I am planning on getting a vacuum bagging system for sheeting foam wings. I am a complete newbie at this (I have built a number of foam core wings, just not bagged) and I am wondering if the EZ Vac system from Aerospace Composites is a decent way to start or if I will find it lacking with a bit of use? The price sure is right and I am not anticipating going into production, just building a few sets of wings per year at most.

http://www.acp-composites.com/acp-vbs.htm

Is there anything that is missing from that kit or extra supplies I will need to get started? The only thing I see is that I will need bigger bagging tube to fit a typical pattern size wing into. Any other advice in this arena?


Thanks,
Mark

The EZ Vac system will serve you well. You are correct about needing larger material for bagging the current crop of pattern wings. I believe the supplied tube is 18" across and most wing chords at the root approach that -- figure in the thickness of the wing and offcuts and the dimension goes up and past 18" quickly. I purchased some of their material (same as the tube) that was just a flat sheet. