v1.0.1 / 01 aug 02 / greg goebel / public domain
* At the dawn of powered flight, aviation pioneers believed that rotary-wing aircraft were right around the corner. In fact, while fixed-wing aircraft were quickly refined and improved, it wasn't until the mid-1930s that the helicopter began to emerge as a practical flying machine. This document outlines the early history of the helicopter, up to Igor Sikorsky's early production machines.
* The basic idea of a helicopter, flight through rotating horizontal wings or "rotors", goes back at least 1,500 years, through a simple invention known as the "Chinese top" that still survives today in different forms. This is a toy with a rotor blade mounted on a stick, and spinning the stick between the palms of the hands or by pulling a string wound around it causes it to soar into the air.
The toy eventually made its way from China to Europe, where it appeared in paintings dating as far back as 1463. Not long after that, in 1483, Leonardo da Vinci illustrated a more sophisticated "rotary-wing" toy in his famous notebooks. However, building a rotary-wing aircraft that was any more than a toy was beyond the technology of the time, and remained so for centuries.
In 1784, two Frenchmen, the naturalist Launoy and the artisan Bienvenu, demonstrated a rotary-wing toy that improved on the Chinese top. Their device consisted of a shaft with rotors on each end, with a string under tension that could be wound around the shaft. Once wound up, the toy then flew into the sky.
Although this device was still a toy, Launoy and Bienvenu had moved a significant step beyond the Chinese top, since their device was self-powered. It also addressed one of the major design considerations of a self-powered rotary-wing vehicle: torque. When a rotary-wing aircraft spins its rotor in one direction, the machine itself tends to spin in the other. The rotors of Launoy and Bienvenu's toy spun in opposite directions, or "contrarotated", cancelling out torque. The two rotors were mounted on the same shaft, a configuration now known as "coaxial".
A young Englishman named Sir George Cayley published a design for a similar toy in 1809 that could be put together from cheap and common materials, using feathers for rotor blades, for example. In the 1840s, Cayley began to consider designs of larger rotary-wing aircraft, drawing a machine with two contrarotating rotors, each on one side of the aircraft. However, Cayley never tried to actually build his machine, as he lacked a practical powerplant.
In the 1860s, a Frenchman named Viscount Gustave de Ponton d'Amecourt experimented with small flying coaxial rotary-wing aircraft models. D'Amecourt's ingenious and competent models used springs for power, and he even designed one that ran on steam power, though that one didn't get off the ground. He named his machines "helicopteres", after the Greek phrase for "spiraling wing".
In the 1870s, another Frenchman, Alphonse Penaud, devised helicopters and fixed-wing aircraft toys powered by wound-up rubber bands, a scheme that is still used for flying toys. Some of Penaud's models flew elegantly, but he was unable to find a power source adequate for larger flying machines. Penaud, frustrated and ridiculed, suffered more than he could bear, and shot himself at age 30.
* The lack of an engine with a sufficiently high power-to-weight ratio held back development of a passenger-carrying helicopter, and indeed of all large heavier-than-air flying machines. The American inventor Thomas Alva Edison tried to develop a helicopter built around a guncotton-powered engine in the early 1880s, but after an explosion that singed him and badly burned one of his staff, he gave it up, though he expressed confidence that the concept would ultimately be made to work.
In 1886, the French writer Jules Verne published a novel titled ROBUR THE CONQUERER or THE CLIPPER OF THE CLOUDS, in which the title character possessed a great flying ship, named the ALBATROSS, that flew through the air on a forest of rotors. Robur used the ALBATROSS to cruise around the world and carry out attacks on different nations. The ALBATROSS was far from a practical flying machine, but the book helped popularize the idea of manned rotary-wing flight.
* The introduction of a practical internal combustion engine by Niklaus Otto of Germany in 1876 opened the door to heavier-than-air flight. The first flight of a man-carrying heavier-than-air aircraft took place in December 1903, when the Wright brothers flew their "Wright Flyer" at Kittyhawk, North Carolina.
In the next few years, flight pioneers worked on both fixed-wing and rotary-wing aircraft. At the time, fixed-wing aircraft were still very primitive, and some workers in the new field of aviation believed that rotary-wing aircraft were the better bet over the long run.
On 29 September 1907, French aviation pioneer Louis Charles Breguet managed to lift off the ground in a helicopter of his own design, the "Gyroplane #1", a great spindly framework in the shape of an "X" with biplane rotors on the corners. It has been described as something like "four fallen windmills lashed together".
The flight lasted about a minute and went no higher than a meter, as the machine was held down to the ground by four men. Breguet had not solved the problem of controlling the direction of flight of his helicopter, a problem that would plague helicopter designers for decades.
The first untethered flight of a helicopter took place a short time later, on 13 November 1907, when another Frenchman, Paul Cornu, flew for a few minutes about a meter off the ground in a helicopter with fore-and-aft contrarotating rotors. Cornu didn't manage to solve the control problem either, and that was about as far as he got.
In 1908, fixed-wing aircraft set a number of records for performance and endurance, and were continuing to improve at a rapid pace. The helicopter was clearly not the best bet over the short run. Breguet moved on to fixed-wing aircraft for the time being.
