Piston

Cierva W.14 / Saunders-Roe Skeeter / AOP.10 / AOP.12

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Skeeter AOP.12

The prototype Skeeter helicopter was designed by the Cievra Autogyro Company as the W14 Skeeter 1 with a 106hp Jameson FF-1 engine and first flew on 8 October 1948 (G-AJCJ), but early development aircraft were under-powered and suffered from resonance problems. The Skeeter had a small, steel tube fuselage structure with a semi-monocoque tail boom section. The three-blade main rotor had metal spars with wooden ribs and a fabric skin, and the two-blade tail rotor was entirely of wood. All the aircraft had tricycle landing gear, although some tests were done with skids.

Cierva W.14 / Saunders-Roe Skeeter Article

1948

A second machine, the Skeeter 2 G-ALUF, was flown on October 20th, 1949, in which the most important of several design changes were the employment of a 145hp Gipsy Major 10 engine, increased rotor diameter and a slightly longer tailboom of circular instead of triangular cross-section. Two further-modified Skeeter 3’s were begun by Cierva which were completed by Saro, for evaluation by the Ministry of Supply, after the latter company had acquired Cierva in January 1951. Two Mk. 3 (Gipsy Major 10) and one Mk. 4 (Bombardier 702) were constructed for Ministry of Supply evaluation. The two Mk. 3’s were later fitted with Bombardier engines, and re-designated Mk. 3B. One similar machine was completed as the Skeeter 4.

During 1960 a new skid undercarriage was adopted on the Skeeter for the British Army in place of the wheels previously fitted.

Saro’s two Skeeter 5 prototypes, built as a private venture, was essentially similar apart from instruments and minor controls such as the positioning of the rotor brake, they differed in detail from the prototype Mark 2 Skeeter. The Mark 5 has a 190 b.h.p. Blackburn Cirrus Bombardier 704 engine, while the Mark 3 has a 180 b.h.p. Bombardier 702. The engine is fan cooled with a belt drive. They were the first machines of the series to be really free of the ground resonance problems which had beset the earlier prototypes. In 1956 the Skeeter 5’s were refitted with 200hp Gipsy Major 201’s.

In its civil form, the Skeeter Mark 5 has a 27 gallon fuel tank, which gives an endurance of about three hours, and a further 11 gallons may be carried in an auxiliary tank. The rotor and control system are simple with the three blades being built up on tubular steel spars, with ply ribs and fabric covering. Each blade weighs in the region of 45 lb. The tail rotor of the Mark 3 differed from that of the Mark 5 in having only two blades.

The government-sponsored Skeeter 6 had a 149kW Gipsy Major 30. The power of these engines is much the same but the latter version is a little heavier, carrying more payload and having a higher cruising speed. The Skeeter is built up from four sections the tail cone, complete with rotor, the rear all metal fuselage boom, the centre section, complete with engine, and the cockpit. This seats two side by side with full dual control and instrumenta¬tion.

The Skeeter Mk.6 made overseas appearances at Paris and Stuttgart in June 1956.

Skeeter Mk.6

After pre-service trials with the Skeeter 6 prototypes, initial production orders were given for two basically similar versions with the Gipsy Major 200 engine. These were the four Skeeter 6A, ordered for the Army Air Corps as the AOP Mk.10, and one Skeeter 6B as the T Mk.11 dual-control trainer for the RAF. Follow-on orders were placed later for the Skeeter 7A (AOP Mk.12) and 7B (T Mk.13), which differed chiefly in having 215hp Gipsy Major 215 engines. The Skeeter 7 was also the subject of a small export order, the Federal German Army and Navy ordering eleven and four as Mk.50 and Mk.51 respectively. Final variant was the Skeeter 8, basically an adaptation of the 7 for commercial operation. Three were built for C. of A. tests, but no civil orders ensued and Skeeter production came to an end in 1960 (by which time Saunders-Roe had become part of the Westland group) after a total of seventy-seven aircraft had been built.

The Skeeter was the first helicopter to enter British Army Air Corps service, replacing fixed-wing Auster aircraft.

