Taxiing (rarely spelledtaxying)[1] is the movement of anaircraft on the ground, under its own power, in contrast totowing orpushback where the aircraft is moved by a tug. The aircraft usually moves on wheels, but the term also includes aircraft with skis orfloats (for water-based travel).
An airplane usestaxiways to taxi from one place on anairport to another; for example, when moving from ahangar to therunway. The term "taxiing" is not used for the accelerating run along a runway prior totakeoff, or the decelerating run immediately afterlanding, which are called the takeoff roll and landing rollout, respectively; however, aircraft are considered to be taxiing when they leave the runway after landing to travel to agate or remote stand for disembarkment.
As early as 1909 aviation journalists envisioned aeroplanes to replace thetaxicab in traffic-congested cities.[2]
Some aviators and some linguists report that around the year 1911 theslang word "taxi" was in use for an "airplane". They suggest that the way aircraft move under power before they take off or after they land reminded someone of the waytaxicabs slowly drove around the block when looking for passengers.[3][4]
Also by 1909, French aviation pioneers likeBlériot,Farman andVoisin used the term "taxi" for atrainer aircraft, that was so constructed that a pupil would not accidentally get airborne.[citation needed]
Usage of the word for an airplane quickly disappeared again, but the verb "to taxi" stuck, and words like the "taxiway" were derived from it.
The thrust to propel the aircraft forward comes from itspropellers orjet engines. Reverse thrust for backing up can be generated bythrust reversers such as on theBoeing C-17 Globemaster III, or reversible pitch propellers such as on theLockheed C-130 Hercules, a rare procedure known aspowerback. Most aircraft, however, are not designed to back up on their own and must be pushed back either by hand or by using anaircraft tug.
At low power settings, combustion aircraft engines operate at lower efficiency than at cruise power settings. A typicalA320 spends an average of 3.5 hours a day taxiing, using 600 liters (160 U.S. gal) of fuel. Hybrid electrically driven nose gear are under development to allow high use aircraft to shut down the engines during taxi operations.[5]
Steering is achieved by turning anose wheel or tail wheel/rudder; thepilot controls the direction travelled with their feet. Larger jet aircraft have a tiller wheel on the left side of the cockpit that acts as a steering wheel allowing the nosewheel to be turned hydraulically. Braking is controlled by differential toe or heel brakes. Not all aircraft have steerable wheels, and in some cases steering is solely by means of differential braking (allVan's aircraft for instance) or solely by means of the rudder (including allfloatplanes).
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Skid-equippedhelicopters and otherVTOL (Vertical Take-Off and Landing) aircraft conduct hover taxiing to move inground effect in the same manner that wheel-equipped aircraft ground taxi. In general hover taxis are conducted at speeds up to 20 kn (37 km/h; 23 mph), or belowtranslational lift.[6]
TheBell CH-135 Twin Huey is hover taxied in a manner typical for skid-equipped aircraft of that size:
This sequence is initiated from a stabilized 5 ft hover. Move the aircraft forward over the ground at a brisk walking pace. Maintain a constant height above ground, constant forward speed and ensure that the skids remain parallel to the direction of movement. Anticipate stopping so that large rearward cyclic applications are not required as this may result in the tail skids striking the ground. You are often required to taxi out of wind; be aware that when taxiing downwind in strong wind conditions there may be insufficient rearward cyclic to ensure adequate control and that the tail will be nearer the ground. Taxiing downwind is limited to 30kts.[7]
When taxiing, aircraft travel slowly. This ensures that they can be stopped quickly and do not risk wheel damage on larger aircraft if they accidentally turn off the paved surface. Taxi speeds are typically 16 to 19 kn (30 to 35 km/h; 18 to 22 mph).[8]
Rotor downwash limits helicopter hover-taxiing near parked light aircraft. The use of engine thrust near terminals is restricted due to the possibility of structural damage or injury to personnel caused byjet blast.[9]
The new, electric nose wheel can power the A320 both forward and backward without requiring power from the aircraft's main engine. In addition to the energy savings, the electric nose wheel completely eliminates engine noise during taxi maneuvers.
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