New Guy question on Tailwheel Spring

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Toddav8r
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New Guy question on Tailwheel Spring

Post by Toddav8r »

Hello, as of last month I'm a new C-170A owner and new TIC170A member. I'm trying to eliminate some tailwheel shimmy that occurs about half of the time. I've installed all new cups/cones/hardware/tube/tire on the wheel, but that didn't do it. Since I can't find anywhere in the logbooks that the tail spring has every been changed, I've already decided I'm going to change the whole set. Where I'm confused and could use some help is it appears I have a B Model tailwheel mounting bracket assembly on my A model airplane....is that normal? Also, does anyone recognize the configuration of the spring set? Seems odd that the bottom spring is small. I probably should've degreased it before taking pics...the plane is exceptionally clean, and the first pictures I post are of the only dirty part...

Thanks in advance for any enlightenment!
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Todd Farnsley
C-170A N9254A
Edmond, OK
Wiley Post Airport (KPWA)
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Bruce Fenstermacher
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Re: New Guy question on Tailwheel Spring

Post by Bruce Fenstermacher »

Wise decision to replace that entire spring pack. It is wrong. The little spring under the thick spring shouldn't be there at all. Probably added because the main spring, or the entire pack got weak. BTW you might also want to get the correct lenght AN-7 bolt that holds on the tail wheel cause that one is to long as it is and will way to long after you remove that extra spring. Can't tell but you might also be missing the chain guard, a thin sheet metal shield that spans the C-clamp on over the bolt and keeps the chain from being caught there.

The cause of your shimmy is likely the angle of your tail wheel caused by this bastard spring pack. Put you didn't include enough of the actual tail wheel to determine the angle.

Yes you have the more desirable B model or later model mount commonly called the fish mouth mount. It is an approved replacement for the early steel mount.

And after you get your new spring pack installed, your steering chain should be tighter than it is in your picture. It shouldn't be tight but have no slack.
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c170b53
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Re: New Guy question on Tailwheel Spring

Post by c170b53 »

Hey Todd welcome to the association. Really good call on your part to question that installation. Looks like that little "adjustment" was designed to counter the sag of the main spring. Most likely cause of a shimmy is the main tail wheel spring's angle, which over time changes. If you log into the members area and look through the past few quarterly issues, you'll come across an article written by Bruce on just that subject. EDIT I thought Bruce had written something on this but I couldn't find it, so sorry if I've misled you.
Again thanks for supporting the club, hope you have the time to post a few pictures.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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n2582d
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Re: New Guy question on Tailwheel Spring

Post by n2582d »

Todd, Let me add my welcome to the Association! I've learned a lot here and I'm sure you will too.
Toddav8r wrote: ... Where I'm confused and could use some help is it appears I have a B Model tailwheel mounting bracket assembly on my A model airplane....is that normal? ...
I'm impressed that as a new owner you realized that you have the later style mounting bracket. It's not something the casual observer would notice. The change should be noted in your airframe logbook. It should read something to the effect, "Installed tailwheel bracket assembly, p/n 0512000-75, IAW Cessna Service Kit SK70A52-4." You can find that here. Compare your bracket installation to those instructions; it appears some rivets may be missing and some too small. Here's another document that might interest you. It's Scott's installation instructions. As you study it you'll find some variation from the Cessna Illustrated Parts Catalog (IPC).
Gary
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c170b53
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Re: New Guy question on Tailwheel Spring

Post by c170b53 »

OK Todd, I couldn't let it go (I thought, man I'm losing it/imagining things :D ), Bruce did write an article on the shimmy. You'll find it in the 170 News 2015 2nd quarter issue. Back issues can be found in the members area page in a square box.
Gary, although I've seen that Scott document a few times, I've never really looked that hard at it until you posted it in this thread. Your note that it omits parts made me realize that it doesn't show the shackle and the chain guard. Can't imagine that they really intended to do that. The note to use eye bolts is another I question because I use the original tabs on the rudder horn to attach the springs to and that seems to work out just fine.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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c170b53
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Re: New Guy question on Tailwheel Spring

