Numerical studies of infrared signature levels of complete aircraft

This paper begins with an outline of the procedure for predicting the infra red signature emissions from the airframe, engine casing. and the plume, an d their attenuation by tile intervening atmosphere. These emissions are con trasted against the background, to obtain the infrared signature levels. Th e infrared detector's - noise equivalent flux density, is proposed an opera tional constraint on the flight envelope. The shift of tills newly imposed constraint on the flight envelope for several engine-operating conditions, and for turbojet and turbofan engines is studied. The signature levels from the casing and plume, of a turbofan and equivalent turbojet engine, are co mpared at different operating paints on the flight envelope. Result in the form of a polar plot OF infrared signature level variation with aspect is a lso examined fur low flying missions. The results are analysed to direct st ealth design and operation.