Editing Lockheed SR-71 Blackbird (section)

===Shape and threat avoidance===
[[File:Sr71 1.jpg|thumb|[[Contrail|Water vapor]] is condensed by the low-pressure vortices generated by the chines outboard of each engine inlet.]]

The SR-71 was the second operational aircraft,<ref name="cia.gov">{{cite web|url=https://www.cia.gov/news-information/featured-story-archive/2015-featured-story-archive/oxcart-vs-blackbird.html|archive-url=https://web.archive.org/web/20151208074002/https://www.cia.gov/news-information/featured-story-archive/2015-featured-story-archive/oxcart-vs-blackbird.html|url-status=dead|archive-date=8 December 2015|title=OXCART vs Blackbird: Do You Know the Difference? |website=Cia.gov}}</ref> after the [[Lockheed A-12]],<ref name="cia.gov" /> designed to be hard to spot on [[radar]]. Early studies in [[stealth technology]] indicated that a shape with flattened, tapering sides would reflect most radar energy away from a beam's place of origin, so Lockheed's engineers added [[Chine (aeronautics)|chines]] and canted the vertical control surfaces inward. Special [[radar-absorbing material]]s were incorporated into [[serration|sawtooth-shaped]] sections of the aircraft's skin. [[Cesium]]-based fuel additives were used to somewhat reduce the visibility of exhaust plumes to radar, although exhaust streams remained quite apparent. Ultimately, engineers produced an aircraft with a wing area of about {{cvt|170|sqm|sqft|order=flip}} but a radar cross-section (RCS) of around {{cvt|10|sqm|sqft|order=flip}}.<ref>{{harvp|Graham|1996|p=75}}</ref> Johnson later conceded that Soviet radar technology advanced faster than the stealth technology employed against it.<ref>Hott, Bartholomew and George E. Pollock [https://web.archive.org/web/20030216054101/http://web.ics.purdue.edu/~gpollock/The%20Advent%2C%20Evolution%2C%20and%20New%20Horizons%20of%20United%20States%20Stealth%20Aircraft.htm "The Advent, Evolution, and New Horizons of United States Stealth Aircraft."] ''archive.is''. Retrieved: 7 February 2014.</ref>

While the SR-71 carried [[Radar jamming and deception|radar countermeasures]] to evade interception efforts, its greatest protection was its combination of high altitude and very high speed, which made it invulnerable at the time. Along with its low radar cross-section, these qualities gave a very short time for an enemy [[surface-to-air missile]] (SAM) site to acquire and track the aircraft on radar. By the time the SAM site could track the SR-71, it was often too late to launch a SAM, and the SR-71 would be out of range before the SAM could catch up to it. If the SAM site could track the SR-71 and fire a SAM in time, the SAM would expend nearly all of the [[delta-v]] of its boost and sustainer phases just reaching the SR-71's altitude; at this point, out of thrust, it could do little more than follow its ballistic arc. Merely accelerating would typically be enough for an SR-71 to evade a SAM;<ref name="SR71 Blackbird 2006"/> changes by the pilots in the SR-71's speed, altitude, and heading were also often enough to spoil any radar lock on the plane by SAM sites or enemy fighters.<ref name="harvp|Graham|1996">{{harvp|Graham|1996}}</ref> At sustained speeds of more than Mach 3.2, the plane was faster than the Soviet Union's fastest interceptor, the [[Mikoyan-Gurevich MiG-25]],{{refn|The [[MiG-25|Foxbats]] could sustain speeds of Mach 2.83, but they also had an emergency option to reach Mach 3.2{{snd}}after which the engines would have to be repaired or replaced.<ref name=GlobalAircraftMiG-25 />|group=N}} which also could not reach the SR-71's altitude.<ref name=GlobalAircraftMiG-25>{{cite web |url=http://www.globalaircraft.org/planes/mig-25_foxbat.pl |title=MiG-25 Foxbat |website=globalaircraft.org |access-date=31 May 2011 |archive-url=https://web.archive.org/web/20141223100252/http://www.globalaircraft.org/planes/mig-25_foxbat.pl |archive-date=23 December 2014}}</ref> No SR-71 was ever shot down.<ref name="Landis_p98-101"/>

The SR-71 featured chines, a pair of sharp edges leading aft from either side of the nose along the fuselage. These were not a feature on the early A-3 design; Frank Rodgers, a doctor at the Scientific Engineering Institute, a [[Central Intelligence Agency|CIA]] [[front organization]], discovered that a cross-section of a sphere had a greatly reduced radar reflection, and adapted a cylindrical-shaped fuselage by stretching out the sides of the fuselage.<ref>Suhler 2009, p. 100.</ref> After the advisory panel provisionally selected Convair's FISH design over the A-3 on the basis of RCS, Lockheed adopted chines for its A-4 through A-6 designs.<ref>Suhler 2009, ch. 10.</ref>

Aerodynamicists discovered that the chines generated powerful [[vortex|vortices]] and created additional [[Lift (force)|lift]], leading to unexpected aerodynamic performance improvements.<ref>''AirPower'' May 2002, p. 36.</ref> For example, they allowed a reduction in the wings' [[angle of incidence (aerodynamics)|angle of incidence]], which added stability and reduced drag at high speeds, allowing more weight to be carried, such as fuel. Landing speeds were also reduced, as the chines' vortices created turbulent flow over the wings at high [[Angle of attack|angles of attack]], making it harder to [[Stall (flight)|stall]]. The chines also acted like [[leading-edge extension]]s, which increase the agility of fighters such as the [[Northrop F-5 Freedom Fighter|F-5]], [[General Dynamics F-16 Fighting Falcon|F-16]], [[McDonnell Douglas F/A-18 Hornet|F/A-18]], [[Mikoyan MiG-29|MiG-29]], and [[Sukhoi Su-27|Su-27]]. The addition of chines also allowed the removal of the planned [[Canard (aeronautics)|canard]] foreplanes.{{refn|See [[:File:Blackbird-Canards.JPG|Blackbird with Canards]] image for visual.|group=N}}<ref>Goodall 2003, p. 19.</ref><ref>''AirPower'', May 2002, p. 33.</ref>