converter comprising a single multiplying digital-to-analog converter for both sin .theta. and cos .theta. synchro functions, and fed to the microprocessor which verifies the appropriate VMO from the preselected VMO curve, and drives the VMO analog pointer via a stepper motor servo loop closed by the microprocessor. If the VMO is exceeded, the microprocessor provides an overspeed alarm control signal. In order to drive the mach number display, both the received measured analog altitude and airspeed synchro signals are received, digitized in the synchro-to-digital converter, and fed to the microprocessor. The microprocessor converts the digital airspeed signal into q.sub.c /P.sub.s signal which is used to determine mach number from the stored values. The microprocessor then drives the mach number counter display via a separate stepper motor servo loop closed by the common microprocessor.