Rib Stitching: Ho Ho Ho :-)

To A Few:

Yes, I think what you're doing is funny, as in worth a laugh. Not in
the building nor the rib-stitching but in that part of rib-stitching
that you are finding so difficult.

It's funny because IT ISN'T IMPORTANT. And you would know that for
yourself if you'll just back away from it for a moment and think about
it.

The Load appears in the fabric. Okay so far.

The load is transferred INTO the ribs by the stitching, for which it
appears you have used a section of Anchor Cable good for about 60psi,
or thereabouts. Which is where I started to smile. But the amount of
load 'seen' by an individual rib-stitch is relatively small, and
that's where I started to chuckle because you've failed to work-out
that amount for yourself. So let's do that before you loose your kewl
entirely and start sending Nasty Grams to guys like me who are really
trying to HELP you, even if that does not appear to be the case. So
here we go, working out the load as 'seen' by your stitches:

First off, there's several ways to work it out. I'm interested in
seeing which method you use but we can IGNORE any load that appears in
the leading edge because for all practical purposes that particular
load never makes it past the SPAR. I see a span of about 24 feet and
a chord of about four feet, with very generous 'abouts' because the
center-section has a nice big cut-out so you can get into the cockpit
without surgery, and because your tips are not square. But for the
purpose of this example let's call the span 24 feet. Using a 4-foot
chord is fairly safe but here again, it is NOT precise becuase of the
cut-out & curvey bits previously mentioned.

And you want to pull SIX G's.

Lemme ask you something... Have you ever done that? Seriously; have
you ever strapped yourself into a flying machine and gone out and
ACTUALLY PULLED SIX GEE's? Okay, I didn't think so. So let's come
back to that later.

Right now let's take your twenty-four feet of span and multiply it by
four feet of chord and come up with our mythical 96 square feet of
lifting surface. (Yeah, I know. Just work with me here for a
minute.)

Now lets take that mythical 800 pounds of gross weight and divide it
by those 96 square feet and come up with the 8.33 pounds per square
foot... which you'll note is about the same thing you got in your
first message, okay?

Now lets 'fit' that weight to one of your rib-bays. First off, we
know that most of the lift -- about 65% of it -- is generated by the
first third of the airfoil. Yeah, pitch has a lot to do with it but
here again, let's just fiddle with the numbers for a while.

See that 14" rib bay? The one between the 16" bay and the 12" bay?
Let's use that one.

Fourteen inches is 1.16 FEET, so we know that section of the wing
'sees' 8.33 pounds times 1.16 feet, or about 9.66 pounds. Now this is
where I started to laugh, so follow me through here.

All of the loads picked up by this rib bay get coupled into the
spars. The leading edge -- the first ten inches of the chord-wise
slice through your wing -- go directly into the main spar. The
fourteen or so inches that extend beyond the rear spar will appear in
that spar. The tricky bit is what happens to the loads that appear
BETWEEN the two spars -- the two feet (24 inches) where you start rib-
stitching. And keep right ON rib-stitching, all the way back to the
trailing edge.

Where you went astray, and the reason I got to laughing at those
pictures -- is because the loads are INSIDE OF THE SPARS. You've no
reason to start using that 80 lb braided fishing line. The load(s)
that appear in the skins of your wings are ALWAYS about the same from
root to tip. They don't get added together until they get INSIDE of
your spars.

So I hope you'll agree that it was a pretty good joke, seeing you
graduate from regular rib-stitch cord to something heavier... and then
heavier still.

So how heavy a cord do you need? I think the stuff I use runs about
forty pounds but it's awful heavy stuff. I 'm sure I could get with
something of lighter weight. But I bought a whole spool of the stuff
during the Eisenhower administration and it looks like I'll be using
it until the cows come home.

-R.S.Hoover