Rob wrote:Anyone with a reasonable amount of mechanical / engineering / suspension background will be able to identify the two logical points it will fail at. It will either fail at the fuselage attach points, or it will fail at the point where the aluminum swing arm attaches to the steel pivot point. The aluminum does flex there, it will work harden, and then it will crack...

Oh.... when NoCOpilot said it does flex like a leaf spring, I was going to ask if it was Al - but then I assumed it had to be made of steel...

That aluminium part acting like "a traditional lead spring" sounds bad to me, the geometry doesn't look right. But on the other hand, I guess some spring gear are made of 7075 aluminium, so maybe it's not a problem from a materials point of view. I didn't specialise in materials technology.

I guess there must be some instructions about how to set these up correctly, to avoid that leaf-spring action.

I tend to agree with Z's earlier comments too - I am not criticising the project to develop this modern tail-spring. I am huge believer in the benefits of spring-damped undercarriage for STOL aircraft, I think they are superior to straight spring gear - that was partly why I selected the Bearhawk.

I totally expect to buy a product like the T3 (or later iteration of the design - T4???) once the design is fully proven. Having already broken off a tail spring in the middle of nowhere, without help, and with a heavy load of passengers aboard - I can appreciate the problems such a failure can cause.

Battson wrote:Oh.... when NoCOpilot said it does flex like a leaf spring, I was going to ask if it was Al - but then I assumed it had to be made of steel...

An aluminium part acting like "a traditional lead spring" sounds bad to me - unless there is some work-hardening resistant aluminium-alloy which I am not aware of.

Hi Battson, I don't have any hands on experience with this system, so take my earlier post with a grain of salt. I'm just intrigued by suspension systems of all kinds, and like you and others have said I think this is potentially a big step forward. I wish Airframes Alaska much success with this design, and I hope over time it proves to be sufficiently durable.

Let me clarify my earlier post a bit. I don't think the swing arm is meant to act as a traditional leaf spring in this design. As long as the shock is set up correctly the shock should be doing most all of the work. What I meant to convey is that being a flat bar subjected to a considerable bending moment it is going to flex some amount. Under normal circumstances it shouldn't flex very much, but if the shock bottoms out it will probably be the next softest component in the mechanism, and that's actually a good thing. I would rather bend or break the swing arm than tear the attachment structure off of the fuselage. The important thing is to set up and maintain the shock correctly so it never comes to that,

NoCOpilot wrote:Hi Battson, I don't have any hands on experience with this system, so take my earlier post with a grain of salt. I'm just intrigued by suspension systems of all kinds, and like you and others have said I think this is potentially a big step forward. I wish Airframes Alaska much success with this design, and I hope over time it proves to be sufficiently durable.

Let me clarify my earlier post a bit. I don't think the swing arm is meant to act as a traditional leaf spring in this design. As long as the shock is set up correctly the shock should be doing most all of the work. What I meant to convey is that being a flat bar subjected to a considerable bending moment it is going to flex some amount. Under normal circumstances it shouldn't flex very much, but if the shock bottoms out it will probably be the next softest component in the mechanism, and that's actually a good thing. I would rather bend or break the swing arm than tear the attachment structure off of the fuselage. The important thing is to set up and maintain the shock correctly so it never comes to that,

Thanks for clarifying that - I just assumed you must have seen one bending.

Also, I edited the comments which you quoted. After thinking more carefully, I remembered that certain alloys of aluminium can be used as a spring. But it has to be designed to work that way, not just any alloy will do.

I understand your comment about that swing arm acting as a "secondary spring". I think that is a good idea, provided the geometry is designed for that. Watching that slow-mo video, I am not sure that is was designed to work that way - it looks like the stresses on that swing arm would be high, when the shock bottoms out. The combination of the shock and swing arm fighting each other would transfer most of the load to the bolted connections.

Bringing this topic back up. I am curious if anyone has any updates on this TW after some long term usage. It seemed to be quite the hot topic when it was introduced but not much has been said about it after the initial introduction.

~60 or so hours. No complaints so far and absolutely love it.

My Cub is light on her tail so it hasn't taken too much abuse, but I will never go back to a leaf spring on this particular bird as long as this continues to hold up.

Keith, I think that's probably a good thing. If people were having issues they'd be letting everyone know. I beat the shit out of mine whenever I can and no complaints here at all

Thanks Shane for the info and help. Contacted Dan and will get one ordered soon.

I've had one on order for a month and a half. Not available for KitFox Yet, but coming soon, they say. Alaska Airframes are the ones Building and selling the T3.

