* The helicopter was not the first successful rotorcraft, that honor going to the "autogiro", invented by Juan de la Cierva of Spain in the 1920s. Although there was considerable enthusiasm over the concept in the 1930s, the development of helicopters during World War II ended work on "gyroplanes", as autogiros are now known, for serious aviation roles, though they have thrived in the hobbyist market, and some companies believe that the concept has unused potential. This document gives a brief history and description of the autogiro / gyroplane.
* Experiments with piloted rotary-wing machines went back to before the First World War, when the Frenchmen Paul Cornu and Louis Breguet, the Ukrainian Igor Sikorsky, and others built helicopters that at best could hop up off the ground, but were not capable of sustained controlled flight.
The first person to build a practical rotorcraft was Juan de la Cierva, who was born in Murcia, Spain, in 1895. He acquired an engineering degree and became a pioneer of Spanish aviation, working on various aircraft projects before and into the First World War. In 1919, he was considering the crash of a bomber that had stalled when he came up with the idea of a stall-proof airplane. All he had to do was mount a free-spinning rotor above the airplane, partly or completely replacing the normal fixed wings. In forward flight, the aircraft's engine and propeller would force a draft through the rotor, generating lift -- incidentally resulting in a short takeoff -- and if the engine failed, the spinning rotor would "autorotate", spinning as the machine fell to result in a soft landing. He patented the concept, calling the machine an "autogiro".
Beginning in 1920, Cierva built a series of autogiro demonstrators, beginning with the "C.1", which didn't work. The following "C.2" and "C.3" didn't work either, but his fourth try was the charm, with the "C.4" credited as performing the first recorded successful flight of a rotary-winged machine on 17 January 1923, with Gomez Spencer at the controls. The C.4 was modified from a wartime French Hanriot fighter and still had wings for flight control.
One of the problems that Cierva had encountered with his early machines was "asymmetry of lift". If a rotary-wing machine is moving forward, the rotor blade that's spinning forward generates more lift than the rotor blade that's spinning backward. The result was that the machine tended to tip over. Cierva's solution was to hinge the rotor blades to the hub, allowing them a degree of travel up-and-down and back-and-forth. Although such a simple scheme sounds like it could have been a disaster, in fact the movement of the blades compensated very well, rising as they moved forward and falling as they moved back. A rotor blade at an upward angle tended to lose lift, balancing the autogiro. He stumbled onto the idea by accident while tinkering with a rubber-band-powered model, and then fitted the hinged rotor scheme to the C.4.
There were other difficulties to work out, in particular the problem that the fixed wings of the C.4 couldn't control the flight of the aircraft at low speeds, and Cierva hadn't figured out how to obtain flight control with the rotor system yet. He continued his research with the "C.5" of 1923, and then the "C.6 / C.6A / C.6B" of 1924, which was based an Avro 504K fighter. The C.6A was the first of the series to chance a cross-country flight, on 12 December 1924.
In the fall of 1925, Cierva demonstrated the C.6A to the British military, with the British Air Ministry interested enough to order several autogiros for evaluation. They were to be built by Avro; Cierva, backed by a group of British industrialists, decided to set up his own firm, "Cierva Autogiro LTD", in the UK to focus British interest. Along with the construction of two "C.7" autogiros by Jorge Loring in Spain, Avro built a litter of "C.8" series machines with variations in configuration for evaluation. A few were also sold on the export market.
* At this point, the story becomes more complicated as Cierva obtained licensees in a number of countries. Avro stayed with the concept, working on:
A total of almost a hundred C.19, C.30, and C.40 machines was built by Avro, with some operated by the British Royal Air Force under the designations of "Rota Mark I", "Rota Mark IA", and "Rota Mark II" respectively. Some were also sold to the civil or export markets.
In the meantime, Cierva was working with various licensees, one of the most prominent being Harold Pitcairn of Pennsylvania. Pitcairn was an aviation enthusiast from the early days and had taken an interest in Cierva's autogiros, ordering a C.8 and flying it in 1928. It was the first operational rotary-wing aircraft to fly in the United States. Pitcairn's firm, the "Pitcairn-Cierva Autogiro (PCA) Company", gave him a platform to allow him to help refine the design, and soon he was flying a series of developmental aircraft -- beginning with the "PCA-1", followed by the "PCA-1A" and "PCA-1B". It was his fourth machine, the "PCA-2", that really captured public attention by a series of demonstration flights over US cities beginning in late 1931 and continuing into 1932.
