Editing Lockheed U-2 (section)

==Design==
[[File:U2-Duxford.JPG|thumb|U-2 at the [[Imperial War Museum Duxford|Imperial War Museum, Duxford]]]]

The design that gives the U-2 its remarkable performance also makes it a difficult aircraft to fly. [[Martin Knutson]] said that it "was the highest workload air plane I believe ever designed and built&nbsp;… you're wrestling with the airplane and operating the camera systems at all times", leaving no time to "worry about whether you're over Russia or you're flying over Southern California".<ref name= "cnncoldwarknutson">{{Cite episode |title=Sputnik |url=http://nsarchive.gwu.edu/coldwar/interviews/ |series=Cold War |network=CNN |date=15 November 1998 |number=8 |access-date=30 May 2017 |archive-date=5 June 2017 |archive-url=https://web.archive.org/web/20170605140747/http://nsarchive.gwu.edu/coldwar/interviews/ |url-status=live }}</ref> The U-2 was designed and manufactured for minimum airframe weight, which results in an aircraft with little margin for error.<ref name="I&T"/> Most aircraft were single-seat versions, with only five two-seat trainer versions known to exist.<ref>{{Cite news |last=Karl |first=Jonathan |date=17 August 2007 |title=So High, So Fast |language=en |work=ABC News |url=https://abcnews.go.com/Technology/story?id=3490523&page=1 |access-date=8 March 2009 |archive-date=24 October 2008 |archive-url=https://web.archive.org/web/20081024205336/http://abcnews.go.com/Technology/story?id=3490523&page=1 |url-status=live }}</ref> Early U-2 variants were powered by [[Pratt & Whitney J57]] [[turbojet]] engines.{{sfn|Eden|Moeng|2002|p=[https://archive.org/details/completeencyclop0000unse_z7c1/page/918/ 918]}} The U-2C and TR-1A variants used the more powerful [[Pratt & Whitney J75]] turbojet. The U-2S and TU-2S variants incorporated the more powerful [[General Electric F118]] [[turbofan]] engine.{{sfn|Donald|2003|p=7}}

High aspect ratio wings give the U-2 [[Glider (sailplane)|glider]]-like characteristics, with an engine out [[Gliding (flight)#Glide ratio|glide ratio]] of about 23:1,<ref>{{cite web |url= https://www.cia.gov/library/center-for-the-study-of-intelligence/utility-flight-hb-1-Mar-1959.pdf |archive-url= https://web.archive.org/web/20120927015901/https://www.cia.gov/library/center-for-the-study-of-intelligence/utility-flight-hb-1-Mar-1959.pdf |url-status= dead |archive-date= 27 September 2012 |title= U2 Utility Flight Handbook |publisher= Department of Defense |date= 1959 |page= {{Not a typo|3-2}} }}</ref> comparable to gliders of the time. To maintain their operational ceiling of {{convert|70000|ft|m|sigfig=2|sp=us}}, the early U-2A and U-2C models had to fly very near their [[V-speed|never-exceed speed]] (V<sub>NE</sub>). The margin between that maximum speed and the [[stall speed]] at that altitude was only {{convert|10|kn|mph km/h|sigfig=2|sp=us}}. This narrow window is called the "[[coffin corner (aviation)|coffin corner]]",<ref>[http://www.flightglobal.com/pdfarchive/view/1989/1989%20-%201182.html "High-flying U-2 takes its final bow."] {{Webarchive|url=https://web.archive.org/web/20130816091515/http://www.flightglobal.com/pdfarchive/view/1989/1989%20-%201182.html |date=16 August 2013 }} ''Flight International'', 29 April 1989, p. 24.</ref><ref name="Powers">{{Cite book |last=Powers |first=Francis |url=https://archive.org/details/operationoverfli0000powe_p1a2/page/18/ |title=Operation Overflight: A Memoir of the U-2 Incident |publisher=Potomac Books, Inc. |others=With Curt Gentry |year=1960 |isbn=9781574884227 |page=18 |url-access=registration}}</ref> because breaching either limit was likely to cause [[Flow separation|airflow separation]] at the wings or tail.{{sfn|Pedlow|Welzenbach|1992|pp=75–76}} For most of the time on a typical mission the U-2 was flying less than {{convert|5|knot|mph km/h|spell=in|0}} above stall speed. A stall would cause a loss of altitude, possibly leading to detection and overstress of the airframe.<ref name="I&T"/>

