tail wheel springs

[herman pahls 9]

I would like a stiffer tailwheel spring than the 2 leaf by 1-1/4 wide I currently have that will not raise the tail and lose angle of incidence.

Kitfox offers a 3 leaf for their newer higher gross weight Models.

What are you Avid flyers using and where do you source them?

Thanks Herman

 

 

[FoxDB 17]

Herman,

My 2 leaf tailwheel spring broke and I replaced it with the Kitfox 3 Leaf. I did not notice enough angle change to worry about. Here is a link to the discussion on teamkitfox: http://www.teamkitfox.com/Forums/showthread.php?t=3007&highlight=broken+tailwheel+spring

Dave

[IFMT 36]

The kitfox 3 leaf is 1 1/4 wide versus the 1 1/2 avid. You will need to bend a shim to wrap around the kitfox spring to make it work. The geometry will be off on the avid so your wheel will not track neutral. I bought one and tried it but I wasn't satisfied with the result. Went down to the local machine shop and got a heavy duty one bent. Used the old avid single spring as a backer for it. I have a lot of extra weight on the tail to counter my soob engine. Have not had trouble since.

Edited 9 Mar 2014 by IFMT

[lostman 198]

While we are on this subject I noticed after trying to install a Matco tailwheel on Pursang that it was not arched enough. IFMT talked about getting his done at a local machine shop. Does that mean you can just put them in a press and slight add arch to the bend to re-arch? I've never really thought about doing it that way. It would be nice to know instead of having to send it off to be done by some a spring shop.

[Av8r3400 1179]

Yes.  Most of these springs are not heat treated and can be re-arched fairly easily.

[akflyer 1427]

I re-arched mine in a press a few weeks ago... if we were smart, we would do our own re-arch so we get the angle just perfect, then take them to the spring shop to have them cooked and tempered so they will actually hold that arch.

 

[lostman 198]

I was wondering about that this morning actually. I may have to find a spring shop in the area....oh yeah, and a shop press since I don't have one or know a single person here.

[1avidflyer 1983]

Funny how it goes, but I was re arching a tail spring yesterday.  I have one of those Northern Tool 20 ton presses,  and it worked nice.  Had a 2X6 on the bed of the press, used 2 long 3/4" bolts that sat on the 2X6, and one long 3/4" bolt on top of the spring that the press pushed down on.  The bottom bolts would push into the wood and didn't want to roll away when the spring started to bend down like they would have if they were setting on steel.  Worked real good.  Hopefully that makes the tailwheel shimmy go away.  Jim Chuk

[herman pahls 9]

Thanks for the tail wheel spring info..

The consensus seems to be the Kitfox 3 leaf so I will order one.

I also store my Kitfox wings folded and the Matco 8" tailwheel leverages the spring more than the stock Maule 6" wheel.

Herman

 

[dholly 718]

Herman - I put a comparison pic of the different tail springs here > http://www.avidfoxflyers.com/index.php?/topic/1192-new-3-leaf-tailspring-and-api-tailwheel-upgrade/

[herman pahls 9]

Hello Doug

Your spring comparison photo was just what I needed.

I was concerned that the 3 leaf spring would raise my tail more than the 2 leaf and it appears it will not. 

The 8" wide Matco tire is a  huge improvement in the sand but unfortunately it raises the tail  2" higher than when the 6" hard rubber Maule tail wheel is installed.

I was hoping the 3  leaf would not raise the tail even more.

The more Angle of Attack my Kitfox has the shorter it takes of and lands.

 

I just read the info. on your recent aircraft purchases.

Sounds like you have owned several Rotax 912's .

Let me know if you know of one for sale.

 

 

Thanks again

Herman

[Av8r3400 1179]

Herman-- any progress on your decision about the "Italian Job"?

[herman pahls 9]

Hi Larry

I am having a hard time getting excited about a project 2500 miles away.

I am curious why if it is a good deal why it has not sold yet.

Maybe it has.

Herman

[lostman 198]

Can anyone tell me the "correct" angle to have on the tail spring? I got talking to the owner of the airport yesterday and he offered me the use of the shop press he had hidden in another building so now I can rearch the spring! I know it's sprung out enough that I can't use the Matco tailwheel due to the lack of angle causing an interference with the tire and control horns. I'm sure it's not correct geometry the way it sits with the old Maule tailwheel either.

