Tailwheel spring design

[HoosierSMW 7]

My kit did not have a tailwheel spring so I am making one from 5160 1/4 x 1 1/4 bar. Before working on the actual spring I am mocking it up in mild steel to check for issues. This will be a two leaf spring but the mockup is just one. My original thought was to make a two bend spring to get a longer working section without raising the tail. Now I'm not sure if that is too long or if (with the shallower angle to the bottom of the rudder) that it may allow it to flex enough to hit the bottom of the rudder. Is this OK or should I just go with a single bend spring with a shorter working section? The tailwheel is a 6" pneumatic.

[1avidflyer 1983]

The longer spring will probably give just a tiny bit more/better  leverage for ground handling, course it puts more leverage against bending it as well.  I think the second leaf is in order.  Especially early on before one is really used to the plane.  Some landings then may not be as soft as some later on....   Maybe it's just the angel things are at, but it looks like the center pivot is angeling just a bit forward.  With weight on the spring, it will perhaps lay over more.  Maybe just a bit of bottom forward can be built in.  Not a lot, but some??? YMMV.   JImChuk

PS.  if you go with a second leaf, you will probably need two bolts holding the leaves in place.  At least that is easy to do without the plane being covered.  

Edited 28 Feb 2021 by 1avidflyer

[Dusty 126]

Your Spring may be a little long so will get a a weird looking sag in the straight part under normal use. By putting a constant curve in it ,this isn't so apparent.

I don't know your setup but Avid/Foxes are typically nose heavy( not so much 2 strokes)  so weight on the tail is a good thing. Extra leaves are advantageous with the benefit of still being able to fly and not having to repair a beat up rudder when a spring breaks.

I run two springs with three staggered /tapered overload springs.

[HoosierSMW 7]

Thanks for the input gentlemen

Jim, do you think the longer spring would put too much stress on the attach point? I was thinking it would allow more flex to protect the structure but may be wrong there. The vertical pivot is angling back a little and the spring does need to be bent a little more. I don't know how much the tail will sag when loaded so I will just have to experiment with that. I am going with two leaves as I don't think the single one will be strong enough. Would I weld in another tube to the spring bracket for the bolt to go through like the original bolt has?

Dusty, I like the idea of a continuous arc to the tailwheel but not sure if I have the equipment to form it. I have access to a press brake with radius dies but not that large of a radius. Our forming rolls may work but would be difficult to end up at an exact angle. I could probably use the press to make a final kink to get just the right angle. May need to play with that one. Sounds like a little shorter spring with the continuous arc would be ideal. 

 

[HoosierSMW 7]

I am using a 582 so hopefully won't need to add weight to the tail. If I do, I would want it to be useful weight (springs, reinforcements, etc.). I am also thinking about upgrading the tail feathers to MkIV size with a trim tab so that would add some weight as well.

[ChrisBolkan 130]

Just a thought. You might consider making the spring flat (tail as low as possible). Just high enough so the spring doesn't bump the rudder when it flexes hard. That will enable maximum angle of attack landing and taking off. 

Edited 1 Mar 2021 by ChrisBolkan

[1avidflyer 1983]

Not sure if its a plus or minus on longer spring for stress on fuselage.  Depends on how stiff the spring is I suppose.  Longer spring would put more pressure on fuselage, but if it's not to stiff would bend more also, so which is worse???  It's still more leverage though, so on second thought, longer may be the worse option for stress.   As far as the second bolt, I would put it as far back as you can just in front of where the two longerons meet.  Maybe a plate tacked on top of the longerons for the top of the bolt to set on.  On my Avid, I ground the head of the bolt, and it fits down in between the longerons.  The bolt will tie the lower spring to the upper one which is held in place by the channel it sets in.   JImChuk

[nlappos 413]

I had Wausau Spring make me a tail spring, they did a good job.

http://www.wausauspring.com/

 

[HoosierSMW 7]

I appreciate the information and lead. My ship is rigged for a 1 1/4” wide spring. Do you feel the single 5/16” thick spring is stiff enough? I was going to use two 1/4” thick leaves. Thanks.

[nlappos 413]

I appreciate the information and lead. My ship is rigged for a 1 1/4” wide spring. Do you feel the single 5/16” thick spring is stiff enough? I was going to use two 1/4” thick leaves. Thanks.

I used a double design, by having a second shorter spring bent to the same angle, but about 2" shorter than the main spring, and placed on top of the first. I clamped the two with a small sandwich to hold them in place, works fine. see the shot below

[allonsye 85]

 

Dusty, I like the idea of a continuous arc to the tailwheel but not sure if I have the equipment to form it. I have access to a press brake with radius dies but not that large of a radius. Our forming rolls may work but would be difficult to end up at an exact angle. I could probably use the press to make a final kink to get just the right angle. May need to play with that one. Sounds like a little shorter spring with the continuous arc would be ideal. 

 

No need for a press to form springs.  I use a 3 ton floor jack.  Run a length of chain under the jack, then bolt it on both ends of the leaf which you lay over the jack saddle.  I use 1 or 2" wide strips of plywood or a 1" wooden dowel as a buck or radius dies between the leaf and the saddle of the jack.  Position leaf accordingly as a you would in a press.  You might need a helper with a breaker bar jimmied into axles of the jack or a means of anchoring it to the ground while your pressing, rather "jacking". I've not needed to ...... yet.

 

Edited 8 Apr 2021 by allonsye