Вертолет "Air Horse" имел два киля на законцовках стабилизатора и кабину для экипажа из трех человек. Общие расходы Министерства поставок на разработку этого проекта оценивались в 350000 фунтов стерлингов

VZ724 performing at Farnborough in 1949, the fin area having been increased by the addition of fore and aft extensions.

VZ724 airborne at Eastleigh Airport, displaying its original tail-fins and the long-stroke undercarriage. The outriggers have already been modified.

After its 1949 Farnborough appearance VZ724 began flight trials at maximum weight, flying at 17,500lb AUW on October 12.

The huge three rotored Cierva W.11 Air Horse was conceived towards the end of World War II and VZ 724 seen here, the first of two ordered, made its maiden flight on December 8th, 1948. Developed to meet a need for a heavy-lift helicopter capable of hauling a 5,000lb payload, the W.11 was powered by a single 1. 620hp Rolls-Royce Merlin 32 that drove a unique three rotor system. Tragically, VZ 724 was to suffer a catastrophic in-flight failure, commencing in the forward rotor hub, but leading to the disintegration of the starboard rear-rotor support structure. All three crew members, Sqn. Ldr. F.J. 'Jeep' Cable, co-pilot Alan Marsh and flight test observer H.J. Unsworth, losing their lives in the ensuing crash. The second W.11, WA 555, is believed to have been flight tested briefly, but only close to the ground and as part of the investigation into the loss of the first machine.

By this time fitted with fins of increased area, VZ724 clatters overhead during a flight in 1949, possibly at that year’s SBAC show, at which it performed a memorable flying display. The fins never incorporated rudders, yaw control being effected by means of fore-and-aft cyclic-pitch variation applied differentially to the rear rotors.

Rotary-wing Cerberus - the Air Horse remains the only helicopter to fly with three rotor-heads. The prototype, VZ724, is seen here during one of the public displays it made after its first free flight on December 8, 1948. Note the open door to aid cooling of the single horizontally-mounted Merlin engine

The Merlin-powered Cierva Air Horse VZ724 demonstrated at the 1949 Farnborough. The forward door had to be kept open to assist engine cooling.

Harold Bolas was greatly involved with development of the Cierva W.11 Air Horse. The prototype was VZ724 (later G-ALCV), here at Eastleigh in 1948.

Both machines at Eastleigh early in 1950, when WA555 was at the ground running stage.

Демонстрация вертолета W-11 "Эр Хорс" на выставке в Фарнборо

The first Air Horse, VZ724, made its public debut at the 1948 SBAC show at Farnborough that September, a month before it began its ground running and tethered hovering trials, and three months before its first free flight. Fitted with its original small fins, it wears its civil registration, G-ALCV, allocated during August-October 1948.

Little and large - another photograph of the prototype Air Horse at the 1948 SBAC show, alongside G-AJCJ, the prototype of its diminutive stablemate, the Cierva W.14 Skeeter, which made the type’s maiden flight at Eastleigh the following month. The Skeeter went on to be developed and built in numbers by Saunders-Roe.

A rear view, showing the spacious interior. The original configuration of the outrigger booms is also shown.

The second Air Horse, WA555, at Eastleigh in July/August 1950 after reassembly following accident investigations. A prototype Skeeter is on the left.

With the second of the two Cunliffe-Owen Concordias, G-AKBE, in the background, work progresses on the first W.11 Air Horse prototype, VZ724, at Eastleigh in the spring of 1949. The extreme nose of the Air Horse’s fuselage could be opened, as seen here, to give access to the rear of the instrument panel and pilot’s controls.

Before the Air Horse came the ‘‘Spraying Mantis”, a full-size mock-up of which is seen here at Eastleigh in the summer of 1946. The design, intended for agricultural work (note the large hopper for insecticide aft of the engine), incorporated forward-projecting booms with a rotor-head on each and a smaller rotor on the tailboom.

Technical illustrator J.H. Clark provided this fine drawing of the Air Horse’s rotor-head for the April 6, 1949, issue of The Aeroplane. We have added a blue circle to show the area of the failure which caused the crash.

Also attached to the RAE’s Structures Accident Note No 228 was Figure 1, a large fold-out detailing the Air Horse’s rotor-head and exactly where and how the critical spindle had failed. The report concluded that “failure of the front rotor swashplate-driving spindle had occurred through fatigue caused through alternating bending in the plane of rotation of the swashplate assembly”.

LEFT Accompanying the RAE’s Structures Accident Note were a number of photographs and illustrations of the relevant parts, including this photograph showing the fractured front rotor swashplate spindle (bottom), alongside the (slightly bent) starboard spindle (middle) and port spindle still attached to one arm of the scissor link.
RIGHT The fracture surface from head-on. Failure had occurred at the change of section from 0-8in (20mm)-diameter to 0-5in (12-7mm)-diameter, and had originated by the initiation of fatigue cracks at diametrically opposite sides, as denoted by arrows “A” and “B” (essentially perpendicular).

Various powerplants were considered for the Air Horse, redesignated W.11T, including a pair of Armstrong Siddeley Mambas (featuring the use of auxiliary propellers for use in forward flight) or two Rolls-Royce Dart turbines or Merlin piston engines, the latter as seen here.

Cierva W.11 Air Horse