Airframes Shock Absorbing Tail Wheel Unit

[Helidesigner]

Alaska Airframes has a slick shock absorbing tail wheel unit for sale. It uses the same three bolt mount as the Bearhawk.They say it fits any Super Cub mount. Does anyone know if the four place Bearhawk uses the same bolt pattern as a Cub? Does anyone know much about their tail wheel unit? I think someone with a Bearhawk might have tried an experimental one, maybe Dan Shilling.

Mark

[jaredyates]

Mike Creek Blackrock was trying out one that might be similar.

[Battson]

Mike Creek Blackrock was trying out one that might be similar.

I think its the exact same model, Airframes Alaska is selling them I think.

I was told this unit is a little undersized for the 4-place, but that it would work well with the Patrol. Mike would be best placed to comment.

Mike is now trialling the Bravo model stinger.

[kestrel]

They are designed by Dan Dufault. When I spoke with him this past fall, he was working on an upgraded model that would be stout enough for the Bearhawk.

[Helidesigner]

Does Dan Dufault work at Alaska Airframes?

[craig4place]

I have a dual shock on my 4 place and it works great. I matched it up to a matco 11" tailwheel. I got it from Dan last year at the Alaska Aviation Show. Dan sold the designs to AK Airframes. Just let them know you want a Bearhawk 4 place and they can get the correct model.

[whee]

Craig, I'm very interested in what your think of the Matco TW. That's the TW I wanted but I let people talk me out of it. I ended up with a Iron Designs that a friend gave me a great deal on. A 11" Matco and a stinger tail spring is what I hope to end up with eventually.

[craig4place]

Several friends here are using the 11" matco, it's on a BushCaddy for the last 2 years with no problems at all. I did have an issue with the tire, it wouldn't hold air. I didn't send it back, I put tire slime in it and it has held for the last 5 months with -20 temps to 40 degrees so far.

[Battson]

The following is reposted from Backcountry Pilot - Blackrock posted extensive information there, and I thought it would be helpful to have in this thread too:

The good review

As many of you know, I’ve been testing the T3 Tailwheel Suspension (dual shock) on a Bearhawk since mid-January and now, after two months of flying with it, wanted to provide an update.



This was a heavy snow winter so initial testing was done on a paved and plowed runway as shown in this previously posted video.

https://vimeo.com/152118904

I was very impressed by the performance and ability of the T3 to absorb landing impacts. Although I was confined to pavement early on, it was very clear that this was a big improvement over leaf springs.

The first chance to take it off pavement came with a camping trip to Death Valley. The two of us didn’t skimp on gear and with large distances between fuel stops we topped off with 70 gallons in Tonapah, NV, about 45 minutes from our camping spot, the Chicken Strip. We made an excursion without the camping gear to Stovepipe Wells and Furnace Creek the next day. Both are paved runways. The following day we loaded all the gear and headed to Panamint Springs (gravel strip), and Ballarat (dirt road landing). The Air Shocks performed very well. Maverick recommended Lizard Skins to cover the shocks so there would be less chance of getting minor pits and dings on the smooth shaft that the seals ride on.


http://shop.lizardskins.com/products...uspension-boot

I removed air shocks to test coil overs, then went on a one week, 2,000 mile trip to Baja Mexico. Heavy loads of maximum 2,700 lbs takeoff weight, 2,500 lbs maximum landing weight; 3 people, baggage, and 70 gallons of fuel. We made over a dozen landings on well graded dirt strips and one off strip desert landing in Arizona plus numerous pavement landings.



Since then, I've made several landings on remote Idaho desert airstrips and several landings on Elko Mountain. I’ll soon post a video of the T3 taking a pounding in Nevada.

Finally, the video showing some landings and takeoffs on a Elko Mountain is up!

Both air shocks and coil overs perform well. Air shocks require checking and adjusting pressures each day before flight. Coil overs don’t and can be adjusted by adjusting the spring pre-load by turning the large adjustment nut at the base of the coil spring and also have a rebound adjustment knob. I was able to turn mind by hand with the tailwheel off the ground.

The weight is comparable with the OEM spring weight:

Leaf Spring – 5lbs
T3 with Air Shocks – 5lbs
T3 with Coil Overs - 6lbs
T3 Steering – 1lb

To install this on a flying Bearhawk, I had to modify the rudder steering arm which is welded to the rudder. On most other planes, this arm is bolted on instead, so the next section only relates to a Bearhawk installation. It is much simpler on Cubs and others.

First, I took the rudder off the plane and used an acetylene torch and pliers to bend the moustache shaped rudder steering arms to horizontal. Then, I cut them off about 1/3 of the length from the rudder attach point. This is done so the rudder can hit the factory stops. Otherwise, the horizontal arms hit the fuselage and prevent the rudder from hitting the stops. In total, this mod only took about an hour so it’s pretty easy to do.





