The design was a product of a competition by the U.S. Navy in 1945 for a compact utility/rescue helicopter to operate from ships including aircraft carriers, battleships, and cruisers.[2] Either 2[1] or 3[3][4][disputed – discuss] prototypes—designated PV-14 by the factory and XHJP-1 by the Navy—were built and subjected to a side-by-side flight evaluation against the 3 prototypes of the Sikorsky XHJS-1; however, the XHJS was fundamentally a scaled-up version of the Sikorsky H-5, and the increased weight and size magnified the design's problems with maintaining proper weight and balance under varying loading conditions.[3] The Piasecki won the competition,[3] and with the introduction of the aircraft configuration letter "U" for Utility in the 1950s,[5] the aircraft was ordered for production as the HUP-1.[1]
The design featured two three-bladed, 35-foot-diameter (11 m) rotors in tandem in which blades could be folded for storage; the relatively small rotor diameter allowed the aircraft to use aircraft carrier elevators with its blades fully extended.[2] The tandem overlapping rotor configuration was a development by Piasecki and was used in future helicopter designs by the company and successors including the H-21, HRB-1/CH-46, and CH-47. The original HUP-1 was powered by a single Continental R-975-34 radial engine, with a take-off rating of 525 hp (391 kW), while later versions used the uprated R-975-42 or R-975-46A with 550 hp (410 kW).[1] To aid search and rescue (SAR) operations, the aircraft was equipped with an overhead winch capable of lifting 400 lb (181 kg), which could lower a rescue sling through an electrically-operated door available after the copilot's seat was folded forward.[2]
During a flight demonstration of its capability to withstand high g-force, the type became the first helicopter to perform a loop, albeit unintentionally.[2]
Operational history
H-25A Army Mule preserved in the US Army Aviation Museum, Alabama
The aircraft first entered service in February 1949 with the delivery of the first of 32 HUP-1 aircraft to the US Navy.[1] The improved HUP-2 (Piasecki designation PV-18) was soon introduced with a more powerful engine, deletion of the inward-canted horizontal stabilizer endplate fins, and various minor changes in equipment; a sub-variant equipped with dunking sonar for anti-submarine warfare was given the designation HUP-2S.[1][2] The HUP-2 was the first production helicopter equipped with an autopilot.[2] The US Navy also tested a radio navigation system called Raydist that allowed an unmanned HUP-2 to be directed from a ground station and by radio ordered to hover within five feet (1.5 m) of the desired point.[6]Edo tested a HUP-2 with a fiberglass hull and outrigger floats for amphibious operations.[7]
An upgraded version of the HUP-2 was built for the US Army and designated as the H-25A Army Mule, but most were quickly withdrawn from Army service and converted for naval use under the designation HUP-3.[1][2][8]
In 1954, the Royal Canadian Navy received three former US Army H-25A aircraft, which were modified and redesignated on delivery to conform to US Navy HUP-3 standards.[8][9][10] The aircraft were used aboard HMCS Labrador for search and rescue and varied utility duties, and were later used to support construction at Distant Early Warning Line radar sites.[8][10] The helicopters were subsequently posted to NAF Patricia Bay and naval air station HMCS Shearwater; after the last two were stricken from inventory on 18 January 1964, one aircraft was donated to a technical school and the other two were sold as surplus.[8][10]
A total of 339 aircraft were delivered during the 6-year production run.[2][disputed – discuss] A large number of surplus US Navy aircraft later appeared on the US civil registry, and at least seven were transferred to the French Navy.[citation needed]
On 7 November 2009, former US Navy HUP-1, BuNo124925,[11] civil registration number N183YP,[12] collided with high-voltage power lines in Adelanto, California; the subsequent crash and post-crash fire killed all 3 occupants and substantially damaged the aircraft.[12] Operated in association with Classic Rotors, the accident aircraft was the only airworthy example in the world.[11] The National Transportation Safety Board attributed the crash to "The pilot’s failure to maintain clearance from powerlines during en route flight."[12]
Variants
XHJP-1
Prototype, powered by a 525 hp (391 kW) Continental R-975-34 piston engine, equipped with large sloping endplate fins on the horizontal stabilizers. Piasecki-Vertol designation was PV-14. 2[1] or 3[3][4] produced.[disputed – discuss]
HUP-1
Utility transport and search and rescue helicopter for the US Navy, largely similar to XHJP-1, Piasecki designation was PV-18. 32 built.[1][2]
A U.S. Navy HUP plane guard conducting a rescue in 1953
HUP-2
Improved version, 550 hp (410 kW) Continental R-975-42 piston engine, horizontal stabilizer endplate fins eliminated.[1][2] 165 built for the US Navy,[1][disputed – discuss] 15 for French Aeronavale.[citation needed] Redesignated UH-25B in 1962.
