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Aviation History
1916
1916 - 0205.PDF
MARCH 9, 1916- [JFLICHT] DESIGNING AND BUILDING A BIPLANE. THE STORY OF A SUCCESSFUL EXPERIMENT. By ROBERT P. GRIMMER. [/;.. !he following story Mr. Grimmer has given a detailed summary of the lips and downs to which an experimenter in aviation has to it Orepartd to submit. He has adopted a very light style in handling his subject, and treats his firm's misfortunes in an almost Mark Taplev spirit, worthy of admiratton. The mistakes made and the difficulties encountered should Iv helpful to new workers in the same direction, a suggesting what to avoid. Mr. Grimmer's views as to the comparative merits of twin-propeller and chain pusher machines as opposed to direct driven tractor machines are worth careful consideration., although it must not be taken that we necessarily are in agreement mith all tic author sets forth. Altogether the story is both amusing and instructive, and we heartily wish the Mann firm the success which Mr. Grimmer foretells in his concluding paragraph in connection with M.J now under construction. — ED.] The Mann biplane M. 1, and some of those who helped to build her. Inset " the firm' and on the right Mr. R. F. Mann. on the left Mr. R. P. Grimmer, THE Mann Gun-Carrying Biplane is probably familiar enough to the average reader of " FLIGHT," but very few people seem to know the raison d'etre of its existence. The general opinion would appear to be that the transmission was put in for a joke, or else was a mis guided attempt to make the 'bus dissimilar to the ordinary type of fuselage machine. Nothing could possibly be more erroneous than these views, and I am now attempting to explain the exact reason "wny M.I came into being. The great majority of aeroplanes belong to the tractor type—that is, with the airscrew .in front drawing the machine forward. The other type with the propeller behind are known as "pushers." Previous to the war, the " pusher " type had been greatly neglected, owing to the fact that its design and construction from a " perform ance " point of view presented great difficulties. The tail booms caustd a certain amount of resistance, and there was always the possibility of their being broken by fragments of a damaged pro peller. Further, there was the objection against the placing of the engine and tanks bthind the crew, which, any way in theory, were liable to break loose and crush the pilot and passenger in ihe event of a had landing. Whether this objection has always been sub stantiated by facts I am not prepared to say, but on paper the " enginebehind " machine certainly does look unhealthy. Uni il the war broke out, all the best aeroplanes, without except ion, •were of the tractor biplane type, and the most successful of these were single-seaters or "scouts.'' Both the British and French Governments possessed a few " pushers," but it is very doubtful if the best ot these had a speed much in excess of 65-70 miles per hour, with a climb of some 300 ft. per minute. The Service value of the " pusher" consists in the excellent view obtained by the crew and the ideal gun emplacement afforded by the projecting body or nacelle. But the " tractor" scored at that time (1914) by virtue of its superior speed and climb. If by a stroke of a magic wand the Allied Governments could have transformed their " tractors" into " pushers," retaining at the same time the superior performance of the former type, there is very little reason to doubt that this would have been d< ne at the beginning i.f the war. It was not until some time afterwards that the dtvice of firing through the tractor screw was introduced by Garros. This device has the great disadvantage ihat 'he gun cannot be properly aimed, as it is on a fixed mounting. The Huns were even worse off as regards " pushers " than ou^elves, as they had pinned their faith entirely to the " performance tractor." I have explained the virtues and vices of the "ttactor" and " pusher" lyres ; the one gave good performance, medium view and a bad gun plalfoim, and the other bad performance, good view and a super excellent gun platform. Mr. Mann and I had been con nected with aviation in various capacities since its inception in 1908, and we had for some time previously recognised what we considered the disabilities of the contemporary types for Service work. The first really successful flying machine was the Wright, which in its time (1908-09) put up some quite as' onishing performances, including a double crossing of the Channel with an engine giving only approximately the same horse-power (20) as the Ford tin-can car ! The great characteristic of the Wright was its twin geareddown propellers driven by chains. It is an undeniable fact that propellers of large pitch rotating slowly are more efficient than propellers of small pitch rotating at very high speeds. Propeller speeds of any thing up to 1,000 r.p.m. are regarded as being slow, anything approaching 2,000 r.p.m. is very fast. High speed propellers have a very large percenage of " slip," and they lack the grip on the air of the slow speed variety. There are other objections as well, the chief being the tendency to disintegrate, owing to the terrific velocity of the tips, but this latter is worse in theory than in practice, though cases are reported from time to time. At one time the Wright machine was supreme, but as the designers made no real attempt to keep pace with the times by installing really high-power engines, their " twin-pusher " was in course of time completely eclipsed by single-propeller types, chiefly of the " tractor " variety. Mr. Mann and I always recognised the possibilities of the " twin-pusher," properly developed, and we had always wished to construct such a machine on medem lines. But in those days we never secured the weighty financial backing necessary for so great a project. Just before the outbreak of the great war Mr. Mann and I were fortunate -enough to secure the interest of Mr. W, H. Bonham- Carter in our project, with the result that we were able to commence construction in September, 1914, Mr. Mann having got out the rough designs in August. I must here pay a tribute to the magna nimity and the disintere-ted patriotism of Mr. Bonham-Carter, who at the time of writing has tome the greater part of the burden of financing our experimental work for a period of over eighteen months, and who at the outset had no guarantee whatever that he was backing the right horse. M.I was designed and built at great pressure in the hope that she might be u ed against the Huns early in 1915. Mature reflection inclines me to the view that we should have done better if we had advanced at a more leisurely pace. The design and construction of such an experimental machine was a very big contract, so big indeed that no established constructor would have risked his reputation by taking it on. Having no reputation as constructors to lose, we took tne risk—there was a distinct risk, although we were unaware of it at the time—and boldly grasped the bull by the horns. The only building we had available for the purpose was a disused tin church 20 ft. by 40 ft., with a vestry that we converted into two offices. This building had the reputation of being haunted, and it certainly had been standing empty for many years before we got possession of it. A particularly gruesome story is told about this epoch, but the episode occurred so many years ago that it is impossible to verify it. Such was the reputation of the building where M. 1 was built. M.i was a. fuselage biplane with twin chain-driven propellers. 205
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