The definitive military version was the AOP12 and deliveries began in June 1958. In the three years this version was in production a total of 64 were built in three separate batches. The Saro Skeeter AOP 12 was a two-seat reconnaissance and artillery-observation-post light helicopter which served with the British Army Air Corps between 1957 and 1967. It was powered by a de Havilland Gipsy Major Type 140 piston engine, delivering 215 bhp at 2850 rpm. It had a cruising speed of 76 knots, a service ceiling of 12800 feet and a range of 160 nautical miles.

In 1957 a small number of Skeeter AOP 10s were delivered to the Army and a T.11 to the RAF and about 50 AOP 12s and T13s were delivered in 1959.

A small number of Skeeters, designated Marks 50 and 51, served in Germany. The German Army and Navy received six and four respectively, which were transferred to the Portuguese Air Force in 1961 but never flown.

Of the fifty or so Skeeters supplied to the British services, the AOP 12’s served mostly at the Army Air Corps Training School, while the RAF T13’s were allocated to the Central Flying School and to No.651 Squadron. Ten of the German Skeeters were handed over in July 1961 to the Forca Aerea Portuguesa, with whom they were still in service in 1968. Dual controls are fitted as standard in all Skeeters. During their early life various Skeeter prototypes were used to flight-test a supercharged Gipsy Major engine, a Blackburn Turmo shaft turbine, and a Napier rocket-powered tip-drive system.

Skeeter with rocket engines at the tip of each blade

With only a single crewman aboard, the Skeeter could be flown in a casualty evacuation role with a stretcher pannier supported on each side of the cabin.

Saunders-Roe Skeeter Mk 6 ambulance (equipped with Napier NRE.19 boost system, rocket-fuel tank above hub)

Most Skeeters were replaced by Scout helicopters in 1967 and 1968 having served with four Army Air Corps Squadrons.

Most Skeeters were replaced by Scout helicopters in 1967 and 1968 having served with four Army Air Corps Squadrons.

Gallery

Cierva W14 Skeeter
Weight: 1210 lb

Cierva W14 Skeeter 1
Engine: 106hp Jameson FF-1
Seats: 2

Cierva Skeeter 2
Engine: 145hp Gipsy Major 10

Cierva Skeeter 3
Engine: 145hp Gipsy Major 10

Saro Skeeter 3B
Engine: 180 bhp Bombardier 702
Rotor dia: 32 ft
Length, 31 ft. 2 in
Tail rotor: 3 blade
Gross wt: 2,100 lb

Saro Skeeter 3B
Engine: 180hp Blackburn Bombardier 702
Tail rotor: 3 blade

Saro Skeeter 4

Saro Skeeter 5
Engine: 190 b.h.p. Blackburn Cirrus Bombardier 704
Fuel capacity: 27 gallon
Auxiliary fuel: 11 gallons
Rotor: three blades
Blade weight: 45 lb
Tail rotor: 2 blade
Endurance: 3 hr

Saro Skeeter 6
Engine: Gipsy Major 30, 186 h.p.
Rotor diameter: 32 ft
Rotors: 3-blade main; 3-blade tail
Fuselage length: 28 ft 5 in
Loaded weight: 2,200 lb
Ceiling: 11,900 ft
Typical range: 260 miles at 101 mph
Seats: 2

Skeeter 6A / AOP 10
Engine: Gipsy Major 200

Skeeter 6B / Skeeter T Mk.11
Engine: Gipsy Major 200

Saro Skeeter 7A / AOP 12
Engine: de Havilland Gipsy Major Type 140, 215 bhp at 2850 rpm
Cruising speed: 76 knots
Service ceiling: 12,800 feet
Range: 160 nm
Seats: 2

Saunders Roe AOP 12 Skeeter
Engine : De Havilland Gipsy Major 200 Mk 30, 200 hp
Length: (blades folded) 28 ft 5 in
Length with rotors turning: 8.66m
Fuselage length: 26.509 ft / 8.08 m
Rotor diameter: 32 ft / 9.75 m
Height: 2.29m
Empty weight: 780kg
Max take off weight: 2200.6 lb / 998.0 kg
Max. speed: 87 kt / 162 km/h
Range: 186 nm / 345 km
Hovering ceiling, IGE: 1680m
Service ceiling: 3900m
Crew: 2

