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Helicopter History:

The Evolution of Aviation's Most Exotic Technology

Copyright 2004 by Richard Harris

Images courtesy of NASA, Defense Dept.,
U.S. Centennial of Flight Commission,
and the Hiller Museum.

Originally published in In Flight USA

The history of the helicopter is one of the most challenging stories to tell. It is the story of the evolution of a simple idea: unlimited flight -- flying vertically or horizontally, or hovering in mid-air. But as with all things simple, it's not so simple.

The helicopter must challenge many forces that the airplane has scant experience with:

While airplanes and gliders can only fly vertically by first flying horizontally, then turning the entire aircraft upwards, the helicopter must be able to start and finish with vertical flight.

Airplanes and gliders -- "fixed-wing" aircraft -- fly by creating lift with their wings, as a result of moving the entire bulk (including their rigidly-attached wings) through the air. As the wings pass through the air, the "relative wind" generates lift on the wings.

But on a helicopter, lift must be produced by moving the wings, alone, through the air. Hence helicopters -- despite the appearance of being lifted by horizontal propellers -- are more accurately said to be lifted by whirling wings. The main rotor of a helicopter is actually a pair (or more) of long, thin wings -- the main rotor blades -- rotating at high enough speed to generate their own relative wind (and lift), even while the rest of the aircraft, itself, is stationary.


Leonardo daVinci sketched his famous "Helix" -- a screw-shaped airfoil over a wooden framework, spun by the pilot's muscle. But daVinci apparently realized (as with his bird-flapping Ornithopter) that man's muscle-to-weight ratio wouldn't normally be enough for powered flight. But the Helix presaged the name "helicopter" -- from the Latin "helix" (circular shape or direction) and "pteron" (wing).

The first known vertical-flying contraption is the 2500-year-old "Chinese top" -- a toy made of wooden dowels, with feathers arranged propeller-like on either end, and spun by a twisted string pulled taut by a small wooden bow. In a sense, this was the first helicopter -- also sometimes known as an Orinithopter.

Britain's Sir George Cayley, father of aeronautical engineering in the 1800's, created some giant model ornithopters, which flew as high as 90 feet, and for long distances -- demonstrating the theoretical possibility of vertical flight. By the 1860's, the "flying top," in various forms -- typically, a rotor launched by pulling on a string wound around its shaft -- became a popular toy. Some adults built massive ones, powered by steam, compressed air, springs, or stretched rubber. But none -- it seems -- carried a man aloft.

Putting power to the principle, Britain's W.H. Phillips made a powered ornithopter model, spewing steam from the rotor tips for propulsion -- and it actually flew, the first mechanically propelled rotorcraft to fly. Italian engineering professor Enrico Forlanni managed to fit a quarter-horsepower steam engine to another model. In 1878, it flew to 40 feet, and hovered there for up to 20 seconds.

But -- as with developments in airplanes -- no suitable power source could be found to power it. Early tinkerers saw the idea as possibly delivering an aerial observation and reconnaissance platform, of "great military value." But neither the models they created, nor the prospective full-size designs, could provide sufficient lift. The overriding problem was a lack of sufficient power, in a light enough engine.

To develop an adequate engine, with a big enough power-to-weight ratio for flight, inventor Thomas Edison (famous for the light bulb and phonograph), tinkered with a lightweight, "explosive engine" -- impregnating tickertape with gunpowder, and squeezing strips of it tightly between metal wheels (to seal in the combustion) into a combustion chamber, where it would be ignited electrically. At first, it worked. But the combustion eventually backfired up through the rollers and ignited the whole roll of "fuel" tape. The mighty explosion drove Edison to quit the idea altogether -- though he later declared "whatever progress the airplane might make, the helicopter will [be the topic of] advanced students of aeronautics".


The Wright brothers had owned a Chinese top, given by their father, back in 1878. But they thought the helicopter idea "more difficult" than glider-flying demonstrated by Cayley and others, and turned away from rotary wings.

