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Vac Bag to fill weave?

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Old 09-16-2004, 05:09 AM
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I-NAV
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Default Vac Bag to fill weave?

Looking for a way to improve the finish when glassing a foam wing. The fill coat always requires huge sanding time. Would bagging the second coat of epoxy in a mylar film even out the finish? Any sugestions?

Mike
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Old 09-16-2004, 07:09 AM
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Ed Smith
 
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Default RE: Vac Bag to fill weave?

I assume you are using no heavier than 3/4 oz cloth when glassing the wing. I have used 1/2 oz cloth the weave is not as deep.

Are you using the peel ply and breather cloth method when glassing the wing?

I would not lay on a second coat of resin with mylar. The weight will increase and the possibility exists of trapped air bubbles between the mylar and the now non absorbent wing surface. If you wish to use Mylar do that first and do it once. You will still end up with countless pinholes in the glossy surface. You may wish to spray primer or paint of your choice on to the Mylar. The mylar will have to be polished with release wax first. This will leave trailing and leading edges to be touched up.

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Old 09-20-2004, 02:21 PM
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Default RE: Vac Bag to fill weave?

There are guys who have pretty much perfected mylar bagging methods & they hang out in DLG (Discus Launch Gliders) SAL (Side Arm Launch) & other soaring related groups. Philip Barnes ?sp? makes an excellent video on this subject & the end product quality is very high. There are related user groups on Yahoo groups.

Basically the composite cloth (glass/kevlar/carbon whatever) gets laid on the mylar, wetted with epoxy, then that layup is transferred to the core & vac bagged. After curing the bag is released, mylar removed revealing a matching mirror finish. The mylar can also be waxed & pre-painted like any normal mold surface. Gapless hinges & razorblade trailing edges are also easily achievable. But there are issues that may not make this suitable for your particular application:

The vacuum bagging surface finish relies on the use of higher denity (2 pcf) type foam. These guys generally have very thin wings & high aspect ratio's so that is not a big deal for them. If you have thick sections & large area, the higher density foam will add much more weight.

If you have any compound curves, nacelles, bumps corners or anything other than a pretty straightforward wing, that complicates the bagging process because the mylar wants to lay basically in a plane. It will not stretch or conform t anything other than say a leading edge radius.

If your wings require any openings to accomodate gear (wheel wells, servo bays, lightening holes etc) that is a problem because the vac force will distort the core with any open cavities. So these can only be cut out of the wing after bagging & may present more work.

If all you want is to borrow this concept for an aesthetic finish, it could probably be done but you will hav eto really whatch that you have enough vac pressure to keep the mylar conformed - but not so much as to crush the wing you have built. Hope this helps.
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Old 09-20-2004, 07:25 PM
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Default RE: Vac Bag to fill weave?

Ed,

You may want to give this a try without dismissing the idea. I recently sanded down a V-Tail for a Q500 racers. Cut the mylar about 1/8" bigger than the tail and waxed it up. Put down a coat of primer on the Mylar and laid my glass (3/4 oz) directly on the mylar. Once its all wetted out on the mylar, you can scrape all the excess resin off. I then put my skinned hinge material (Kevlar) on the glass at the hingeline and then placed the balsa tail in the middle of the sandwich and threw it in the bag. By applying the resin to the cloth while it is on the mylar instead of the balsa you get no soak in like you would otherwise.

The finish came out smoother than I ever would have expected. You will need to sand the edges up a little, but I think you will be happy with the results.
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Old 09-21-2004, 07:47 AM
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Default RE: Vac Bag to fill weave?

Sounds like it's worth a try. I'll try it on the bottom of my F-22 wing and see how it works. Worse case I'll end up sanding as much as the traditional method. The key will be to get a good surface prep on the wing or else it's all for nothing. Any problems with Z-poxy curing over model magic type fillers?

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Old 09-21-2004, 11:54 AM
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Default RE: Vac Bag to fill weave?

I normally use EZ Lam finishing resin, but this last tail I did use the Zpoxy finishing resin and it worked fine. I did delute it down a little with 99% pure alcohol (Easy Ed, not Rum).
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Old 09-21-2004, 10:28 PM
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Default RE: Vac Bag to fill weave?

ORIGINAL: I-NAV

Sounds like it's worth a try. I'll try it on the bottom of my F-22 wing and see how it works. Mike
It is worth to try. I just bought Phil Barnes video ( http://www.paonline.com/hayman/video.htm )
Phil is showing his technique of bagging glider wing in a mylar. Result is AMAZING.
Go for it.
George
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Old 09-23-2004, 11:02 AM
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Default RE: Vac Bag to fill weave?

George, that is the video that gave me the ambition to try this. Very much worth the money.
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