Autogyro
From Wikipedia, the free encyclopedia
An autogyro is a type of rotary wing aircraft supported in flight by lift provided by a rotor. Unlike a helicopter, the rotor of an autogyro is driven by aerodynamic forces alone once it is in flight, and thrust is provided by an engine-powered propeller similar to that of a fixed-wing aircraft. However, the autogyro is a distinct type of aircraft and not a hybrid between fixed-wing aircraft and helicopters.
The autogyro was invented by Juan de la Cierva y Codorniu in 1919, and it made its first successful flight on 17 January 1923 at Cuatro Vientos Airfield in Madrid, Spain. De la Cierva's pioneering rotor technology paved the way for the invention of the helicopter 13 years later.
Autogyros are also known as gyroplanes, gyrocopters, or rotaplanes. When the term is spelled autogiro it is a trademark that can only be applied to products of the Cierva Autogiro Company or its licensees.
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[edit] Principle of operation
An autogyro is characterised by a free-spinning rotor that turns due to passage of air upwards through the rotor. The vertical component of the total aerodynamic reaction of the rotor gives lift for the vehicle, and sustains the autogyro in the air. Forward thrust is provided by a separate propeller, or alternately, jets, as used on the Lockheed XH-51A Compound when flying in autogyro mode.
Whereas a helicopter works by forcing the rotor blades through the air, pushing air downwards, the gyrocopter rotor blade generates lift in the same way as a glider's wing by changing the angle of the air as it moves upwards and backwards relative to the rotor blade. The free-spinning blades turn by autorotation; the rotor blades are angled so that they give not only lift, but also so as to accelerate the blades' rotation rate, until the rotor turns at a stable speed with the drag and thrust forces in balance.
Pitch control of the autogyro is by tilting the rotor fore and aft; roll control is by tilting the rotor laterally (side to side). Tilt of the rotor may be effected by a tilting hub (Cierva), swashplate (Air & Space 18A), or servo-flaps (Kaman SAVER). Yaw control is provided by a rudder, usually placed in the propeller slipstream to maximize control at low airspeed.
[edit] History
[edit] Early Developments
Juan de la Cierva, a Spanish engineer and aeronautical enthusiast, invented the first successful rotorcraft, which he named 'autogiro' in 1923. His aim was to create an aircraft which would not stall, following the stall-induced crash of a three-engine bomber he had designed for a Spanish military aeronautical competition. His craft used a tractor-mounted forward propeller and engine, a rotor mounted on a mast, and a horizontal and vertical stabilizer. His first three designs, C.1, C.2, and C.3, were unstable due to aerodynamic and structural deficiencies in their rotors. His fourth design, the C.4, fitted with flapping hinges to attach each rotor blade to the hub, made the first successful flight of a rotary-wing aircraft, piloted by Alejandro Gomez Spencer, on 17 January 1923. The C.4 was fitted with conventional ailerons, elevators and rudder for control. During a later test flight, the engine failed shortly after takeoff and the aircraft descended slowly and steeply to a safe landing, validating la Cierva's efforts to produce an aircraft that could be flown safely at low airspeeds.
This success eventually became well known and after further limited Autogiro development in Spain, la Cierva accepted an offer from Scottish industrialist James G. Weir to establish the Cierva Autogiro Company in England following a demonstration on 20 October 1925 to the British Air Ministry at RAE Farnborough. Test pilot for these flights was Frank T. Courtney. From this point on, Britain became the world center of rotary-wing aircraft development.
A crash due to blade root failure in February 1927 led to an improvement in rotor hub design. Adjacent the flapping hinge a drag hinge was incorporated to allow each blade to slightly oscillate horizontally and relieve in-plane stresses generated as a byproduct of flapping motion. Development work on means to accelerate the rotor prior to takeoff was also undertaken. Efforts with the C.11 in Spain showed that development of a light and efficient mechanical rotor transmission was not a trivial undertaking and led to the adoption of the intermediate expedient of inclining the horizontal stabilizer to redirect the propeller slipstream into the rotor while on the ground. This feature was later introduced on the production C.19 series of 1929.
