Matco Fat Tailwheel trashed

13 posts in this topic

Posted (edited)

Well, 42 hours on my Matco Fat Tailwheel and I broke an internal part...

I made my first jump out of the 50 mile ring the phase one kept me in and had a real eye opener of a landing.  I was at a high elevation field that sits on a slanting mesa.  When I approached the field the winds were variable at 2 to 3 knots and some powered gliders were taking off on the downsloped runway, so instead of fighting traffic I decided to land on the downsloped runway to see what that was like...what I got was the perfect storm.  The approach was fine until about 75' high and there was a 5-10 knot crosswind, it died out and as soon as I straightened out there was no wind, right as I felt I was going to squeak one on a nice 5 knot tailwind hits.  I have my tires a bit overpressured for asphalt so those 31" of kinetic energy amplify any bounce...needless to say, I bounced about 3 times and the bounces were getting bigger so I pushed the power in and went around.  I enjoy a good challenge so I had the same experience 2 more times before I decided to land long to get some more consistent air.  It worked, I was able to get her settled on the mains and then slowly lower the tail, but as soon as the Tailwheel hit the plane began to shudder  and I had no left or right control, I was slow enough that the rudder was ineffective and I was working the brakes, but it felt as if the Tailwheel was pulling me left, I was drifting left off of the runway slowly.  I cut the engine before leaving the runway and got ready for a ride...as soon as the Tailwheel hit the grass the tail broke to the left, I did a slow 180 degree slide thanks to the wide gear and big tires, and came to a stop about 10' off in the grass.

All of the factors leading up to the Tailwheel touching the asphalt were self induced.  My newness in the aircraft led me to think that I just needed to figure things out, when I should have reversed traffic and landed on the upsloping runway...a local told me that they will land on the upsloping runway until the other runway has a 10mph favoring wind, so keep that in your pocket...

The Tailwheel had it's own issues...all the vibration had actually worked the attach nut (metal locking nut) and bolt loose and once I had weight off of the Tailwheel I could move it up or down an inch or two!  Yikes!

The cause of the vibration was a product of a stop breaking internally in the Tailwheel and it was allowing the Tailwheel to free caster in one direction and then hard catch in the other, over and over again.

I don't know what caused the damage, but I will say that asphalt is hard on the fat Tailwheel and rudder hardware.  It was hard to turn, with just too much surface contact.  I didn't even like it on grass, because the support arms were too close to the tire and would fill up with grass and dirt to the point that the wheel wouldn't free spin!

These are just my observations and experiences I want to pass on to the next guy, so don't get your feelings hurt if you love your Matco Fat Tailwheel.  It looks cool and probably works well on a lighter aircraft, and on grass and dirt.  Hope this helps somebody...

 

Ron

P.S.  I put the Maule Tailwheel on and it is much more steerable on asphalt.

Edited by RDavidson
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Posted

I'm replying to my own post again which is the first sign of a posting problem :)

I verbally trashed the Matco Tailwheel, but after finally getting time to look at the tail wheel, there is nothing wrong with it!  It is a simple design and a quite hearty design.

I had a lot of trouble taxiing with it on pavement, just because it had enough surface area on the pavement to stretch my springs instead of turning the wheel.  Things got better with forward momentum, but still kind of stiff feeling.

I also got some of our Pueblo mud stuck between the tire and the forks, which barely clear each other...after flying for about an hour the mud dried like concrete and when I set the tail down it started hopping!

But as I said above, the real problem was that the shimmy I had experienced with it actually shook the metal lock nut loose and helped cause the slow motion runway excursion...

If I were doing most of my operations off airport I would be putting it back on!

I just wanted to clarify that the Tailwheel did not fail, it is a solid part...

 

Ron

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Posted

Hi Ron,

 

long time no words from me... -_-

I did quite a few things on my Magnum. Will grab some pictures later on. One thing I did was to replace the 6.00 - 6 with 8.50 - 6 tires on the main and I got myself a Matco, too to lift the tail and get a softer ride on it. But only the 8" version. Overall look is better, the mains are only a little more spongy but still good to handle. The Maule tail wheel was pretty loud on the asphalt as it was not pneumatic and somewhat worn out.

Just recently I went through my annual (I could do a lot of things myself under the supervision of my workshop on site). Looking at the tailwheel, we figured out the spring could be bent a little more downwards to get more castor angle heading backwards on the pivot axis of the wheel. I thought no big deal, but when I saw the lower leaf spring today it appeared to me, it has seen some heating. So the elasticity is gone, the steel is soft, bending doesn't make much sense (at least that's what I recall from these old days at school).  I guess the expert at the spring mending shop won't tell me any different tomorrow. That explains, why the angle wasn't correct - the spring probably sagged due to the lack of material tension.

So that means, I'm hunting for a new set of leaf springs. Or at least the lower one, that had been heated. Do you have an idea, where to get a tailwheel spring? Do you remember, where you have sourced yours from? Assuming our attachment points on the fuselage are identical your source may save me a lot of research...