7B / T Mk.13
Engine: de Havilland Gipsy Major Type 140, 215 bhp at 2850 rpm

Skeeter 8

Skeeter Mk 50
Main rotor diameter: 9.75m
Maximum speed: 267km/h

Skeeter Mk 51
Main rotor diameter: 9.75m
Maximum speed: 267km/h

Skeeter 6

Cierva W.11 Air Horse

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In September 1945 Pest Control Ltd had discussed the last possibility with Cierva and the W.11 design was modified to meet this role. As a result, Cierva received a development contract for one W.11 in July 1946, drafted to Specification E.19/46, and a second was ordered in early 1947. Cunliffe-Owen Aircraft Ltd were contracted to build the two aircraft at Southampton/Eastleigh Airport under the technical and financial control of the Cierva company.

1948

The Cierva W.11 Air Horse, built in 1948, featured three tri-bladed rotors mounted on outriggers from the fuselage and driven from a centrally-installed engine. Two prototypes were built for the British Ministry of Supply.

Power from a single Rolls-Royce Merlin 24 engine of 1208kW was transmitted through shafting to three-bladed rotors mounted on outriggers, each at the tip of a triangle. All three turned in the same direction, but their plane of rotation was sufficiently tilted to compensate for torque. Each rotor hub had a control spider which ensured cyclic and collective pitch control. The engine with its distribution gearbox to drive the rotors was situated just behind the cockpit in the fuselage. The fuselage was designed to carry twenty-four passengers in a compartment measuring 5.79 x 2.31 x 1.77 metres.

There was a tricycle landing gear, each leg of which was fitted with an oleo-pneumatic shock absorber. Twin fins were carried at the end of a mid-mounted tailplane on the rear fuselage and there was accommodation for a crew of three.

The prototype, the largest in the world at that date, made its maiden flight on 7 December 1948, but shortly after being displayed at the Farnborough Show it crashed, and work did not start on it again until the Gierva Company was taken over by Saunders Roe.

The Colonial Office made a grant of GBP45,000 to assist in the development costs since the type offered prospects of overseas use in the spraying role (total Ministry of Supply development costs were estimated at GBP350,000), but before the second W.11 had flown the first crashed on 13 June 1950, killing the three flight test crew members; the second W.11 never flew and was scrapped in 1960. The designation W.11T was allocated to a project for an enlarged W.11 with two 1208kW Rolls-Royce Merlin 502 engines and the W.12 was a projected freighter development with Rolls-Royce Dart turboprops. Neither of these materialised since by that time Cierva, not having used the number W.13, was involved in development of the W.14 which became the Skeeter and was built by Saunders-Roe Ltd.

Cierva W.11
Engine: 1 x Rolls-Royce Merlin 24, 1208kW
Rotor diameter: 14.33m
Length with rotors turning: 27.0m
Width with rotors turning: 28.96m
Max take-off weight: 7938kg
Loaded weight: 5507kg
Max speed: 225km/h
Cruising speed: 153km/h
Service ceiling: 8535m
Range with max fuel: 531km
Crew: 4-5
Passengers: 24

Cierva W.9 / Weir W.9

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The W.9 was an experimental helicopter to E.16/43, with a three-blade main rotor. Torque compensation was achieved by a jet of air discharged from the port side of the rear fuselage and supplied by a fan which also cooled the engine. The jet was controlled by two vanes. The air from a multi-bladed fan which cooled the engine was ducted through the inside of the fuselage, heated by the exhaust gases and then ejected through an opening on the port side. Two horizontal shutters controlled the flow of this air. The controllable efflux was also used to impart turning movements to the rotorcraft, which had neither fin nor rudder. The multi-bladed variable-pitch fan was coupled to the rudder pedals and thus provided yawing control.

First flown in 1945, only one was built.