Further Autogiro development led to the Cierva C.8 L.IV which on 18 September 1928 made the first rotary-wing aircraft crossing of the English Channel followed by a tour of Europe. The US industrialist Harold F. Pitcairn had in 1925 visited la Cierva in Spain upon learning of the successful flights of the Autogiro; in 1928 he visited la Cierva in England after taking a C.8 L.IV test flight piloted by Arthur H.C.A. Rawson and being particularly impressed with the Autogiro's safe vertical descent capability, purchased a C.8 L.IV with a Wright Whirlwind engine. Arriving in the United States on 11 December 1928 accompanied by Rawson, this Autogiro was redesignated C.8W.
The Cierva "Autodynamic" rotor used drag hinges with offset axes to perform this to good effect with great simplicity, but the Pitcairn collective pitch control advanced the "jump" ability.
The C-19 technology was licensed to a number of manufacturers, including Harold Pitcairn in the U.S. (in 1928) and Focke-Achgelis of Germany. In 1931 Amelia Earhart flew a Pitcairn PCA-2 to a then world altitude record of 18,415 feet (5613 m).
[edit] World War II
In World War II, Germany pioneered a very small gyroglider "rotor-kite", the Focke-Achgelis Fa 330 "Bachstelze" (Water-wagtail), towed by U-boats to provide aerial surveillance.
The Japanese Army developed the Kayaba Ka-1 Autogyro for reconnaissance, artillery-spotting, and anti-submarine uses. The Ka-1 was based on an American design first imported to Japan in 1938. The craft was initially developed for use as an observation platform and for artillery spotting duties. The Army liked the craft's short take-off span, and especially its low maintenance requirements. In 1941 production began, with the machines assigned to artillery units for spotting the fall of shells. These carried two crewmen: a pilot and a spotter.
Later, the Japanese Army commissioned two small aircraft carriers intended for coastal antisubmarine (ASW) duties. The Ka-1 was modified by eliminating the spotter's position in order to carry two small depth bombs. Ka-1 ASW autogyros operated from shore bases as well as the two small carriers. They appear to have been responsible for at least one successful submarine sinking.
[edit] Postwar Developments
The autogyro was resurrected after World War II when Dr. Igor Bensen (a Doctor of Divinity) saw a captured German U-Boat's gyroglider and was fascinated by its characteristics. At work he was tasked with the analysis of the British "Rotachute" gyro glider designed by expatriate Austrian Raoul Hafner. This led him to adapt the design for his own purposes and eventually market the B-7.
Later autogyros, such as the Bensen B-8M gyrocopter, generally use a pusher configuration for simplicity and to increase visibility for the pilot. For greater simplicity, they generally lack both variable-pitch rotors and powered rotors. Bensen autogyros and its derivatives have a poor safety record due to their deficient stability and control characteristics greatly worsened by use of a teetering rotor, and their marketing as a "build it yourself and teach yourself how to fly" aircraft.
In the 1950s and 1960s there was interest in developing a VTOL capability in autogyros while retaining the efficiency of an undriven rotor in horizontal flight. This led to a number of gyrodynes (also called "heliplanes") which were functionally like autogyros during flight but could apply power to the rotor at take off and for hovering.
Three different autogyro designs have been certified by the FAA for commercial production: the Umbaugh U-18/Air & Space 18A of 1965, the Avian 2-180 of 1967, and the McCulloch J-2 of 1972. All have for various reasons been commercial failures.
A miniature autogyro craft, the Wallis autogyro, was developed in England in the 1960s by Ken Wallis and autogyros built to Wallis designs appeared for a number of years. Little Nellie, the autogyro featured in the James Bond film You Only Live Twice, was actually a Wallis design, and was piloted in its film scenes by its inventor, Ken Wallis. Ken Wallis's designs have been used in various scenarios including military training, police recon, and in another case a search for the Loch Ness Monster.
[edit] Flight controls
There are three primary flight controls: control stick, rudder pedals, and throttle.
The control stick is termed cyclic and tilts the rotor in the desired direction to provide pitch and roll control. The rudder pedals provide yaw control, and the throttle controls engine power.