In 1908, Emile Berliner, inventor of the "gramophone" (earliest device for recording sound), differed with the Wright brothers' approach. "The way to fly," he insisted "is straight up." Aided by J. Newton Williams, Berliner developed a coaxial helicopter -- that used twin "co-axial contra-rotating rotors." By rotating in opposite directions, on the same shaft (with internal gearing), they each canceled out the torque of the other, keeping the helicopter from spinning helplessly out of control. Their craft could lift its own weight, though not a pilot's. They would later, in 1924, produce one of the first vertically flyable piloted aircraft -- a sort of biplane with rotors on the wingtips.

But, before Berliner, came the two French firsts: we shall quickly see.

By the early 1900s, before World War I, the Age of Invention was reaching its zenith. With the airplane now thoroughly "invented," there was a passion for all things flying, and the helicopter idea, well, took off -- especially in Europe.

In France, engineers Louis and Jacques Breguet, from a famed clockmaking family, built a huge framework contraption made up of what looked like four windmills laid on the ground (above, right), with their bases linked around an engine. September 19, 1907 (some say August 24), the fragile collossus, with a total of 32 whirling wings, actually lifted off the ground, and hovered for a few seconds in ground effect -- but could only be controlled by daring volunteers on the ground, gripping ends of the framework, as the rotors slashed through the air just above their heads. Despite repeated efforts, the impracticality of the idea led Breguet to abandon it -- taking up fixed-wing aircraft development, as one of France's most important plane-makers, eventually creating the great airline Air France.

The following November, fellow Frenchman Paul Cornu flew a helicopter that had some promise of controlled free flight. Smaller than Breguet's beast, it used a pair of paddle-like rotor blades projecting from each of a pair of horizontal spoked wheels. The wheels were spun by a long belt run around their rims, from the small hub emanating from the motor's transmission. This first "tandem rotor" helicopter not only could hover, but could actually move back and forth a bit, propelled by downwash directed by a couple of simple vanes -- one under each rotor -- which deflected some of the downwash for "translation" into horizontal flight. Hovering a foot off the ground, it could creep forwards at a snail's pace.

Another Frenchman, Charles Renard, in 1904, had conceived of independently articulated rotor blades, allowing the pitch of each blade to be twisted during flight, for controllability.

And in 1906, Italy's Gaetano A. Crocco had patented "cyclic pitch control" -- allowing the entire spinning "rotor disk" to be tilted in flight -- aiming its lift/thrust downwash at slight off-vertical angles -- for directional control and translation to horizontal flight.

These two methods eventually would become critical to modern helicopter design.

Crocco also discovered a basic problem of rotorcraft: differential lift in horizontal flight. That is, while a helicopter hovers in one place in calm air, the rotor's airspeed is the same all the way around the "rotor disk." But as the helicopter starts to move forward, the airspeeds of the "relative wind" -- hitting the advancing and retreating blades -- become increasingly unequal, causing unequal lift, causing the rotors on the advancing side of the disk to generate so much more lift that they rise up and roll the aircraft to the other side.

In 1909, young Russian engineer Igor Sikorsky tried to fly a wooden helicopter built along the same coaxial scheme as Berliner & Williams' first. But this first "Sikorsky" aircraft failed, for lack of better rotors and a bigger engine (he was stuck with only 25 horsepower). Sikorsky, too, abandoned the helicopter to seek his fortune in airplanes, eventually becoming a leading architect of giant airplanes. Fleeing the Communist revolution in 1917, he came to the U.S. and became the master architect of giant flying boats. But the helicopter idea would come back to him, in a decisive way, a generation later.

Other Russians, though, were making a difference. K. A. Antonov (later master of giant Soviet airplanes) built a 1910 helicopter similar to Sikorsky's. Moscow student Boris Yuriev created a 1911 helicopter that pioneered "anti-torque" tail rotors -- now a standard necessity on most helicopters -- to counter the torque of the main rotor, and prevent the machine from spinning in the opposite direction.

Back at the
coaxial twin-rotor idea, though, the Spanish Marquis de Pescara created the first helicopter that was truly "manageable." His Pescara No.3 looked like a tractor dangling from a horizontal windmill. But it actually flew, and incorporated modern flight technology:

And Russian immigrant Professor George de Bothezat -- an egotistical and tempermental "mad Russian" scientist, who was the world's acknowledged expert on rotorcraft design theory, also fled the bloody Communist revolution, for the U.S. He persuaded the U.S. Army into hiring him to build a helicopter for them at their experimental flight technology center at McCook Field, in Dayton, Ohio. In secrecy, Bothezat, built America's first military helicopter along the same lines as the Breguet giant, but added several propellers for various flight-control purposes.

