The Boulton Paul P.108 Balliol was designed as a turboprop powered trainer but saw limited service as a standard piston engine powered trainer with the RAF and Fleet Air Arm.
The P.108 was designed in response to Air Ministry specification T.7/45, for a three seat turbo-prop powered advanced trainer to replace the Miles Master and North American Harvard. The new aircraft was to use either the Rolls-Royce Dart or the Armstrong Mamba, both turbo-prop engines, as the Air Ministry wanted their pupils to get some experience with turbine engines before moving onto jet engines. As an alternative the new aircraft should also be able to use an improved version of the Bristol Perseus piston engine.
The aircraft was to carry a crew of three - pilot and main student in side-by-side seating at the front and a second student in a single rear seat. The aircraft also had to be usable as a naval trainer, so needed folding wings, arrester gear and a stronger than usual undercarriage. It was also to be used for armament training, and so needed to be able to take guns and bombs.
The specification was issued on 16 March 1945. Boulton Paul responded with a fairly conventional aircraft, with low mounted straight tapered wings and a high glazed cockpit canopy that covered all three seats. The aircraft was of all metal construction. In the original design the exhaust from the Rolls-Royce Dart was placed below the rear fuselage, the top of the rear fuselage was level with the top of the canopy and the third crew member sat sideways across the cabin.
The turbo-prop powered version was given the designation P.108, and the Perseus powered alternative the P.109. The P.108 was submitted in mid April, and the P.109 two weeks later. The Perseus requirement was dropped in August 1945, when the specification was reissued, and work on the P.109 ended.
In August 1945 Boulton Paul were given a contract for four P.108 prototypes, to be powered by the Dart engine. At first the fourth prototype was to for the naval version, but this idea was soon abandoned, and two of any pre-production batch were allocated to this role instead.
The only other design to be given a prototype order was the Avro Athena T.1.
Work on the aircraft progressed at speed, but the Dart was delayed. In August 1946, when Boulton Paul were given a contract for twenty pre-production Balliols, the Dart was still behind schedule, and so the company decided to fit the prototypes and ten of the pre-production aircraft with the Armstrong Siddeley Mamba I turbo-prop engine instead. This was a straight-through gas flow engine, based on the larger Armstrong Siddeley Python, and expected to produce 1,320hp.
The Mamba was also behind schedule. A series of piston engines were considered as a temporary alternative, and as a result when the first prototype made its maiden flight on 26 May 1947 it was powered by an 820hp Bristol Mercury radial engine. After tests at Boulton Paul this aircraft went to Boscombe Down for handling trials late in 1947. The aircraft performed well in most situations, but was difficult if operated at sustained high 'g', or in a slow roll.
In the post-war period the future needs of the RAF weren't at all clear, with technology advancing at a rapid pace, and defence budgets shrinking at a similar speed. In June 1947, only six weeks after the maiden flight of the Balliol, the Air Ministry decided that it no longer needed a three man turbo-prop powered trainer, and issued a new Specification T.14/47, this time calling for a two man piston engined trainer. Boulton Paul was given a contract to produce four new prototypes, using the existing P.108 airframe but powered by the Rolls-Royce Merlin engine, taking advantage of the plentiful supply of surplus Merlin engines, while the existing four prototypes would be completed with the Mamba turbo-prop.
The second prototype (VL917) was completed with the Mamba engine, and became the first single engined turbo-prop powered aircraft to fly when it made its maiden flight on 24 March 1948. The turbo-prop engine was carried in front of the cockpit, with the jet exhaust on the lower starboard fuselage. This took the exhaust away from the tail, and operated against the torque from the propeller. The exhaust provided around 20% of the aircraft's power.
The third prototype followed on 27 May 1948. This was fortunate, as the second prototype was damaged in a crash during test flights. The first prototype was also given the Mamba engine, and this version of the aircraft became the Balliol T.1, but the fourth Mamba prototype was cancelled.
