In the years following the Second World War, newly-formed helicopter manufacturers created a raft of new designs they hoped would take the world by storm. This is the story of three such aircraft that never made it to full-scale production.

Following the introduction of helicopters in the latter part of the Second World War and the start of the commercial rotary-wing industry in 1946, the newly formed helicopter manufacturers prepared for an expected surge in both military and civilian sales.

Having produced the R-4, R-5, and R-6 helicopters during the war, Sikorsky Aircraft was successful in its introduction of the four-place S-51 (for military and civil markets) and the two-place S-52. 

Bell Aircraft succeeded in putting its two-place Model 47 into production, which had become the first commercial helicopter in the world during 1946. Its Model 42 and Model 48 helicopters had only limited success at the time.

Hiller Aircraft had perfected its one-place coaxial XH-44 helicopter, and Stan Hiller was already looking at getting into commercial production. Kaman and Piasecki were also both producing helicopters for military and limited civil use.

Even with the many notable successes of the late ’40s, there were many more attempts to bring newly designed helicopters to market that failed. This is the story of three of the more noteworthy aircraft that never were.

The Hiller X-2-235

The Hiller-copter Model XH-44, created by a young Stan Hiller, is generally considered to have performed the world’s first successful co-axial helicopter flight. It recorded the noteworthy achievement near San Francisco, California, in the early 1940s. The first free flight of the type took place on July 4, 1944, with an initial public showing on Aug. 30, 1944. Hiller was determined to get his new helicopter into commercial production, but also knew this would require additional financial support.

This support eventually came from wealthy shipbuilder and helicopter enthusiast Henry J. Kaiser. Kaiser had himself manufactured a two-place helicopter called the Fleetwings XR-10 Twirleybird in Bristol, Pennsylvania, in 1944. The same year, Hiller demonstrated his XH-44 to Kaiser at his shipyard, and during a second demonstration visit, Kaiser actually hovered the XH-44. He was ecstatic after he got out of the helicopter, and told Hiller that he wanted arrange a contract for Hiller to build a helicopter for him. 

Kaiser wanted the new helicopter to be built at Fleetwing’s facilities in Pennsylvania. Hiller agreed to the production contract, but not to the relocation. Still, Hiller Aircraft became the Hiller-copter Division of Kaiser Cargo, and Hiller benefitted from new finances and the experience of Kaiser’s knowledgeable staff. Under the Kaiser contract, Hiller designed, built, and tested a new two-place co-axial helicopter with super-rigid metal rotor blades. Each of the two main rotors had two blades. Powered by a Lycoming 235-horsepower engine, the aircraft — called the X-2-235 — was created to be a successor to the XH-44, and was designed for speed. 

During October 1944, construction began on three X-2-235 helicopters, but the program was veiled in wartime secrecy. Ground tests started in the summer of 1945 in Berkley, California, and although Hiller did not have any military contracts in hand, he planned to solicit the U.S. Navy to use the new helicopter as an observation and training machine. While the Navy never procured the helicopter, it did accept the third unfinished X-2-235, designated as the UH-1X, for wind tunnel testing at the National Advisory Committee for Aeronautics (NACA) in Langley Field, Virginia. 

It was Hiller’s first ever Navy contract, but vibration problems with the UH-1X/X-2-235 brought a swift end to the program. Hiller was a quick learner, and redesigned the X-2-235’s main rotors to include three blades, as well as a rear propeller, stub wings, and retractable landing gear. 

As the new helicopters were getting close to tethered flight in early 1945, Hiller and Kaiser clashed over finances, with Hiller having requested an injection of additional cash to get the aircraft into production. Kaiser agreed to continue financing the project, but only at the existing level — there would be no additional funds. As a result, Hiller and Kaiser parted ways and the X-2-235 program came to an end.

The three existing X-2-235 helicopters remained with Kaiser, but appear to have disappeared with the passage of time. Years later, Hiller himself tried to locate them, but had no luck doing so.

In time, Hiller — whose new company was called United Helicopters Ltd. — was successful in obtaining financial backing in California. With this support, he was able to certify and manufacture his famous Hiller Model 360 three-place helicopter, which found a home in both the civil and military helicopter markets. On Oct. 14, 1948, Hiller’s was the third company in the U.S. to certify a commercial helicopter for civil use, following in the footsteps of Bell and Sikorsky.

The Bell Model 54

Over at Bell Aircraft in Niagara Falls, New York, the company had obtained a contract from the U.S. Army Air Forces (the predecessor to the U.S. Air Force) to build a prototype for a competition to produce a new observation and utility helicopter. The contract, awarded in February 1946, saw the creation of the Model 54/XR-15 — a three-seat helicopter powered by a supercharged engine. Bell had, in fact, only won second place in the design competition (G&A Aircraft/Firestone was awarded first place, for its XR-14-GA), but was still asked to develop three prototype Model 54s.

