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Avro 671 “Rota”
United Kingdom — single-engine two-seat autogyro


Archive Photos [1]


[Avro 671 “Rota” (K4232) on display 1994 at the Royal Air Force Museum, RAF Hendon Aerodrome, London (John Shupek photo copyright © 2002 Skytamer Images) ¹]

[Avro 671 “Rota” (K4232) on display 1994 at the Royal Air Force Museum, RAF Hendon Aerodrome, London (John Shupek photo copyright © 2002 Skytamer Images) ¹]

[Airplane Trade Card: Avro 671 Rota (G-ACWF) Aeroplanes & Carriers, Amalgamated Press, 1936, UK, Card 22 of 32]

[Avro 671 Rota, Airplane card: 1938 “Flying”, J.A. Pattreioux, 48-cards, UK (The Skytamer Archive)]

Overview [2]


Avro “Rota Mk.I” (Cierva C.30)

  • Role: Autogyro
  • Designed by: Juan de la Cierva
  • First flight: 1933
  • Introduced: 1934
  • Number built: 148

The Cierva C.30 was a type of autogiro designed by Juan de la Cierva and built under licence from the Cierva Autogiro Company by A.V. Roe & Co Ltd, Lioré-et-Olivier and Focke-Wulf. The “Autogiro” consists of a fuselage with a propulsive power-plant comprising an engine coupled to an airscrew similar to that of the conventional aeroplane. It is supported in flight by an autorotative rotor comprising a number of sustaining blades connected to a hub member or axle which is mounted on a pylon structure over the center of gravity of the machine. The blades rotate freely in flight about an approximately vertical axis, their rotation being due to the upward component through the rotor disc of the relative wind. As this component can never be negative or zero for any steady condition of flight, the blades must continue to rotate until the machine lands, whether the engine is on or off. The engine is connected to the rotor through a clutch for imparting an initial rotation before the machine takes off but the clutch is disengaged entirely during flight and no external torque is applied to the rotor.

The “Autogiro” can take-off, fly and maneuver in a similar manner to the aeroplane, and derives its support-just as does an aeroplane-from the relative motion of the supporting surfaces and the air. As these supporting surfaces are in practically constant rotation, there is relative motion even when the machine has no forward speed, and the “Autogiro” has therefore no definite minimum translational speed of support. In other words, it is capable of vertical descent, and is incapable of stalling. The detail design of the rotating wing system of the “Autogiro” is remarkable for its simplicity and ingenuity. Each blade is attached to the hub by a “flapping” hinge and a “drag” hinge. The former allows the blades to cone upwards in flight so that the lift from the blades is communicated to the hub only in shear. The latter suppresses bending moments in the plane of rotation at the root of the blade spar.

The standard production model known as the C.30, is produced by the firm of A.V. Roe & Co., Ltd., under a non-exclusive license from the Cierva Autogiro Co., Ltd., granted early in 1934, and a number of these machines are used in many countries. This model has a three-bladed rotor and is the first “direct-control” type. There are no ailerons, elevators or rudder. Longitudinal and lateral control are obtained by tilting axis of the rotor so that the rotor thrust line moves away from the center of gravity of the aircraft, thereby causing a couple which tilts the machine in the appropriate manner. There is no rudder and turns are made by banking only.

A license has also been granted to G. & J. Weir Ltd. The latest experimental model produced by this company is a small single-seat machine of the auto-dynamic type described hereafter. In 1934, Senor de la Cierva succeeded in producing an “Autogiro” which took off vertically, without any forward run.

Much experimental work has been carried during 1935 and 1936 on this principle and as a result there has been perfected an entirely new conception of flying machine called “The Autodynamic Autogiro.” Its most spectacular quality is its ability to take-off and land without any forward run whatsoever, but it derives its name from its ability to adjust itself automatically to the varying conditions of flight. For direct take-off, the blades move automatically to substantially zero pitch when the rotor-clutch is engaged. In this position the blades are driven to a higher speed of rotation than is required for normal flight, and when the clutch is released the blades automatically increase their pitch. This sudden change in blade pitch produces lift in excess of the weight of the machine and the aircraft is projected into the air in a vertical direction.

During flight the rotor is driven by the relative wind, only the airscrew being driven from the engine. The speed of the blades in flight is independent of forward speed and remains substantially constant from top speed in level flight to zero forward speed, i.e. vertical descent. Some of the principal features of the new rotor are stability in gusts and disturbed air conditions, constancy of lift from the two blades as they rotate, optimum blade pitch for all forward speeds and altitudes, no tendency of the blades to slow down due to ice formation and the elimination of friction dampers. The application of the rotor brake after the machine touches the ground decreases the blade pitch to zero thereby taking away all the lift from the rotor. This prevents the machine from overturning after landing and is especially useful in gusty wind conditions. The characteristic of direct take-off combined with that of vertical descent places this new type of aircraft in a completely different category from the conventional aeroplane and the machine is rendered practically independent of the nature of the terrain from which it operates.

