https://en.wikipedia.org/wiki/Cierva_Air_Horse
The Cierva W.11 Air Horse was a helicopter developed by the Cierva Autogiro
Company in the United Kingdom during the mid-1940s. The largest helicopter in
the world at the time of its debut, the Air Horse was unusual for using three
rotors mounted on outriggers, and driven by a single engine mounted inside the
fuselage.
The W.11 "Air Horse" heavy lift helicopter was developed by the G & J Weir,
Ltd., Aircraft Department, reconstituted in 1943 as the Cierva Autogiro Company.
The "W" in the designation is a continuation of the autogiro and helicopter
The W.11 was a development of the Weir W.6 dual transverse rotor helicopter. It
is the only helicopter of its type ever built and included three lifting rotors
all turning in the same direction. The adoption of three rotors was due to
concerns over the capability of a single large rotor to generate the required
lift.
Torque balance was provided by slightly inclining each rotor axis to generate
horizontal thrust components to provide anti-torque moments. The three rotor
configuration was foreseen by Belgian helicopter experimenter Nicolas Florine in
his patent of 1926 which presented the aforementioned means for balancing the
reaction on the fuselage of two or more torque driven lifting rotors turning in
the same direction.
A Rolls-Royce Merlin piston engine in the fuselage drove three 47-foot-diameter
(14 m) three-blade rotors mounted on outriggers which projected from the
fuselage. The blades, following the Focke-Achgelis designs, were constructed
from resin-impregnated wood, which provided enormous strength, and were
manufactured by the Glasgow furniture firm H. Morris & Co., Ltd. The W.11 rotor
control system was hydraulically powered. It was the second helicopter ever to
fly using such a system, the first being the Cierva W.9. The landing gear had a
stroke of 5 ft (1.5 m) to cater for high descent rates in the event of engine
failure during low-altitude operations.
Role
Single-engine three-rotor helicopter
Manufacturer
Cierva Autogiro Company
Designer
Cyril Pullin
First flight
7 December 1948
Retired
1950
Primary user
Ministry of Supply
Number built
2
Developed from
Weir W.6
A proposed enlarged development using two Merlins or two Rolls-Royce Dart
turboprops was designated as the W.11T. This was abandoned after the accident
with the first W.11. The death of three long-time colleagues in the accident
prompted financier James G. Weir to decline to provide additional funds since
the Cierva Autogiro Company required ever-increasing investment. As result all
its development contracts were transferred to Saunders Roe. Development of the
W.11 continued for a short time thereafter but was terminated by the British
Government, and the remaining airframe, which had flown for less than 20 hours
in total, was scrapped. Saunders-Roe continued development of the smaller Cierva
W.14 Skeeter, which was a main/tail rotor configuration helicopter.
W.11 G-ALCV made its first flight on 7 December 1948 and was displayed at the
Farnborough Air Show in 1949.
G-ALCV crashed on 13 June 1950, claiming the lives of Alan Marsh (chief test
pilot) John "Jeep" Cable, (Ministry of Supply test pilot), and Joseph K.
Unsworth (flight engineer). The cause of the crash was due to fatigue failure of
a swashplate carrier driving link in the front rotor hub.
The second W.11, G-ALCW, after additional development work, was scrapped about
one year later.
Specifications (W.11)
General characteristics
Crew: 3
Capacity: 800 cubic feet (23 m3) cabin
Length: 88 ft 7 in (27.00 m)
Width: 95 ft 0 in (28.96 m)
Height: 17 ft 9 in (5.41 m)
Empty weight: 12,140 lb (5,507 kg)
Max takeoff weight: 17,500 lb (7,938 kg)
Main rotor area: 5,205 sq ft (483.6 m2)
Performance
Maximum speed: 140 mph (225 km/h; 122 kn)
Cruise speed: 95 mph (153 km/h; 83 kn)
Range: 330 mi (287 nmi; 531 km)
Service ceiling: 28,000 ft (8,500 m)
*
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