* Other inventors kept tinkering with helicopters. Many designed craft that were as laughable as they were unflyable, but a few managed to get off the ground, though their pilots were generally glad to get back on it again before very long.
In 1909 and 1910, a Ukrainian named Igor Sikorsky, born in Kiev in 1889, designed a pair of helicopters. He had been inspired by Jules Verne's stories and da Vinci's sketches. Sikorsky's machines didn't fly, but Sikorsky filed the idea away for later. A Russian named Boris Yuriev also tried to fly a helicopter in 1912.
Jacob C.H. Ellehammer of Denmark hopped into the sky on his machine in 1912. In the United States, a German immigrant named Emile Berliner and his son Henry built a series of helicopters beginning in 1908, but none of them flew very well.
Another immigrant to the US, a Russian named George de Bothezat, built a helicopter named "the flying octopus" in the early 1920s with US Army funds, but the Army finally decided to scrap the project. Later in the decade, yet another American helicopter researcher named Maitland Bleecker got the Curtiss company to fund work on a helicopter with a rotor spun by propellers at the rotor tips! The propellers were driven by shafts running down the rotor blades from a single piston engine.
Marquis Raul Pateras Pescara, an Argentine working in Spain and France, built several coaxial helicopters in the early 1920s that actually stayed in the air for an extended period of time. A Frenchman named Etienne Oehmichen designed an elaborate helicopter with six rotors and eight propellers that won a prize in 1924 for a flight over a one-kilometer course. A Russian-born inventor living in Belgium named Nicholas Florine developed a fore-and-aft contrarotating helicopter in the early 1930s that stayed in the air for ten minutes. These successes were limited, and gave nobody reason to believe that the age of the helicopter was right around the corner.
* The first practical rotary-wing aircraft was built by a Spaniard named Juan de la Cierva after the First World War. His "autogiro" or "autogyro" was not a helicopter, instead being a somewhat odd but perfectly practical cross between a fixed-wing aircraft and a helicopter.
La Cierva's autogyros were essentially the fuselage of a fixed-wing aircraft with a rotor mounted on top. The rotor was unpowered, spinning up from the draft of the propeller in the front of the aircraft and from the wind caused by the forward motion of the aircraft. This allowed it to take off in a short distance; or land straight down, by cutting power and letting the aircraft drop with the rotor spinning, a process known in modern helicopters as "autorotation". An autogyro could even hover if faced into a stiff breeze. There was no need to counter torque, as the rotor was not power-driven.
One of the obstacles that la Cierva had to deal with was "asymmetry of lift", another fundamental helicopter design issue. If a helicopter is moving forward, the rotor blade that is moving in the forward direction generates more lift than the rotor blade that is moving in the backward direction. Early helicopters, which had fixed rotor blades, tended to tip over because of this problem.
La 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 autogyro.
* La Cierva began work on autogyros in 1920, but didn't actually make one that could safely get off the ground until he discovered the principle of hinged blade system. He stumbled onto the idea by accident while tinkering with a rubber-band-powered model. His "C-4" autogyro, which incorporated the hinged-rotor scheme, first flew on 9 January 1923.
The C-4 was modified from a wartime French Hanriot fighter and still had wings for flight control. Later la Cierva autogryos did not have wings, achieving the appropriate steering through what is now called "cyclic pitch control".
This is the same scheme used in modern helicopters to control directional motion. A set of linkages is used to change the pitch of the blades as they spin around the helicopter, for example giving a blade a high angle of attack as it moves forward to increase lift, and a low angle of attack as it moves backward, causing the aircraft to shift sideways.
Other pitch configurations can be used to allow the helicopter to move forward. A modern helicopter has a "cyclic" stick to adjust the cyclic pitch of the blades, and a "collective" stick that adjusts all the blades equally, adjusting the vertical lift of the aircraft. Late-model la Cierva autogyros also had a clutch to allow the aircraft's engine to "spin up" the rotor blades before takeoff, though it rotated freely once in flight.
Some sources claim that Pescara invented the concept of cyclic pitch control and implemented it in his experimental helicopters. It is plausible that both inventors discovered it independently, but it is clear that la Cierva was the first to implement cyclic pitch control in a production machine. La Cierva established a factory for building autogyros in Britain, and the "flying windmill" proved to be something of a sensation. They were built in many countries, with the Japanese producing a total of 240.
La Cierva licensed the enthusiastic Harold Pitcairn to build them in the United States. The DETROIT NEWS used one to send reporters to the scene of accidents or other newsworthy events, and the US Postal Service experimented with them for mail delivery. Pitcairn believed that they could be sold as a "flying car" for wealthy customers, and designed a prototype two-seater that had folding rotors and could be driven on city streets.
The Kellett company of the US also built autogyros, with one taken by Admiral Byrd on an Antarctic expedition in 1933, and delivered a few for US Army Air Force (USAAF) evaluation as the "XR-2" and "XR-3". The autogyro never became much more than a popular curiosity, however. Military forces didn't have a serious need for them, and as the Great Depression was in progress, there was no market for them as a rich person's toy, no matter how sexy they were.
