Powering unmanned aircraft

Pratt & Whitney Canada is developing and testing a commercial turbofan engine derivative for high-altitude unmanned air vehicle applications.

Testing of an instrumented, “off-the-shelf,” commercial turbofan engine to altitudes greater than 65,000 ft has been completed recently by Pratt & Whitney Canada in conjunction with NASA and MTU (Motoren-und Turbinen-Union, Munchen GmbH). The two-phase test program has been conducted at the Propulsion Systems Laboratory of the NASA Glenn Research Center in Cleveland, OH. The first phase, which was completed in August 1999, investigated basic performance and operability characteristics to identify possible shortcomings. Completed in May 2001, the second phase investigated the response to inlet distortion and high power off-takes, and included extensive steady-state and transient instrumentation in the low-pressure turbine for the correlation of analytical predictions.

The overall requirement for various types of air vehicles operable at high altitudes is increasing, particularly in the small, high-bypass-ratio turbofan class. Aggressive cost drivers are also favoring the adaptability of commercial, “off-the-shelf” engines vs. new centerline designs. A typical turbofan engine for commercial use is designed, developed, and certified to operate to altitudes of approximately 45,000 ft. For unmanned air vehicles (UAVs), such as HALE (High Altitude Long Endurance), these engines will need to operate at altitudes in excess of 60,000 ft. Pratt & Whitney Canada's High Altitude Program, first conceived in 1998 in conjunction with NASA's Glenn Research Center and MTU, had the following objectives:

Test a commercial, off-the-shelf, small, high-bypass-ratio turbofan engine in the high altitude, low-Reynolds No. regime to determine the performance and operability characteristics and limitations on a system and component level

Based on baseline test data and refined analytical predictions, define an optimized configuration and investigate performance and operability under the full range of operating conditions (inlet distortion, bleed, loads, etc.)

Extend design/modeling criteria and computational techniques for low Reynolds Nos.