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Unmanned Air Vehicle Technology Development

SPONSOR: Defense Airborne Reconnaissance Office

This project entailed the support of future UAV development with studies of the potential performance of alternate engines for application in Predator and Global Hawk classes of UAVs.

Current reciprocating engines do not have the reliability of gas turbines and can not use heavy fuels. Analytical studies examined the potential impact of gas turbine engine variants on reconnaissance vehicles with emphasis on the recuperated gas turbine cycle. An experimental study sought to establish performance characteristics of small gas turbines operating with JP fuel.

A small test stand was built and a JPX-240 micro-jet engine (with 17 pounds of thrust) was tested to establish performance levels available in relatively inexpensive commercial engines. Potential turboprop performance, using the engine as a gas generator, was then projected using an engine code.

The Concorde is the only supersonic transport aircraft currently in service on limited airline routes. Although a marvel of technology it uses relatively unsophisticated turbojet engines with afterburners. While larger, faster, more efficient supersonic commercial aircraft are under consideration they remain only a future possibility because of limitations on engine development. The maximum speed operational aircraft in use by the military was the SR-71 (now NASA research aircraft) which routinely attained Mach 3 with two Variable Cycle turbojet Engines (VCE). Missile and experimental aircraft systems have reached much higher speeds.

Although the speed of the next generation Super-Sonic Transport (SST) is considered at a range between Mach 2.0 to 2.4, this project is aimed at an establishment of fundamental technologies necessary for a Combined Cycle Engine (CCE), that has the capability of speed range between 0 to Mach 6. This speed range is selected as a target to bridge the gap between more traditional VCE and highly sophisticated SCRAMJET engines which are proposed to operate in the Mach 5+ range. At takeoff and landing the high bypass ratio of the turboramjet engine is advantageous to lower the noise level by reducing jet velocity due to entrainment of the secondary air around the turbojet. Noise levels could be reduced further by using a low bypass ratio turbofan engine within the turboramjet, which would transition to pure turbojet mode in the Mach 1 to 3 range. However this technology has been proven in existing modern Military engines.

With this background a free-jet facility is being developed to test microjet engines at sea level flight conditions. The facility is also be used for intake configuration studies as well as ramjet studies (free-jet operation).