Tundra Tailwheel Update

[Enewton57]

Hi Everyone,

I have had a lot of people expressing an interest in the Bearhawk Tundra Tailwheel. So I tasked Bob Barrows with designing a Tundra version of his famous Bearhawk Tailwheel. A couple of changes were made to accomodate the larger and wider tire used on the Tundra and to strengthen it to take more abuse.

First the wheel had to be made 1" wider to accommodate the wider tire.

Second, the forks had to be spread wider and also made longer to account for the 12" tire diameter.

Because of the added stress on the forks, Bob increased the wall thickness on 4130 tubing used to make the fork assembly and the fork cross tube at the top.

The kingpin had to be angled slightly more as we found the larger tire wasn't clearing the Round Tailspring rod on the Patrol version, when you turned it all the around backward.

The forks are designed to leave only a 1/8" to 3/16" gap between the tire and the forks and between the cross tube and the top of the tire. This helps prevent you from getting rocks jammed in there and locking your tailwheel up when you are doing those riverbed landings.

Lastly, if you look closely at the tailwheel body, you will see that we've added a friction adjustment device. Its a Bronze bolt with jam nut. If you find that you are getting some shimmy on asphalt, you can slightly tighten it and create a little more friction in the pivot. That will reduce the tendency of your tailwheel to shimmy.

I am not quite ready to start selling these yet. I have shipped the prototype of the Bearhawk Tundra Tailwheel to Bob for testing and his approval. Bob should have it next week, so anyone attending Bob's cookout will be able to see it in person.

I am hoping to start offering these for sale in November or December, depending on how well the testing goes.

I will post up another announcement to the group when I am ready to start offering these for sale. I just wanted to let Y'all know that I'm working on it as promised. see pictures below.

[Enewton57]

Forgot to add - the pictures show a comparison of the Tundra with the 8" Bearhawk Tailwheel.

The 8" Tailwheel weighs 7 Lbs., 15 oz. The Tundra Tailwheel weighs 8 Lbs., 7 oz.

[Battson]

Hi Eric - very interesting development.

Do those weights include the tire? What brand of tires are you using? Are they still run at 60psi?

Any chance of a comparison to the 10" tailwheel. I guess that most who are interested in the tundra option will currently be using the larger 10" option.

Floatation is a huge issue. I often land on sand, mud, or gravel where the 26" mains ride high but the tailwheel acts like an anchor.

Anyone serious about flying the BH off airport should definitely have one of these.

[Enewton57]

Yes that's the weight with paint, wheel tube and tire. The 10" weight is right at 8 Lbs. The tundra tire is about 1" wider than the 10" so it should do a better job at riding on top of soft surfaces rather than digging in. I would run the inflation at about 20 psi or maybe even less. The tire is a 400 x 4 Aero-Classic 8 ply with Leakguard tube Eric Newton - Long Beach, MS http://mybearhawk.com

[bestbearhawk1231]

Eric, will Bob be providing an engineering bulletin for regarding the changes to the tailwheel? I currently hold the plans for the tailwheel and am interested in the differences over the 8"/10" version, thanks.

[DRLPatrol]

Ditto

Doug

[Enewton57]

That's a question for Bob. I just asked him to help me with suggestions for modifications that I can add to the Tailwheels that I manufacture and sell. I wanted to make sure that I can minimize shimmy tendencies for the ones that I sell. I don't know if Bob wants to make a design change to the basic Tailwheel design or not. Eric Newton - Long Beach, MS http://mybearhawk.com

[Chewie]

Eric,
Generally speaking, what controls shimmy? I recall reading somewhere that a major contributor is the angle between the pivot axis and the line between the axle and the contact point on the ground. Kinda made sense in theory but you have the practical design experience; curious on you thoughts (unless of course it's proprietary!).

[Battson]

Eric, I would also be interested to hear about any loss of cruise speed, or increase in fuel burn, which you experience during the testing phase.

The guys running the Baby Bushwheel tailwheel on Maules report that it creates a measurable change. I wonder how this one will compare. Either way, I want one!

