IMechE Archive and Library

By Eric Edwards

Depending upon which date one uses (or which authority one believes), this year marks the 100th anniversary of what many aviation historians consider the first successful free flight of a helicopter. On 18 February 1921, French engineer and inventor Étienne Oehmichen reportedly hovered his experimental “vertical flying machine” approximately 20 feet off the ground for a minute or so over the countryside [1, 2]. As far as we know, no one got hurt, and nothing flew apart. And the rest, as they say, is history.


Admittedly, Oehmichen’s historic accomplishment may seem a bit unremarkable today, as the fixed horizontal propellers on his odd-look­ing, skeletal-framed aircraft restricted its functionality to just lifting and lowering, with no real capability for controlled forward flight. As such, the prototype was just one in a long line of early helicopter designs (including Leonardo da Vinci’s famous “aerial screw” design in the 1400s), some of which worked and some of which didn’t. Nonetheless, according to an article in the June 1921 issue of Popular Science Monthly, Oehmichen’s demonstration of untethered, manned flight earned the Frenchman (pictured in Figure 1) the distinction of being “the first man . . . ever to rise from the ground with a helicopter” [3].

Figure 1. Étienne Oehmichen in One of His Vertical Flying Machines.

The article—authored by Henry Mathis, an engineer, correspondent, and former classmate of Oehmichen’s—also provided some details of the experimental rotorcraft’s composition and capabilities. The machine reportedly weighed 570 lbs, was powered by a two-cylinder 25-hp motor, and featured two “recuperating screws” (or rotors), as well as a large hydrogen-filled balloon attached to the top of the airframe. Some people thought the balloon was meant to provide the aircraft’s lifting power; however, its primary purpose, as Mathis explained, was actually to provide aerial stability (countering the torque reaction caused by the rotors spinning in the same direction) [3].

Mathis also predicted one advantage the helicopter would likely have over fixed-wing airplanes and dirigibles. Namely, people would no longer have to go to a large airstrip (or “flying field”) outside of town to be able to access the skies [3]. Little did Mathis know just how important this predic­tion would turn out to be. Not only would the helicopter make flight a much more accessible possibility for everyone, but it would also soon give the world’s militaries—especially the U.S. military—important tactical capabilities they’d never had before. The whole planet would now be one big potential helipad, and U.S. air defense operations could be con­ducted not just from a static runway or airfield but from virtually any place a rotorcraft could touch down, including a small jungle clearing in a Southeast Asia, the edge of a rickety rooftop in Afghanistan, and a rolling deck of a warship in the middle of the ocean.

Not everyone, however, was con­vinced by Oehmichen’s accomplishment (or Mathis’s descrip­tion of it). In fact, Waldemar Kaempffert, the editor of Popular Science at the time, published a short “disclaimer” alongside Mathis’s article doubting its assertions. Kaempffert wrote [3]:

“The fact that Oehmichen has used a balloon in rising from the ground makes us question the validity of his results as Mr. Mathis presents them. No one will be convinced that a practical helicopter has been invented until it has flown without buoyant gas. In its present form, Oehmichen’s helicopter is nothing but an airship driven vertically by horizontal propellers. A successful helicopter must not only ascend straight up, but be able to descend slowly; it must be able to fly horizontally like an airplane; it must be stable. In our opinion, Oehmichen has not yet succeeded in solving the highly important problem of stability.”

But Oehmichen would not be deterred. Within a year, the Frenchman had addressed the stability issue (both real and perceived), as well as improved the overall design of his rotorcraft. Instead of using a stabilizing balloon, the Oehmichen No. 2 model (shown in Figure 2) used two small, vertically mounted rotors that spun in the opposite direction of the main lifting rotors (essentially becoming the forerunners to the modern helicopter tail rotor) [2].

Figure 2. Oehmichen’s No. 2 Model.

In 1924, Oehmichen would also set the first helicopter world record, flying his quadrotor aircraft almost 1,200 ft; and he would win a competition to complete the first closed-circuit helicopter flight, flying a 1-km triangu­lar flight path in just under 8 minutes. In addition, the same year his aircraft would successfully carry two passen­gers [2].


Oehmichen’s early proof-of-concept would, of course, be followed by many more advances in helicopter technol­ogy and application over the next century. In particular, it wouldn’t take long for U.S. military planners to realize the value of this versatile new vehicle for defense operations. After all, if one could carry multiple passen­gers on these machines, why not Warfighters, weapons, and the wounded? And thus began a nonstop stream of advancements in military rotorcraft that continues to this day.

The 1930s would see the world’s first truly operational, practical helicopter—the German Focke-Wulf (Fw) 61 (shown in Figure 3)—which imple­mented twin counter-rotating main rotors to handle the aforementioned torque problem [4, 5]. However, during the same decade, Russian-born aviation innovator Igor Sikorsky, would replace the coaxial rotor design with a single, three-bladed main rotor and a smaller vertical tail rotor on his VS-300. This landmark change by Sikorsky, who is often called the father of the modern helicopter, would be adopted by most future helicopter developers (even though the VS-300 would be nicknamed “Igor’s Nightmare” by Sikorsky mechanics who had to constantly wrestle with its notorious vibration problems) [6].

Figure 3. The Focke-Wulf 61 (Courtesy of Wikimedia Commons).

The first record of a U.S. helicopter being used in combat came during World War II, when a Sikorsky R-4 (designated HNS-1) rescued four downed airmen behind enemy lines in Burma in 1944 [7]. With more than 130 R-4’s ultimately built, the aircraft (shown in Figure 4) was also consid­ered the first “production” helicopter, as well the first to operate from the deck of a ship [6, 8].

Figure 4. An R-4 During World War II (NASA Langley Photo).

The Bell Model 47 (designated the H-13 Sioux by the Army) would likewise see action in the skies over Korea in the 1950s. With its signature “soap bubble”-shaped canopy and twin medical evaluation (medevac) litters, the helicopter would evacuate more than 15,000 wounded U.S. troops from the battlefield (see Figure 5) [6]. The rotorcraft would also be widely recognized long after the war as it regularly appeared on the hit 1970s television series M*A*S*H.

Figure 5. Offloading a Wounded Soldier From a Bell 47 in Korea (U.S. Army Photo).

Stanley Hiller’s popular UH-12 would also be used in Korea, as would a couple of his unique-looking “Hiller Hornets.” The Hornet was an ultra­light helicopter powered by a ramjet on each end of the aircraft’s lone rotor blade. The U.S. military would end up purchasing only a couple of the innovative rotorcraft, however, due to several safety and survivability issues. In particular, while operating at night, the spinning ramjets created a “halo” of fire above the helicopter [6]. Though the effect (shown in Figure 6) made a spectacular display for observers, it also made a pretty good target for adversaries.

Figure 6. The Hiller Hornet’s Ramjet Ring of Fire (U.S. Army Aviation Museum).

Vietnam would be the conflict in which the helicopter would prove its true worth as a critical U.S. wartime asset. The “workhorse” of the 20-year war was the UH-1 utility helicopter—or “Huey,” as it came to be called. Initially intended to be an Army medevac vehicle, the turbine-powered Huey (shown in Figure 7) ended up trans­porting nearly 900,000 wounded U.S. personnel during the war, which was more than 50 times that of Korea. Furthermore, the Huey became the U.S. military’s virtual Swiss army knife, ferrying a wide assortment of cargo and personnel all across Southeast Asia. Its accessibility and versatility also helped permanently change the way U.S. troops are deployed for quick assaults [6].

Figure 7. UH-1 Troop Insertions in Vietnam (U.S. Army Photo).

The CH-47 Chinook was another innovative and important helicopter asset that first appeared during the Vietnam era. The Chinook met the U.S. forces’ critical need for a heavy-lift helicopter to move large loads of troops and equipment (even downed aircraft) across warzones. Designers of the helicopter would forego the tail rotor and return to the use of two large counter-rotating rotors, one on a front pylon and one on a rear pylon, so that all of the blade power could be directed to lift and thrust. In addition, because each rotor could be indepen­dently controlled, the helicopter offered much better stability than single-rotor aircraft when loading and unloading large amounts of weight. This stability would later be famously demonstrated in Afghanistan when a Chinook was photographed hovering in place with its tail perched on the edge of a roof while personnel were being loaded (see Figure 8).

Figure 8. Chinook Loading Personnel in Afghanistan (Photo Courtesy of U.S. Army SGT Greg Heath).

