May 2017

2017 May

USMC/Sikorsky HUS-1D (UH-34D) Seahorse
Recovery of Astronaut Alan Shepard, Jr. and Mercury capsule after Mercury-Redstone 3/Freedom 7 sub-orbital flight, May 5, 1961
S-58 first flight: March 8, 1954

The Sikorsky H-34 (company designation S-58) is a single piston-engine, two-crew member military helicopter originally designed as an anti-submarine warfare (ASW) aircraft for the United States Navy. It was one of the last piston-powered helicopter designs before its replacement by turbine-powered types such as the UH-1 Huey and CH-46 Sea Knight. A total of 2,108 H-34s were manufactured between 1953 and 1970.

H-34s served, mostly as medium transports, with the armed forces of 25 countries. It saw combat in Algeria, the Dominican Republic, Nicaragua and throughout Southeast Asia. Other uses included saving flood victims, recovering astronauts, fighting fires and carrying presidents.

The Sikorsky S-58 was developed with company funds as a lengthened and twice as powerful version of the Sikorsky Model S-55, or H-19 Chickasaw, with a similar nose, but with a tail-dragger rear fuselage and landing gear, rather than the high-tail, 4-main gear pattern. It retained the nose-mounted piston engine with the driveshaft passing through the cockpit placed high above the cargo compartment.

The S-58 features a 56 ft (17.1 m) diameter 4-bladed main rotor and a 4-bladed tail rotor, both utilizing the symmetrical NACA 0012 airfoil. Sikorsky chose a 4-blade rotor for the S-58 because it produced a lower blade loading compared to the 3-blade S-55 rotor, allowing the aircraft to fly faster before encountering blade stall, and for reduced vibration.The S-58 fuselage was also improved by wind tunnel testing.

The aircraft first flew on March 8, 1954. The first production aircraft was ready that September and entered service for the US Navy. It was initially designated the HSS-1 Seabat (anti-submarine configuration) and HUS-1 Seahorse (utility transport) under the US Navy designation system for US Navy, Marine Corps and Coast Guard aircraft. The US Army and Marine Corps, respectively, ordered it in 1955 and 1957. Under the United States Army's aircraft designation system, also used by the United States Air Force, the helicopter was designated H-34. The US Army also applied the name Choctaw to the helicopter. In 1962, under the new unified DoD aircraft designation system, the Seabat was redesignated SH-34, the Seahorse as the UH-34, and the Choctaw as the CH-34.

Clamshell doors on the engine compartment allowed easy access for servicing, as well as expediting engine changes. The all-metal fuselage utilized magnesium skins in certain areas as a weight-saving measure. Corrosion and the fire hazard experienced with certain S-58 models discouraged further use of magnesium for airframe components by Sikorsky on subsequent models.

The conventional landing gear (main wheels in front, tail wheel in back) enhanced ground handling by greatly reducing the turning radius of the helicopter. The rear tail wheel also improved safety by making the tail wheel the first thing to hit the ground in a quick stop landing rather than the tail rotor blades. A manually folded main rotor and a folding pylon were provided to allow the helicopter to fit on aircraft carrier elevators.

Roles included utility transport, anti-submarine warfare, search and rescue, and VIP transport. In its standard configuration, transport versions could carry 12 to 16 troops, or eight stretcher cases if utilized in the Medevac role, while VIP transports carried significantly fewer people in much greater comfort. A small fleet of H-34 helicopters served US Presidents Dwight D. Eisenhower and John F. Kennedy from 1958 to 1961 using the call sign “Army One.” The Marine Corps took their UH-34D helicopters to Vietnam in large quantities where they proved their worth as a tough and reliable machine.

However, the H-34's lift capacity was marginal in lifting a Mercury space capsule. In 1961, the hatch of Mercury-Redstone 4 was prematurely detached and the capsule quickly filled with seawater. NASA Astronaut Virgil "Gus" Grissom escaped into the water and was subsequently rescued by a second Seahorse. At that point the capsule weighed approx 5,000 lb (2.3 t), which was 1,000 lb (450 kg) more than the hook lift capacity. The extra weight was too much for the H-34 and the capsule, Liberty Bell 7, was emergency released and sank in the Atlantic Ocean to approx 15,000 ft (4,600 m) depth, 300 nm (550 km) from Cape Canaveral. The capsule was recovered in relatively good shape on July 20, 1999, the 30th anniversary of the Apollo 11 lunar landing.

Description: Pete Noell
Photo credit: NASA

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