THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 88-GT-321 345 E. 47 St., New York, N.Y. 10017 The Society shall not be responsible for statements or opinions advanced in papers or 1n d'1s­ cussion at meetings of the Society or of its Divisions or Sections, or printed in its publications Discussion is printed only if the paper is published in an ASME Journal. Papers are available from ASME for fifteen months after the meeting. Printed in USA. Copyright © 1988 by ASME Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T02A027/2397578/v002t02a027-88-gt-321.pdf by guest on 27 September 2021 Evaluation of Potential Engine Concepts for a High Altitude Long Endurance Vehicle EDWARD J. KOWALSKI Boeing Advanced Systems P. 0. Box 3707, M/S 33-18 Seattle, WA 98124-2207 ABSTRACT till a speed of Mach 0. 6 has been attained. The aircraft continues to climb at this speed till the A potential need has been identified for a High cruise altitude of 45,000 feet has been reached. The Altitude Long Endurance (HALE) aircraft to augment aircraft will continue to cruise at this flight current surveillance and engagement capability. HALE condition for a total of 200 nm. llhen the mission platforms offer mission flexibility and survivability radius has been reached, the aircraft will loiter for which can complement ground based surveillance and 24 hours at Mach 0.6 and an altitude of 45,000 ft. The engagement systems. Current mission requirements aircraft cruises back at Mach 0. 6 at an altitude of include a loiter altitude of 45,000 to 60,000 feet and 45,000 feet then descends to sea level and loiters for a loiter time of 12 to 24 hours. The HALE aircraft 30 minutes at Mach 0. 3 before landing. The aircraft is will also be required to carry a sensor payload weight required to maintain a minimum rate of climb capability between 50,000 and 100,000 pounds. This paper will of 100 fpm at the start of the 24 hour loiter segment. evaluate the potential of several propulsion system candidates. Engines to be examined include the "classical" turbofan engine with bypass ratios up to ------ eight, the "ultra high bypass ratio" turbofan with ------ '' ® bypass ratios up to 20, General Electric's Unducted Fan ---6� (UDF) and the turboprop in a pusher and tractor ,- --� configuration with single and counter rotation © prop fans. INTRODUCTION The Boeing Advanced Systems has had an Independent ® Research and Development ( IR&D) project entitled Propulsion System and Airframe Integration in existence for more than ten years. As one of its objectives, studies are conducted which will identify propulsion nm systems applicable to advanced military weapons CD 200 systems. Dialogue is maintained between BAS and engine G) companies in order to keep abreast of the latest engine company offerings. Takeoff at maximum power ® 2 In order to evaluate the potential of several @ Climb at q=200 lb/ft propulsion system candidates on a HALE vehicle, work was jointly done with Boeing Advanced Systems "Advanced Climb at Mn=0.6 Long Endurance Vehicle Technology" program. It is the © intent of this paper to understand the impact of high ® Cruise at Mn=0.6, ALT=45000 ft altitude surveillance mission requirements on aircraft design characteristics, engine cycle characteristics ® Loiter at Mn=0.6, ALT=45000 ft for 24ft hr and propulsion system concepts. (i)Cruise back at Mn=0.6, ALT=45000 Mission Description @ Descend to sea level The mission used for this analysis is depicted in Figure 1. The aircraft is required to takeoff at Loiter at Mn=0.3, ALT =0 ft for 1/2 hr maximum power then climb at a constant q of 200 lb/ft2 Presented at the Gas Turbine and AeroengineFigure 1. Congress High Altitude Long Endurance Mission Profile Amsterdam, The Netherlands-June 6-9, 1988 I Aircraft Description "Classical" Turbofan Engine Description and Cycle Selection Figure 2 depicts a configuration designed to satisfy HALE mission requirements. This configuration The Pratt & llhi tney Aircraft parametric engine features a 50,000 pound sensor with near 360° viewing performance program (Ref. 2) was used to generate engine capability. The sensor which it carries consists of a performance, geometry and weight for a set of large phased array radar incorporated into the side of "classical" turbofan engines. the aircraft's fuselage. This sensor's field of view is to the side and from the horizon downward. Hence, A "first order" method was devised to determine the aircraft's wings and engines are mounted out of the the optimum engine cycle for a HALE