The joy of fixing 'repairs'

This year I decided to replace the interior in my airplane.

The brilliant person who installed my carpet clearly had his own
approach to doing things. In order to remove the carpet, I had to
remove the seat track rails and diassemble the controls for the fuel
valves. I asked around, and discovered that this was improper - the
seat rails are supposed to be bolted to the floor. Carpet will
compress, and the seat rails will move around, putting excees stress
on the attach points (4 10-32 nut plates per rail). So I decided to
pull the main floor panels (not normally done on an annual, since
inspection panels are installed) and take a look.

Unsurprisingly, two of the nut plates were cracked, with cracking in
the supporting stiffeners. The real doozy, though, was the third nut
plate.

First off, it was the wrong kind. The right kind allows the nut to
move about 1/16" in each direction, but this one allowed no movement
at all. There was also a doubler on the stiffener holding the nut
plate. Clearly there had been a repair. The doubler itself was well
made, but the only thing holding the nut plate to the doubler was a
pair of 3/32" Aluminum pop rivets. Not CherryMax. Not Monel. Not
even Avex. Ordinary hardware store Aluminum non-structural rivets.
The steel cores (if they were ever there) had long ago been lost. The
pop rivets were stretched. The doubler was cracked around them.

I have no idea who the idiot was who thought a pair of non-structural
pop rivets were an acceptable substitute for the solid rivets Piper
used (which were marginal themselves) but this same person used not 2,
not 4, not 6, not 8, but 10 (TEN!!!) 1/8" steel core CherryMax
structural rivets to hold the doubler to the stiffener - and the
doubler needed to come out.

In the end, I wound up giving up on drilling them out, and cut the
rivets off with a Dremel tool. It took longer to remove that one
dobler than it did to fabricate and install three doublers and their
associated nut plates.

Folks, think before you repair. Your repair is only as strong as the
weakest point. It does no good at all to beef up anything that isn't
the weakest point - it only makes it harder on the next guy.

Michael

"Michael" wrote:
This year I decided to replace the interior in my airplane.

I guess this means you're keeping the Twinkie...?
--
Dan
C172RG at BFM

"Dan Luke" wrote
This year I decided to replace the interior in my airplane.

I guess this means you're keeping the Twinkie...?

At least for a while. Have you looked in TAP lately? Now is a lousy
time to sell a light twin.

Michael

(Michael) wrote in message . com...
This year I decided to replace the interior in my airplane.

The brilliant person who installed my carpet clearly had his own
approach to doing things. In order to remove the carpet, I had to
remove the seat track rails and diassemble the controls for the fuel
valves. I asked around, and discovered that this was improper - the
seat rails are supposed to be bolted to the floor. Carpet will
compress, and the seat rails will move around, putting excees stress
on the attach points (4 10-32 nut plates per rail). So I decided to
pull the main floor panels (not normally done on an annual, since
inspection panels are installed) and take a look.

Unsurprisingly, two of the nut plates were cracked, with cracking in
the supporting stiffeners. The real doozy, though, was the third nut
plate.

First off, it was the wrong kind. The right kind allows the nut to
move about 1/16" in each direction, but this one allowed no movement
at all. There was also a doubler on the stiffener holding the nut
plate. Clearly there had been a repair. The doubler itself was well
made, but the only thing holding the nut plate to the doubler was a
pair of 3/32" Aluminum pop rivets. Not CherryMax. Not Monel. Not
even Avex. Ordinary hardware store Aluminum non-structural rivets.
The steel cores (if they were ever there) had long ago been lost. The
pop rivets were stretched. The doubler was cracked around them.

I have no idea who the idiot was who thought a pair of non-structural
pop rivets were an acceptable substitute for the solid rivets Piper
used (which were marginal themselves) but this same person used not 2,
not 4, not 6, not 8, but 10 (TEN!!!) 1/8" steel core CherryMax
structural rivets to hold the doubler to the stiffener - and the
doubler needed to come out.

In the end, I wound up giving up on drilling them out, and cut the
rivets off with a Dremel tool. It took longer to remove that one
dobler than it did to fabricate and install three doublers and their
associated nut plates.

Folks, think before you repair. Your repair is only as strong as the
weakest point. It does no good at all to beef up anything that isn't
the weakest point - it only makes it harder on the next guy.

Michael

Sounds like owner involvement pays off again! The carpet under the
seat rails is a first(at least for me). That guy really was an idiot.
Let us know how the interior turns out. Sounds like you are doing it
right. Also,the 3/32" pop rivets on the nut plates really isn't all
that bad. The only function they serve is to hold the nutplate in
place while the screw is installed. Once in place, they should not be
part of the load path, if done correctly.

Regards,
Bruce Cunningham