Author: Bob White
I became interested in using PVC foam for the ribs, and possibly other parts of the plane after reading two articles in the "Newsletters", Issue 15 page 7 and issue 16 page 5, written by Paul Kauffman. The advantage of PVC foam is that is is relatively strong, very light and easy to work. On August 25, 2001 I spoke to Paul about his experience using PVC foam for ribs on his BD-4 and some other items dealing with constructing a BD-4.
Using PVC Foam for the
Ribs
Paul has destroyed the wings he described in
the article. The airfoil was bad. He got a lot of lift for good
climb, but couldn't go as fast. He recommends the original
airfoil. Both are 15% but his was thicker farther back. He used 4"
spacing with ½" PVC ribs per the instruction of glider
builders. The wings were heavy. He made fiberglass skins in a mold
to fit over the ribs. One cold day he found the skins were
wrinkled due to difference in coefficient of expansion between
fiberglass and (I think he said) the aluminum spar. He re-skinned
with aluminum. Paul strongly suggests building all metal wings.
Scott DeGaynor's panel ribs are excellent. Paul is making a new
all aluminum wing with individual ribs and three 4 ft. wide sheets
of aluminum for the skin. His aluminum ribs have a 1.5"
flange. (He thinks Scott's have a 1.5" flange also.)
Paul used 4" spacing, but thinks 10" spacing would be OK if the ribs were skinned with 0.016" 2024T3 Al on both sides. I think this may be overkill. Jim Bede's panel ribs are made of 0.020" 6061 T6 for the ribs, skin, and rear channel. It might be good to use an aluminum skin at the ends of the fuel section though. Jim's panel ribs are also almost 12" wide as opposed to Scott D's 10" and the original fiberglass panel ribs which were 10". I wonder if anyone is flying Jim's panel ribs. Paul didn't have a source for PVC foam. He bought his from Dick Schrader a long time ago. He suggests using ½" thick PVC. He didn't know what density he used. I have seen 5 lb/ft3 recommended in other places. Pro-Seal is still a good adhesive for the PVC.
How To Form Aluminum Leading Edge
Clamp back edges together to make sure everything is square.
Take a 2 X 4 with a rug on it. Bend the leading edge as much as you can (0.032" 2024 T3). It is possible to over bend it but not easily.
Use tiedown straps at each rib location to clamp the skin to the ribs real tight. Use shims under the strap if necessary to get the skin tight against the rib. Use a 2 X 6 rounded on one edge at the rear to keep from distorting the wing when clamping. Set everything up and make sure it is OK before using the adhesive.
Pro-Seal is good for both adhesive and sealant. When he took his wing apart, he had used Pro-Seal in the gas tank area and Hysol on the rest of the wing. It was much easier to pull the aluminum off where he had used the Hysol. He thought it was good enough though. Jim Bede is using a new adhesive on the BD-17 that may be better. It is made by a company in New Hampshire.
Cover the gas tank area with the first sheet. Be sure to test for leaks before continuing with the rest of the wing. The critical area's are the inboard rib, outboard rib and trailing edge.
New Method for making Flaps &
Ailerons
Instead of trying to bend an aluminum sheet 80"
to a 2 ¼" dia., use an aluminum tube with a 2 ¼"
diameter X .040" wall (thinner would be OK if you can find
it) and attach a flat sheet to the top and bottom of the tube to
form the flap/aileron without any bending.
Author: Bob White, sent in on August 25th, 2001
Reorganized by Bob White, August 27th, 2001