Sikorsky Archives Photo
Sikorsky’s “last-ditch” effort to save his company established an industry.
The vertical aviation industry is on the threshold of a new era, one promising frequent flights of multirotor aircraft powered by distributed sets of computer-managed electric motors. Advocates for this fledgling sector of electric vertical takeoff and landing (eVTOL) aircraft are developing vehicles capable of carrying small loads of passengers and light payloads between urban and suburban vertiports, independent of runways.
Nearly 200 eVTOL projects were unveiled in 2021, with estimated funding doubling, according to the Vertical Flight Society, which closely monitors the sector. Another 100 were added through July 2022. Most are still confined to drawing boards, but some developers are flight testing aircraft, with ambitious certification goals.
This surge in engineering, development, and financing mirrors a two-decade period 100 years ago in which increased interest, energy, and funding—and the dedicated pursuit of solutions by aircraft designers and engineers—led to the rotorcraft industry’s birth with Igor Sikorsky’s development in 1939–41 of the first practical helicopter, the VS-300.
In both eras, engineers and entrepreneurs aimed to advance the state of the art in vertical flight. But their tasks were distinctly different. Sikorsky and his colleagues were working out the essential issues of lift and control in rotorcraft. Today’s eVTOL teams are focused largely on building new aircraft power systems that will use multiple small rotors, each with its own motor, and advanced avionics to manage them as lifting devices and flight controls.
A century ago, the task for the pioneers in rotorcraft was less complicated but completely fundamental to vertical aviation: figuring out how to lift and control their aircraft.
Engine choice, while critical, was limited in the early 1900s to what was available from the automobile and early airplane markets. “There was no useful, analytical engineering base” on performance and stability, aeronautical engineer Eugene Liberatore wrote in his 1998 classic, Helicopters Before Helicopters. (It was based on the 18-volume Rotary Wing Handbooks and History that he edited in the 1950s for the US Air Force.)
Before beginning his first helicopter design effort in Russia in 1909, Sikorsky visited Paris, then aviation’s epicenter. He sought to learn from experts and to find an engine. He returned with knowledge and a 25-hp. (18.6-kW) aircraft engine built by Alessandro Anzani. While that model would power Louis Blériot’s first airplane flight across the English Channel on Jul. 25, 1909, the Anzani could not lift Sikorsky’s H-1, a basic coaxial-rotor helicopter, off the ground that year in Kiev, which at that time was part of Russia. It could lift his H-2, tested in 1910, but not both craft and pilot.
“Less bad than the rest” was how Sikorsky is said to have described his first engine choice.
Working the Problem of Vertical Flight
Inventors’ struggles “to give the helicopter a place” in world transportation have well-documented histories going back more than 250 years, as Franklin Harris summarized in NASA’s 2012 Introduction to Autogyros, Helicopters, and Other V/STOL Aircraft. Two and a half centuries ago or so, there were several attempts with small coaxial aircraft in Russia, France, and England. Experimentation accelerated through the 1800s. Almost all used coaxial designs to address torque reaction and dissimilar lift in forward flight. All that testing was done with models, according to John Fay, a 1950s and ’60s Westland Aircraft test pilot.
“Given the minimum knowledge of how a propeller worked and some form of power… it was not difficult to design a model lifting device,” Fay wrote in The Helicopter: History, Piloting & How It Flies, his 1976 book. “It was a much more complex exercise, however,” to design an aircraft capable of taking off, hovering, and moving forward under control while carrying a human.
In Germany, Nikolaus Otto’s 1876 invention of the four-stroke internal combustion engine created the possibility of power-to-weight ratios sufficient to carry helicopters and their pilots aloft, Fay noted. “But before helicopter flight became a practical reality, there were the mysteries of translational flight and stability to be solved.”
The reliance entirely on test models waned in 1907. Brothers Louis and Jacques Bréguet—guided by scientist Charles Richet—built and flew their first gyroplane in a tethered flight south of Lille, in northern France. It rose about 2 ft. (0.6 m). The pilot’s only control was an engine throttle.