Design and Development [2]


Before the experimental Cierva C.19 Mk.V, autogyros had been controlled in the same way as fixed wing aircraft, that is by deflecting the air flowing over moving surfaces such as ailerons, elevators and rudder. At the very low speeds encountered in autogyro flight, particularly in the landing phase, these controls became useless. The experimental machine showed that the way forward was to have a tiltable rotor hub and a control rod coming down from the hub to the pilot's cockpit with which he could change the rotor plane. This was known as "direct control" and was adopted by the C.30. The production variant, called C.30A in England was preceded by several development machines.

The first in the series was the C.30, a radial engined autogyro with a three blade, 37 ft (11.3 m) rotor mounted on an aft-leaning tripod, the control column reaching back to the rear of the two cockpits. The engine was the five-cylinder, 105 hp (78 kW) Armstrong Siddeley Genet Major I used in the C.19 series. The fabric covered fuselage carried an unbraced tailplane, without elevators but with turned up tips. The port side plane had an inverted Aerofoil section to offset the roll-axis torque produced in forward flight by the advancing port side blades. As with most autogyros, a high vertical tail was precluded by the sagging resting rotor, so the dorsal fin was long and low, extending well aft of the tailplane like a fixed rudder and assisted by a ventral fin. A wide track undercarriage had a pair of single, wire braced legs; there was a small tail wheel. It flew in April 1933. It was followed by four improved machines designated C.30P (P here for pre-production) which differed in having a four-legged pyramidal rotor mounting and a reinforced undercarriage with three struts per side. The rotor could be folded rearwards for transport. The C.30P used the more powerful (140 hp, 104 kW) seven-cylinder Armstrong Siddeley Genet Major IA radial engine.

The production model, called the C.30A by Avro, was built under licence in Britain, France and Germany and was similar to the C.30P. The main alteration was a further increase in undercarriage track with revised strutting, the uppermost leg having a pronounced knee with wire bracing. There was additional bracing to the tailplane and both it and the fin carried small movable trimming surfaces. Each licensee used nationally built engines and used slightly different names. In all, 143 production C.30s were built, making it by far the commonest pre-war autogyro.

Between 1933 and 1936, Cievra used one C.30A (G-ACWF) to perfect his last contribution to autogyro development before his death in a DC-2 (fixed wing) crash in late 1936. To enable the aircraft to take off without forward ground travel, he produced the “Autodynamic” rotor head, which allowed the rotor to be spun up by the engine in the usual way but to higher than take-off rpm at zero rotor incidence and then to reach operational positive pitch suddenly enough to jump some 20 ft (6 m) upwards. At least one of the RAF C.30As was in January 1935 on floats as a “Sea Rota”.

Production [2]


  • Avro: Avro obtained the licence in 1934 and subsequently built 78 examples, fitted with an Armstrong Siddeley Genet Major IA (known in the RAF as the Civet 1) 7-cylinder radial engine producing 140 hp (100 kW). The first production C.30A was delivered in July 1934.
  • Lioré-et-Olivier: Twenty-five aircraft were built in France by Lioré-et-Olivier as the LeO C.301 with a 175 hp (130 kW) Salmson 9NE 9-cylinder radial engine.
  • Focke-Wulf: Forty aircraft were built in Germany by Focke-Wulf as the C 30 Heuschrecke (Grasshopper) with a 140 hp (105 kW) Siemens Sh 14A 7-cylinder radial engine.

Operational History [2]


Of the 66 non-RAF aircraft built in the UK by Avro, 37 appeared at least for a while on the UK register. Some (maybe a dozen) were sold on abroad, but others were flown by wealthy enthusiasts and by flying clubs who anticipated autogyro training needs. By the end of the decade private flyers were moving back to the comforts and economies of fixed wing aircraft and more C.30s moved abroad, leaving the Autogyro Flying Club at Hanworth as the major UK user. 26 aircraft were directly exported by Avro. These went both to private owners and to foreign air forces who wish to investigate the autogyro's potential.

In 1934, one Spanish Navy C.30 piloted by Cierva landed on the Spanish Seaplane tender “Dedalo” anchored in Valencia harbor and later made a takeoff.

Twelve C.30A built by Avro for the Royal Air Force (RAF) entered service as the Avro 671 Rota Mk.I (Serials K4230 to K4239 and K4296 & K4775). The twelve were delivered between 1934 to 1935. They equipped the Army School of Co-operation at Old Sarum near Salisbury. Many of the surviving civil aircraft were also taken into RAF service between 1939 and 1940. In 1940 they equipped No. 1448 Flight at RAF Duxford. Later they equipped No. 529 Squadron RAF at Halton on radar calibration work. They disbanded in October 1945. At the end of the war the twelve survivors were sold. Most of these did not last long, though two were used for pilot rotary wing experience by Fairey in their Fairey Gyrodyne helicopter program. Rota Towels kept one ex-RAF Rota airworthy until an accident in 1958. G-ACCU, the Imperial War Museum's C.30A exhibit at Duxford had one of the longest active lives. It joined Air Service Training Ltd in 1934, was impressed (as Rota HM580) in 1942, returned as a civilian to Elmdon with its original registration plus the nickname “Billy Boy” and was not withdrawn from use until 1960.

