23-1 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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

23-2 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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

23-3 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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

23-4 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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 knot cruise speed Mission profile assumes cruise climb - We will define initial and final cruise altitudes

23-5 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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!)

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

23-7 Design of UAV Systems Methodology Correlationc 2002 LM Corporation F-16 aero Overall model coefficients selected to approximate F-16C - Clean aircraft Cdmin ≈ 190 cts  Cfe =.019*300/1404 = 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

23-8 Design of UAV Systems Methodology Correlationc 2002 LM Corporation F-16 propulsion Model constructed to fit published F values from the Mattingly engine design website* - Military power thrust (SLS) = lbf - Military power SFC0 (SLS) = 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 = pps (248pps/1.4) or f/a = SFC was increased 5% per spec mission rules Thrust, air flow and fuel flow at speed and altitude were fall outs of the model *

23-9 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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)

23-10 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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

23-11 Design of UAV Systems Methodology Correlationc 2002 LM Corporation Global Hawk comparison Maximum range/endurance mission from 1999 Global Hawk Public Release International Presentation - Maximum internal fuel 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

23-12 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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 = 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

23-13 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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 = % 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 kt cruise and loiter speed 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 Model cont’d

23-14 Design of UAV Systems Methodology Correlationc 2002 LM Corporation Model as constructed approximated published performance - Operational loiter = 23.1 hrs vs. 24 hrs at 3200 nm - Max range = nm vs nm - Max endurance = 41.2 hr vs 38 hr - L/Dmax vs 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 GH model matching

23-15 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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, 0% (buried engine) - U-2 airframe, DS system weights (7.5 psf and 18%) - Landing gear from RayAD Table Non-payload/fuel misc items (2% useful load)

23-16 Design of UAV Systems Methodology Correlationc 2002 LM Corporation Result DS Model - Lfus = 14.9ft - Wfus = 12 ft - Hfus = 3.5 ft - LoDavg = W0 = We = Sref = Swet = Hdot3 (SL) = 2104 fpm - Hdot4 (42 Kft) = 56 fpm 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 = Sref = Swet = n/a - Hdot3 (SL) = 2000 fpm - Hdot7 (45 Kft) = n/a nm = 8hr+ - Max range = n/a - Max endurance = 12+

23-17 Design of UAV Systems Methodology Correlationc 2002 LM Corporation 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

23-18 Design of UAV Systems Methodology Correlationc 2002 LM Corporation Intermission