I had a shop install an Alaskan Bushwheel fork on my Scott 3200 .
Went over to pick it up and started to taxi away and noticed I couldn’t turn left without breaking. Tailwheel tension was way too tight
I believe
Had the shop loosen it a bit and it taxis fine
However I am getting a shimmy on every three point landing
I do know to push forward on the yoke to unload it and it does calm down
But sometimes it starts at a speed to
Low to
Lift the tail and continues to a complete stop
The shop used the AB rebuild kit also

The tail wheel spring was recently re-arched so that’s not the issue
All tail wheel spring mounting points are tight
This started with the Bushwheel fork

I’m running a 404 tire on pavement
I have it at 50 psi

Last night I loosed the tension more and it feels better on the sawhorse. I know this is supposed to be checked on the ground but can anyone explain in more detail about how a correctly tensioned tail wheel should behave ?

Specifically what happens when it’s too tight ?

And too loose ?

Thanks. And sorry for the long post

Look at the caster angle of the head. They may not have re-arched the spring enough. Pacers tend to be tail heavy so you have to look at it when you have a full load of fuel/passengers. The fact that it go's away when you lift the tail is the giveaway. I prefer my chains to have no slack and no spring tension. That is kind of hard to do because if you remove a link ti tends to get too tight/loose. However if you can make small adjustments just by squeezing a link or two flat.
DENNY

Thanks Denny. Head to spring angle is good and springs are tight. About to go for a test taxi then test flight
Hope it isn’t too loose

DENNY wrote:Look at the caster angle of the head. They may not have re-arched the spring enough. Pacers tend to be tail heavy so you have to look at it when you have a full load of fuel/passengers. The fact that it go's away when you lift the tail is the giveaway. I prefer my chains to have no slack and no spring tension. That is kind of hard to do because if you remove a link ti tends to get too tight/loose. However if you can make small adjustments just by squeezing a link or two flat.
DENNY

What he said. Gilbert Pierce wrote an article on it a few years back, looks like Z posted it up in 2006!


https://backcountrypilot.org/forum/inte ... shimmy-687

Here is an excellent video by Steve Pierce on Baby Bushwheel assembly and understanding how the parts work and should be adjusted.

https://www.youtube.com/watch?v=8MGri0D50hg

Every airframe has it's issues with tailsprings... never had any luck rebending springs... on our Maule,we plan on replacement every 2 years, or when the shimmy lets you know the geometry requires it...

Another BCP article that is helpful in explanation of tailwheel shimmy:

https://backcountrypilot.org/forum/interesting-article-on-tailwheel-shimmy-687

Edit...Ah, I see I'm repeating the info...I'm a slow typist...

The $10,000 Stearman I borrowed to finish a spray season no longer had the tw springs; just bailing wire. It worked amazingly well, but I got the tail up quickly and wheel landed very slowly.

The dirty little secret is that the Baby Bushwheel WILL shimmy on pavement. Not ALL the time, but they seem to do so pretty regularly. One of the reasons I don't care for them. They can be set up "better", but be prepared to screw with them regularly.

So, don't three point. Keep that tail up as long as you can, then set it down gently, and with no drift.

MTV

Thank you guys for all of your input
Things are looking better. I flew this morning after loosing the tension , and the results were worse
I returned to the hanger and tightened to where it was when I picked it up from the shop and I also added more air
I was at 45 but wanted to go up to 70
Unfortunately at 70 psi my 404 tire is now out of round and hits the top of the fork
Backed off to 60 psi and took it up
It’s working pretty good now.
As pointed out I think that’s the best it’s gonna be on pavement but it’s pretty good
I would say I’m 95 percent happy ?
I am learning g a lot lately on how all this works
And yes I read the article Gilbert wrote up and used his template to re- arch my spring
Steve Pierce has some excellent videos to rebuild but I needs a 337 for the fork so I had to hire it out
Unfortunately there really is no good guide on just how tight that Head should be but I believe I’m there

I had the baby bushwheel for 6 months. Wish I could get the maintenance hours I paid to address the shimmy that never got better. Finally went back to my old tail wheel. Shimmy problem went away. Sold the baby bushwheel. Since then every mechanic I talk to says thats been their experience too. You could keep it if you never want to 3 point on pavement again. It makes you perfect your wheel landing!

Brad

I never quite found the sweet spot on my 180 because I think the stinger was flat from 60 years of abuse. I have been able to find the sweet spot of tension/tightness for my scout. Regardless, all of my mentors in tailwheel have agreed:

"tailwheels are for taxiing"

While I agree with the sentiment "tailwheels are for taxiing" and I aspire for a perfect tail low wheel landing while rolling up onto the mains and applying either perfect braking for my short field or just the right amount of throttle to taxi on the mains and pull a cool 360 at my parking spot with my tail in the air, my Cessna 185 POH clearly gives instructions on how to 3 point. So they designed it to 3 point, and while its not cool to admit it, I occasionally 3 point my 185, and its nice to not feel like the rear of the plane is going to shake off. I have about 1200 hours in my 185, someday I'll be good enough to only use my tail wheel for taxiing. While we are at it, I am also going to exercise more and eat less cheezy poofs.

Is the 3200 the same as the 3400?
I added a couple more coil springs to my 3400 and that took care of 95% of shimmy problems.
I think there is room for 5 or 6 springs? There were 3 installed, I added 2 or 3.