Since I was adding steering, I next drilled and bolted a new steering arm, affectionately named the “batwing” and provided by Dan to the old rudder arm stubs.



Then I made and added 3/16 spacer that goes between the T3 mounting plate and the 2-hole mount point on the fuselage to provide a little more clearance. This may not be needed in all cases as the unit just bolts on.

The steering is still being fine-tuned on my plane, and while it isn’t really needed. It does make taxing easier, especially in cross winds.



So to sum this all up, both the air shocks and coil overs work well and make the ride much smoother, air frame stresses are reduced, and the pilot is much happier not feeling the spring induced jarring and bounces. The weight is comparable to a spring so that isn’t much of a change or concern. Steering is a take it or leave it, but I will admit it is nice to have for long x-wind taxis. I’ve been hoping to make more off airport landings, but this was a bad snow year for us so I haven’t been off airport as much as I would have liked. I have put it through some abuse (as shown in the to be posted video) and it has held up well. In the 35 hours I’ve flown with it, it has performed very well and is holding up great.

It is too early to tell what the maintenance frequency will be long term, but it is easy to take apart and reassemble. Since this system has more moving parts, I assume there will be a maintenance requirement, but the suspension performance is enough to justify it my opinion. With the leaf spring, I was re-arching that at least once a year, and after two re-arches I would just order a new spring to avoid breakage from metal fatigue, so even leaf springs, as basic as they are, required annual maintenance too.

We recently measured the static tail height against Cowdog's and Maverick's Bearhawk which has a new leaf spring on it (for now at least, they will soon be ordering a T3). The T3 on my plane vs theirs was 1/2-inch lower. Since the range of movement in the T3 is greater it will be even lower with additional weight or load from acceleration and/or up elevator. The point being the wing angle of attack would increase, potentially allowing for shorter takeoffs. Other planes maybe different, but that has been my experience to date.

The more landings I make with this, the more I like it; there is no going back to leaf springs for me.

The in-service failure

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

[Battson]

I was initially excited by this product, now I am not so sure. Since hearing about the overloading / low cycle fatigue failure which Blackrock experienced, I am waiting until the results from the stinger testing come back, before I make a tail-spring decision. I also want the T3 fleet have been thoroughly tested before I would buy one.

[Helidesigner]

First off thanks for reposting the T3 report, and thanks to Blackrock for writing it. My initial impression is still favorable. When you load up 1200 lbs of useful load vs 1000 lbs that extra 200 lb most likely goes aft and really loads up the tail wheel. If the shocks were bottoming out it puts a very high load in the swing arm. I am not surprised that it broke under the repeated conditions described. I think between 1000 lb springs, keeping the struts at a stronger setting, and adhering to 2500 lbs for rough field operations, the T3 should hold up. The Bearhawk sits at about an 11 deg angle with 8:5x6 tires. If the T3 compression gives you one more degree that is 9% more lift at liftoff, or a 4% lower liftoff speed, probably about 1.5 kts. I'm not crazy about modifying the steering arms but it is doable. I got the bolt pattern dimensions from Alaska Airframes and confirmed it fits the Bearhawk.

[Helidesigner]

One other thought, a leaf spring and/or its mount may have failed under the same conditions and amount of use. It certainly would have come loose.

[jaredyates]

The Bearhawk is very hard on any tailwheel assembly for sure. My first question upon seeing the setup was how it is going to handle side loads, because it doesn't look like there is any provision to absorb a side load, as there would be with a stinger.

I wonder what we have to do to convince Mike to post that kind of stuff over here, or in the Beartracks... not to mention one of those awesome dirt landing pictures in the calendar. Being such a high-hour user, he's got gobs of good information about the Bearhawk.

[Helidesigner]

I was thinking the same thing about side loads but remember the tail wheel swivels if subjected to a side load at any speed which offers a lot of relief.

[jaredyates]

I was thinking the same thing about side loads but remember the tail wheel swivels if subjected to a side load at any speed which offers a lot of relief.

True, I wonder how that goes with the locking pin. There would be a delay while the arm is displaced far enough to disengage the locking pin, of a duration depending on the spring tension, rudder position, etc.

[Battson]

The Bearhawk is very hard on any tailwheel assembly for sure. My first question upon seeing the setup was how it is going to handle side loads, because it doesn't look like there is any provision to absorb a side load, as there would be with a stinger.

The leaf spring twists and bends as you taxi across a seriously rocky surface, even if you taxi slowly it deflects a lot under side loads.

In the weekend, I was walking behind my plane while it taxied over these rocks, watching the spring twist and thinking about a stinger vs leaf spring. The ability to twist is important off-airport.