The Boulton & Paul P.29 Sidestrand was a twin engined bomber that was the company's first military aircraft to enter production.
In 1918 the company had produced the P.7 Bourges, a promising twin engined figure bomber that had reached the prototype stage by the end of the First World War, but didn't enter production. This was followed by a single P.15 Bolton, the first all-metal aircraft to be delivered to the RAF. This has a similar design to the P.7, as did the P.25 Bugle, which used some light alloys. Next came the P.27 which was a design for a version of the Bugle powered by Napier Lion engines, but that didn’t reach the prototype stage.
The Sidestrand was developed in response to Specification 9/24, which called for a three or four man medium day bomber, powered by two Napier Lion engines. Boulton & Paul's chief designer John North submitted a more advanced version of the Bourges/ Bolton/ Bugle/ P.27 design, but ignored the official engine specification and instead chose the 425hp Jupiter VIa, which was mounted on the lower wings at the inner wing strut position. The engines were hinged at the back so they could be moved to one side for maintenance.
The Sidestrand was a three bay biplane. It was powered by two engines carried in nacelles that were mounted just above the lower wings, at the bottom of the innermost struts. It had a narrow fuselage with flat side, but a streamlined nose and upper and lower surfaces, eliminating the angular nose of the earlier designs.
The wings had a level central section and dihedral on the outer sections (starting at the engines). The wings and tail all had Boulton & Paul's distinctive square profiles. The wing span was 71ft 11in and the wings were noticeably staggered.
The Sidestrand had a metal fuselage structure, built using Boulton & Paul's locked joint tube system. The nose had a plywood covering, and the tip of the nose was on hinges and could swing aside to give access to the back of the pilot's instruments. The cockpit, bomb bay and ventral gun positions were given plywood and spruce covers, the rest of the structure was fabric covered. The fuel tanks were carried in the central section of the fuselage, with the bomb racks below. The Sidestrand could carry 1,050lb of bombs, two 220lb or 250 lbs and one 520lb or 550lb or four 112lb bombs, all carried in open, semi-recessed, open bomb bays below the fuselage and inner wing roots.
The Sidestrand could carry a crew of four - nose gunner/ bomb aimer, pilot, rear gunner and optional navigator/ co-pilot (in a cockpit just behind the pilot). The rear gunner had dorsal and ventral guns, but the plan was for only one to be carried on a particular sortie, depending on the individual aircraft's position with the formation.
The undercarriage had two main wheels with oleo-pneumatic legs and a similar wide track to the P.25 Bugle.
Two prototypes were ordered in 1925, and made their maiden flights in 1926. The first prototype made its maiden flight with a faulty elevator, and the test pilot, Squadron Leader C. A. Rea, who had spotted the problem, was only just able to avoid a crash. The elevator movement was corrected, and the aircraft then went to Martlesham Heath for official trials early in 1927. After these trials Frise-type balanced ailerons, Handley Page slots and a servo rudder were all added to make the aircraft easier to control.
The new aircraft was very manoeuvrable, and was capable of looping, rolling and spinning. It could also fly fairly safely on one engine. The Sidestrand was armed with three machine guns - one in an open nose position and two in a rear gunners position (one in a dorsal position and one in a ventral position).
The first prototype made its maiden flight in the late summer of 1926, followed by the slightly modified second aircraft later in the same year.
The prototypes were followed by a series of orders for eighteen production aircraft, enough to equip a single bomber squadron. First came an order for six aircraft, placed in July 1927. These were delivered as the Sidestrand II, powered by the Jupiter VI. These went to No.101 Squadron, which was reformed specifically to use the type. Deliveries began in 1928.
The next nine were the Sidestrand III, which used geared Jupiter VIIIF engines with Townend rings. This configuration was tested out on the second prototype, using Jupiter XFB engines. This prototype, the Mk IIIS, reached a top speed of 167mph. The first five Sidestrand IIIs were ordered in April 1928, the second four in November 1929. The Sidestrand III also got a modified bomb aimers position with a large nose window
The final three aircraft were delivered as replacement Sidestrand IIs, bringing the total production to twenty aircraft (including the prototypes).
Three Mk IIIs were converted to the Sidestrand Mk V standard, a significant modification that included the first enclosed power operated gun turret in an RAF aircraft and an enclosed cockpit. In March 1934 the Sidestrand Mk V was renamed as the Boulton Paul Overstand
A number of other more advanced versions of the Sidestrand were proposed, but without success. The P.57 was more streamlined, but had a biplane tail unit, and was developed for the Irish Free State. The P.60 was a modification of the P.57 with geared Jaguar engines, and was developed as a photographic aircraft for the Royal Canadian Air Force. The P.61 was a mail carrier version, using the Mk IIIS wings, the streamlined fuselage and Jupiter XFB engines. The P.62 was a torpedo bomber variant. The P.62A was a civil transport version of the P.62.
The Sidestrand was named after a village near Cromer.
No.101 Squadron was formed in 1928, as an experiment in the use of medium bombers. The prototype Sidestrand arrived by the start of 1929, and the first production Sidestrand II was delivered in March 1929. Seven aircraft were available by the end of 1929. During 1930 enough aircraft were available to carry out comparative operational trials, testing how effective two flights of four of five aircraft was compared to three 'vic's of three. The squadron was officially split into two flights, but tended to operate in the 'vics'. During 1930 the Sidestrand took all of the RAF bombing records, and it even outperformed the 'heavy' bombers of the period, combining their bomb load and range with impressive speed and manoeuvrability. As late as 1932 the Sidestrand was used in a dogfighting display at Hendon.
Sidestrand Mk III
Engine: Two Bristol Jupiter VIIIF radial engines
Power: 460hp each
Crew: 3 or 4
Span: 71ft 11in
Length: 46ft 0in
Height: 14ft 10in
Empty weight: 6,010lb
Maximum take-off weight: 10,200lb
Max speed: 1144mpg at 11,000ft, 140mph at 10,000ft
Service ceiling: 24,000ft
Range: 500 miles
Armament: Three 0.303in Lewis guns (nose, dorsal and ventral positions)
Bomb load: 1,050lb