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Aviation History
1929
1929 - 0439.PDF
FEBRUARY 28, 1929 -with a reasonable torque curve. I have selected what I believe to be ideal bore and stroke conditions, and the figures do not necessarily refer to any particular type of engine. In practice most engines have to cover a wide range and there is some reason why the most ideal dimensions have not been chosen. Following up the chart you will note in diagram form the crank lay-out of each type of engine and that the firing order is regular in every case, except the one example of the 4-cylinder 90° twin in the lowest horse-power category. Passing to the first four main sections of the graph, these have been plotted as the result of an investigation of the balance and firing order of the different types under review. As far as possible freak lay-outs have been avoided, and such arrangements as 6, 9, and 18 cylinder Y engines, which have, I think, from time to time been suggested, are not included, as the balance or firing order becomes impossible. As a general principle, the graph shows that one of the first considerations is the desirability of approaching as nearly as possible perfect balance. Heading No. 5 has been obtained by taking an area enclosing the cylinders and cooling gear, plus the area of a circle enclosing the engine bearers. Such a compilation is hard on the radial, in the light of the latest experiences on cowling, and complimentary to the larger in-line engine, for the reasons stated elsewhere in this paper, and alternative figures have been given which are considered to most nearly represent a fair comparison. These alternative figures are based on results obtained on wind-tunnel work in this country and the recent X.A.C American report. I have made no attempt to alter the curves in respect to the large in-line air-cooled engines, but I seriously submit that when a sufficient air flow has been provided the frontal area will be increased. For heading No. 6 an allowance of 0-32 sq. in. per b.h.p. has been made, equivalent to 20 cub. ft. required per*>.h.p. at a speed of 100 m.p.h. Heading No. 7 is certainly open to criticism and is purely t-mpirical, as so much depends upon quantity, production, class of workmanship, etc. It has been assumed that the first two categories are intended for the smaller classes of commercial aircraft, where price is of the utmost importance, whereas the third and fourth categories are intended for military and large com- mercial aircraft, where the highest class of workmanship is desirable. An accurate figure for heading Xo. 8, without investigating the design details of each engine, is impossible, but the results are obtained from another graph, not shown, in which the standard wt./h.p. was plotted against a considerable number of different engines already in existpnee, and where it has been assumed that an air-cooled engine of given type and size would weigh the same as the corresponding water- cooled engine dry. If conclusions are permissible from such a heterogeneous collection of data, I would like to add the following comments on the four categories of engines :— The. 80 to 100 h.p. Light Plane Engine—In spite of the unbalanced forces in the four-cylindered in-line engine, the fact that it has already given excellent service is an argument in favour of it being, most probably, the best compromise. Reasonable balance, combined with low cost, are more important that specific weight in this category. Psychology also plays its part on this type, and the fact that the in-line engine more nearly approaches the motor-car engine has, I believe, affected its popularity. The six-cylinder in-line would appear to be a good lay-out for the more expensive type of engine. I am not in favour of upside-down in-line engines for the light 'plane : they are more vulnerable than the radial on a crash, and the induction system is difficult. We seem to be some way off the £100 engine, but I believe the five-cylinder radial could be made a most excellent and cheap production job. I should be very intrigued to try out a five-cylinder radial in which the cylinders and crank-case were cast iron in one piece, with end aluminium casings for covers with aluminium-cast heads and duralumin-articulated rods. I believe that with reasonable production a sound engine could be produced very cheaply. The 200 to 250 h.p. Engine.—In this category, where price and simplicity are still of considerable importance, the radial family would seem to be able to hold the field. The objec- tions to the eight-cylinder horizontally opposed are obvious. The eight-cylinder Hex is excellent from a balance point of view, but probably more expensive than the single bank radial. The 350 to 450 h.p. Engine and the 500 to 600 h.p. Engine — The qualities required from the last two categories are approximately the same, except that the larger engine demands a greater number of cylinders, and, allowing that it will probably be installed in slower machines where gearing will be necessary, the cooling difficulties will be considerably greater. The Wright Vee 1460 is a very interesting engine indeed, and represents the very latest practice in compact air-cooled in-line layout, for which so much has been claimed of late. The burning question is how much less drag, compared with the radial, will an engine of this type give when the opening in the cowling is sufficient to provide the necessary cooling air to each cylinder. Without in any way criticising the in-line Wright engine as a design, I believe the radial will require a good deal of displacing, at any rate for the third category, provided it can be installed in a Suitable manner. The drawings on p. 172 show in diagram form and to scale, two similar machines, with 9-cylinder radial and 12-cylinder Vee air-cooled engines, of approximately 400 b.h.p. In the case of the radial engine machine the drag has been reduced by a suitable lay-out and engine cowling, and the weight of the aircraft with radial engine will be undoubtedly less. In the large engine category the radial family should ail score on weight, cost and fnaintenance. The drag depends upon the type of machine and consequently the body behind the engine. If the machine is such that the body allows a complete fairing to the engine the drag will probably approach that of the in-line engines, and the cooling should certainly be an easier proposition than on the latter. The horizontally opposed 12-cylinder looks to be a very useful engine for multi-engine machines. In conclusion, I would like to thank all those firms, both in England and America, who have so readily come forward with information, without which this paper would have been impossible, and also Messrs Owner and Fraser, of the Bristol Engine Department, for assistance in compilation of the tables. The Autogiro in America FOLLOWING on the purchase of an Autogiro in August last by Mr. Harold F. 1'itcairn of Land Title Building, Philadelphia, negotiations have now been completed for the sale of the United States rights in the invention to the Pitcairn Cierva Autogiro Company of America, Incorporated, a Delaware Corporation. The Cierva Autogiro Co., Ltd., of Bush House, London, also retains a substantial interest in the American Company. The new Company will grant licences to manufacturers and others to make, use and sell the Autogiro throughout the United States. Thr interest of the purchasers in the Autogiro dates back to 1925 when Mr. 1'itcairn visited Senor dc la Cierva in Madrid. Since that time he has kept in touch with the development of the invention in England and a machine was taken over in the autumn of last year to Philadelphia where a series of practical flight tests were made under the direction of Mr. 1'itcairn and his executive and engineering staffs. These tests which were of a very complete and thorough nature have resulted in the formation of the American Autogiro Company mentioned above. Air Chartering THE first charter for air transport was signed on February 15. the signatories being S. Instone and Co., Ltd., and Imperial Airways, Ltd. The charter was compiled by the former, the main point about it being that it introduces into air transport the same principles as those in shipping and facilitates the employment of aircraft for business purposes. The innovation has been well received in the City and business circles. High-Speed Flight Appointment FLYING OFFICER H. R. D. WAGHORN, an instructor at the Central Flying School, near Stamford, Lincolnshire, has been appointed to the High-speed Flying Section, Felixstowe, where practice is going on for this year's Schneider Trophy Race. 173
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