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What are the advantages / disadvantages of a live and fixed nose landing gear axle and how do they work? Maybe certain aircraft need a particular type fitted? I can't see the need of a moving axle (assuming that's what 'live' means) unless it is somehow powered by a motor or something similar for push back..

Or.. Maybe on an aircraft a live axle is one where it rotates with the wheel and a fixed one is where the wheel rotates around the axle?

The reason I ask is that I saw in a textbook that nose wheels are either on a fixed or live axle and nose wheel shimmy is prevented by using a twin nose wheel set up attached to a live axle.

I'm now not sure if the terms live and fixed axle are in relation to the vertical component or horizontal component of the nose gear.

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    $\begingroup$ A live axle transmits power to the wheels. I know of no aircraft with such a powered nose landing gear. Can you give us some context around why you are asking so we might better understand the root of your confusion? $\endgroup$
    – Michael Hall
    Commented Jan 19, 2020 at 17:40
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    $\begingroup$ @ Michael Hall: I think - extrapolating from automotive use, since I've never heard the term used in aviation - a live axle would be one with two or more wheels that move independently. As you say, powered axles don't make sense for aircraft. $\endgroup$
    – jamesqf
    Commented Jan 19, 2020 at 18:30
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    $\begingroup$ A live axle is simply one that moves in some fashion. On a nose gear, I would assume it to mean the axle is fixed to the wheels and rotates with them, and the bearing interface is between the NG strut and axle. I've never seen such a thing on an airplane myself. Maybe the Soviets did it? $\endgroup$
    – John K
    Commented Jan 19, 2020 at 18:51
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    $\begingroup$ Hi John, on most aircraft are nose wheels usually fitted to a fixed axle and the bearing being the interface between wheel and axle? $\endgroup$
    – Jono
    Commented Jan 19, 2020 at 19:46

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A live axle is when the two wheels rotate together. Its function is to reduce shimmying.

The Lockheed JetStar and the Space Shuttle Orbiter have live NLG axles.

References:

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Source: Aircraft Landing Gear Design: Principles and Practices

The nose wheel is a split, forged aluminum alloy design but its bearings are located on a rotating or "live" axle rather than in the hub such as in the main wheel design. Both nose wheels are splined to the "live" nose axle providing a corotating feature which improves stability or reduces the tendency to shimmy.

Source: Orbiter wheel and tire certification, NASA

Tire friction can also be used to increase the damping in the castor mode. If the gear has two wheels, connecting them by a live axle can have this effect. In the case of a single wheel, it is possible to obtain ‘anti-shimmy’ tires incorporating two contact areas.

Source: Landing Gear (Aircraft), sciencedirect.com

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    $\begingroup$ Must've took some sleuthing to find that. Nice job. $\endgroup$
    – John K
    Commented Jan 19, 2020 at 22:50
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A fix Nose Landing Gear is a landing gear where the vertical axe between the aircraft and the wheel cannot rotate. The wheel can rotate of course on an horizontal axe (it is how it moves on the ground), but it can not rotate on a vertical axis. This mean that if you try to change your direction on the ground, the wheel will remain in the axis of your current direction, and it will drift when you turn.

A live NLG means that the wheel could rotate on a vertical axis, compared to the direction currently held by the fuselage of the plane. Thus, it is easier to turn when rolling on the ground, but when the airplane takes off or lands, it needs an anti-shimmy device (usually, as you said, a twin nose wheel) to perturbations on the landstrip to make the plane turn hard.

An example of such a thing is when you have a supermarket caddie, and the forward wheels are blocked. It is difficult to turn, but you still can if you put enough torque to the center of gravity of the caddie. On an airplane, having motors on the wings gives easily enought torque on the middle axis of the plane.

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  • $\begingroup$ Thanks for the input.. Just so I understand you correctly when you talk about fixed and live NLG on the vertical axis this is in relation to the nose landing gear leg /oleo strut and not the horizontal axle? Are you saying a fixed leg (vertical axis) can't turn on the ground? I find that hard to believe, it must have some steering?.. I understand how NLG steering works if this is what you call a 'live' system. My original question was in relation to the horizontal axle being fixed or live.. say for example on a twin wheel NLG.. Some clarification would be much appreciated. $\endgroup$
    – Jono
    Commented Jan 19, 2020 at 21:43
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    $\begingroup$ Not only are these definitions incorrect, but I can't think of any airplanes with nosewheels where the gear can't turn left & right. Some are steerable and some are free-castering, but they can all turn. A nosewheel that can't turn would be nearly impossible to taxi with and would probably blow the tire when landing in any kind of crosswind. $\endgroup$
    – pericynthion
    Commented Jan 20, 2020 at 3:03

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