View source for Engineering:Piasecki HUP Retriever

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{|{{Infobox aircraft begin
 |name= H-25/HUP Retriever
 |image= File:HUP-2 from USS FD Roosevelt (CVA-42) in flight 1959.jpg
 |caption= A U.S. Navy HUP-2 from {{USS|Franklin D. Roosevelt|CV-42|6}}
}}{{Infobox aircraft type
 |type= Utility [[Engineering:Helicopter|helicopter]]
 |manufacturer= Piasecki Helicopter
 |designer=
 |first flight= March 1948
 |introduced= February 1949<ref name=SB1911>Swanborough and Bowers 1976, p.461.</ref>
 |retired= 1958 US Army<br />January 1964 RCN<br />1964 USN<br />1965 French Navy
 |status=
 |primary user= United States Navy
 |more users= United States Army <br /> Royal Canadian Navy <br /> French Navy
 |produced=1949–1954<ref name=Boeing_HUP/>
 |number built= 339<ref name=Boeing_HUP/>{{Disputed inline|Number built|date=November 2018}}
 |unit cost=
 |variants with their own articles=
}}
|}
The '''Piasecki HUP Retriever/H-25 Army Mule''' is a compact single radial engine, twin overlapping [[Engineering:Tandem rotors|tandem rotor]] utility [[Engineering:Helicopter|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 [[Engineering:Autopilot|autopilot]] and also the first to perform a loop.

==Design and development==
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.<ref name=Boeing_HUP/> Either 2<ref name=SB1911/> or 3<ref name=archives/><ref name=Watkins>{{cite web |url=http://1000aircraftphotos.com/Contributions/WatkinsRay/8891.htm |title= Piasecki PV-14 XHJP-1 US Navy|website=1000aircraftphotos.com |access-date=26 January 2014}}</ref>{{Disputed inline|Number built|date=November 2018}} 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 [[Engineering:Sikorsky H-5|Sikorsky H-5]], and the increased weight and size magnified the design's problems with maintaining [[Center of gravity of an aircraft#Incorrect weight and balance in helicopters|proper weight and balance]] under varying loading conditions.<ref name=archives>{{cite web|title=S-53 (U.S.Navy (XHJS-1) |last1= Devine |first1= Vinny |url=https://www.sikorskyarchives.com/S-53%20(U.S.Navy%20(%20XHJS-1).php |date=10 April 2013 |website= Sikorsky Product History |publisher= Igor Sikorsky Historical Archives |access-date=1 November 2018}}</ref> The Piasecki won the competition,<ref name=archives/> and with the introduction of the aircraft configuration letter "U" for Utility in the 1950s,<ref>Swanborough and Bowers 1976, pp.8–9.</ref> the aircraft was ordered for production as the '''HUP-1'''.<ref name=SB1911/>

The design featured two three-bladed, {{convert|35|ft|m|adj=mid|-diameter}} 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.<ref name=Boeing_HUP/> The tandem overlapping rotor configuration was a development by Piasecki and was used in future helicopter designs by the company and successors including the [[Engineering:Piasecki H-21|H-21]], HRB-1/CH-46, and CH-47. The original HUP-1 was powered by a single [[Engineering:Wright R-975 Whirlwind#Production by Continental Motors|Continental R-975-34]] radial engine, with a take-off rating of {{convert|525|hp|kW|0|abbr=on}}, while later versions used the uprated R-975-42 or R-975-46A with {{convert|550|hp|kW|0|abbr=on}}.<ref name=SB1911/> To aid search and rescue (SAR) operations, the aircraft was equipped with an overhead winch capable of lifting 400&nbsp;lb (181&nbsp;kg), which could lower a rescue sling through an electrically-operated door available after the copilot's seat was folded forward.<ref name=Boeing_HUP>{{cite web |url=https://www.boeing.com/history/products/hup-h-25-army-mule.page |title=HUP-1 Retriever/H-25 Army Mule Helicopter |author=<!--Not stated--> |website=boeing.com |publisher=[[Company:Boeing|Boeing]] |access-date=1 November 2018}}</ref>

During a flight demonstration of its capability to withstand high [[Physics:G-force|g-force]], the type became the first helicopter to perform a loop, albeit unintentionally.<ref name=Boeing_HUP/>