La Cierva was killed in an airliner crash near London in December 1936. By this time, workable helicopters were beginning to appear, and the autogyro went into eclipse. They survived mostly as an ultralight aircraft for enthusiasts such as the Bensen gyrocopters and gyrogliders, with thousands sold, mostly in kit form, to the present day. The relative obscurity of the autogyro since the death of la Cierva does not diminish the importance of his work, as he had solved many of the fundamental problems of helicopter design.
* By the mid-1930s, helicopter technology was reaching a critical mass. In 1930, inspired by la Cierva's work, Louis Breguet returned to experiments with helicopters. As he was busy manufacturing fixed-wing aircraft, he set up a separate business organization and delegated the detail work to a young engineer named Rene Dorand.
The result was a coaxial helicopter of almost modern appearance that was light-years beyond Breguet's Gyroplane #1 of 1907. However, by this time, Breguet was older and wiser, and the new aircraft was purely experimental, as reflected by its name, the "Gyroplane-Laboratoire". He also did not invest major funds in its development, using parts salvaged from other aircraft to build the helicopter.
Attempts to fly the Gyroplane-Laboratoire began in 1933, initially with no success. However, Breguet and Dorand kept at it, continuing to refine the machine, and in November 1937 it won a French Air Ministry prize for a helicopter that could fly an extended circuit and perform other specified flight tests.
Although some partisans of Breguet and Dorand claim that the Gyroplane-Laboratoire was the first workable helicopter, it was difficult to control and "shook like a bag of walnuts". Breguet and Dorand continued to work on the aircraft, but made little progress, and it was finally badly damaged in a hard landing in June 1939. With war looming, Breguet abandoned his work on helicopters. The Gyroplane-Laboratoire was destroyed in an air raid in 1943.
* The Gyroplane-Laboratoire was a huge step forward, but the generally recognized inventor of the first practical helicopter was Professor Heinrich Focke of Germany, who had helped found the Focke-Wulf aircraft firm. Focke did not like the Nazis, and after they came to power they forced him out of the company in 1933. Focke turned to building and refining autogyros.
In 1933, Focke began design of his Model 61 helicopter. Two were built, the first flying in the spring of 1936. It was the first practical, fully-controllable helicopter to take to the air. It wasn't easy to fly, but it could reliably do all the essential maneuvers of a modern helicopter.
The Model 61 clearly demonstrated roots in autogyro design. It was built around the fuselage of a Focke-Wulf FW-44 Steiglitz biplane, and looked like an autogyro with twin rotors on outriggers to each side of the fuselage. It retained an engine and propeller in the nose, but the 160 horsepower radial engine actually drove the rotors in a contrarotating fashion.
The Focke Model 61's propeller was not used for flight power. There's an old joke among private airplane pilots that a propeller isn't used to power an airplane, it's just used to keep the pilot cool, and this can be proven because a pilot starts sweating in a big way when the propeller stops turning. In the case of the Model 61, this was almost true, since the only function of the little propeller was to keep the radial engine cool.
The Model 61 attracted little public attention at first, since it seemed to be little more than a freakish variation on the autogyro. Then, in February 1938, it attracted widespread notice when it was flown in the enclosed Detschlandhalle sports arena in Berlin at a huge Nazi gathering, with 25-year-old Hanna Reitsch at the controls.
Reitsch was a German superstar, an expert test pilot with first-class flying skills and very cool nerves, a personal friend of Adolf Hitler himself. Her petite size came in useful in flying experimental aircraft, which were often small and underpowered. She flew the Model 61 inside the arena every night for three weeks, making the helicopter front-page news all over the world. In her hands, it seemed to effortlessly float in any direction with complete command of the air, though given Reitsch's flying skills she probably could have performed aerobatics with a concrete block if it had been fitted with wings and an engine.
* The Focke-Achgelis company, organized under Nazi consent with aviator Gerd Achgelis as a partner to produce Focke's helicopters, went on to build an enlarged, six-passenger version of the Model 61, designated the "Fa-266 Hornisse (Hornet)", for the Deutsche Lufthansa airline. It performed its first flight in August 1940, but by this time development funding had been taken over by the military, which redesignated the helicopter the "Fa-223 Drache (Dragon)".
The Fa-223 was a practical operational helicopter, and indeed more capable
than any other helicopter produced during the war. It was powered by a 1,000
horsepower piston engine, could carry a pilot and an observer, and could be
fitted with an electric rescue hoist and a machine gun in the nose. It could
carry a load of up to 1,280 kilograms (2,820 pounds) slung underneath the
helicopter or inside its spacious cabin, and could be fitted with bombs or
mines.
FOCKE-ACHGELIS FA-223:
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spec metric english
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rotor diameter 12 meters 39 feet 4 inches
span over rotors 24.5 meters 80 feet 5 inches
fuselage length 12.25 meters 40 feet 2 inches
height 4.35 meters 14 feet 3 inches
empty weight 3,175 kilograms 7,000 pounds
max loaded weight 4,310 kilograms 9,500 pounds
maximum speed 175 KPH 109 MPH / 95 KT
service ceiling 2,000 meters 6,600 feet
range 700 kilometers 435 MI / 378 NMI
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* The one aircraft to be produced by the Focke-Angelis company in quantity was the "Fa-330 Bachstelze (Wagtail)". 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). About 200 were built, with the type beginning service in mid-1942. At least two were provided to the Japanese.