Secondary flight controls include the rotor transmission clutch which when engaged drives the rotor to start it spinning before takeoff, and collective pitch to reduce blade pitch before driving the rotor. These secondary controls are found on Air & Space 18A and McCulloch J-2 autogyros.
[edit] General characteristics
Autogyros can take off and land in significantly smaller areas than fixed-wing aircraft, and, depending on the model, can operate from helipads. When fitted with a jump takeoff feature, an autogyro can take off from a standing start into forward flight, accelerate while in ground effect, and then climb.
Autogyros cannot hover however, since the rotor is declutched from drive before starting the takeoff procedure. If rotor collective pitch control is provided, an autogyro can execute a collective flare; otherwise, landings are always made with a cyclic flare.
It is possible to land an autogyro in an area from which it cannot take off again. An autogyro can easily execute a steep approach to a no-roll landing; however, the climb angle after takeoff is relatively shallow, similar to that of a fixed-wing aircraft. Sufficient clearance area must be available after takeoff for the autogyro to turn and avoid obstacles during climb. This limitation, as well as their lack of hovering performance, is primarily responsible for autogyros being superseded by helicopters.
As intended by la Cierva, the rotor always turns regardless of the airspeed of the aircraft, though as airspeed decreases rotor rpm reduces to a minimum value at zero airspeed. Reduction of engine power increases the descent rate, though the autogyro remains fully stable and controllable. Directional control, provided by a rudder, can become nonexistent at low airspeed and low propeller thrust. For example, the Air & Space 18A gyroplane rudder rapidly loses effectiveness below 50 mph airspeed when the engine is throttled back.
Most autogyros are neither efficient nor very fast, although Wing Commander Ken Wallis has achieved 120 mph from 60 bhp in one of his designs. More recently the CarterCopter achieved a speed of 170 mph. Fixed-wing aircraft are faster and use less fuel over the same distance, while helicopters generally require more power (and hence more fuel) than either fixed wing aircraft or autogyros for the same speed and load. Autogyro development ceased before World War II, and with few exceptions, has not benefited from modern rotary wing advances applied to helicopters. When improvements in helicopters made them practical, autogyros became largely neglected. They were, however, used in the 1930s by major newspapers, and by the US Postal Service for mail service between the Camden, NJ airport (USA) and the top of the post office building in downtown Philadelphia, Pennsylvania (USA).
Autogyros can be of tractor configuration (with the engine(s) and propeller(s) at the front of the fuselage), e.g., Cierva, or pusher configuration (with the engine(s) and propeller(s) at the rear of the fuselage), e.g., Bensen. Early autogyros were fitted with fixed rotor hubs, small fixed wings, and control surfaces like those of a fixed wing aircraft. These designs were problematic, because at low airspeeds, the control surfaces became ineffective and could readily lead to loss of control, particularly during landing. The direct control rotor hub, which could be tilted in any direction by the pilot, was first developed on the Cierva C.19 Mk.V and saw production on the Cierva C.30 series of 1934.
Rotor drives initially took the form of a rope wrapped around the rotor axle and then pulled by a team of men to accelerate the rotor - this was followed by a long taxi to bring the rotor up to speed sufficient for takeoff. The next innovation was a fully deflectable horizontal stabilizer that directed propeller slipstream into the rotor. Cierva {license?}, Pitcairn-Cierva Autogiro Company of Willow Grove, Pennsylvania, finally solved the problem with a light mechanical transmission driven by the engine.
The Groen Brothers Hawk 4 design of 1992 is advertised as possessing "Ultra-Short Take-Off and Landing" (USTOL) capability, enabling the aircraft to take off and land within a very short distance (25 feet). This is merely a new name for performance autogyros have always possessed.
