The Bristol Aeroplane Company had more than a passing interest in rotary aircraft and during the period post World War II, it invested heavily in the development of some iconic British helicopter designs, one of the most famous of which was the Bristol Type 171 Sycamore.
The Austrian designer Raoul Hafner, produced a nimble Autogyro (the Hafner ARIII), which flew in 1935, which had some notable innovations, including the use of 'cyclic pitch' applied via a compact rotor head.
The pitch change of the blades took place at the centre of the rotor head, controlled by a ‘spider’ mechanism and applied to a torsion bar attachment for each blade. These features were quite revolutionary and still continue in use today on Westland’s Lynx helicopter.
In 1944, and after the Allied invasion of Europe, the success of the Airspeed Horsa and General Aircraft Ltd (GAL) Hamilcar gliders during Operation Overlord resulted in increased priority in helicopter development.
Bristol Aeroplane Company acquired Hafner’s company and its design rights, with Hafner himself becoming Chief Designer of their Helicopter Division. Their first design was an all-new four seat helicopter, named the Bristol Type 171 Sycamore, the name inspired by the view of the side elevation which resembled a Sycamore seed. It was said that in addition to falling with a rotating motion, it also bears a striking resemblance with the bulbous forward cabin, seeping up to a slim tailboom and high-mounted tail rotor.
The first prototype Bristol Type 171 Sycamore (VL958) flew for the first time on 27th July 1947, powered by a Pratt & Whitney 450hp Wasp Junior engine, as was the second aircraft.
The Bristol Type 171 Sycamore was the first British-designed helicopter to enter production and to be granted a civilian Certificate of Airworthiness. It was also the first helicopter to serve with the Royal Air Force.
The Bristol Type 171 Sycamore Mk.2 prototype was flown in September 1949, this time with a 550 hp Alvis Leonides engine, this becoming the standard fit for subsequent aircraft. Later, the Bristol Type 171 Sycamore Mk.3 had a shorter nose and a wider fuselage, which increased capacity to five occupants; 23 were built.
The main production model was the Bristol Type 171 Sycamore Mk 4, of which 154 were built. The aircraft saw long service with the RAF who operated 85 of the type as the Sycamore HR.14, with smaller numbers of other marks.
The Bristol Type 171 Sycamore Mk.4 re-positioned the pilot to the right (which is now the standard pilot-in-command position in helicopters) and adopted as standard, the four door configuration of the earlier HC.10 version of the Bristol Type 171 Sycamore Mk.3.
In military service, the Bristol Type 171 Sycamore was designated HC, whilst in civilian use it was simply referred to simply as the Bristol Sycamore.
The main duties of the RAF Sycamores were as Air Ambulances (HC.10), Army communications (HC.11) and as Search and Rescue (HR.12 to HR.14).
Foreign users included Belgium (3), Royal Australian Navy (10) and German Federal Government (50).
In addition, the Australian Defence Force operated 7 aircraft and in total (including prototypes and civil demonstrators) 180 were built.
|Powerplant||One 550 hp Alvis Leonides|
|Rotor diameter||48 ft 7 in|
|Maximum Weight||5,600 lb|
|Capacity||Two crew and three passengers|
|Maximum Speed||132 mph|
|Endurance / Range||330 miles|
|180||All variants - see table below|
|Bristol 171 Mk.1||2 prototypes|
|Bristol 171 Mk.2||1 prototype|
|Bristol 171 Mk.3 & 3A||15 civil and military models|
|Bristol 171 Mk.4||Main production model for UK and export military service|
|Sycamore HC.10||1 built air ambulance variant based on Mk 3|
|Sycamore HC.11||4 built for Army communications based on Mk 3|
|Sycamore HR.12||4 for RAF SAR trials|
|Sycamore HR.13||2 for RAF SAR trials|
|Sycamore HR.14||85 RAF SAR operations|
|Sycamore Mk.14||3 Belgian Air Force|
|Sycamore HR.50||3 for RAN SAR / plane guard|
|Sycamore HR.51||10 for RAN SAR / plane guard|
|Sycamore HR.52||50 for West German Army / Navy|
HR.52 (Flying) (OE-XSY / XG345)
|‘Flying Bulls’ organisation in Salzburg, Austria|
|RAF Museum Cosford|
|Museum of Army Flying at Middle Wallop|
|Newark Air Museum|
|RAN Museum at Nowra, NSW|
|Helicopter Museum Weston-super-Mare|
|Australian National Aviation Museum, Moorabbin, VIC|
|Norfolk & Suffolk Air Museum, Flixton|
|Roy Museum of Armed Forces and Military History, Brussels www.klm-mra.be/D7t/|
|Boscombe Down Aviation Collection, Old Sarum www.boscombedownaviationcollection.co.uk|
|Hubschrauber Museum, Buckeburg www.hubschraubermuseum.de|