|D.1 and D.4|
|Manufacturer||Army Balloon Factory|
|Designer||John William Dunne|
|First flight||July 1907|
|Primary user||British Army|
The Dunne D.1, was an experimental tailless aircraft built in the United Kingdom in 1907. It comprised a main unit which could be flown as a glider, to which a chassis unit with power train could be added. The glider achieved a short flight in 1907. The D.1 was later rebuilt as the powered D.4, which achieved short hops in 1908.
Lieutenant J.W. Dunne was employed by the Army Balloon Factory at Farnborough in 1906, to develop full-size aircraft based on his previous work with tailless, swept-wing models which were inherently stable. The key feature which gave them stability was a conical upper wing surface, arranged to give a progressive decrease in the angle of incidence towards the wingtips, a feature known as washout.
Dunne and the Balloon Factory's Commander, Col. J.E. Capper, wanted him to build a monoplane, but the Army insisted on a biplane, believing it to be both lighter and stronger.
Design and development
The first design to be built was the D.1, a biplane glider of wire-braced wooden construction and silk covering, to which could be added a powered chassis unit.
The glider was designated the D.1-A. Its undercarriage consisted of a pair of skids underneath the lower wing. Takeoff was achieved by launching the glider from a wheeled platform. The pilot's seat was placed centrally at the front, between the upper and lower planes.
The separate, wheeled chassis unit incorporated twin Buchet engines on a common driveshaft, together with twin counter-rotating pusher propellers, belt-driven from the shaft. The arrangement delivered only around 15 hp (11 kW) of power, but was all that the Army was prepared to fund. When mounted on its chassis, the craft was designated the D.1-B.
Construction was carried out in the utmost secrecy, with different parts made in different workshops and brought together in a locked room for final assembly. The glider was finished in time for initial flight trials in 1907, while the chassis took longer to make and was taken to the trials site afterwards.
Piloted by the Commander of the Balloon Factory Colonel J. E. Capper, its only flight lasted 8 seconds and ended in a crash in which Capper was slightly injured. The flight had however convincingly demonstrated the automatic stability which was it chief design goal.
It was repaired on site and the powered chassis unit, now arrived from Farnborough, was fitted. A flat guide track was installed, reminiscent of the system used by the Wright brothers for some of their early flights. A wheeled launching trolley ran on the track. During a test in October, the trolley slipped sideways off the launching ramp and the aircraft was severely damaged. It was dismantled again and taken back to Farnborough.
Over the winter of 1907-08, the aircraft was substantially redesigned and rebuilt to become the D.4. The wing was modified with more conventional elevons, hinged parallel to the trailing edge. It was mounted directly to a new steel-frame chassis. A single 25 hp (19 kW) R.E.P. engine now drove a similar pair of pusher propellers. The framework projected forward of the wing and was partly covered in fabric, forming a shallow nacelle to house the pilot. Vertical endplate fins were added between the ends of the biplane wings. In 1908, trials were again made at Blair Atholl, piloted by Lt Lancelot D.L Gibbs.
Successful flights in the wholly new and smaller D.3 glider were followed by attempts to fly the D.4. Engine power proved insufficient for the aircraft to take off, but several short hops were achieved during November and December 1908.
- Walker, 1974.
- Lacey, G. W. B. "History and Secrecy" (letter), Flight, 17 June 1955, p.852.
- Lewis, P.; British Aircraft 1806-1914. London: Putnam, 1962
- Taylor, Michael J. H.; Jane's Encyclopedia of Aviation. London: Studio Editions, 1989, pp. 347. ISBN 978-0-517-10316-6.
- Percy Walker, Early Aviation at Farnborough, Volume 2: The First Aeroplanes, Macdonald, 1974.
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