FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1932
1932 - 0523.PDF
FLIGHT, JUNE 3, 1932 giant 60-ft. x 30-ft. jet tunnel. When the British Air Ministry asked the Aeronautical Eesearch Committee to advise on the construction of a very large wind tunnel, the Committee advised that: '' There are three main classes of research which could be better and more econo mically performed in a large wind tunnel than by other means, viz., (1) experiments on the cooling of air-cooled necessary for absolute safety. The fresh air was intro duced around the inlet jet, and the surplus was drawn away from the periphery of the exit cone. By way of explaining why the A.R.C. did not recom mend the construction of a tunnel as large as the American, Mr. Wimperis said that it had not been considered neces sary to build a tunnel large enough to take the complete WIND TUNNELS Description. Size of jet. N.P.L. 7 ft. No. 1 No. 2 No. 3 N.P.L. Duplex N.P.L. C.A.T N.P.L. 9 ft. x 7 ft R.A.E. 7 ft. No. 1 No. 2 R.A.E. 5 ft. low speed R.A.E. 5 ft. high speed R.A.E. 24 ft. 7 ft. x 7 ft. 7 ft. x 7 ft. 7 ft. X 7 ft. 14 ft. x 7 ft. R ft. diam. 9 ft. x 7 ft. 7 ft. x 7 ft. 7 ft. X 7 ft. 5 ft. diam. 5 ft. diam. 24 ft. diam. N.A.C.A. C.A.T. (before reconstruction) .. 5 ft. diam. N.A.C.A. 20 ft. ( 20 ft. diam. N.A.C.A. 60 ft. x 30 ft 60 ft. x 30 ft. Speed. (ft./sec.) 67 83 96 100 90 210 (expected) 90 140 162 315 (expected) 176 (expected) 74 1 62 169 Pressure : Atmospheres. i i i i 25 I 1 1 1 1 1 20 1 1 H.P. 60 120 200 400 500 400 125 300 75 500 2,000 250 2,000 (Diesel) 6,500 Ratio of energy passing per sec. to input to fan motor. 0-53 0-51 0-48 0-53 2-3 2-6 0-61 0-95 2-4 2-4 2-4 1 35 1-45 2-2 Nature of circuit. Open. Closed. " Open. Closed. »» •• Closed. " >• and water-cooled engines ; (2) measurements directed towards the reduction of the resistance of the central parts of actual aeroplanes ; and (3) tests of full-scale airscrews." After full thought, it was advised that there would be no material advantage in going beyond a jet of 24-ft. diameter. A 5-ft. jet model was made of the proposed design, and for economy of power a closed-return circuit was decided upon. This model was of great service in assisting in the design of the 24-ft. tunnel, but was also subsequently found to be a very successful piece of equip ment in itself. With an engine of but 75 h.p. an air speed of 115 m.p.h. was attainable. With the motor of 500 h.p. now being installed, the air speed should be 215 m.p.h., making the model of permanent use for model airscrew investigations. Closed circuits were preferred, because, apart from being more compact, the power required to maintain the air stream was lower. The energy ratio of a number of tunnels was given in the above table. It was estimated that in the new Farnborough tunnel an air speed of 120 m.p.h. would be attained with a horse power of 2,000. The general layout of the building was such that an aeroplane with a wing span of as much as 56 ft. could be got in. The first work to be done in this tunnel as soon as it was ready, Mr. Wimperis said, would be the investigation of the air-cooling of engines, the per formance of airscrews, the effect of excrescences on the fuselage in adding to resistance or adversely affecting the flow near the tail, and on the draughtiness of cockpits. As the new tunnel would be used for testing with actual aero engines running, the question of poisonous gases from the exhaust was important. It was estimated that about 250,000 cu. ft. of fresh air would have to be drawn in every minute in order to ensure the degree of dilution aircraft, as the Parnall research monoplane was available for testing wings of the most various types in actual flight. What could not, however, be done in flight was modifica tion of the engine cowling with simultaneous observation of cylinder-head temperatures and change in drag of the aircraft. The R.A.E. Seaplane Model Testing Tank After referring to the tank built by Short Brothers at Rochester some years ago, the first to be constructed ex pressly for testing models of seaplane floats and flying-boat hulls, Mr. Wimperis outlined briefly the particulars of the new large tank built recently for the American N.A.C.A., stated to be capable of speeds of 50 m.p.h. or more, with a cross-section of 24 ft. in width and a depth of 12 ft., no less than 2,000 ft. long. In this country the conclusion had been ai rived at that a tank 9 ft. wide by 4| ft. in depth and only 650 ft. long would do what was necessary. The speed aimed at in the new British tank was only 40 ft./sec. (27 m.p.h.). Mr. Wimperis. asked the question: "Are we being too modest? " He answered this question himself by examin ing the data of the sort of model tests contemplated. "If we suppose," Mr. Wimperis said, " that we desire to make measurements on the model of a very large flying boat, say 110 ft. in overall length, the length at the water line when at rest will be about 80 ft. and a model to a ninth scale would have a length just equal to the width of the tank, namely, 9 ft. If the taking-ofi speed of the boat were 60 knots, the equivalent speed at which the model must be towed would be 35 ft. /sec, or well within the 40 ft./sec. which I named above as the full speed of the tank carriage." If, Mr. Wimperis said, larger models and higher speeds Diagrammatic view of the compressed-air tunnel at the N.P.L. (Illustra tion by courtesy of the N.P.L.)' 483 c 2
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
