Today I removed my original dual air-shock T3 and installed the new dual coil over shock T3 that Dan sent me. The springs are rated at 1,000 pounds each and my initial feeling after installing and bouncing on the tail is they are too stiff for my needs. With the SQ2 loaded for Alaska play (full survival kit, tool kit, sleeping bag, tent, 460 magnum, sat phone, etc) I can still lift the tail by myself with one hand (ok barely).

I removed all the spring preload and duct taped the threads below so the nuts wouldn’t back off in flight. And headed out to try it and shoot a video which I will post probably this evening.

The steering head now has a whole lot less caster then before, which is great for eliminating wheel shimmy, but that has an interesting affect in stuff as you’ll see in the video. Dan is sending me a pair of 750 pound shocks to try, I’ll report on those as well.

The video shows that the 1,000 pound springs work more then I expected they would. I'm still going to test the 750 pound springs as well.

Takeaways from this video include:

1. As stated above, the heavy springs performed better then I expected based on my ground testing.

2. The tail wheel staying at a 90 degree position (at touch down speed) might explain the "whollips" on my Matco tailwheel that to this point have confused me as to how they got there. I now believe it likely happened when I was landing in some volleyball to basketball sized rocks, the wheel was kicked 90 degrees and then got wholliped. I've been planning on putting the steering back on, but forget the parts in Texas. Getting a new Matco wheel but now I believe I'll delay installation until I get the steering.

3. Interesting to see the squared profile Matco drag itself through the sand momentarily at a 90 degree angle. The Matco is lighter then the Bushwheel which is why it's on my plane. Wonder if the round profile bushwheel behaves the same way? BTW Bushwheel is planning on building a lighter setup, but they also told me not to hold my breath (okay that’s not actually what they said but it is what they meant).

4. Clearly I should unload the tail all the time I’m taxiing off airport, not just when I’m in the big hard stuff or small soft stuff. It’ll just be better on that little wheel in the back.

5. And lastly, it’s a worthwhile exercise to point a video at the tail even if one hasn’t changed anything. Stuff to learn.



https://vimeo.com/175179739

Point 3 was very interesting. I wouldn't have expected that.

Almost 50 hours and at least that many landings on this bird and the single coil tail
Shock is awesome.

I do not like the Matco tail wheel though. The big flat square wheel makes no sense and drives around not the best off field. The baby Bushwheel will react much better I'm certain.

https://vimeo.com/175216514


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aktahoe1 wrote:Almost 50 hours and at least that many landings on this bird and the single coil tail
Shock is awesome.

I do not like the Matco tail wheel though. The big flat square wheel makes no sense and drives around not the best off field. The baby Bushwheel will react much better I'm certain.

https://vimeo.com/175216514


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Hey Kevin, if you Adjust the rebound dampening knob, it will stop the bouncing. Turn the knob all the way clockwise then back a half turn.


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aktahoe1 wrote:I do not like the Matco tail wheel though. The big flat square wheel makes no sense and drives around not the best off field. The baby Bushwheel will react much better I'm certain.

+1, this is my experience also. I've not been impressed by them for anything above an LSA (super-light tail).

Barnstormer wrote:2. The tail wheel staying at a 90 degree position (at touch down speed) might explain the "whollips" on my Matco tailwheel that to this point have confused me as to how they got there. I now believe it likely happened when I was landing in some volleyball to basketball sized rocks, the wheel was kicked 90 degrees and then got wholliped. I've been planning on putting the steering back on, but forget the parts in Texas. Getting a new Matco wheel but now I believe I'll delay installation until I get the steering.

3. Interesting to see the squared profile Matco drag itself through the sand momentarily at a 90 degree angle. The Matco is lighter then the Bushwheel which is why it's on my plane. Wonder if the round profile bushwheel behaves the same way? BTW Bushwheel is planning on building a lighter setup, but they also told me not to hold my breath (okay that’s not actually what they said but it is what they meant).

4. Clearly I should unload the tail all the time I’m taxiing off airport, not just when I’m in the big hard stuff or small soft stuff. It’ll just be better on that little wheel in the back.

To your questions in (2.)
Yes - a baby bushwheel without steering chains does this 90 degree trick too. I have watched it happen on several aircraft, Super Cubs, Pacers, etc.

(3.)
Personally I doubt the BabyBW would drag through the sand at 90 degrees. I have never seen any other tailwheel do that, and I have watched several. Scott, Bearhawk, etc. I was very surprised by what I saw.

And (4.)
I have been trying to do this - removing load from aft stowage is the best idea.
Don't be tempted to taxi with the stick hard forward, like someone I know did. The prop will just blow small stones into the tail. It does more damage than you might expect. Same goes for trying to lift the tail too early during the take-off roll.

So after returning from a couple weeks of PNW flying I want to look at another tailwheel option. Mine cracked at the welds on the 1.5 yoke. Probably due to the main bolt going into the springs becoming loose.

