Univair tail spring

How to keep the Cessna 170 flying and airworthy.

Moderators: GAHorn, Karl Towle, Bruce Fenstermacher

User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Univair tail spring

Post by Bruce Fenstermacher »

Or maybe find an original 170 with say 490 TT and assume the springs are original. I think I know just the plane if TOM is reading.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
c170b53
Posts: 2527
Joined: Mon Apr 22, 2002 8:01 pm

Re: Univair tail spring

Post by c170b53 »

Buck, I really think you will regret not sorting out the issue. There should not be a problem installing the springs from Univair. Even if you do not remove the second spring from the bottom aft bottom sharp edge you will get 500 hours at least from the main (does help to remove that edge though.its easy enough to do). I really don't understand why bigger is better in the case of the L-19 main spring but if owners feel differently, heck its their plane. So if you could stand my attempt to understand (or my indulgence) in your issue. How long have you owned your aircraft ? We think its a later 170B model, is it ? I say this because I've come across planes that have had a data plate swap. I've also come across planes that from a straight on picture, I could tell the plane represented at least 4 planes. Sometimes the owners don't know that. Has the tail been damaged or has the fish mouth been replaced ?
If we review the pictures between your tail spring install and mine, you can see that your U bolt top plate is resting against the fish mouth whereas mine is a distance away to accommodate the spring pack. If you look at the retaining plate on mine the aft top edge is slightly proud of the fish mouth top aft side, your spring retaining plate should be similar. At the bottom aft inner channel of the fish mouth there's the small shim which should be retained with a rivet that has been back riveted flush to retain that shim. I believe that shim prevents the main spring from contacting the radius of the internal surfaces of the fish mouth thus preventing a stress riser and eventual crack. That's a clue that even Cessna knew this area is routinely subjected to possibly the highest loads imposed on the aircraft in regular service. And if you don"t believe that participate as a judge in a short field contest and see the kind of steps taken during the tail wheel dance.
Success loves preparation, and that certainly applies to tail wheel area repairs.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
User avatar
c170b53
Posts: 2527
Joined: Mon Apr 22, 2002 8:01 pm

Re: Univair tail spring

Post by c170b53 »

Oh I should also mention my thoughts may not be valid if you're landing skills are the in the same a class as a certain helicopter pilot that regularly greases his plane on short field competitions. :)
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
User avatar
sfarringer
Posts: 309
Joined: Wed Jan 12, 2005 10:49 pm

Re: Univair tail spring

Post by sfarringer »

I finally got to the building where my spare tailwheel spring is.

Main leaf .313
2nd leaf .263
3rd leaf .200
4th leaf .200

Very similar to Gary's measurements.

I agree with Jim's assessment. I would want to sort this out and be able to use the standard spring stack, even it meant some new parts and some work. You will of course want to talk it over with whomever signs off your annual inspection (hopefully they are familiar with C170's).

My bracket assembly was purchased from Air Repair 15 years ago, due to original steel bracket being found during the pre-purchase inspection to have been previously welded and then cracked again .
I have two complete tailwheel spring assemblies that came from Univair, and they both fit my bracket. I rotate them every so often, and have had a couple of new main leaves in each set over the years.
Ragwing S/N 18073
User avatar
ghostflyer
Posts: 1390
Joined: Mon Apr 21, 2008 3:06 am

Re: Univair tail spring

Post by ghostflyer »

I have a steel bracket that isn’t fish mouth and doesn’t have a fill in plate under the bracket . I found a very small crack next to weld about 18 years ago and it hasnt got bigger . This unit has been doing a great job so is there a service bulletin or AD to change it . If it isn’t broke why try and fix it. This tail wheel fitting has been hammered over the years and had no issues except the biggest spring had to be changed due to a gouge in it.
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Univair tail spring

Post by GAHorn »

David, there is no "requirement" to change from the steel/box bracket to the aluminum "fish mouth" bracket but there is a Service Kit to accomplish that should it become necessary. The small steel box places a lot of stress in a smaller area which eventually/usually leads to cracks in the tailcone and bracket. Cessna applied the larger aluminum bracket to the L019/O-1 and B-models as it has greater area that attaches to the tailcone and spreads the load more.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
snellbob
Posts: 37
Joined: Thu Sep 23, 2010 8:49 pm

Re: Univair tail spring

Post by snellbob »

About 8 years ago I replaced my my 4 tailwheel leaf springs with the Univair set. Kind of a struggle to install but after using a seat clamp and creating some new cuss words I achieved success and the tailwheel tracked straight with no problems. I chose to do this after finding some logbook entrys of rudder skin replacementon on my airplane and personally witnessing a tailwheel leaf spring failure on a different 170B. That is an ugly sight to see!
My goal is to replace at least the main leaf spring each 800 landings or so. A few months back I replaced the main leaf spring after achieving an estimated 800 lndgs and had a tough time getting the new main leaf spring (Univair part) installed but with a clamp and few more choice words acieved success. I thought at the time that the bottom of tailwheel was cocked slightly to the left (as viewed from behind), but then when viewed by others, they could not see it and thought I was crazy.
Now after reading this initial post and doing some measuring, yes indeed, my tailwheel is slightly canted. The tire also puts an uneven pattern across the hanger floor. I operate from grass mostly so have not seen uneven tire wear yet I’m but sure that is coming soon. Looks like a call to Univair about this as well.
User avatar
lowNslow
Posts: 1530
Joined: Mon Apr 22, 2002 4:20 pm

Re: Univair tail spring

Post by lowNslow »

I ordered a new bottom leaf from Univair about a week ago and they advised me it would be 3-4 weeks before they had them in stock. I'm thinking they may have sent back their existing stock due to the warpage issue??
Karl
'53 170B N3158B SN:25400
ASW-20BL
User avatar
DaveF
Posts: 1516
Joined: Sat Nov 03, 2007 1:44 am

Re: Univair tail spring

Post by DaveF »

Univair fabricates the springs in their factory.