==Operational history==
[[File:Piasecki H-25A 116616 Fort Rucker AL 14.12.02R edited-2.jpg|thumb|left|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.<ref name=SB1911/>   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'''.<ref name=SB1911/><ref name=Boeing_HUP/> The HUP-2 was the first production helicopter equipped with an [[Engineering:Autopilot|autopilot]].<ref name=Boeing_HUP/> The US Navy also tested a [[Radio navigation|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 {{convert|5|ft|m|spell=in}} of the desired point.<ref>{{cite magazine|magazine=Popular Mechanics|author=Hearst Magazines|title=Radio Waves Hold Helicopter In Fixed Hovering Position|url=https://books.google.com/books?id=oN0DAAAAMBAJ&pg=PA122|date=May 1954|publisher=Hearst Magazines|page=122}}</ref> Edo tested a HUP-2 with a fiberglass hull and outrigger floats for amphibious operations.<ref>{{cite magazine|title=Picture News: Watertight hull makes helicopter amphibious|magazine=Popular Science|date=February 1958|volume=172|issue=2|page=149}}</ref>

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'''.<ref name=SB1911/><ref name=Boeing_HUP/><ref name=Walker_RCN/>

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.<ref name=Walker_RCN/><ref>{{cite web |url=https://ingeniumcanada.org/aviation/collection-research/artifact-piasecki-hup-3.php |title=Piasecki HUP-3 |website=ingeniumcanada.org |publisher=Ingenium Canada - Canada Air and Space Museum |access-date=31 October 2018 }}</ref><ref name=Shearwater_HUP-3>{{cite web |url=http://www.shearwateraviationmuseum.ns.ca/exhibits/hup.htm |title=Piasecki HUP-3 |website=www.shearwateraviationmuseum.ns.ca |publisher=Shearwater Aviation Museum |access-date=1 November 2018 }}</ref> 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.<ref name=Walker_RCN/><ref name=Shearwater_HUP-3/> 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.<ref name=Walker_RCN/><ref name=Shearwater_HUP-3/>

The US Army '''H-25''' designation was adopted by the US Navy in 1962<ref name=SB1911/> on introduction of the 1962 United States Tri-Service aircraft designation system. The final units were withdrawn from US service in 1964.{{Citation needed|date=October 2018}} It also served with French Naval Aviation (Aeronavale) from 1953{{Citation needed|reason=Need more info on French service|date=October 2018}} to 1965.<ref name=Boeing_HUP/>

A total of 339 aircraft were delivered during the 6-year production run.<ref name=Boeing_HUP/>{{Disputed inline|Number built|date=November 2018}} 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.{{Cn|date=September 2022}}

On 7 November 2009, former US Navy HUP-1, BuNo ''124925'',<ref name=Allnutt/> civil registration number ''N183YP'',<ref name=NTSB_N183YP/> 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.<ref name=NTSB_N183YP>{{cite report|url=https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/75019/pdf|title=NTSB Aviation Investigation Final Report|docket=WPR10LA048 |date=18 July 2011 |publisher=National Transportation Safety Board|access-date=25 February 2023}}</ref> Operated in association with Classic Rotors, the accident aircraft was the only airworthy example in the world.<ref name=Allnutt>{{cite news |last=Allnutt |first=Richard Mallory |date=25 December 2009 |title=Piasecki crash claims three lives |work=Aircraft Illustrated |location=Stamford, Lincolnshire, UK |publisher=Key Publishing Ltd. |issn=0002-2675}}</ref> The National Transportation Safety Board attributed the crash to ''"The pilot’s failure to maintain clearance from powerlines during en route flight."''<ref name=NTSB_N183YP/>

==Variants==
;XHJP-1
:Prototype, powered by a {{convert|525|hp|kW|0|abbr=on}} Continental R-975-34 piston engine, equipped with large sloping endplate fins on the horizontal stabilizers. Piasecki-Vertol designation was '''PV-14'''. 2<ref name=SB1911/> or 3<ref name=archives/><ref name=Watkins/> produced.{{Disputed inline|Number built|date=November 2018}}

;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.<ref name=SB1911/><ref name=Boeing_HUP/>
[[File:Piasecki HUP of HU-2 rescues pilot near USS Block Island (CVE-106) on 12 August 1953.jpg|thumb|A U.S. Navy HUP plane guard conducting a rescue in 1953]]
;HUP-2
:Improved version, {{convert|550|hp|kW|0|abbr=on}} Continental R-975-42 piston engine, horizontal stabilizer endplate fins eliminated.<ref name=SB1911/><ref name=Boeing_HUP/> 165 built for the US Navy,<ref name=SB1911/>{{Disputed inline|Number built|date=November 2018}} 15 for French Aeronavale. Redesignated '''UH-25B''' in 1962.

