Boulton Paul P.108 Balliol

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Contents

Type Description

• P.108 Balliol T.1
• Two seat advanced trainer to Specification T.7/45 to meet the requirements of OR.159. A stipulation was the fitting of a three-seat cockpit; the pilot and instructor were sat in a side-by-side arrangement, while a second student could be accommodated in a third seat to the rear, positioned as to enable them to closely observe the pilot and the instructions being issued. The resulting aircraft was a conventional low-wing monoplane, featuring a conventional landing gear, of which the two main gear were retractable but the tailwheel was not. It was designed to be both durable and as easy to maintain as possible, featuring around 40 inspection hatches, typically secured by quick-release fasteners, across the fuselage to facilitate this. For greater simplicity of maintenance, wherever feasible, components were designed to be interchangeable, such as the fin, tailplane, wing tanks, main gear oleos, and other elements. Structurally, the Balliol comprised seven main sections, three of which form the fuselage, two for the wing sections, and the remaining two for the tail unit. The majority of exterior covering was light alloy stressed-skin, supported by a combination of subframes and longerons, while the rear section incorporated a monocoque approach. Fuel was accommodated within a mixture of wing tanks and a single fuselage tank, the former being easy to remove while the wing was folded. For additional safety, various measures to reduce potential accident-related damage were incorporated into the design, such as the strengthened crash-resistant structure around the cockpit, and the three rubber crash skids on the underside of the fuselage to minimise damage from a wheels-up landing. The wings of the Balliol featured two-spar construction within an uninterrupted rigid torsion box. Most of the wing's structure comprised pressed light alloys, while an auxiliary spar was used to support the trailing edge skinning and flaps and the forward section accommodated the steel box wells for the retractable main undercarriage. The outer wings were fitted with simple dive brakes, along with conventional inner and outer split flaps that ran as far as the ailerons. While the starboard wing featured a single G45 cine-camera, the port wing featured a single .303 in Browning machine gun. The wings were designed to be manually foldable, needing only two bolts to be removed, without affecting the control runs.
  Amongst the requirements specified was the use of the newly developed turboprop engine, as it was felt that the new generation of advanced trainers would better prepare pilots for flying jet-powered combat aircraft. The four prototypes were to be powered by a single Rolls-Royce Dart turboprop engine, but delays to development of the Dart meant that the prototypes would now be fitted by the 1,000 s.h.p. Armstrong Siddeley Mamba turboprop. The engine compartment featured distinctly different construction from the rest of the aircraft, being composed of light alloys supported by steel tubing; the engine itself being mounted on three struts attached to the firewall between the compartment and the cockpit. The jet pipe was angled downwards, running beneath the cockpit to an exhaust on the lower starboard side of the fuselage, somewhat counteracting the torque generated by the aircraft's three-bladed propeller as well as contributing roughly 20 percent of the aircraft's total static thrust. Access to the engine compartment was provided via numerous detachable hatches on the sides and lower portions. As the Mamba was not flight-ready at the time of the first prototype's completion, it was instead powered by a 820 hp Bristol Mercury 30 radial engine during its initial test flights
  Production of the T.1 to Specification 29/46P was superseded by production of the T.2.

• P.108 Balliol T.2
• Production variant to Specification T.14/47, requiring a two-seat trainer that was powered by a Rolls-Royce Merlin piston engine. This engine which was available in large numbers from surplus stocks leftover from the war, rather than expensive turboprops that would have to bought in new. One 1,245 h.p. Rolls-Royce Merlin 35 powerplant driving a 4-bladed de Havilland constant speed propeller.

• P.108 Balliol T.21
• Navalised variant of T.2 to Specification N.102D and P to meet the Naval Staff Requirement NA.11. Various design changes were made to the aircraft as to better adapt it for shipboard use on board the service's aircraft carriers. These included the fitting of folding wings and an arrestor hook, the former to minimise space while parked or stowed while the latter was necessary for landings at sea.

Projected Variants

• P.108 Balliol T.2A
• Balliol T.2 fitted with Pratt and Whitney Wasp R-1820-SIC3-G powerplant.

• P.109
• Two seat advanced trainer to Specification T.7/45 fitted with a Bristol Perseus powerplant.

• P.112
• Elementary trainer variant with new, high aspect ratio wings. Alvis Leonides VM powerplant.

• P.112A
• P.112 fitted with Pratt and Whitney Wasp R-1340 powerplant.

Production Details

Production References

1. Boulton Paul Aircraft Since 1915, Alec Brew (Putnam, 1993)
2. Air Britain RAF Aircraft Register Series, Various Volumes (Air-Britain Publications)
3. The Boulton Paul Balliol, Alec Brew (Fonthill 2015)
4. RAF Air Historical Branch: RAF Aircraft Movement Card (A.M. Form 78) (Dept of Archive and Aviation Records, RAF Museum, Hendon, Records MFC-77-15-10)
5. Ministry of Aircraft Production Aeroplane Price Books (Dept of Archive and Aviation Records, RAF Museum, Hendon, Records X005-2126)