Bushwheel Fork and Tail Shimmy

[sierrasplitter]

Yes, I think you are right Gilbert. But, In San Diego TW's are not that prevalent so I have a couple of TW guys who are going to help . I want to track this down and understand the internal workings . In other words Im pissed and need to master this in my own head.
I have kinda kept a hands off approach because its an airplane. But, its still a mechanical object and the basic laws of mechanics apply.
I am going to disassemble and using Steve's videos and local help I can get this thing fixed
I also tried to break it loose using the rudder last night. The rudder hits the stops before anything breaks loose. So No, I cant break it loose using the rudder

Two questions Im still working on
How many springs? My narrow fork has 5 sitting in it from the rebuild. I think I will find 5 in the AB fork when I tear it down
Pawl length . The old narrow one had the narrow Pawl

This video also cleared a lot up for me.

[tnowak]

I have just dismantled my Scott 3200 tailwheel to clean it out, inspect and re-grease it.
Mechanically it is very simple and straight forward to take apart - and put back together!
My tailwheel has five springs.

Go to the ACS website and search for Scott 3200 and you will find the detailed parts diagram which shows how it goes together.
I tightened up the main nut about 6 turns to get the tension of the assembly correct.

I think Gilbert meant "push on your fuselage handle to see if you can "break" the tailwheel so it pivots". Should be similar pressure to break left/right.
TonyN

[sierrasplitter]

Thanks tnowak Found an Excellent video about tension adjustment

[Glen Geller]

Splitter,
This site lists dozens of crop dusting services in California.
http://www.cropdustingservices.com/c..._services.html
Look for the companies closest to your area and call, ask if they fly tailwheel planes and can they recommend a local shop knowledgeable in tailwheel maintenance.

Good luck,
GG

[Troy Hamon]

We have baby bushwheels on the top cubs and the 185 at work. They all tend to shimmy when we land on pavement. We deal with that by landing as slow as possible and either keeping the tail up or if the tail comes down and there is a shimmy, stopping completely. They are not designed for pavement and my impression is that some combination of the soft bushwheel rubber on the tail and all the other factors make for a lot more common shimmy issues. We use these things all over the Alaska Peninsula, and when we have smaller tailwheels we are reminded why we want the bigger one...definitely makes the soft environment work a lot more straightforward.

But if you are operating on pavement and you don't need to baby bushwheel...I wouldn't use it. If you are like us, needing to operate both places, it is possible you will find you need to manage a little more shimmy than you would with other tailwheels.

[Subsonic]

Just another reason why a simple 4 place piston engine nose-wheel plane capable of rough field landing is needed. No, I don't know of a good one. You are all fighting physics. If you're going to fight by insisting on landing with your CG aft of your wheel contact (typical tail-wheel) you want to live with the risk so to land in fun places. Cool. Regarding the mechanics and structural compliance of the tailwheel, you have to calculate the loads (3D) at the interface (the tire contact patch as it contacts the surface and springs and rebounds through travel) and carry the load analysis back through the structure. All of it. At all angles and load factors. Really. Apparently the scruffy-loose rough country big tail-wheel manufacturing folks haven't done that. Good luck. Lots of loads aren't reacted properly to understand the range of responses, or you would not have these troubles. Start with longer moment arms and stronger springs and more damping to facilitate stability. Just my 2C.
-Subsonic

[Subsonic]

Without any calculations, and only looking at the problem for 5 minutes I would wager a fair sum I could fix a large percentage of the problems with a larger diameter bearing. Like 50% larger. No offense intended.

[sierrasplitter]

None Taking. Im learning aircraft . Well, simple aircraft anyway . And yes, This big tire is most of the issues. I can go back if needed. However, I do enjoy flying tail wheel. And, I will continue to fly tail wheel.
Thank all of you for your input . I am going to spend a day or two taking the head apart to check for anything wrong, try different air pressures , and test
If it still is giving me too many issues I will revert back to the stock fork and tire, find another head assembly and use the bigger tire when Im heading out to the desert

Again, Thank You

[dgapilot]

Don’t forget that tire pressure will also impact your shimmy. I’ve never flown a baby bushwheel, but have lots of time with both an 8” Maule and Scott 3200. Also lots of time with the 10SC in the Howard. In all of them, tire pressure could dampen or exacerbate the shimmy. Try increasing or decreasing pressure a couple pounds and see what happens.


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[sierrasplitter]

Thanks dgapilot . I will be playing with air pressure. Have a brand new tire , will mount and check to see if its out of round before any landings. have a guide on how tight the head shold be. Chains and rigging look good. Castor angle looks good. Will slow down below 60mph before a 3 point , and if all of that does not change I will go back to the stock fork