The forgotten delta – Boulton Paul P.111A, VT935
Tags: '..an Iron Curtain has descended across the Continent', 'Yellow Peril', 1940s, 1950s, 1951 SBAC Display, 1958, 1985, 45º delta-wing research aircraft, 5100 st, 60° delta wing, 648 mph in level flight, a ramjet for high-speed flight, advanced aerodynamics of German jet fighters, air brakes, air data probes, Air Ministry, Air Show, aircraft, airframe was retired, airspeed indicator, Alexander 'Ben' Gunn, all-over silver scheme, all-over yellow scheme, allohistory, altimeter, Aviation, aviation fuels, Bedfordshire, Bell P-59 Airacomet, belly landing, Boulton Paul, Boulton Paul Aircraft Ltd, Boulton Paul's Chief Test Pilot, braking parachute, broke up in mid-air, brought back to the U.K., calibrated series of control inputs, coal dust, completed Lippisch Li P.13a, Coventry, Cranfield College of Aeronautics, De Havilland Vampire, Defiant turret fighter, delta, delta wing, delta-winged, Dr Alexander Lippisch, ejected from the P.120, England, Europe, explosive mixture of coal dust and air, Farnborough, Fascism, fibreglass wing extensions, first flew on October 10th 1950, first generation of jet aircraft, first man to Mach 2.0, full-size glider, German, German jet fighters, German jet technology, Germany, Gloster Meteor, Gloster-Whittle E.28/39, Great Britain, handling at the lower end of the speed envelope, high-speed flight, Hussenot A.22 flight recorder, in-cockpit F-73 camera, induced oscillations, instructional use, issued Specification E. 27/46, Lippisch delta, Lippisch Li P.13a, liquid-powered rocket, Lockheed YP-80, long series of flights, Mach 0.93, Mach 2.6, many examples of German aircraft, Midland Air Museum, model of the P.13a, museum, Museums, P.111, P.111A, P.120, Pendeford facility, piloting an aircraft powered by pulverized coal, powered controls, produced a series of traces on paper, propelled by a ram jet, prototype never flew, pulverized coal, radical mixed-power interceptor, RAF, RAF Boscombe Down, rate of roll and yaw, record readings on the airspeed indicator and altimeter, Rolls-Royce, Rolls-Royce Nene RN.3 turbojet, Royal Air Force, Royal Aircraft Establishment, scientists and engineers, short of conventional aviation fuels, split along ideological lines, straight tapered wings, substantially re-built, tall triangular fin, test pilots, test programme, tested in a wind-tunnel, the Allies, the DM-1, the forces of Fascism, the Vampire first flew on September 20th 1943, the world of aviation, three aspect ratios, very clean design, VT935, VT951, Warsaw Pact, Western Allies, Wiltshire, Winston Churchill said, WW2
The late 1940s and early 1950s were a time of great experimentation in the world of aviation. The Allies had prevailed over the forces of Fascism, but had soon split along ideological lines. As Winston Churchill said, ‘..an Iron Curtain has descended across the Continent’. Either side of it the Western Allies and the Warsaw Pact strove to perfect their first generation of jet aircraft. They had both captured large quantities of German jet technology – and the scientists and engineers to go with it. Undoubtedly, one of the great surprises was the advanced aerodynamics of the German jet fighters. All five of the Allied fighters and research jets which had so far flown (Gloster-Whittle E.28/39 ‘Pioneer’, Gloster Meteor Mk.1, Bell P-59 Airacomet, Lockheed YP-80 Shooting Star, and the De Havilland Vampire – yes, the Vampire first flew on September 20th, 1943) had conventional straight, tapered wings.
One of the most advanced German thinkers, in aeronautical terms, was Dr Alexander Lippisch. Towards the end of the war he proposed a radical mixed-power interceptor – a liquid-powered rocket to get the aircraft up to speed, then a ramjet for high-speed flight. The aircraft was the Lippisch Li P.13a, an incredible design with a tall, triangular fin and a 60° delta wing. Although the prototype never flew, a full-size glider, the DM-1 was built to test out handling at the lower end of the speed envelope. A model of the P.13a was tested in a wind-tunnel to Mach 2.6, with satisfactory results.
After the war, the Air Ministry issued Specification E. 27/46 for a 45º delta-wing research aircraft. It was taken up by Boulton Paul Aircraft Ltd (who had built the Defiant turret fighter during WW2), and they produced a very clean design in their Pendeford facility with a thin wing, powered by a Rolls-Royce Nene RN.3 turbojet of 5,100 st. Ultimately, this aircraft achieved 648 mph in level flight, and Mach 0.93 in a dive. The only example of the type, VT935, first flew on October 10th, 1950 and test pilots from the Royal Aircraft Establishment at RAF Boscombe Down, Wiltshire began a long series of flights to explore induced oscillations following a calibrated series of control inputs. A Hussenot A.22 flight recorder, which produced a series of traces on paper (!) was used to measure the rate of roll, and yaw, and the control inputs. An in-cockpit F-73 camera was used to record readings on the airspeed indicator and altimeter during the test phase of each flight, which lasted approximately 20 minutes.
The P.111 was flown at the 1951 SBAC Display at Farnborough, finished in an all-over silver scheme with a blue flash. The addition of Boulton Paul’s Chief Test Pilot, Alexander ‘Ben’ Gunn, to the test programme meant that data began to accumulate rapidly. There were fibreglass wing extensions made (two sets) which meant that VT935 could be flown with three aspect ratios – 2.3, 3.0 and 3.8, and the data compared. Unfortunately, a belly landing meant that the aircraft had to be substantially re-built, complete with air brakes, new air data probes, different powered controls and a braking parachute; following this it became the P.111A, and due to a new all-over yellow scheme, was known as the ‘Yellow Peril’.
In 1958, the airframe was retired to the Cranfield College of Aeronautics, Bedfordshire for instructional use, and then in 1985 – very appropriately – it was transferred to the Midland Air Museum at Coventry, where it is shown in the above photograph, after a long, and very valuable, testing life. ‘Ben’ Gunn, who I was fortunate enough to meet, was saved on August 29th, 1952, when he ejected from the successor aircraft to the P.111A, the P.120, VT951, when it broke up in mid-air. This was the last aircraft that the company ever built.
‘Ben’ Gunn can count himself fortunate to have escaped, but imagine if he had been asked to fly a completed Lippisch Li P.13a, had it been finished and brought back to the U.K., as many examples of German aircraft were (I do so enjoy allohistory!) Not only would he have been the first man to Mach 2.0, but he would have done it piloting an aircraft powered by pulverized coal. Yes, the Germans were so short of conventional aviation fuels, that the little Lippisch delta was to be propelled by a ram jet which used an explosive mixture of coal dust and air!