M.Goodall, A.Tagg British Aircraft before the Great War (Schiffer)
Deleted by request of (c)Schiffer Publishing
P.Lewis British Aircraft 1809-1914 (Putnam)
Mumford Helicopters 1 and 2
In 1906 Edwin H. Mumford and J. Pollock Brown, of Wm. Denny & Brothers, Dumbarton, who were in charge of the firm's experimental tank and had studied the theory of ships' propellers, designed a direct-lift aircraft based on the results of their researches. I t comprised a tubular framework of rectangular plan-form carrying six large two-bladed rotors of 25 ft. diameter and 19 ft. pitch, whose axes were inclined outward and forward at 10° from the vertical. The first rotors were constructed of silk stretched over a framework and braced by wires from a central king-post. The propeller frames were made first in bamboo - which soaked up water and rotted - and then of steel tubes. These, however, were found to be too flexible, but, finally, the elm frames used in 1909 were satisfactory for the purpose. The three rotor shafts on each side were parallel to each other and were driven through bevel gearboxes by a longitudinal shaft, the two side shafts in turn being geared to inclined cross-shafts driven by the centrally-mounted engine. The first engine, a 25 h.p. Buchet, was replaced in 1909 by a four-cylinder two-stroke N.E.C. of 25 h.p., and this in turn gave way in 1911 to a V-4 N.E.C. of 40 h.p. The pilot sat behind the engine, and the control surfaces provided were an elevator above the pilot's head and a vertical rudder at the rear of the machine. The helicopter rested on two long wooden skids. The structure and transmission shafts were of aluminium tubing, and the complete aircraft weighed originally 886 lb. with the pilot. As modifications were made, the weight increased until it reached 1,580 lb. in flying condition.
The gearboxes were of exceptionally efficient design, and very few transmission difficulties arose. Tests were made first with an electric motor on the ground and, in 1912, tethered flights to 10 ft. were achieved successfully with the V-4 engine installation, in January, 1913, a side shaft broke and caused two adjacent rotors to foul, with the conseqent wrecking of the machine.
Experiments were resumed in 1914, when a second helicopter of generally similar design, but with much detail improvement, was built in Denny's Leven yard. This version was more compact and of stiffer construction and was mounted on long parallel floats. The same power unit and transmission as before were used, but the aluminium struts were replaced by composite tubes manufactured from paper, wood and fabric. In this form the machine weighed 1,508 lb. empty. In the autumn of 1914 it was launched on the River Clyde and made a successful flight of 300 ft. at a height of 10 ft., during which it lifted a total weight of 1,600 lb. and achieved a forward speed of about J 5 knots. It was then returned to the slipway because of an approaching gale, by which it was wrecked completely later that night. War had already broken out, and it was not possible to undertake any further helicopter experiments.