;HUP-2S
:Anti-submarine warfare version of HUP-2 fitted with dunking sonar. 12 built.<ref name=Boeing_HUP/>

;HUP-3
:Naval utility conversion of H-25A aircraft transferred from US Army: 50 to US Navy, 3 to Royal Canadian Navy.<ref name=Walker_RCN>{{cite web|title= Royal Canadian Navy – HUP detailed list  |last1= Walker |first1= R.W.R. |url=http://www.rwrwalker.ca/RCN_HUP_detailed.html |work= Canadian Military Aircraft Serial Numbers |access-date= 31 October 2018 }}</ref>

;H-25A Army Mule
:Utility transport helicopter for US Army, similar to HUP-2 but powered by a {{convert|550|hp|kW|0|abbr=on}} Continental R-975-46A piston engine, and fitted with large doors, power-boosted controls, and strengthened floors.<ref name=SB1911/><ref name=Boeing_HUP/> 70 were delivered from 1953, but they were unsuitable for front-line use,<ref name="Harding p197-8"/> with 53 transferred to the Royal Canadian and US Navies in 1954–1955,<ref name=Walker_RCN/> and the remaining helicopters used for training, being withdrawn from army service by 1958.<ref name="Harding p197-8">Harding 1990, pp. 197–198.</ref>

;UH-25B
:HUP-2 redesignated after 1962.

;UH-25C
:HUP-3 redesignated after 1962.

==Operators==
; {{flag|Canada|1921}}
* Royal Canadian Navy<ref name=" Piasecki H-25 History">{{cite web| title =Piasecki H-25 History| publisher =Boeing| url =http://www.boeing.com/history/boeing/hup.html| access-date =2013-02-02|url-status=dead| archive-url =https://web.archive.org/web/20121029172611/http://www.boeing.com/history/boeing/hup.html| archive-date =2012-10-29}}</ref>
; {{FRA}}
* French Navy<ref name=" Piasecki H-25 History" /><ref>{{cite web|url=http://www.pictaero.com/en/pictures/picture,47204 |title= Piasecki PV-18 (HUP/H-25/UH-25) (Photo) |publisher= pictaero.com |access-date=2 February 2013}}</ref>
; {{USA}}:
* United States Army<ref name=" Piasecki H-25 History" />
* United States Navy<ref name=" Piasecki H-25 History" />

==Surviving aircraft==
[[File:HUP3-01A.JPG|thumb|Royal Canadian Navy HUP-3 ''51-16621'' at the Canadian Museum of Flight; this aircraft was later traded to Classic Rotors.<ref name=Shearwater_HUP-3/> ]]
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.<ref name=Walker_RCN/>

===Canada===
;On display
* UH-25B (HUP-2) 128529 at Shearwater Aviation Museum in Shearwater, Nova Scotia.<ref name=Skaarup>{{cite book |last=Skaarup |first=Howard |date=2009 |title=Canadian Warplanes |location=Bloomington, Indiana |publisher=iUniverse |page=520 |isbn=978-1-4401-6758-4 }}</ref> This aircraft has been restored to the appearance of ''51-16621'', the first Royal Canadian Navy HUP-3.<ref name=Shearwater_HUP-3/>
* UH-25C (HUP-3), 51-16623 - Canada Aviation and Space Museum in Ottawa, Ontario.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=9090 "Piasecki HUP Retriever/51-16623."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref><ref>{{cite web|url=http://casmuseum.techno-science.ca/en/collection-research/artifact-piasecki-hup-3.php|title=Piasecki HUP-3|author= Canada Aviation and Space Museum|work=techno-science.ca|access-date=5 May 2016}}</ref>

===Netherlands===
* 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.<ref>{{cite web|url=https://www.baris.nl/onze-helikopter/|title=De helikopter |website=www.baris.nl |date=11 November 2013 |publisher= Baris Groep |access-date=1 November 2018 |language=nl |trans-title=The helicopter }}</ref>

===United Kingdom===
* UH-25C (HUP-3), 51-16622 – displayed at The Helicopter Museum in Weston-super-Mare, England, wearing Canadian markings.<ref name=Walker_RCN/><ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=11752 "Piasecki HUP Retriever/622 RCN."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>

