Beware the T3 tailwheel shock

Where I fly there are small vertical-sided water potholes in the tundra, deep narrow, eroded animal trails across the face of an otherwise smooth hill, etc that will eat a baby Bush wheel and cause a dead stop to sideways motion during a turn. Any maneuvering I do loaded heavy, I'm thinking about the tail. Having even a little sideways flex would seem like a good thing. At altitude and loaded there is not enough power to blow the tail up.

Sent from my SM-G965U1 using SuperCub.Org mobile app

wireweinie said:

If I don't like your tail wheel set up, then prove me wrong. Show me that your idea is better. Tell me the concept behind the design. If I don't like it, I'll tell you why and show my evidence to back up my case.
...
I'm glad the T3 works for you. Sounds like the upgrade was an improvement.

Click to expand...

Did you even watch the video I posted? I took the T3 off my airplane. It did not work for me, although it is a vast improvement over the J3 spring.

I bolted something on my airplane, determined what I did like, what I didn't like, then contributed to a thread with specific information on the exact part being discussed.

The confusion came in when those full of opinions yet no direct experience with the T3 offer life coaching advice on how high I should lift my pickup truck. Post that garbage in every other thread in this forum, but not in the Experimental section please. There are still a few people out here interested in something other than a Pawnee spring and a Scotts 3200 and are tired of the pontification.

Steve Pierce said:

I have seen side loads from people taxiing into a hole but wouldn't the tailwheel swivel in most other cases?

Click to expand...

You’d think it would, assuming it’s well lubed and functioning correctly

It seems like a leaf spring will provide a little rotation in response to torque loads.

For small obstacles that makes sense. On the other hand, longerons do get bent, I doubt it has much to do with tail wheels failing to swivel. A round tapered spring just seems like it would address more scenarios than a leaf spring.

Sent from my SM-G965U1 using SuperCub.Org mobile app

Although I have no data to support the claim, specifically with my setup, I believe side loads and lack of allowable twist when encountering side loads are what led to the demise of the swingarm bushing in my T3.

Like DJ, I do not run steering chains. Video data didn't show any oddball loads during taxi/takeoff/landing that could exacerbate wear but it is possible.

Given time I have no doubt we'll see bent longerons with these tail suspensions, too. That's a product of the attachment. We want simple bolt-on so we retain the weakest part of the system. In my case I received a swingarm tail suspension with my kit. I wasn't willing to have so many moving parts hidden in the tail. I bought a T3. I wasn't convinced it was a solution to anything so I returned it and bought a BBW assembly since I wasn't a big fan of the Matco tailwheel I had in hand at the time. My BBW is bolted to a Pawnee spring and except for the tendency for it to rebound when I hit tail first? I have no issues with it at all. If the 3200 tailwheel on my shelf was 2 bolt instead of 1 bolt I'd remove the BBW and use a little 8" 3200 to lower the tail and increase AOA. I've looked at the Acme Stinger and I have pics of the similar concept tail suspension TK1 is working on. I think those are an improvement over the T3 but they still bolt on the same way so ultimately they're limited to how much they can protect the tail section from torque. Bigger tailwheel tires solve some problems and create others. A longer leverage arm transferring torque is one.

Re: tapered round springs? Cessna springs transfer stress to the airframe, too. The bigger the tailwheel the bigger the leverage and the more torque problems. I had a 14" tailwheel for years and watched it closely. I was relieved to replace it with the shorter BBW wide fork assembly.

reliableflyer said:

120 lbs on a tailwheel in a cub of any kind is a red flag for me. I would check the weight and the CG limits and your CG paper work. in an effort to soften my statement after my stepping on toes the other day I’ll say maybe I’m mistaken. I suggest you do some checking in case I’m not.

Click to expand...

Thank you for your concern. The CG is well within limits. So is the weight. My PA-12 has been weighed on scales. For the official CG weight, the tail was in level flight position. I was curious, so we also weighed the tail as it sat on the ground. It has a short-mount with an O-360 and with 3” extended gear & 31” tires, it all works together make the tail a tad heavy on the ground.

motosix said:

....Like DJ, I do not run steering chains. .....

