View source for Assisted take-off

{{short description|System used to help aircraft get into the air}}
{{more citations needed|date=December 2007}}
{{other uses of|ATO}}
[[File:Glider in flight.JPG|thumb|right|Tow line and towing aircraft seen from the cockpit of a [[Glider (sailplane)|glider]]]]

In [[aviation]], '''assisted takeoff''' is any external system for helping [[aircraft]] (more specifically [[fixed-wing aircraft]]) to become airborne ([[takeoff|take off]]) for [[flight]], as opposed to doing so [[CTOL|conventional]]ly using strictly their own [[propulsion]]. The reasons assistance might be needed include: the combined [[weight]] of the aircraft and its [[payload]]s exceeding the [[maximum takeoff weight]];i insufficient [[aircraft engine|engine]] power by design or malfunction, insufficient available [[runway]] length (such as on the [[flight deck]] of an [[aviation-capable naval vessel|aviation warship]]), or a combination of the above. Assisted takeoff is also required for [[glider (sailplane)|glider]]s, which do not have any engine and thus are unable to propel themselves for takeoffs.

== Catapult-assisted ==
[[File:F18-on catapult.jpg|thumb|left|F/A-18 attached to steam catapult preparatory to launch]]
{{main|CATOBAR}}
The most well-known type of assisted takeoff is via an [[aircraft catapult]], which is used on modern [[aircraft carrier]]s to launch fixed-wing [[carrier-based aircraft]] from the short [[runway]] distances available on the [[flight deck]]. The catapult is built into the flight deck as a slot track, with a [[sliding (motion)|sliding]] piece known as a ''shuttle'', which protrudes above the deck. The aircraft is attached to the shuttle using a tow bar or launch bar mounted to the nose landing gear (an older system used a steel cable called a catapult bridle; the forward ramps on older carrier bows were used to catch these cables), and is flung off the deck at about 15 knots above minimum flying speed, achieved by the catapult in a four-second run.

The current mainstay catapult system is [[steam catapult]], first invented by the [[United Kingdom|British]] in the 1950s. It is essentially a [[single- and double-acting cylinders#Single-acting|single-action]] [[steam engine]], in which the shuttle is attached to a [[piston]] and [[propulsion|propelled]] down the track under the high pressure of the [[superheated steam]] within the [[cylinder (engine)|cylinder]] under the catapult track. The [[steam]] can be generated by [[superheater]] [[boiler (power generation)|boiler]]s or, in the case of [[nuclear marine propulsion|nuclear-powered]] [[supercarrier]]s, by heating from [[nuclear reactor]]s. The [[United States Navy]] and [[French Navy]] are the only current users of steam catapults, with the latter using the same C-13-3 catapult imported from the [[United States]].

Into the [[21st century]], the United States have planned to replace steam catapults with an [[electromagnetic catapult]] system based on the working principles of [[linear induction motor]], which instead of [[pneumatics]] uses [[Laplace force]] generated by the track [[armature (electrical)|armature]]s to propel the catapult shuttle, allowing shorter launch intervals, more variable, precise control over the launch power, less [[impulse (physics)|impulsive]] wear on the aircraft's airframe, and reduced maintenance against [[rusting]] and [[leak]]ages. The new EM catapult system, called the [[Electromagnetic Aircraft Launch System]] (EMALS), was developed by [[General Atomics]] based on an [[AC motor]]-[[flywheel]] construct and is currently installed on the [[lead ship]] of the [[Gerald R. Ford-class aircraft carrier|''Ford''-class aircraft carrier]]s, the {{ship|USS|Gerald R. Ford|CVN-78}}. A separate EM system based on a [[DC motor]]-[[supercapacitor]] construct has also been developed in [[China]] jointly by the [[China Shipbuilding Industry Corporation]] and the [[Chinese Academy of Engineering]], and is currently installed on the newly commissioned [[People's Liberation Army Navy]] aircraft carrier {{ship|Chinese aircraft carrier|Fujian|18|3}}, as well as the currently [[fitting-out]] [[Type 076 amphibious assault ship]] {{ship|Chinese amphibious assault ship|Sichuan|51|3}} and the upcoming [[Type 004 aircraft carrier]]s.

