At the Royal Air Establishment in Farnborough, England, Louis Brennan conducted experiments on the propeller-driven rotor concept from 1919 to 1926. The 1360kg empty weight machine used a single 18m rotor. Propellers at the rotor tips produced torqueless rotation and were powered by a 230hp Bentley BR-2 driving transmission shafts that ran down the length of the rotor blades. Compressed air was used to control the rotor pitch angle, effecting translation through cyclic control. Tethered flights were conducted during 1924 in a hanger with free flights the following May. Power was sufficient to lift four "passengers" when tethered, but stability and control were still very poor. Over 80 take-offs were made, but the maximum altitude was only 2.4m and maximum distance only about 183m. The machine crashed in 1926, ending the tests.
In Great Britain, serious efforts to build a full scale rotary wing machine began in 1916, although design work on the Brennan Helicopter was initiated by Louis Brennan in 1884. Following discussions with the Ministry of Munitions and the Royal Aircraft Establishment at Farnborough, where the helicopter was to be built and tested, construction progressed in secrecy and on 22 December 1921 indoor tethered lift tests were carried out with the assistant engineer, Robert Graham, as pilot. The engine was a 170kW Bentley B.R.2 rotary. Outdoor tethered flights took place on 16 May 1924. A year later the Brennan Helicopter was making short flights of 18-27m at heights up to 1.5m, but on 2 October 1925 disaster struck — during the seventh small flight, the machine lurched at a height of about 1m and the rotors struck the ground.
At this critical time in the helicopter's development Juan de la Cierva arrived in England with his promising "autogiro" and official interest in the Brennan Helicopter rapidly faded. Finally, in March 1926 funding ceased, and Louis Brennan, at the age of 74, moved on to other inventions.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984