FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1943
1943 - 1385.PDF
MAY 2/TH, 1943 FLIGHT 561 The Mumford Helicopter Six Lifting Screws on a Very Spidery Framework : 40 Pounds per Jtlorse- power ; Some 1906-1914 Experiments OUR recent articles on rotating-wing aircraft have remindedan old reader and friend, Mr. J. Pollock Brown, of some experi- ments in which he took part during the period 1906-1914. Mr. Pollock Brown, it may be necessary to remind our readers, was the moving spirit in the firm P.B. Deviators and the inventor- designer of those ingenious turn indicators and mechan- ical pilots. He was at one time a technician at the Royal Aircraft Establishment, but during the period here under review he was associated with Denny Brothers, of Dum- barton, who were developing a direct-lift aircraft to the ideas of the late Mr. E. R. Mumford. In 1906 little was known about the thrust (or lift) obtainable from airscrews, although as chief of the Froude tank at the National Physical Laboratory at Teddington Mr. Mumford knew pretty well all there was to know about marine propellers. Another great drawback was that there was no petrol engine available light enough to leave sufficient over for lifting the frame- work, screws and pilot. Too Much Supercharge "Our first engine," Mr. Pollock Brown says, "was an 8-cylinder 'Farcot,' which had practically to be rebuilt before it even approached the guaranteed power. Then, in about 1908, I incorporated a supercharger in the engine and got so much extra power that the dyna- mometer was wrecked and the engine damaged! '' The next engine was a British N.E.C., a four-cylinder two-stroke, water-cooled, which was used a good deal by early British experimenters. Interesting sidelights on early aviation engines are thrown by Mr. Pollock 3rown, who says : "We never made any attempt to fit an engine to the craft before it had been independently proved. The N.E.C. was tested on our own dynamometer at their works, and certainly ' toed the line' after some coaxing.'' The N.E.C. engine had a bore of 3-7rn- and a stroke of 4.5m. It was rated at 50 h.p., although it is doubt- ful if it ever developed more than 40. The weight was 150 lb., which was remarkably light for those days. Scavenging was by a Roots blower, one part of which expelled the exhaust gases and the other delivered a fresh explosive charge. Denny Brothers were, of course, first and foremost interested in shipping matters, and the helicopter experi- ments had to be made in spare time, often enough against scepticism, one may suppose. Consequently, it With an N.E.C. four-cyl. two-stroke engine of 40 h.p. the, Mumford helicopter lifted 1,600 lb. This picture shows it on floats, in 1914. is scarcely surprising that they spread over many years without spectacular achievements. Moreover, know- ledge of aerodynamics and of light structures was scarce, and pretty well everything had to be schemed out, de- signed and tested before it could be incorporated. Work on the lifting screws proceeded step by step, through computation and trial, beginning with single screws. Ultimately no fewer than six were used! They were mounted on a very flims)' spider framework since every possible ounce of weight had to be saved on account of the heavv engines which were the only on'*s then available. Fabric Lifting1 Screws The screws themselves were flimsy affairs: fabric stretched over Canadian elm rims, with a few bracing members inside. The main lifting screws had a diameter of about 24ft. and a pitch of 35ft. It was calculated that they would have to run at 45 r.p.m. in order to give a lift of 1J600 lb., which was the weight of the apparatus with Mr. Pollock Brown on board. The whole contrap- tion was fragile in the extreme, but, Mr. Pollock Brown says: "It was remarkable how little squirming took place with all these propellers working together and over- lapping. This was due to the generous wire bracing, though the factor of safety .was reduced to about 4 in an endeavour to cut down the weight, which had a knack of increasing with the development of the power installa- tion. The lift was definitely checked and.the power recorded on a torsion dynamometer, first from an elec- tric motor on the ground, transmitting through a vertical sliding shaft, and later confirmed on another dynamo- meter at the engine clutch." From the known engine power and the loaded weight of the machine it was definitely proved, although free flight was not attempted, that direct lift was possible. The lift corresponded to 40 lb./h.p., which must be considered a very fine effort with such crude apparatus. The machine was mounted on both skis and floats, but the spectacular results achieved by Wilbur and Orville Wright and others caused the experiments to cease, and thus it was never possible to develop the machine to the point where it could make use of them by making actual free flights.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