Post by c170b53 »

Todd looking at your pics again, I'd say your shackle is a owner's produced part (it looks a bit large) and likely won't fit when you get your new spring pack.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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Bruce Fenstermacher
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Re: New Guy question on Tailwheel Spring

Post by Bruce Fenstermacher »

Jim, as that Scott instruction is the instruction method required by the TCDS, any deviation from it must have some bases of approval. Like maybe a minor alteration. I've noted this before, 99% of 170s with the Scott 3200 installed are not installed according to the instruction when it comes to the control chain.
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c170b53
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Re: New Guy question on Tailwheel Spring

Post by c170b53 »

I'd wager that nothing would be affected if the springs were attached at either location. The eye bolts are definitely going to be beefier, maybe Scott needed a larger comfort zone. Bruce, what do you think of the missing shackle Assy? An oversight or have you removed yours? :wink:
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
swixtt
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Re: New Guy question on Tailwheel Spring

Post by swixtt »

todd, can post up those pics larger?
i'm almost looking at what i had on mine a while ago. does the bolt on the Scott go through both leaf packs using a bushing?
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Bruce Fenstermacher
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Re: New Guy question on Tailwheel Spring

Post by Bruce Fenstermacher »

c170b53 wrote:I'd wager that nothing would be affected if the springs were attached at either location. The eye bolts are definitely going to be beefier, maybe Scott needed a larger comfort zone. Bruce, what do you think of the missing shackle Assy? An oversight or have you removed yours? :wink:
Jim, I've written about this before. Many times in fact. :wink:

We have no idea what was behind the differences in the I-68 Scott instructions vs the original control rigging Cessna built for the standard Scott 3-24B, a smaller tail wheel. There is no doubt the eyelets are beefier and if they would wear can easily be replaced without riveting. The engineer in me says the eyelets do make a favorable change to the control chain angle and maybe that is what Scott was after but it also puts a twisting force on the rudder control horn. There was a time when I have my tail wheel rigged exactly per I-68 instructions. I found no difference in control.

Missing shackle in the Todd's photo? What missing shackle? Maybe you have a spare on your springs?
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c170b53
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Re: New Guy question on Tailwheel Spring

Post by c170b53 »

Gary mentioned there were parts missing in the Scott instructions...there's no shackle in the graphic, which made me look at Todds shackle, which to me, albeit hard to visually gauge it size precisely, looks a bit big to me.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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Bruce Fenstermacher
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Re: New Guy question on Tailwheel Spring

Post by Bruce Fenstermacher »

c170b53 wrote:Gary mentioned there were parts missing in the Scott instructions...there's no shackle in the graphic, which made me look at Todds shackle, which to me, albeit hard to visually gauge it size precisely, looks a bit big to me.
That part of the Scott drawing, to me, is obviously not accurate at it does not pertain to the installation to the tail wheel or the steering chains. Notice it doesn't have much detail in the fuselage bracket either.

I took note and agree, the shackle in Todd's picture looks is long, which it would have to be to a go around 4 springs rather than the 3 springs it should be going around.
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Toddav8r
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Re: New Guy question on Tailwheel Spring

Post by Toddav8r »

Gary - thank you so much for those document links! I was relieved to find my hardware configuration in the Service Pack drawings, as it's different than any IPC. I will definitely be replacing the whole spring pack and all the hardware I can get hold of.
Todd Farnsley
C-170A N9254A
Edmond, OK
Wiley Post Airport (KPWA)
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n2582d
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Re: New Guy question on Tailwheel Spring

Post by n2582d »

Todd, glad to help! There's a wealth of information here on maintaining, rebuilding, and altering the tailspring, its mounting bracket, and the Scott 3200 assembly. Did you find item number 29 (p/n 0512126) in place on yours?
IMG_0403.JPG
Here's a discussion where some guys found that part missing. I'm considering adding nutplates in place of the "41" nuts. Arash has used teflon tape between leaves to prevent chaffing. Chamfering the second from the bottom spring is a common practice to avoid a stress riser on the top of the bottom spring.
Gary
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