Click to expand...

I guess this means there's no tailwheel steering, and the t/w is free-swivelling all the time.
I've seen this done before, but I'm curious as to the thinking behind this?
Seems like this would promote shimmy.
FWIW I fly a 180 not a cub.

If you were running a 3200, I'd guess that internal spring p/n 3222 would have to be removed,
in order to allow the t/w fork to free-swivel with any steering chains hooked up.
But it sounds like you're running a Matco tailwheel, did it need to be modified?

hotrod180 said:

I guess this means there's no tailwheel steering, and the t/w is free-swivelling all the time.
I've seen this done before, but I'm curious as to the thinking behind this?
Seems like this would promote shimmy.
FWIW I fly a 180 not a cub.

If you were running a 3200, I'd guess that internal spring p/n 3222 would have to be removed,
in order to allow the t/w fork to free-swivel with any steering chains hooked up.
But it sounds like you're running a Matco tailwheel, did it need to be modified?

Click to expand...

Although my landing speeds are higher than a real SuperCub, I do not have any problems with shimmy. As shared in various ways on this site, the secret is the angle of the steering stem in relation to the offset of the axle. In motorcycles the term is called "trail" and is a calculated number that describes the sweet spot where the handling is controlled yet responsive. (google "motorcycle trail" and "tank slappers" if you want to see the equivalent to shimmy in that context).

Like everyone else I have used the standard Maule tailwheel, then moved to different flavors of Matco's; the 8" wide dual fork and then the 11" dual fork. Modification of all to free caster are straight forward (simple removal of the arms mostly although I did machine the 11" eventually) and both Matco units have their pros/cons. I just recently started testing a free castering tailwheel assembly of my own design inspired by the Matco 11", and it is coupled to the Acme Stinger which replaced the T3.

There is a certain beloved SQ2 very local to me that uses a free castering 3200 (and is probably reading this thread). He could probably confirm which spring would have to be removed for that unit to function correctly in that method of operation.

hotrod180 said:

I guess this means there's no tailwheel steering, and the t/w is free-swivelling all the time.
I've seen this done before, but I'm curious as to the thinking behind this?

Click to expand...

Sorry -- I did not answer the most important question for you:

It is just my preference really. I prefer how it feels, both in the air and on the ground. I can keep cross wind rudder control long after touchdown and in the air my feet only feel the pressure of the wind on the rudder and not the stiff tailwheel springs turning the tailwheel in the air. I also like the maneuvering on the ground, but as you might guess, I don't spend much time taxing on long paved controlled airports.

This old thread came to mind when I read about the failure in the original post.

https://www.supercub.org/forum/showthread.php?52647-Tailwheel-101-WTF

I had tail shimmy when on my J3 spring, but only when the tail ski was on. Now that I think of it, this winter the shimmy went away, I chalked it up to a different ski mount, but probably was the different T3 geometry. Lucked out.

Steve Pierce said:

Windy has a PA12, almost a Super Cub but not quite. Don't 12s seem to be heavier on the the tail? Don't confuse tail weight on the ground with tail weight when weighing.

Click to expand...

(My experience only, not fact just opinion) can’t speak to all 12’s only the one I had. I had an 18 tail, an O-320 on a short mount, 18 wings with an 18 angle of incidence and an 18 door. early on 25x11x4’s later gar aero 29’s. I found the original plane with a long mount too nose heavy and moved the battery aft and used the short mount. I found that it flew more like an 18 and it flew better with the weight moved aft. Still nose heavy especially when light on fuel. Always kept some survival gear in the extended baggage.

motosix said:

Sorry -- I did not answer the most important question for you:

It is just my preference really. I prefer how it feels, both in the air and on the ground. I can keep cross wind rudder control long after touchdown and in the air my feet only feel the pressure of the wind on the rudder and not the stiff tailwheel springs turning the tailwheel in the air. I also like the maneuvering on the ground, but as you might guess, I don't spend much time taxing on long paved controlled airports.

Click to expand...

