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1. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Objectives • Lesson objective - • Methodology correlation • including … • F-16 • RQ-4A (Global Hawk) • DarkStar Expectations – You will have a better appreciation for the validity of the integrated design and analysis spreadsheet methods 23-1

2. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Importance • It is important that we understand how well (or poorly) the simplified methods reflect reality • - We know the methods are approximate • - But are they good enough for concept design? • We will first compare against a manned aircraft (F-16 ferry mission) • - Available database (geometry, aero, weight, propulsion and performance) • Then we will do UAV comparisons • - Global Hawk and DarkStar are reasonably well documented • Turboprop and piston powered aircraft comparisons are still in work • To date correlations have focused on propulsion • Addressed in Lesson 18 23-2

3. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Overall F16 comparison • Parametric model calibrated to F-16C • - Overall geometry (span, tail ratios, etc) • - Basic unit weights and fractions (structure, gear, propulsion, etc) based on ferry GTOW • - Overall aero coefficients (Cfe and e) • - Sea level static propulsion (T0, TSFC0, BPR, etc) • Model estimates compared with actuals • - Wetted area • - Cruise and climb aero • - Cruise and climb propulsion • - Overall weight history and range/endurance 23-3

4. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Comparison mission • Spec F-16 ferry mission with external tanks • - (2) 370-gallon wing tanks • - (1) 300-gallon centerline tank • - Wing tip mounted missiles included • - 480 knot cruise speed • Mission profile assumes cruise climb • - We will define initial and final cruise altitudes 23-4

5. Design of UAV Systems c 2002 LM Corporation Methodology Correlation F-16 geometry • Overall geometry parametrics were matched • - AR = 3;  = .2275; Sht = Svt = 0.21*Sref; etc. • Sref - defined by wing loading • Fuselage diameter - estimated from fuselage maximum cross sectional area • - Df = 2*sqrt(2600/) = 4.8 ft • Other fuselage geometry defined in relative terms • - Lf/Df = 9 • - Nominal nose (0.2) and aft (.1) body length fractions • Nacelle Swet defined as 50% of a constant radius cylinder • - Dnac = f(engine size), Ln/Dn = 4; • Resulting geometry model came out very close • - Swet predicted within 4 sqft (accuracy coincidental!) 23-5

6. Design of UAV Systems c 2002 LM Corporation Methodology Correlation F-16 weights • Model defined to match F-16C ferry weights • - Initial fuel fraction with full internal fuel + (2) 370g + (1) 300g = 0.394 • - Overall airframe weight/Sref = 26.72 • - Engine installation factor = 1.2 • - Other fractions to match F-16C • - Payload = external tanks+AIM-9s+chaff = 1700 lbm • - Misc weight fraction = [pilot + provisions + fluids + unusable fuel]/W0 = 0.009 • By definition the individual weight fractions matched • - But overall weights had to converge on their own 23-6

7. Design of UAV Systems c 2002 LM Corporation Methodology Correlation F-16 aero • Overall model coefficients selected to approximate F-16C • - Clean aircraft Cdmin ≈ 190 cts • Cfe = .019*300/1404 = .004 • - Cdmin with tanks = 1.4*clean aircraft • Other parameters selected at nominal values • - e = 0.8, etc. • Induced drag, lift coefficient and L/D calculated using Lesson 17 methodology 23-7

8. Design of UAV Systems c 2002 LM Corporation Methodology Correlation F-16 propulsion • Model constructed to fit published F-100-229 values from the Mattingly engine design website* • - Military power thrust (SLS) = 17800 lbf • - Military power SFC0 (SLS) = 0.74 • - Military power WdotA (SLS) = 248 pps • - Fsp-fn was selected to match Fsp0 at BPR = 0.4 with Fspgg = 90 • - Fuel-to-air ratio was calculated from fuel flow assuming WdotAgg = 177.1 pps (248pps/1.4) or • f/a = .0218 • - SFC was increased 5% per spec mission rules • Thrust, air flow and fuel flow at speed and altitude were fall outs of the model * www.aircraftenginedesign.com 23-8

9. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Mission level comparison • Negligible differences in gross weight (-377 lbm) • Some differences in fuel consumption • 30% underestimate of start-taxi-takeoff fuel (-218 lbm) • 2% overestimate of fuel to climb (+26 lbm) • 2% underestimate of cruise fuel (-253 lbm) • 8% underestimate of loiter/landing reserves (-138 lbm) • Negligible difference in landing weight (+205 lbm) • Negligible difference in overall cruise range (+6nm) • 27% underestimate of time to climb (-3.1 min.) • 36% underestimate of distance to climb (-31 nm) • 3% overestimate of cruise range (+46nm) 23-9

10. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Overall assessment - F16 • Predicted size, weights and performance are within concept design accuracy requirements • Time and distance to climb not an issue for this design phase • Gross weight, empty weight and radius are the key parameters of interest 23-10

11. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Global Hawk comparison • Maximum range/endurance mission from 1999 Global Hawk Public Release International Presentation • - Maximum internal fuel • - 350 knot cruise speed • - 50 to 65 Kft cruise, 65 Kft loiter • - 13,500 nm maximum range • - 38 hour maximum endurance • - 24 hour endurance at 3200 nm operational radius 23-11

12. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Model development • Geometry model calibrated to match known or estimated GH data • - Overall aero surface geometry known (span,areas) • - Overall Swet estimated from published L/Dmax and span assuming state-of-the art Cfe =.0035, e = 0.75 • Fuselage areas unknown - estimated from fuselage length and diameter • Weight model developed from various sources • - Payload, gross and empty weight from NG data • - RR AE3007H weight from Janes, installed at 120% • - Other fractions (gear and systems) estimated • - Fuselage, wing and tail unit weights estimated at nominal values and iterated to match published EW • - Resulting Airframe Wt/Sref = 6.42 psf 23-12

13. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Model cont’d • Propulsion model calibrated to match published data • - T0 = 8290 lbf, TSFC0 = 0.33, BPR = 5 • - Fuel-to-air ratio adjusted to fit TSFC0 • - Assumed Fspgg = 90; Fspfn = 30 • - 10% installation loss assumed • - Airflow scaled to match SLS thrust • Performance model inputs from published data • - 25 minute ground idle, 5 minute full power takeoff • - 50 Kft initial and final cruise altitudes, loiter at 65 Kft • - 350 kt cruise and loiter speed • - 200 nm distance to climb to 50 Kft • - Outbound leg = 3000 nm; inbound = 3200 nm • - 60 minute landing loiter, assume 5% landing reserve • - Range and mid-mission operational loiter a fallout 23-13

14. Design of UAV Systems c 2002 LM Corporation Methodology Correlation GH model matching • Model as constructed approximated published performance • - Operational loiter = 23.1 hrs vs. 24 hrs at 3200 nm • - Max range = 14026 nm vs 13500 nm • - Max endurance = 41.2 hr vs 38 hr • - L/Dmax - 34.8 vs 33-34 • - Multipliers could be applied make the numbers match published data • But there were disconnects in thrust available • - 50 Kft model data was OK (Ta  D) • - 65 Kft thrust was not (Ta < D) • - At final cruise and initial loiter weights • - Thrust available multipliers required = 2.1 • Either model is off or GH has a high altitude thrust available problem • Answer – GH has a high altitude thrust problem 23-14

15. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Another example • All wing UAV (DarkStar type) • - Wpay = 1100 lbm (inc. comms) , Vcr = 250 kt at 45 Kft • - W0/Sref = 28.7 psf; AR = 14.1; FF = 0.33; T0/W0 = 0.22 • What we change (from GH) • - t/c = 16% (est.); Cfe = .003 (RayAD Table 12.3) • - e = 0.8 (chart 17-6) • - Dfus-equiv = 6.5 ft (estimated from sketch) • Lfus/Dequiv-fus = 2.3; Wfus/Hfus = 3.4 • See chart 20-19, Eq 20.8 for Deq and fuselage Swet methodology • - Neng = 1, BPR = 3.2, T0/Weng = 4.25 lbm/lbf (FJ-44) • - 5% propulsion installation loss (estimate) • - L/Dnac = 4, Swet-nac @ 0% (buried engine) • - U-2 airframe, DS system weights (7.5 psf and 18%) • - Landing gear from RayAD Table 15.2 • - Non-payload/fuel misc items (2% useful load) 23-15

16. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Result • DS Model • - Lfus = 14.9ft • - Wfus = 12 ft • - Hfus = 3.5 ft • - LoDavg = 30.2 • - W0 = 8759 • - We = 4466 • - Sref = 305 • - Swet = 921 • - Hdot3 (SL) = 2104 fpm • - Hdot4 (42 Kft) = 56 fpm • - End @ 500 nm = 12.5 hr • - Max range = 4068 nm • - Max endurance = 16 hr • DS (DARO FY1996) • - Lfus = 15 ft • - Wfus = 12 ft • - Hfus = 3.5 ft • - LoDavg = n/a • - W0 = 8600 lbm • - We = 4360 • - Sref = 300 • - Swet = n/a • - Hdot3 (SL) = 2000 fpm • - Hdot7 (45 Kft) = n/a • - End @ 500 nm = 8hr+ • - Max range = n/a • - Max endurance = 12+ 23-16

17. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Conclusion • Hopefully these comparisons help convince you that simplified performance and geometry models do a reasonable job of predicting real aircraft trends • - Once you get confidence in the approach and learn how to adjust models using multipliers, you can approach configuration design, configuration trades and technology trades from a whole new perspective • - Develop an analysis model first, use it to help you define a better initial configuration • - Then draw and analyze the configuration • - Recalibrate the model to match the new analysis • - Use the new model to guide trade study planning to reduce the size of the matrix and to predict trends • - Define a new configuration and repeat to convergence 23-17

18. Design of UAV Systems c 2002 LM Corporation Methodology Correlation Intermission 23-18