Editing Transonic (section)

{{Short description|Flight condition in which airflow speeds are concurrently above and below the speed of sound}}
{{Use dmy dates|date=May 2022}}
{{About ||the American company|Transonic Combustion}}

{{Stack |
[[File:FA-18 Hornet breaking sound barrier (7 July 1999).jpg|thumb|Aerodynamic condensation evidences of [[Prandtl–Meyer expansion fan|supersonic expansion fans]] around a transonic [[F/A-18 Hornet|F/A-18]]]]
[[File:Sears-Haack.png|thumb|right|The [[Sears–Haack body]] presents a cross-sectional area variation that minimises [[wave drag]].]]
[[File:Shock wave above airliner wing (7).jpg|thumb|Shock waves may appear as weak optical disturbances above airliners with [[supercritical airfoil|supercritical wings]]]]
[[File:Transonic flow patterns.svg|right|thumb|Transonic flow patterns on an [[airfoil]] showing flow patterns at and above [[critical Mach number]]]]}}

'''Transonic''' (or '''transsonic''') flow is air flowing around an object at a speed that generates regions of both subsonic and [[Supersonic speed|supersonic]] airflow around that object.<ref name=":2" /> The exact range of speeds depends on the object's [[critical Mach number]], but transonic flow is seen at flight speeds close to the [[speed of sound]] (343&nbsp;m/s at sea level), typically between [[Mach number|Mach]] 0.8 and 1.2.<ref name=":2">{{Cite book|last=Anderson|first=John D. Jr. |url=https://www.worldcat.org/oclc/927104254|title=Fundamentals of aerodynamics|date=2017|isbn=978-1-259-12991-9|edition=Sixth|location=New York, NY|pages=756–758|oclc=927104254}}</ref>

The issue of transonic speed (or transonic region) first appeared during World War II.<ref name=":0">{{Cite journal|last1=Vincenti|first1=Walter G.|last2=Bloor|first2=David|date=August 2003|title=Boundaries, Contingencies and Rigor|url=http://dx.doi.org/10.1177/0306312703334001|journal=Social Studies of Science|volume=33|issue=4|pages=469–507|doi=10.1177/0306312703334001|s2cid=13011496|issn=0306-3127|url-access=subscription}}</ref> Pilots found as they approached the sound barrier the airflow caused aircraft to become unsteady.<ref name=":0" /> Experts found that [[shock wave]]s can cause large-scale [[Flow separation|separation]] downstream, increasing drag, adding asymmetry and unsteadiness to the flow around the vehicle.<ref name=":1">{{Cite book|last=Takahashi|first=Timothy|url=http://worldcat.org/oclc/1162468861|title=Aircraft performance and sizing. fundamentals of aircraft performance|date=15 December 2017|isbn=978-1-60650-684-4|pages=107|publisher=Momentum Press |oclc=1162468861}}</ref> Research has been done into weakening shock waves in transonic flight through the use of [[Anti-shock body|anti-shock bodies]] and [[supercritical airfoil]]s.<ref name=":1" />

Most modern [[jet engine|jet]] powered aircraft are engineered to operate at transonic air speeds.<ref>{{cite book |last1=Takahashi |first1=Timothy |title=Aircraft Performance and Sizing, Volume I |date=2016 |publisher=Momentum Press Engineering |location=New York City |isbn=978-1-60650-683-7|pages=10–11}}</ref> Transonic airspeeds see a rapid increase in drag from about Mach 0.8, and it is the fuel costs of the drag that typically limits the airspeed. Attempts to reduce wave drag can be seen on all high-speed aircraft. Most notable is the use of [[swept wing]]s, but another common form is a wasp-waist fuselage as a side effect of the [[Whitcomb area rule]].

Transonic speeds can also occur at the tips of [[Rotorcraft|rotor]] blades of helicopters and aircraft. This puts severe, unequal stresses on the rotor blade and may lead to accidents if it occurs. It is one of the limiting factors of the size of rotors and the forward speeds of helicopters (as this speed is added to the forward-sweeping [leading] side of the rotor, possibly causing localized transonics).