[Enewton57]

Eric,
Generally speaking, what controls shimmy? I recall reading somewhere that a major contributor is the angle between the pivot axis and the line between the axle and the contact point on the ground. Kinda made sense in theory but you have the practical design experience; curious on you thoughts (unless of course it's proprietary!).

Hi Mark,

There are a couple of things you can do to make your tailwheel have less of a tendency to shimmy:

1. Load your airplane up to gross weight and maximum aft CG that you can. (important - don't take this measurement with your airplane empty). Now take a carpenter's square and set it on the shop floor next to your tailwheel. The kingpin (which aligns with the tailwheel body) should be either perpendicular with the shop floor, or leaned slightly back at the top. I have seen several airplanes cure their shimmy issues by adjusting this angle. Here is a write up on it with pictures. http://mybearhawk.com/flying/shimmy.html

2. Lift up the tail and block it up so the tailwheel is hanging free off the ground. Remove the steering springs. Now turn the tailwheel left or right until it unlocks and turns around 360 degrees. Now turn it back and forth left to right. There should be a slight amount of drag. If it pivots freely and you can just spin around easily, then you have no friction at all in the system. You need to have a little friction or it will just be free castoring like an annoying shopping cart wheel. Tailwheels with no friction are m ore likely to shimmy.

3. Now spin the tire on the axle. Remeber how we were taught on cars to tighten the axle nut until the tire turns hard and then back it off until it spins free? Not so on your tailwheel. It helps to have just a bit of friction. When you spin the tire, it shouldn't spin more that one full revolution before coming to a stop.

All of that said, any tailwheel will shimmy given the right (or should I say "wrong") circumstances. Heavily grooved runways, crosswind 3-point landings where the tailwheel is turned slightly at the point of contact with the runway, hard bounced in landings with a little side slip at touchdown, can all set up a shimmy in the tailwheel. If you feel your tailwheel starting to shimmy, get the stick forward and get the weight off of it until you slow down a bit.

I hope this helps.

[Enewton57]

Eric,
Generally speaking, what controls shimmy? I recall reading somewhere that a major contributor is the angle between the pivot axis and the line between the axle and the contact point on the ground. Kinda made sense in theory but you have the practical design experience; curious on you thoughts (unless of course it's proprietary!).

Hi Jonathan,

I would be surprised if it makes much difference at all. I use the same body but the tire is 2" more diameter and 1" wider. I guess it could make a very small difference in lower powered aircraft. I will ask Bob if he can test that as well when he does the test flying.

[DRLPatrol]

"...The kingpin (which aligns with the tailwheel body) should be either perpendicular with the shop floor, or leaned slightlty forward at the top...."
Eric, don't you have that backwards. Your link, if I read it right, agrees with what I always thought. Slightly back at the top, forward at the bottom.

Doug

[marcusofcotton]

Ditto. Gilbert Pierce has written on this as well, a search on Supercub.org and shortwing Piper sites among others should turn up his info. I think that may be where Eric's pictures originated.

Mark J

[Chewie]

http://mybearhawk.com/flying/shimmy.html

Yes, that's the one! Thanks. Also found that diagram (and a bunch of other juicy bits) in Budd Davisson's Shop Talk, SportAviation January 2014.

[Enewton57]

"...The kingpin (which aligns with the tailwheel body) should be either perpendicular with the shop floor, or leaned slightlty forward at the top...." Eric, don't you have that backwards. Your link, if I read it right, agrees with what I always thought. Slightly back at the top, forward at the bottom. Doug

Yes - I did get itbackwards, sorry. The kingpin should be straight up and down or leaned slightly back at the top, not forward. Thanks for catching that. I will correct the original post.

[Battson]

I have my BH tailwheel installed as it came 'out of the box', without any mods / tuning. I have never had a single shimmy problem, they are a top of the line tailwheel from where I am sitting.

[Enewton57]

I have my BH tailwheel installed as it came 'out of the box', without any mods / tuning. I have never had a single shimmy problem, they are a top of the line tailwheel from where I am sitting.

Thank you Jonathon. I cant think of a better endosement from a better person. The type of flying that you do speaks volumes about the durability and toughness of these tailwheels. I appreciate your positive comments.