Hi, I just did the install of a tailski on my 185. It is an home made tailski.
I did 4 landings and 2 of them had really bad shimmy associated with the tailwheel. Never had that before.
Pretty straight forward installation, the only new thing is the axle that needed to be longer and bearings were regreased.
When I did my last landing everything was fine and i gave a little bit of rudder to go on a high speed taxi way and it started the shimmy. It lasted almost until the airplane was full stop.
Any thoughts?

Cheers!

Raise the tail! Don't land pavement with long taxis!

I had the same when using my tail ski, sometimes it would do it, other times it wouldn't, take the ski off and the issue goes away. The ski must change things back there, not too big of a surprise I suppose, mine was bad enough that I would never put up with it in the warmer months, but I just avoided the issue by taxiing tail up, (Rans S-7S) landing in deep powder is pretty effective also!

This year, due to a new T-3 tail spring, I totally redesigned the way I mount my Datum ski, using a tailwheel dedicated to winter ops, come spring it will all come off as a unit, and my bigger and tougher tail wheel go on. I have not had to taxi on pavement yet so don't know if it will be the same. Ignore that red thing, that's my tail release. It's mass probably won't help, or, who knows it may dampen any shimmy. Note that now it's more like the mains, limit cables and a bungee. It should make life easier on the attach bracket as now it can conform to whatever comes along.

You may find that you trash your mounting bracket, as you have no give in that ski. My first home made attachment for my ski was similar, no give. As a result, my mount hardware got beat up, things got bent. Here's a pic of my current setup.

From a fundamental perspective, adding weight and vertical surface area ahead of the pivot will make the tailwheel more unstable and likely to shimmy. Not sure if there is a great solution, just offering a possible reason why

asa wrote:From a fundamental perspective, adding weight and vertical surface area ahead of the pivot will make the tailwheel more unstable and likely to shimmy. Not sure if there is a great solution, just offering a possible reason why

Along these lines, I think you are better off having the ski shorter going forward and longer behind. The mass looks mostly forward on your setup which, like Asa says, will make the shimmy worse.

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A1Skinner wrote:

asa wrote:From a fundamental perspective, adding weight and vertical surface area ahead of the pivot will make the tailwheel more unstable and likely to shimmy. Not sure if there is a great solution, just offering a possible reason why

Along these lines, I think you are better off having the ski shorter going forward and longer behind. The mass looks mostly forward on your setup which, like Asa says, will make the shimmy worse.

I agree with ASA and A1. Add length or weight to the rear of the ski.

With the tail ski on my 185, I must use the tailwheel lock to keep the plane from vibrating apart. That is the primary benefit of the lock mechanism in my opinion. I don’t normally use it when the tail ski is off, but occasionally when there is a crosswind and I know I will be putting the tail down with the tailwheel canted off in one direction because of my rudder deflection, I will use the tailwheel lock to prevent a shimmy situation.

Thanks guys, I really appreciate your feedback. My ski should have been done differently with more weight on the back. I also believe the locking mechanism would be a great thing. I wish I had one. I will see if I can find one.
Thanks again for your comments!

I never met a tail ski on a 185 that wouldn't shimmy often. Maybe not always, but certainly frequently. As noted above, ALWAYS wheel land with a tail ski installed.....keep the tail off as long as possible. I've probably flown five or six different 185s with tail skis, and they all would shimmy.

If it shimmies, STOP as soon as possible, without putting the plane up on its nose, of course.

I don't like the attachment on your ski to the tailwheel yoke. I think that tailwheel should be able to float some, nose up. Not sure if that'll cause undue wear on the yoke. Yokes are spendy, BTW.

MTV

Mike, can you run Burl’s tail ski on a 185 and if so what are your thoughts?

Kurt

G44 wrote:Mike, can you run Burl’s tail ski on a 185 and if so what are your thoughts?

Kurt

Yes, Burl’s ski is approved on the 185. It is a much better design than any other tail ski I’ve flown, in a couple regards, but they will still shimmy.

I’m not sure changing the relationship of ski forward or aft will eliminate the shimmy. It MAY reduce it. Frankly, I think the weight and differences in weight on those tailwheels, due to load differences, change the angle of the wheel, and may just make them more susceptible to shimmy, at least more so than lighter planes. Adding mass to that wheel may be just the straw that flattens the camel.

Every Cessna taildragger I’ve ever flown has, at some time or other, exhibited tailwheel shimmy. The cause is usually easy to fix.....except on wheel skis.

As Squash noted, the best solution is a tailwheel lock. Unfortunately, our maintenance folks didn’t like fiddling with them, so removed from all our Cessnas. I’ve only flown a couple 185s with locks, and none on skis.

MTV

I have the Burl’s tail ski. (C-180). It is a great ski; but it too will shimmy.

Reiterating in part what others have suggested; we’ve got it to where it hardly ever shimmies.

-check the tailwheel geometry, see the picture below. The tail spring could be sagging, for example.
-do some maintenance inside the tailwheel, (or get a nice new one from Alaskan Bushwheels)

As to operation:

I wheel land, then hold the tailwheel off as long as possible. Be careful; but with some manipulation of elevator, power, and brakes, the tail can be set down at a very low speed.

Also, and this may seem obvious; make sure the airplane is going perfectly straight at the moment you set the tail down. The slightest degree of variation seemed to start the shimmy on mine.

Agree with MTV, never met a tail ski that did not want to shimmy on occasion.... or on any occasion. Helps to wheel land and let the the tail sink slow when tail plane wants to stop flying. Never figured out how to consistently avoid it. If it starts to shimmy you have to pretty much stop and then start again or it will shake the whole time you are taxiing regardless of the taxi speed.

I can only reiterate what everyone else has said. Even with my Stinson at probably 100 lbs at 3-point on the tailwheel will shimmy. I wish I could add a tailwheel lock. I personally love them.

Something about all that mass out around the castering wheel physics doesn't like. Then shakes like mad until you just stop.