# How do plane landing-gear tyres roll before take off? [duplicate]

How do plane tyres roll? Are they equipped with special engines like cars or are they rolling using the plane flying engines? Or can both methods be found with different constructors?

Normally, aircraft wheels are rotating freely around their axle, unless the brakes are activated. The ground roll was a convenient time for engine warm-up in the days of piston aircraft.

However, rolling on the ground using jet engines is very inefficient; fuel consumption could be reduced if the aircraft uses other means of propulsion on the ground and only starts the engines right before take-off. Therefore, electric propulsion using hub motors is actively studied. The batteries could be charged (partially) during landing, when the hub motors are switched to generator mode, and the rest of the power could be provided by the APU.

Pushing back from the gate using jet engines is unwise, so a tug is used to move the aircraft to a position from which it can continue the ground roll to its take-off position. These tugs push a bar which is linked to the nose wheel of the aircraft. Towbarless (TBL) tugs scoop up the nosewheel and lift it off the ground, allowing more-secure control and faster maneuvering.

Conventional tug Goldhofer F110E (picture source)

Boeing 777 being pulled by Goldhofer TBL aircraft tug (picture source). They are really hard to see when you are sitting in the cabin.

Towbarless tug detail (picture source)

• It is actually possible for jet aircraft to push themselves back from the gate using thrust reverse, but it is just a stupid idea to do. – SMS von der Tann Mar 26 '16 at 13:20
• @SMSvonderTann a stupid idea to do - it's standard practise at many regional airports. – Simon Mar 26 '16 at 13:33
• @Simon Ah, you might want to edit this question then because it says: "Pushing back with jet engines is impossible" right above the images. – SMS von der Tann Mar 26 '16 at 13:41
• It's called a power back and it can be done. Here is a DC9 doing it and even some prop GA aircraft like the Aviat Husky can reverse by putting the prop in beta – Ron Beyer Mar 26 '16 at 14:43
• @PeterKämpf Yes, although I'm not sure why you mention it, the Husky is a light GA aircraft with a generic piston engine if that is what you are referring to. The DC9 is certainly equipped with Jet engines... – Ron Beyer Mar 26 '16 at 18:36

During take-off roll, the aircraft tyres move due to the thrust generated by the engines (or propellers for that matter). They don't have any engines (motors) fitted inside them to help in movement. In case the engine is not producing thrust, the aircraft are towed using a tug.

• I sure I saw Bombardier Dash 8 walking its way to the runway (I was in) with the propellers OFF and without any tug – mikmik Mar 26 '16 at 10:44
• @MakhloufGharbi The Dash 8 cannot move without a tug, or it's engines. – Simon Mar 26 '16 at 10:49
• I was in, so perhaps I didint seen the tug :) . I'm not sure – mikmik Mar 26 '16 at 10:52
• Some aircraft actually do have motors inside the wheels, but this technology is still in a testing/demonstration phase. EGTS and WheelTug are the two competing products under development. – Cody P Aug 26 '16 at 22:33