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Aviation History
1941
1941 - 1906.PDF
FLIGHT AUGUST 2IST, 1941. CARBURETTOR, INJECTION, Or — ? without much success. Bendix-Stromberg also carried out a good deal of work in this direction. Investigation still goes forward, both in U.S.A. and this country, and nobody can foretell what developments may take place in the future. (y) Timed Injection into the.Inlet Port or Manifold of Each Cylinder.—Considerable work was carried out by the Bristol Aeroplane Co., Ltd., using a medium-supercharged Pegasus engine, and injecting the fuel into the elbow of the inlet manifold of each cylinder. According to Judge,* the rated altitude was lower than that produced by the standard engine, the reason doubtless being due to the loss of pressure ratio at the supercharger Owing to the absence of fuel. This arrangement of timed manifold injection was also developed by the Marvel Carburettor Co. of America, and a number of aircraft so equipped were flown for some time. Another design, known as the Hasbrouck, was the object of much investigation by one of the great American aero engine concerns and did a good deal of flying, but never reached production. While it is most likely that on small engines the ortho- dox carburettor will be retained for some years to come, it will be recalled that Flight has made previous mention of the system adopted on the Continental Series A engine of 50 h.p. This embraces timed injection into the mani- fold by plunger pumps, an arrangement developed in conjunction with the Fuel Injection Co. of Mich., U.S.A. On the whole, however, there appear to be no special advantages in timed manifold injection as against the other two types, and its future is a matter for conjecture. (z) Continuous Injection into the Supercharger Eye or Entry.—This design is one which particularly engages our interest, since it has been developed in the United States concurrently with both arrangements described above, yet has outstripped them both and has now been in large-scale production for three years. (It is a product of the Strom- berg Division of Bendix, and the unit is fitted to a large proportion of the American aircraft arriving in this country.) It is hoped to publish a full description of the Bendix- Stromberg system in a subsequent article. In the mean- time, its importance in the field of aeronautics warrants a few words upon its operation. In essentials, it consists of delivering a continuous (metered) spray of fuel, which is injected into the eye of the supercharger, or at any other selected position in the supercharger entry which is found by experiment to give the best fuel distribution, The pressure of the fuel at the nozzle is maintained con- stant and is of the order of 5 lb. per sq. in. The fuel is metered as in the conventional carburettor, and the airflow passes through venturi and throttle valves, but no fuel passes through the latter, since injection occurs separately on the engine side of the throttles. Checking the characteristics of this arrangement against those in the table, it should possess the first five advan- tages of cylinder injection, for the following reasons: — (1) No fuel passes the throttles. • A. W. Judge, Aircraft Engines, Chapman and Hall (2) Carburettor and fuel line always full and under pressure (minimum 5 lb per sq. in.). (3) Same as (2). (4) Ability to locate injector nozzle at any point which is found to give satisfactory fuel distribution. (5) No fuel is taken through the airflow passage of the carburettor, so that carburettor loss is small for a given airflow. And since the fuel is injected between the car- burettor and the blower, there is no loss of pressure ratio as in the case of cylinder injection. While the fuel distribution of cylinder injection should theoretically be better than that of the conventional car- burettor or any other form of fuel injection, it is yet to be proved whether this factor is reflected in actual con- sumption. The continuous spray system, however, while not possessing the theoretical claim of cylinder injection to good distribution, achieves this end very well by its ability to have injection nozzles ,of any required number or form located at any desired point in the supercharger entry. On the other side of the scale, while none of the factors (a) to (h) in the table can be levelled against the system, it is indeed slightly heavier than the conventional car- burettor and has more parts, and is slightly more costly. But in no case do these increases approach those of cylinder injection. The fact that American aircraft engines are not fitted with boost controls has no connection with the design or operation of the injection system, but is merely due to the trend of > design in American aviation circles. It is most probable that the influence of civilian flying is respon- sible for the absence of demand for boost control, and no American engines are so equipped, whether they are fitted with orthodox carburettors or the injection system. - v What of the Future ? The battle of fuel injection versus conventional car- burettor is thus seen to be a three-sided affair, with two entirely different forms of fuel injection already in the field, each backed by enormous production and service experience. However the battle may go, the war will doubtless prohibit any drastic changes of British policy, for while production and still more production is the cry, nothing that is not vital must clog the wheels. But if one may hazard a conjecture, it is that when post-war design has settled down after a period of peacetime research, all the larger engines, particularly those for aircraft-of-war, will be equipped with some form of carburation by injec- tion, probably one of the two types outlined above, or developments of them. Smaller engines may retain the orthodox aero carburettor, which in its present state of development is an excellent instrument and up to the work demanded of it. Yet who can tell? It may be that from the ashes of war some entirely fresh ideas will be born, and that in twenty years' time the petrol engine as we know it, as well as its accessory the carburation system, may have changed beyond anything within our present conception. SPITFIRES AND MOONSHINE DANGEROUS Moonlight" (Regal, Marble Arch) is acurious blending oi fact and fiction. The R.A.F. sup- plies the fact, Hollywood the fiction. The two do not blendhappily, for the contrast is too striking. Hollywood material actually goes more comfortably with pictures of air fightingdeliberately faked in Hollywood itself, as in such films as "Hell's Angels." Then the cameraman naturally gets betteropportunities, and his pictures show the same photographic quality as do the shots oi love-making on the ground. Filmstaken in actual air combat are more real, but look less so. The Hollywood part concerns a Pole (Anton Walbrook) whois a great musician and also a fighter pilot. He escapes from Warsaw to the United States and marries an American girl(Sally Gray). Then he hears of the Polish squadron being formed in England, but his wife tries to prevent his going tojoin it. The problem of conflicting duties is as old as fiction itself, and in this film it is presented in very ordinary fashion,supported by competent but hardly inspired acting. However, the great family of film fans will doubtless revel in all this, andpossibly will teel their eyes grow moist and red. Ultimately the Pole joins the Spitfire squadron, and thencomes the R.A.F. contribution to the story. Real fights are shown, and German machines are shot down. The take-off ofthe squadron in formation is a stirring sight, and we much enjoyed the slow roll by a single Spitfire after a victory. Areally good insight into fighter methods of operation is given and, to some spectators, this will be worth all the rest of thyfilm put together. One wants to forget all about the Holly- wood part, and wishes that echoes of it would not intrude intothe mess scenes. However, it all ends happily. All proceeds of the world premiere of the film last Thursdaywere devoted to the R.A.F. Benevolent Fund.
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