In 1922-1923, the de Bothezat craft surprised everyone by performing respectably. It even carried the first helicopter passengers -- three volunteers clinging to the craft's rigging -- as it hovered about, a mere 10 feet above the ground. It also performfed the first documented controlled precision vertical landing of a rotorcraft -- establishing the potential of the rotorcraft as a means of flying to and from even the smallest places. But the beast was still complex and squirrelly, and especially so in engine-failure scenarios. The Army cancelled the project, noting that it saw the future in single-rotor helicopters.

In May of 1924, Frenchman Etienne Oehmichen, went one better, with a modernized version of the old Breguet contraption, making the first lengthy, closed-circuit helicopter flight -- two kilometers in 14 minutes. But none of these early helicopters had sufficient combination of light weight, efficiency and power to fly out of "ground effect" -- the cushion of air created by air squeezed between the rotors and the ground. Consequently, few ever flew sustained flights more than a dozen feet high, or so. Obviously this severely limited the practicality of the helicopter.

Meanwhile, airplanes were doing great things, lifting off grass fields in a few hundred feet, and roaring up into the skies at speeds over 150 miles per hour, to distant places at unlimited altitudes, commonly carrying passengers and other substantial loads. Though vertical flight was still the domain of the helicopter, real progress seemed to belong to the airplane.


How could the helicopter compete? By joining forces with the airplane, as it turns out. In 1920, the Spanish aircraft designer Juan de la Cierva lost the prototype of one of his large airplanes, when a foolish military pilot stalled it stunting near the ground. Cierva thought there should be some way that a plane could keep aloft when the engine quit, or the craft ran out of airspeed. The idea of whirling wings seemed promising. Cierva added a helicopter's rotor to an airplane, to produce the "autogyro."

Rather than spinning the rotor with engine power, the autogyro was designed to fly forwards like an airplane (it even had short, fixed wings), until the air began to drag on the rotor, spinning it without any mechanical drive system ("autorotation"). As the drag on the inner parts of the rotor accelerated the spinning, the outer parts of the rotor -- now rushing in circles at high speed -- began to generate lift.

And it flew.

While wings provided much of the autogyro's lift, the big rotor provided the quick and essential lift to make for short takeoffs, and even shorter -- even vertical -- landings. Some autogyros didn't even use wings at all. And no "anti-torque" or "contra-rotating" rotor was needed, because the engine wasn't turning the rotor -- the air was.

But the first autogyro was destroyed in an accident, when it rolled over on its side during taxiing. Cierva had become the first person to move fast enough with a rotor to discover -- quite unexpectedly -- the extent to which differential lift would challenge the helicopter. As the rotor spun, the advancing blades would rush into the oncoming wind -- encountering an airspeed much higher than the blades retreating on the other side of the rotor disk. As a result, one side of the rotor disk was generating more lift than the other, and the aircraft rolled over onto the side of the retreating blades.

The cure, it turned out, was to apply the lessons learned from airplane "dihedral" -- an airplane wing's upwards tilt towards the wingtips, which keeps airplanes stable in flight, resisting roll. The rotor blades of a flat, horizontal rotor, had a tendency to "cone" -- that is, flex upwards at the tips -- from the force of lift, while in flight. That cone provided some dihedral, with resulting stability, and (like airplanes) allowed some loss of lift on the side tilted upwards, while increasing lift slightly on the side tilted comparatively lower (more towards straight horizontal).

By mounting horizontal "flapping hinges" at the roots of the blades, the blades were allowed to flap up and down slightly -- essentially tilting the rotor cone like an airplane with dihedral would tilt if upset by a gust of wind. The side tilted down towards horizontal would produce more lift, and the side tilted upwards would "release" some, and the craft would stay righted. [NOTE: To be frank, this is actually a scientifically inaccurate description, but close enough for the novice's practical grasp.] Centrifugal force tended to keep the blades stretched out, and they only flapped enough to compensate for differential lift.