The Kellett company of the USA also got into the autogiro business, building a series of "KD-1" machines along the lines of the Cierva C.30, one of which achieved notoriety for being used on an experimental mail run in Washington DC in 1939. Some sources also claim that a Kellett autogiro was taken on an Antarctic expedition by US Navy Admiral Richard Byrd in 1933.
The US Army was interested in autogiros and evaluated a number of Kellett machines from 1935 under the general designation of "YG-1", with the US Army Air Forces (USAAF) following up this effort during 1942 by obtaining a handful of "XO-60 / YO-60" autogiros for the battlefield observation role. The USAAF never put autogiros into combat, however, and though Kellett did modify some of their machines to more powerful "XR-2 / XR-3" prototypes, the company decided to get out of the business.
A number of companies all over the world also built Cierva autogiros:
* In maturity, the autogiro was a perfectly practical flying machine. Cierva had figured out how to control flight without use of fixed wings, using two innovations:
Pitcairn added a useful innovation of his own, the "prerotor", which coupled the engine to the rotor while on the ground, allowing the machine to achieve a "jump takeoff" once power was transferred back to the propeller. Cierva had already considered the idea but was using a rope pull starter to get the rotor up to speed.
The two-seat Cierva C.30 / Avro Rota Mark IA makes a good benchmark for the Cierva machines, the C.19 and C.40 being of roughly similar configuration aside from the seating arrangements. It had no wings; a "tadpole"-like tailfin that wrapped around the tail, with a tailplane tipped with auxiliary tailfins; a three-bladed rotor; and tandem open cockpits. It was powered by an Armstrong-Siddeley Civet 1 aircooled radial engine providing 104 kW (140 HP).
CIERVA C.30 / AVRO ROTA MARK IA: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ rotor diameter 11.28 meters 37 feet fuselage length 6.02 meters 19 feet 9 inches height 3.38 meters 11 feet 1 inch empty weight 555 kilograms 1,220 pounds max loaded weight 815 kilograms 1,800 pounds maximum speed 175 KPH 110 MPH / 95 KT ceiling 2,440 meters 8,000 feet range 460 kilometers 285 MI / 250 NMI _____________________ _________________ _______________________
* Although Cierva developed the autogiro into a safe and effective machine, even as the technology appeared to be ready for widespread use, events were conspiring to shoot it down. The first was the death of Cierva in the crash of a Dutch Douglas DC-2 airliner in England on 9 December 1936. The second was the flight of the first unarguably workable helicopter, the German Focke-Achgelis Fa-61, in 1938, making the autogiro seem like a half-measure and focusing work on true helicopters. The third was the outbreak of World War II in the next year, 1939, with industrial development focusing on weapons needed in the conflict.
Autogiros saw very limited use during the war. Avro Rotas were used by the RAF for radar calibration duties, with an autogiro stationed near a radar station to provide a flying "target" for radar observation. The Japanese pressed their Kayaba machines into service late in the war as antisubmarine warfare platforms, carrying two depth-charges each, making them likely the only autogiros to ever carry a combat load. Some Soviet TsAGI autogiros were used in the observation role during the war with the Germans.
However, by the end of the conflict, helicopter development was going full steam and Cierva's autogiro had become a curiosity at best. The Cierva company survived his death, under the direction of Dr. J.A.J. Bennett, but focused on development of helicopters. It would develop one of the first British-designed helicopters, which would become the "Sanders-Roe Skeeter" after the Cierva firm was absorbed by the Sanders-Roe company. Still, Cierva had designed the world's first practical rotorcraft, and had solved a number of problems needed for helicopter development. He would not be forgotten, and work would continue, if at a low and intermittent level on his autogiros -- or "gyroplanes" as they became known in later days to avoid the Cierva trademark name.BACK_TO_TOP
* There was some development of Cierva's ideas during the war, the most prominent being the German Focke-Achgelis "Fa-330 Bachstelze (Wagtail)". It was what as known as a "rotor kite" or "gyrokite" or "gyroglider", which had to be towed into the air since it lacked an engine. It looked a little like an ultralight helicopter, with a metal-tube frame, a standard aircraft tail assembly, and the pilot sitting exposed on a frame seat under a rotor. It had a three-bladed rotor with a diameter of 8.5 meters / 28 feet (7.3 meters / 24 feet in early production), and a total weight of about 72 kilograms (160 pounds).
