Weight Watchers Anonymous

Browsing though a July '94 newsletter for Tidewater Model Soaring Society, I read an interesting article that looked at the hair splitting statistics of the weights that are involved in skinning or covering model surfaces. Since there has recently been some fine examples of weight conserving finishes, I thought this article was timely:

Building Light
By Russell Bennett

There is nothing quite like the feeling of watching the glider that you just tossed into the air get sucked up by a small energetic thermal. This is, for me, one of the real joys of handlaunch glider flying. So in order to have more fun, I try to build planes that thermal easier. Now, when it comes to indicating lift and staying up in light lift, lighter is better. But how do you build a light airplane? Two areas I have often wondered about are wing skinning adhesives and covering materials. In the past I had read things like "Micafilm is the lightest covering" and "diluted yellow glue is lighter than epoxy" but I had never seen any numbers. So I decided to do a little research.

I cut squares of balsa wood and covering materials, each approximately 20 square inches. The dimensions of each piece were measured and the area calculated. Using a balance which had a resolution of 0.0001 grams I started weighing. For the liquids, I would weigh a piece of balsa wood, applied the adhesive or paint, allow it to dry, then weigh the wood again. The weight of applied liquids will vary depending on who does the applying, however the relative weights of the different materials should remain the same.

The results were interesting. Take the Micafilm as an example. When used on an open structure Micaflim is very light, however, when used on a sheeted surface where it's necessary to have a continuous coat of Balsarite, it is actually on the heavy side. You would be better off using transparent Monokote. For all the materials tested, the transparent colors were significantly lighter than the opaque colors. This is due to the transparent colors being tinted with a dye while the opaque colors require a layer of relatively dense pigment sufficiently thick to block most of the light. The 3M 77 spray adhesive is an example of how much the weight of coatings can vary between "just enough to do the job" and "that shouldn't ever come unglued". If anyone has a material that they would like weighed, let me know. I only need a small piece and it would help make the list more complete.

Materials Weight (oz. / ft2):