See my pictures of the machines in this thread.
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Univair tail spring

Post by Bruce Fenstermacher »

lowNslow wrote:I ordered a new bottom leaf from Univair about a week ago and they advised me it would be 3-4 weeks before they had them in stock. I'm thinking they may have sent back their existing stock due to the warpage issue??
DaveF wrote:Univair fabricates the springs in their factory.

See my pictures of the machines in this thread.
Guess return shipping to the manufacturer was reasonable. :D Jim sure didn't have to go far to review the manufacturing procedures either.

Jim didn't offer they made them, I didn't question who did. He just offered they twist in the heat treating process and I took it from our conversation, if not done right they'd all twist, but still when carefully done some twist. The goal of course being none twisted. It was clear he did not want to sell unusable parts.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
cfzxo
Posts: 137
Joined: Sat Oct 19, 2002 3:29 pm

Re: Univair tail spring

Post by cfzxo »

I still have the twisted main leaf spring that was sent to me several years ago sitting on the shelf. I called them about returning it for a straight one and was told to bad so sad nothing we can do. :evil:
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Univair tail spring

Post by GAHorn »

snellbob wrote:About 8 years ago I replaced my my 4 tailwheel leaf springs with the Univair set. Kind of a struggle to install but after using a seat clamp and creating some new cuss words I achieved success and the tailwheel tracked straight with no problems. I chose to do this after finding some logbook entrys of rudder skin replacementon on my airplane and personally witnessing a tailwheel leaf spring failure on a different 170B. That is an ugly sight to see!
My goal is to replace at least the main leaf spring each 800 landings or so. A few months back I replaced the main leaf spring after achieving an estimated 800 lndgs and had a tough time getting the new main leaf spring (Univair part) installed but with a clamp and few more choice words acieved success. I thought at the time that the bottom of tailwheel was cocked slightly to the left (as viewed from behind), but then when viewed by others, they could not see it and thought I was crazy.
Now after reading this initial post and doing some measuring, yes indeed, my tailwheel is slightly canted. The tire also puts an uneven pattern across the hanger floor. I operate from grass mostly so have not seen uneven tire wear yet I’m but sure that is coming soon. Looks like a call to Univair about this as well.
It is possible to push the tailcone to one side and then view the tailwheel to observe it appears "canted" one way or the other... then pushing the tailcone the opposite direction will either straighten it up...or cant it the opposite way. On subsequent landings it has appeared to straighten up again. I've observed this on numerous airplanes and consider it a personality-trait of the flat-springs.

Of course, a twisted, new spring is undesireable.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
cessna170bdriver
Posts: 4059
Joined: Mon Apr 22, 2002 5:13 pm

Re: Univair tail spring

Post by cessna170bdriver »

I haven’t researched my logs, but I’m pretty sure I lived in Mississippi the last time I replaced the main leaf in the tail spring, so I estimate at least a thousand hours on this one. There is a slight ridge just behind where the second spring ends, so it is time for a new one. Regardless of that, it was time to clean up and paint the rest of them anyway. And, for the record, the new spring thickness is identical to that of the old spring (also from Univair IIRC), 0.321” per my calipers, and I was able to remove the stack without removing the 0510000-31 spring retainer channel.

17987862-19E1-45B1-94CF-4C093AA6C779.jpeg
Miles

“I envy no man that knows more than myself, but pity them that know less.”
— Thomas Browne
User avatar
cessna170bdriver
Posts: 4059
Joined: Mon Apr 22, 2002 5:13 pm

Re: Univair tail spring

Post by cessna170bdriver »

An update on my previous post.

Due to pitting of the three upper spring leaves, I decided to order replacements for them. After over a month of Univair having issues with their heat treat vendor, I finally received them late last week. Earlier tonight I attempted to install them but was unsuccessful due to the fact that the top three new springs total over 0.100 thicker than the three that they replace. With the top retainer channel in place and the forward bolt installed through the channel, spring pack, and retainer block, the cross holes in the retainer block would not line up with the holes in the fish mouth. Due to the proximity of the Convention I just reinstalled the old three old ones (along with the new Univair main leaf).

Here are the thicknesses of the top 3 springs (according to my calipers, after I painted the springs to match the airplane):

U0442109-2: 0.210” (Old leaf: 0.180”)
U0442108-2: 0.220” (Old leaf: 0.180”)
U0542105: 0.270” (Old leaf: 0.235”)

As I mentioned in the previous post, both the old and new main leaves measured 0.321”. This should be expected, as the old leaf is also a Univair part.

New Univair stack: 1.021” Old stack: 0.916”

I’ll call Univair in the morning and get their take on it.
Miles

“I envy no man that knows more than myself, but pity them that know less.”
— Thomas Browne
User avatar
cessna170bdriver
Posts: 4059
Joined: Mon Apr 22, 2002 5:13 pm

Re: Univair tail spring

Post by cessna170bdriver »

I talked to “Bill” at Univair today, and he says that of the upper three leaves, their data says two of them should measure 0.204 and one should measure 0.262. This is still significantly thicker than my original leaves and will not fit my bracket. They are taking them back, but I’ll still be out about $50 in shipping.

I bought a full spring stack at the Convention auction labeled “1948 C170 NEW TAIL WHEEL SPRING PACK” by the donor that pretty much match Univair’s data. :? I guess I’ll just keep and use my originals.

As a warning to any future readers of this thread, I’d advise measuring your old ones and contacting Univair for their current data before ordering.
Miles

“I envy no man that knows more than myself, but pity them that know less.”
— Thomas Browne
Post Reply