On the Design and Test of a Low Noise Propeller - CAFE Foundation

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Report No. 4764Bolt Beranek and Newman Inc.Table 1Aircraft CharacteristicsParameter Value Comment13.44 M' 144.6 ft2 wing area-05 ,skin frictioncoefficient7. 415 aspect ratio0.65 span efficiency9029.9 N 2030 lbs (utilitywe igh t )The heavy dashed line in Fig. 1 re2resents the poweravailable from the production engine prbopeller combination, withthe engine operated at full throttle. This power is the productof the propeller thrust times the aircraft velocity. The productionengine propeller power was deduzed from two observations.First, the fastest sea level veloci4;y attained by tht aircraftwas 63.2 M/S (141.4 mph). Second, the best rate of climb occursat 40 M/S (90 mph) and is approximately 4 M/S (800 ft/min).Wherever the power available exceeds the power needed to overcomeaircraft drag, the aircraft can climb. The velocity at which thetwo curves intersect is the peak forward velocity.The acoustic design point is the full power flyover at 305 m(1000 ft) altitude which is specified in PAR 364. The acousticgoal Is to reduce the propeller noise, as measured by a groundobserver, with no loss in aerodynamic performance. Hence, thedesign point is to match the propeller performance during a fullpower level flyover. The procedure is to design a propeller
Report No. 1761Bolt Beranek and Newman Inc.which minimizes the induced losses at the design condition.There are six parameters needed to specify the design of aminimum induced loss propeller. These are given in Table 2,along with the associated values for the existing propeller.Table 2Propeller Design SpecificationsParameter Ex1 s t ingPropellerAirDensity 1.225 KG/M~Velocity 63.2 M/SRotation Rate 2700 RPMPower 122 kw (164 hp)Blades 2Radlus .97 M (38")NewPropellc A-Comment1.225 KG/M~ Sea Level63.2 M/S Max. Velocity2700 RPm Max .RotationSpeed122 kw (164 hp) Max Eng. Pwr.3-87 (34")The implied constraint is that the efficiency (85%) beapproximately the same for bath.This is discussed in greaterdetail in the next section.The measured properties of the new and ./existing propellnrs demonstrated that they were identical duringa full power flyover.However, as evident in Fig. 1, it is important to maintainaerodynamic performance of over a range of airspeed.procedure used to analyze this performance is indicated in Figs.2a, 2b, 2c. Fig. 2a represents the measured engine power versusrotation speed on the OSU aircraft.ximate equationP122.3 + .0447 (X-2700)TheThis was given by the appro-
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