The U-2's flight controls are designed for high-altitude flight; the controls require light control inputs at operational altitude. However, at lower altitudes the higher air density and lack of a power-assisted control system make the aircraft very difficult to fly: control inputs must be extreme to achieve the desired response, and a great deal of physical strength is needed to operate the controls. The U-2 is very sensitive to crosswinds, which, together with its tendency to float over the runway, makes the aircraft notoriously difficult to land. As it approaches the runway, the cushion of air provided by the high-lift wings in [[Ground effect (aircraft)|ground effect]] is so pronounced that the U-2 will not land unless the wings are fully stalled. A landing U-2 is accompanied on the ground by a [[Chase plane|chase car]], which is driven by a second U-2 pilot who assists the landing U-2 by reporting the aircraft's altitude.<ref>Hennigan, W.J. [https://www.latimes.com/business/autos/la-fi-hy-autos-u2-chase-cars-20121119,0,2750231.story "New Camaros tear down runway to help U-2 spy planes."] {{Webarchive|url=https://web.archive.org/web/20240820210644/https://www.latimes.com/business/autos/la-fi-hy-autos-u2-chase-cars-20121119-story.html |date=20 August 2024 }} ''[[Los Angeles Times]]'', 22 November 2012, Retrieved: 8 January 2013.</ref><ref name=smith>Smith, Sam. [http://www.popularmechanics.com/technology/military/planes-uavs/chasing-the-u-2-spy-plane-in-a-pontiac-gto-11000804 "Chasing the U-2 spy plane – in a Pontiac GTO."] {{Webarchive|url=https://web.archive.org/web/20140913014926/http://www.popularmechanics.com/technology/military/planes-uavs/chasing-the-u-2-spy-plane-in-a-pontiac-gto-11000804 |date=13 September 2014 }} ''[[Popular Mechanics]]'', 28 August 2012. Retrieved: 12 September 2014.</ref> In practice, once the aircraft has descended to an altitude of {{convert|2|ft|spell=in|}} above the runway the pilot initiates a stall and the aircraft falls from this height. Chase cars and live calling of aircraft altitude are necessary because the landing gear is not designed to absorb the weight of the aircraft when falling from altitudes much above {{convert|2|ft|spell=in|}}.

Instead of the typical tricycle landing gear, the U-2 uses a bicycle configuration with a forward set of main wheels located just behind the cockpit and a rear set of main wheels located behind the engine. The rear wheels are coupled to the rudder to provide steering during taxiing. To maintain balance while taxiing and take-off, two auxiliary wheels called "pogos" are attached under the wings. These fit into sockets underneath each wing at about mid-span and fall off at takeoff. To protect the wings during landing, each wingtip has a titanium skid. After the U-2 comes to a halt, the ground crew re-installs the pogos, then the aircraft taxis to parking.<ref>Bennett, Christopher W. [http://www.blackbirds.net/u2/c_bennett/bbird-06.html "The U-2 World, January 1991 – July 1994, May – October 1996."] {{Webarchive|url=https://web.archive.org/web/20010630165323/http://www.blackbirds.net/u2/c_bennett/bbird-06.html |date=30 June 2001 }}''Blackbirds.net'', 16 January 1997. Retrieved: 8 March 2009.</ref>

Because of the high operating altitude and the cockpit's partial pressurization, equivalent to {{convert|28000|ft|m|-2}} pressure altitude, the pilot wears a partially pressurized [[space suit]], which delivers the pilot's oxygen supply and provides emergency protection in case cabin pressure is lost. While pilots can drink water and eat various liquid foods in squeezable containers<ref name=foodcare>Norris, Guy. [http://aviationweek.com/blog/what-do-spy-plane-pilots-eat "What do spy plane pilots eat?"] {{Webarchive|url=https://web.archive.org/web/20150823221656/http://aviationweek.com/blog/what-do-spy-plane-pilots-eat |date=23 August 2015 }} ''Aviation Week'' 21 August 2015. Retrieved: 7 December 2015.</ref> through a self-sealing hole in the face mask, they typically lose up to 5% of their body mass on an eight-hour mission.<ref>{{Cite book |url=https://books.google.com/books?id=IT-chpAkCZ0C&pg=PA89 |title=Spacesuit: Fashioning Apollo |isbn=9780262015202 |last1=Monchaux |first1=Nicholas De |year=2011 |publisher=MIT Press |access-date=14 June 2018 |archive-date=20 August 2024 |archive-url=https://web.archive.org/web/20240820210633/https://books.google.com/books?id=IT-chpAkCZ0C&pg=PA89#v=onepage&q&f=false |url-status=live }}</ref> 

Initially, pilots had the option of carrying a [[suicide pill]], although most chose not to. If put in the mouth and bitten, the "L-pill"—containing liquid [[potassium cyanide]]—would cause death in 10–15 seconds. After a pilot almost accidentally ingested an L-pill instead of candy during a December 1956 flight, the suicide pills were put into boxes to avoid confusion. When in 1960 the CIA realized that a pill breaking inside the cockpit would kill the pilot, it destroyed the L-pills, and as a replacement, its [[Technical Services Division]] developed a needle poisoned with a powerful shellfish toxin and hidden in a [[United States one-dollar coin|silver dollar]]. Only one was made because the agency decided if any pilot needed to use it the program would probably be canceled.{{sfn|Pedlow|Welzenbach|1992|pp=62–66, 124–125}} Like the suicide pill, not all pilots carried the coin, and Knutson did not know of any that intended to commit suicide; he carried it as a weapon to escape in the event of capture.{{r|cnncoldwarknutson}}

