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Author Topic: Foam Vs Frame Weight  (Read 1461 times)

Offline Motorman

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Foam Vs Frame Weight
« on: August 27, 2019, 06:46:10 PM »
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« Last Edit: September 01, 2021, 08:36:38 AM by Motorman »
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Offline Mike Alimov

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Re: Foam Vs Frame Weight
« Reply #1 on: August 28, 2019, 05:33:41 PM »
Not sure you will ever get a definite answer to this - it depends on who/how the two wings are built, types of glues used, balsa density, method of built up construction, covering/ finish method, etc etc. For example, my SV-11 arf wings were about 15 oz (no flaps, covered with Brodak-cote). I have a set of sheeted SV-11 wings ( builder unknown) that are about 10 oz - who knows how much they will weigh when finished? At the same time, if you order built up sv-11 wings from Tom Morris, they will be feather light.
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Offline Dennis Adamisin

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Re: Foam Vs Frame Weight
« Reply #2 on: August 29, 2019, 09:19:13 AM »
If comparing fully sheeted wings, the answer is closer to 2 ounces, not 4.  BTW, a fully sheeted built up is just as resistant to warps as a foamie.

If comparing a fully sheeted foamie to a open bay built up D-tube, and finishing with dope, I would expect the FINISHED weight of the foamie to be the same or lighter than built up.

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Offline Tim Wescott

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Re: Foam Vs Frame Weight
« Reply #3 on: August 29, 2019, 10:44:24 AM »
Quote from: Dennis Adamisin on August 29, 2019, 09:19:13 AM
If comparing fully sheeted wings, the answer is closer to 2 ounces, not 4.  BTW, a fully sheeted built up is just as resistant to warps as a foamie.

If comparing a fully sheeted foamie to a open bay built up D-tube, and finishing with dope, I would expect the FINISHED weight of the foamie to be the same or lighter than built up.

Are you saying that the actual weight of just the finish for dope over sheeting is less than the finish for dope over open bay?
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Online Brett Buck

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Re: Foam Vs Frame Weight
« Reply #4 on: August 29, 2019, 02:04:22 PM »
Quote from: Dennis Adamisin on August 29, 2019, 09:19:13 AM
If comparing fully sheeted wings, the answer is closer to 2 ounces, not 4.  BTW, a fully sheeted built up is just as resistant to warps as a foamie.

If comparing a fully sheeted foamie to a open bay built up D-tube, and finishing with dope, I would expect the FINISHED weight of the foamie to be the same or lighter than built up.

   Agreed, and we have abundant evidence showing what happens when a particular builder build a specific design with foam and then D-tube. They end up weighing the same, since any weight difference in the structure it compensated for in the finishing. Saving any significant weight with a D-tube requires some special circumstance, like you removed structure to the point that the D-tube is substantially less stiff.

   This tends to get swapped around when you need to make the wing removable, and thus incorporate hard points. In that case, a build-up wing makes a lot more sense, because the structure lends itself to putting hard points as spars, etc, that don't really correspond to anything in a foam wing. You can do it, but there's a lot of dead weight.

    Brett
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Offline Paul Smith

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Re: Foam Vs Frame Weight
« Reply #5 on: August 30, 2019, 06:24:29 AM »
Quote from: Tim Wescott on August 29, 2019, 10:44:24 AM
Are you saying that the actual weight of just the finish for dope over sheeting is less than the finish for dope over open bay?

Well, a fully-sheeted wing is easier to sand than open bay.  So you have a better chance to sand off some excess material without risking a disaster.
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Paul Smith

Offline phil c

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Re: Foam Vs Frame Weight
« Reply #6 on: October 18, 2019, 08:28:29 PM »
I built several 700+ wings for the Giles series I played around with.
The wing panels complete weighed a total of about 12-13 ounces.
Finish with film added 1.5 ounces.  Silkspan and Rustoleum added another 6-7 ounces.
18-19 oz. for 700 squares.  Maybe 15-16 ounces for a 600 sq. in. wing. ready to fly.

Phil C
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