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May 19, 2019, 07:55 AM
Registered User
Thread OP
Discussion

Vacuum bagging - vacuum down to beds?


Using the shucks top/bottom as the bed for the bagged wind seems the norm. As a one-off I used 3m77 to glue the bottom shuck of a tail to a flat 20mm thick piece of MDF. Then when I vacuum bagged and then used a second bag and vacuumed it to the bed. It seemed to work well - very flat. Has anyone done this with a wing or is it simply not required/a better method?
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May 19, 2019, 08:53 AM
The Junk Man
As far as the "vacuum down to bed" technique goes, yeah... it works fine. I use it all the time in my other hobby, woodworking, to bag veneer to substrates like plywood.

Tom
May 19, 2019, 10:49 AM
Scott
Pylonracr's Avatar
I only use 1 vacuum bag when I do wings. My table is dead flat with a piece of 1/4" glass on it that I bag to when making flat composite panels and such. For wings I put the skins on the core with epoxy and in the bag. I set the bottom Shuck on the table, bagged core on it, and top Shuck on top. A flat board and some weight will keep it from moving or twisting as it cures.

There is an alternative method, which I use when the cores are lightened by cutting holes in them. Sheet the cores and place a release film on them so you don't glue them to the shucks. Put the cores in the Shucks and bag the whole mess. Again, a board and some weight to keep it flat while it cures.

Hope this helps.
Scott
May 19, 2019, 06:22 PM
Registered User
Thread OP
Thanks for the replies. I'm planning to make f5j wings and 4m of wing is more than I've done before. Given the investment in materials I'm keen to minimize mistakes.
May 20, 2019, 11:13 PM
Registered User
Hi Scott,

can you amplify the reason for the different methods?

Kindest regards,

M
May 21, 2019, 09:39 AM
Scott
Pylonracr's Avatar
Sure. I use 1/16" contest balsa and light 1 pound foam. I put the resin on the sheeting and bag it, placing the bagged core in the Shucks. I find this method the easiest for me.

When the cores are lightened by cutting away large pieces of foam, the light balsa tends to follow the outlines of the missing foam if that makes sense. You can see depressions in the finished wing when you pull it from the bag as the vacuum will pull the balsa down into the voids where there is no foam to support it. Putting the cores into the Shucks and placing the whole mess into the bag evens out the vacuum pressure, for lack of a better term, making the wing stay straight.

Keeping in mind I use about 5 inches of vacuum on solid foam cores and 3 to 4 inches on lightened cores.

Hope this helps.

Scott
May 21, 2019, 12:52 PM
Registered User
Hi Scott,

thank you for your time to respond, which makes sense, especially since it is based on experience.

Why do not use this method even for non-lightened cores? In other words, what is the conceptual difference between the two methods? From my reading, majority are using the former method.

Kindest regards.

M
May 21, 2019, 01:36 PM
Scott
Pylonracr's Avatar
I bag just the cores as it is easier for me. The guy that cuts my cores for me bags his with the shucks in the bags. I have always done it the first way so I am more comfortable doing it like that.

No real difference. Which ever way works for you is the right way to do it.

Scott
May 24, 2019, 04:01 PM
Registered User
Hi Scott,

thank you for the reply.

Kindest regards,

M
May 24, 2019, 10:08 PM
Scott
Pylonracr's Avatar
Glad to help.

Scott
Jun 07, 2019, 09:37 AM
Registered User
JF1980's Avatar
Is it possible to bag a wing without the beds? If so then any tips?

I'd like to skin a Blejzyk wing (http://www.blejzyk.pl/en/model-elf-2.html) with carbon and glass but I don't believe the kits come with the beds, just the veneered wing cores.
Jun 07, 2019, 10:36 AM
Scott
Pylonracr's Avatar
Probably possible, but I wouldn't try. Unless you can find a way to keep the wing perfectly flat you stand the chance of doing more harm than good if you introduce a warp.

Scott
Jun 07, 2019, 10:44 AM
The Junk Man
Quote:
Originally Posted by JF1980
Is it possible to bag a wing without the beds? If so then any tips?

I'd like to skin a Blejzyk wing (http://www.blejzyk.pl/en/model-elf-2.html) with carbon and glass but I don't believe the kits come with the beds, just the veneered wing cores.
Yes, and no problem at all, provided you keep the panel flat. Which isn't exactly rocket science.

in almost all bagging of wings, the shucks are not in the bag anyway. They are there to keep the panel flat.

Tom
Jun 07, 2019, 01:51 PM
It's time for me to fly
JimZinVT's Avatar
Quote:
Originally Posted by T_om
Yes, and no problem at all, provided you keep the panel flat.
That's the trick, but not always so easy to do. On a flat bottomed foil like a Clark Y, sure, just weigh down the wing on a flat surface and pull vacuum. But on many glider foils there isn't a flat surface anywhere on the wing, and often some under camber and washout too. Trying to shim up the wing to maintain that complex shape while you pull vacuum seems like a crapshoot at best. I'd love to see how it's done, because I have some cores I've lost the beds for.
Jun 07, 2019, 04:01 PM
Scott
Pylonracr's Avatar
Quote:
Originally Posted by JimZinVT
That's the trick, but not always so easy to do. On a flat bottomed foil like a Clark Y, sure, just weigh down the wing on a flat surface and pull vacuum. But on many glider foils there isn't a flat surface anywhere on the wing, and often some under camber and washout too. Trying to shim up the wing to maintain that complex shape while you pull vacuum seems like a crapshoot at best. I'd love to see how it's done, because I have some cores I've lost the beds for.
Kind of my take on the deal. IF you can keep it flat.

Scott


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