The Murphy Builders Site

Hi Ron
That's what I get for displaying my plane!!! Went down and re-read the
chapter #20 again and yr absolutely right. There shud have been 5 not 4
bolts there. Again, I read the lovely, very explicit, helpful, and easily
understood manuel wrong again. I could swear that the bag of bolts only had
16 in it that lead me on to thinking that's what was required. Oh well,
good thing I didn't shed a strut while flying back!

Steve W.

From: Ron Shannon <rshannon@cruzcom.com>
Reply-To: <rebel-builders@dcsol.com>
To: Rebel Builders <rebel-builders@dcsol.com>
Subject: [rebel-builders] strut block bolts
Date: Tue, 01 Aug 2006 10:56:09 -0700

If the manual is read literally, it looks like there are supposed to be
a total of five (5) bolts through each strut block, and pictures I have
seen show five. (See http://n254mr.com/gallery2/v/Rebels/Misc/) However,
five looks like a lot, leaving quite a bit of the block (and strut)
drilled out.

At Oshkosh I saw Steve Whitenecht had four (4) bolts in each strut
block, which certainly looked quite adequate, at least through this
non-engineer's eyes. Steve (who was really helpful giving me a tour of
his very nice work -- thanks Steve) said he had used four because that's
all MAM had delivered with his kit.

So, which should it be, 4 or 5? Has anybody else used 4?

Ron
254R
http://n254mr.com



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You might ask MAM if it is OK as you are not the first to fly with only
4 bolts there.
If you use MAM's tie down rings, they replace one of the bolts with a
continuously threaded rod welded to the ring rather than an AN bolt.
That is a bit like removing a bolt...
Ken

steve whitenect wrote:

Hi Ron
That's what I get for displaying my plane!!! Went down and re-read the
chapter #20 again and yr absolutely right. There shud have been 5 not 4
bolts there. Again, I read the lovely, very explicit, helpful, and easily
understood manuel wrong again. I could swear that the bag of bolts only had
16 in it that lead me on to thinking that's what was required. Oh well,
good thing I didn't shed a strut while flying back!

Steve W.

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Ha. Sorry, Steve. Truth is, I thought your 4-bolter was the better plan.
The manual actually isn't absolutely, totally, unambiguously crystal
clear either. (My eighth grade grammar teacher would have preferred even
more precision.) My uncertainty started with the manual, not your build,
which affirmed what I was thinking would be the better interpretation of
the manual, though a little strained -- before I even saw your fine
airplane. Like the rest of your plane, it looked like the best of the
best to me -- still does.

My thinking was the bolts need to take shear loads, probably something
on the order of at least 10 times 1/2 the GW of the plane (some kind of
healthy margin over the rated 5.x positive G's, for one half the
airplane?) Engineers in the crowd may want to multiply that to some
other big number. But in any case, the G load ends up in the single 3/8"
bolt at the bracket. How many 1/4" bolts does it take to equal one 3/8"
bolt? I haven't looked it up, but I don't think it takes five.

Then there's also potential for a sort of twisting shear load between
the strut and block itself, but that couldn't amount to much in the
scheme of things, certainly nothing four bolts couldn't handle, that is,
unless a forward wing root attach bolt cracked and fell out, and you had
to rely on the remaining single rear root attach bolt and the strut to
get you to the ground. Hmmmm. OK, I'll use five. :-)

[The alert reader will easily recognize why I'm no aeronautical engineer.]


steve whitenect wrote:

Hi Ron
That's what I get for displaying my plane!!! Went down and re-read the
chapter #20 again and yr absolutely right. There shud have been 5 not 4
bolts there. Again, I read the lovely, very explicit, helpful, and easily
understood manuel wrong again. I could swear that the bag of bolts only had
16 in it that lead me on to thinking that's what was required. Oh well,
good thing I didn't shed a strut while flying back!

Steve W.

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