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Aviation History
1935
1935 - 1024.PDF
486 FLIGHT. MAY 2, 1935. A TWO-STAGE SUPERCHARGER Interesting Features in a Blower Developed by the Farman Com pany for Stratosphere Flying SEVERAL years have elapsed since it was first announced that the Farman Brothers, the famous French aircraft constructors, were designing and building an aeroplane for fly ing at very great altitudes. Since then little has been disclosed about the progress made, but that the firm was actively engaged upon research and experiment was generally admitted. Less well known, probably, is the fact that on his recent long-distance flights at great heights Wiley Post, the American pilot, has been using in his Winnie Mae a supercharger designed by Farmans and built under licence in America. Still more recently a series of tests have been made in France with superchargers for the U.S.S.R. These were of the two-speed type, one gear ratio maintaining a pressure of 760 mm. Hg up to an altitude of 2,000 m. (6,560ft.) and the other up to 5,500 m. (16,400ft.). The effi ciency of the two-speed supercharger is claimed to have been such (68 per cent.) that the use of an inter-cooler was unnecessary. During the tests the speed was changed 250 times without reducing the speed of the engine, and on strip ping after the tests the parts were found to be in good condition Operation of the two-speed drive, incidentally, was by hydraulic control requiring a very small effort from the pilot. Still more recently, we are informed, the Far- man company has brought out a two-stage super charger iu which the two impellers, which are in series, are driven by friction clutches, .that of the second impeller being under the control of the pilot. The two-stage supercharger is shown diagrammatically in the accompanying sketch. It would be possible to obtain a high degree of supercharg ing with one impeller, but its speed would have to be very high and would give rise to various troubles, among them being that a point is soon reached at which the tips of the impeller blades reach the velocity of sound, and this is accompanied by a marked drop in efficiency. To get over the AIR DELIVERY GROUND LEVEL IMPELLER DRIVE The Farman two-stage supercharger in diagrammatic form. As in other French superchargers, the carburetter is on the delivery side of the super charger ; British practice is to fit it on the intake side. difficulties the Farman designers adopted the two-stage blower, the first being used during the earlier stages of the climb, with the second impeller declutched. When a certain altitude has been reached—in this case 4,300 m. (13,000ft.)— the second impeller is engaged by means of a hydraulic con trol, and the two impellers together will then maintain the power of the engine up to a height, it is claimed, of 8,000- 9,000 m. (26,oooft.-29,500ft.). Another advantage claimed for the two-stage supercharger is that it occupies very little more space than does a single-stage. COUPE DEUTSCH PREPARATIONS Caudrons Qualify at Over 250 m.p.h. : 500 h.p. from 8 Litres in New Models THREE of the Caudron monoplanes entered for the Coupe Deutsch contest which takes place on Sunday, May 19, have passed their qualifying tests at speeds higher than those achieved in the actual race last year. According to the rules governing the race, qualifying flights much be made before 8 p.m. on May 2, under the following conditions: Each of the machines must fly over a closed circuit of 312^ miles at a speed not less than 187.5 m.p.h. ; fuel tanks must be s>aled—no refuelling during the flight is permitted; the take off must occupy less than 1,640 ft., and the machine at the end of this run must clear two cords stretched across the aero drome 3.28 ft. above the ground and 164 ft. apart; landings must be effected within 1,640 ft., and two obstacles, placed similarly to those mentioned above, must be cleared. The three Caudron machines which have just passed their qualifying tests are similar to those which flew in last year's contest. They have, in fact, the same six-cylinder super charged 300 h.p. Renaults, and the same variable-pitch Ratier airscrews with which they were originally fitted. Last year mechanical trouble precluded the use of the retract able undercarriages designed for the machines, but during this year's contest they will be flown with the landing gear retracted, as was originally intended. The following table gives the results of the qualifying tests of the three Caudrons mentioned above;— Time made over full circuit. Beit time for 100 km. Take-off. Landing. 390,04 kmjhr (249.75 m.p.h.) 401,212 kmjhr (250.75 m.p.h.) 409,42 hmjhr (255.80 m.p.h.) 422,75 kmjhr (2«4m.p.h.) 426,54 kmjhr (266.55 m.p.h.) 421,54 kmjhr (203.05 m.p.h.) 275 m. 300 m. 408 m. 447 m. Accomplished as required. Figures not given. Two other Caudron machines, equipped with a new type oi Renault twelve-cylinder supercharged inverted air-cooled engine, its cylinders arranged in vee formation, have been specially constructed for the race, and are expected to quality this week. Despite the fact that the new engine is of only 8 litres (488.8 cubic inches) capacity it is expected to develop about 500 h.p. Two other machines, a Nening and a Regnier—the latter equipped with a Regnier 300 h.p. six-cylinder inverted air- cooled engine—are expected to qualify before May 2. This year the contest will be run over a closed circuit oi 62J miles (100 km.) and will be flown in two sections with an hour's interval between. The start and finish will take place at Etampes (Mondesir) aerodrome, which is situated about 45 miles south of Paris. Thus the circuit, which touches Etampes-Roinville-l'Hopiteau-Tivernon-Etampes, will be flown ten times during each section of the race. R. C. \V.
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