The Parnall Possum was an experimental

Experimental aircraft

An experimental aircraft is an aircraft that has not yet been fully proven in flight. Often, this implies that new aerospace technologies are being tested on the aircraft, though the label is more broad....

 triplane

Triplane

A triplane is a fixed-wing aircraft equipped with three vertically-stacked wing planes. Tailplanes and canard foreplanes are not normally included in this count, although they may occasionally be.-Design principles:...

, with a single, central engine driving wing mounted propellers via shafts and gears. Two of these British aircraft were built in the mid-1920s.

Design and development

The Parnall Possum was one the few large aircraft to have had its engine in its fuselage but propellers on its wings. The concept arose immediately after World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

, when The British & Colonial Aeroplane Co., later Bristol began thinking about large transport aircraft powered by steam turbines mounted in an "engine room" in the fuselage and driving wing mounted propellers. They intended to develop the idea using their large Bristol Braemar

Bristol Braemar

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 triplane bomber, initially modified to be powered by four 230 hp (172 kW) Siddeley Pumas and called, in anticipation of steam power the Tramp

Bristol Tramp

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. They sought and obtained Air Ministry

Air Ministry

The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...

 support for this project, the Ministry appreciating the extra safety of an aircraft whose engines could be serviced in flight. Consequentially, the Ministry also issued specification 9/20 for a smaller aircraft of the same configuration and placed orders for two prototypes with Parnall, for the single-engined Possum, and with Boulton & Paul for their twin-engined Bodmin

Boulton Paul Bodmin

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. They were described as "Postal" aircraft but were clearly experimental bombers. All three types were built, but only the Possum and the Bodmin flew.

The Possum was a single bay triplane, with equal span, parallel chord wings without sweep or stagger. The lowest wing joined the lower fuselage longerons and the middle wing the upper longerons, with the upper wing held well above the fuselage on cabane struts. There were ailerons on all wings. The propeller shafts were mounted in the middle wing within small fairings and placed as close to the fuselage as the two-bladed, 9 ft 6 in (2.90 m) propellers would permit. One advantage of the triplane layout was that each propeller shaft could be symmetrically braced with a pair of X shaped struts to upper and lower wings. One set of Xs joined the forward spars and the other the rear. The wing structure was wood, fabric covered.

The fuselage structure was also wood; slab sided and plywood covered. From the side the nose was rectangular, but it was rounded in plan, rather like that of the Vickers Vimy

Vickers Vimy

The Vickers Vimy was a British heavy bomber aircraft of the First World War and post-First World War era. It achieved success as both a military and civil aircraft, setting several notable records in long-distance flights in the interwar period, the most celebrated of which was the first non-stop...

. Thee front gunner 's position was a little way back from the nose, with the pilot's cockpit just behind and well in front of the wings. A rear gunner's cockpit was placed at the trailing edge of the high set upper wing. Both gunners' cockpits were fitted with Scarff ring

Scarff ring

The Scarff ring was a type of machine gun mounting developed during the First World War by Warrant Officer F. W. Scarff of the Admiralty Air Department for use on two-seater aircraft...

s. The 450 hp Napier Lion

Napier Lion

The Napier Lion was a 12-cylinder broad arrow configuration aircraft engine built by Napier & Son starting in 1917, and ending in the 1930s. A number of advanced features made it the most powerful engine of its day, and kept it in production long after contemporary designs had stopped production...

 engine, a water-cooled unit with 12 cylinders in W or broad arrow arrangement was placed at the centre of gravity inside the fuselage, though with its cylinder heads exposed. There was a radiator on each side of the fuselage near the trailing edge; unusually, these were hinged so that they could be adjusted in flight more or less directly into the slipstream as the pilot chose. The Lion was mounted inline with the fuselage, with its output close to the leading edge of the middle wing, where a bevel gear transmitted the power via drive shafts to gears behind the propellers. The propellers counter-rotated at low speeds.

At the rear of the Possum the fabric covered wooden empennage was conventional. The fin had a straight and vertical leading edge, but a curved top that blended into a rounded rudder which extended downwards between separate elevators. The tailplane was mounted just above the fuselage. Underneath, and unusually for the time there was a tailwheel rather than a skid; remarkably, this wheel was both steerable and fitted with an automatic brake which provided increasing resistance with increasing load. The pilot could override the brake if he chose. The main undercarriage wa less innovative, with a pair of wheels single axle mounted on short oleo

Oleo

Oleo is a term for oils. It is commonly used to refer to a variety of things:* Margarine* Oleic acid* Oleo , A type of shock absorbers on airplane landing gear* Oleo , a bebop composition by Sonny Rollins...

 legs to the wings plus rearward bracing.

Preliminary pre-flight runs had resulted in an increase in rudder area before the Possum's maiden flight on19 June 1923. It was piloted by Norman Macmillan, accompanied by the Possum's designer, Harold Bolas. On 15 April 1924 the Possum went to Royal Aircraft Establishment

Royal Aircraft Establishment

The Royal Aircraft Establishment , was a British research establishment, known by several different names during its history, that eventually came under the aegis of the UK Ministry of Defence , before finally losing its identity in mergers with other institutions.The first site was at Farnborough...

 at Farnborough

Farnborough, Hampshire

-History:Name changes: Ferneberga ; Farnburghe, Farenberg ; Farnborowe, Fremborough, Fameborough .Tower Hill, Cove: There is substantial evidence...

 and appeared at the RAF Hendon Air Pageant in June that year. After some delay a second Possum was built, flying in April 1925 and transferred to the Aeroplane and Armament Experimental Establishment

Aeroplane and Armament Experimental Establishment

The Aeroplane and Armament Experimental Establishment was a research facility for British military aviation from 1918 to 1992.-History:...

 at RAF Martlesham Heath

RAF Martlesham Heath

RAF Martlesham Heath is a former Royal Air Force airfield in England. The field is located 1½ miles SW of Woodbridge, Suffolk.- RFC/RAF prewar use:Martlesham Heath was first used as a Royal Flying Corps airfield during World War I...

 in August 1925. They were both active at Martlesham some time thereafter.

Specifications