Editing Lee wave (section)

==Aviation==

Lee waves provide a possibility for [[Glider (sailplane)|gliders]] to gain [[altitude]] or fly long distances when [[Gliding|soaring]]. World record wave flight performances for speed, distance or altitude have been made in the lee of the [[Sierra Nevada (U.S.)|Sierra Nevada]], [[Alps]], [[Patagonia|Patagonic]] [[Andes]], and [[Southern Alps (New Zealand)|Southern Alps]] mountain ranges.<ref>[http://records.fai.org/gliding/ FAI gliding records] {{webarchive|url=https://web.archive.org/web/20061205015245/http://records.fai.org/gliding/ |date=2006-12-05 }}</ref> The [[Perlan Project]] is working to demonstrate the viability of climbing above the [[tropopause]] in an unpowered glider using lee waves, making the transition into [[stratosphere|stratospheric]] standing waves. They did this for the first time on August 30, 2006 in [[Argentina]], climbing to an altitude of {{convert|15460|m|ft}}.<ref>{{cite web |url=http://www.fai.org/fai-record-file/?recordId=14043 |title=Fai Record File |access-date=2015-01-27 |url-status=dead |archive-url=https://web.archive.org/web/20150413093412/http://www.fai.org/fai-record-file/?recordId=14043 |archive-date=2015-04-13 }}</ref><ref>[http://www.perlanproject.com/ Perlan Project]</ref> The [[Mountain Wave Project]] of the [[Organisation Scientifique et Technique du Vol à Voile]] focusses on analysis and classification of lee waves and associated rotors.<ref>[http://www.pa.op.dlr.de/ostiv/projects.htm OSTIV-Mountain Wave Project]</ref><ref name="MWP">[http://mwp.flightplanner.info/Defaultengl.htm] {{Webarchive|url=https://web.archive.org/web/20160303204340/http://mwp.flightplanner.info/Defaultengl.htm|date=2016-03-03}} – accessed 2009-11-03</ref><ref>{{cite magazine
|title=Leewaves in the Andes Region, Mountain Wave Project (MWP) of OSTIV
|last=Lindemann
|first=C
|author2=Heise, R. |author3=Herold, W-D.
 |date=July 2008
|volume=32
|issue=3
|page=93
|magazine=Technical Soaring
|issn=0744-8996
}}</ref>

The conditions favoring strong lee waves suitable for soaring are:

* A gradual increase in windspeed with altitude
* Wind direction within 30° of perpendicular to the mountain ridgeline
* Strong low-altitude winds in a stable atmosphere
* Ridgetop winds of at least 20 knots

The rotor turbulence may be harmful for other small [[aircraft]] such as [[Balloon (aeronautics)|balloons]], [[Hang gliding|hang gliders]] and [[Paragliding|paraglider]]s. It can even be a hazard for large aircraft; the phenomenon is believed responsible for many [[aviation accidents and incidents]], including the in-flight breakup of [[BOAC Flight 911]], a [[Boeing 707]], near [[Mount Fuji]], [[Japan]] in 1966, and the in-flight separation of an engine on an [[Evergreen International Airlines]] [[Boeing 747]] cargo jet near [[Anchorage, Alaska]] in 1993.<ref>[https://www.ntsb.gov/investigations/AccidentReports/Pages/AAR9306.aspx NTSB Accident Report AAR-93-06]</ref>

The rising air of the wave, which allows gliders to climb to great heights, can also result in high-altitude upset in jet aircraft trying to maintain level cruising flight in [[lee waves]]. Rising, descending or turbulent air, in or above the lee waves, can cause [[Overspeed (aircraft)|overspeed]], [[Stall (flight)|stall]] or loss of control.