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Aviation History
1932
1932 - 0756.PDF
FLIGHT, JULY 29, 1932 The Percival "Gull 130 h.p. "Hermes IV" Engine ;; S [II—'HERE are those who maintain that practically all \^) I the progress made during the last ten years or _IIL so has been due to improvements in aero engines, and that of real advance in the aerodynamic design of aircraft there has been almost none. It is cer tainly true that the aero engine has been improved out of all recognition. A gradual decrease in specific weight has been accompanied by a pronounced increase in reliability. This was amply proved during the recent race for the King's Cup, when engine trouble was almost entirely absent in spite of the running of the engines at full throttle for a distance of 1,230 miles. That progress has been made in the aerodynamic design of aircraft becomes evident every so often, when a new type is produced which shows a very much better performance than previously existing machines of comparable type. There was an instance of this with the de Havilland " Fox Moth " flown by Hope in the King's Cup, which he won easily. That machine was very- much faster than anyone had expected, and its aerodynamic design must be very clean indeed. Another type which flew in the King's Cup Race, and one of the " dark horses," being quite a new machine, was the Percival " Gull," fitted with the new " Hermes IV " inverted engine. Although the " Gull " did not succeed in getting a place in the race, it was quite evident, from the fact that it averaged 142.75 m.p.h. around the whole course, that here was a new machine of more than average efliciency. An examination of the data relating to the machine shows that this impression is indeed well founded. It is our custom, when describing new aircraft, to endea vour to get an idea of their aerodynamic and structural efficiency by examining certain " figures of merit " which represent, in a general way, these two qualities. For the former the Everling " High-speed Figure " is useful, and a very fair indication of structural efficiency is provided by the ratio of gross to tare weight. When using British units, but keeping the actual " High speed Figure " value the same as it would be in the units employed by Dr. Everling in his original article, the for mula for the " High-speed Figure " is 2kv V >' 147,000 " H.P. where V is the speed in m.p.h., S is the wing area in square feet, H.P. the maximum horse-power of the engine, kj, the " absolute " drag coefficient, and »j the propeller efficiency. In the case of the Percival " Gull," the wing area is 169 sq. ft., the maximum engine power 130 b.h.p., and the maximum speed claimed is 145 m.p.h. These figures give to the Everling " High-speed Figure " jrr- a value of 27, EFFICIENCY : This front view of the Percival "Gull " helps to explain why the machine has such a high performance. (FLIGHT Photo.) 708
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