Mine too. Especially with the t3 which extends and puts tension on the chains. The rudder feels much better without. My 3200 seems to swivel fine without chains. I did not gut it in case I want to put the steering back on someday.

Sent from my SM-G965U1 using SuperCub.Org mobile app

DJ said:

Mine too. Especially with the t3 which extends and puts tension on the chains. The rudder feels much better without. My 3200 seems to swivel fine without chains. I did not gut it in case I want to put the steering back on someday.

Click to expand...

Agree 100%. I hooked the steering chains up with the T3 for a bit but didn't like it at all. When the T3 would rise/squat due to terrain it would pull extra hard on the springs and the ground handling was just stiff.

For those that do run the chains, it is important to take into account the extension that happens when the tailwheel is unloaded. The spring+chain length that works best on the ground while the spring is loaded becomes very taught just as soon as you become airborne. It will be slightly different for everyone because everyone will have slightly more or less squat based on weight, spring, preload, and gross.

Yeah it took me a while to catch on to that, as I re-attached my chains after installing the 3 while the tail was still elevated. An easy fix, and as a past "no chain" (tried it while still on the J-3 spring, for about 20 hours) guy, I still prefer them.

Ditto on the difference in spring/chain geometry in the air and on the ground. I got to know several spring companies really well in searching for a spring that would solve the issue to my satisfaction. I needed a spring that would have sufficient tension when off the ground that it still had tension when on the ground after the geometry changed. In my case, not a quick fix but I finally did find a spring I was satisfied with. If you try to accomplish a fix with chain length alone, when using standard (extension or compression) springs commonly found at aviation suppliers, you might have a fun time. Complicating the matter, light sport such as mine usually do not have rudder control horns that are built like tanks and they cannot withstand the stress of pretension with such a strong spring. My case took a lot of experimentation. I am happy with the outcome but it didn't come easily or quickly.

WYflyer said:

Ditto on the difference in spring/chain geometry in the air and on the ground. I got to know several spring companies really well in searching for a spring that would solve the issue to my satisfaction. I needed a spring that would have sufficient tension when off the ground that it still had tension when on the ground after the geometry changed. In my case, not a quick fix but I finally did find a spring I was satisfied with. If you try to accomplish a fix with chain length alone, when using standard (extension or compression) springs commonly found at aviation suppliers, you might have a fun time. Complicating the matter, light sport such as mine usually do not have rudder control horns that are built like tanks and they cannot withstand the stress of pretension with such a strong spring. My case took a lot of experimentation. I am happy with the outcome but it didn't come easily or quickly.

Click to expand...

S7?

If so, I am jealous of you and Tom...

Savage Cub; basically a ripoff of an early short tail S-7.

I experienced two failures of an early version of the T-3 suspension on my Carbon Cub EX. The tailwheel is the Airframes Alaska baby bush wheel which looks like a Scott 3200 clone. The first failure was the shock spring shaft. Airframes Alaska sent me a stronger spring assembly. The second failure occurred in Jul 2019 at the swing arm strap. I installed the upgraded kit which has a one-piece swing arm. It has performed satisfactorily since with 1000 landings on dirt and lots of operations on clump grass.
I have been in experimental aviation for a long time and understand that many early innovations experience deficiencies. I value the capability of the T-3 suspension to noticeably reduce shock loading to the airframe and will continue operations with it. Also, my wife has chronic back pain appreciates the comfort the suspension affords.

Looks like that scenario could damage the rudder.

Sent from my SM-G965U1 using SuperCub.Org mobile app

The saga is over. I rebuilt the wing, replaced the aileron and put the Pawnee spring back on and rebuilt the tail wheel.
Flies straight and taxis straight.

I can't thank supercub.org enough for the technical and moral support. I owe SJ and Laura big time for letting me crash at their place while putting it back together and Dave P for letting Astrid hang out with his 170 in Bentonville.

Oh, and the next time one of you have a failure like this, please post so others can avoid the same fate. Maybe we need a service bulletin type thread like medical matters. Be safe out there.

Jake

Sent from my SM-G970U using SuperCub.Org mobile app