3tracks wrote:I've had one on order for a month and a half. Not available for KitFox Yet, but coming soon, they say. Alaska Airframes are the ones Building and selling the T3.

Is AA building it or just selling? I assumed Dan is manufacturing. Either way, get one. I can't say enough good things about it

The way I understand it, A A are manufacturing and selling. I talked to Dan first, and he referred me to Airframes Alaska.

Same here, I contacted Dan and he refered me to Airframes Alaska and to Rocky Mountain Kitplanes. I sent a message to RMK due to them being in the lower 48 and am guessing they would be more intune with having one for the RANS S7. I have not heard back yet, so am going to give them a call today.

I haven't been on BCP for awhile due to being really busy with work/life events. My T3 was one of the early prototypes since I asked Dan to let me have one to try on the heavy tailed 4-place Bearhawk. I like it a lot and have put it through it's paces and then some. Dan has been great about sending me heaver/different shocks to try and making up replacement parts and beefing up weak areas/spots in the swing arm. Keep in mind I'm flying at a TO GW of 2700 lbs and a landing GW of 2500 lbs. I also land at gross on unimproved LZ's and generally work the plane pretty hard on outings so its been a really good test platform. Up until the Alaska trip, I didn't have any issues that would have caused me to stop flying the T3 but I did note some weak points and Dan addressed those.

When I was loaded up for the Alaska trip, I had dual 750 lb dual coil overs on and they were nearly bottomed out just sitting on the ramp. I realized that at GW, I was at the limit of what they would support, but decided to launch anyway since, I figured I could always be gentle on the tail. Anyway on the Alaska trip, I broke the swing arm while taxing across tundra hummocks. It broke just at the front of where the TW attaches.

I had had quite a few hard landings over the preceding days and was not gentle on it like I'd intended. Myself and others doubt that the failure was caused by any single event, but instead consistent abuse over many landings, some on pavement, some off airport and some in between. It was a fatigue failure. When it did break, I was taxing over large tundra hummocks, in near darkness, while heavily loaded. It was a place I would not have taxied over if I had enough light to see what I was getting into. However, it would have failed at some point later on; I just expedited the failure in those conditions. The ultimate cause was repeatedly bottoming out the shocks while heavily loaded.

A friend flew out and picked up a Pawnee spring and we installed that the next day and I was off and running. When I made it back through Palmer a few days latter, the Airframes AK guys exchanged the springs for 1,000 pounders and installed a new swing arm.

I've done very little flying since I got home and was out of the country for several weeks in addition to other travels. In the mean time, Dan and Airframe AK guys have been making some design changes and I'll reinstall when updates arrive in a week or two.

The moral of the story is just don't overload to the point where the springs will bottom out repeatedly. I really like the T3 and have no hesitations about it, other than I'll be sure to make adjustments when heavily loaded so that I'm not bottoming out the springs.

I'm not sure what I'll have to do to accomplish that, but will work on a solution. It may turn out that I'll have to swap out springs to to be able to repeatedly carry gross weight but I'll just have to wait and see how the 1,000 lbs springs work. My empty weight is 1,510 lbs when on 8:50 tires so with a 1,200 lb TO useful load, I've got a really wide weight range to account for.

Blackrock

blackrock wrote:I'm not sure what I'll have to do to accomplish that, but will work on a solution. It may turn out that I'll have to swap out springs to to be able to repeatedly carry gross weight...

Blackrock, you might consider my solution. For me the pair of 1,000lb springs were too stiff when light, the 750lb pair to light when heavy. So I used one 1,000lb spring and then one airshock. Works great. All I need do is add or remove air from the shock to accommodate my load. Very pleased with the result.

[not related to your issue but I removed the steering today,was a worthwhile experiment but like it so much better without steering]

Thanks Phil, that looks like a workable solution and easy to adjust.

I agree with no TW steering. That works better for me as well.

Setting up T3 for Cessna 170 and Bird Dog


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Dufault wrote:
Setting up T3 for Cessna 170 and Bird Dog


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Sweet! And chance we'll see it come out for our C180s?

Dufault wrote:Setting up T3 for Cessna 170 and Bird Dog

That looks great! Is that going to be STC'd?

Since, Sweet was already mentioned....I will have to say that TW looks absolutely AWESOME!!

That looks great Dan. Gabe (AA) sent me the picture of the prototype and I passed it along to my 170 buddies. I know of 5 including myself that are.......giddy.

100 hours in and still loving it!



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