HUP-2S
Anti-submarine warfare version of HUP-2 fitted with dunking sonar. 12 built.[2]
HUP-3
Naval utility conversion of H-25A aircraft transferred from US Army: 50 to US Navy, 3 to Royal Canadian Navy.[8]
H-25A Army Mule
Utility transport helicopter for US Army, similar to HUP-2 but powered by a 550 hp (410 kW) Continental R-975-46A piston engine, and fitted with large doors, power-boosted controls, and strengthened floors.[1][2] 70 were delivered from 1953, but they were unsuitable for front-line use,[13] with 53 transferred to the Royal Canadian and US Navies in 1954–1955,[8] and the remaining helicopters used for training, being withdrawn from army service by 1958.[13]
For surviving aircraft, hyphenated numbers are original US Army Serial Numbers; six-digit numbers are original US Navy Bureau of Aeronautics (BuAer) Bureau Numbers (BuNo). All 50 H-25A/HUP-3 aircraft transferred from the US Army to the US Navy were given new bureau numbers; 3 aircraft transferred to the Royal Canadian Navy were redesignated, but retained their original US Army serial numbers.[8]
Canada
On display
UH-25B (HUP-2) 128529 at Shearwater Aviation Museum in Shearwater, Nova Scotia.[16] This aircraft has been restored to the appearance of 51-16621, the first Royal Canadian Navy HUP-3.[10]
UH-25B (HUP-2), 130076 (construction number 253) – Baris Business Park roadway roundabout in Rotterdam. This aircraft was originally used by the US Navy and was later transferred to the French Navy.[19]
United Kingdom
UH-25C (HUP-3), 51-16622 – displayed at The Helicopter Museum in Weston-super-Mare, England, wearing Canadian markings.[8][20]
51-16621 – Classic Rotors in Ramona, California.[34] As of December 2019, this is the only Piasecki Helicopter-manufactured aircraft with valid FAAaircraft registration.[35] This former Royal Canadian Navy aircraft is reportedly the last HUP/H-25 capable of being restored to airworthy condition; it was exchanged in 2000 by the Canadian Museum of Flight for unflyable HUP-2 128529, which was subsequently traded again in 2002 to the Shearwater Aviation Museum and repainted as 51-16621.[10][16]
^ abcdDevine, Vinny (10 April 2013). "S-53 (U.S.Navy (XHJS-1)". Sikorsky Product History. Igor Sikorsky Historical Archives. Retrieved 1 November 2018.
Bridgman, Leonard. Jane's All The World's Aircraft 1956–57. New York: The McGraw-Hill Book Company, 1956.
Harding, Stephen. U.S. Army Aircraft Since 1947. Shrewsbury, UK:Airlife, 1990. ISBN1-85310-102-8.
Swanborough, Gordon; Bowers, Peter M. (1976). United States Navy Aircraft since 1911 (2nd ed.). Annapolis, Maryland: Naval Institute Press. ISBN0-87021-968-5..
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