Sikorsky CH 37 Mojave

Design and development

The S-56 came into being as an assault transport for the United States Marine Corps (USMC), with a capacity of 26 fully equipped troops. An order for the aircraft was placed in 1951 utilizing the U.S. Navy/U.S. Marine Corps designation of the time of HR2S. The first prototype, the XHR2S-1 flew in 1953 and production deliveries of the HR2S-1 began in July 1956 to Marine Helicopter Squadron One (HMX-1), with a total of sixty aircraft being produced.

The United States Army evaluated the prototype in 1954 and ordered 94 examples as the CH-37A, the first being delivered also in summer 1956. All Marine Corps and Army examples were delivered by mid-1960. Army examples were all upgraded to CH-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 from HR2S-1 to CH-37C.

At the time of delivery, the CH-37 was the largest helicopter in the Western world and it was Sikorsky's first twin-engined helicopter. Two Pratt & Whitney R-2800 Double Wasp radial engines were mounted in outboard pods that also contained the retractable landing 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 three M422 Mighty Mite (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.

The CH-37 was one of the last heavy helicopters to use piston engines, which were larger, heavier and less powerful than the turboshaft engines subsequently employed in later military helicopters. This accounted for the type's fairly short service life, all being withdrawn from service by the late 1960s, replaced in Army service by the distantly related CH-54 Tarhe and in the Marine Corps by the CH-53 Sea Stallion.

Four CH-37Bs were deployed to Vietnam in 1963 to assist in the recovery of downed U.S. aircraft. 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.

Variants

XHR2S-1

Prototype Assault Transport for the US Marine Corps, powered by two 1,900 hp (1,400 kW) R-2800-54 engines, four built.

HR2S-1

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, two built.

YH-37

One HR2S-1 helicopter evaluated by the US Army.

H-37A Mojave

Military transport version of the HR2S for the US Army, changes included dorsal fin and modified rotor head fairing, 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. Later redesignated CH-37B.

CH-37A

H-37A redesignated in 1962.

CH-37B

H-37B redesignated in 1962.

CH-37C

HR2S-1 redesignated in 1962.

S-56

Sikorsky company designation for H-37.

Derivatives

S-60

a prototype "sky-crane" with a skeletal fuselage with a crew cockpit at the front.

Westland Westminster

Unable to get support for licence production, 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 Napier Eland turboshafts for power. Subsequently changed to use S-64 rotor.

Operators

 United States

United States Army

United States Marine Corps

United States Navy (two examples)

Survivors

CH-37B (Army Ser. Np. 55-644) is on display at the U.S. Army Aviation Museum at Fort Rucker, Alabama.

CH-37B (Army Ser. No. 56-1005) "Tired Dude" is on display at the Pima Air Museum adjacent to Davis-Monthan Air Force Base in Tucson, Arizona.

CH-37B (Army Ser. Np. 57-1651) is on display at the U.S. Army Transportation Museum at Fort Eustis, Virginia.

CH-37B (Army Ser. No. 58-0999) is on display at the Evergreen Aviation & Space Museum in McMinnville, Oregon.

CH-37C (BuNo 145864) is on display at the National Museum of Naval Aviation at Naval Air Station Pensacola, Florida.

CH-37B (Army Ser. No. 57-1646) is on display at the Classic Rotors Museum at the Ramona Airport, Ramona, CA.

Specifications (CH-37 Mojave)

Data from U.S. Army Aircraft Since 1947

General characteristics

Crew: three

Capacity: 26 troops or 24 stretchers

Length: 64 ft 3 in (19.59 m)

Rotor diameter: 72 ft 0 in (21.95 m)

Height: 22 ft 0 in (6.71 m)

Disc area: 4,080 ft² (379 m²)

Empty weight: 20,831 lb (9,469 kg)

Max. takeoff weight: 31,000 lb (14,090 kg)

Powerplant: 2 × Pratt & Whitney R-2800-54 Double Wasp radial engine, 2,100 hp (1,583 kW) each

Performance

Maximum speed: 130 mph (113 kn, 209 km/h)

Cruise speed: 115 mph

Range: 145 mi (126 nmi, 233 km) with maximum payload

Service ceiling: 8,700 ft (2,650 m)

Rate of climb: 910 ft/min (4.6 m/s)