Editing Unmanned aerial vehicle (section)

===Endurance===
[[File:UAV-741-F.jpg|thumb|UEL UAV-741 Wankel engine for UAV operations, used on [[AAI RQ-7 Shadow]]]]
[[File:Flight time against mass of small drones.svg|thumb|Flight time against mass of small (less than 1&nbsp;kg) drones<ref name="Nature - Future of sUAVs"/>]]
UAV endurance is not constrained by the physiological capabilities of a human pilot.

Because of their small size, low weight, low vibration and high power to weight ratio, [[Wankel rotary engines]] are used in many large UAVs. Their engine rotors cannot seize; the engine is not susceptible to shock-cooling during descent and it does not require an enriched fuel mixture for cooling at high power. These attributes reduce fuel usage, increasing range or payload.

Proper drone cooling is essential for long-term drone endurance. Overheating and subsequent engine failure is the most common cause of drone failure.<ref>{{Cite news|url=https://www.pelonistechnologies.com/blog/proper-cooling-drone-performance|title=The Importance of Proper Cooling and Airflow for Optimal Drone Performance|website=Pelonis Technologies|access-date=22 June 2018|archive-date=22 June 2018|archive-url=https://web.archive.org/web/20180622220335/https://www.pelonistechnologies.com/blog/proper-cooling-drone-performance|url-status=live}}</ref>

[[Hydrogen fuel cells]], using hydrogen power, may be able to extend the endurance of small UAVs, up to several hours.<ref>{{Cite web|title = Flying on Hydrogen: Georgia Tech Researchers Use Fuel Cells to Power Unmanned Aerial Vehicle {{!}} Georgia Tech Research Institute|url = http://www.gtri.gatech.edu/casestudy/flying-hydrogen|website = www.gtri.gatech.edu|access-date = 4 February 2016|archive-date = 3 February 2016|archive-url = https://web.archive.org/web/20160203120006/http://www.gtri.gatech.edu/casestudy/flying-hydrogen|url-status = live}}</ref><ref>{{Cite web|title = Hydrogen-powered Hycopter quadcopter could fly for 4 hours at a time|url = http://www.gizmag.com/horizon-energy-systems-hycopter-fuel-cell-drone/37585/|website = www.gizmag.com|access-date = 4 February 2016|date = 20 May 2015|archive-date = 4 February 2016|archive-url = https://web.archive.org/web/20160204194507/http://www.gizmag.com/horizon-energy-systems-hycopter-fuel-cell-drone/37585/|url-status = live}}</ref>

Micro air vehicles endurance is so far best achieved with flapping-wing UAVs, followed by planes and multirotors standing last, due to lower [[Reynolds number]].<ref name="Nature - Future of sUAVs"/>

Solar-electric UAVs, a concept originally championed by the AstroFlight Sunrise in 1974, have achieved flight times of several weeks.

Solar-powered atmospheric satellites ("atmosats") designed for operating at altitudes exceeding 20&nbsp;km (12 miles, or 60,000 feet) for as long as five years could potentially perform duties more economically and with more versatility than [[low Earth orbit]] satellites. Likely applications include [[weather drone]]s for [[Weather reconnaissance|weather monitoring]], [[Emergency management#Recovery|disaster recovery]], [[Earth imaging]] and communications.

Electric UAVs powered by microwave power transmission or laser power beaming are other potential endurance solutions.<ref>{{Cite news|url=https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-087-DFRC.html|title=NASA Armstrong Fact Sheet: Beamed Laser Power for UAVs|last=Gibbs|first=Yvonne|date=31 March 2015|work=NASA|access-date=22 June 2018|language=en|archive-date=5 April 2019|archive-url=https://web.archive.org/web/20190405021645/https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-087-DFRC.html|url-status=live}}</ref>

Another application for a high endurance UAV would be to "stare" at a battlefield for a long interval (ARGUS-IS, Gorgon Stare, Integrated Sensor Is Structure) to record events that could then be played backwards to track battlefield activities.

