Tables for use in an improved method of airscrew strip theory calculation

Abstract

An improved method of calculating the performance of an airscrew has been described in prcv:ious reports (Refs. I and 2), which includes an allowance for tip loss. The present report contains tables of a parameter (x) required in the calculation of the blade interference by the new method ; these tables being available, the labour invloved is no greator than in a calculation by the standard vortex theory. A simplified method of calculation involving the use of charts is described in a separate report (Ref. 6). The tables given here cover the case of two-, three-, and four-bladed airscrews at a series of standard radii and for all values of pitch. Details of the method of calculation (due to Goldstein, Ref. 3) are given in an Appendix together with a method of interpolation which can be used to extend the results to any other number of blades. The results for three blades were interpolated by this method but are probably quite accurate enough for practical purposes. All formulae required in the present method of strip theory calculation are given here, together with complete details of a specimen calculation. A preliminary comparison is included between results of calculations by the present method and the new experiments on high pitch model airscrews described in Ref. 5, for two-bladed airscrews of pitch ratio 1.5 and 2.5 and a four-bladed airscrew of 2.5; these show satisfactory agreement (below the stall) and reasons are given to suggest that the agreement should be at least as good over the whole range of pitch ratio. It is concluded that the present formulae and tables may be used with confidence to calculate the performance of any airscrew below the stalling angle, provided that suitable aerofoil data are available.