Design of Jet STOVL Aircraft using RDS-Professional

of design penalties to the aircraft designer. Recent studies including those described in ref.<br><br> (2) point to an alternative - using the catapult for launch, but using aircraft vertical landing capabilities for at-sea recovery (CAT-VL). This may offer design weight penalties no worse than the CAT-TRAP option, and with enhanced operability and safety. Perhaps even more importantly, it may substantially increase commonality in a multi-service design.<br><br> This paper describes the development and analysis of a notional future multirole fighter with optional vertical land capability, developed to be used as a tool for assessment of the CAT-VL concept. That assessment, and a discussion of the implications and benefits of CAT-VL, is contained in the companion paper (1). Design work was done starting with the notional design concept previously developed by the lead author in the 1994-1995 time frame and publicly reported in references (2) and (3).<br><br> This concept is shown in fig.1, and was used at that time as a point of departure for a variety of trade studies on missions, roles, technologies, and multi-service commonality strategies as reported. 2 T/W = 0.78 W/S = 70 psf Wf/W ~ 0.3 Length = 56 ft Span = 40 ft 1 Notional Derivative Engine ~ 35000 lb Thrust Figure 1. Design Concept from Ref.<br><br> (2) The Air Force version of this design had an empty weight of 25, 505 lb., and a design takeoff weight of 41, 245 lb. It was powered by a notional advanced fighter engine of about 35,000 pounds of thrust, with a wing area of 590 sq. ft.<br><br> This notional design concept was then revised to better reflect current thinking. Based on information in ref. (4), the vertical lift concept was changed from the Lift-Plus-Lift/Cruise to the Shaft-Driven Lift Fan (SDLF).<br><br> The engine was moved forward to allow incorporation of the type of vectoring nozzle used on the YAK-141. This required a revision to the tail arrangement, wherein the V-tails were mounted on boom-like structures alongside and aft of the engine. These changes resulted in a configuration as shown in Figure 2.<br><br> The design requirements from the prior study (refs. 3 & 3) were retained for this study, as follows: " 550 n.mi.radius, high-medium-medium-high flight profile " internal carriage of two 1000lb. JDAMs, two AIM-120Cs, gun and ammo " 7.33 g load factor at mid-mission fuel weight " 3.5 g sustained turn rate at .9 M and 30,000 feet " 4000 foot takeoff and landing.<br><br> Design layout and analysis work was done using done using the RDS-Professional design software, a product of Conceptual Research Corporation (5,6). Based on the methods in the AIAA textbook `Aircraft Design: A Conceptual Approach' (7), RDS features a 3-D CAD module for design layout, and has analysis modules for aerodynamics, weights, propulsion, and cost. RDS includes capabilities for aircraft sizing, mission analysis, and performance analysis including takeoff, landing, rate of climb, Ps, fs, turn rate, and acceleration.<br><br> RDS also provides graphical output for drag polars, L/D ratio, thrust curves, flight envelope, and range parameter, and features both traditional carpet plot optimization and a multivariable design optimizer. Comparative studies indicate that RDS-Professional produces results within the usual accuracy for conceptual design efforts. Aerodynamics analysis included subsonic parasite drag, estimated by the component buildup method.<br><br> Supersonic wave drag was determined by the equivalent Sears-Haack technique. Transonic drag was determined by empirical methods. Drag due to lift was calculated by the leading-edge suction method using a calculated Cl-alpha based upon DATCOM methods.<br><br> Maximum lift was estimated using DATCOM charts. Figures (3) through (6) show aerodynamic results. Fig.<br><br> 3. Parasitic Drag Fig. 4.<br><br> CL-alpha vs. Mach 3 Figure 2. Revised Notional Design Concept Fig.<br><br> 5. Drag-due-to-Lift Factor (K) Fig. 6.<br><br> Lift-to-Drag Ratio in Level Flight Weights and balance were estimated statistically using equations from chapter 15 of reference 7. Weights were adjusted based on application of composites and other advanced materials, and weight increments were estimated for use of internal weapons bays, stealth treatments, and additional equipment such as an APU. Weights adjustments for the use of a catapult launch and vertical land were made including weight estimates for the shaft-driven lift fan system (table 1).<br><br> Summary weights result are shown as Table (2). Table 1. Miscellaneous empty weight breakdown APU 300 Wep bay 1500 Stealth 1000 Lift fan 2000 Doors/nozzle 300 Main nozzle 400 Stovl controls 200 Fuselage cutout 250 Total STOVL 5950 Add cat struct.