Actually, the Fa-330 was a towed autogyro, called a "rotor kite" or, in modern terms, a "gyroglider". It was pulled behind a German U-boat (submarine) during surface cruise to provide a long-range observation platform for spotting targets or threats. It could be broken down and stowed in a few minutes, and then pulled out of storage and reassembled for use just as quickly.
The Fa-330 proved impractical for U-boat patrols in the North Atlantic, since wide-ranging Allied air patrols made U-boat commanders reluctant to do anything that prevented him from diving quickly, but it was used to some extent in the Indian Ocean.
* The Focke-Achgelis company also designed an ultralight one-man helicopter designated the "Fa-336" along the lines of the Fa-330, and also primarily intended as an observation platform for submarines. It could be broken down and stowed. The Fa-336 never went into production, though apparently Sud-Est built an ultralight helicopter based on it after the war.
In fact, Professor Focke and his team worked on a number of interesting rotary-wing projects that didn't get beyond the paper design stage. The "Fa-284" was an enlarged Fa-224 with twin piston engines, and was intended to be a "flying crane" to lift heavy loads slung underneath. It was abandoned in favor of a flying crane consisting of two Fa-224s connected end to end, but this aircraft wasn't completed, either.
Even more imaginative concepts included a "tilt-rotor" aircraft designated the "Fa-269", which resembled a conventional aircraft with twin props that could tilt downward to provide short takeoff and landing capabilities, and the "Fa-283", which was a turbojet-powered autogyro transport. Both appear to have been little more than pipe dreams.
* Another German, an experienced aviation engineer named Anton Flettner, had been working on helicopters in parallel with Focke. His first helicopter, built in 1930, was a bizarre and unworkable machine with twin engines and propellers attached to the main rotor. It was wrecked in testing, but Flettner simply decided to back up and try again.
He designed an autogyro, the Flettner "Fl-184", to get his concepts on track. After initial test flights, Flettner then powered the rotor of the machine and removed the propeller from the nose, replacing it with two small propellers, each on an outrigger, to provide control and forward thrust. It was inelegant, but it worked.
In 1937, Flettner began work on a much more refined helicopter, the "Fl-265". This aircraft had a single engine driving two contrarotating rotors through a gearbox. The twin-bladed rotors were on shafts on either side of the gearbox, with the gear arrangement keeping the two rotors at a right angle to each other, and the shafts turned outward slightly so the rotors intermeshed without colliding. This is known as an "eggbeater" configuration, and is still used in some modern helicopters.
The German Navy began to provide funding to Flettner in 1938, and the Fl-265 made its first flight in May 1939. The Fl-265 led to a bigger and refined production version, the "Fl-282 Kolibri (Hummingbird)", with a 160 horsepower radial engine. The Kolibri was much smaller than the Fa-223 Drache, but could carry a crew of three, and was extremely agile. The German Navy conducted exercises in early 1941 in which a Kolibri dodged attacks by two fighter planes for 20 minutes.
The Kolibri promised to be an excellent naval scout and observation machine,
and a thousand were ordered, but as with the Fa-223, only a small number were
completed.
FLETTNER FL-282 KOLIBRI (V21 PROTOTYPE):
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spec metric english
_____________________ _________________ _______________________
rotor diameter 11.96 meters 39 feet 3 inches
fuselage length 6.56 meters 21 feet 6 inches
height 2.20 meters 7 feet 2 inches
empty weight 760 kilograms 1,676 pounds
max loaded weight 1,000 kilograms 2,200 pounds
maximum speed 150 KPH 93 MPH / 81 KT
service ceiling 3,300 meters 10,800 feet
range 170 kilometers 106 MI / 92 NMI
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Another Austrian, named Friedrich von Doblhoff, also developed the first successful "tipjet" helicopter, the "WNF-342". In this scheme, the rotor has some type of jet unit at the tips to cause rotation. Since the rotor turns itself, this eliminates the need to cancel torque. Von Doblhoff's designs used a piston engine to compress air, which was pumped to the rotor tips through pipes, and then mixed with fuel in a small combustion chamber in the rotor tips to create a fast gas jet. The rotor was only driven for takeoff and landings. The machine had a pusher propeller and flew like an autogyro in normal flight.
Von Doblhoff built four prototypes between 1942 and 1945, the last of them having a weight of 640 kilograms (1,410 pounds), a rotor diameter of 9.9 meters (32 feet 6 inches), and an Argus As-411 engine with 135 horsepower. His machines never went into production, and in fact no tipjet helicopter ever has, though the tipjet concept has been revisited many times in different forms, it has never been used in any full-production helicopter design.
While the Germans were pioneers in helicopter development and operations, the country's defeat in World War II meant that leadership in the postwar development of the field would pass to other countries, in particular the United States.
