3D Demystifying Vacuum Bagging of foam wings!!

[Terryscustom]

Don't be scared, once you've taken the leap you will never go back! Vacuuming foam parts for airplanes does require some upfront investment, but the good news is the items required can be re-used dozens of times. If you are a builder and have friends that build planes consider going in on a system together if needed. The finished weight, strength, quality and time investment all benefit from vacuum bagging.

I drug my feet for two years, since I'm a relatively new builder it seemed like a huge step. @Fixed Wing kept giving me grief about it so I finally caved. I really really hate to give a link to "the other site", but it's a short thread so if you get in and get out you should be safe. Dean did a nice description of his vacuum system over there and you can find that here: http://www.GiantScaleNews.com/forums/showthread.php?t=61274&highlight=fix wing vacuum system

I opted to buy a ready built system from ACP composites. I've purchased a number of things from them over the years and they have great prices and service. They have all of the parts and components needed for a simple system. I also built another system of my own with a larger pump and all the switches and accessories from ACP, so you can also do that and safe a few bucks.

Here is the ACP Systems and accessories page: http://www.acpsales.com/Vacuum-Bagging.html

 

[ericb]

It has been very enlightening to be able to watch Terry in person. The wings that come out of his shop are second to none.

 

[Bartman]

edit: Left in thread for sake of ruling out a bad option?....see post #5

Terry,

Here's another option for pulling a vacuum. I've been told they work well using shop air to create a vacuum but I've never tried one myself. Listing says they use 4.2 CFM @ 90 PSI, fwiw.

http://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html

Bart

 

[Terryscustom]

Lets take a look at the parts of the system:

1 - Pump / Motor
2 - Pump line - this line needs to have several small holes in it with an hobby knife to relieve pressure between pump cycles!!
3 - Check valve
4 - Electronic pressure switch (adjustable)
5 - Vacuum pressure gauge (Hg = inches of mercury of vacuum).
6 - Vacuum line to bags
7 - Relief / safety valve - mechanical: http://www.mcmaster.com/#48935k25/=un2cgy
8 - Reservoir

The ACP system does not come with the safety valve, but I added it as a safety feature in case the electronic pressure switch fails. Since we are vacuuming foam parts at 6-7 Hz and these systems will go more than 20 Hg......it's cheap safety to make sure you don't come out in the morning and your nice wings are now 1/2" thick!!!

 

[Terryscustom]

Bart, glad you mentioned that but one word of caution. You will need a huge supply of air (large air compressor) and the compressor will run for at least 8-10 hours while resin sets up. If you are using poly glue you only need a couple of hours but still many small home air compressors may very well run continuously to pull that vacuum.

Edit, another consideration for those is the volume of vacuum that the venturi pulls will take a tremendous amount of time to evacuate a large wing bag. Especially for foam adhesive, your foam will likely be kicked and tacky before the vacuum pulls which could lead to poor adhesion.

 

[Terryscustom]

Here are a few accessories needed for the actual bagging. One thing not shown is some breather mat, shown at the bottom of this page: http://www.acpsales.com/Vacuum-Bags-Films-Peel-Plys.html The breather mat for our application is mainly just needed to make a small path from the nipple in the vacuum bag over to the foam shucks that the parts are in. The foam does a good job of transferring air so a complete blanket of breather mat is not needed.

1 - Vacuum bag
2 - Quick lock seals (two required per bag)
3 - T's
4 - Vacuum bag connector
5 - Vacuum line lock
- Also not shown, neoprene tubing to run vacuum lines between pumps and bags. Using the T's I have joined my two pumps together so I can literally vacuum an entire airplane at one time and also have a redundant system so if one pump should fail for some reason, the other will take over.

 

[BalsaDust]

Sub'd. One day I will try this. Having to much fun with profiles at the moment though.

 

[Terryscustom]

Sub'd. One day I will try this. Having to much fun with profiles at the moment though.

A profile with a foam wing may not fold in half, LOL. I could not resist

 

[Pistolera]

Terry...thanks for taking the time to post this! I'm sure it'll help many....and maybe even me someday

 

[BalsaDust]

A profile with a foam wing may not fold in half, LOL. I could not resist

LOL its cool live and learn. I'm building new wings for it now the problem was my wing joiner block. It had removable wings and for some reason I thought it would be a good idea to build the joiner block out of 1/4" hardwood over 1/4" plywood. I'm pretty sure under the load of a wide open throttle snap that I was starting to do it just sheared the bottom half off. The pocket in the wing survived for the most part but hte wings are to far gone to mess with. Fused survided great though. WOT lawn dart and the only thing on the fuse that broke was around the wing and the horzontial broke free. 20 minutes worth of work and it is ready again.

2nd pic is the broke joiner block and 1st pic is what I think happened. I should have known better as there is no cross grain in hard wood.