Begun as a promising aeronautical development in the 1920s but flourishing for little more than a decade before almost disappearing completely, the autogyro was the victim of what could rightly be described as a false start.
In my article “Birth of the Autogyro” (page 18, August Aviation News), I described the rotorcraft’s beginnings, and how British and American aircraft manufacturers experimented with and developed a promising concept, only to be stymied by the simultaneous arrival of WWII and of the gyrocopter’s more versatile counterpart, the helicopter.
Prior to the helicopter, the autogyro had a lot going for it. It could land in confined areas, it required less runway than fixed wing aircraft for takeoff and it was largely unaffected by strong winds and turbulence.
But one feature which detracted from the autogyro becoming a roaring success prewar was its cost. Development of the autogyro had largely been by trial and error. A new idea was tried and, if it proved to be not as successful as hoped for, or worse still, the aircraft crashed and was destroyed, it was back to the drawing board.
The autogyro was in its infancy and this was an expensive method of development. Pitcairn’s PA-36, the first autogyro with an all-metal airframe, is reputed to have cost the company $US3m to develop — a lot of money in 1936 — and only two were completed. Costs needed to be recovered and this reflected in the price tag of the finished product.
Autogyros, which more often than not had just two or three seats, were almost three times the cost of most comparable sized light aeroplanes, a factor which deterred all but the most affluent buyer and was reflected in dismal private sales.
But where there is a will there is a way. Following WWII a Russian migrant brought about radical change to the design with a simple flying machine he named the gyrocopter.
Igor Bensen was born in 1917 at Rostav, Russia, but four years later at the height of the Russian revolution he escaped with his mother to Czechoslovakia. There they were reunited with his father who had earlier been sent there as an agricultural advisor.
At the age of 17 Bensen, who had already shown interest in rotary wing flying machines, having built an electric-powered contraption which flapped around the family’s kitchen floor trying to fly, travelled to Belgium where he began studying engineering at Louvain University. Three years later, however, after being offered a scholarship to study at the Stevens Institute, New Jersey, he moved to the USA, graduating in 1940 with a degree in mechanical engineering.
His first employer was General Electric where he worked on air conditioning design and developed over 40 inventions, including a starter for fluorescent lighting. He later moved to the company’s Bridgeport, Connecticut, facility where he undertook R&D work on the electron microscope.
While working at General Electric, Bensen was contacted by another Russian rotorcraft pioneer, Igor Sikorsky.
Sikorsky had known the Bensen family back in Russia and offered the younger Igor a position on his helicopter design team, but Bensen was unable to accept as he had still not received American citizenship.
When he finally did become a US citizen in 1944 and announced to his employer he was resigning to join the Sikorsky team, GE responded by placing him in charge of its own helicopter developments which had been spurred on by Germany’s triumph with its Focke-Achgelis 61.
Hanna Reitch’s successful demonstration of the German helicopter at a Berlin sports arena had created a worldwide frenzy in helicopter research, effectively killing off any further autogyro experimentation. Like many other companies which foresaw the rewards to be had in developing a successful helicopter, GE was promptly on the bandwagon and Igor Bensen was to lead the charge.
Bensen flew the world’s first jet-powered helicopter when an Austrian-built machine, captured by the American army towards the end of the war, was returned to the USA for evaluation. Bensen then went on to design a helicopter powered by GE gas turbine engines which pumped compressed air through the rotor blade hollow centres and out the tips. This aircraft was built for General Electric by the Kellett Autogiro Company which, prior to the war, had designed and built several successful autogyros.
Bensen’s time with General Electric saw him experimenting with plastic rotor blades, but his employer’s loss of interest in autogyro development proved fortuitous for this Russian-born engineer. Able to requisition the company’s two autogyros — a Kellett KD-1B which had once carried mail from Philadelphia’s post office roof and an experimental Kellett XR-3 which now lay idle — he was able to fly them whenever he desired.
He was thus able to become an extremely accomplished autogyro pilot which led to experimentation with improvements to the autogyros’ handling qualities. In due course he designed a cyclic control system for the XR-3 which permitted it to be flown hands-off.
By the early 1950s Sikorsky had proved itself to be at the forefront of helicopter involvement and General Electric chose to abandon further rotary wing development. As a result, Igor Bensen went to work for Kaman Helicopters for a short while before resigning and, borrowing finance from a sympathetic brother, set up his own Bensen Aircraft Corporation in 1953 at Raleigh, North Carolina.