* Focke, Flettner, and some of the other German inventors had made workable helicopters, but Igor Sikorsky would be the first to actually make a real success of the thing.
Following his frustrated experiments in helicopters before the First World War, Sikorsky turned his attention to fixed-wing aircraft. He built the first multi-engine aircraft, the Sikorsky GRAND, and then went on to the ILYA MORONETS, a great four-engined luxury passenger airliner that looked like something out of a Jules Verne novel. The name was that of a tenth-century folk hero. When the war broke out, Sikorsky built about 79 of these huge aircraft for the Tsarist government.
When the Bolsheviks seized power in 1917, Sikorsky decided he was on the wrong side of the class struggle and fled to France in 1918. Failing to find steady work there, he went to the United States in 1919, inspired by the work of Edison and Ford to seek his fortune in a land where a person with "ideas of value" might have a good chance to succeed.
After a few lean years, in 1923 he and a few associates founded the Sikorsky Aero Engineering Corporation on Long Island, New York. He finally achieved success in 1928 with his "S-38" amphibian aircraft, which established the Sikorsky name and associated with amphibians and flying boats that would evolve into the great and elegant ocean-spanning Sikorsky Clippers.
In 1929, Sikorsky moved the Sikorsky Aviation Corporation to Stratford, Connecticut, where the company was soon bought out by the giant United Aircraft conglomerate, becoming the Sikorsky Division. Although he spent most of his time working on his seaplanes, he still tinkered with helicopter concepts in his spare time. He patented one of his designs in 1931, and by 1935, his son Sergei was building flying models of his father's helicopters, which Igor would demonstrate to his engineers or the board of United Aircraft.
In 1938, United Aircraft, suffering under the prolonged Depression, had to shut down production at its Sikorsky division. However, in an amazingly far-sighted and generous action, the company allowed Igor Sikorsky to retain a small team and work on a helicopter project on a low-budget basis. Sikorsky was now effectively out of the fixed-wing aircraft business and into the helicopter business full-time. United Aircraft's investment would turn out to be more than they anticipated, but would still pay off handsomely.
* Igor Sikorsky's helicopter concepts were based on an aircraft with a single main rotor, with a small sideways-mounted "tail rotor" to cancel torque. The idea was not new, but nobody had got it to work so far. In fact, some aerodynamic experts believed the idea was completely unworkable.
Igor Sikorsky proved them wrong. On 14 September 1939, his "Vought-Sikorsky 300 (VS-300)" helicopter lifted momentarily off the ground, with Sikorsky himself at the controls, his businessman's trilby hat jammed on his head to keep it from blowing away. The name "Vought-Sikorsky" was the result of the merger of United Aircraft's Vought and Sikorsky divisions, which were both sited at Stratford at the time.
The VS-300 was tethered to the ground in its early flights, but Sikorsky kept tweaking it until it could be controlled, and free flights began in the spring of 1940. The VS-300 originally did not have a fuselage or cockpit, being a naked framework with a main rotor, a tail rotor, an exposed pilot's seat, a 65-horsepower Lycoming engine, and the hardware to glue them all together. The machine was reengined with a 90-horsepower Lycoming engine in the summer of 1940.
The skeletal arrangement of the aircraft made it easy to perform tweaky modifications. There was a lot of work to be done. For example, once the VS-300 began free flights, it proved to be able to fly controllably in any direction except forward. Sikorsky got so frustrated at this problem that he even considered reversing the seat arrangement and leaving it at that, but he eventually realized that in forward flight the downwash from the main rotor system was washing out the effect of the tail rotor system, indicating a need to do some adjustment in position.
The machine was also difficult to control, leading to a crash on 14 October 1940 that damaged the machine, though Sikorsky was unhurt. In fact, at that time the VS-300 wasn't flying much better than the Breguet-Dorand Gyroplane ever did. Sikorsky was patient and persistent, methodically working through the problems. The mechanics grew so tired of making little changes to the machine that they called it "Igor's Nightmare".
By the spring of 1941, the VS-300 was finally outflying any other helicopter ever built. It was reengined again with a 100-horsepower Lycoming engine and in principle redesignated "VS-300A", but everyone still called it the "VS-300". Tweaks continued, with the machine fitted with a simple fuselage in October 1941. By the end of 1941, the VS-300 was flying so well that it was clear Sikorsky had the technology to build a production machine.
Many of the changes during the development process had been to the tail rotor configuration. Sikorsky started out with a single tail rotor, went to two and even three tail rotors, and then back to a single tail rotor again. Multiple tail rotors had been adopted because Sikorsky had encountered problems with cyclic pitch control early on, and had deleted it for a while. This meant fitting multiple tail rotors to counteract torque and also provide directional control. However, Sikorsky managed to get cyclic pitch control working, and the additional tail rotors proved unnecessary.
The tail rotor in a modern helicopter not only counteracts the torque of the main rotor, it also allows the pilot to pivot the aircraft around, using a pair of foot pedals to change the collective pitch of the tail rotor, increasing or decreasing sideways thrust to turn the helicopter in one direction or another.
