Editing Plug nozzle (section)

==In rockets==
Plug nozzles belong to a class of [[altitude compensating nozzle]]s, much like the [[Aerospike engine|aerospike]], which, unlike traditional designs, maintains its efficiency at a wide range of altitudes.<ref name="Nozzle Design">{{cite journal
 |url         = http://www.pwrengineering.com/articles/nozzledesign.htm
 |title       = Nozzle Design
 |publisher   = Pratt & Whitney Rocketdyne
 |journal        = Threshold
 |date        = Spring 1992
 |author      = O'Leary, R.A.
 |author2     = Beck, J. E.
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20100402105625/http://www.pwrengineering.com/articles/nozzledesign.htm
 |archive-date = 2010-04-02
}}</ref>

Similar to the garden hose example, plug nozzles use a shaped [[rocket nozzle]] with a poppet-shaped plug to allow the pattern of the rocket exhaust to be changed. This is used to adjust for changes in altitude; at lower altitudes the plug is pulled back to cause the exhaust to spread out, while at higher altitudes the lower air pressure will cause this to happen naturally. An alternative construction for the same basic concept is to use two nozzles, one inside the other, and adjust the distance between them. This pattern has the advantage of better control over the exhaust and simpler cooling arrangements.

Confusingly, the term "plug nozzle" may also be used to refer to an entirely different class of engine nozzles, the aerospikes. In theory the aerospike should look roughly like a [[lance]], with a wide base and long tapering forebody. However, the "spike" portion can be cut off with only minor effects on performance, leaving just the base section. This looks very similar to a common [[Plug (sanitation)|drain plug]] or [[bung]], and leads to widespread use of the term "plug nozzle" for this design as well.