==Jet/rocket-assisted ==
{{details|JATO}}
In jet-assisted takeoff (JATO) and the similar rocket-assisted takeoff (RATO) systems, additional engines are mounted on the [[airframe]] which are used only during takeoff. After that these attached engines are usually jettisoned, or else they just become parasitic deadweight that add [[drag (physics)|drag]] to the aircraft. However, some aircraft such as the [[Avro Shackleton]] MR.3 Phase 2, had permanently attached JATO engines.  The four J-47 turbojet engines on the B-36 were not considered JATO systems; they were an integral part of the aircraft's propulsion, and were used during takeoff, climb, and cruise at altitude. The [[Lockheed C-130 Hercules|Hercules LC-130]] can be equipped with a JATO rocket system to shorten takeoff as used in the LC-130 Skibird for polar missions.<ref>{{Cite news|url=https://dod.defense.gov/News/Article/Article/1264863/lc-130-skibird-aircrews-train-for-polar-operations/|archive-url=https://web.archive.org/web/20181005194800/https://dod.defense.gov/News/Article/Article/1264863/lc-130-skibird-aircrews-train-for-polar-operations/|url-status=dead|archive-date=October 5, 2018|title=LC-130 Skibird Aircrews Train for Polar Operations|work=U.S. DEPARTMENT OF DEFENSE|access-date=2018-10-05|language=en-US}}</ref>

During WW2 the German [[Arado Ar 234]] and the [[Messerschmitt Me 323]] "Gigant" used rocket units beneath the wings for assisted takeoff.  Such systems were popular during the 1950s, when heavy bombers started to require two or more miles of runway to take off fully laden. This was exacerbated by the relatively low power available from [[jet engine]]s at the time—for example the [[Boeing B-52 Stratofortress]] required eight [[turbojet]] engines to yield the required performance, and still needed RATO for very heavy payloads (a proposed update of the B-52 replaces these with half the number of much more powerful engines).  In a [[Cold War]] context, RATO and JATO bottles were seen as a way for fighter aircraft to use the undamaged sections of runways of airfields which had been attacked.

==Gliders==

Glider aircraft which do not have an engine also require an assisted takeoff. Apart from self launching gliders, [[EASA]] recognizes four other launch methods: [[winch-launch|winch launches]], [[aerotow]]s, [[bungee launch]]es and [[car-tow|car tows]].<ref>{{cite book |last1=Part FCL Handbook |first1=EASA |title=EASA |publisher=European Aviation Safety Agency |edition=1 |url=https://www.easa.europa.eu/sites/default/files/dfu/Part-FCL.pdf}}</ref>

==Gravity assistance==
Early pioneers in powered and unpowered flight used gravity to accelerate their aircraft to a speed which allowed its wings to generate enough lift to achieve independent flight. These included attempts to achieve flight from towers, city walls and cliffs. Generally more successful were attempts in which speed was built up by accelerating down hills and mountain slopes, sometimes on rails or ramps.

==Mother ship (carrier) aircraft==
[[File:X-15 launched bw.jpg|thumb|right|An [[North American X-15|X-15]] pictured just after release from a [[B-52 Stratofortress|B-52]] carrier aircraft]]
{{see also|Parasite aircraft}}

Another form of gravity assistance is when an aircraft is released from a larger [[mother ship]] or mother craft. This may be because the daughter craft is incapable of taking off normally e.g. the atmospheric flight tests of the [[Space Shuttle Enterprise#Approach and landing tests|Space Shuttle]].

Usually the rationale for such a system is to free the daughter craft from the need to climb to its release height under its own power. This allows the daughter craft to be designed with fewer weight and aerodynamic restrictions allowing for exotic configurations to be used or tested, for example the recent [[Scaled Composites SpaceShipOne|SpaceShipOne]], and previously the [[Bell X-1]] and other [[X-plane (aircraft)|X-planes]].

In the interwar years, in order to achieve long ranges with the technology of the time, trials were undertaken with floatplanes piggy-backed atop flying boats. With the floatplane carried part of the way to its destination and freed from having to use any of its own fuel in the initial climb, these combinations could deliver light but time-critical cargos faster and farther than a single individual aircraft (for example the [[Short Mayo Composite]]).

Hot air balloons have acted as "motherships" to [[Hang gliding|hang gliders]] and [[Paragliding|para gliders]] in altitude and distance record attempts.

==See also==
* [[Colditz Cock|Colditz Cock glider]], for an example of gravity assistance.
* [[History of aviation]], for the work of the early pioneers.
* [[Silbervogel]], a long-range bomber proposal, using a rail-mounted captive rocket booster.

==References==
{{Reflist}}

{{Types of take-off and landing}}

[[Category:Types of take-off and landing]]