Hi Mark –

A couple of things:

The bagging material is reusable from one job to the next – the nylon material is fairly thick and does not stretch much. I was surprised when I first encountered it. This material is unlike vapor barrier material used in home construction or painting drop cloths. I have used the same bag for wings of different planforms with no problems. Little if any glue will get on the bag so it doesn’t get gobbed up, and the edges of the foam offcuts and whatever balsa (like leading edges) that sticks out will not snag or puncture the bag requiring patching or disposal. The glider guys that bag foam wings are usually (from what I know) bagging epoxy wetted glass onto foam -- they will use mylar sheets against the glass to get the finish – no foam offcuts like we would use. Their bags may well be messy after one or more uses and require replacement. Ours should last for some time. If a tiny leak can be located it can be fixed with a square of 3M shipping tape. The current bag – which is 10+ years old has no patches. The stab bag which dates from my first use of vacuum bagging does have a patch or two but there is no reason to replace it because it doesn’t leak – if it works, don’t fix it!

Because of space constraints I only do one wing panel at a time. Many times I only have time to bag one at a time anyway so it is not an issue. With the time to work through two panels I could see using two separate bags teed into the vacuum source. I’m shooting from the hip now and typing as I think (may get scattered or miss something). I would want a valve in the line leading to the second bag being left off when the first wing goes in the bag – that way the second wing doesn’t have to be hurried – making sure alignment is kept and that LE and TE are flat/straight and that the bag gets pulled down evenly all over, etc. Once satisfied with the first bag, then I would start gluing up the second panel. Once slid into the bag and the bag sealed, I would slowly open the valve to pull down the second bag. Now that I think about it, some kind of one way check valve might be necessary to inhibit the loss of vacuum to the first bag while the second is being pulled down. Maybe the first bag line should just have a valve that can be turned on/off like the one we talked about for the second bag. That way the first could be turned off as the second is turned on (maybe turn on the second after the first is off temporarily sealing the first bag). The pump would not be harmed by a few seconds of being shut off like that. This pump is a constant run oscillating something or other that doesn’t really have any mechanical parts to wear out. Where I build the temps are cool and I have left a panel in the bag with the pump running for 48 hours. There is not much air moving when the pump has pulled the bag tight so a few seconds of having a line shut off will not hurt it. Once satisfied with the pull down of the second bag, the valve to the first could be re-opened. Capacity/volume with the basic vacuum pump from Aerospace might be an issue with two giant scale wing panels in separate bags being pulled down at the same time. It probably would be OK to pull them down one at a time – it might/should be able to maintain both when pulled down one at a time.

I made my current tube from sheet/bulk material I purchased from Aerospace Composites. Determine how much you need for a comfortable circumference for the root end of the panel and bag – just right gives room for a hand or two in the way plus the whole wing panel (top and bottom shucks, core and sheeting). I made it rectangular as opposed to wing planform shaped. One long side will be a fold of the material (no leaks there), one end will be a permanent seal as will the other long side. Seal it up with 2” wide 3M Packing Tape – the original tape is still there. I may have had another set of hands to help with the long side – basically just fold the tape over the joint you are making.

Reinforce the hole in the bag for the vacuum fitting with quality duct tape inside and out. It won’t deteriorate or leak (or put stress on the bag material that could cause problems down the road.

I can’t speak to using the urethane glue/timing for sheeting – I’m just starting to use it for some construction items – haven’t used it for sheeting. I know some pattern builders who use them with great success – I don’t know if they lay up both wings at the same time.

Apologies for the “stream-of-consciousness” discussion/typing!

It was nice to see Aussie Knife Edge’s confirmation of my experience of using less glue!

Sounds like CST is a good source for vacuum supplies also.

That’s all I can think of at the moment. If you have questions or need follow-up or whatever, holler!

Later, Tom