The Fa-330 was intended to be towed by a submarine to spot targets. A few hundred were built, but it appears they were not put to much use, since German U-boat captains were reluctant to do anything that kept them from diving in a hurry to escape Allied destroyers and sub-hunter aircraft. The Fa-330 was mostly a curiosity in hindsight.
The British developed a gyrokite along much the same lines, developed by an Austrian named Raoul Hafner and called the "Rotachute". It was intended to drop paratroops or agents, but it never went into production. The British then even experimented with light ground vehicles fitted with a rotor for airdropping, but nothing came of that work, either. However, the Fa-330 and the Rotachute would contribute to keeping the gyroplane alive over the longer term.
* Igor Bensen had been born to Russian parents in 1917, with his family fleeing the Russian Civil War a few years later. He went to the University of Louvain in Belgium to work towards an engineering degree, obtaining a scholarship for further studies at Stevens Institute in the United States in 1937. He graduated in 1940 and was hired by the General Electric company, which at the time was interested in helicopters and put him to work on the technology.
In 1943, Bensen got the opportunity to fly a Kellett XR-3, becoming a skilled gyroplane pilot. When he found out that the US Army Air Forces had obtained some Fa-330 rotor kites and a Hafner Rotachute, he was intrigued enough to lobby the military for use of the Rotachute -- which he flew himself, though the military had specified that it not be flown. Bensen's investigation led to development of his first gyrokite, the Bensen "B-1". It was of mixed wood-metal construction and abandoned the three-blade flapping rotor system of the Rotachute in favor of a "teetering rotor", a two-blade assembly fixed across its length that tilted to one side or another on the rotor hub to deal with asymmetric lift. The B-1 crashed, leading to the all-metal "B-2", which was the basis for a "GE Gyro-Glider" that never reached the market.
In 1951, Bensen joined Kaman Aircraft Company to work on helicopters, but after two years he dropped out to form the "Bensen Aircraft Corporation" in Raleigh, North Carolina, borrowing money from his brother to set up shop. In 1953 he introduced his "B-5" gyro-glider. It could be bought complete, or as the "B-6" in kit form, or just as plans. It led in turn by the summer of 1955 to the "B-7" gyro-glider, followed before the end of the year with the "B-7M" -- "M" for "motorized" of course -- powered by a 31 kW (42 HP) Nelson two-stroke piston engine driving a pusher prop.
Bensen had suffered a forced but safe landing in the B-7M and so did some minor redesign, resulting in the definitive "B-8" gyro-glider and "B-8M" gyroplane -- or "gyrocopter" as he trademarked it. It was in production by 1957, being sold complete, in kit form, or as plans. It would prove a popular ultralight aircraft. In 1962, Bensen helped found the Popular Rotorcraft Association (PRA) to help promote use of ultralight rotorcraft.
The B-8M was built of aluminum tubing, with a two-blade teetering rotor and an overhead cyclic control stick; the rotor had fixed pitch, which would be common in machines of its class. The B-8M was powered by a 54 kW (72 HP) McCulloch two-stroke piston engine and could take off in about 15 meters (50 feet), and land almost vertically through autorotation. The B-8M could taxi fairly well and could be in principle driven on city streets with the rotor tied fore and aft -- though despite the existence of publicity shots showing this being done, it seems likely that local police tended to have an opinion on whether it was a good idea or not.
BENSEN B-8M GYROCOPTER: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ rotor diameter 6.10 meters 50 feet fuselage length 3.45 meters 11 feet 4 inches height 1.9 meters 6 feet 3 inches empty weight 112 kilograms 250 pounds max loaded weight 225 kilograms 500 pounds maximum speed 135 KPH 85 MPH / 75 KT ceiling 5,000 meters 16,500 feet range 160 kilometers 100 MI / 85 NMI endurance 90 minutes _____________________ _________________ _______________________
A pontoon-equipped variant, the "B-8MW", was also available. A "B-8V", powered by a Volkswagen flat-four aircooled engine, was offered as well, presumably to appeal to kitbuilders who had their hands on a VW engine. A B-8M and a B-8 were acquired by the US Air Force in 1968 under the designation of "X-25A" and "X-25B" respectively to investigate, ironically, the old Rotachute concept of a controlled parachute, or what the service called the "Discretionary Descent Vehicle (DDV)".
