In 1908 Lord Tullibardine offered to help, and with Capper and his assistant, Captain Carden, they set up the Blair Atholl Aeroplane Syndicate and had Short Brothers build them a new tailless biplane with a 60-hp Green engine driving two propellers.
The D.5 was a two-seater which Dunne elected to test fly himself. The recalcitrant motor put Dunne and his D.5 into the marsh at the end of Eastchurch aerodrome, in Essex, where the team had moved after leaving Scotland, but during the spring of 1910 his arrow-shaped aircraft became a familiar sight in the area and was noted for the steadiness with which it flew. The tests culminated in a 1.25-km (2-mile) flight during which Dunne never touched the controls and a demonstration in front of Orville Wright. The D.5 had combined elevators and ailerons (elevons) at the tips of its wings. These were operated by two levers which could be locked into position on a ratchet to maintain a desired attitude, and the machine's stability vindicated Dunne's theories about the tailless configuration.