Estimated reading time 14 minutes, 12 seconds.
Photos Courtesy of the Jeff Evans Photo Collection
During the Second World War, Sikorsky Aircraft introduced the R-4 — the world’s first mass-produced military helicopter. A raft of other rotorcraft companies — including Piasecki, Kaman, Hiller, and Bell — quickly established themselves, and a new rotary-wing aviation industry was born.
Sikorsky manufactured over 400 R-4, R-5, and R-6 helicopters during the war for military use. Very few were used operationally, with most flown for pilot training and for rescues. Early aircraft were used by the U.S. Coast Guard, the U.S. Army Air Forces and U.S. Navy, and overseas by the British Royal Navy and Royal Air Force.
The first Sikorsky aircraft were barely capable of carrying two to three people, were complicated to fly, and had limited payload and endurance. They were also very expensive compared to fixed-wing aircraft, and required extensive maintenance to keep in the air.
In 1946, Sikorsky began producing the four-place S-51 for the commercial and military markets. The two-place (later four-place) S-52 program followed in 1947. The same year, Sikorsky designed and built three S-53 (military XHJS-1) four-place utility helicopters for a U.S. Navy contract. A single modified twin-rotor experimental R-4B model, the S-54, was manufactured and flown in 1948, but for less than five hours. Igor Sikorsky abandoned the project in early 1949.
The next program was to result in the biggest and largest helicopter the company had manufactured by that point: the 12-passenger S-55/H-19 utility and transport helicopter. It was created to meet a requirement from the U.S. Air Force (USAF) for a larger helicopter with more range and a greater payload capacity for its Air Rescue Service. The helicopter needed to be large enough to carry six or more litters or up to 10 passengers. In addition, it needed to be able to fit inside a Fairchild C-82 cargo aircraft. The USAF also wanted new and improved metal rotor blades, a more simplified control system, and amphibious landing gear. As a result, the USAF ordered five YH-19 service test and evaluation helicopters for rescue work.
“The aircraft had four-wheel quadricycle landing gear, but could also be fitted with amphibious gear for water landings.”
Sikorsky engineers sent plans for the S-55/H-19 to the USAF’s Air Materiel Command at Wright Field in Dayton, Ohio. The USAF agreed to Sikorsky’s submission committing the company to the manufacture, with an initial first flight planned for November 1949. It would be a major challenge for Sikorsky to complete this task in just seven months.
Edward F. Katzenberger, Sikorsky’s chief engineer, pulled the project together, with engineer Don Plumb in charge of coordinating the program as the project engineer. Numerous drawings and work orders were issued, including for the design and manufacture of new tools and all the parts required to build the type.
A new approach
The new helicopter differed from previous Sikorsky rotorcraft in that the passengers were located in a monocoque cabin under a simplified new main rotor head. The rotor head was designed with offset hinges originally developed for the Sikorsky S-52. This helped avoid weight and balance problems that had affected the S-53. The two-man crew cockpit was located above and aft of the engine, next to the main rotor system.
The S-55/H-19 was originally powered by a 600-horsepower Pratt & Whitney R-1340 radial piston engine, mounted on an angle, that was easily accessed by opening two clamshell doors in the nose of aircraft. Later versions of the S-55 came with a 700-horsepower Wright 1300-3 radial piston engine. The aircraft had a manual temperature control with an internal preheat provision for the engine and transmission.
The aircraft had four-wheel quadricycle landing gear, but could also be fitted with amphibious gear for water landings.
There was no fairing behind the spacious cabin and the tail boom on the original S-55/H-19 — this was added on later production models. The first aircraft also had no stabilizers on the tail boom. Several types of stabilizers were tried before anhedral (downward-angled) V-type stabilizers/fins were chosen. Later models of the H-19 had downward inclined tail booms to help prevent the main rotors from hitting them during rough landings. Both the main rotor blades and the tail rotor were metal.
For work with a long line or hoist, the S-55 had a 2,000-lb. (910-kg) external lift capacity. The rescue hoist, capable of lifting 400 lb. (180 kg), was an improved version from earlier models.
The dimensions of the S-55/H-19 were such that the U.S. Navy would be easily able to fit the helicopter on existing aircraft carrier elevators.
Actual fabrication of parts for the new helicopter commenced in June 1949. Sikorsky produced over 2,123 drawings, and 3,606 work orders before the S-55/H-19 began flying. Over 650 engineering revisions were required on the project.
