W.11 Air Horse

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Contents

Type Description

• W.11 "Spraying Mantis"
• In July, 1945, the preliminary brochure was issued for the W.Il heavy-lift helicopter, with three two-bladed wooden rotors, intended for a variety of duties, ranging from heavy crane lift, passenger transport, and air ambulance to agricultural use including crop-spraying. By September, 1945, the W.II had been revised in design, now specifically intended as a crop-spraying helicopter to meet the requirements of Pest Control Ltd. of Cambridge. It had an elementary "skeleton" fuselage, with enclosed cabin for two pilots and a large externally mounted tank for liquid or solid insecticide. The original Pest Control Ltd. requirements were adapted as a basis for the Civil Aviation Operational requirement CAOR 3/46 and this was issued on 28 June, 1946. Cierva's had, in the meantime, gone ahead with the construction of a mock up of the W.II at Eastleigh. Known as the "Spraying Mantis", the W.II mock-up was an unusual looking machine,with two three-bladed rotors at the front and one at the back. The rotors were mounted at the end of skeletal frame outriggers, to which were attached spray bars and associated nozzles. A special long-stroke undercarriage designed by Automotive Products Ltd. The payload of three tons of insecticide was contained in a tank aft of the centrally mounted engine bay and could be jettisoned in five seconds in .an emergency. Specification E. 19/46 was drafted around the requirements of CAOR 3/46. This configuration, however, was destined not to proceed beyond mock-up.

• W.11 Air Horse
• RAE Farnborough wind-tunnel tests on the three rotor configuration were successful in major respects although it was suggested that fore-and-aft pitching control would be more effective if the single rotor was moved forward instead of aft, and this was adopted on the definitive W.II of September, 1946. At the same time, the decision was taken to make the fuselage fully enclosed to enable It to be used as a cargo carrier or passenger transport.
  The new fuselage, of rectangular cross-section with rounded corners and bluntly faired ends, was a semi-monocoque structure with closely spaced stringers and frames. The two-seat, side-by-side dual control cockpit was in the upper part of the cigar-shaped nose, enclosed by a Perspex cupola affording a very wide field of view. On the after side of the cockpit bulkhead were a pair of folding seats for extra crew members. The crew entry door was on the port side, opening rearward into the engine compartment containing the Rolls-Royce Merlin and its accessories, together with the distributor gearbox, the cooling fan and a Marston Excelsior light-alloy radiator unit. Conventional fuel and oil systems were fitted. The cooling system was of the “shunt” type, with cooling air for the radiator and oil coolers provided from a variable-pitch fan, drawing air via a circular, mesh-guarded inlet in the roof at the root of the forward rotor outrigger. Venting to atmosphere was through a mesh grille in the underbelly of the fuselage. A specially developed cross-over exhaust manifold was provided, surrounded by a jacket through which cooling air was drawn by the ejector action of the exhaust gasses. The Merlin engine drove a distributor gearbox via its own standard reduction gear and a clutch unit, splitting the power into the three main aluminium alloy transmission shafts to the rotors.
  The freight/passenger compartment was located aft of the engine compartment, separated from It by a fireproof bulkhead. Aft of the main cabin, the tail section featured hinged clamshell doors, opening on the centre-line to permit unobstructed entry for loading. The tail section also carried the fixed tailplane, with twin fins.
  The three rotors were carried on outrigger systems. The front rotor was supported on a front boom containing the drive shaft, with stabilizing struts forward if the cockpit. The rear rotors were supported on triangulate supporting structures, “king posted” round the Lockheed main undercarriage legs. The main outrigger boom containing the drive shaft swept backwards from the engine bay to the aft rotors, while the remaining bracing was in the plane of the main undercarrige members, just aft of the fuselage centre. The outrigger booms and struts were of semi-monocoque construction. The rotor blades were of all-wood construction, manufactured by H. Morris of Glasgow, with a main spar of high-density, resin-bonded, laminated wood which formed the leading edge The hollow trailing edge portion was covered by pressure-moulded skin supported by longitudinal auxiliary spars. Initially intended to be powered by one Merlin 32, eventually the 1,610 h.p. Rolls-Royce Merlin 24 was chosen due to better availability.

W.11 Air Horse Specification
Width *	Length *	Height *	Rotor Dia	Empty Wt	Max AUW	Cruise Speed **	Maximum Speed **	Range **	Service Ceiling **
95 ft	88 ft 7 in	17 ft 9 in	47 ft	11870 lb	17500 lb	125 mph/ 109 kn	140 mph/ 122 kn	320 mi	15000 ft
28.96 m	27 m	5.41 m	14.33 m	5384 kg	7938 kg	201 kph	225 kph	515 km	4572 m

* Overall, across rotors
** Estimated

Projected Variants

• W.11T Air Horse
• (T most probably stood for twin). Of similar size to the W.11, with two Rolls-Royce Merlin 502 powerplants on stub outriggers either side of the forward fuselage. The main undercarriage members, rotor drive outriggers and bracing were moved aft in line with the aft rotor hubs, with forward-raked bracing to the fuselage sides. Large fairings around the main undercarriage legs acted as fins.

• W.12
• Larger than the Merlin powered W.11T, with two Rolls-Royce Dart powerplants on stub outriggers either side of the forward fuselage. The rear fuselage was extended aft, though the aft rotors remainded in the same location, the drive outriggers now sloping forward from the rear of the fuselage. Large fairings around the main undercarriage legs acted as fins.

Production Details

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Notes

1. The prototype was loaned to Cierva for static exhibition at the SBAC Show, Farnborough from 7-12 September 1948, delivered 31 August 1948 under Contract 6/Acft/28611CB.9(a). For this it featured the civil registration G-ALCV, but when it first flew it was marked as VZ724.

Production References

1. British Research and Development Aircraft, Ray Sturtivant (Haynes, 1990)
2. Air-Britain Digest December 1970
3. BARG Roundel Oct 1989
4. BARG Roundel Jan 1981
5. Flight 7 Apr 1949
6. The Aeroplane 17 Dec 1948
7. Project Tech Profile 06 - The Air Staff and the Helicopter, Chris Gibson (Blue Envoy Press, 2017)