Igor Bensen was quite the tinkerer and obtaining a full and accurate list of every flying machine he ever built would be difficult, but a short list of some of the highlights is interesting enough:
* The Bensen Aircraft Corporation finally closed its doors in 1986 after over 30 years of existence, Bensen dying in 2000. The reasons for the company's closure are unclear. There were those who claim the teeter-bar rotor configuration is dangerously unstable; advocates reply that the handling of a gyroplane isn't that unpleasant, it's just different from that of a fixed-wing aircraft. Abrupt changes in pitch can "unload" the rotor, with the machine then dropping, resulting in oscillations or even a deadly somersault -- if the pilot fights it, instead of allowing the machine to smoothly recover.
The accident rate of the Bensen gyrocopter doesn't appear to have been particularly high by the standards of ultralight aircraft -- though ultralight aircraft are not in general recommended to the faint-hearted. However, the 1980s brought in an age of litigation that helped suppress US private aircraft manufacturers and likely didn't help Bensen's cause.
The company's exit from the marketplace hardly killed off the gyroplane, and in fact many other manufacturers were inspired by Bensen to build gyroplanes of their own. American enthusiasts included as Ken Brock -- who invented the word "gyroplane" in 1970 when Bensen got stuffy about his trademark; Martin Hollmann; and Bill Parsons. Overseas enthusiasts included Jukka Tervmaki of Finland; Vittorio Magni of Italy; Jim Montgomerie of Scotland; and Wing Commander Kenneth H. Wallis of England.
Wallis would become a particular prominent gyroplane enthusiast, setting a series of world records for the class. While some of his machines had a good resemblance to the Bensen B-8M, in development his machines were much more sophisticated in appearance, the best example being the Wallis "WA-116", which had a real fuselage with an open cockpit and an improved rotor system. The prototype performed its first flight in 1961.
In 1967 a WA-116, LITTLE NELLIE, was used in the Sean Connery James Bond move YOU ONLY LIVE TWICE. The gyroplane was fitted with an impressively dubious array of lethal armament -- including heat-seeking missiles that could do a U-turn after being fired forward and attack a pursuer, an impossibility at the time. Wallis did the honors for piloting the machine in the movie. The Wallis designs have proven an inspiration for gyroplane kit makers elsewhere. Bensen-style designs continue to be built as well; the plans for one such, the "Gyrobee", are available free on the internet to anyone who wants to build one.BACK_TO_TOP
* The Bensen gyrocopter and its descendants kept the gyroplane alive, but all efforts to develop more capable machines in the meantime failed. Attempts to revive Pitcairn and Kellett designs went nowhere. However, an attempt to build a large gyroplane, a machine much larger and more capable than anything Cierva ever seriously thought of building, proved impressive, if still a failure in the end.
The Fairey "Rotodyne" was the brainchild of the Cierva company's Dr. Bennett and Captain A. Graham Forsyth. It was a "covertiplane" or "gyrodyne", something like a small airliner with a capacity of 50 passengers, clamshell doors in the rear for cargo loading, twin Napier Eland turboprop engines providing 2,090 kW (2,800 HP) each, stubby wings, twin tailfins, and a four-blade rotor. At takeoff and landing, compressors driven by the turboprops drove air jets out the wingtips of the rotor, with the two compressors each driving two blades of the rotor to provide redundancy, but in forward flight the rotor simply spun freely, as it did in a gyroplane.
Initial work on the concept had been performed from the late 1940s using a series of relatively small "Gyrodyne" demonstrators, leading to the initial flight of the full-scale Rotodyne on 6 November 1957. It was an impressive machine, with a top speed of 320 KPH (200 MPH), and got a lot of press at the time.
FAIREY ROTODYNE: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ rotor diameter 27.43 meters 90 feet wingspan 14.17 meters 46 feet 4 inches fuselage length 17.88 meters 58 feet 7 inches height 6.76 meters 22 feet 1 inch empty weight 10,000 kilograms 22,000 pounds max loaded weight 15,000 kilograms 33,000 pounds cruise speed 300 KPH 185 MPH / 160 KT ceiling 4,000 meters 12,200 feet range 725 kilometers 450 MI / 390 NMI _____________________ _________________ _______________________
A license agreement was signed with Kaman Helicopters of the US in 1958. Fairey was swallowed up by Westland the next year, but work was still proceeding on a 75-passenger stretched version powered by twin Rolls-Royce Tyne turboprops. Then the program abruptly ran out steam, with the prototype grounded in 1962 and then scrapped.