To decrease the risk of developing [[decompression sickness]], pilots breathe 100% oxygen for an hour prior to taking off to remove nitrogen from the blood. A portable oxygen supply is used during transport to the aircraft.{{sfn|Polmar|2001|p=64}} Since 2001, more than a dozen pilots have reportedly suffered the effects of decompression sickness, including permanent brain damage in nine cases; initial symptoms include disorientation and becoming unable to read. Factors increasing the risk of illness since 2001 include longer mission durations and more cockpit activity. Conventional reconnaissance missions would limit pilot duties to maintaining flight paths for camera photography. Operations over Afghanistan included more real-time activities, such as communication with ground troops, increasing their bodies' oxygen requirements and the risk of nitrogen bubble formation. U-2 pilots now exercise during oxygen pre-breathing.<ref>Betancourt, Mark. [http://www.airspacemag.com/military-aviation/Killer-at-70000-Feet.html "Killer at 70,000&nbsp;feet: The occupational hazards of flying the U-2."] {{Webarchive|url=https://web.archive.org/web/20121118140320/http://www.airspacemag.com/military-aviation/Killer-at-70000-Feet.html |date=18 November 2012 }} ''Air & Space magazine'', May 2012, pp. 42–47.</ref> In 2012, modifications were initiated under the Cockpit Altitude Reduction Effort (CARE), increasing the [[Cabin pressurization|cabin pressure]] from 3.88 psi to 7.65 psi, a {{convert|15000|ft|adj=on|}} altitude equivalent. The urine collection device also was rebuilt to eliminate leakage.<ref name=foodcare/><ref>Nickel, Shawn, (Senior Airman). [http://www.beale.af.mil/news/story.asp?id=123336640 "CARE modifications place pilots at better Elevation."] {{webarchive|url=https://web.archive.org/web/20130305203742/http://www.beale.af.mil/news/story.asp?id=123336640 |date=5 March 2013}} ''Beale Air Force Base'', 13 February 2012. Retrieved: 21 May 2013.</ref>

===Sensors===
[[File:U2withExperiments.jpg|thumb|upright=1.4|U-2 with range of possible payloads (2009)]]

Existing cameras had ground resolution down to {{convert|7|m|ft|order=flip}} from an altitude of {{convert|33000|ft|m}}, and were inadequate for the {{convert|70000|ft|m}} altitude. Ground resolution of {{convert|3|m|ft|order=flip}} was required, at a maximum payload weight of {{convert|200|kg|lb|order=flip}}. The U-2's camera was specially designed by [[James G. Baker]] of Harvard and [[Richard Scott Perkin]] of the [[Perkin-Elmer]] Company, initially in collaboration and later separately.{{sfn|Pedlow|Welzenbach|1992|loc=Chapter 2: Developing the U-2}}

Initial missions were flown with the [[trimetrogon]] "A" camera, consisting of three {{convert|24|in|mm|adj=mid|-focal-length}} cameras, with F/8 resolving 60 lines per mm, and the ground resolution can be inferred by calculation to be {{convert|60|cm|in|order=flip}}. This was followed by the "B" camera with a {{convert|36|in|mm|adj=mid|-focal-length}} lens with F/10 and image motion compensation, resolving 100 lines per mm, and the ground resolution can be inferred by calculation to be {{convert|23|cm|in|order=flip}}. It was a panoramic camera which took pictures of an extremely large area of the earth's surface. The lens design consisted of a single [[aspheric]] [[singlet lens]]. {{convert|6000|ft|spell=In|adj=on}} reels of film were used, with the [[Photographic emulsion|emulsion]] being coated on a polyester ([[Polyethylene terephthalate|PET]]) base that offered significantly improved dimensional stability over extremes of temperature and humidity compared to conventional [[cellulose acetate]].{{sfn|Brugioni|2010|p=115}}<ref>{{cite journal |last1=Calhoun |first1=J. M. |last2=Adelstein |first2=P. Z. |last3=Parker |first3=J. T |title=Physical Properties of Estar Polyester Base Aerial Films for Topographic Mapping |journal=Photogrammetric Engineering |issue=June 1961 |pages=461–470 |url=https://www.asprs.org/wp-content/uploads/pers/1961journal/jun/1961_jun_461-470.pdf |publisher=American Society of Photogrammetry |access-date=5 July 2022 |archive-date=5 July 2022 |archive-url=https://web.archive.org/web/20220705192007/https://www.asprs.org/wp-content/uploads/pers/1961journal/jun/1961_jun_461-470.pdf |url-status=live }}</ref>

In addition, the U-2 also carried a low-resolution Perkin-Elmer tracking camera using a 3-inch lens, which made continuous horizon-to-horizon photographs. This is common practice in high resolution cameras in later systems also, where the large image helps localize the small high-resolution images.

The aircraft carries a variety of sensors in the nose, Q-bay (behind the cockpit, also known as the camera bay), and wing pods. The U-2 is capable of simultaneously collecting [[signals intelligence|signals]], imagery intelligence and air samples. Imagery intelligence sensors include either wet film photography, electro-optic, or radar imagery—the latter from the [[Raytheon]] [[ASARS-2]] system. It can use both line-of-sight and over-horizon data links.
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