From the outset Igor Bensen’s goal was to develop an autogyro which was simple to construct from everyday materials. It followed naturally that the craft would also be inexpensive to build and radically different in design from the Ciervas, Kelletts and Pitcairns of two decades earlier.
At his North Carolina facility, Bensen began experimenting with numerous designs, developing what can best be described as the most basic of rotary wing craft. These experimental machines were unpowered, towed behind vehicles to become airborne, and were referred to by Bensen as gyrogliders.
By 1955 Igor Bensen was working on his seventh design, simply referred to as the Model B-7 Gyroglider and his first machine constructed entirely from aluminium. The B-7 design was a stroke of genius, for not only did it utilise recently released Reynolds Aluminium Company “Do-it-Yourself” extruded aluminium shapes, its design was so simple it could be built by the average hobbyist in a home workshop. And to prove this point Bensen built the first B-7 using only basic hand tools.
Flight trials of the B-7 proved encouraging, and it was put into production in kit form. A B-7 rotor and mast were added to a 12ft aluminium boat and this, following trials, was marketed as the B-8 B Gyroboat. Income from sales of these and B-7 gyroglider kits provided the necessary finance for the Bensen Aircraft Corporation to undertake further development, and the B-7 was trialled on discarded Republic Seabee floats which were later redesigned, enabling them to be built at home from plywood. A B-7 Gyroglider fitted with these floats was known as the B-7 W Hydroglider.
Powered autogyros
Conversion of the B-7 Gyroglider to a powered autogyro was a natural progression, adding a pair of coupled 20hp Chris-Craft outboard engines. Flight trials of the powered B-7, which remained tethered behind a vehicle, were encouraging, although problems were experienced with engine control and the twin-engine concept was abandoned.
With the B-7 re-engined with a 42hp Nelson four-cylinder unit designed for the military, a breakthrough came on 6 December 1955 when, in front of a group of sceptical CAA inspectors (these were pre-FAA times), Igor Bensen successfully demonstrated the B-7M Gyrocopter in untethered powered flight. Not only were CAA inspectors impressed by Bensen’s Gyrocopter but also state officials. The North Carolina state government’s Department of Industrial Development arranged a sponsored air display to demonstrate Bensen’s Gyroglider and Gyrocopter to the public and press.
As promising as trials with this engine may have been, Bensen soon found himself looking for an alternative powerplant. The Nelson engine was prone to overheating and required constant cylinder barrel changes to prevent seizures — a costly and entirely unsatisfactory situation if the aircraft were to be marketed commercially as Igor Bensen intended.
Ultimately the McCulloch four-cylinder two-stroke engine was chosen and became the standard powerplant for Bensen gyrocopters for several decades, until more efficient engines such as Rotax came on the market.
Following success with the B-7 Gyroglider, Bensen Aircraft Corporation established a series of dealerships throughout the USA to market the machine, supported by Bensen’s setting up a flight training facility to teach dealers and B-7 buyers the art of gyroglider flying.
Trainee pilots first learned to “fly” a static point trainer which generated instinctive reflexes in the student who then progressed onto an outdoor point trainer. This was essentially a fully-built gyroglider mounted on a universal joint under its centre of gravity, allowing the aircraft to be rolled in all directions in response to rotor tilt.
Finally the student moved onto what was known as the training trailer, a B-7 attached through a universal joint to a vehicle by a rigid boom to allow the gyroplane to become airborne behind the moving vehicle but at the same time limiting the student’s movements.
Should the student pilot make a mistake, it was a simple matter of the vehicle driver slowing down, resulting in the gyro landing before the pilot’s action could result in a crash.
The fourth training phase was to replace the rigid tow boom with a rope.
During the late 1950s and into the 1960s, many dealerships and rotorcraft clubs used these methods to train pilots.
All early Bensen designs were controlled with an overhead control stick. This was not particularly popular with conventional pilots who were converting on the gyroplane, as its responses were the reverse of fixed-wing aircraft controls. As a result, Bensen developed a modification which allowed the use of both overhead and conventional control sticks and could be retrofitted to existing craft. Later this was dispensed with and conventional controls were incorporated into the Bensen design.
