Boulton Paul Sidestrand

The Boulton Paul Sidestrand was a British twin‑engine biplane bomber developed in the early 1920s by Boulton Paul Aircraft. Designed to replace the aging Airco DH.10, the Sidestrand first flew on 30 May 1926 and entered service with the Royal Air Force in 1928, remaining operational until 1935. Its most striking feature was the side‑mounted engine nacelles suspended between the upper and lower wings, a layout that gave the type its name and provided excellent forward visibility for the crew. Powered by two 450‑hp (336 kW) Bristol Jupiter radial engines, the aircraft could carry up to 1,200 lb (545 kg) of bombs and achieved a top speed of about 130 mph (210 km h⁻¹). The Sidestrand incorporated a fully enclosed cockpit, defensive machine‑gun positions in the nose and dorsal turret, and a robust steel‑tube fuselage with fabric covering, reflecting the transitional shift from wood to metal construction. Though quickly outclassed by later monoplane bombers, the Sidestrand served as a valuable testbed for aerodynamic refinements and crew ergonomics, influencing subsequent designs such as the Boulton Paul Overstrand and contributing to the RAF’s inter‑war modernization program. Its legacy endures as an early example of integrated twin‑engine bomber design in the interwar period.