Survivors [2]


  • There are no flying survivors.
  • Avro Rota I (K4232): On display at the Royal Air Force Museum, London, England.
  • Cierva C.30A (AP506): On display at the Helicopter Museum, Weston-super-Mare, England.
  • Cierva C.30A (AP507): On display at the Science Museum in London, England.
  • Avro Rota I (HM580/G-ACUU): On display at the Imperial War Museum Duxford, England.
  • Cierva C.30A (LN-BAD): On display at the Aviodome, Netherlands.
  • Cierva C.30A (LV-FBL): On display in Argentina.
  • Cierva C.30A (VH-USR): On display at the Powerhouse Museum, Sydney, Australia.
  • Leo C.302 (F-BDAD): On display at the Musée de l'Air et de l'Espace, Paris, France.
  • Cierva C.30A (H-KX): On display at the Fantasy of Flight Museum, Florida, USA.
  • In addition, a full-scale flying reproduction was built in Spain in the mid-1990s. After a brief flying career a crosswind accident led to the damage to the rare rotor blades. The aircraft is now on display at the Museo del Aire, Cuatro Vientos, Madrid, Spain.

Military Operators [2]


  • Argentina
  • Austria
  • Belgium
  • Denmark
  • Italy
  • Soviet Union
  • Spanish Republic
  • United Kingdom: Royal Air Force, No. 80 Squadron RAF, No. 529 Squadron RAF
  • Kingdom of Yugoslavia

Avro 671 “Rota” (Cierva C.30) Specifications [3]


Type:

  • Two-seat autogiro

Rotor:

  • Three blades, each composed of a steel-tube with wooden ribs, plywood covering and fabric over all, are hinged to a hub so that, besides being able to rotate, each blade is free to move through a limited vertical angle and also through a limited horizontal one.
  • For control in the air the axis of the of the hub can be inclined forwards or backwards or to either side.
  • Its motion is constrained by adjustable springs.
  • For starting, the hub is spun round by the engine.
  • There is also an internal expanding brake for stopping it.
  • The whole gear is carried by four struts from the fuselage.

Fuselage:

  • Structure of welded steel-two covered with fabric over wooden formers and stringers.

Tail Unit:

  • The long low vertical fin is so shaped to clear the revolving blades in their lowest positions.
  • It is internal with the fuselage and covered with fabric.
  • There is no rotor, but a small portion of the fin at the trailing-edge can be set for adjustment.
  • The tips of the metal-framed and fabric-covered tail-plane are set at very marked dihedral angles.
  • Flaps along the whole trailing-edge can be set for adjusting trim.
  • Also the whole tail-plane can be adjusted on the ground.
  • The port side of the latter has the cambered surface downwards and the starboard side has it upwards.

Undercarriage:

  • Specially wide track of 9 feet.
  • Avro shock-absorbers.
  • Palmer wheels.
  • Bendix brakes.
  • Steerable tail-wheel on sprung fork with Palmer pneumatic tire.

Power Plant:

  • One 140-hp Siddeley “Genet-Major” seven-cylinder radial air-cooled engine.
  • Fuel tank of 23 gallons in front of front cockpit.
  • Oil tank of 3&frac2; gallons in front of fireproof bulkhead.

Accommodation:

  • Two open cockpits in tandem, front one has sliding door in port side.
  • Dual control.
  • Parachute seats.

Dimensions:

  • Rotor diameter: 37 ft
  • Height overall: 11 ft 1 in
  • Length overall: 19 feet 8½ in
  • Wheel track: 9 ft 0 in
  • Span of tail-plane: 10 ft 2 in
  • Incidence of tail-plane: 1 deg
  • Incidence of rotor blade: 2 deg 40 min

Areas:

  • Area of rotor blade (each): 15.60 ft²
  • Area of tail-plane: 15.60 ft²
  • Area of upturned tips (both) of tail-plane: 8.55 ft²
  • Area of the upper fin: 12.90 ft²
  • Area of lower fin: 3.38 ft²

Weights:

  • Weight empty: 1,265 lbs
  • Pilot: 165 lbs
  • Observer: 165 lbs
  • Fuel and oil: 210 lbs
  • Normal loaded weight: 1,805 lbs
  • Military equipment: 95 lbs
  • Maximum permissible loaded weight: 1,900 lbs

Performance:

  • Maximum speed at sea level: 100 mph
  • Cruising speed: 85 mph
  • Minimum horizontal speed: 15 mph
  • Landing speed: Nil
  • Initial rate of climb: 600 ft/min
  • Service ceiling: 8,000 feet.
  • Absolute ceiling: 10,000 feet.
  • Rate of descent: 15 ft/sec
  • Landing run: nil
  • Take-off run in still air: 70 yds
  • Range: 215 miles

References


  1. Shupek, John. The Avro 671 Rota photos and card image via The Skytamer Archive, Copyright © 1994, 2002, 2014 Skytamer Images. All Rights Reserved
  2. Wikipedia. Cierva C.30
  3. Grey, C. G., and Leonard Bridgman, “Avro: The Autogiro Type C.30.” Jane's All the World's Aircraft 1935. Sampson Low, Marston & Company, Ltd., London, 1935. pp. 26c

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