Durango Skywagon wrote:While I agree with the sentiment "tailwheels are for taxiing" and I aspire for a perfect tail low wheel landing while rolling up onto the mains and applying either perfect braking for my short field or just the right amount of throttle to taxi on the mains and pull a cool 360 at my parking spot with my tail in the air, my Cessna 185 POH clearly gives instructions on how to 3 point. So they designed it to 3 point, and while its not cool to admit it, I occasionally 3 point my 185, and its nice to not feel like the rear of the plane is going to shake off. I have about 1200 hours in my 185, someday I'll be good enough to only use my tail wheel for taxiing. While we are at it, I am also going to exercise more and eat less cheezy poofs.

I didn't mean that to be critical to your previous comment, it's always just been a joke.

asa wrote:

Durango Skywagon wrote:While I agree with the sentiment "tailwheels are for taxiing" and I aspire for a perfect tail low wheel landing while rolling up onto the mains and applying either perfect braking for my short field or just the right amount of throttle to taxi on the mains and pull a cool 360 at my parking spot with my tail in the air, my Cessna 185 POH clearly gives instructions on how to 3 point. So they designed it to 3 point, and while its not cool to admit it, I occasionally 3 point my 185, and its nice to not feel like the rear of the plane is going to shake off. I have about 1200 hours in my 185, someday I'll be good enough to only use my tail wheel for taxiing. While we are at it, I am also going to exercise more and eat less cheezy poofs.

I didn't mean that to be critical to your previous comment, it's always just been a joke.

No offense taken! But it felt good to defend the often maligned 3 pointer, & apparently I had a bit of a rant built up. Rant Over. Carry on with: how to adjust shimmy out of the Alaskan Bushwheel.

Are those kinds of pressures (60 or 70psi) normal for a BBW?

We run our Bearhawk Tundra Tailwheel at 25psi, even heavily loaded. Works great. Anything above 35 psi seems to be too stiff to cushion much, which is the main benefit IMHO.

Battson wrote:Are those kinds of pressures (60 or 70psi) normal for a BBW?

We run our Bearhawk Tundra Tailwheel at 25psi, even heavily loaded. Works great. Anything above 35 psi seems to be too stiff to cushion much, which is the main benefit IMHO.

The BBW is 25 psi. But hes running the glider tire. They need more pressure.

I tighten the fork to head nut by hand, until it wont move and I back off the nut a flat or two, just so the fork/head will turn by hand. Once its on the plane, pump grease into the zerk as you turn the fork back and forth until it starts to come out (either the dust shield or the bottom). This will further tighten things up.

Folks seem to know about the caster angle, so that is good. A bigger tire will decrease that angle. But usually bigger tail wheel goes with bigger mains, so that doesn't matter much. With the BBW, these guys I work with don't really land on pavement, but with the harder tires (404 or garaero) I inflate them to 45-55 psi.

Sounded like the OP could turn right but not left....... there is something not right internal. It's going to be something with the steering arm, the paw, or... likely... the spring that they work.

And, as good as Airframes has been, they are only human. I have had them assemble and sell me (a client) a complete, new , tail-wheel assembly and it had problems with steering. I took it apart, couldn't make out what the problem actually was, and took it in... those guys saw it instantly, and gave me new parts, no cost. I guess my point is, just cause its new, doesn't mean it's good.

I personally generally land my BBW/tundra tire slow and tailwheel low, and then perch on the mains till I can’t hold the tail up. This has caused consternation with at least one instructor who apparently had a flip over. Nevertheless, it keeps the little wheel off the rough strip where I’m based. That works for shimmy on asphalt, too. Two additional things I found which help combat shimmy are keeping my tire pressure at max recommended and the excerpt below from the Skywagon Club Manual, using a pull “fish weighing” gauge:

Terry wrote:Is the 3200 the same as the 3400?
I added a couple more coil springs to my 3400 and that took care of 95% of shimmy problems.
I think there is room for 5 or 6 springs? There were 3 installed, I added 2 or 3.

The 3200 & 3400 are quite different.
As I recall, the 3200 has a plate with 3 prongs that hold the compression springs.
But there are holes for 2 more, so I guess you could run a total of 5,
although my all my 3200's have only had 3.

The 3400 has a bunch of holes in the t/w head.
My 3400 has 4 springs, I believe that's the minimum recommended number.,
but I think there's room for up to 9 of them.
I've had some shimmy issues, I'm planning on buying 6 new springs & seeing how it works with those.
BTW the compression spring p/n is the same for the 3200 & the 3400.

FWIW I believe that Arirames Alaska (aka Alaskan Bushwheel) sells a "replacement parts kit" for both the 3200 & 3400,
don't know exactly what parts are included though.

A1Skinner wrote:

Battson wrote:Are those kinds of pressures (60 or 70psi) normal for a BBW?

We run our Bearhawk Tundra Tailwheel at 25psi, even heavily loaded. Works great. Anything above 35 psi seems to be too stiff to cushion much, which is the main benefit IMHO.

The BBW is 25 psi. But hes running the glider tire. They need more pressure.

Isn’t the glider tire just a 400x4? The BH Tundra tailwheel takes a 400x4. I air mine up to 25ish lbs.