[edit] Flight characteristics
Flight in any rotorcraft can be summed up as feeling similar to a cork bobbing on the sea. The rotor sweeps a large area and though it is very effective at damping out disturbances provides a somewhat nautical element to the flying qualities. Moving the cyclic stick tilts the entire rotor to a new position within no more than about one revolution and is thus a very sensitive control. There is nevertheless a small time lag between cyclic stick movement and aircraft response since the control system is essentially a mechanical relay system that only indirectly tilts the rotor: the cyclic control merely establishes the conditions for aerodynamic forces to reorient the rotor in the desired direction. Additionally, since the rotor is always turning at or above a minimum rpm, control sensitivity does not vary significantly with changes in airspeed.
Effectiveness of the rudder is dependent on airflow, and it rapidly loses authority as airspeed decreases; this can be partially offset by maintaining propeller thrust to generate the required airflow at low airspeeds.
A certificated autogyro must meet mandated stability and control criteria; in the United States these are set forth in Federal Aviation Regulations Part 27: Airworthiness Standards: Normal Category Rotorcraft. Such autogyros are issued a Standard Airworthiness Certificate by the US Federal Aviation Administration. Bensen-type autogyros are generally home built, either from plans or from a kit. Home-built aircraft are operated under a Special Airworthiness Certificate in the Experimental category, so there is no guarantee they will perform as claimed by their manufacturers. It is important to note that Bensen-type autogyros have a poor safety record - this is due to two factors: (1) significant stability and control deficiencies inherent in the design, and (2) an unfortunate record of this type of gyroplane being flown by unqualified / untrained pilots. NTSB accident records give a clear picture of the safety of autogyros with Standard Airworthiness Certificates compared to those with Special Airworthiness Certificates.
In 2005 the United Kingdom Civil Aviation Authority (CAA) issued a mandatory permit directive (MPD) [1] which restricts operations for single seat autogryos. The MPD is concerned with the offset between the centre of gravity and thrust line, and apply to all aircraft unless evidence is presented to the CAA that the CG/Thrust Line offset less than 2 inches in either direction. The restrictions, which are considered onerous by many in the UK autogryo community, are summarised as follows:
- Aircraft with a cockpit/nacelle may only be operated by pilots with more than 50 hours solo flight experience following the issue of their licence.
- Open frame aircraft are restricted to a minimum speed of 30mph (26 knots), except in the flare.
- All aircraft are restricted to a Vne of 70mph (61 knots)
- Flight is not permitted when surface winds exceed 17mph (15 knots) or if the gust spread exceeds 12mph (10 knots)
- Flight is not permitted in moderate, severe or extreme turbulence and airspeed must be reduced to 63mph (55 knots) if turbulence is encountered mid-flight.
[edit] Bensen's design
The Bensen Gyrocopter was adapted directly from the Hafner Rotochute and Focke-Achgelis Fa 330A-1 "Bachstelze" autogiros of World War II. Bensen's adaptation, termed Gyrocopter, was available in three versions, B-6, B-7 and B-8. All three were designed in both unpowered and powered forms.
The basic Bensen Gyrocopter design is a simple frame of square aluminium or galvanized steel tubing, reinforced with triangles of lighter tubing. It is arranged so that the stress falls on the tubes, or special fittings, not the bolts.
Power can be supplied by a variety of engines, though rarely one certificated for use in aircraft. McCulloch drone engines, Rotax, and other designs have been used in Bensen-type designs.
The rotor is atop the vertical mast. Outlying mainwheels are mounted on an axle. A front-to-back keel mounts a steerable nosewheel, seat, other tubes, engine, a vertical stabilizer, and commonly a small fixed tailwheel. Some versions mount seaplane-style floats for water operations.
Many light gyroplane rotors are made from aluminium, though GRP-based composite blades (Sport Copter, Averso, Revolution, RAF eg) and GRP-skinned blades are increasing in number. Aircraft-quality birch was specified in early Bensen designs, and a wood/steel composite is still used in the world speed record holding Wallis design.
The rotor system of all Bensen-type autogyros is of two-blade teetering design. This single feature is responsible for the majority of accidents in this type of autogyro due its lack of tolerance for mishandling. A teetering rotor does not directly control the fuselage attitude but merely reorients the thrust vector which then causes the fuselage to swing into alignment beneath it. If a low G condition occurs, rotor thrust decreases and causes degradation of control. A certificated rotorcraft fitted with a teetering rotor is required by airworthiness standards to maintain a loading of at least 0.5G. If the rotor is powered as in a helicopter, rotor RPM is maintained even though control authority decays; in the case of an autogyro, rotor RPM and control degrade simultaneously and prompts the usually "self-trained" pilot to overcontrol and precipitate contact between the rotor and the rudder.
