Maule Tailwheel kingpin alignment

[flyingfool]

Can anyone tell me on an 11AC what angle the kingpin should be? I have a Pneumatic 8" wheel.

My questions are:

1) Should the top of the pin be forward or aft of vertical? And by how much?

2) How do you check the angle? Is it just eyeball?

3) What kind of weight should be in the airplane? Should it be empty, gross weight or somewhere in between or does it even matter?

4) If the angle is not correct, how do you bend the spring? Can you just put it in a vise or metal brake and bend it cold? Or do you have to bring it to an automobile spring place and have it bent and heated or re-heat treated after a bend?

5) How do you know if your steel springs are just plane worn out/fatigued and need replacement?

6) If I fly mostly off grass, would a solid rubber wheel be better? Or maybe the better question, is a solid rubber better in general whether on grass or pavement? Which resistst shimmey better?

Sorry for the long list.

Tom

[Nathan K. Hammond]

Hey Tom, great questions!

The king-pin should have a negative angle (top = aft). As for how much is hard to say; but it needs to stay negative when you've got the back of the airplane loaded with gear and passengers, assume the heaviest weight you could carry. If the king-pin goes positive, typically at a heavy weight, the tail wheel will shimmy.

You can try to bend it yourself, and if you don't have to gain much angle, it shouldn't be too hard. But it's just as easy to take it too a spring shop and have them do it for you. There's no need to heat treat the spring after bending it. It will cost maybe $10 to bend it; or $120 to replace: if you re-arch it and find it's flattened back out next annual, you know it's time to replace. Generally speaking, you can re-arch a spring 2 or 3 times before it's shot; or a leaf cracks.

Solid rubber or pneumatic....... They're both fine tail wheels. The solid rubber will resist shimmeing a little bit more because it sits lower and has a better king-pin angle. The large pneumatic is nice for grass because it can absorb more bumps and smooth things out.

Personally, I preffer the smaller tailwheel for day to day use, but install a larger 8" Maule / Scott 3200 if I'm going off airport or into REALLY soft ground/sand.

Check out this artical from Steve Pierce...
http://www.pierceaero.net/tws.php


nkh

[Ted Karver]

Tom,

Can not add anything to what Nathan said except to recommend a tail wheel that I've had no shimmy with since putting on my champ. Contact Aviation Products at (806) 646-6042.

Ted

[flyingfool]

Thanks guys. I'm a bit surprised that the top of pin needs to be aft or negative. But if that is the way it needs to be then it just shows my lack of experience in this area.

I only got my airplane on Saturday and only have flown it 1.6 hours. The previous owner said that it will only shimmy a little when you are too fast on landing. And I found that to be true at least in the entire 8 landings that I've made.

So I think that the alignmnet etc is close. The previous owner said that he bent the spring a little. Maybe just a degree or two more is all that I would need to eliminate the shimmy altogether. But I don't think I'll do anything until I get more experience and can determine a pattern.

[Paul Agaliotis]

Ted,
I've used many of their tail wheels. I don't know of any better wheels on the market. ACA has started using them on their 7EC. I'm not sure I would use one on a Citabria. I'd have to use it on my plane first.
It's good to see other satisfied customers.
Paul

[Wheeler]

A friend gave me a Maule tailwheel today, he said it shimmied on his plane and purchase a new tail wheel. I put it on my Champ and it does the same for me! The kingpin bushing is loose, I have no idea what is too loose or what is causing the shimmy. The wheel had 20 psi, I will try 10 psi in the morning. here are pix, any advice will be of great help.

[Mikek]

Ok, just looking at the pictures:

Side view:

1. Both compression springs could use less slack, left one one link,
right two links.

2. If this is when it has 200 # in rear just in proper alignment but if
empty might need more arch.

Rear view:

1. Wheel leans way to much to the right at the top, Three problems?:

A. Spring is slightly twisted due to leaf spring weak or not properly
bolted at frame.

B. "U" clamp loose or missing pad.

C. Also looks like part of the lean to the side is due to the wheel
bearing loose or bad fit.

I would raise the tail and but it on a saw horse with a pad just forward of the main bolt into the frame, when get a hold of the wheel and see if it is tightly mounted.