Also in 1907, in Lisieux, France, Paul Cornu built a twin-rotor helicopter with control vanes below the blades. The rotors were powered by a 24-hp. (18-kW) Antoinette engine built by French engineer Léon Levavasseur. A frame mounted on four bicycle wheels held the machinery. On Nov. 13, 1907, Cornu straddled the frame just behind the engine and ran it and the 20-ft.-diameter (6-m-diameter) rotors up. The helicopter lifted slightly off the ground for about 20 seconds, with no tethers or ground-crew support.
Cornu is credited by, among others, world’s record keeper Fédération Aéronautique Internationale, with being the first person to pilot a helicopter in free flight. Some question whether his craft actually flew, saying flight would have required at least a 40-hp. (30-kW) engine. Regardless, Cornu would go on to conduct 15 piloted flights, according to Liberatore.
The significance of Cornu, who died in the 1944 Allied forces bombing of Nazi-occupied Lisieux, lies “in his systematic and scientific attempts to understand the relationship between rotor thrust and power requirements,” according to the Vertical Flight Society, “and in exploring methods of controlling a helicopter in flight and in its forward propulsion.”
In the 20th century’s first decades, aviation focused on expanding the Wrights’ successes. Wilbur Wright’s 200-plus demonstrations, starting in 1908, in France, Italy, and Germany whet the appetite of thousands of inventors, some of whom pursued vertical flight. One was Danish engineer Jacob Ellehammer, whose 1912–16 flights in his aircraft with two 25-ft.-diameter (7.62-m-diameter) counter-rotating discs—powered by a custom-built 36-hp. (27-kW) radial engine—demonstrated an early form of cyclic control.
The Autogiro’s First Flight
World War I focused aviation’s attention entirely on fixed-wing craft. After the war, numerous inventors returned to vertical lift. Among the most influential was a man who never built a helicopter: Juan de La Cierva, inventor of the autogiro. The Spanish engineer’s aircraft used a tractor engine to propel a fixed-wing airplane and an unpowered rotor to help lift it, with the rotor spinning in autorotation in forward flight. La Cierva’s aircraft gained acceptance and success in the 1920s in Spain and England, where he established the Cierva Autogiro Company.
La Cierva concentrated on refining rotor design, relying on other manufacturers to provide the fixed-wing portion of the autogiro. This led in 1922 to his most important rotorcraft contribution: the flapping-hinge rotor, which offsets the differential lift of advancing and retreating blades. Flapping reduces roll resulting from dissimilar lift. It became a common rotorcraft design feature.
La Cierva’s success caught the attention of Harold Pitcairn, a Pennsylvania business owner who had founded the predecessor to Eastern Airlines and an airplane manufacturing company, both bearing his name. He licensed rights to develop autogiros.
On Dec. 18, 1928, a Cierva C.8W assembled by Pitcairn Autogiro Company became the first rotary-wing aircraft to fly in the United States. According to the Vertical Flight Society: “Pitcairn subsequently developed a range of autogiros and related technologies” and patents. Many found their way into the first American helicopters. Among them was Pitcairn’s articulated rotor-head technology, which Sikorsky licensed for the VS-300.
Born of Necessity
The VS-300 was a last-ditch effort to save Sikorsky’s company. Parent United Aircraft Corporation owned engine maker Pratt & Whitney, Vought Aircraft, and Hamilton Standard Sikorsky. The company merged the latter two into the Vought-Sikorsky Division.
After emigrating to the United States in 1919, Sikorsky had made his name building flying boats for the US Navy and airlines, most famously Pan American Airways. But in 1938, the Navy declined to order the next-generation XPBS-1 “Flying Dreadnought.” All previous aircraft orders had been filled. With none on the horizon, United Aircraft planned to shutter Vought-Sikorsky.
A company vice president summoned Sikorsky to the Hartford, Connecticut, headquarters to break the news and suggest to Sikorsky that he could undertake a new, small research project. Sikorsky proposed developing the direct-lift aircraft for which he had submitted a patent and plan in 1930, provided he could retain a team of engineers and mechanics. He estimated the work would cost $60,000. United Aircraft gave him $30,000.
Working nights and weekends, Sikorsky and his team turned that 1930 idea into a test aircraft, the H-3. In a 1930 paper titled “The Helicopter Problem,” Sikorsky explained to management about the H-3 design: “The most important problem to be solved in order to achieve complete success and to build a directly useful machine appears to be in the question of proper stability and control.”
