Editing Power take-off (section)

{{short description|Methods for transmitting power from a source to an application}}
[[File:Zapfwelle eines Traktors - power take-off of a tractor.jpg|thumb|A PTO at the rear end of a farm [[tractor]]]]
[[File:A Tractor's rear.jpg|thumb|A PTO (in the box at the bottom) in the center of the [[three-point hitch]] of a tractor]]
A '''power take-off''' or '''power takeoff''' ('''PTO''') is one of several methods for taking power from a power source, such as a running [[engine]], and [[power transmission#Mechanical power|transmitting]] it to an application such as an attached implement or separate machine.

Most commonly, it is a [[spline (mechanical)|splined]] [[drive shaft]] installed on a [[tractor]] or [[truck]] allowing implements with mating fittings to be powered directly by the engine.

Semi-permanently mounted power take-offs can also be found on industrial and marine engines. These applications typically use a drive shaft and [[bolted joint]] to transmit power to a secondary implement or accessory. In the case of a marine application, such as shafts may be used to power fire pumps.

In [[aircraft]] applications, such an [[accessory drive]] may be used in conjunction with a [[constant speed drive]]. Jet aircraft have four types of PTO units: internal gearbox, external gearbox, radial drive shaft, and bleed air, which are used to power engine accessories. In some cases, aircraft power take-off systems also provide for putting power ''into'' the engine during engine start.<ref name="X29PTO">NASA Technical Memorandum 101731; Monitoring Techniques for "X-29A Aircraft's High Speed Rotating Power Takeoff Shaft"; David F Voracek, Ames Research Center, Dryden Flight Research Facility, Edwards, California, December 1990 [http://www.nasa.gov/centers/dryden/pdf/88209main_H-1680.pdf nasa.gov]</ref> See also [[Coffman starter]].