Dunne D.7

Although J. W. Dunne is best known for his inherently stable tailless biplanes such as the D.8, he also developed a series of inherently stable monoplanes. He first submitted a monoplane design to the War Office when he joined the Army Balloon Factory at Farnborough in 1906, but they told him to build a biplane instead.

It wasn't until Dunne left the Balloon Factory and started his own company, the Blair Atholl Aeroplane Syndicate Ltd., that a monoplane could be built. The D.6 was finished in 1911, with a 60 hp (45 kW) Green in a pusher configuration. Three A-frames supported the wing engine, pilot and undercarriage. All Dunne's tailless aircraft had swept wings with marked washout (reduction of angle of incidence) at the tips. Since sweepback placed the tips well behind the centre of gravity, they provided longitudinal (pitch) stability in just the same way as a conventional tailplane, mounted at lower incidence than the wing.[1] The wing camber increased outwards, causing the outer leading edge to droop further.[2] The inherent design of the wing provided some directional (yaw) stability, which was augmented on the D.6 using down-turned wingtips. The wing had wingtip elevons for control, though because of the down-turned tips these also provided some rudder-like forces. The D.6 was tested at Larkhill on Salisbury Plain in January 1911 but failed to take off.[3]

The D.7, major parts of which were built by Short Brothers,[4] re-used the same wing but with a very different structure supporting it. The wing was straight edged, tapering from a central chord of 6 ft 3 in (1.91 m) to 5 ft 0 in (1.52 m) at the tips. The leading edge was swept at 35°. The heavy A-frames were replaced with a pair of rectangular frames which extended above and below the wings, linked at the bottom by two transverse members. These frames served as double kingposts from which each wing was wire braced above and below. A substantial undercarriage structure was mounted at the bottom of the frames, comprising a long pair of skids which extended from the pusher propeller line well forward beyond the nacelle and curving strongly upwards. Each skid was multiply braced to its frame and inwards to the nacelle; the pair were joined by a cross strut near the forward tip. Both carried a pair of wheels and, at the rear, an articulated and sprung extension to absorb landing shocks.[2][5]

The nacelle that carried the pilot's seat and the engine behind him was no more than an open wooden framework. Initially, the same Green engine was used as before, driving a two bladed, 7 ft 3 in (2.21 m) diameter propeller. A tall, rectangular radiator was placed longitudinally above the wing, positioned to raise the centre of gravity as high as possible. A pair of levers, one for each hand, controlled the aircraft.[2][5]

This aircraft was tested at Eastchurch airfield on the Isle of Sheppey in June 1911, flown by Dunne. Designated the Dunne D.7 or D.7 Auto Safety. This was very similar to the D.6, but had a 1 ft (305 mm) shorter span and a 50 hp (37 kW) 7-cylinder Gnome rotary engine. It first appeared, not quite ready for flight, at the Olympia Aero Show in March 1911 and was on test at Eastchurch that June.[5] Dunne was pleased with the improved performance.[6] In January 1912 Dunne demonstrated the D.7 to members of the Royal Aeronautical Society, writing a note whilst flying hands off at 60 mph.[5]

The Dunne D.7 bis was an improved variant with a 70 hp (52 kW) Gnome rotary engine and capable of carrying a passenger. Having a 1 foot (0.30 m) shorter span wing, it was successfully flown at Villacoublay in France by both Dunne and N.S. Percival in April 1913.[7]

Data from Flight, 1911

General characteristics

• Crew: 1
• Length: 21 ft 0 in (6.40 m)
• Wingspan: 36 ft 0 in (10.97 m)
• Wing area: 230 sq ft (21 m²) including elevons
• Powerplant: 1 × Green water cooled inline, 60 hp (45 kW)
• Propellers: 2-bladed, 7 ft 3 in (2.21 m) diameter