The combination of cyclic stick, collective stick, and twin pedals was confusing for pilots trained with fixed-wing aircraft. Even the great aviator Charles Lindbergh had troubles when he later took the controls of the VS-300, claiming it made him feel completely out of his profession. He slept on it overnight and then got the hang of it. The VS-300 was finally donated to the Edison Institute Museum in Dearborn, Michigan, in October 1943.
* While Sikorsky was refining the VS-300, the US Army Air Corps (USAAC) had conducted a design competition for a helicopter. Sikorsky submitted a derivative of the VS-300, but a design from the Platt-LePage Aircraft Company won the competition in July 1940.
W. Lawrence LePage had worked for Harold Pitcairn on autogyros and had been impressed by the German Fa-61. He wanted to build his own helicopter along the same lines as the Fa-61, and he joined up with another engineer, Havilland H. Platt, to form Platt-LePage.
The USAAC signed a contract with the Platt-LePage company to build a helicopter designated the "Experimental Rotorcraft 1 (XR-1)". The result was a machine that resembled a smaller version of the Fa-223 Drache, with contrarotating rotors mounted on outriggers on each side of the aircraft. In fact, LePage had discussed the possibility of license-building the "Fa-224", a two-seat refinement of the Focke Model 61 that never actually flew, with the Focke-Achgelis company, but the outbreak of war put a stop to the matter.
The XR-1 was powered by a Pratt & Whitney R-985 radial engine with 440 horsepower, had a loaded weight of 2,150 kilograms (4,730 pounds), and had rotors 9.3 meters (30 feet 6 inches) in diameter.
The Army selected the Platt-LePage design mostly because it was based on a configuration that was known to work. However, the Army Air Force (the Air Corps was renamed in June 1941) wasn't committed to the Platt-LePage XR-1 to the exclusion of other designs. In July 1940, Captain Frank Gregory, in charge of the USAAF's helicopter effort, visited the Sikorsky plant and took a trial flight at the controls of the VS-300. Gregory initially felt that the helicopter handled "like a bucking bronco", but after some further instruction by Sikorsky, Gregory managed to fly the VS-300 successfully and was impressed by it.
On 10 January 1941, the Army Air Corps awarded Sikorsky a contract to develop a prototype of an operational helicopter based on the VS-300, but substantially bigger, with the designation of "XR-4". Funds for the contract were diverted from the Platt-LePage XR-1 project. This was a big vote of confidence in Sikorsky, as he still hadn't worked all the bugs out of the VS-300.
The Platt-LePage XR-1 performed its first flight in May 1941, but by the end of 1941 the VS-300 was clearly the leader of the pack. The Platt-LePage XR-1 was still suffering through development problems. Sikorsky was already working hard on his XR-4, and the the Platt-LePage machine never entered production.
Interestingly, Platt-LePage proposed a version of their XR-1 helicopter that mounted four machine guns to the US military. This was probably the first time anyone had formally suggested the concept of a dedicated helicopter "gunship", but the idea was much too far ahead of its time. Helicopters would not be rugged enough to engage in shooting matches for decades, and the military wasn't interested.
* The VS-300 was the first successful American helicopter, and its configuration was the basis for the majority of future helicopter designs, though coaxial, fore-and-aft contratrotating, and eggbeater designs are still being successfully built and operated.
Sikorsky would become the most famous of the helicopter pioneers, leading to a widespread myth that he was actually the inventor of the helicopter himself, which he was always careful to deny. However, he did become a father figure for the industry, not merely for his pioneering efforts but because of his reputation for extreme competence as a manager, designer, and even pilot; his sensibility; and his understated old-world civility.
The XR-4 prototype that the Army had ordered in early 1941, with the company designation of "VS-316A", first flew on 14 January 1942. It was about twice the size of the VS-300, with a 165 horsepower, seven-cylinder Warner R-500 Super Scarab radial engine; side-by-side seating for two; and a boxy cloth-covered tube-frame fuselage with plexiglas windows. The XR-4 had originally featured triple tail rotors, but the single tail rotor system was working and in place by the time of the first flight. This machine would eventually end up in the hands of the Smithsonian National Air & Space Museum in Washington DC.
In December 1942, the USAAF ordered a batch of three "YR-4As" for evaluation, and shortly after that 27 "YR-4Bs" for service tests. These machines were much like the XR-4, but had a 180-horsepower Super Scarab engine and a wider rotor. Three of the YR-4Bs went to the US Navy and were evaluated under the designation "HNS-1".
The YR-4A/Bs were followed by a hundred production "R-4Bs" with a 200 horsepower engine, which were the first American helicopters to reach operational service. 35 of this batch went to the USAAF; 20 went to the US Navy as HNS-1s; a few went to the Coast Guard; and 45 went to Britain, where is was designated the "Hoverfly I" and used by the British Royal Air Force (RAF) and Royal Navy's Fleet Air Arm (FAA).
Ironically, the British had actually ordered the R-4Bs, asking Sikorsky to build 150, but then the helicopter bandwagon got rolling and the US armed forces pulled priority on the British to take the R-4Bs themselves. The British were last in line for the helicopters, but it didn't matter too much, as their requirements had changed in the meantime and better machines than the R-4 were on the way.
