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This question already has an answer here:

From the answer to the question 'How are forces on the landing gear reduced or compensated for at touchdown?' I note:

"For what it's worth you do not necessarily want to spin up the gear before landing for a few reasons. First off you would need to spin up the gear to precisely (or at least very close to) the speed that the plane was going to touch down at."

And:

"Spinning the gear up can also have a serious gyroscopic effect that will affect the handling of the aircraft."

So why is this not a takeoff problem?

You do not need to spin to landing speed to have a dramatic effect. If you start the spin, you have added angular momentum to the wheel. It is much easier to increase angular momentum in a spinning wheel than it is to instantaneously impart it to a stationary wheel. A few scupper cups on the rim of built into the tyre edge would do the job.

"This is a great research paper on the topic that suggests (in their conclusion) a pre spin situation would see 1.07% of the wear of a static situation."

Sounds like a worthwhile saving on so many aircraft.

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marked as duplicate by Dave, Pilothead, jwzumwalt, GdD, Peter Kämpf Jul 6 '18 at 7:43

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ "I note..." - where do you see the text you're referring to? "This is a great research paper..." - what is? Please take a moment to structure your text so that your questions are clear, and please add the references. $\endgroup$ – user31680 Jul 6 '18 at 2:30
  • $\begingroup$ I have edited the question to make it a bit more readable as the quotes are from my answer here. $\endgroup$ – Dave Jul 6 '18 at 2:36
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    $\begingroup$ It is not clear what you are asking. Is it just the single question about why gyro forces are not a problem on takeoff? The title refers to shock on landing. $\endgroup$ – Pilothead Jul 6 '18 at 2:48
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I don't believe there is problem with gyro precession in spinning wheels; it's more of a vibration issue. On most airliners the brakes are applied automatically after liftoff to stop the mains and the main reason is unpleasant vibrations as the wheels slow down without the damping effect of being pushed into the pavement. On less complex aircraft pilots are taught to tap the brakes after liftoff to stop the main wheels from shaking (to the extent that they do) as they wind down.

Airliner wheels get statically balanced after tire installation but they don't usually get balanced dynamically like car tires, and there is often minor vibration that is not noticeable while rolling but can be quite noticeable while spinning on a gear leg dangling in the open when the wheel's natural frequency comes into phase with the gear, scaring the crap out of the pax.

Nose wheels are typically stopped by a snubber in the nose gear well upon retraction so they spin down until then. Being so much smaller, they aren't as big a problem but if the static balance is not good you can get a pretty noticeable vibration under your feet that grows and then declines as the wheels slow down, then stops as soon as the gear is up. If it's bad enough crews will snag it.

Anyway, to have all that mass spinning all the time the gear is out? Even if there was a simple way to do it, without the usual weight/cost/complexity issues, airlines would probably be forced to dynamically balance their wheel assemblies and purchase hugely expensive equipement.

Cheaper to just let them wear down and recap them. Aircraft tires can be retreaded indefinitely as long as the carcass is sound.

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  • $\begingroup$ Wheel vibration is mainly due to flat spot wear. Flight paths aligned with the runway benefit from wheel gyro influence by improved lateral stability, but will not affect descent or ascent aspects of the flight path. Touching the brakes will assist flight paths including banking, Tyre wear is reduced if the blue smoke zone can be avoided. Having the wheels turning even slowly would make a significant difference. Wheel landing speed can be adjusted to suit. I imagine the overall effect should be less tyre wear, more landing alignment stability, less gear stress, and greater passenger comfort. $\endgroup$ – Robert Beatty Jul 6 '18 at 20:57

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