<br><br> 500 Total CATVL 6450 4 Table 1. CAT-VL Weights Est. STRUCTURES GROUP 10392 Wing 3252.3 Vert.<br><br> Tail 866.5 Fuselage 4627.6 Main Lndg Gear 775.1 Nose Lndg Gear 318.1 Engine Mounts 63.3 Firewall 113.0 Engine Section 53.3 Air Induction 322.9 PROPULSION GROUP 6355 Engine(s) 4930.0 Engine Cooling 273.0 Oil Cooling 37.8 Engine Controls 21.2 Starter 66.4 Fuel System 1027.0 EQUIPMENT GROUP 4921 Flight Controls 1020.8 Instruments 128.8 Hydraulics 171.7 Electrical 706.5 Avionics 1945.4 Furnishings 391.7 Air Conditioning 536.0 Handling Gear 20.7 MISC EMPTY WEIGHT 6450 TOTAL WEIGHT EMPTY 28119.1 USEFUL LOAD GROUP 15981 Crew 220.0 Fuel 12850.9 Oil 50.0 Payload 2860.0 TAKEOFF GROSS WEIGHT 44100.0 (* - Lift Fan and other STOVL gear included in Misc We allocation) Since the propulsion data used for the design studies of reference (2) was proprietary and is therefore unavailable to this study, a suitable engine data set had to be substituted. The Afterburning Turbofan of Appendice E of reference 7 had been defined with estimated year 2000 technologies and has a cycle and bypass ratio somewhat similar to current advanced engines. It was therefore used as representative, although not identical to likely engine data for such an advanced fighter.<br><br> Jet engine installation analysis was done including corrections for pressure recovery, bleed, inlet drag, and nozzle drag. Jet thrust and specific fuel consumption (SFC) for maximum afterburning and dry operations are shown in figures 7 through 10. Fig.<br><br> 7. Max. Afterburning Thrust Fig.<br><br> 8. Max AB. SFC Fig.<br><br> 9. Max Dry Thrust 5 Fig. 10.<br><br> SFC at Max. Dry Thrust Performance analysis of this notional baseline design was done based on the calculated aerodynamics, weights, and performance. Sample results are shown in figures 11-13.<br><br> Fig 11. Rate of Climb Fig. 12.<br><br> Specific Excess Power (Ps) at 30,000 ft. Fig. 13.<br><br> Turn Rate at 30,000 ft. Next, the notional designed was analyzed as to range over a typical high-medium-medium-high strike mission. Typical allowances for dash, combat, loiter, and recovery were included in the analysis.<br><br> Figure 14 shows the change in aircraft weight and fuel weight during the mission, and table (3) details the range analysis results. Fig. 14 CATVL Fuel Usage and Aircraft Weight 6 Table 3.<br><br> CAT-VL Range Analysis Seg. 5 CRUISE : 505.0 kts at 43000.0 ft RANGE = 500.7 nmi Seg. 6 CRUISE : 540.0 kts at 15000.0 ft RANGE = 50.0 nmi Seg.<br><br> 9 CRUISE : 540.0 kts at 15000.0 ft RANGE = 50.0 nmi Seg. 11 CRUISE : 510.0 kts at 48000.0 ft RANGE = 500.7 nmi Seg. 12 LOITER : 210.0 kts at 200.0 ft ENDURANCE = 0.2 hrs TOTAL RANGE = 1101.4 TOTAL LOITER TIME = 0.17 FUEL WEIGHT = 12822.5 EMPTY WEIGHT = 28147.5 USEFUL LOAD (-Wf)= 3130.0 AIRCRAFT GROSS WEIGHT = 44100.0 A variety of range-related trade studies were performed to assess the design's sensitivity to changes in requirements, technologies, and design parameters.<br><br> Several of these are shown in figures 15 and 16. Fig. 15.<br><br> Effect of SFC on Range Fig. 16. Effect of Dead Weight on Range SUMMARY & CONCLUSIONS A notional design concept representative of an advanced single-engine strike fighter has been defined and analyzed as a tool for study of the potential for catapult-launch, vertical-land operation from aircraft carriers.<br><br> This notional concept incorporates the Shaft-driven Lift Fan technology for vertical lift, and represents current design technology and thinking. The analysis indicates results representative of current fighter developments, and appears to validate this concept as a viable tool for study usage. The companion report (1) details the use of this notional concept in the assessment of the feasibility and desirability of CATVL as an operational and design concept.<br><br> 7 REFERENCES (1) McCrea, M., O 9Brimski, F., Strickland, P., and Raymer, D., Breaking the Paradigms: Catapulting STOVL, International Powered Lift Conference, Oct. 2000 (2) Raymer, D., Next Generation Attack Fighter: Design Tradeoffs and Notional System Concepts , The RAND Corporation, MR-595-AF,1996 (3). Raymer, D., " Next-Generation Attack Fighter Conceptual Design Study ", Aircraft Design (Pergamon Press), Vol.<br><br> 1 No. 1 March 1998 (4) Jane's All the Worlds Aircraft , 1999-2000, Jane's Information Group, London, 1999 (5) Raymer, D., "RDS: A PC-Based Aircraft Design, Sizing, and Performance System," AIAA Paper 92- 4226, Aug. 1992 (6) Raymer, D., "Multivariable Aircraft Optimization on a Personal Computer" , SAE/AIAA Paper 9965609, World Aviation Congress, 24 Oct.<br><br> 1996 (7) Raymer, D., AIRCRAFT DESIGN: A Conceptual Approach , Third Edition, American Institute of Aeronautics and Astronautics, Washington, D.C., 1999

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