W.9
Engine: 1 x Gipsy Six Series II, 155kW
Main rotor diameter: 10.98m
Max take-off weight: 1200kg

Cierva C.30 Rota / Avro 671 Rota

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Rota Mk.I

The Cierva C.30A marked a major step forward in rotorcraft development, being the first production autogiro in which the engine was geared directly to drive the rotor blades for take-off. The degree of direct control was increased still further by having the control column, which acted directly on the rotor, suspended from the pylon so that the rotor head could be tilted in any direction to produce the manoeuvre desired. The new-style control system was first installed in G-ABXP, a Cierva C.19 designated Mk.V with a 100hp Genet Major I engine. This was basically a C.19 Mk.IV modified to have a clutch and transmission shaft, a tilting rotor head and (later) a small, fixed tailplane.

Cierva C.30 Rota / Avro 671 Rota Article

The prototype C.30 (G-ACFI) differed chiefly in having a tripod rotor pylon and dihedral on the tailplane tips; the fuselage was modified by Airwork from a standard Cierva C.19, and assembly was undertaken by National Flying Services at Hanworth, where G-ACFI made its maiden flight early in April 1933. Take-off run of the C.30 was about 30 yards (27.43m), while the landing was achieved in about 3 yards (2.74m) with the rotor blades autorotating. Another 1933 prototype was G-ACKA, the first C.30P, with 140hp Genet Major 1A, folding rotor blades and other improvements.

Cierva C-30A

First customer for the production C.30A was the Royal Air Force, for whom the type was built by Avro and given the name Rota. One twin-float Sea Rota and ten standard Rotas with wheeled undercarriages were completed to Specification 16/35, and were delivered to the School of Army Co-operation at RAF Old Sarum from December 1934. By the outbreak of the Second World War they had been allocated for use by a highly secret unit engaged on ground radar calibration duties. One other military C.30A was K4775, a Civet Major-engined machine sent to the Royal Aircraft Establishment in 1935 for blade-flexing tests.

Nearly 150 were built under licence in the UK (Avro and Airwork), Germany (Focke-Wulf) and France (Lioré-et-Olivier). Airwork produced the C.30 and C. 30P, and Avro the C.30A and C.30P. The C.30A was built by A. V. Roe as the Avro Type 671 Rota for RAF and civil market.

The C-30A was the most widely produced Cierva autogyro design. Avro built the type under licence, as the Avro Type 671 Rota.

Avro production of C.30 types was in the region of seventy aircraft, three of which were C.30P’s. Thirty-seven C.30A’s appeared on the pre-war British civil register, and others were completed for customers in Europe, India, China, Australia and South Africa. In Britain the C.30A, like the C.19 before it, was used for traffic reporting duties at major sporting and similar events, and one aircraft (G-AGUT) was used for filming the 1936 F.A. Cup Final.

During 1933 the C.30 prototype, G-ACFI, was converted for jump-start trials with a modified rotor head, and in 1936 a perfected form of this was fitted to G-ACWF when it made the first genuine vertical take-off by an autogiro, by keeping the engine and rotor system engaged throughout the take-off sequence. This machine was, in effect, the prototype for the C.40, five of which were ordered for the R.A.F. as the Rota II to Specification 2/36. These were built by the British Aircraft Manufacturing Co., having side-by-side seats, wooden semi-monocoque fuselages and 175hp Salmson 9NG engines. Two of the original five Rota II’s were diverted to civilian customers, replacements being built in 1938-39. The R.A.F. C.40’s served with No.1448 Flight (later 529 Squadron). On the outbreak of World War 2 over a dozen civil C.30A’s were impressed for military service; these and the surviving Rota I’s were allocated singly to R.A.F. radar stations in the United Kingdom for calibration duties.

C.30A G-AHMJ was used by Fairey Aviation in the 1940’s for research that led to the Fairey Gyrodyne design. After retirement, it was moved to the rear of TS Broke, North Hyde Road, Southall, Middlesex, in the care of the Sea Cadet unit based there. In the early 1950’s it was aquired by the Shuttleworth Trust and restored in the 1970’s to it’s wartime camouflage scheme and serial number as an Avro Rota. It is now in the Fantacy of Flight Museum in Florida.

