Editing Boeing CH-47 Chinook (section)

===Initial development===
During late 1956, the United States Department of the Army announced its intention to replace the [[Sikorsky CH-37 Mojave]], which was powered by [[Radial engine|piston engines]], with a new, [[Gas turbine|gas turbine-powered]] helicopter.<ref name="Tolsonarmy">{{cite book |url=https://www.history.army.mil/html/books/090/90-4/index.html |title= Vietnam Studies: Airmobility 1961–71 |department= Department of the Army |author= Lt General John J. Tolson |year= 1989 |publisher= US Government Printing Office |id= CMH Pub 90-4 |access-date= 19 August 2010 |archive-url= https://web.archive.org/web/20100612073527/http://www.history.army.mil/books/Vietnam/Airmobility/airmobility-fm.html |archive-date= 12 June 2010 |url-status= dead}}</ref> Turbine engines were also a key design feature of the smaller [[Bell UH-1 Iroquois|UH-1 "Huey"]] utility helicopter. Following a design competition, in September 1958, a joint Army–Air Force source selection board recommended that the Army procure the [[Piasecki Helicopter|Vertol]]-built medium transport helicopter. However, funding for full-scale development was not then available, and the Army vacillated on its design requirements. Some officials in [[United States Army Aviation Branch|Army Aviation]] thought that the new helicopter should be operated as a light tactical transport aimed at taking over the missions of the old piston-engined [[Piasecki H-21]] and [[Sikorsky H-34]] helicopters, and be consequently capable of carrying about 15 troops (one [[squad]]). Another faction in Army Aviation thought that the new helicopter should be much larger, enabling it to [[airlift]] large [[artillery]] pieces and possess enough internal space to carry the new [[MGM-31 Pershing|MGM-31 "Pershing" missile system]].<ref name="Tolsonarmy"/>

[[File:HC-1B in flight being tested and evaluated.jpg|thumb|left|HC-1B during in-flight evaluation]]
During 1957, Vertol commenced work upon a new tandem-rotor helicopter, designated as the Vertol Model 107 or V-107.<ref name=Apostolo>Apostolo, Giorgio. ''The Illustrated Encyclopedia of Helicopters''. New York: Bonanza Books. 1984. {{ISBN|978-0-517-43935-7}}.</ref><ref name=vect_V-107>Goebel, Greg. {{usurped|1=[https://web.archive.org/web/20120623191825/http://www.vectorsite.net/avch47.html#m1 Origins: Vertol V-107 & V-114]}}. Vectorsite.net, 1 December 2009.</ref> During June 1958, the U.S. Army awarded a contract to Vertol for the acquisition of a small number of the rotorcraft, giving it the ''YHC-1A'' designation.<ref name="whirly">Spenser, Jay P. ''Whirlybirds, A History of the U.S. Helicopter Pioneers''. University of Washington Press, 1998. {{ISBN|0-295-97699-3}}.</ref> As ordered, the YHC-1A possessed the capacity to carry a maximum of 20 troops.<ref name="Tolsonarmy"/> Three underwent testing by the Army for deriving engineering and operational data. However, the YHC-1A was considered by many figures within the Army users to be too heavy for the assault role, while too light for the more general transport role.<ref name="Tolsonarmy"/> Accordingly, a decision was made to procure a heavier transport helicopter, and at the same time, upgrade the UH-1 "Huey" to serve as the needed tactical troop transport. The YHC-1A would be improved and adopted by the Marines as the [[Boeing Vertol CH-46 Sea Knight|CH-46 Sea Knight]] in 1962.<ref>{{cite news |url= https://pqasb.pqarchiver.com/latimes/access/454317782.html?dids=454317782:454317782&FMT=ABS&FMTS=ABS:AI&type=historic&date=Oct+26%2C+1962&author=&pub=Los+Angeles+Times&desc=The+Quiet+Americans--Our+Marines+Overseas&pqatl=google |title= The Quiet Americans-Our Marines Overseas |first= Alexander |last= Holmes |work= Los Angeles Times |date= 26 October 1962 |access-date= 5 July 2017 |archive-url= https://web.archive.org/web/20121026080022/http://pqasb.pqarchiver.com/latimes/access/454317782.html?dids=454317782:454317782&FMT=ABS&FMTS=ABS:AI&type=historic&date=Oct+26,+1962&author=&pub=Los+Angeles+Times&desc=The+Quiet+Americans--Our+Marines+Overseas&pqatl=google |archive-date= 26 October 2012 |url-status= dead}}</ref> As a result, the Army issued a new order to Vertol for an enlarged derivative of the V-107, known by internal company designation as the Model 114, which it gave the designation of HC-1B.<ref>{{cite web |url= http://www.flightglobal.com/articles/2008/04/01/222553/chinook-five-decades-of-development.html |title= Chinook: Five decades of development |first= Graham |last= Warwick |work= Flight International |date= 1 April 2008 |access-date= 29 March 2010 |archive-url= https://web.archive.org/web/20081011030804/http://www.flightglobal.com/articles/2008/04/01/222553/chinook-five-decades-of-development.html |archive-date= 11 October 2008 |url-status= live}}</ref> On 21 September 1961, the preproduction [[Boeing Vertol]] YCH-1B made its initial hovering flight. During 1962, the HC-1B was redesignated the CH-47A under the [[1962 United States Tri-Service aircraft designation system]]; it was also named "Chinook" after the Chinook people of the Pacific Northwest.<ref>{{cite web|url=https://www.defense.gov/News/Inside-DOD/Blog/Article/2052989/why-army-helicopters-have-native-american-names/|archive-url=https://web.archive.org/web/20210923214323/https://www.defense.gov/News/Inside-DOD/Blog/Article/2052989/why-army-helicopters-have-native-american-names/|url-status=dead|archive-date=23 September 2021|title=Why Army Helicopters Have Native American Names|first=Katie|last=Lange|date=2019-11-29|access-date=2021-12-20|publisher=Department of Defense}}</ref>

{{Listen
| filename= Chinook helicopter flying over Greenwich in London.ogg
| title= Chinook helicopter flying overhead in Greenwich, London
| description= The distinctive sound of the Chinook helicopter, recorded May 2016.
}}
The CH-47 is powered by two [[turboshaft]] engines, mounted on each side of the helicopter's rear pylon and connected to the rotors by drive shafts. Initial models were fitted with [[Lycoming T55]] engines rated at {{convert|2200|hp|kW|abbr=on}} each. The counter-rotating rotors eliminate the need for an antitorque vertical rotor, allowing all power to be used for lift and thrust. The ability to adjust lift in either rotor makes it less sensitive to changes in the center of gravity, important for the cargo lifting and dropping. While hovering over a specific location, a twin-rotor helicopter has increased stability over a single rotor when weight is added or removed, for example, when troops drop from or begin climbing up ropes to the aircraft, or when other cargo is dropped. If one engine fails, the other can drive both rotors.<ref>{{cite web|url=http://www.chinook-helicopter.com/standards/areas/drive_train.html|title=Chinook Information and diagrams about the transmission system|access-date=13 November 2014|archive-url=https://web.archive.org/web/20150330094029/http://www.chinook-helicopter.com/standards/areas/drive_train.html|archive-date=30 March 2015|url-status=dead}}</ref> The "sizing" of the Chinook was directly related to the growth of the Huey and the Army's tacticians' insistence that initial air assaults be built around the squad. The Army pushed for both the Huey and the Chinook, and this focus was responsible for the acceleration of its air mobility effort.<ref name="Tolsonarmy"/>