===United States===
;On display
;;H-25A Army Mule
* 51-16616 – United States Army Aviation Museum in Fort Rucker, Alabama.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=17233 "Piasecki HUP Retriever/51-16616."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>

;;HUP-1
* 124915 – USS Hornet Museum in Alameda, California.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=10923 "Piasecki HUP Retriever/124915."] ''aerialvisuals.ca'' Retrieved: 25 April 2017.</ref>

;;UH-25B (HUP-2)
* 128479 – American Helicopter Museum in West Chester, Pennsylvania.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=63563 "Piasecki HUP Retriever/128479."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>
* 128517 – Wings of Freedom Aviation Museum in Horsham, Pennsylvania.<ref>{{cite web|title=Piasecki HUP-2 "Retriever"|publisher=Wings of Freedom Aviation Museum|url=http://wingsoffreedommuseum.org/index.php/our-aircraft/13-aircraft/aircraft-rotorcraft/33-aircraft-hup-2-retriever|access-date=26 August 2016}}</ref>
* 128519 – Intrepid Sea, Air & Space Museum in New York City, New York.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=35971 "Piasecki HUP Retriever/128519."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>
* 128596 – Flying Leatherneck Aviation Museum in San Diego, California.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=419 "Piasecki HUP Retriever/128596."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>
* 130059 – USS Midway Museum in San Diego, California.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=29266 "Piasecki HUP Retriever/130059."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>
* 130082 – on the deck of the USS Iowa Museum in San Pedro, California.<ref>[http://www.dailybreeze.com/general-news/20161018/historic-wartime-helicopter-to-be-pieced-together-for-san-pedros-battleship-iowa "Piasecki HUP Retriever/130082."] ''Daily Breeze'' Retrieved: 25 April 2017.</ref><ref>{{cite web|url= https://www.pacificbattleship.com/visit-us/special-exhibits|title= New Exhibits|access-date= 20 February 2022|author= Pacific Battleship Center|work= pacificbattleship.com|year= 2019 |archive-url= https://web.archive.org/web/20200424002946/https://www.pacificbattleship.com/visit-us/special-exhibits/|archive-date= 24 April 2020|url-status= dead}}</ref>

;;UH-25C (HUP-3)
[[File:Air Zoo December 2019 094 (Piasecki HUP-3 Retriever).jpg|thumb|HUP-3 Retriever on display at the Air Zoo]]
* 147595 – Pima Air & Space Museum in Tucson, Arizona.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=34520 "Piasecki HUP Retriever/147595."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>
* 147600 – Air Zoo in Kalamazoo, Michigan.<ref>{{Cite web|url=http://www.aerialvisuals.ca/AirframeDossier.php?Serial=10772|title=Piasecki HUP Retriever/147600|website=www.aerialvisuals.ca|access-date=2016-06-08}}</ref>
* 147607 – National Naval Aviation Museum in Pensacola, Florida.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=26108 "Piasecki HUP Retriever/147607."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>
* 147628 – Mid-America Air Museum in Liberal, Kansas.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=75028 "Piasecki HUP Retriever/147628."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>
* 51-16621 – Classic Rotors in Ramona, California.<ref name=N7089F>{{cite web|url = https://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=7089F|title = N-Number Inquiry Results N7089F|access-date = 1 November 2018|last = Federal Aviation Administration|date = 1 November 2018}}</ref> As of December 2019, this is the only Piasecki Helicopter-manufactured aircraft with valid FAA [[Engineering:Aircraft registration|aircraft registration]].<ref name="FAA_Piasecki">{{cite web|url = https://registry.faa.gov/aircraftinquiry/AcftRef_Results.aspx?Mfrtxt=PIASECKI&Modeltxt=&PageNo=1|title = Manufacturer Inquiry Results Piasecki|access-date = 16 December 2019|last = Federal Aviation Administration|author-link = Federal Aviation Administration|date = 16 December 2019|archive-date = 4 January 2020|archive-url = https://web.archive.org/web/20200104033145/https://registry.faa.gov/aircraftinquiry/AcftRef_Results.aspx?Mfrtxt=PIASECKI&Modeltxt=&PageNo=1|url-status = dead}}</ref> 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''.<ref name=Shearwater_HUP-3/><ref name=Skaarup/>

