Editing Area rule (section)

==Description==
At high-subsonic flight speeds, the local speed of the airflow can reach the speed of sound where the flow accelerates around the [[aircraft]] body and [[wing]]s. The speed at which this development occurs varies from aircraft to aircraft and is known as the [[critical Mach | critical Mach number]]. The resulting [[shock wave]]s formed at these zones of sonic flow cause a sudden increase in [[Drag (physics)|drag]], called [[wave drag]]. To reduce the number and strength of these shock waves, an [[aerodynamic]] shape should change in [[Cross section (geometry)|cross section]]al area as smoothly as possible from front to rear.

===Transonic area rule===
The area rule says that two airplanes with the same longitudinal cross-sectional area distribution have the same wave drag, independent of how the area is distributed laterally (i.e. in the fuselage or in the wing). Furthermore, to avoid the formation of strong shock waves the external shape of the aircraft has to be carefully arranged so that the cross-sectional area changes as smoothly as possible going from nose to tail. At the location of the wing, the fuselage is narrowed or "waisted". Fuselage cross-sectional area may need to be reduced by flattening the sides of the fuselage below a bubble canopy and at the tail surfaces to compensate for their presence, both of which were done on the [[Hawker Siddeley Buccaneer]].<ref>From Spitfire To Eurofighter 45 Years of Combat Aircraft Design, Roy Boot,{{ISBN|1 85310 093 5}}, p.93</ref>

===Supersonic area rule===
A different area rule, known as the supersonic area rule, developed by NACA aerodynamicist Robert Jones in  "Theory of wing-body drag at supersonic speeds",<ref name="RTJones"/> is applicable at speeds beyond transonic, and in this case, the cross-sectional area requirement is established with relation to the angle of the Mach cone for the design speed.  For example, consider that at Mach 1.3 the angle of the Mach cone generated by the nose of the aircraft will be at an angle μ = arcsin(1/M) = 50.3° (where μ is the angle of the Mach cone, also known as [[Mach angle]], and M is the [[Mach number]]). In this case the "perfect shape" is biased rearward; therefore, aircraft designed for lower wave drag at supersonic speed usually have wings towards the rear.<ref name="RTJones">{{Citation |url = http://naca.central.cranfield.ac.uk/reports/1956/naca-report-1284.pdf | title = Theory of wing-body drag at Supersonic speeds | author-link = Robert Thomas Jones (engineer) | first = Robert T | last = Jones | year = 1956 | place = [[United Kingdom|UK]] | publisher = NACA | type = report | id = 1284 | access-date = 2008-09-12 | archive-date = 2020-12-05 | archive-url = https://web.archive.org/web/20201205131851/http://naca.central.cranfield.ac.uk/reports/1956/naca-report-1284.pdf }}.</ref>