On Nov. 4, 1949, the S-55/H-19 was complete. “It was the toughest schedule that we ever had to meet, but we finished on time,” said Don Plumb in an article in the spring 1954 edition of United Aircraft Corporation’s Bee-Hive newsletter.
On Nov. 8, small groups of engineers and mechanics watched as chief test pilot Dmitry (Jimmy) Viner and co-pilot Robert Decker moved the big helicopter around the Sikorsky airfield in Bridgeport, Connecticut. Viner was very happy with the way the helicopter handled, as he lifted into a hover at a height of about four feet. He held this hover for only a few minutes before gently landing, completing the S-55/H-19’s first flight.
More ground tests were still required, and the helicopter was tied down and run continuously for a 50-hour endurance test.
Following these tests and routine inspections, the new utility helicopter was ready for the start of flight testing. This began on Nov. 21, 1949, with Viner and co-pilot Jim Chudars at the controls. Viner maneuvered the aircraft and flew beyond the Sikorsky factory fence towards Long Island Sound, over the Bridgeport area. The two pilots were ecstatic with how the helicopter handled.
Sikorsky test-pilot Harold Thompson and co-pilot Decker later had their own chance to fly the S-55/H-19, and they were similarly impressed — pointing out that the hydraulic servo units assisted immensely in the quality of the ride.
By this point, the helicopter had accumulated just over 4.5 hours of flight time, and it was now ready for inspection and testing by the USAF’s Rescue Evaluation Board. This took place over several days, during which the S-55/H-19 easily met performance expectations and even performed several autorotative landings with ease. The USAF was excited to receive its five new rescue and utility YH-19/S-55 helicopters for service field testing. The first of these was delivered in April 1950.
The U.S. military got its first opportunity to field the new S-55/YH-19 helicopters during the Korean War. Two of the type were transported to Korea in March 1951, and soon after arriving, they flew evacuation rescue operations with great success. One of the YH-19 helicopters was later used on secret missions into North Korea by the Central Intelligence Agency.
Soon, all the U.S. military services were ordering new variants of the Sikorsky S-55/H-19. This included the USAF (H-19), U.S. Army (CH-19), U.S. Navy (HO-4S), U.S. Marines (HRS), and the U.S. Coast Guard (HO-4S). The U.S. Navy ordered their first 10 HO4-S aircraft (for anti-submarine warfare) in 1950; the USAF ordered 50 H-19As in 1951, followed by new additional H-19Bs; while the U.S. Army ordered 72 H-19Cs and 338 H-19Ds in 1952.
A legacy of success
The S-55 was a huge success story for Sikorsky. A licensing agreement with Westland Aircraft saw the British company manufacturing a variant of the S-55 called the Whirlwind. A turbine version came later. France and Japan also signed licensing agreements with Sikorsky to build the S-55.
All told, Sikorsky manufactured 1,281 S-55s in various forms, and these were joined by a further 477 built on license.
Among the more notable flights completed by the type was the first transatlantic crossing by helicopter, completed by two USAF H-19As in July 1952.
In Canada, the Royal Canadian Air Force (RCAF) and the Royal Canadian Navy (RCN) purchased versions of the S-55 during the mid-1950s. The RCAF used its first S-55s to build the Mid Canada Radar Line across Northern Canada, while the RCN used them for anti-submarine warfare duties.
Commercial operators were interested in a civil S-55, but priority was given to the military in the early 1950s. A commercial S-55 was certified by the Civil Aviation Authority (CAA) in March 1952. It could carry two pilots and only seven passengers. The cost for a new S-55 was US$120,000.
The first commercial S-55 was delivered to Los Angeles Airways in California in March 1952. Deliveries then followed around the world, with Sikorsky ultimately manufacturing 216 commercial S-55s.
In later years, a new market for the venerable S-55 emerged with a turbine engine upgrade, known as the S-55T. The Allied Signal 650-horsepower turboshaft engine removed over 900 lb. (400 kg) from the aircraft’s empty weight.
A more recent modification was the S-55QT Whisper Jet, which used a five-bladed rotor, improved soundproofing, and a much quieter muffler to reduce the type’s noise signature. The helicopter was designed for Papillion Helicopters in Las Vegas, Nevada, for Grand Canyon tours, but was only used for a couple of years. Three S-55QTs are reported to still be airworthy today.
After 70 years of operation, the Sikorsky S-55 is still used by a few commercial operators. That’s not too bad for a vintage aircraft, designed at speed as the first step towards a greater carrying capacity during the rotorcraft industry’s infancy.