;Under restoration or in storage
;;UH-25B (HUP-2)
* 128598 - Stored at New England Air Museum in Windsor Locks, Connecticut.<ref name=Demobbed>{{cite web|url=http://www.usdemobbed.org.uk/locations.php?location=6388|title=Bradley - Museum, Connecticut|accessdate=20 September 2023}}</ref>
* 130053 – Stored at Quartzsite, Arizona.<ref>[https://www.aerialvisuals.ca/AirframeDossier.php?Serial=33423 "Piasecki HUP Retriever/130053."] ''aerialvisuals.ca'' Retrieved: 15 July 2021.</ref>
* 130063 - Stored at New England Air Museum in Windsor Locks, Connecticut.<ref name=Demobbed/>
;;UH-25C (HUP-3)
* 147610 – Yanks Air Museum in Chino, California, in storage.<ref>[http://www.aerialvisuals.ca/AirframeDossier.php?Serial=161310 "Piasecki HUP Retriever/147610."] ''aerialvisuals.ca'' Retrieved: 5 May 2016.</ref>

==Specifications (HUP-2)==
[[File:Piasecki H-25 orthographical image.svg|right|350px]]
{{Aircraft specs
|ref=''Jane's All The World's Aircraft 1956–57.''<ref name="jawa56 p345">Bridgman 1956, p. 345.</ref>
|prime units?=imp
<!--
        General characteristics
-->
|crew=two
|capacity=four passengers
|length ft=56
|length in=11
|length note=
|height ft=13
|height in=2
|height note=
|empty weight lb=4132
|empty weight note=
|gross weight lb=5750
|gross weight note=
|max takeoff weight lb=6100
|max takeoff weight note=
|fuel capacity=
|more general=
<!--
        Powerplant
-->
|eng1 number=1
|eng1 name=Continental R-975-46A
|eng1 type=9-cylinder air-cooled radial piston engine
|eng1 hp=550
|eng1 note=

|rot number=2
|rot dia ft=35
|rot dia in=0
|rot area sqft=1924.5
|rot area note=
* '''Blade section:''' [[Physics:NACA airfoil|NACA 0012]]<ref name="Selig">{{cite web |last1=Lednicer |first1=David |title=The Incomplete Guide to Airfoil Usage |url=https://m-selig.ae.illinois.edu/ads/aircraft.html |website=m-selig.ae.illinois.edu |access-date=16 April 2019}}</ref>
<!--
        Performance
-->
|max speed mph=105
|max speed note=
|cruise speed mph=80
|cruise speed note=
|never exceed speed mph=
|never exceed speed note=
|range miles=340
|range note=
|ferry range miles=
|ferry range note=
|endurance=<!-- if range unknown -->
|ceiling ft=10000
|ceiling note=
|climb rate ftmin=1000
|climb rate note=
|time to altitude=
|disk loading lb/sqft=3
|disk loading note=
|fuel consumption lb/mi=
|power/mass={{cvt|0.09|hp/lb}}

|more performance=
|avionics=
}}

==See also==
{{aircontent
<!-- include as many lines are appropriate. additional lines/entries with carriage return. -->
|related=<!-- related developments -->
* [[Engineering:Piasecki H-21|Piasecki H-21]]
* CH-46 Sea Knight
|similar aircraft=<!-- similar or comparable aircraft -->
* [[Engineering:Bell HSL|Bell HSL]]
* Bristol Belvedere
* [[Engineering:Harbin Z-5|Harbin Z-5]]
* [[Engineering:Mil Mi-4|Mil Mi-4]]
* [[Engineering:Sikorsky H-19 Chickasaw|Sikorsky H-19 Chickasaw]]
|lists=<!-- related lists -->
|see also=
}}

==References==
;Notes
{{Reflist}}
;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}}.
* {{cite book |last1=Swanborough |first1=Gordon |last2=Bowers |first2=Peter M. |date=1976 |title=United States Navy Aircraft since 1911 |edition=2nd  |location=Annapolis, Maryland |publisher=Naval Institute Press |isbn=0-87021-968-5}}.

==External links==
* [https://web.archive.org/web/20080506193518/http://www.redstone.army.mil/history/aviation/factsheets/h25.html H-25 US Army Aviation history fact sheet]

{{Piasecki/Vertol aircraft}}

[[Category:Single-engined piston helicopters]]

{{Sourceattribution|Piasecki HUP Retriever}}