The Austrian designer Raoul Hafner produced a nimble Autogyro, the Hafner ARIII, which flew in 1935 and had some notable innovations, including the use of cyclic pitch applied via a compact rotor head.
Blade pitch change took place at the centre of the rotor head controlled by a ‘spider’ mechanism and applied to a torsion bar attachment for each rotor blade. These features were quite novel and continue in use today on Westland’s Lynx helicopter.
In 1944, and after the Allied invasion of Europe, the success of the Horsa and Hamilcar gliders during Operation Overlord resulted in increased priority in helicopter development. Bristol acquired Hafner’s company and design rights, with Hafner becoming Chief Designer of the Helicopter Division. The success of the Horsa and Hamilcar gliders during Operation Overlord resulted in increased priority in helicopter development.
The first design was an all-new four seat helicopter, named the Sycamore, in view of the type’s side elevation which resembled a Sycamore seed which, in addition to falling with a rotating motion, bears a striking resemblance with the bulbous forward cabin, seeping up to a slim tailboom and high-mounted tail rotor.
The first prototype (VL958) flew for the first time on 27th July 1947, powered (as was the second aircraft) by a Pratt & Whitney 450hp Wasp Junior engine.
The Sycamore was the first British-designed helicopter to enter production and be granted a civilian Certificate of Airworthiness. It was also the first to serve with the Royal Air Force.
A Mk.2 prototype was flown in September 1949 with a 550 hp Alvis Leonides engine and this became the standard fit for subsequent aircraft.
The 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 Sycamore Mk 4, of which 154 were built, seeing long service with the RAF, 85 being operated as the Sycamore HR.14, with smaller numbers of other marks.
The Mk.4 re-positioned the pilot on 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 Sycamore Mk.3.
In military service the Sycamore was designated HC whilst in civillian use it was referred to simply as the Bristol Type 171.
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 Aurtsalian 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|
(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/?lang=en|