On the aerodynamic optimization of mini-RPV ... - CAFE Foundation

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p 1.00 ,* i I I I INASA Axial1Transition0.4 -Thrust Coefficient CT = T/qoVa6Fig. 9The denomination ofFan pressure-rise coefficient CH2s vsThrust coefficient CT$ is the fan flow parameter:0’3 -Fan System Resistance0. 2 -@=$-7 d:utYThe denomination of + is the fan total-pressureparameter:The fan diameter corresponds to the jet diameterd, ; ut = ndSn is the fan tip speed and P is theair mass density. Figure 10 presents the $4 plotwith two fan system resistance curves, representingthe max. and min. encountered in this study, andwith the experimental performance curves $4 and$-n~ of the selected NASA axial rotor/stator stage518;’ it can be seen that a fairly good match isachieved, i.e. the fan will operate between 88.3and 90.6% efficiency. Fan aerodynamic selectionprocedures are discussed thoroughly in Section 6of Ref. 10.11. The fan speed is computed:n =-- cq5 ‘a 130.13 RPS$ VO.33The value of the fan flow parameter + is determinedin Fig. 10 from the intersection of the fan systemresistance curve with the NASA 518 performancecurve. The range of $ is from 0.485 to 0.508.Similarly, the fan efficiency n~ is determined inFig. 10 from the NASA 51B efficiency curve at theabove 0 location.The fan diameter is assumed to correspond to thestern jet diameter: ds = 0.1625D.12. The fan shaft power can be computed now fromthe CHP25 value of Step 7 and the above efficiencydetermination for an available fan design:0.1 - I I I I0 0.2 0.3 0.4 0.5 0.6Fan Flw Parameter 0Fig. 10 Fan pressure parameter + and totalefficiency QF vs fan flow parameter $13. The jet total-head coefficientCHT,Hs- Poqo= __is determined from the plot of Fig. 11 and the jetvelocity ratio Us/U, is determined from the plotof Fig. 12 for the free transition or the trippedtransition cases, as warranted by Reynolds numberand opera t i onal con si dera ti on s.14. The jet static base pressure coefficient CP,is determined from the plot of Fig. 13. It can beseen that the static base pressure coefficient rangeis very high; CPs will be over 0.8 for the thrustcoefficient range of this study. As a reference,Ref. 11 shows that the’ base pressure coefficientof conventional boattail/jet afterbodies is in the0.10 to 0.15 range.15. The final step is the computation of theaerodynamic efficiency index:The index expresses the power required to fly theaircraft’s gross weight at the max. cruise speed;therefore, it i s a good indication of the efficiencyof the aerodynamic design when comparingtwo aircraft at the same speed.5
~Mini -RPVL& 9,- '\FreeTransiiionfiConi. Wake1 andTransitionTripped B 58% 0I I I I I0.01 0.02 0.03 0.04 0.050.66Thrust Ccefficient CT = T/q V0Fig. 11 Jet total-head coefficient CHT, vSThrust coefficient CTMini-RPV aerodynamic design has not achieved yetan adequate degree of efficiency for the missionspeed and endurance requirements. Considering typicalcurrent vehicles such as the Air Force/BoeingPave Tiger, the Atmy/Lockheed Aquila, the Israel WAircraft industries Scout, the Tadiran Mastiff MK3and the Developmental Sciences Sky Eye, it is foundthat the gross weight ranges from 220 to 380 lb,the maximum cruising speed ranges from 85 to 100Kn and the engine powers range from 22 to 30 HP.The aerodynamic efficiency index ranges from 2.5to 3.5.The wind-tunnel test model,2"'4 with its diameterD = 20.0 in. and 100 Kn speed, may be classifiedas a full-scale mini-RPV; Table 1 presents itsperformance data for 125, 150 and 175 lb grossweights with a suitable wing (CL = 0.40) and empennage.Table 1 20" Diameter (V = 6.2 ft3) Mini-RPVP 100 Kn (qo = 34.1 PSF)(Free Transition)1.8 I I I I1Gross Weight W, lbWing loading qoCL @ CL= 0.4PSF125 It13.6150 lb13.6175 lb13.60. 2 c01001 lo-II I I I J0.01 0.02 0. m 0. M 0.05Thrust Ccefficient CT = TPoVo'66Fig. 12 Jet velocity-ratio U,/U,coefficient CT1.4, I I I Ivs ThrustI I I I I0 0.01 0.02 0.03 0.M 0.05Thrust Ccefliclent Cl =T/qoVo'MFig. 13 Jet static base pressure coefficient CP,Thrust coefficient CTIvsWing area A = Wo/qoCL, ft2Wing chord, C ftWing span, B ftLift/drag ratio of wing,CL/CD @ CL = 0.40Drag of wing, Fw = WCLo / ~Thrust coeff. for wingCTwTotal thrust coeff. CTaFan air power coeff. CHP,Fan flow coeff. CQ,Fan flow 9CFSFan pressure-risecoeff.CHzsFan pressure-riseAH2 iPSFFan system-resi stancecoeff.@2/*Fan speed, nRPMFan diameter, d, in.Fan efficiency, '?F %Fan shaft powerHPJet total-head coeff. CHT5Jet velocity ratio U,/UoJet static basepressure coeff.cp5Aerodynamic efficiency F.index9.190.9589.5837.63.320.02850.034E0.0600.023713.502.5486.360.78533,9643.2589.752.352.661.351.0416.3411.031.05010.5037.63.990.03480.04120.06850.025214.352.8095.200.80535,7563.2590.502.782.901.421.1017.20__12.861.13411.3437.64.651.04061.04761.07551.026415.033.05103.700.81137,3113.2590.753.123.161.511.1018.22V6
Page 1 and 2: AI AA-84-2 163On the Aerodynamic Op
Page 3 and 4: proved conclusively that boundary-l
Page 5: Compute6. Compute the drag of the w
Page 9 and 10: ~~~~Table 334" Diakter (V = 30.5 ft
Page 11 and 12: ~~~Table 7 lists th'e pertinent par
Page 13: ~~ --~ ~~,References1. F. R. Goldsc

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