application. Due Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T02A027/2397578/v002t02a027-88-gt-321.pdf by guest on 27 September 2021 sensor's field of view. Additional sensors are located to the 24 hour loiter requirement, it was assumed that in the nose and tail of this aircraft as well as in a the engine cycle which had the minimum combination of small turret on top of the fuselage. This fuel consumption (during the loiter segment) and engine configuration serves as the baseline for this study to weight would be the optimum engine cycle. Engine determine the impact of engine cycle and concept on the performance and weight were generated for engines with size of a HALE aircraft. The aircraft was redrawn for the following ranges of cycle characteristics: each propulsive concept: turbofan ("classical" and ultra high bypass) turboprop (pusher and tractor) and 4 < BPR < 8 UDF. 1900°F < T 4 < 3200°F 25 < OPR < 35 The subsonic inlet on the baseline configuration 1 < e < 1. 035 is designed with a relatively thin lip and has no boundary layer bleed or bypass system. Blow-in doors A power line of thrust versus specific fuel are used at takeoff and low speed. Axisymmetric consumption was generated at the mission loiter convergent nozzles were also used. condition, Mach=0. 6 and an altitude of 45,000 feet. It was assumed that the aircraft would loiter at the Aircraft Installation minimum specific fuel consumption (SFC) point. The thrust at that point was determined and then scaled to The Boeing Advanced Systems developed Engine a value required by the aircraft per engine at the Installation Analysis Program (Ref.1) was used to loiter condition. At the minimum SFC point, the amount account for the installation losses that occurred when of fuel burned by the engine during the 24-hour loiter the engines were integrated onto the airplane with its time was calculated. The engine weight was also scaled inlet and nozzle. to reflect the loiter thrust requirement. The fuel �i:- ,,,.1, � / 1- - I o _j"T'T--16ft---- in ·-------- 295 ft 0in 80 ft 0in --)F1-. -1 .- /�-: --�rr��I I 84ft9in , L_�-�� i 1 I ,, � c �;,:;,,m / Figure 2. Aircraft Configuration for High-Altitude Surveillance 2 burned was added to the scaled engine weight. This Vehicle Sizing with "Classical" Turbofan Engines total weight will be referred to as the Propulsive System Yeight Parameter (PSYP). Figure 3 shows a For each of the three engine cycles described above a range of aircraft wing loa<!ings (Y/S=70-105 carpet plot of PSYP for three bypass ratios (BPR=4, 6 2 and 8) varying overall pressure ratio (OPR) and maximum lb/ft ) and thrust-to-weight ratios (T/Y=0.28-0. 45) were examined. Figure 4 shows a performance map of the turbine inlet temperature (T4) for a throttle ratio of 1. 035. As the design BPR increased from 4 to 8, the resulting sized aircrafts for the BPR=8 engine. The same performance maps were generated for the aircrafts m1n1mum design T4 which could be run in Pratt & Yhitney's parametric engine performance program using the selected BPR 4 and 6 engines. Aircraft Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T02A027/2397578/v002t02a027-88-gt-321.pdf by guest on 27 September 2021 increased due to the deck's design limit on fan constraints and mission requirements were accounted pressure ratio (FPR) of 1. 5. Figure 3 also shows that for. On each plot, a wing span limit of 300 feet and a for the engines designed with BPRs of 6 and 8, minimum rate climb of 100 fpm were imposed. The resulting minimum TOGY and the corresponding Y/S and combination of minimum T4 and maximum OPR resulted in the overall minimum Propulsive System Yeight Parameter. T/Y for each engine are as follows: The hook which results for the set of engines designed BPR TOG\l (lb) Y/S T/Y with a bypass ratio=4.0 at a T4=1900°F occurs due to the parametric engine performance program's limit on 4 356,000 92 o.27 fan pressure ratio of 1. 5. 6 342,000 94 0.28 8 340,000 96 0. 29 For the design bypass ratios of 4, 6 and 8, the following engine design cycles were selected to size Propulsion System Yeight Parameter Method Validation the HALE vehicle due to their respective minimum values of the PSYP: To further understand the effect of PSYP on final aircraft takeoff gross weight and hence validate the 4 6 8 PSYP method as a screening tool in the preliminary 35 35 35 design of these types of aircraft, vehicle s1z1ng 2200 2200 2400 studies were performed on a total of nine engines from 1. 035 1. 035 1. 035 each of the groups of bypass ratio engines for a total of 27 sized vehicles. These engines are highlighted (large circle symbols) on Figure 3.