The first Merlin powered Balliol made its maiden flight on 10 July 1948. The remaining three Merlin powered prototypes were also completed, before Boulton Paul was given a contract to produce 17 pre-production aircraft, replacing the original order for 20 turbo-prop powered pre-production aircraft (the original 24 turbo-jet powered aircraft had thus been replaced by 3 turbo-jet prototypes, 4 Merlin prototypes and 17 pre-production aircraft, still a total of 24 aircraft).
The project survived the loss of the first prototype on 3 February 1949, during a flight to check the controls at high speeds. Lindsay Neale and Peter Tishaw, the pilot and co-pilot, were both killed in the crash. The problem that was being investigated at the time of the crash was fixed by modifying the tailplane.
Despite the crash the Balliol won its competitive trials against the Avro Athena, and early in 1950 an order was placed for large scale production of the Merlin powered T.2. The first order, in February 1950, was for 100 aircraft. Another 138 aircraft were ordered from Boulton Paul in January 1951, alongside an order from 120 Blackburn.
The production aircraft were powered by the 1,245hp Merlin 35 engine, and had a new chin air intake. The first of the production aircraft made its maiden flight in April 1952. They also lacked the third seat, which was replaced with radio equipment.
The idea was for the Balliol to replace the wartime Harvard trainer, but in 1951 the Air Ministry changed its plans for a second time. This time the idea was to go straight for jet powered trainers, and so the orders for the Balliol were scaled back. It was still produced in some numbers, with as many as 175 being completed (132 T.2s were completed at Boulton Paul and 30 at Blackburn).
Twelve of these aircraft went to newly independent Ceylon's Air Force, the first export order received by Boulton Paul for several decades. Five were existing RAF aircraft and seven came from the cancelled part of the order.
In RAF hands the pre-production aircraft were used by the Central Flying School, while the production aircraft went to No.7 Flying Training School at Cottesmore, where they arrived in the first half of 1952. The standard training route was to begin with 60 hours in the Percival Prentice, followed by 120 hours in the Balliol. No.7 FTS only operated the Balliol until the middle of 1954. They were then passed on to the RAF Collage, Cranwell, where they remained in use until the end of 1955. They were replaced by the Vampire T.Mk 11 in 1956.
Elsewhere more than twenty Balliols were used by No.288 (Control and Reporting) Squadron at Middle Wallop, most of which then went onto 3/4 Civil Anti-Aircraft Co-operation Unit at Exeter, and then onto the School of Flying Control at RAF Sopley.
No.238 OCU (first at Colerne and then at North Luffenham) used thirty Balliols as target tugs. No.228 used eleven aircraft.
The Royal Navy also ordered a version of the Balliol, as the Sea Balliol T.Mk 21. This has a smaller propeller, stronger landing gear and an arrestor hook. One of the pre-production Merlin powered T.2s was used as the prototype for the naval version, and made its maiden flight in this format in October 1952, although deck landing trials had been conducted two years earlier using normal pre-production aircraft. A total of 30 were produced, with deliveries completed by December 1954. These were used by the Ship's Flight on HMS Triumph, No.702, the Junior Officers Training Course at Ford (later becoming No.781 Squadron at Ford), No.796 Squadron Observer and Air Signals School at Culdrose, No.727 Squadron Dartmouth Cadet Air Training Squadron and No.1843 Squadron, RNVR, at Abbotsinch, Glasgow. The last P.108 Sea Balliol T.21 to be built was the final Boulton Paul aircraft to be completed, coming after the experimental P.120 jet aircraft.
Engine: Rolls-Royce Merlin 35 inline engine
Span: 39ft 4in
Length: 35ft 1.5in
Height: 12ft 6in
Empty weight: 6,730lb
Loaded weight: 8,470lb
Max speed: 288mph at 9,000ft (307mph on turbo-prop powered T.1)
Climb Rate: 1,790ft/ min
Service ceiling: 32,500ft
Range: 660 miles
Endurance: 3 hours
Armament: One 0.303in Browning machine gun in port wings
Bomb load: Four 60lb rockets or eight 8.5 to 25lb practise bombs