The heavy reliance on cargo and transport helicopters during the Vietnam War also made clear the increasing need to protect them and their occupants from enemy assault, especially during take-off and landing. Though the Hueys and other utility helicopters were equipped with some armaments to protect themselves—and even served as dedicated “gunships”—they weren’t really designed to be “weapons.” The Bell AH-1 Cobra, on the other hand, was. The first true “attack” helicopter, the Cobra (shown in Figure 9) had a smaller frontal target signature (incorporating a cockpit that placed the pilot and copilot in front of, instead of next to, each other). It also had the ability to carry twice as much ammuni­tion as a Huey gunship, arrive on target in half the time, and stay there three times longer. In short, the helicopter was specifically designed to go looking for a fight. And it found a lot of them, reportedly logging a million operational hours in Vietnam [9].

Figure 9. AH-1 Cobra Gunship (U.S. Army Photo).

Admittedly, some of the lessons regarding rotorcraft technology and operations during the Vietnam War were hard lessons to learn. Many helicopters were shot down, and many U.S. combat personnel perished. However, these hard lessons would also lead to an unprecedented, concerted effort between the Department of Defense (DoD)—par­ticularly the Army—and industry to better analyze and improve the safety, survivability, and effectiveness of all current and future rotorcraft. From now on, survivability would no longer be something to be considered after a helicopter was fielded. It would be a formal engineering discipline that would be part of every new helicopter design.

Perhaps the fruit of this new approach was best seen in the emergence of the tough and highly versatile Black Hawk utility helicopter, or UH-60, in the late 1970s. The development of the Black Hawk (shown in Figure 10) adopted a much more holistic approach to survivability and safety than any previous helicopter. Its numerous advancements included twin-engine redundancy, a more crash-resistant cabin, an energy-absorbing landing gear, and the ability to be transported in a C-130 cargo hold without having to remove the blades [6]. In addition, this highly adaptable rotorcraft would continue to be upgraded and modern­ized over the years, with the latest versions featuring significant enhance­ments in electronic warfare and stealth technologies [10]. Thus, it’s not surprising that the UH-60 continues to be heavily used not only by the Army but by the Navy, Air Force, and Coast Guard as well.

Figure 10. UH-60 Black Hawk (U.S. Army Photo by SGT Taresha D. Neal).

Likewise, the Apache attack helicopter, or AH-64, entered production in the 1980s to provide better firepower, maneuverability, and range capabilities than its AH-1 predecessor. It incorporated more damage-tolerant materials and armoring, numerous redundant critical systems, better sensors and signature reduction capability, improved crash resistance, as well as a devastating 30-mm chain gun and changeable missile and rocket packages. As a result, the Apache (shown in Figure 11) continues to be one of the most survivable and lethal helicopters in the skies today, and it has continued to prove its status as the Army’s (and several allied coun­tries’) main attack helicopter everywhere from Kuwait to Iraq to Panama to Kosovo to Afghanistan [11].

Figure 11. AH-64 Apache (Photo Courtesy of Tim Felce).

Another revolution in helicopter technology occurred in the late 1980s, when the V-22 Osprey first took to the skies. The large multimission helicop­ter (shown in Figure 12) introduced a unique new tiltrotor design to combine the vertical takeoff and landing (VTOL) advantages of a rotorcraft with the high-speed and long-range advan­tages of a turboprop fixed-wing airplane. Though the tiltrotor technol­ogy has, at times, presented unique challenges for engineers and opera­tors—largely due to an aerodynamic instability that occurs during the transition of the rotors from horizontal to vertical flight—the Osprey has been successfully deployed for transport and medevac missions in numerous conflicts. Thus, tiltrotors continue to be one of the most promising technolo­gies for future helicopter designs [12].

Figure 12. CV-22 Osprey (U.S. Air Force Photo by Yasuo Osakabe).

Finally, how ironic it is that one of the last major developments to occur in the first century of helicopter history has been the emergence of unmanned aerial vehicles (or UAVs), or drones. As difficult as it was for Oehmichen and others to be able to get people aloft with a rotary-wing aircraft a century ago, military planners have increasingly realized the value and versality of being able to take to the skies without having to risk (or accommodate) the safety of human operators and occupants. Thus, many efforts continue throughout the DoD to develop and deploy unmanned rotorcraft of all sizes for a wide range of missions, including intelligence, surveillance, and reconnaissance; troop and equipment transport; medevac; resupply; and assault (see Figure 13) [13, 14].

Figure 13. MQ-8B Fire Scout UAV (U.S. Navy Photo).


As far as the next 100 years of helicopter development goes, one can only imagine what new heights these versatile machines, and the military’s application of them, will be able to reach. As we speak, DoD and industry practitioners are working hard to optimize the capabilities of the current U.S. fleet as well as develop brand-new rotorcraft—such as the Army’s Future Long Range Assault Aircraft (FLRAA) (a demonstrator of which is shown in Figure 14)—which are planned to be faster, more survivable, more lethal, and more effective than any before [14, 15].