At the same time, Cierva fitted another hinge, a vertical "drag hinge," at the rotor's root, allowing for some difference in speed between the advancing and retreating blades. Again, centrifugal force tended to keep the blades stretched straight out, but the hinge allowed the blades to "lag" and "lead" as necessary to minimize stress on them.

The greater drag on the advancing blades would cause them to rock back on the drag hinge ("lag") -- slowing their progress, and airspeed, and reducing their excess lift. The lesser drag on the retreating blades would cause them to swing forward more aggressively ("lead") under driveshaft pressure and centrifugal force -- increasing their airspeed and lift.

When the autogyro bounced on rolling landings, though, the flapping, lagging and leading blades tended to set up a severe rhythmic oscillation that could tear the craft apart from "ground resonance." Cierva added dampers to the drag hinges, to settle things down.

Now Cierva had -- somewhat unintentionally -- resolved all the major remaining design problems with the helicopter rotor system.

To shorten takeoffs, he hooked a driveshaft from the autogyro's engine to a clutch connected to the rotor. Just before takeoff, he would engage the clutch long enough to start the rotors spinning, and then disengage the clutch and takeoff. But then why not simply leave the clutch engaged, and have it "helicopter" the autogyro into the air for vertical takeoff? Some later Cierva craft, with strong engines and rotors, did just that, popping up into ground effect before translating fully to horizontal autorotative flight..

Cierva's machines were enormously popular during the late 1920's to mid-1930's, and were used for all kinds of things, including European military operations, and American urban air mail express service (from suburban airports to the rooftops of city centers), and other challenging and creative applications. Amelia Earhart became one of the autogyro's biggest promoters, and most experienced test pilots, for an American manufacturer. Many other manufacturers, at home and abroad, began to copy them.

However Cierva's dandy machines were not intended for prolonged vertical flight, and therefore couldn't perform the key missions which would initially bring special value to the helicopter: vertical hoisting and lowering of heavy loads, and hovering rescue. For that, a REAL helicopter, incorporating Cierva's ideas, and those of his predecessors, along with more refined machinery and structure, would be required.


In Europe, many folks were hard at work developing various helicopter ideas, either directly, or through evolutions of the autogyro. These included Italy's d'Ascanio, who flew a twin-rotor coaxial craft well in 1929-1930, topping 57 feet in altitude, covering over a kilometer in distance, and managing only 8 minutes of flight.

Louis Breguet came back to the helicopter, with a fine-performing coaxial twin-rotor design, his Gyroplane Laboratoire, which traveled a record 27 miles in a November, 1936 flight, and clearly established that helicopters were not tied to ground effect, by rising over 500 feet.

German professor Heinrich Focke -- whose Focke-Wulf Fw-186V1 autogyro failed to unseat the Fieseler Storch as a STOL (short take-off and landing) forward-support military aircraft -- triumphed with the Focke-Achgelis FA-61 helicopter. A big beast, it was essentially an altered convential airplane design, with the wings replaced by frames sticking out from the sides of its fuselage, mounting a matched pair of counter-rotating rotors, whose counter-rotation neutralized the torque created by each. . The FA-61 showed off the potential of the helicopter -- particularly at the hands of aviatrix Hanna Reitsch, who flew it around Germany and in a famous performance in a Nazi exhibition hall in 1938.

Helicopters were getting out of ground effect, carrying loads, and traveling long distances. The helicopter was becoming a practical machine.


In the U.S., Igor Sikorsky's flying boats were slowly being eclipsed by long-range landplanes. His parent company, United Aircraft, turned him loose on the idea of the helicopter. They were not disappointed. The Russian-American dove into the business with the passion of a parent, and the savvy of a skilled, experienced airplane maker.

By May 1940, he'd pioneered the VS-300 -- a polished, open-cockpit helicopter using a single main rotor, balanced in torque by a small tail rotor. It incorporated the various lessons of his predecessors about helicopter rotor systems and flight controls. Cyclic and collective pitch controls allowed for the full range of helicopter motion, while the use of flapping hinges and drag hinges in the rotor hub made the craft stable and efficient at reasonable horizontal speeds. Sikorsky's helicopter could fly smoothly in all directions, and within a year was breaking all helicopter records -- achieving a speed of 60 miles per hour.