The XR-4 suffered from excessive vibration, with the problem persisting in the evaluation and production machines. It turned out to be due to maddeningly subtle differences in the internal weight distribution of the rotor blades. The Sikorsky company implemented much more careful production procedures; insisted on blades being sorted into matched sets of three, with an entire set replaced if one blade were damaged; and also developed an adjustment mechanism in the rotor head to allow "calibration" of the rotor system in the field. These were strictly stopgap measures, and the company set to figuring out a real fix for the long term.
In short, the R-4 was still not quite ready for serious field use, all the more so because it was very limited in performance and payload, particularly on hot days. One flight demonstration for USAAF brass of a YR-4A on a hot, windless day in the summer of 1942 at Wright Field in Ohio ended in embarrassment when the machine simply refused to leave the ground.
However, the R-4 quickly demonstrated the value of the helicopter, performing a number of rescues and emergency deliveries under field conditions in the last year of the war. It was the first helicopter to land on a ship, when Frank Gregory put one down on the tanker BUNKER HILL on 6 May 1943, and it could be fitted with pontoons for water landings.
The R-4's service life was short-lived, but it did serve to train the first
generation of American and British military helicopter pilots, and gave the
military some good ideas on what might be done with more capable machines.
SIKORSKY R-4B:
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spec metric english
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rotor width 11.6 meters 38 feet
fuselage length 10.8 meters 35 feet 5 inches
height 3.78 meters 12 feet 5 inches
empty weight 916 kilograms 2,020 pounds
max loaded weight 1,150 kilograms 2,535 pounds
maximum speed 132 KPH 82 MPH / 71 KT
service ceiling 2,440 meters 8,000 feet
range 209 kilometers 130 MI / 113 NMI
_____________________ _________________ _______________________
Five trials "XR-6As" with a 240 horsepower Franklin engine were built by Sikorsky, and 26 similar "YR-6As" were built by the Nash-Kelvinator company. Nash Kelvinator also built 193 production "R-6As", beginning in 1945, with 36 going to the US Navy as the "HOS-1" and 40 going to the British RAF as the "Hoverfly II". Like the R-4, the R-6 could be fitted with pontoons, and like the R-4, the R-6's service life was short, particularly because its engine proved unreliable.
* When Sikorsky committed to development of the R-6, the company also committed to development of a a substantially more capable helicopter, the "R-5" or "VS-337". It was originally conceived in response to a British request for a helicopter suitable for antisubmarine warfare, with good visibility and the capability to carry depth charges. The USAAF was interested and ordered five prototype and evaluation machines, along with the order for YR-4s placed in December 1942.
The R-5 was a tandem-seat helicopter with a 450 horsepower Pratt & Whitney R-985-AN-5 Wasp Junior engine, a larger rotor, a glassed-in cockpit, and all-metal construction. The fuselage featured rounded corners, since the R-4's boxy shape had proven to disrupt the rotor downdraft, and had a tailwheel landing gear configuration.
Initial flight of the prototype "XR-5" was on 18 August 1943. Just as the scale-up from the VS-300 to the R-4 had led to vibration problems, the next scale-up to the R-5 led to a new set of very nasty vibration problems that proved very difficult to iron out. However, the military really wanted helicopters now, and despite the problems, the USAAF followed up the initial order for five with an order for 26 "YR-5As" (later designated "YH-5A") for evaluation, followed by another order for 100 production "R-5As" (later "H-5A"), though only 34 of this version were built. The R-5A had provisions for carrying a stretcher on each side of the cockpit.
21 R-5As were modified with a third seat, auxiliary fuel tank, tricycle-style
landing gear, and a rescue hoist, and given the new designation of "R-5D"
(later "H-5D"). Three of this batch were evaluated by the US Navy as the
"HO2S-1". Five of the evaluation YR-5As were also given dual controls and
used for training as "YR-5Es" (later "YH-5E").
SIKORSKY R-5A:
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spec metric english
_____________________ _________________ _______________________
rotor diameter 14.63 meters 48 feet
length 17.4 meters 57 feet 1 inch
height 3.96 meters 13 feet
empty weight 1,715 kilograms 3,780 pounds
max loaded weight 2,190 kilograms 4,825 pounds
maximum speed 171 KPH 106 MPH / 92 KT
service ceiling 4,390 meters 14,400 feet
range 580 kilometers 360 MI / 313 NMI
_____________________ _________________ _______________________
The result was the "S-51", with four seats instead of two. It was one of the first helicopters that was really suitable for operational use. Initial flight was on 16 February 1946. With military sales slow, Sikorsky tried to sell the time commercially, but though a few were bought by airlines, it was an expensive and somewhat questionable toy and was not a commercial success.
Sikorsky turned back to the military, and pitched it to the Navy. The Navy was impressed, and bought 90 S-51s as the "HO3S-1" to rescue pilots who had gone into the sea after carrier landing or takeoff accidents, and the Air Force obtained 11 of the type as the "H-5D".