Figure 14. SB-1 Defiant Demonstrator (U.S. Army Photo by SGT Dana Clarke).

Of course, many questions also remain. Will the rotorcraft a century from now be as radically different from those of today as the latest prototypes are from Oehmichen’s first flyers? Will the age-old line between utility/cargo and attack/reconnaissance helicopters (and maybe even between fixed- and rotary-wing) be increasingly blurred as developers build in adaptability for different capabilities and missions? And are there unknown technologies waiting just over the horizon that will make our current rotorcraft technolo­gies and applications largely obsolete?

Furthermore, in the world of safety and survivability, will the skies over future battlefields be filled with swarms of unmanned (and maybe even “disposable”) drones rather than manned rotorcraft? Will the focus on cyber warfare and threats eventually overtake traditional ballistic survivabil­ity concerns and efforts? And will ongoing advancements in stealth technology and targeting be such that future hostile forces will never even see or know the helicopters that hit them?

Ultimately, only time can answer these questions. But whatever happens, may the spirit and optimism of the next 100 years of helicopter history be just as strong as those of the first. May the imaginations of rotorcraft innovators never be dimmed by the fear of failure or the voices of criticism. And may the great potential embodied in this unique air vehicle continue to rise to greater and greater heights with the passage of time. After all, when it comes to the helicopter, the sky is truly the only limit.


[1] McEvoy, Janet. “Ten Ways Helicopters Changed the World.” International Business Times,, 11 February 2021.

[2] Institute of Mechanical Engineers. “Experimental Helicopters.” https://imechearchive., 16 July 2013.

[3] Mattis, Henry. “Straight Up From the Ground: Oehmichen Invents a New Flyer.” Popular Science Monthly, June 1921.

[4] Prime Industries. “History of the Helicopter From Concept to Modern Day.” https://primeindus­, 31 August 2015.

[5] Markowitz, Mike. “World War II German Helicopters—Henrich Focke’s Fa 61.” Defense Media Network, https://www.defensemedianetwork. com/stories/nazi-helicopters-henrich-fockes-fa-61/, 25 March 2013.

[6] Lemos, Robert. “The Helicopter: A Hundred Years of Hovering.” WIRED, https://www.wired. com/2007/12/gallery-helicopter/, 12 December 2007.

[7] Kreisher, Otto. “Rise of the Helicopter During the Korean War.” HistoryNet, https://www. use%20of,behind%20enemy%20lines%20in%20 Burma, accessed March 2021.

[8] “First Combat Helicopter.” https://, accessed March 2021.

[9] Joiner, Stephen. “Birth of the Cobra: Mike Folse Proved That a Helicopter Could Fly and Shoot at the Same Time.” Air & Space Magazine, https:// aug2017-birth-of-the-cobra-180963930/, August 2017.

[10] Trevithick, Joseph, and Tyler Rogoway. “This Is the First Photo Ever of a Stealthy Black Hawk Helicopter.” The War Zone, https://www.thedrive. com/the-war-zone/35342/this-is-the-first-image-ever-of-a-stealthy-black-hawk-helicopter, 4 August 2020.

[11] Harris, Tom. “How Apache Helicopters Work.” HowStuffWorks, apache-helicopter6.htm, accessed March 2021.

[12] Nye, Logan. “How America’s Most Troubled Aircraft Will Define the Future.” We Are the Mighty, tilt-rotor-v-22-helicopter/, 29 April 2020.

[13] Keller, John. “Northrop Grumman to Build Five New MQ-8C Fire Scout Unmanned Shipboard Helicopters in $55.1 Million Deal.” Military & Aerospace Electronics, https://www.militaryaero­ northrop-grumman-to-build-five-new-mq8c-fire-scout-unmanned-shipboard-helicopters-in-551-mil­lion-deal, 31 July 2019.

[14] Keller, John (editor). “Army’s Scout and Reconnaissance Helicopter Should Be Able to Operate Unmanned Aircraft From Its Cockpit” Military & Aerospace Electronics, https://www. helicopter-scout-unmanned, 6 July 2020.

[15] Future Vertical Lift Cross-Functional Team. “Army Chief of Staff on FVL Assault Aircraft: ‘We’re Flying Before Buying.’” army_chief_of_staff_on_fvl_assault_ aircraft_were_flying_before_buying, 9 November 2020.