Editing Thrust reversal (section)

==Types of systems==
Small aircraft typically do not have thrust reversal systems, except in specialized applications. On the other hand, large aircraft (those weighing more than 12,500&nbsp;lb) almost always have the ability to reverse thrust. [[Reciprocating engine]], [[turboprop]] and jet aircraft can all be designed to include thrust reversal systems.

===Propeller-driven aircraft===
[[File:US Navy 060403-N-0499M-151 A Sailor performs maintenance to an E-2C Hawkeye.jpg|thumb|Variable-pitch propellers of an [[Grumman E-2 Hawkeye|Grumman E-2C Hawkeye]]]]
Propeller-driven aircraft generate reverse thrust by changing the angle of their [[Variable-pitch propeller (aeronautics)|controllable-pitch propeller]]s so that the propellers direct their thrust forward. This reverse thrust feature became available with the development of controllable-pitch propellers, which change the angle of the propeller blades to make efficient use of engine power over a wide range of conditions. Reverse thrust is created when the propeller pitch angle is reduced from fine to negative. This is called the beta position.<ref>{{Cite web|url=https://www.aopa.org/news-and-media/all-news/2017/march/pilot/turbine-reverse-thrust|title=Reverse thrust: Stopping with style|date=3 January 2017|access-date=31 August 2020|archive-date=8 September 2024|archive-url=https://web.archive.org/web/20240908042114/https://www.aopa.org/news-and-media/all-news/2017/march/pilot/turbine-reverse-thrust|url-status=live}}</ref>

While piston-engine aircraft tend not to have reverse thrust, [[turboprop]] aircraft generally do.<ref>FAA: Airplane Flying Handbook (FAA-H-8083-3B) Chapter 14: Transition to Turbopropeller-Powered Airplanes</ref> Examples include the [[PAC P-750 XSTOL]],<ref>{{cite web|title=P-750 XSTOL Specifications|url=http://www.aerospace.co.nz/aircraft/p-750-xstol/specifications|publisher=Pacific Aerospace|access-date=9 September 2013|archive-date=1 February 2020|archive-url=https://web.archive.org/web/20200201013748/https://www.aerospace.co.nz/aircraft/p-750-xstol/specifications|url-status=live}}</ref> [[Cessna 208 Caravan]], and [[Pilatus PC-6 Porter]].

One special application of reverse thrust comes in its use on multi-engine [[seaplane]]s and [[flying boat]]s. These aircraft, when landing on water, have no conventional braking method and must rely on [[Zigzag|slaloming]] and/or reverse thrust, as well as the [[Drag (physics)|drag]] of the water in order to slow or stop. In addition, reverse thrust is often necessary for maneuvering on the water, where it is used to make tight turns or even propel the aircraft in reverse, maneuvers which may prove necessary for leaving a dock or beach.{{Citation needed|date=July 2013}}

===Jet aircraft===
[[File:JT15D Thrust Reverser Functional Test.ogv|thumb|thumbtime=3.5|right|alt=|A target-type thrust reverser being deployed on a Cessna Citation.]]
On aircraft using jet engines, thrust reversal is accomplished by causing the [[jet blast]] to flow forward. The engine does not run or rotate in reverse; instead, thrust reversing devices are used to block the blast and redirect it forward. High [[Bypass ratio|bypass ratio engines]] usually reverse thrust by changing the direction of only the fan airflow, since the majority of thrust is generated by this section, as opposed to the core. There are three jet engine thrust reversal systems in common use:<ref name=Purdue />