Some S-51s were built with 600 horsepower engines and wider rotors, and the rotors could be folded back for storage. A further batch of 39 S-51s with improved rescue gear were sold as "H-5Gs", while 16 "H-5Hs" were delivered in 1949 with pontoon / wheel landing gear. Total production quantity of the S-51 is unclear, but was about 300.
* The S-51 was a big improvement over the R-4, but the Sikorsky company saw it as possibly too big and expensive to sell to the civilian market, and so Sikorsky decided to develop a intermediate-sized helicopter, the two-seat "S-52", which first flew in 1947. It featured a 178-horsepower Franklin engine, as well as metal rotor blades, which Sikorsky adopted because the wooden blades of previous machines had proven so hard to balance.
Although the S-52 was regarded as a very sophisticated design, by that time Sikorsky had competition in the helicopter business, and nobody bought the S-52. However, the type was regarded as promising by the military, and Sikorsky developed a four-seat variant, the "S-52-2", with a 245-horsepower Franklin engine. The US Army evaluated the type as the "H-18", but did not purchase it in quantity, though a total of 89 served with the US Marines as the "HO5S-1" and the Coast Guard as the "HO5S-1G".
In the interim between the S-52 and S-52-2, Sikorsky also developed a five-seat helicopter, the "S-53", a follow-on to the S-51 designed for a US Navy competition. The S-53 first flew in 1948, and had a 500 horsepower Continental R-975 engine, plus metal folding rotor blades. The Navy evaluated it in 1949 as the "XHJS-1", but it proved so inferior to other entrants in the competition that Sikorsky all but suppressed any mention of the type from that time on.
* In fact, other American helicopter pioneers, including Frank Piasecki, Arthur Young (of Bell Aircraft), Stanley Hiller, and Charles Kaman had developed their own helicopters that were a match or more for Sikorsky's products, and put them into production.
In Europe, helicopter companies sprang up as well, led by Westland in the UK. Westland had an advantage in having a relationship with Sikorsky, initially obtaining a license for the S-51. The first "Westland-Sikorsky WS-51" performed its initial flight on 5 December 1948, and led to a production batch of "Dragonfly Helicopter Rescue Mark 1 (HR.1)" machines for the Royal Navy FAA, with an Alvis Leonides 50 radial engine providing 540 horsepower.
The Dragonfly HR.1 equipped the first operational helicopter squadron in the Royal Navy. The RAF obtained a similar variant with external litters for casualty evacuation as the "Dragonfly HC.2". Addition of an all-metal rotor to these versions led to the FAA "Dragonfly HR.3" and the RAF "Dragonfly HC.4". The FAA also obtained a final version with minor improvements over the HR.3, designated the "Dragonfly HR.5".
Westland also sold commercial versions, including the "WS-51 Mark 1A", with an Alvis Leonides 521/1 engine with 520 horsepower, and the WS=51 Mark 1B", which was similar to the Mark 1A but had a Pratt & Whitney R-985-B4 Wasp Junior radial engine with 450 horsepower. These machines were sold in small numbers to commercial operators, as well as Japanese, Italian, and Thai military services. About 150 Dragonfly / WS-51 machines were sold in all.
The company also produced a derivative of the R-5 in the mid-1950s known as the "Widgeon", which featured a new automobile-style fuselage with seating for four passengers plus the pilot, an Alvis Leonides 521/1 engine, and the improved rotor of the bigger Sikorsky "S-55" helicopter, to be discussed elsewhere. A total of 14 Widgeons were built, some of them (including the prototype) being conversions of Dragonflies.
Westland's license construction of the Sikorsky S-51 gave the British firm a head start in helicopter development in the UK that it would never lose, and in fact Westland eventually absorbed all its British competitors. Westland continued their profitable license production of Sikorsky designs, but very often added their own improvements and optimizations, and designed excellent rotorcraft of their own.
Other European companies followed Westland, including Aerospatiale in France, Agusta in Italy, and Messerschmitt-Boelkow-Bohm (MBB) in Germany. The Soviets also worked on their own rotorcraft designs, pioneered by a series of experimental helicopters developed by Ivan Bratukhin. Bratukhin would never build a production helicopter, but two of his contemporaries, Mikhail Mil and Nikolai Kamov, would established design bureaus that have survived to this day and produced large numbers of helicopters.
* From these beginnings, the helicopter proved its value in peace and war. The technology would be improved, with turbine powerplants largely replacing piston engines in the 1960s.
The helicopter continues to be refined and even reinvented. After decades of development work, tilt-rotor aircraft are now starting to enter operation, where they provide performance similar to that of a turboprop fixed-wing aircraft and the vertical-takeoff capabilities of the helicopter. As the 21st century begins, the helicopter can look forward to new achievements.
* This document began as a set of notes from the US History Channel's MODERN MARVELS TV series on the the origins of the helicopter and its evolution to the present day. Other sources include:
I also found a surprising amount of good information on the Web, more than I normally expect to find. Gary Webster's JAGDFLIEGER HOMEPAGE, which discusses German vertical-take-off and helicopter designs, is first-class.
* Revision history:
v1.0 / gvg / 01 feb 01
v1.0.1 / gvg / 01 aug 02 / Minor cosmetic update.