"Airplanes don't kill

On 16 May 2005 03:53:35 -0700, "Flyingmonk" wrote:

The space craft comment was, LOL, in ref. to your Fly Baby.

Ah, well, the answer to that is, "Houston, we have a problem."

Went flying Saturday after a month or so (weather/out of town). When I taxied
back and tried to turn sharply to the left to point the tail into the hangar,
the Maule tailwheel refused to kick into swivel mode.

I didn't think much of it...just killed the engine and hopped out. Then I
noticed that the tailwheel spring was cocked sideways, relative to the fuselage
center line. A closer examination showed that one of the two bolts that clamped
the spring to the tailpost was missing.

The tailwheel spring attach system consists of a sort of T-bracket bolted to the
tailpost...

http://www.bowersflybaby.com/safety/tailpost2.GIF

....with a clamp plate bolted below. The bolts go through metal spacers to pin
the spring. This picture (of someone else's airplane) shows the general setup,
except on my plane, the horizontal stab turnbuckles are bolted to the fuselage
just above the spring instead of the ends of the clamp plate.

http://www.bowersflybaby.com/safety/tail_brace3.JPG

Anyway, one of my bolts and the spacer block (1/2" thick aluminum) were gone
from one side. It was obvious that the repair costs would be minimal, but I was
deeply curious *why* the bolt was gone. Due to the narrowness of the stock
T-bracket, the clamp bolts are mounted head-down, so any failure means the loss
of the bolt. I wanted to know whether the bolt broke or whether the nut backed
off....and, for that matter, it would be nice not to have to cut and fit a new
spacer block. There was also that nagging worry that maybe the bolt had been
gone during my preflight, and I'd missed it. The airport is swept every week,
so finding the parts would mean they'd at least been on the airplane when I'd
started up.

A quick walk-down down the taxiway a bit didn't turn up the parts. I've got a
buddy who works at the airport, so I figured I'd ask him to keep an eye out for
the stuff when he did the end-of-day taxiway/runway check. I put the plane to
bed and drove to the office.

It was my buddy's day off, but he was sitting in the pilot's lounge (he owns a
172) talking to a couple other friends of mine. I made the request...and
everyone decided to help look. Immediately. One took off in his truck, another
hopped on his bicycle, and the third wandered out on foot.

I was horribly embarrassed...it's bad enough to lose parts of your airplane, but
it had turned into a group FOD walkdown. I hadn't meant to chase everyone from
their coffee cups and BS session.

I was walking with the third guy, babbling about "Geeze, I didn't want to bother
everyone, and maybe we should just forget it," when he said, "Well, then you
don't want THIS!"

He leaned down and picked up a shiny aluminum block.

Yep, that was it. It had dropped off on the taxiway just a couple of dozen of
feet from the office.

A foot or so away were the nut and the bolt. The bolt had broken right at the
point where it pinches in form the threads.

The failure is curious. The only tension load on this bolt is its own preload
and half the weight of the tailwheel assembly in flight (just ten pounds or so).
The major loads are the side load as the plane turns. The double plate should
nominally have the bolt loaded in double shear, though most of the load will be
on the top plate where the bolt failed.

The bolt is old and I'd worked on the bracket quite a bit for some dry rot
repair a year or so ago. There may have been some mechanical damage or it just
may have got some corrosion (though I don't see any). I'm hauling the bits in
to work to run them by a couple of ME types. I'll replace it and its mate with
some NAS bolts I've got handy...these are about 20% stronger than stock AN.

Ron Wanttaja