In 1947, the U.S. Air Force replaced the Army Air Forces, and took over the contract, which called for the aircraft to be developed for both the Air Force and Army Ground Forces. In 1948, the Model 54/XR-15 became the XH-15, and in September of that year, Bell received a contract from the Air Force for the aircraft. On March 15, 1948, the XH-15 performed its first flight, with Bell test pilot Owen Niehaus at the controls. 

The three-place observation helicopter permitted a high degree of versatility for military use, with a Continental X0-470-5 or Franklin X0-425-7 300-horsepower turbocharged engine maintaining sea level performance in excess of 10,000 feet (3,050 meters). Its range was 200 miles (320 kilometers), it had a four-hour endurance, a maximum speed of 110 mph (170 km/h), and a service ceiling of 20,000 feet (6,100 meters). It had a normal gross weight of around 3,000 pounds (1,360 kilograms), and a length of 27 feet, 10 inches (8.49 meters).

The helicopter had a semi-monocoque construction, with a high inertia autorotation rotor system similar to the Model 47, and came with interchangeable wheels, floats, skid, and ski gear. It was equipped for instrument flying, and could easily be winterized for Arctic operations.

“While flight testing the XR-15 Sept. 1, 1948, with Charlie Barr project engineer, a fuel line break was experienced while doing saw-toothed climbs through 10,000 feet,” Niehaus recalled in a written memoir of his career in helicopters. “We autorotated successfully north of Bond Lake, N.Y. The smell of fuel in the cabin was overwhelming.”

Development of the XH-15 reached the flight test stage, but, according to an Air Force historical report, the program was terminated because of the incompatibility of the rotor system and supercharged engine. This incompatibility resulted in engine surging, which could not be eliminated. The family of engines available for conventional liaison helicopters was not suitable because of their high weight/horsepower.

While the Model 54/XH-15 was extensively tested by the Air Force into the 1950s for high altitude research vehicles, they purchased no further helicopters from Bell. Unfortunately, no examples of the Model 54/XH-15 helicopters appear to have survived or were preserved.

The Sikorsky S-53

In 1947, Sikorsky Aircraft designed and manufactured the S-53/XHJS-1 for a U.S. Navy competition. The Navy was looking for a four- to five-seat rotary-wing aircraft to be used for observation, utility operations, and search-and-rescue duties. Sikorsky’s S-53 was up against Piasecki Aircraft’s tandem-rotor XHJP-1/HUP-1 helicopter for the tender. During 1947/1948, Sikorsky manufactured three prototypes for the XHJS-1 contract, which was the only experimental military contract obtained by Sikorsky at the time. The S-53 first flew on Sept. 22, 1947, piloted by Robert Decker.

The Sikorsky S-53 was developed from the S-51, but was slightly larger and had several modifications. The two-bladed tail rotor, which spanned eight feet, eight inches (2.7 meters) in diameter, was raised above the height of the main rotor head for safety. Its three-bladed metal main rotors were 49 feet, three inches (15 meters) in diameter, and featured an eight-degree twist. They were also fitted with a folding mechanism. The three-wheeled landing gear was strengthened for shipboard operations, and there was an option for amphibious landing gear.

The S-53 had a rescue hoist, used through a trap door in the cabin floor. This also allowed the aircraft to carry sling loads or a camera. 

The helicopter was powered by a Continental R-975-34 engine, which provided 525 horsepower for takeoff, and normal rated power of 500 horsepower.

It had a gross weight of 4,750 lb. (2,155 kg), a fuselage length of 40 feet, eight inches (12.5 meters), and a height of 12 feet, four inches (3.8 meters). The S-53’s cruising speed was 78 knots (90 mph), and it had a range of 285 nautical miles (525 kilometers). Its service ceiling was 18,900 feet (5,760 meters).

The flight tests of the Sikorsky and Piasecki aircraft were conducted at Naval Air Test Center Patuxent River, Maryland, by Navy pilots. It was not long before they noted a major deficiency in the S-53’s design: it was severely limited in the allowable center of gravity range (CG). The aircraft was not able to handle the changes in CG caused by loading or unloading rescue personnel and equipment. As a result, the U.S. Navy ended up selecting the Piasecki HUP-1 tandem rotor for its search-and-rescue helicopter.

Sikorsky recognized the problem, and eventually came up with a solution in a new transport helicopter, called the S-55/H-19, in 1949.

No additional S-53 helicopters were obtained by the Navy, and all three S-53/XHJS-1 helicopters were struck off charge. None were saved for preservation or historical purposes. 

Unfortunately, as with many of the early helicopters that were developed, but never made it to mass production, no one thought to keep them for future generations to see. However, their role in laying the groundwork for future successful types will never be forgotten.