That is a reoccuring theme in my case so a cotter pin instead of a nylock ought to solve that bit.
I would like to hear what ither options are out here. Can the T3 be built with a single shock for the Bearhawk (heavy) tail?

Cathy

Cathy, Airframes Alaska is going to have available a newly designed Super Duty T3 that would work great on your Bearhawk. It will allow you to use your original steering and weighs about the same as a Pawnee four leaf tail spring.


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acroflyrgirl wrote:Mine cracked at the welds on the 1.5 yoke.

Say again where it cracked, please?

I can't sing enough high praises about my T3. Lighten up the spring for light loads and let it flex. Tighten up as needed when you load er down. Anything I can do to relieve stress on my tail section, I'm game for.

I'm honestly surprised it took this long for someone to come up with something to replace the antiquated leaf spring design. Sure it was simple, but it can't take the abuse a lot of us subject our planes to. Some say it's a solution to a problem that doesn't exist. I think those people will be swallowing their words the first time they break a leaf spring. Courtesy of Murphy, I assure you it will happen at the most inopportune time in the middle of nowhere with no one around to help. If you're thinking about it, pull the trigger and don't look back

Battson wrote:

acroflyrgirl wrote:Mine cracked at the welds on the 1.5 yoke.

Say again where it cracked, please?

Here...

acroflyrgirl wrote:

Battson wrote:

acroflyrgirl wrote:Mine cracked at the welds on the 1.5 yoke.

Say again where it cracked, please?

Here...

I think a T3 would he a bug improvement for sure. Interesting to see the TW breaking and not the springs.

acroflyrgirl wrote:

Battson wrote:

Thank you very much - that is very interesting - I reckon that's worth posting on the Bearhawk forum too.

At a guess, I would say that king bolt which holds the tailwheel to the spring has been allowed to loosen off. I change mine every 200hrs and torque it every 50. If you keep that tight, forces should be transferred to the spring and not damage the tailwheel.

To that end - I think the T3 would have made no difference to this failure whatsoever.
The T3 protects the fuselage, by reducing the impulsive forces transferred to it.
The largest forces borne by the tailwheel would not materially change - it's still being smashed into the ground during a hard landing, for instance.

Battson wrote:To that end - I think the T3 would have made no difference to this failure whatsoever.
The T3 protects the fuselage, by reducing the impulsive forces transferred to it.
The largest forces borne by the tailwheel would not materially change - it's still being smashed into the ground during a hard landing, for instance.

From my airchair laboratory with my 2 semesters of strength of materials (failed the first) at the furthest reaches of my memory, would you agree that the spring rate has an effect on stress? (It's not strain until there's material deflection, right?)

The leaf, loaded perfectly in the ideal axis, has an initial spring rate that is progressive with increasing deflection. Even the first 1/4" of flex is a very high spring rate. Very steep graph for stresses applied to either end of the spring.

Now compare the T3 with its initial 1/4" of shock stroke: the coil spring, by my reckoning, would ramp the stress up over a longer time frame and longer deflection, making the stress graph a little flatter, right? Active suspension is going to allow more useable travel whereas the leaf spring seems to me that even deflected a little the spring rate is climbing exponentially.

This is all in reference to the tailwheel head itself, as you mentioned it wouldn't benefit from the T3.

My bullshit generator is working overtime, perhaps.

Zzz wrote:

Battson wrote:To that end - I think the T3 would have made no difference to this failure whatsoever.
The T3 protects the fuselage, by reducing the impulsive forces transferred to it.
The largest forces borne by the tailwheel would not materially change - it's still being smashed into the ground during a hard landing, for instance.

From my airchair laboratory with my 2 semesters of strength of materials (failed the first) at the furthest reaches of my memory, would you agree that the spring rate has an effect on stress? (It's not strain until there's material deflection, right?)

The leaf, loaded perfectly in the ideal axis, has an initial spring rate that is progressive with increasing deflection. Even the first 1/4" of flex is a very high spring rate. Very steep graph for stresses applied to either end of the spring.

Now compare the T3 with its initial 1/4" of shock stroke: the coil spring, by my reckoning, would ramp the stress up over a longer time frame and longer deflection, making the stress graph a little flatter, right? Active suspension is going to allow more useable travel whereas the leaf spring seems to me that even deflected a little the spring rate is climbing exponentially.

This is all in reference to the tailwheel head itself, as you mentioned it wouldn't benefit from the T3.

My bullshit generator is working overtime, perhaps.

I agree with your reckoning. But I was thinking that since the T3 is a softer deflection it would be easier of the TW head as well. Simply because I was thinking the TW would have less pressure on it when bouncing over objects. It should be easier on the aircraft and the TW head itself.
This is coming from a simple mind, but it makes sense to me.

In my case, the nylock had loosened up. I thought due to the washer used on the bottom side that was cupping because the washer material is soft.

We, "my awesome mechanic" Terry, welded the cracks. There was one on the right side also.

