Aeronautical Research Council
https://reports.aerade.cranfield.ac.uk/handle/1826.2/1
2022-10-05T21:10:56ZThe design of wind tunnel fans.
https://reports.aerade.cranfield.ac.uk/handle/1826.2/4869
The design of wind tunnel fans.
Collar, A. R.
Summary.—The present report is one of a series dealing with N.P.L. methods for the design of return flow wind tunnels. Reports already issued deal with the design of the Compressed Air Tunnel¹ and Open Jet Tunnels,² with the design of corner cascades³ and fan straighteners, ⁴ and with the improvement of velocity distribution by means of windmills⁵ and gauzes.⁶
An explanation is now given of the method usually adopted in the design of fans for return flow tunnels ; as an example of the method, the design of the fan for the N.P.L. non-turbulent tunnel is considered in detail. It is shown that for a wind tunnel a fan with blades of constant chord is advisable ; and a formula is given by means of which a rapid estimate can be made of the variation in rotational speed of the fan corresponding to a variation in power factor at constant power.
1940-08-10T00:00:00ZStrip theory method of calculation for airscrews on high-speed aeroplanes
https://reports.aerade.cranfield.ac.uk/handle/1826.2/4112
Strip theory method of calculation for airscrews on high-speed aeroplanes
Lock, C. N. H.; Pankhurst, R. C.
The report describes a simplified 8-point strip theory method of calculating the free-air performance of a propeller up to tip Mach numbers near the velocity of sound. It is based on the assumptions of R. & M. 1674 and 1849 together with the further simplifying assumption that the curve is straight (valid below the stall) and that the curve also is straight (valid for J > 1.0). The report includes tables of parameters which are required in the calculations as functions of J, r, and N for eight standard radii (r, = 0.3, 0.45, 0.6, 0.7, 0.8, 0.9, 0.95, 0.975) for the range of values of J from 1.0 t o 7.0; these are of universal application. In addition, tables of section data for various section shapes are required; these are given for Clark Y sections over a range of thickness in R. & M. 2036; they were derived, by methods described in R. & M. 2020, from overall measurements of thrust and torque on full scale propellers at low values of J in the Royal Aircraft Establishment 24-ft. tunnel and are subject to revision in the light of subsequent experimental research.
1945-10-01T00:00:00ZGraphical method of calculating performance of airscrew
https://reports.aerade.cranfield.ac.uk/handle/1826.2/4111
Graphical method of calculating performance of airscrew
Lock, C. N. H.
A rapid method is described of making calculations of airscrew performance by means of charts. The first application is to ordinary strip theory calculations on the basis of the formulae of Ref. 5. Six charts are required for each radius for which the value of thrust grading, etc., are to be derived; of these six, four depend on number of blades but are otherwise universal, since they are independent of shape of blade section, and do not involve the blade width or blade angle explicitly; they are based purely on the application of Prandtl theory to the airscrew and contain no empirical adjustments. The remaining two charts involve the lift and drag curves of the section. The second application gives a considerable further simplification in that the charts are required for a single standard radius (0.7) only; the thrust coefficient corresponding to a given working condition can then be deduced by a simple operation with three charts while the torque involves three further charts and a simple addition. The accuracy of the second method is increased if the lift and drag charts are deduced by analysis of observations on (model) airscrews, an analysis which can be performed rapidly by means of the remaining four charts; such an analysis of the results of the wind tunnel tests of high pitch airscrews shows that the method will give reasonably consistent results over a range of pitch ratio from 0.3 to 2.5, while there is little doubt that the method will cover the range of blade width likely to occur in practice. Changes of blade section and also of plan form and twist may be included if necessary by modifying the lift and drag curves. The second method has also been remarkably successful in its application to the stalled range of an airscrew, a range in which there is at present no other available method. It is further suggested that the first method might prove very convenient for analysing wind tunnel tests of model airscrews at high tip speed; the accuracy of application of the second method might be improved by basing the lift curves on full scale values of power, speed and revolutions, combined with an estimate of profile drag.
1934-10-01T00:00:00ZWind tunnel tests of high pitch airscrews
https://reports.aerade.cranfield.ac.uk/handle/1826.2/4110
Wind tunnel tests of high pitch airscrews
Lock, C. N. H.; Bateman, H.; Nixon, H. L.
The main series of tests of the original family of airscrews described in R&M 829 consisted of measurements of overall thrust and torque on 5 two-bladed and four-bladed airscrews of pitch diameter ratios 0.3, 0.5, 0.7, 1.0 and 1.5. These tests have now been extended to much higher pitch values and the original tests repeated at a uniform Reynolds number. The additional tests were made with the blades of P/D 1.5 rotated to the equivalent pitch values 1.0, 1.25, 1.8, 2.2 and 2.5. Some of the tests on the low pitch screws were made in a closed 7 ft. tunnel, but the tests of the highest pitch screws were made in the new open jet tunnel No.1 in order to use the higher maximum tunnel speed. Thus a comparison was obtained between observations in the closed and open jet tunnels for a number of airscrews and these support the standard methods of correction for tunnel interference. New apparatus was used including a new 15 H.P. induction motor of 9 in. diameter to drive the airscrew. The effect of the airscrew boss was eliminated by using a cylindrical guard body of 0.27 airscrew diameters with faired nose and tail of sufficient length to give a uniform flow in the absence of the screw. The thrust readings were corrected by pressure plotting the airscrew boss, so that the recorded thrust and torque coefficients refer to the exposed portions of the blades only. Instructions are given for correcting the performance data for the effect of interference when the screw is mounted on the fus elage of an actual aeroplane. The results show that the maximum thrust coefficient for the higher pitches is limited by the stalling of the blades, so that after reaching a value of about O.135 for the two-bladers and 0.26 for the four-bladers, the value of kT remains very roughly constant and independent of pitch for all smaller values of J. These values are however subject to a scale effect on maximum thrust coefficient of 5 to 10 per cent. for an increase of Reynolds number from 1.8 x 105 to 3 x 105 but there is some evidence to suggest that the full scale values will not differ greatly from those of the model. The torque coefficient increases with increase of pitch at all working conditions. The maximum efficiency for the two-bladers increases slightly from 88.4 per cent. at P/D 1.5 to an absolute maximum of 89.7 per cent at a P/D rather less than 2.5. For the 4-bladers the corresponding figures are 84.8 and 86.8.
1934-10-01T00:00:00Z