S-58/HUS-1/UH-34D SeaHorse
Sikorsky S-58 (XHSS-1) first flight: 8 March 1953
By June 1950, Sikorsky had lost two major US Navy helicopter competitions to tandem-rotor helicopters, first to Piasecki for carrier-plane guard (HUP) — a new use for helicopters that Sikorsky had demonstrated — and the second to Bell Helicopter to find and destroy submarines (HSL). The major shortcoming of Sikorsky’s plane-guard proposal was its limited center-of-gravity range due to the location of the engine directly under the rotor. Igor Sikorsky addressed that issue with the S-55, which relocated the engine to the nose, the longer drive shaft angled upward to the transmission, and moved the cabin under the rotor. When the Navy became concerned about HSL program-schedule delays, Sikorsky proposed a backup, the S-58, which utilized the S-55 engine/drive train configuration and a more powerful piston engine for the greater useful load required. The Navy ordered it as the HSS-1 in June 1952.
Sikorsky was able to fly the XHSS less than a year later — the same month as the HSL’s first flight — due to its design commonality with the S-55, and then win a fly-off, resulting in the termination of the Bell program. Moreover, the size required for the Navy’s ASW dipping-sonar mission resulted in a 400-cubic foot (11.3 cubic meters) cabin that could accommodate 12 troops or cargo weighing up to 4,000 lb (1,817 kg). That vertical-lift capability meant that the S-58 was also utilized as a utility transport by the US Navy, Marine Corps, Coast Guard, and as the H-34 Choctaw, by the Army, as well as the militaries of at least 25 other countries. Sikorsky produced about 2,400 of the aircraft, including licensed production in England and France. The Marine/Navy HUS transport became the UH-34D because of the 1962 DoD-directed tri-service aircraft designation system.
Official US Marine Corps photo by Corporal R. G. Musolf
Description by Tommy H. Thomason
Resources:
- Sikorsky UH-34D Seahorse, Vertipedia, Vertical Flight Society
- Sikorsky S-58, Igor I. Sikorsky Historical Archives website
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