H-25/HUP Retriever
A U.S. Navy HUP-2 from USS Franklin D. Roosevelt
General information
Type	Utility helicopter
Manufacturer	Piasecki Helicopter
Primary users	United States Navy United States Army Royal Canadian Navy French 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

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.

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]

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]

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^[2] 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.^[2][1]

HUP-2

Improved version, 550 hp (410 kW) Continental R-975-42 piston engine, horizontal stabilizer endplate fins eliminated.^[2][1] 165 built for the US Navy,^{[2][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.^[1]

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.^[2][1] 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]

UH-25B

HUP-2 redesignated after 1962.

UH-25C

HUP-3 redesignated after 1962.

 Canada

• Royal Canadian Navy^[14]

 France

• French Navy^[14][15]

 United States

• United States Army^[14]
• United States Navy^[14]

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]

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-25C (HUP-3), 51-16623 - Canada Aviation and Space Museum in Ottawa, Ontario.^[17][18]

• 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]

• UH-25C (HUP-3), 51-16622 – displayed at The Helicopter Museum in Weston-super-Mare, England, wearing Canadian markings.^[8][20]

On display

H-25A Army Mule

• 51-16616 – United States Army Aviation Museum in Fort Rucker, Alabama.^[21]

HUP-1

• 124915 – USS Hornet Museum in Alameda, California.^[22]

UH-25B (HUP-2)

• 128479 – American Helicopter Museum in West Chester, Pennsylvania.^[23]
• 128517 – Wings of Freedom Aviation Museum in Horsham, Pennsylvania.^[24]
• 128519 – Intrepid Sea, Air & Space Museum in New York City, New York.^[25]
• 128596 – Flying Leatherneck Aviation Museum in San Diego, California.^[26]

• 130059 – USS Midway Museum in San Diego, California.^[27]
• 130082 – on the deck of the USS Iowa Museum in San Pedro, California.^[28][29]

UH-25C (HUP-3)

• 147595 – Pima Air & Space Museum in Tucson, Arizona.^[30]
• 147600 – Air Zoo in Kalamazoo, Michigan.^[31]
• 147607 – National Naval Aviation Museum in Pensacola, Florida.^[32]
• 147628 – Mid-America Air Museum in Liberal, Kansas.^[33]
• 51-16621 – Classic Rotors in Ramona, California.^[34] As of December 2019, this is the only Piasecki Helicopter-manufactured aircraft with valid FAA aircraft 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]

Under restoration or in storage

UH-25B (HUP-2)

• 128598 - Stored at New England Air Museum in Windsor Locks, Connecticut.^[36]
• 130053 – Stored at Quartzsite, Arizona.^[37]
• 130063 - Stored at New England Air Museum in Windsor Locks, Connecticut.^[36]

UH-25C (HUP-3)

• 147610 – Yanks Air Museum in Chino, California, in storage.^[38]

Data from Jane's All The World's Aircraft 1956–57.^[39]

General characteristics

• Crew: two
• Capacity: four passengers
• Length: 56 ft 11 in (17.35 m)
• Height: 13 ft 2 in (4.01 m)
• Empty weight: 4,132 lb (1,874 kg)
• Gross weight: 5,750 lb (2,608 kg)
• Max takeoff weight: 6,100 lb (2,767 kg)
• Powerplant: 1 × Continental R-975-46A 9-cylinder air-cooled radial piston engine, 550 hp (410 kW)
• Main rotor diameter: 2 × 35 ft 0 in (10.67 m)
• Main rotor area: 1,924.5 sq ft (178.79 m²) * Blade section: NACA 0012^[40]

Performance

• Maximum speed: 105 mph (169 km/h, 91 kn)
• Cruise speed: 80 mph (130 km/h, 70 kn)
• Range: 340 mi (550 km, 300 nmi)
• Service ceiling: 10,000 ft (3,000 m)
• Rate of climb: 1,000 ft/min (5.1 m/s)
• Disk loading: 3 lb/sq ft (15 kg/m²)
• Power/mass: 0.09 hp/lb (0.15 kW/kg)

Related development

• Piasecki H-21
• CH-46 Sea Knight

Aircraft of comparable role, configuration, and era

• Bell HSL
• Bristol Belvedere
• Harbin Z-5
• Mil Mi-4
• Sikorsky H-19 Chickasaw

Notes

Bibliography

• 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. ISBN 1-85310-102-8.
• Swanborough, Gordon; Bowers, Peter M. (1976). United States Navy Aircraft since 1911 (2nd ed.). Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-968-5..

• H-25 US Army Aviation history fact sheet
• HUP Retriever warbird at the 2002 Chino Air Show