Concerning license manufacture of the type by Focke-Wutf, it is to be noted that Focke-Wulf did not obtain rights to produce the C 30 under license in 1933 as has claimed. License negotiations began in February 1935, initially with the “Hamburger Flugzeugbau G.m.b.H”, however these collapsed for financial reasons. Focke-Wulf entered the negotiations in July 1935. The start of license construction by Focke-Wulf was delayed on account of currency exchange difficulties until December 1935, when the exchange rate was guaranteed for 36 examples of the C 30.

Preliminary shipboard trials with the C 30 autogiro began on November 10, 1936 at E-Stelle See (Naval Test Station) Travemünde. The trials ended unsatisfactorily as a result of the type’s inadequate performance, its less than satisfactory handling characteristics in gusts and the poor view offered the pilot during deck landings on small platforms. Further development of the C 30 for military use was therefore abandoned.

Gallery

C.30A
Engine: 1 x Armstrong Siddeley Civet 1, 140 hp
Main rotor diameter: 37 ft
Rotors: 3-blade
Fuselage Length: 19 ft. 8.5 in
Loaded weight: 1,900 lb Empty weight:
Max speed: 100 m.p.h
Ceiling: 8,000 ft
Range: 250 miles at 85 m.p.h
Seats: 2

C.30A
Engine: 1 x Armstrong Siddeley Genet Major IA, 104kW
Main rotor diameter: 11.28m
Length: 6.01m
Height: 3.38m
Max take-off weight: 816kg
Empty weight: 553kg
Max speed: 177km/h
Cruising speed: 153km/h
Range: 459km

Avro Rota Mk I.
Engine: Armstrong Siddeley Genet Major 1A, 140 hp
Length : 19.718 ft / 6.01 m
Rotor diameter: 41.995 ft / 12.8 m
Max take off weight: 1799.3 lb / 816.0 kg
Max. speed: 96 kt / 177 km/h

Cierva C.24 / C.26

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De Havilland CIERVA C24

The C24 was built by de Havilland’s at Stag Lane on a De Havilland DH.80 Puss Moth’s fuselage and first flown in September 1931. It was modified in October 1931 to have a two-blade rotor in place of the three-blades fitted for the first flight and a dorsal fin.

It was certificated in April 1932 and extensively demonstrated that summer, having been re-designated the C26.

It was stored by the Science Museum until restored as the C.24 by the Mosquito Museum on loan from the Science Museum.

De Havilland CIERVA C24

Engine: de Havilland Gipsy III, 120 hp
Rotor diameter: 34 ft
Length: 18 ft 9 in
AUW: 1800 lb
Max speed: 115 mph

Cierva C.19 / Avro 620

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C.19 Mk.III

Cierva developed progressively more sophisticated designs with a means to tilt the rotor head and altering the pitch (angle) of each individual rotor blade, called collective and cyclic control.
The Mk.III had a modified tail and rudder assembly to enable steep tail wheel first touchdowns.
Making use of Pitcairn’s prerotator, achieved a “jump takeoff” capacity with the C19MkIV in 1931-32 The rotor would be spun up at zero pitch and then “snapped” into a positive angle, causing the aircraft to “jump” into air.
Focke-Achgelis, the German aircraft company, became licensed by Cierva to manufacture his patented components. For a number of years before the outbreak of World War II, Focke-Achgelis produced the C-19 Autogyro, and they drew heavily from the knowledge and experience gained from Cierva’s design to rapidly advance the development of their FA-61 helicopter.

C.19 Mk.III

The Cierva C.30A marked a major step forward in rotorcraft development, being the first production autogiro in which the engine was geared directly to drive the rotor blades for take-off. The degree of direct control was increased still further by having the control column, which acted directly on the rotor, suspended from the pylon so that the rotor head could be tilted in any direction to produce the manoeuvre desired. The new-style control system was first installed in G-ABXP, a Cierva C.19 designated Mk.V with a 100hp Genet Major I engine. This was basically a C.19 Mk.IV modified to have a clutch and transmission shaft, a tilting rotor head and (later) a small, fixed tailplane.

Gallery

C-19 Mk.III
Seats: 2