====External types====
{{main|Target-type thrust reversal}}

[[File:Klm f100 ph-kle arp.jpg|thumb|Target 'bucket' thrust reverser deployed on the [[Rolls-Royce RB.183 Tay|Rolls Royce Tay]] engines of a [[Fokker 100]]]]
The target thrust reverser uses a pair of [[hydraulic]]ally operated ''bucket'' or ''clamshell'' type doors to reverse the hot gas stream.<ref name="Airplane handbook2011"/> For forward thrust, these doors form the propelling nozzle of the engine. In the original implementation of this system on the [[Boeing 707]],<ref>[https://books.google.com/books?id=zSADAAAAMBAJ&pg=-PA24 "Boeing's Jet Stratoliner."] {{Webarchive|url=https://web.archive.org/web/20240908042237/https://books.google.com/books?id=zSADAAAAMBAJ&pg=-PA24#v=onepage&q&f=false |date=2024-09-08 }} ''Popular Science'', July 1954, p. 24.</ref> and still common today, two reverser buckets were hinged so when deployed they block the rearward flow of the exhaust and redirect it with a forward component. This type of reverser is visible at the rear of the engine during deployment.<ref name=Purdue />

====Internal types====
[[File:VC10 Aircraft at an Airfield in the Middle East MOD 45150451.jpg|thumb|Clamshell outlet grating open (outboard engine) on a [[Rolls-Royce Conway]] turbofan of a [[Royal Air Force]] [[Vickers VC10|Vickers VC-10]] [[Aerial refueling|tanker]]]]

Internal thrust reversers use deflector doors inside the engine shroud to redirect airflow through openings in the side of the nacelle.<ref name="Airplane handbook2011"/> In [[turbojet]] and mixed-flow bypass turbofan engines, one type uses [[pneumatic]]ally operated ''clamshell'' deflectors to redirect engine exhaust.<ref name=Purdue /><ref name="MacIsaacLangton2011 Propulsion" /> The reverser ducts may be fitted with cascade vanes to further redirect the airflow forward.<ref name="MacIsaacLangton2011 Propulsion" />
[[File:Airbus A330 (Aeroflot) Sheremetyevo (5369213039).jpg|thumb|Clamshell-type thrust reversers deployed on the [[Rolls-Royce Trent 700]] engine of an [[Airbus A330]]. The redirected thrust blows water from the wet surface, making the air flow observable.]]
[[File:PH-BVC KLM (3701878334).jpg|thumb|Cold-stream type thrust reverser being deployed on a Boeing 777-300]]
In contrast to the two types used on turbojet and low-bypass turbofan engines, many high-bypass turbofan engines use a ''cold-stream'' reverser. This design places the deflector doors in the [[bypass duct]] to redirect only the portion of the airflow from the engine's fan section that bypasses the [[combustion chamber]].<ref name="Soares2011 Gas turbines" /> Engines such as the A320 and A340 versions of the [[CFM International CFM56|CFM56]] direct the airflow forward with a ''pivoting-door'' reverser similar to the internal clamshell used in some turbojets.<ref>{{cite book |last = Linke-Diesinger |first = Andreas |title = Systems of Commercial Turbofan Engines: An Introduction to Systems Functions |publisher = Springer Berlin Heidelberg |year = 2008 |chapter = Chapter 8: Thrust Reverser Systems |doi = 10.1007/978-3-540-73619-6_8 |isbn = 978-3-540-73618-9}}</ref> ''Cascade'' reversers use a vane cascade that is uncovered by a sleeve around the perimeter of the engine [[nacelle]] that slides aft by means of an air motor. During normal operation, the reverse thrust vanes are blocked. On selection, the system folds the doors to block off the cold stream final [[nozzle]] and redirect this airflow to the cascade vanes.<ref name=Purdue /> 

In cold-stream reversers, the exhaust from the combustion chamber continues to generate forward thrust, making this design less effective.<ref name="Airplane handbook2011" /><ref name=Purdue /> It can also redirect core exhaust flow if equipped with a hot stream spoiler.<ref name="MacIsaacLangton2011 Propulsion" /> The cold stream cascade system is known for structural integrity, reliability and versatility, but can be heavy and difficult to integrate into nacelles housing large engines.<ref name="AsburyYetter2000 NASA" />