Author: "John Williams" <frate.dawg@...> Time: Tue Oct 1, 2002 5:18 am PDT Link
-----Original Message-----
From: John Williams [mailto:frate.dawg@a...]
Sent: Monday, September 30, 2002 9:55 AM
To: 'RV9A@yahoogroups.com'
Subject: FW: Center Nose Ribs (Part 1)
Folks: I wrote a long treatise on the center nose riveting debacle,
mostly for the archives, but also to thank those of you who offered
help. I was appalled to find out that only Part 2 uploaded, sort of a
non-sequitur without Part 1. Here is the original Part 1, with
apologies. Regards, John Williams
-----Original Message-----
From: John Williams [mailto:frate.dawg@a...]
Sent: Wednesday, September 25, 2002 11:37 AM
To: 'RV9A@yahoogroups.com'
Subject: Center Nose Ribs (Part 1)
Gentlemen: To all of you who responded (10 of you, in all) to my cry
for help in installing the H.S. center nose ribs, let me say Thank You,
one and all. Your suggestions were all good, and I used most of them.
The job is now complete and satisfactory, if not outstanding. My
previously beautiful and pristine H.S. assemblies still look pretty
good, although in the center nose rib areas, I have dime-sized
depressions around two or three rivets on each side. These can be
easily remedied when I get to the skin-prep process prior to priming and
painting down the road. More importantly, the moral support you offered
was invaluable. It allowed me to unscrew myself from the ceiling,
restored my confidence, and press on with "plan B" . As Steve Moore
wrote, it was very demoralizing to do such a fine, painstaking and
meticulous job of drilling, deburring, dimpling, alodining, priming and
riveting, only to have it look like it was in a midair collision after
trying to rivet in the two center nose ribs and "preserve the curve" of
the leading edges. Knowing that others had the same problem but got
through it one way or another was very reassuring.
What follows, for the archives, is how I chose to do MY center nose
ribs----what worked, and what didn't. First, however, let's examine the
theory that the center nose ribs are "too small". Not so. The H.S.
airfoils are constant-chord, constant-radius D-cell structures, which
means that all main ribs, nose ribs and spar dimensions are identical,
and that is exactly what we got in our kits. WE individually chose, at
random, which nose ribs would be installed in the center positions, and
marked them accordingly. WE cleco'd them into place, match-drilled
them, and in essence fitted them to the leading edge. Van didn't do that
for us---he only CNC machined the ribs to very close, and IDENTICAL
TOLERANCES, as is proper in a constant chord (non-tapered) airfoil with
a constant leading edge. The problem was not due to undersized ribs,
but rather the behavior of folded flat sheets, whether steel, paper,
aluminum, PVC, etc. You can prove this to yourself by folding any
rectangular sheet of paper lengthwise, then grasping and lining up the
four corners with your thumb and forefinger. Notice how the two edges
between the corners of the ensuing rectangle tend to bow out in the
center of the rectangle, even though the edges and corners are perfectly
aligned and held in place with your fingers. This tension in the center
section causes our suffering, and accounts for the springiness which
tries to pull the skin away from the rib flanges in that area. This
bowing-out tendency of the skin also occurs in the long runs between the
end ribs and the center rib, which gives rise to the rather large area
of flattening or the "dented-in" look on either side of the center rib
after you snug down the skin to the flange, or the "daylight" between
the skin and the flange if you don't tighten it down. Not only is it
butt-ugly! It probably alters the airflow to some degree, and probably
not in a positive manner. I felt it was more important to "preserve the
curve" of the leading edges and avoid the caved-in look and flattening
of the surface of the H.S. center-span, than to have two lines of
perfectly flush beautifully-driven rivets there. I will accept small
depressions around the rivet heads, because they can always be filled
and sanded smooth later on. So, how do we maintain the smooth curves of
the leading edge, while at the same time providing a structurally sound,
stiffened joint?
The easiest way would be to order four more nose ribs from Van's, cleco
'em to the front spar using the mid-rib holes in the spar, and then
back-drill through the flange holes to match-drill the skin from the
inside. These would add very little extra weight, could be blind
riveted into place like the center nose ribs, and would greatly mitigate
the effects of the spring tension "bow-out" tendency along the interior
leading edge as well as the "flat spotting" on either side of the rivet
lines. They would also add stiffness and strength, and help to
"preserve the curve". Or, you could make your own form blocks, cut and
flange additional ribs, match drill the flanges exactly as the supplied
nose ribs, and install in front of the main mid-ribs as above. Problem
is, not many of us know how to make ribs from scratch; nor is there an
adequate stock of spare rib material in the scrap bundle for this; and
it is a very time-consuming side process. If I had it to do all over
again (I don't, thank God!) I would simply just buy four more nose ribs
from Van's, and install them in front of the midribs. End of problem.
No anger, disgust, heartburn, recrimination, feeling of abandonment. No
drilled out rivets, scratch and dent sessions, body shop techniques,
etc. Press on. Work on something else while you wait for the parts to
arrive. Make progress. Get on with it. Life is Good!!!
Another way
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