Hillson Bi - mono The Hillson Bi - mono was a British experimental aircraft of the 1940s . It was designed to test the idea of " slip - wings " , where the aircraft could take off as a biplane , jettison the upper , disposable wing , and continue flying as a monoplane . A single example was built , which successfully demonstrated jettisoning of the slip wing in flight . Design and development . In the 1930s , as take - off weights of aircraft continued to increase , designers grew increasingly concerned about the effects that these weights would have on take - off runs , and several designers investigated the concept of a " slip - wing " , which could be jettisoned after take - off . Amongst the proponents of the " slip - wing " was Noel Pemberton Billing , the founder of Supermarine , who wrote several articles in the aviation press promoting the idea , either with a manned , reusable auxiliary wing , or a disposable or " scrap - wing " . Blackburn Aircraft also investigated " slip - wings " . Following the outbreak of the Second World War , F Hills and Son , a light aircraft manufacturer based at Trafford Park , Manchester offered a design for a light fighter aircraft to the British Air Ministry . The fighter would be cheap to build and could be operated from small fields or open roads . To give the required take - off performance , the design was to be fitted with a disposable " slip - wing " . While the proposal was not accepted by the Air Ministry , Hills and Sons decided to continue with the project as a private venture , and so built a scale test - bed , to prove the slip - wing process . The test bed , known as the Bi - mono , was a small tractor monoplane with a fabric - covered steel - tube construction fuselage and a wooden wing . It had a fixed tailwheel undercarriage while an enclosed cockpit was provided for the pilot . The auxiliary wing was attached to the top of the cockpit canopy and to the lower wing by interplane struts . Two different upper wings were designed with different wingsapns , the shorter wing having the same span as the lower wing . The aircraft was powered by a single de Havilland Gipsy Six engine . The Bi - mono was not the only slip - wing project built by Hills and Sons , as they were also contracted by Pemberton Billing to build his PB . 37 design for a slip - wing dive - bomber , with a pusher monoplane lower component powered by a 290 hp ( 216 kW ) engine , while the manned slip - wing upper component was a tractor monoplane powered by a 40 hp ( 30 kW ) engine . Construction work started on the PB . 37 early in 1940 , but work was abandoned in July 1940 when construction was almost finished but the aircraft was unflown . Operational history . The Bi - mono , which carried no serial number or civil registration , made its maiden flight from Barton Aerodrome during 1941 . Test flights were made both as a monoplane and as a biplane , with the shorter upper wing being chosen . In order to avoid the potential hazards to people on the ground of dropping the wing , wing jettisoning tests were carried out from Squires Gate Airport , Blackpool , with the upper wing being successfully dropped over the Irish Sea on 16 July 1941 . The test proved successful , with no great change in trim and a few hundred feet in altitude being lost when the upper wing was jettisoned . The Bi - mono was subject to further testing by the Aeroplane and Armament Experimental Establishment at Boscombe Down from October 1941 . The A & AEE found that the maximum speed of the biplane configuration was slower than the stalling speed of the monoplane configuration resulting in a stall . Its landing character was likened to a kangaroo . Hills and Sons went on to further develop the slip - wing concept , flying the Hillson FH . 40 , a Hawker Hurricane fitted with a slip - wing .