All autogiros produced by the Cierva Autogiro Company and its licensees were fitted with articulated rotors controlled about a tilting hub. This design has significantly higher tolerance to mishandling due to offset flapping hinges which generate a control moment even under low G conditions and provides control of the rotor. Overcontrol of this rotor can still result in contact with part of the fuselage however. Unlike the majority of Bensen-type autogyros, Cierva Autogiros were invariably flown by trained and qualified pilots, which produced a safety record not exceeded in general aviation until 1972.
Bensen-type designs commonly also have an unstable relationship between propeller thrustline, aircraft center-of-gravity, and rotor drag. If the propeller thrustline passes above the aircraft center-of-gravity and rotor drag decreases suddenly, the Gyrocopter goes out of balance and pitches down rapidly. This has the additional effect of unloading the rotor. This condition is unrecoverable and has caused many fatalities.
The thrust line of autogiros produced by the Cierva Autogiro Company and its licensees passed through the aircraft center-of-gravity, thus eliminating any pitching moment due to reduction of rotor drag.
[edit] Records
As of 2002, Wing Commander Ken Wallis, an enthusiast who has built several gyroplanes, holds or has held most of the type's record performances. These include the speed record of 111.7 mph (186 km/h), and the straight-line distance record of 543.27 miles (905 km). The record picture is continually changing, and on 16 November 2002, Ken Wallis increased the speed record to 207.7 km/h - and simultaneously set another world record as the oldest pilot to set a world record See: [1]
[edit] Speed
Andy Keech made a transcontinental flight from Kitty Hawk, N.C. to San Diego, Ca. in October 2003 and set 3 world records. The 3 records are for 'speed over a recognised course', and are verified by tower personnel or by official observers of the U.S. National Aeronautic Association. In February 2006 he set further world speed records, ratified by the FAI:
- Sub-class : E-3a (Autogyros : take-off weight less than 500 kg)
- Category : General
- Group 1 : piston engine
- Speed over a closed circuit (500km) without payload : 168.29 km/h,
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- Date of flight: 09 February 2006
- Pilot: Andrew C. KEECH (USA)
- Course/place: North Little Rock, AR (USA)
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- Sub-class : E-3a (Autogyros : take-off weight less than 500 kg)
- Category : General
- Group 1 : piston engine
- Speed over a closed circuit (1000km) without payload : 165.07 km/h,
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- Date of flight: 09 February 2006
- Pilot: Andrew C. KEECH (USA)
- Course/place: North Little Rock, AR (USA)
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- The CarterCopter fixed wing/autogyro hybrid has been unofficially flown in tests at speeds above 170 mph. The theoretical top speed for this general design exceeds 450 mph.
- In the late 1950s, the (15 tonne) Fairey Rotodyne, a gyrodyne hybrid was capable of 213 mph.
[edit] Endurance
- Autogyros are often used to herd range animals. An autogyro 'cowboy' holds the world record for total hours in the air each week [citation needed].
[edit] Distance
(as ratified by FAI)
- Sub-class E-3b (Autogyros : take-off weight 500 to 1,000 kg)
- Category : General
- Group 1 : piston engine
- Distance over a closed circuit without landing : 1 019.09 km
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- Date of flight: 09/02/2006
- Pilot: Andrew C. KEECH (USA)
- Course/place: North Little Rock, AR (USA)
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[edit] Applications
The Bensen design has also been used by hobbyists, sight-seers and scientists (for game counting). NASA is said to be exploring the use of autogyros as a future mode of "personal air transportation" for the general public.
[edit] Kits
Many autogyros are assembled from kits. Kit vendors often say that since it has few parts, hobbyists can assemble it more rapidly and correctly than most fixed-wing kit aircraft. Kits with all parts, ready to assemble, are listed for US$19,550 as of 18th July 2002. This is inexpensive for an aircraft and includes an engine.
