TheSikorsky CH-37 Mojave (company designationS-56) is an American large heavy-lift militaryhelicopter of the 1950s. It entered service as theHR2S-1 Deuce with USMC in 1956, and as the H-37A Mojave with the U.S. Army that same year. In the early 1960s, the designation was standardized to CH-37 for both services, with the HR2S-1 redesignated as CH-37C specifically.
Developed in the early 1950s, with its first flight in 1953, it filled a 1950Navy requirement for anassault helicopter that could carry up to 20 Marines and haul combat equipment.[1] The design includes a front-loading ramp with side opening clam shell doors on the nose. It was powered by tworadial piston engines. It served in active military service well into the 1960s, including inIndochina, before being replaced, and many ex-military models went onto civilian service in the 1970s. This was the biggest helicopter in the world to enter service at the time, and one of the earliest twin engine models. It was known for being noisy but earned a good reputation for reliability. The Navy also adapted it to carry a naval radar, with two entering service asHR2S-1W.
The design led to a production attempt as theWestland Westminster in the United Kingdom; prototypes were produced, but it did not go into full production. The S-56 was also the basis for theS-60 Skycrane helicopter prototype.
HR2S-1Loading aDodge WCHR2S-1 with M422 Mighty Mite
TheS-56 came into being as an assault transport for theUnited States Marine Corps (USMC), with a capacity of 26 fully equipped Marines. An order for the aircraft was placed in 1951 using the U.S. Navy/U.S. Marine Corps designation of the time ofHR2S. The first prototype, theXHR2S-1 flew in 1953,[2] and production deliveries of theHR2S-1 "Deuce" began in July 1956 to Marine Helicopter Squadron One (HMX-1), with a total of sixty aircraft being produced.[3]
The HR2S-1 set three records in 1956: a speed record without payload of 162.7 mph (141.4 kts); an altitude record of 12,100 ft (3688.1 meters) with a 11,023 lbs (5000 kg) load; and a load carrying record of 13,227 lbs (6000 kg) to 6,561 feet (2000 meters).[4]
TheUnited States Army evaluated the prototype in 1954 and ordered 94 examples as theCH-37A, the first being delivered in summer 1956. All Marine Corps and Army examples were delivered by mid-1960. Army examples were all upgraded toCH-37B status in the early 1960s, being given Lear auto-stabilization equipment and the ability to load and unload while hovering. In the 1962 unification of United States military aircraft designations, the USMC examples were redesignated fromHR2S-1 toCH-37C.
At the time of delivery, the CH-37 was the largest helicopter in the Western world and it wasSikorsky's first twin-engine helicopter. TwoPratt & Whitney R-2800 Double Wasp radial engines were mounted in outboard pods that also contained the retractablelanding gear. This left the fuselage free for cargo, which could be loaded and unloaded through large clamshell doors in the nose. The early models could carry a payload of either threeM422 Mighty Mites (a lightweight jeep-like vehicle) or 26 troops. For storage, the main rotor blades folded back on the fuselage and the tail rotor mast folded forward on the fuselage.[5]
The CH-37 was one of the last heavy helicopters to usepiston engines, which were larger, heavier and less powerful than theturboshaft engines employed in later military helicopters. This accounted for the CH-37's fairly short service life, all being withdrawn from service by the late 1960s, replaced in Army service by the distantly relatedCH-54 Tarhe and in the Marine Corps by theCH-53 Sea Stallion.
Six CH-37C's were deployed toVietnam in September 1965 to assist in the recovery of downed U.S. aircraft, serving in this role fromMarble Mountain Air Facility until May 14, 1967.[6][7] They were very successful at this role, recovering over US$7.5 million worth of equipment, some of which was retrieved from behind enemy lines.[8] The CH-37 was also used to recover film capsules descending from space by parachute.[9]
A total of 154 were produced by the time production ended. Of those, 94 were H-37A, and 90 that were converted to H-37B (later CH-37A and B respectively). It remains the largest piston powered helicopter.[citation needed]
Production model for USMC with modified engine nacelles, twin mainwheels and dorsal fin, redesignated CH-37C in 1962, 55 built (order for additional 36 cancelled).
HR2S-1W
Airborne early warning aircraft for the US Navy,[11] two built.
H-37
The H-37 followed the HR2S-1 in 1954 as an army helicopter. 94 were build between 1954 and 1960. It is credited with a maximum speed of 126 mph.[10]
H-37A Mojave
Military transport version of the HR2S for the US Army, changes included dorsal fin and modifiedrotor head fairing,[4] redesignated CH-37A in 1962, 94 built.
H-37B Mojave
All but four of the H-37As were modified with a redesigned cargo door, automatic stabilization equipment and crashproof fuel cells.[4] Engine oil tank capacity was increased from 13.3 gallons to 30 gallons per engine. Rear split cargo door was replaced with a sliding cargo door.[4] Later redesignated CH-37B.
Unable to get government support for license production of the civil S-56,Westland Aircraft used the S-56 control systems, rotors and gearbox as the basis for the Westminster but used their own tubular frame and twin 2,900 hp (2,200 kW)Napier Eland turboshafts for power in a flying test rig.[12] Due to vibration they changed to a six-bladed S-64 rotor. The private venture project was ended when Westland took over three British helicopter companies and their more advanced and funded projects.
^Jenkins, Dennis R. (2012).Dressing for altitude: U.S. aviation pressure suits-- Wiley Post to space shuttle. NASA SP. United States. Washington, DC: National Aeronautics and Space Administration.ISBN978-0-16-090110-2.
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