Modifying my tailwheel while minimizing distortion.

[whee]

I have a Iron Designs 400x4 tailwheel that was built for a flat tail spring. Since purchasing it I have decided to use a tapered rod tail spring. Iron Designs originally said he would make me a new body to accommodate the stinger but he has since gone AWOL and I'm tired of trying to nail him down. I've decided to modify my existing tailwheel by cutting off the existing spring mount and welding on a new stinger mount. I have the TW drawings from Bob in hand. Mig welding will reduce the heat input and if I keep the body in an oil bath with only the portion being welded exposed it should further minimize distortion.

Anyone have any other ideas on how I can do this successfully? What do you think my chances for success are? Success = the distortion is small enough that the TW is functional when done. I'm thinking a little better than 50/50.

[S Lathrop]

Don't MIG weld.

When I have to weld around bearing bores I use a aluminum or brass plug the exact diameter of the bearing but longer. I then weld in short steps and allow the part to cool enough to touch in between each step. I have placed a wet rag over the inserts to speed the process. I would only use TIG welding. You are welding thick materials and it might take several passes to fully weld the part. With TIG you have infinitely better control of the heat, weld from and quality than you do with MIG. And you can better control the heating and cooling process as you weld.

[Bdflies]

First time I read Whee's post, I'll confess to a bit of confusion. A little more study and I think I understand the question. My concern isn’t so much about which process to use, it’s the thought that the stinger receptacle would be butt welded to the body, in a manner not designed nor tested. With the tailwheel cantilevered off the back of the rod, your weld will be subjected to an impact test every landing. Welds are well suited for tension and compression applications, but less reliable in 'bending'.

I think I'd try to get an adapter made with a rod receptacle that would bolt to the existing spring pad. My $0.02

Bill

[jaredyates]

Another option is that I've got a tailwheel body designed for a rod spring on the shelf. I was planning to convert to the round spring using the adapter that bolts onto the airplane end, but after a few cracked tailposts Bob issued the safety update and advised against it otherwise. I'm not needing the round spring mod bad enough to weld the tail post, so I have the extra parts. Currently they are assembled to the tundra wheel which I might could also be convinced to part with. I'm not positive that Eric's body will work with Scott's fork, but if it didn't, you'd only be out the shipping.

[whee]

Don't MIG weld.

When I have to weld around bearing bores I use a aluminum or brass plug the exact diameter of the bearing but longer. I then weld in short steps and allow the part to cool enough to touch in between each step. I have placed a wet rag over the inserts to speed the process. I would only use TIG welding. You are welding thick materials and it might take several passes to fully weld the part. With TIG you have infinitely better control of the heat, weld from and quality than you do with MIG. And you can better control the heating and cooling process as you weld.

Thanks you for your input. A brass or copper plug would be my desired heat sink but I don't have any of adequate size.

The material being welded are 0.125" 0.120" and 0.190" which can be welded with a single pass. I agree that it must be welded in short sections and allowed to cool between each section.

First time I read Whee's post, I'll confess to a bit of confusion. A little more study and I think I understand the question. My concern isn’t so much about which process to use, it’s the thought that the stinger receptacle would be butt welded to the body, in a manner not designed nor tested. With the tailwheel cantilevered off the back of the rod, your weld will be subjected to an impact test every landing. Welds are well suited for tension and compression applications, but less reliable in 'bending'.

I think I'd try to get an adapter made with a rod receptacle that would bolt to the existing spring pad. My $0.02

Sorry I confused you Bill. I left a lot of detail out of the post because I didn't think they were necessary, maybe I was wrong.

As far as the stinger receptacle being butt welded to the tailwheel body; that is exactly how Bob designed it so it will be done as designed and tested. The only unknown here is if I can do it without warping the tailwheel body.

Another option is that I've got a tailwheel body designed for a rod spring on the shelf. I was planning to convert to the round spring using the adapter that bolts onto the airplane end, but after a few cracked tailposts Bob issued the safety update and advised against it otherwise. I'm not needing the round spring mod bad enough to weld the tail post, so I have the extra parts. Currently they are assembled to the tundra wheel which I might could also be convinced to part with. I'm not positive that Eric's body will work with Scott's fork, but if it didn't, you'd only be out the shipping.

Thanks Jared! Replacing the TW body is my preferred path. I asked Eric about using his but he didn't know if it would work. I'll take my TW apart and compare it to the drawings and send you a PM.

[Peter Girard]

400x4 tire

[whee]

Peter, That doesn't look like a 400x4 to me. It looks like a standard tailwheel tire; either a 350x4 or 250x4.

Here is my 400x4 TW

[Mark Moyle]

Scott did offer a stinger type tail wheel that bolted to the spring mount..pad at the rudder post and single bolt through the bushing.. I’ll ask Marv if he’s spoken with Scott recently.

Mig welding even short cold beads will guarantee the creation of martensite crystals along the perimeter of the weld...which is where it will crack. Post heating the area to a dull red, cooling slowly will change the crystal structure of the steel...to a finer crystal or grain structure which is much less likely to crack..

[PaulSA]

With the 4-place Bravo, there were some initial issues with the strength in that area when they changed to a stinger and used an adapter and some mods were mandated. It may not be quite as simple as you might think.

[whee]

Mig welding even short cold beads will guarantee the creation of martensite crystals along the perimeter of the weld...which is where it will crack. Post heating the area to a dull red, cooling slowly will change the crystal structure of the steel...to a finer crystal or grain structure which is much less likely to crack..

Absolutely right. But post heating is almost guaranteed to warp the body to a point where it won't be usable.

With the 4-place Bravo, there were some initial issues with the strength in that area when they changed to a stinger and used an adapter and some mods were mandated. It may not be quite as simple as you might think.

Tail post mods have already been done.