In its final form, the VS-300 was very nearly a practical helicopter.

World War II brought the development of the VS-300 into the fully operational REAL helicopter, the enclosed-cabin Sikorsky R-4 (right). Using a large main rotor and small tail rotor, and the various control and adaptation features pioneered by countless others, the R-4 set the shape of things to come -- pioneering the basic design package that has remained the dominant shape of helicopters ever since.

[NOTE: for more commentary and photos on the Sikorsky VS-300 and R-4, see the article "The Sikorsky R-4 Helicopter," in the Eight Great Aircraft, section of this website.]

Other designs have been tried, from the heavy-lifting tandem-rotor helicopters of Piasecki (later acquired by Boeing) to the tilt-rotor airplane/helicopter hybrid concept pioneered by Britain in World War I, tried by countless developers ever since (most famously, the current Bell V-22 Osprey).

While various rotor technologies have been tried, from "rigid" rotors to rotor/wing hybrids, the experiences of many helicopter lessons have continued to most strongly sustain the model derived from over a century of pioneering ideas, shaped into the classic main-rotor/tail-rotor helicopter designs of the mid-20th Century -- still dominant, and increasingly profitable, today.


Helicopter History links

This Helicopter History article is just the beginning of the story. Much more information about this subject can be found on others' websites, listed here:

The History of Rotorcraft

History of the Helicopter, Copter News, Hiller Museum
V-STOL The First Half-Century (AIAA)
US and Russian Helicopter Development, 20th Century (Hirschberg & Daley, Amer. Helicopter Soc. Int'l)
Helicopters through history
French and British Helicopters history (
A History of Helicopter Flight (Prof.J.Gordon Leishman, Aerospace Engineering, U. of Md., College Park)
Ed Holmes' Soundings - Aeromedical History Page
A Century of Flight - HELICOPTERS section
spectacularly elaborate, detailed website on every aspect of helicopters -- history, technology, brands and models (with specifications & data), stories, news, and various databases.


Bell 47 WEB Site Project, UToronto Bell 47 Helicopter Movies, Videos, and Television
Bell 47 WEB Site The Bell 47 Helicopter Library

Cessna / Seibel

The Cessna CH-1 Helicopter, by Steve Remington, CollectAir
(superb history of Charles Seibel's pre-Bell designs)
Cessna Helicopter -- on Yahoo "flickr"
(good photos of Seibel's designs, and of related articles)
Virtual Aviation Museum:
  • Seibel S-4 "Skyhawk" / YH-24 (1951)
    (good photos of Seibel's early designs, with some explanatory/historical text)
  • Cessna CH-1 / YH-41 "Seneca" (1954)
    (good photos of Seibel's Cessna designs, and a drawing, with some explanatory text)
  • Eurocopter / Aerospatiale / Messerschmitt-Bolkow-Blohm

    Eurocopter (official company history)
    Eurocopter history, organization & aircraft (
    Aerospatiale (history, organization & aircraft) Helis-com


    Hiller Aviation Museum
    Stanley Van Winkle Hiller

    Hughes Helicopter

    Hughes / McDonnell Douglas / Boeing Mesa (Amer. Helicopter Soc., Int'l)

    Piasecki/Vertol/Boeing family

    P-V / Piasecki / Vertol / Boeing-Philadelphia   (Am. Helicopter Soc., Int'l)
    Boeing-Vertol SeaKnight
    Boeing-Vertol Chinook


    Igor I. Sikorsky Historical Archives, Inc.
    Igor I. Sikorsky Historical Archives, 1st rescue


    Google's Rotary Wing directory
    Westland Helicopters since 1915 (official company history)
    Westland & Agusta Merger (Int'l Herald Tribune)
    Westland history (unofficial)
    Robinson Helicopter Company - Intro Movie Page

    VTOL/Rotorcraft Technology

    Principles of Rotary Flight (Westland Helicopters)