{| class="wikitable"
|+ Lengthy endurance flights
|-
! UAV !! Flight time<br />hours:minutes !! Date !! Notes
|-
| [[Boeing Condor]] || 58:11 || 1989 || The aircraft is currently in the [[Hiller Aviation Museum]].
<ref>{{citation |url=http://www.hiller.org/files/docs/2003Q3.pdf |title=Vertical Challenge: "Monsters of the sky" |archive-url=https://web.archive.org/web/20130911145056/http://www.hiller.org/files/docs/2003Q3.pdf |archive-date=11 September 2013 }}</ref>
|-
| [[General Atomics Gnat]] || 40:00 || 1992 ||<ref>{{cite web|url=http://www.designation-systems.net/dusrm/app4/gnat.html|title=General Atomics Gnat|publisher=Designation-systems.net|access-date=8 January 2015|archive-date=11 December 2008|archive-url=https://web.archive.org/web/20081211063639/http://www.designation-systems.net/dusrm/app4/gnat.html|url-status=live}}</ref><ref>{{cite web|url=http://www.vectorsite.net/twuav_12.html |title=UAV Notes |url-status=usurped |archive-url=https://web.archive.org/web/20130730032004/http://www.vectorsite.net/twuav_12.html |archive-date=30 July 2013 }}</ref>
|-
| [[The Spirit of Butts Farm|TAM-5]] || 38:52 || 11 August 2003 || Smallest UAV to cross the Atlantic
<ref>{{cite web|url=http://tam.plannet21.com/|title=Trans atlantic Model|publisher=Tam.plannet21.com|access-date=8 January 2015|archive-url=http://arquivo.pt/wayback/20160522211703/http://tam.plannet21.com/|archive-date=22 May 2016}}</ref>
|-
| [[QinetiQ Zephyr]] Solar Electric || 54:00 || September 2007 || <ref>{{cite press release |url=http://www.qinetiq.com/home/newsroom/news_releases_homepage/2007/3rd_quarter/qinetiq_s_zephyr_uav.html |date=10 September 2007 |publisher=QinetiQ |title=QinetiQ's Zephyr UAV exceeds official world record for longest duration unmanned flight
|archive-url=https://web.archive.org/web/20110423162325/http://www.qinetiq.com/home/newsroom/news_releases_homepage/2007/3rd_quarter/qinetiq_s_zephyr_uav.html |archive-date=23 April 2011}}</ref><ref>{{cite web|first=  Tom |last=Simonite |url=https://www.newscientist.com/blog/technology/2007/09/solar-flyer-en-route-to-everlasting.html |title=New Scientist Technology Blog: Solar plane en route to everlasting flight |work=New Scientist |access-date=8 January 2015|archive-url=https://web.archive.org/web/20150402090342/http://www.newscientist.com/blog/technology/2007/09/solar-flyer-en-route-to-everlasting.html|archive-date=2 April 2015}}</ref>
|-
| [[RQ-4 Global Hawk]] || 33:06 || 22 March 2008 || Set an endurance record for a full-scale, operational uncrewed aircraft.<ref>{{cite web |url=http://www.spacewar.com/reports/Northrop_Grumman_Global_Hawk_Unmanned_Aircraft_Sets_33_Hour_Flight_Endurance_Record_999.html |title=Northrop Grumman's Global Hawk Unmanned Aircraft Sets 33-Hour Flight Endurance Record |publisher=Spacewar.com |access-date=27 August 2013 |archive-date=1 July 2013 |archive-url=https://archive.today/20130701060609/http://www.spacewar.com/reports/Northrop_Grumman_Global_Hawk_Unmanned_Aircraft_Sets_33_Hour_Flight_Endurance_Record_999.html |url-status=live }}</ref>
|-
| [[QinetiQ Zephyr]] Solar Electric || 82:37 || 28–31 July 2008 || <ref>{{cite press release|publisher=QinetiQ|date=24 August 2008
|url=http://www.qinetiq.com/home/newsroom/news_releases_homepage/2008/3rd_quarter/qinetiq_s_zephyr_uav.html |title=QinetiQ's Zephyr UAV flies for three and a half days to set unofficial world record for longest duration unmanned flight |archive-url=https://web.archive.org/web/20110524020631/http://www.qinetiq.com/home/newsroom/news_releases_homepage/2008/3rd_quarter/qinetiq_s_zephyr_uav.html |archive-date=24 May 2011}}</ref>
|-
| [[Airbus Zephyr|QinetiQ Zephyr 7]] || 336:22 || 9–23 July 2010 || Solar electric powered. Remained aloft for 14 days. Also filed for FAI altitude record of 70,740&nbsp;ft (21,561 m)<ref name="qinetiq.com">{{cite press release | url=http://www.qinetiq.com/home/newsroom/news_releases_homepage/2010/3rd_quarter/qinetiq_files_for.html | title=QinetiQ files for three world records for its Zephyr Solar powered UAV | work=QinetiQ | date=24 August 2010 | archive-url=https://web.archive.org/web/20100924231501/http://www.qinetiq.com/home/newsroom/news_releases_homepage/2010/3rd_quarter/qinetiq_files_for.html | archive-date=24 September 2010}}</ref>
|}

The delicacy of the British [[PHASA-35]] military drone (at a late stage of development) is such that traversing the first turbulent twelve miles of atmosphere is a hazardous endeavor. It has, however, remained on station at 65,000 feet for 24 hours. Airbus' Zephyr in 2023 has attained 70,000 feet and flown for 64 days; 200 days aimed at. This is sufficiently close enough to [[Kármán line|near-space]] for them to be regarded in "pseudo-satellites" as regards to their operational capabilities.<ref>{{Cite news|url=https://www.wsj.com/articles/drones-reach-stratospheric-heights-in-race-to-fly-higher-longer-a29ceea3|title=Drones Reach Stratospheric Heights in Race to Fly Higher, Longer|first=Alistair|last=MacDonald|newspaper=Wall Street Journal |date=14 July 2023|via=www.wsj.com}}</ref>