The reasons for the cancellation are still argued. The Rotodyne was very noisy, a problem commonly associated with tipjet rotorcraft, but work was underway to deal with the noise problem. The main problem seems to have been that prospective commercial and military buyers didn't materialize as expected, and so the additional development costs for the stretched capable production variant were hard to justify. Some admirers of the Rotodyne suggest that more might have been made of it if the British government had been more enthusiastic about backing the project; that's also arguable, but it was an era when the British government seemed to take a perverse pleasure in killing off promising aerospace programs.
* The USSR also built a gyrodyne, the Kamov "Ka-22", in the same class as the Rotodyne, though of considerably different and arguably less elegant appearance. The Soviets called it the "Vintokyrlya (Screw Wing)", while NATO codenamed it "Hoop". It featured a turboprop on each wingtip, driving a forward propeller in flight and a rotor for takeoff; fixed landing gear; and a high-perched canopy to give the flight crew a good field of view. The boxy fuselage was apparently derived from that of the Antonov An-8 turboprop cargolifter.
The project was initiated in late 1954, before the Rotodyne had been completed. The early date shows that the Ka-22 was not a copy of the Rotodyne, as some sources have hinted -- oblivious to the fact that while the two machines were comparable in many ways, they were also clearly different at a detail level. Initial untethered flight of the Ka-22 prototype, fitted with Kuznetsov TV-2VK turboprops, was on 15 August 1959; there were serious control problems, but they were generally resolved in the flight trials program, with a order for three preproduction machines with D-25VK turboprops placed in 1960. The machine was displayed publicly at the Tushino air show near Moscow on 9 July 1961, causing something of a sensation.
The Ka-22 set a number of records for rotorcraft. One of the four Ka-22s crashed on 28 August 1962, killing all seven crew, but the accident was traced to a manufacturing defect, not a design problem, and the program continued up to 12 August 1964, when another Ka-22 crashed, three of the crew surviving and two being killed. Enthusiasm for further work on the machine faded out; it might well have been made into something, but it was complicated, the engine and drive system proving a particular nuisance, and the Mil Mi-6 Hook heavy-lift helicopter seemed to do the job as a heavy-lift rotorcraft. The program was canceled and advanced derivatives such as the "Ka-34" and "Ka-35" never went beyond the model stage.BACK_TO_TOP
* There were other, less spectacular efforts to push gyroplane technology in the 1960s. A pair of two-seat autogiros for the commercial market, the McCulloch J-2 and the Umbaugh U-18A, were designed and received FAA certification, but less than a hundred of each were sold. For the rest of the century, gyroplanes would remain a hobbyist technology, with a number of companies selling them into that market, usually as kits.
While gyroplanes remain alive and well in the domain of hobbyists, so far they have run into a "glass ceiling" for use in general and commercial aviation. Groen Brothers Aviation (GBA) of Salt Lake City, Utah, has been working hard to break through that glass ceiling. For the last few years the company has been promoting the tidy "Hawk 4T" gyroplane, which is definitely in a league above the Bensen B-8M.
The Hawk 4T is a four-seat gyroplane with a two-bladed rotor, is powered by a Rolls-Royce 250 B17C turboshaft engine providing 336 kW (450 HP), and has a payload capacity of 545 kilograms (1,200 pounds). It follows a "Hawk 4" piston-powered demonstrator of similar configuration. The Hawk 4T's engine can spin up the rotor before takeoff, allowing the aircraft to lift off near vertically, and it can also land near vertically by autorotation.
GBA HAWK 4T: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ rotor diameter 12.8 meters 42 feet fuselage length 7.3 meters 24 feet height 4.12 meters 13 feet 6 inches max loaded weight 1,590 kilograms 3,500 pounds cruise speed 210 KPH 132 MPH / 115 KT ceiling 4,900 meters 16,000 feet range 590 kilometers 365 MI / 320 NMI _____________________ _________________ _______________________
GBA believes the Hawk 4T has an edge because it provides helicopter-like utility at lower cost: gyroplanes can't do some things that helicopters can, in particular hover, but they are in principle cheaper, lighter, simpler, and have greater range and speed. The company feels that other attempts to build gyroplanes for the general and commercial market focused on machines that were too small to be particularly useful. GBA claims the Hawk 4T combines capability with economy, and is targeting civilian applications, particularly in agriculture. GBA realizes that the track record of attempts to revive the gyroplane is not encouraging, and a company official admitted: "We still have to break the credibility barrier."