He also made a washer out of 4130 that won't deform. I thought that would get us home fine. It did that, but just. The last landing at home had a little shimmy and when I checked, the bolt thru the spring was a bit loose already.

Next move will be a longer, drilled bolt with a cotter pin.

acroflyrgirl wrote:In my case, the nylock had loosened up. I thought due to the washer used on the bottom side that was cupping because the washer material is soft.

We, "my awesome mechanic" Terry, welded the cracks. There was one on the right side also.

He also made a washer out of 4130 that won't deform. I thought that would get us home fine. It did that, but just. The last landing at home had a little shimmy and when I checked, the bolt thru the spring was a bit loose already.

Next move will be a longer, drilled bolt with a cotter pin.

For my money, they loosen because the bolt is straining (stretching).

And just to be clear - those cracks - this isn't a 'Bearhawk Tailwheels" tailwheel, it's a home-made job by the look of it?

Zzz wrote:

Battson wrote:To that end - I think the T3 would have made no difference to this failure whatsoever.
The T3 protects the fuselage, by reducing the impulsive forces transferred to it.
The largest forces borne by the tailwheel would not materially change - it's still being smashed into the ground during a hard landing, for instance.

From my airchair laboratory with my 2 semesters of strength of materials (failed the first) at the furthest reaches of my memory, would you agree that the spring rate has an effect on stress? (It's not strain until there's material deflection, right?)

The leaf, loaded perfectly in the ideal axis, has an initial spring rate that is progressive with increasing deflection. Even the first 1/4" of flex is a very high spring rate. Very steep graph for stresses applied to either end of the spring.

Now compare the T3 with its initial 1/4" of shock stroke: the coil spring, by my reckoning, would ramp the stress up over a longer time frame and longer deflection, making the stress graph a little flatter, right? Active suspension is going to allow more useable travel whereas the leaf spring seems to me that even deflected a little the spring rate is climbing exponentially.

This is all in reference to the tailwheel head itself, as you mentioned it wouldn't benefit from the T3.

My bullshit generator is working overtime, perhaps.

From a mechanical engineering point of view, we're taking about a failure caused by low-cycle fatigue: basically a microscopic crack growing as cyclic stress is applied - a very high stress applied a low number of times (10,000's or 100,000's of cycles).

For the stress - I recall that all that really matters is the magnitude of the net force applied, and the magnitude of the impulsive force applied (how quickly the force is applied), and how often it's applied to that magnitude. There are some assumptions built into that approach, but the answer should be "close enough" for this example.

Imagine you're landing and the wheel hits a rock at Vso (highest force scenario), or perhaps if you're taxiing on the rough stuff and the tail is bouncing around. The cushioning effect of the spring will reduce the impulsive force as the tail hits ground, because it takes time for the spring to soak it up.

In both cases (T3 and leaf spring) they are supporting the same weight, so the net force applied is the same. The impulsive force will be slightly different in each case. Because the T3 moves further and takes a longer time to do so, the impulsive force will be less. But if you watch the videos, the tailwheel itself is still moving pretty darn fast... (but the fuselage is not!). There is probably not enough difference in velocity to dramatically reduce the impulsive forces acting on the tailwheel.

Now, a secondary point - the normal spring will rebound and unload the tail after each impact, maybe even throw your tail back in the air, when it comes back down again this adds another stress cycle (albeit lower stress) to the parts. The dashpot may prevent this in the T3, but that may not matter. If that rebound stress is large enough to grow the crack, then the T3 could make a big difference. If the rebound stress is not enough to grow the crack, it might make no difference either way (T3 vs leaf spring). You you need to know about the flaw size (crack size), material strengths, and calculate the magnitude of the overall stress to find the answer. I can say, the bigger the crack, the less force it takes to make it grow even larger.

Aside:
^ This is why, once a crack starts growing, you can't usually stop it growing unless you "stop drill" it. This is done to remove the microscopic crack interface, where the growing actually occurs (where the metallic bonds are broken at an atomic level).

My guy feel is, for smooth field operations, the T3 would not provide enough additional "cushioning" to be of any real benefit to the tailwheel itself and prevent the kind of cracking shown above - especially once the cracks has started. Clearly that was a pretty poor weld, or a weld over-top of an existing crack. It should not have cracked like that.

Not owning a T3 (yet) and not having the experience with tuning one, I would fall back on my motocross suspension experience and bring up the importance of preload. Preload sets the sag and initial spring rate, and is also what helps the shock rebound back in those opportunities when the tail is unloaded a little. Without proper preload, the shock can wallow in the bottom of the stroke and really feel stiff, because it's experiencing no travel.

An elastomer bottom-out bumper would also be a good addition too-- a last vestige against hard metal-to-metal bottom-out. I'm not sure if current T3s have this or not.

I saw this video on Instagram today of them drop testing a T3: https://instagram.com/p/BIIV1lcAOnY/

Does anyone else see that shock blowing through its travel and bottoming out? Or just me?