Tail spring mount replacement

Hi all,

I've managed to damage the tail wheel mount following a prop strike event. The hole through the mount holding the spring in place has become elongated so that the spring can rotate a small amount. I'm looking at the best way to replace it, but it looks like I'm going to have to de-rivet some of the rear skin to get the mount out, and the new one in. Not having built an RV (yet!) I just wanted to see if that thinking was correct, or to get advice from anyone else unfortunate enough to have had to do this!

Michael

Taper Pin

Hi Michael,
You might try replacing the through bolts with taper pins. You should be able to do that just using the existing access plates. If that doesn't work, you might consider installing one or more new access plates to accomplish the work instead of removing the skin.

My tail spring was a little loose when I bought the airplane and taper pins was the solution I considered. Fortunately though, all I had to do was tighten the existing bolts and the play went away.

Best regards,
Randy

Michael,
Randy has good advise above.

You most likely did not hurt the mount in the strike event. The normal wear has the bolt getting loose and the movement enlongates the bolt hole. So Randy advise should fix you up.

Replacing the mount will require small hands and lots of patients. Pretty sure the mount will come out the access hole but you may have to disconnect the elevator push rod to get room to let it pass. The mount is bolted in between the last two bulkheads.

If you find yourself needing to disassemble more of the tail, you can just remove the empenage. Vertical Stab first, then HS. Then you can unrivet the last bulkhead (a double bulkhead) and have perfect access to the mount.

If you get into this...it is a good time to consider switching to a full swivel tailwheel if you don't already have one. Plus there is a SB on the HS spar that can be accomplished as well.

Full disclousure, I did not build my plane but I did convert to full swivel tailwheel and years later installed a new empenage on my -6. While doing that I replaced the end bulkhead. While the bulkhead was out, I cleaned the tail assembly mount and repainted it. Then reassembled it.
Good luck.

Michael,

You can't remove the WD-409 weldment without removing the #12 bulkheads. It is sandwiched in tightly.

The tapered pin is a good fix. Send us an email and we can send you some part numbers for what is needed.

It may also be possible to upsize that bolt to a 7mm. Drill undersize then ream to size.

Follow Mr Frazier.

Hi

Ignore the guessers and follow Mr Frazier he knows what he is talking about.

I have just completed a repair on a 7 and there is no way the mount will come out without the rear bulkhead being removed. The suggestion of a taper pin or 7mm bolt are both good, that is what I would try first as there is a lot of work pulling off the empennage and drilling out the bulkhead

If you do drill out the bulkhead all the rivet holes will be enlarged. The first thing that happens when you set a rivet is that it swells and enlarges the hole, so you would probably have to go th mk319bs or 1/8 cheaters. It would be best to fit new bulkheads because of this.

Do not be tempted to enlarge the access holes unless you put additional stiffeners in as making the access hole s larger takes away skin which is transmitting the load from the rear bulkhead through the mount to the second bulkhead.

There is a thread on repairs carried out on a number of sevens where the rear fuselage skins have bulges because of the larger access panels and reduction in skin carrying the load. That us why I had to do the repair on the 7, skin bulging allowing the spring to move up and the tailwheel to hit and break the bottom ruder fairing.

I would Go for the taper pin or 7 mm bolt option first, but it's your call.

Thanks for all the great replies.

I'd already removed the vertical fin and elevator control tube to get access to all the bolts, and did find that the mount won't come out without removing one of the bulkheads as it is held in so tightly.

The tapered pin or enlarged hole would certainly be my preferred option, so will speak to my inspector about going down this route first. I'll need to measure up the bottom hole to see just how badly it is elongated first though!

If we do end up having to remove the rear bulkhead I think I'd certainly choose to replace it.

I think the damage to the mount was largely due to the fact that we do have a full swivel tailwheel and it was at almost 90 degrees to the tailspring as I was doing a tight turn at the time. This means there would of been quite a load on the side of the retaining bolt when the tail came back down...