v1.0.0 / 01 dec 06 / greg goebel / public domain
* 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 moving forward generates more lift than the rotor blade that's moving 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, fitting 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 in the story becomes more complicated as Cierva obtained licencees in a number of countries. Avro stayed with the concept, working on the "C.9", which was the first autogiro to be built from the ground up instead of being based on an existing aircraft; a floatplane conversion of the C.9 called the "Hydrogiro"; the "C.17" series; the "C.19" series, the first real production machine; the two-seat "C.30" series; and the side-by-side seating "C.40" series. A total of almost a hundred C.19, C.30, and C.40 machines were 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 Air Forces (USAAF) were interested in autogiros and evaluated a number of Kellett machines from 1935 under the general designation of "YG-1", 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.
Plenty of other 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. The first was what is now called "cyclic pitch control", in which a set of linkages were used to change the pitch of the blades as they spun around. For example, cyclic pitch control could give a blade a high angle of attack as it moved forward to increase lift, and a low angle of attack as it moved backward, causing the aircraft to shift sideways. Other pitch configurations could be used to allow the autogiro to move forward. The second was what is now known as "collective" control, in which the pitch of all the blades were adjusted equally, with a strong pitch useful for takeoffs and landings and a shallow pitch for forward flight. The same ideas were developed at the same time by Marquis Raul Pateras Pescara, an Argentine working in Europe, and it is unclear if Cierva invented them, but he was certainly the first to incorporate them into a successful flying machine.
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 that ended in
auxiliary tailfins; a three-bladed rotor; and tandem open cockpits. It was
powered by an Armstrong-Siddeley Civet 1 aircooled radial with 104 kW (140
HP).
CIERVA C.30 / AVRO ROTA MARK IA:
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spec metric english
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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
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* 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 flying from near a radar station to provide a "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 ever to 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 company 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.
* 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 that tilted to one side or another 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, with the powered "B-7M" -- "M" for "motorized" of course -- with a 31 kW (42 HP) Nelson two-stroke piston engine driving a pusher prop following before the end of the year.
Bensen had suffered a forced but safe landing in the B-7M and did some minor resdesign, resulting in the definitive "B-8" gyro-glider and "B-8M" gryoplane -- 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 teeter rotor and an
overhead cyclic control stick. It 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 this
was a good idea or not.
BENSEN B-8M GYROCOPTER:
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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
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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 very 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. The reasons for the company's closure are unclear; there were those who claimed the teeter-bar rotor configuration was dangerously unstable, though the accident rate of the gyrocopter doesn't appear to have been particularly high by the standards of ultralight aircraft, which are not in general vehicles 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 type. While some of his gyroplanes 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.
* 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:
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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 licence agreement was signed with Kaman Helicopters of the US in 1958.
Fairey ended up being 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 just 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 is 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-12 turboprop cargolifter.
The project was initiated in late 1954, before the Rotodyne had been completed and showing 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 cancelled and advanced derivatives such as the "Ka-34" and "Ka-35" never went beyond the model stage.
* 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. As with most modern
gyroplanes, 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:
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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 Sparrohawks at airshows across the USA.
GBA has other schemes in the works. 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 for the moment, though the company has worked on the design of a combat search and rescue gyroplane for the US Defense Advanced Research Projects Agency. What can be made of GBA's efforts remains to be seen, but it would be hard-hearted not to wish them luck.
* A California company has been floating an idea for an interesting 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 have chosen to focus on the terms "gyrokite", "gyroplane" and "gyrodyne" since as far as I can see neither is 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 completely 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.
