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The Piasecki HUP Retriever or H-25 Army Mule, later UH-25, is a compact single radial engine, twin overlapping tandem rotor utility helicopter developed by the Piasecki Helicopter Corporation of Morton, Pennsylvania. Designed to a United States Navy specification, the helicopter was produced from 1949 to 1954, and was also used by the United States Army and foreign navies. The HUP/H-25 was the first helicopter to be produced with an autopilot and also the first to perform a loop.
| H-25/HUP Retriever | |
|---|---|
_in_flight_1959.jpg) A U.S. Navy HUP-2 from USS Franklin D. Roosevelt | |
| General information | |
| Type | Utility helicopter |
| Manufacturer | Piasecki Helicopter |
| Primary users | United States Navy |
| Number built | 339[1][disputed – discuss] |
| History | |
| Manufactured | 1949–1954[1] |
| Introduction date | February 1949[2] |
| First flight | March 1948 |
| Retired | 1958 US Army January 1964 RCN 1964 USN 1965 French Navy |
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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.[1] Either 2[2] 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.[2]
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.[1] 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).[2] 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.[1]
During a flight demonstration of its capability to withstand high g-force, the type became the first helicopter to perform a loop, albeit unintentionally.[1]
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The aircraft first entered service in February 1949 with the delivery of the first of 32 HUP-1 aircraft to the US Navy.[2] 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.[2][1] The HUP-2 was the first production helicopter equipped with an autopilot.[1] 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.[2][1][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]
The US Army H-25 designation was adopted by the US Navy in 1962[2] on introduction of the 1962 United States Tri-Service aircraft designation system. The final units were withdrawn from US service in 1964.[citation needed] It also served with French Naval Aviation (Aeronavale) from 1953[citation needed] to 1965.[1]
A total of 339 aircraft were delivered during the 6-year production run.[1][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, BuNo 124925,[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]
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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]
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Data from Jane's All The World's Aircraft 1956–57.[39]
General characteristics
Performance
Related development
Aircraft of comparable role, configuration, and era
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