Gear Leg Vibration - Ti vs. Steel

Searched the threads but couldn't find anything...

Does anyone have any opinions, evidence, data, premonitions or otherwise to show whether steel or Titanium tapered rod gear are more prone to vibration or shimmy during ground handling or landing roll out?

Thanks!

It's only a function of stiffness and mass (taking out wheel balance and alignment issues). So your results will vary with those two factors.

I tried a Titanium tailwheel spring on my -8 (didn't have the right heat treatment and after a few hours use, it yielded/bent).

My *opinion* is that it would be a great deal of expense and added variability that may not be worth the cost and headache for essentially no improvement in flexibility/vibration.

My 2 cents...

The modulus of elasticity of titanium is 16 million psi, and for steel it's 29 million psi.

The main mass item for shimmy or vibration is at the bottom end of the leg, so the density of the leg is only a small contributor to the natural frequency of any vibration.

So for the approximate change in frequency of the vibration would be the square root of 16/29 or about .74. The new titanium gear leg would vibrate at about 74% the frequency of the original steel leg.

One of the easiest ways to reduce vibration is to increase the natural frequency of the member that's vibrating. This is usually easier than changing the forcing function, which in this case is the rotating wheel and tire and the effects of possibly scrubbing on the ground.

Another way is to add damping to the system. The wooden dampers do both and are modestly effective.

You certainly don't want to lower the natural frequency of the gear leg.

Bottom line - if you used titanium gear legs, assuming you could make them strong enough, they'd be more likely to vibrate.

Now the caveat - There's nothing preventing a person from developing a titanium gear leg that would work. It would have a larger diameter than the steel and would be a totally new design, and would require a new mount.

Dave

All of the Rockets use titanium gear legs and IMHO vibration is about the same. Wooden stiffeners are also commonly used on the Rockets.

The titanium saves a lot of weight, but it will lighten your wallet by a similar amount.

Good input!

Thanks for the feedback, that is what I was looking for!