The B-7M evolved into the B-8M, built from square section tube and incorporating other refinements. The Bensen Aircraft Corporation went on to develop many variations of the B-7M and B-8M Gyrocopters, including one with a fully enclosed cockpit, a ski-equipped variant and several with pre-rotators which shortened the takeoff run considerably.
Several multi-engine versions were produced, including, incredibly, one fitted with six McCulloch Mc75 go-cart engines, each producing just 9hp.
For almost three decades Igor Bensen’s Gyrocopter dominated the rotorcraft market, becoming the most prolific amateur-built aircraft of its time. Bensen was a man who always stood behind his product and, in order to better support his gyroplane and builders of his kits, established the Popular Rotorcraft Association.
But as the 1980s approached, the company failed to introduce new designs. Interest in Bensen’s products began to diminish as a number of more advanced designs, taking advantage of new ultralight regulations and recently developed two-stroke engines, began to emerge on the marketplace.
By 1987 the Bensen Aircraft Corporation was in dire straits and the decision to close operations was finalised the following year. The company that reintroduced the autogyro after WWII was no more.
Other developments
Postwar development of the gyroplane had, however, not been the sole preserve of Igor Bensen. In the UK Wg Cdr Ken Wallis became famous in the field of gyrocopter development and one of his more than 20 craft, Little Nellie, appeared in the 1966 James Bond film “You Only Live Twice”.
Even here in New Zealand the autogyro glider had its early followers, with Dick Brett experimenting with rotary flight at Gisborne as early as 1954. Dick’s tubular steel frame craft was constructed to his own specifications, but it is not recorded what success, if any, he achieved with New Zealand’s first indigenous rotorcraft.
He did, however, receive the blessing of the Civil Aviation Administration with its director E.A. Gibson, whose progressive attitude had been the catalyst behind the rapidly developing agricultural aviation industry, congratulating him on his achievements.
In a letter to Dick, “Gibby” Gibson wrote that it was the wish of the CAA that every avenue of study and investigation into all fields of aeronautics should be supported, and he offered to provide any technical assistance the administration had at its disposal. Dick Brett was also issued with the country’s first helicopter licence which authorised him to legally operate his autogyro glider.
A decade after Dick Brett’s autogyro trials, Auckland brothers Ernie and Arthur Everson built an autogyro glider of their own design, and after trials with the craft towed behind a car along Muriwai beach fitted it with a small engine. Today the Everson brothers’ gyrocopter is displayed at MOTAT.
By the early 1960s, examples of Bensen’s B-7 Gyroglider were beginning to emerge here too, and in the decades that followed many Bensen rotorcraft were built. The New Zealand Rotorcraft Association was formed by an enthusiastic group to foster the sports development, but the Department of Civil Aviation proved to be a stumbling block. Having experienced many changes in its administration over the years, the aviation authority was less enthusiastic toward recreational rotorcraft than it had been at the outset and refused to permit the operation of two-place autogyros for flight training purposes.
Despite gyrocopters having featured in several fatal accidents, some of which were attributable to inexperience, the DCA steadfastly refused to approve the use of dual-seat training craft. It appeared that the authorities were willing to allow gyroplane operators to learn by trial and error rather than through a structured training regime.
In 1983 gyrocopter owner Ross Trebilco, a Waikato farmer, took matters into his own hands. Importing a two-place gyroglider from Australia, he established a flight training school on Matamata aerodrome and engaged an experienced Australian rotorcraft instructor to train students.
The first six-day course, which began on 29 September that year, was fully booked and another was due to begin the following month. However, the Civil Aviation Division of the Ministry of Transport, having got wind of the school, closed down the operation prior to the second course, dashing the hopes of many prospective gyrocopter pilots.
Almost another decade passed before the authorities warmed to the idea that legalised flight training could improve the gyrocopter’s safety record. In an interview with New Zealand Rotorcraft Association president Richard Martin in 1991 he informed this writer that “talks with Air Transport Department personnel in recent months regarding flight training had been fruitful. We are hopeful of putting a rotorcraft training programme into operation later this year.”
Since that time local interest in rotorcraft has increased significantly, to the stage where a number of commercial flight training operators exist. Rotorcraft design continues to evolve and today the acceptance of these once much maligned flying machines, developed and first flown by Spaniard Juan de la Cierva more than 90 years ago, continues to advance at a healthy rate.
- Report by Murray E Kirkus with photographs from his collection.