* While GBA is focusing on the Hawk 4T, the company also produced a neat two-place kit-built gyroplane, the "Sparrowhawk", which is sold through the associated "American Autogyros" company. It is powered by a piston engine, has an enclosed side-by-side seating cockpit, and has proven popular, with enthusiasts making occasional appearances in Sparrowhawks at airshows across the USA.
GBA has offered other schemes. The company has promoted a gyroplane based on a remodeled Cessna C337 Skymaster, with its rear engine removed, front engine replaced by a Rolls-Royce 250 turboprop, rotor added, wings clipped off, and tail flipped over to ensure rotor clearance. It would have a payload capacity of 900 kilograms (2,000 pounds). A demonstrator, the "Revcon 6A", was flown in 2000.
In addition, the company has promoted concepts for large gyrodynes -- or as GBA refers to them, "heliplanes" -- along the lines of the Fairey Rotodyne, with imagery envisioning conversions of twin-turboprop light cargolifters or even a Lockheed-Martin C-130 Hercules four-turboprop cargolifter, named the "Monsoon", to be used for firefighting. The big Groen gyrodynes are clearly just intriguing paper concepts, though the company did work on the design of a combat search and rescue gyroplane for the US Defense Advanced Research Projects Agency (DARPA).
* Another gyroplane designer, Carter Aviation of Wichita Falls, Texas, has been testing a two-seat prototype of the "CarterCopter". The company promotes it as a "hybrid" air vehicle, though on inspection it's of generally conventional gyroplane arrangement, with a two-bladed rotor and a pusher prop. It does, however, have some innovative features. The rotor features depleted-uranium tips; at cruise speed, the rotor is feathered to prevent its drag from slowing down the aircraft, with the heavy tips ensuring that the rotor spin is smooth and continuous. Rotor controllability is aided by a tilting rotor mast.
Carter Aviation claims a four-seat production CarterCopter "Personal Air Vehicle (PAV) will be cheaper, simpler, and have better performance than an equivalent helicopter, with the maximum speed limit being seen as up to 800 KPH (500 MPH). The CarterCopter can perform vertical jump takeoffs and vertical landings, with an advanced digital flight-control system handling all the details, though of course it can't really hover.
So far, there has been no commitment to production, though Carter Aviation has been talking about a two-seater kitbuilt, and has been working with DARPA on a "flying car" scheme. Carter Aviation has also pushed designs for a large gyroplane for civil and military applications, roughly along the lines of the Fairey Gyrodyne.
Both the Groen Brothers and Carter Aviation are trying to make a go of a technology that has persistently refused to take off in a big way, but it would be hard-hearted to fail to wish them the best of luck. And even if the more extreme visions of the Groen Brothers never fly -- they're certainly vastly entertaining to look at.BACK_TO_TOP
* A California company named SkyWindPower floated an idea for an unusual application of gyrokites, flying four-rotor systems on an "H"-configuration frame up into the jet stream to generate electric power. It seems like something of a long shot but it's certainly an intriguing idea.
The proliferation of terms in this topic -- autogiros, autogyros, gyrocopters, gyroplanes, helikites, rotorkites, gyrokites, gyrodynes, rotodynes, heliplanes -- is very confusing. I've chosen to focus on the terms "gyrokite", "gyroplane" and "gyrodyne" since as far as I can see none are trademarked, though gyroplane is a relatively modern term. Trying to trace down the precise history of different types of gyroplanes is also very confusing, and I decided to give a quick mention of most types and focus on a few of the more representative or interesting machines. Most of the data on the more obscure gyroplanes is so sketchy as to be untrustworthy.
* Sources include:
This document owes a good deal to a portion of "From Autogyro To Gyroplane: 1923:2003" by Dr. Bruce Charnov, which was reprinted on the Groen brothers website, a useful source of details on GBA projects.
* Revision history:
v1.0.0 / 01 dec 06 v1.0.1 / 01 dec 08 / Review & polish. v1.0.2 / 01 nov 10 / Review & polish. v1.1.0 / 01 apr 11 / Fixed-pitch rotors, CarterCopter. v1.1.1 / 01 mar 13 / Review & polish.BACK_TO_TOP