Mike k

A friend gave me a Maule tailwheel today, he said it shimmied on his plane and purchase a new tail wheel. I put it on my Champ and it does the same for me! The kingpin bushing is loose, I have no idea what is too loose or what is causing the shimmy. The wheel had 20 psi, I will try 10 psi in the morning. here are pix, any advice will be of great help.

[joea]

Mike,

Glanced at the pics and agree with your findings. The spring needs more arch, especially if the plane is empty when the picture is taken.

Also the alignment of the wheel from the rear is off, with its being canted to the right for some reason.

Wheeler, either get a new spring or take the old one off and take it to a truck spring place and get it re-arched. Do NOT tell them its for an airplane unless you know them well.

Would check the other things that Mike mentioned.

Joe

[Wheeler]

Thanks for the info. I will make some changes and let you know how it works.

[Tim Juhl]

I've had three tailwheels on my Champ in 24 years - The first was a Scott 2200 solid which I didn't care for. I later replaced it with a pneumatic maule and later a pneumatic maule tundra tailwheel. The maules have been excellent - never a shimmy. The first maule was very old, built when Maule was in Napoleon, Michigan. I eventually decided to rebuild it and was going to do so when somebody decided to put a Scott 3200 on their starduster and made me a good deal on the maule tundra. The same guy didn't like the Scott either and later found his problem wasn't with the tailwheel

Good luck!

Tim

[gusc]

Wheeler,

The Maule is a very good tail wheel but has taken an undeserved rap. I've used them for 30 years on two different airplanes.

The only two things I know of that will cause a Maule to shimmy are the wrong spring or angle and a worn main shaft bushing. The main shaft bushings don't last long but are cheap and easy to replace(be sure to drill the hole for the Zerke fitting). The Maule will tolerate no wear in the bushing or shaft but the shaft is steel and the bushing is bronze so the shaft seldom wears. The good part is Maule part prices are reasonable.

The wheel bearings do wear but not if you don't let it shimmy very much. The last ones I replaced I used inexpensive sealed bearings made for a lawn tractor so I eliminated the Zerke. The bearing p/n is 1621-2RS. 1621 is the core bearing number.

[MikeB]

I'm still playing with the TW shimmy problem or moreso thinking about it but I sometimes wonder if the problem can't be caused by tailwheel springs that are a combination of being too tight and uneven strength. Thus causing the TW to contact the ground at a crooked angle and somewhat 'sideways' so it kind of 'skips' along and doesn't necessary track. I know Maule makes the 'anti shimmy' spring setup but I haven't much luck with it. Right now I'm using regular tension springs without a whole lot of pressure and it seems to be working OK, even on hard surface.

Mike

[flyingfool]

Mike. You may have provided the cause for my shimmy.

I recently put in eyebolts and took out the slack in the tailwheel compression springs. The only way we were able to get the springs to adjust was to have more pressure on one spring than the other. One side has ZERO chain links. If I put one link on, it would go slack. The other side we had to get the adjustment the best we could get to balance between slack and too much.

The ground handeling now that the slack is removed has improved significantly. however when landing on pavement I notice shimmy nearly every time. Your theory of a slightly out of perfect alignment makes some sense.

Any solutions?

I will try to take pictures of my tailwheel springs etc and post them to see if I have other issues to deal with. I'm also thinking as my first post on this thread that I may need a re-bent leaf spring or new spring to get more arch.

Tom

[MikeB]

No Solutions other than jacking up the rear and seeing how the TW sits in relationship to the centerline. I'm back to my little Firestone TW right now as I gave up on the Maule temporarily. There has to be a solution but I think I've tried every suggestion that anyone has made. Obviously you need some tension so the springs don't kick off if it does shimmy (been there and done that ). Technically, I guess it should self center as there's a certain amount of side to side motion allowed, although there's a Sonex tail dragger being built on our field and I believe it's direct linked to the rudder controls.

After spending a couple hundred dollars for the Maule TW and being somewhat of a tight Norwegien I'm not about to buy another TW unless it's absolutely necessary. The ##%%** thing should work.

Mike

[gusc]

Mike,

My Champ came with TW compression springs which are installed with no tension on the springs and they work great.

No, they don't fall off if the TW shimmies if properly installed. Tension springs can't be secured because the attachment loop is open. If one comes off the other quickly follows, been there.

Wish I had used them years ago on my Stinson. I really got tired of trying to guess which tension spring should have the most tension and how much!