Editing Turbojet (section)

=== Air intake ===
An intake, or tube, is needed in front of the compressor to help direct the incoming air [[Laminar flow|smoothly]] into the rotating compressor blades. Older engines had stationary vanes in front of the moving blades. These vanes also helped to direct the air onto the blades. The air flowing into a turbojet engine is always subsonic, regardless of the speed of the aircraft itself.

The intake has to supply air to the engine with an acceptably small variation in pressure (known as distortion) and having lost as little energy as possible on the way (known as pressure recovery). The ram pressure rise in the intake is the inlet's contribution to the propulsion system's [[overall pressure ratio]] and [[thermal efficiency]].

The intake gains prominence at high speeds when it generates more compression than the compressor stage. Well-known examples are the Concorde and [[Lockheed SR-71 Blackbird]] propulsion systems where the intake and engine contributions to the total compression were 63%/8%<ref>{{cite book | last1=Trubshaw | first1=Brian | last2=Edmondson | first2=Sally |title=Brian Trubshaw: Test Pilot |publisher=Sutton Publishing |year=1999 |isbn=0750918381 |at=Appendix VIIIb}}</ref> at Mach 2 and 54%/17%<ref>{{cite report|url=http://www.enginehistory.org/Convention/2013/HowInletsWork8-19-13.pdf |title=How Supersonic Inlets Work: Details of the Geometry and Operation of the SR-71 Mixed Compression Inlet |access-date=16 May 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160509025601/http://www.enginehistory.org/Convention/2013/HowInletsWork8-19-13.pdf |archive-date=9 May 2016  |author=J. Thomas Anderson |at= Fig.26 |publisher=Lockheed Martin Skunk Works |date=August 19, 2013}}</ref> at Mach 3+. 
Intakes have ranged from "zero-length"<ref>{{cite journal | last=Sóbester | first=András | title=Tradeoffs in Jet Inlet Design: A Historical Perspective | journal=Journal of Aircraft | volume=44 | issue=3 | date=2007 | issn=0021-8669 | doi=10.2514/1.26830 | doi-access=free | pages=705–717 | url=https://eprints.soton.ac.uk/46202/1/AIAA-26830-529.pdf }}</ref> on the [[Pratt & Whitney TF33]] [[turbofan]] installation in the [[Lockheed C-141 Starlifter]], to the twin {{convert|65|ft}} long, intakes on the [[North American XB-70 Valkyrie]], each feeding three engines with an intake airflow of about {{convert|800|lb/s|kg/s}}.