Some people who have completed an autogyro have said that it took them about a year, working in their spare time. Estimates place most build times at 100 to 200 hours.
[edit] Warnings
Most vendors recommend that a new pilot have at least ten hours of instruction by a rated instructor in small fixed-wing aircraft, followed by at least two hours of instruction in a dual-place autogyro with an experienced instructor. An autogyro is more similar to a fixed-wing aircraft than to a helicopter.
Autogyros are relatively safe, but not foolproof. There were 19 fatal autogyro accidents reported to the FAA between 1996 and 2001, and many more serious injuries. Safety precautions, training, instrumentation, flight rules, preflight checklists, and periodic inspections and maintenance must not be neglected.
There is a slight delay between control input and aircraft response - a characteristic of inertia in the spinning rotor blades. Inexperienced pilots may be inclined to repeat or overemphasise a control input owing to a perceived lack of response. The resulting response may then be excessive and the pilot may attempt to compensate with opposing inputs, again with excessive control motion. These inputs can quickly put the aircraft into an increasing cycle of responses which may exceed the safe flying limits. This phenomenon is termed "Pilot Induced Oscillation" (PIO), and has led to loss of control crashes and fatalities. Pilot Induced Oscillation is readily corrected in a certificated autogyro operated by a trained pilot; in a Bensen-type autogyro no amount of training may be sufficient to avoid catastrophe.
In the United States, private, recreational, and commercial pilot licenses with rotorcraft category and gyroplane class rating are issued, or the rating is added to an existing license for other aircraft; holders of sport pilot licenses can also qualify to fly autogyros. Requirements include completing required training times, passing written exams, and successfully doing oral and practical tests. Sport pilot license in-flight tests can be conducted in single-seat aircraft, but a "single place only" limitation is placed on the certificate in such cases.
"Learning to fly the rotor" is a vital ingredient for safe flight in an autogyro - models and rotary kites can help the learning process, and towed gyro-gliders and boom-trainers are ideal tools for this as well as being cheap to build and fly.
[edit] See also
Hybrids
- Groen Brothers Aviation
- Gyrodyne - helicopter/fixed wing hybrids
- Fairey Rotodyne
- Carter Copter - the company recently broke the important Mu-1 barrier.
- Piasecki Aircraft Corporation - World's First Autonomous Autogyro
- Raven
- Helicopter
[edit] References
- ^ UK CAA (2005). MPD 2005-008.
[edit] External links
[edit] Technical information
- Jeff Lewis' in-depth Autogyro paper, complete with multiple diagrams. Excellent resource.
[edit] Manufacturers, etc.
Tractor configuration (engine and propeller at the front of the fuselage) (Cierva-type)
Pusher configuration (engine and propeller at the rear of the fuselage)
- Magni Gyro Austria / Hungary - Information about Gyrocopter, Autogyro, Magni Gyro (Austria)
- Rotary Air Force
- Groen Brothers Aviation
- Wallis Autogyros
- The Gyrobee
- Sport Copter
- RotorSport UK - Information about the MT-03, a modern sport autogyro
- ELA AVIACIÓN - Information about the ELA-07 and ELA-07s, modern sport autogyros
- The Hornet - Ultralight Concept. Documentation package available for download.
- Air Command International
- Magni Gyro
- GyroTec
- Autogyro Europe
- Ebnet Airsports - Autogyro - Information about the MT-03 autogyro.
[edit] Groups and societies
- Popular Rotorcraft Association (United States)
- South African Gyroplane Association
- British Rotorcraft Association
- GyroPilot, a web site for people interested in autogyros
- Popular Flying Association - the organisation which holds responsibility for inspecting UK Gyroplanes (and much more)
- Autogirototal - big collection of links
- Rotary Wing Forum - Largest and most active Autogyro discussion forum in the world
- Helicopter and Gyrocopter Links
- North West Gyroplane Club - Most active autogyro flying club in the UK. Home base for the only full time autogyro instruction in the UK.