Thomas

 

small tires.JPG

bigger tires.JPG

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Posted

http://www.wausauspring.com/
 That is where some of our members got springs.  I hear that they can make whatever you need.  EDMO

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Posted (edited)

Thomas,

Your Magnum looks great!  I like the changes you have made.

Springs can be reheated and tempered if you find a shop willing to do it.

I used this place http://www.alcanspring.com/

I talked to Bill.  He is a good guy and made a spring for me for cheap!  Just make a detailed drawing and send it to him.

I modified my tailpost mount and went with a Husky type spring with three leaves.  I did it so I might have a more universal spring and mount, so later I could maybe go with one of those fancy T3 shock systems.

Let me know if you need anything else.

 

Ron

 

 

Edited by RDavidson

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Posted

Whow - that was a quick turnover with your supplies. Thank you! I had a phone conversation with the spring mender shop this afternoon and they started reproducing the affected spring. Hopefully I'll get it back by tomorrow. The new spring is slightly thicker and wider, but that shouldn't be a major issue. We'll see...

I'll keep you posted!

Thomas

 

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Posted

Alcan makes sweet leafs for off road rigs too lol

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Posted

Ha!  That is actually how I found them Joey!  I wish we lived closer, we share the same hobbies!

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Posted (edited)

I learned that the only thing that will cure tail wheel shimmy is lots of friction damping. And it makes sense if you really think about it. Changing castor angle will only slightly change the conditions under which shimmy might occur. It took me a long time to figure out that a shimmy is exciting a resonance in a mechanical tuned system of spring(s) and weight. Just like an inductor and capacitor in an electrical circuit. Without a damping resistor the electrical circuit can resonate if excited. Without mechanical damping (lots of friction in the back and forth movement of the tail wheel) it WILL shimmy under the right conditions regardless of castor angle. I went down the castor angle black hole ultimately to learn that the only REAL cure for tail wheel shimmy is resistive damping. 

Happy your plane is OK!

Edited by Chris Bolkan

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Posted

Chris,

Thanks!

Did you go with different sized compression type springs on the chains to dampen the shimmy?

I’m running a Maule pneumatic tailwheel and tire now and I don’t have a shimmy anymore, but I think I used different sized springs this time which probably helped...

Thanks,

Ron

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Posted

Hi Ron,

Different springs on the chains may change the characteristics of shimmy and maybe affect the onset of shimmy, but all you are really doing by changing springs is changing the amount of spring, not adding friction. Friction damping is the ONLY way to ensure the system won't shimmy. If the tail wheel assembly itself does not have a provision for adjusting the amount of friction required to move the tire back and forth, so you can critically dampen the resonance of the system, it will shimmy at some point.

There is a company now (maybe more than one) that offers a big ass tail wheel that has no steering chains or springs at all. I think they got the idea for it from the RV style nose gear that is not connected to rudder pedals. The RV nose gear would shimmy like mad if it weren't for a couple of big bellville washers that you are supposed to tighten down until it takes about 10LB of force to move the wheel back and forth at all. Differential breaking is used to force the wheel to turn. That large amount of friction prevents the wheel from ever developing a shimmy in the first place. Same with that big ass tail wheel it operates solely on friction. No amount of springs, castor angle change or anything else will absolutely prevent shimmy. Only enough friction to critically dampen the resonance of the spring/lever/tire weight combination.

It took quite a while to get my head around what is actually going on, but now that I understand it seems so simple. The potential for shimmy can only be eliminated with friction, not changing spring rate or mass or moment arm or castor angle. Those things only change the frequency of shimmy and maybe change the conditions of onset. Friction (enough opposition to the back and forth movement of the tire) is the only sure cure for shimmy.

Unfortunately not all tail wheel manufacturers have the provision to adjust friction. Only ones that do provide a friction adjustment can be positively set up not to shimmy.

That's my experience anyway! :-)

Chris

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Posted

The only time I have ever had tailwheel shimmy is when something got loose or the castor angle was too far out of whack.  The spring mounting bolts on the fuse got loose and created a good shimmy on me but that's about it.  I have run with and without springs, compression springs, loose chains, tight chains etc.  Pay attention to the different sized springs and which side you put them on.  using a geared engine you would put them on the opposite side of what you would a conventional engine.

I do get the tail off the ground ASAP with full down elevator to get the drag cleaned up and accelerate faster.  I also almost never wheel land, I drag it in more often than not 1 point :lol: 

:BC:

 

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Posted

I'm part owner in an 11 BC Chief as well as the other stuff, and we started getting a tailwheel shimmy at times.  It's got a Scott 3200 so it's a real good tailwheel.  The shimmy went away when we put a new tail spring on that made the castor correct.  The old spring had sagged over the years (or hard landings it experienced).  Probably lots of different reasons why a shimmy can start, but I think ours was from the sagging spring.  JImChuk

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