Tailwheel Bolts

spiro · Post by **spiro** » Tue Apr 06, 2004 10:10 am

A few weeks ago I broke the AN7 bolt that holds the tailwheel onto the tailspring. This is the 3rd time I've broken one. They've all failed in tension, near the threaded end, either at the 1st thread or at a stress riser crack at the bottom face of the spring. 2 of these 3 incidents were on skis, in rough terrain, when the tailski flipped over and started plowing.

I bring this up because several posts on this forum have avocated the periodic replacement of tailsprings. I've never broken a tailspring but I've snapped 3 of these bolts, so I'd argue for periodic replacement of them as well. The consequences of either failure are similar.

This is the same bolt that George is trying to find eyebolt replacements for. Hopefully the welding of the ring onto the bolt head won't affect the strength of the shank at the other end. In any case I'd certainly install them ring side up.

- paul

Roesbery · Post by **Roesbery** » Tue Apr 06, 2004 3:18 pm

Don't know what your ski setup is, But mine have a saftey cable to prevent the ski from flipping.

spiro · Post by **spiro** » Wed Apr 07, 2004 4:08 am

standard Landis setup w/ safety cable installed on the fork per the drawings. Doesn't prevent it from flipping, only from losing it when something else breaks. I've looked at this pretty hard for a better solution, a better attachment point would prevent the full-swivel action. Both Burl's and Fluidyne's have better setups for a true safety, but they're more than a mere cable.

Roesbery · Post by **Roesbery** » Wed Apr 07, 2004 2:45 pm

Mine is the old Federal wheel ski setup, have never had a problem.

Post by **GAHorn** » Wed Apr 07, 2004 5:58 pm

Paul, years ago (so I don't remember if the part was correct or not) that bolt broke on a Cessna 140 while landing in front of an airliner that had to go around. The owner of the company stated it was a common problem to the entire fleet of pipeline 140's. So I agree that the bolt should be periodically replaced. I arbitrarily recommend 500 hours for both tailwheel mainspring and bolt based upon anecdotal evidence they tend to let go between 700 and 1000 hours.
The bolt is an AN7-20A bolt (undrilled but a drilled AN7-20 should theoretically be no disadvantage.) Hopefully I will soon have a new aircraft hardware manufacturer who will be making a ready source for the mooring-ring bolts.

spiro · Post by **spiro** » Thu Apr 08, 2004 7:39 am

fwiw, mine takes an AN7-22A, the extra length accomodating washers under both bolt head and nut as well as some shims on that spacer between tailwheel and tailspring (as discussed in a parallel thread).

zero.one.victor · Post by **zero.one.victor** » Thu Apr 08, 2004 5:13 pm

I might be interested in buying an eyebolt if the price is reasonable. $21 seems kinda steep,considering my Spruce catalog has the (non-eye) AN7-22 (couldn't find AN7-22A) for less than 4 bucks.
I generally tie the tail down by putting the wheel right on top of the tiedown ring & wrapping my rope thru the ring & around the top of the tire,
topping it off with a big square knot. Pretty easy,and the rope (my own!) doesn't get all greasy.
BTW,is the eyebolt usually mounted eye-up or eye-down?

Eric

Post by **GAHorn** » Thu Apr 08, 2004 9:38 pm

First of all, it's been pointed out that the Cessna PN 0642105, "eyebolt" is not really and eyebolt, despite the IPC's misnomer. It's a mooring ring/bolt. An AN eyebolt is virtually without a head and has a thinner cross-section of the ring, being intended primarily for attachment of other AN hardware rather than tie down ropes.
The L-19 IPC shows it mounted eye-down, but several Army and Air Force mechanics told me the first thing they did in the field was reverse it and place it eye-up. They explained that the fuselages were somtimes shipped less the wings and the fuselage was tied down in-place using freight tie downs to a point immediately beneath the fuselage, but when tied down at airports the rope anchors were located, as we all know, at some distance away, and required the rope be attached on top of the tailwheel.
The bolt doesn't care.
Paul, extra washers/shims may have been used because the different bolt is being used. The original bolt called for is AN7-20A.

Dave Clark · Post by **Dave Clark** » Fri Apr 09, 2004 1:35 pm

I just did my annual teardown, cleanup, and regrease of the TW assembly. My bolt is an AN7-20A and has a standard washer under the head and nut. Interesting that it was only a couple of years old but showed a little wear and since I had another I replaced it. Couldn't wait on my eyebolt on order George

Seriously I apreciate very much the work you're doing getting these parts for us.

I see the fellow has one on Ebay right now. I think this is the guy that had some made before and when I asked him about who did the replating and if it was certified he knew nothing of the proper plating/baking proceedures or if it was done properly. Beware people, if not done correctly the bolt could fail prematurely.

robert.p.bowen · Post by **robert.p.bowen** » Sat Apr 10, 2004 5:10 pm

Air Repair has lots of these mooring ring/tie-down bolts that it got while buying up all its L-19 parts inventory.

Don't know the cost, but call them at 662-846-0228. Most other stuff I've bought from them has been quite reasonable.

Post by **GAHorn** » Tue Apr 13, 2004 4:34 am

Unless Pete Jones at Air Repair has mislead me, he has none in stock. This is one of the suppliers I've been canvassing. (And his regular price on this bolt, IF he had any is ridic...er...I mean,...profitable.)

In any case, he's agreed to sell us 50 of them as a single order....IF....and WHEN....he gets some. None presently available. I'll let you know as soon as they become available. I presently have an order out for a AN hardware mfr to make them. We'll see what he does.