The Problem of Noise Reduction with Reference ... - CAFE Foundation

NACA TN ~0, 1145Airplane speed.,tiles per hour . . . . . . . . . . ‘-oHorsepower . . . . . . . . . . . . . . . . . . . . 1Propeller speOd, r,pm . . . . . . . . . . . . . . . 215;Propeller diameter,” feet . . . . . . . . . . . . . 6Number cf propeller blades . . , . ● . . * . . . . 2.xNoise intensities were measured in the oabi.n of thisairplane with a c omnercial portable meter; the absolutereadin(;s are therefore not too accurate. The measurementswere made to give an idea of’the noise level fordif fal’e~tflight cotiitt ons ati.are in t?air agreementv j.t~ ~Elculat~ OKIS made for airplane A, whi ch this airplaneresembles> The data obtained ~or airplane C are as follows:tIIAir;?lane~ou.ndintensityJ?rGpe-Ller(db) speed lsp9ed(mph) (rpm)—.I90 tO 929410698 to 10193 to 958.4925040608565I10CY31500230023ao2150 ,,300TaxiingMagnetoTake-offClimbCm-dsingRemarkscheckNorma 1 glideLard ing approacẖ ---Finallv. a radical modification of air~lane A is.‘plane D, !s supposed.-to efiploy a fan-type propellersThe val~e of the propeller adva,n~eratio Ls i.n_creased~omI?,51Jfor atrplane A to 1.62 for airplane D by reducing thetfp speed of””the propeller in tlm ratio of 3 to 1.efght”ublade fan-t,yp’~. propeller ts chosen for airplane Dto reduce the nols6 level, Tn order to keep the induced1.0ss0s of the propeller at a corlstant value, it isnecessary to increase the disk area fn the ratio of themass coefficients (reference ~.), The mass coef#’icientfor airplane A at cruising speed Is 0! 68. For theprojected eight-blade propeller the mass coefficientis 0.4.0.The disk area must be thus increased in theratio of O,68/0.4.8 or l.hl and the propeller diameter12v .