To help solve that problem, Sikorsky’s team designed and built the first helicopter simulator, Test Rig #4950. Sikorsky and aerodynamicist Serge Gluhareff (who would share VS-300 test-pilot duties) would use it to learn a new skill: how to fly a helicopter.
To power the VS-300’s three-blade, 28-ft.-diameter (8.5-m-diameter) main rotor and 40-in.-diameter (1-m-diameter) tail rotor, Sikorsky acquired a 1939 Lycoming four-cylinder piston O-145-C3. Team members bought it secondhand at a local airport, Sikorsky’s son Sergei told ROTOR. “The whole program was fairly low budget, low priority at the beginning,” he said.
Begun as a mid-1800s manufacturer of sewing machines and bicycles, the company that became Lycoming started producing automobile and truck engines in 1907. After Charles Lindbergh’s 1927 solo transatlantic flight, the company began making aircraft engines. The O-145 was Lycoming’s first horizontally opposed, air-cooled engine. The O-145-C3 was its most powerful version, producing 75 hp. (56 kW) at 3,100 rpm.
Mounted horizontally, Engine No. 510 powered the VS-300 through a V-belt transmission. On Sep. 14, 1939, Sikorsky flew the VS-300 in its first tethered flight. The aircraft rose a few inches during the 10-second flight at the Stratford, Connecticut, plant. Through 1939, the team tweaked the VS-300 continually, resolving control and stability issues. Tethered flights continued until Dec. 19, 1939, when the prototype was damaged severely in a rollover.
The VS-300’s second configuration added arms to a new, steel-tube tail boom that supported two horizontal tail rotors for pitch and roll control. (The main rotor’s cyclic control was removed because of controllability issues.) The O-145-C3 went to work again on Mar. 6, 1940, when the redesigned VS-300 flew in a tethered flight. On May 13, 1940, before the public in Bridgeport, Connecticut, Sikorsky lifted off the VS-300 in its first free flight.
Engine 510 logged fewer than 50 hours through Jul. 22, 1940. At that point, Vought-Sikorsky sold it for $225. “They had enough experience to realize they needed more horsepower,” Sergei Sikorsky said. An Aircooled Motors Franklin 4AC-199-E replaced it.
The air-cooled, four-cylinder horizontally opposed Franklin produced 90 hp. (67 kW) at 2,500 rpm. It powered the VS-300 through April 1941, when an upgraded 4AC-199 was installed, achieving 90 hp. (67 kW) at 2,680 rpm and 100 hp. (75 kW) at 3,050 rpm. Franklin engines powered the VS-300’s 1941 US and international endurance records.
The timing of Vought-Sikorsky’s threatened closure proved fortuitous. Impending war in Europe had increased US interest in all aviation. In June 1938, the Dorsey-Logan law called for the War Department to invest $2 million in research, development, purchase, and testing of rotary-wing and other aircraft. Next came a 1940 US Army competition for an aircraft capable of vertical flight and hovering.
The Platt-LePage Aircraft Company won with its XR-1 transverse-rotor design, considered more capable than the bid proposed by Vought-Sikorsky based on the VS-300. But Platt-LePage experienced testing delays. So the army awarded Dorsey-Logan funds to Vought-Sikorsky to develop the aircraft that became the R-4.
Purchased by the US Army Air Forces, Navy, and Coast Guard and by the Royal Air Force and Royal Navy, the two-seat R-4 became the first large-scale, mass-produced helicopter.
Today’s eVTOL and advanced air mobility (AAM) sector “is a thriving market with many start-ups that vie to certify and produce new and innovative aircraft this decade,” says Sergio Cecutta, a partner at SMG Consulting, which specializes in aerospace, defense, and automotive technology. Several analysts predict this fledgling industry could be a $1 trillion market by 2050.
But just like Sikorsky and the VS-300, there are still some details to work out.
“You may have an aircraft with six lifting rotors, three or four tilting rotors, and a pusher rotor,” says Jia Xu, Honeywell chief technology officer and senior director of engineering for advanced air mobility. “There’s not a great way for the pilot to directly control those rotors or some easy way to blend them together mechanically.” eVTOL will need systems that can “allocate control power across all of your actuators and all your rotors” in an optimized fashion.