[akflyer 1427]

It depends on the tail wheel head you have. I uses a protractor to figure out how much I needed to bend mine to make the king pin on the tail wheel line up with the rudder.

[1avidflyer 1983]

There was a good article in the last Sport Aviation magazine about tailwheels and correct castor and such.  In there, is said the bottom of the verticle axle should be ahead of the top.  As the spring gets bent to far, the bottom of the verticle axle gets behind the top and that is one of the main problems causing tail wheel shimmy.  Just googled it and found this picture which describes what I was trying to say.  JIm Chuk

[Trackwelder 12]

Just or general information I have had spring shops re-arch my truck springs without heat treating and they have held up for years do not be afraid to use the press

[Av8r3400 1179]

If you have a local spring shop, just re arch the main leaf to where you need it and have them make you two more making a three leaf pack. That's what we did, then we had them make two more complete packs to match. I think it cost $100 total.

[EDMO 1078]

Jim,

       I read that article too - and I am probably one of the last to claim to be an expert on tailwheels - However, I have studied two or three books on this subject, and they all disagree with that article on that subject.

       Pazmany, the engineer who wrote the book on landing gears, says just the opposite, as I understand it.

When the top of the pivot bolt is ahead of the bottom end, the tailwheel is stabile in its center track - any turning of the tailwheel raises the tail and the force of that tends to re-center the tailwheel.   That sounds logical to me.

This angle should be about 5 degrees.

       When the top of the bolt is behind the bottom, the tailwheel is in an unstabile position, and it is free to wobble to either side, and the weight of the tail tries to push it off center.

My castoring nose gear is set up according to Pazmany's engineering theories.

       Also, when the distance from the center of the pivot bolt to the axle is less than one radius of the wheel, there is more tendency to shimmy without some dampener - as you get less than 60% of wheel radius, this becomes critical.

      I don't mean this as a cure - we are currently trying to find the cause of the shimmy on the J3 tailwheel, but believe it is because of misalignment of the main gear which makes the tail track off center.

      I don't like to write things which may not help and are conflicting with other posts, but this is what I read.

EDMO

Edited 16 Mar 2014 by Ed In Missouri

[Av8r3400 1179]

Remember on the tailwheel what happens to the caster of the king pin as the spring compresses. This is something often overlooked. A free hanging tailwheel with a little under caster would be near perfectly perpendicular (optimal) to the ground once a little weight is placed on it.

[lostman 198]

Thanks all! Great information. I guess I'll just get out the protractor and figure it out, bend it a little bit over so it's nearly perpendicular to the ground and call it good.

 

I have no shimmy at all right now and certainly don't want to cause any but I would like to set it up so I can use the Matco tailwheel that I have. I'm also still considering the 8" from them but really can't justify spending the money on it until I get the flight characteristics in check first.

[EDMO 1078]

I would agree that the tailwheel should be set so that it is in the right position when the plane is loaded.

I have seen drawings that show the spring bent enough from a load so that nothing sets right.

EDMo

Edited 16 Mar 2014 by Ed In Missouri

[lostman 198]

I re-arched the tail springs on the Pursang yesterday and think I might have gone just a bit too far for the current spring. without a load on the spring (tail down), I have just a couple degrees rake with the bottom of the bolt pointing slightly forward. However I think it will be just about perfect for the Matco tailwheel. I'm still thinking I won't change it out until I test fly the plane from a few other things but I did find that Matco tells you in their technical literature that the spring will be at a 45 degree angle to make the pivot point perpendicular to the ground. At least that's a start!

[Tree top pilot 13]

I have made my own tailspring from 1.24" X 6mm titanium. Formed over a 6 " radius - limit of radii for that thickness cold bending. Single leaf as my MTOW will be less than 600lds. If you bend one....make sure there are no sanding marks or anything else on the edges of both sides before hand...sand and polish mirror finish. This is where the cracks will begin as it does it's job over cycling a lot. Made the wheel on the CNC with a urethane convoluted tire. Machined the arm and block from 7075 ally...with a bronze bushing. I have not done the math for anything over 600lds service duty....I am sure a 4mm top leaf would bolster it more than enough. Just food for thought on saving weight....cut off more than 2 lds. with my setup.

[akflyer 1427]

TTP that looks sweet!  I wish I could go to a lighter tail spring, but I need all the weight I can get back there.