Open Bay Covering Weight

LAST EDITED ON Jun-09-01 AT 10:06 AM (EST)

Gang --

Sometimes we make the same errors as the ancient Greek philosophers -- we debate things instead of collecting data. In a six sigma world, shame on us.

We ought to be able to compile data on open bay covering weight fairly easily. If you have a crashed plane and need to cut out the bays to repair, weigh the panels (after cutting to a standard size) and calc the weight in grams / square inch or whatever is convenient for you. Obviously, you need access to a lab scale to do this.

We don't need a crashed plane for the monokote / ultracote data.

Recording total weight gain for particular finishing techniques and materials doesn't cut it, because of the differences in weight gain between finishing balsa surfaces and open bays.

List the finishes (number of coats of sealer, clear, polar gray, Krylon, poly, color, finish clear, etc.), substrate (silkspan weight, silk momme, synthetic), and we'll have it all. As someone said here, never believe advertised weights, so let's go from scratch.

Any players? I volunteer to compile the data.

I refinished it in dope and silkspan.

But silk, nylon, heavier materials can get heavier. And then it is going to depend on how well you finish the weave. (Anybody got a gram scale that reads to the thousandths of a gram?)

>Weight gain can be horribly different
>depending on how many coats
>of what thickness of what
>material (thinned, not so thinned).

In the penultimate paragraph I mentioned that number of coats of whatever should be recorded. Your silkspan finishes are probably lighter than mine, and that variation is important data.

>. . . And then
>it is going to depend
>on how well you finish
>the weave. (Anybody got
>a gram scale that reads
>to the thousandths of a
>gram?)

In big round numbers, say you are interested in weight differences in a 500 square inch wing. Not all that is open bay, and there are two sides, so say we are talking 800 square inches of open bay in big round numbers. Now, 1/4 oz. difference is maybe important. That is 7 grams in big round numbers. A crashed wing could provide 200 square inches sample size. Measuring that sample to the nearest .1 gram would provide significant data, well below the 1/4 oz. total weight difference criteria of importance. (I am doing this in my head as I type, so I will retract if I am wrong). My cheap Ohaus scales go to .1 grams, and I think the old analog lab scales at work go .01 grams.

Let this thread die. The lack of response says a lot. The death of this thread is similar to the problems in what I do for a living. Data analysts are just a pain in the butt.

I give up on this project.

Any other thoughts on this kind of thinking? What are your thoughts on Open Bay -v- Built up Sheeted -v- Foam/Sheeted construction, as they relate to weight? The Sheeted wing seems to offer better (read: easyer by degree) finishing technique, ..or not? what do you all think?

My comments: A light foam wing will end up an ounce or two heavier than a light built up wing. A fully sheeted wing is always easier to finish IF you don't have ripples which can happen on a fully sheeted-over-ribs type of wing. However, there are "fixes".

In theory, a partially sheeded foam wing would save weight (as per Tom Dixon's suggestion.) However, instead of using 1/16 inch wood on a partially sheeted wing, why not use 1/20 or even 1/32 wood on a fully sheeted wing? You will maintain the strength and actually save weight on a fully sheeted 1/32 wing over a partially sheeted 1/16.

On most of our wings we use the same construction troughout. They are thus overbuilt at the tips and weakest in the center where the maximum load is. We need to change our building techniques to increase the structure in the center and decrease it at the tips. There are several ways of doing this including tapering our spars, using carbon fiber, tapering the leading and trailing edge sheeting.

And, yes, you could make the wing a little heavier and try to shave the weight elsewhere, but why not save the weight elsewhere and then make the wing lighter, too? Keep the weight down while maintaining adequate flying structure, and you will always come out in the flying end.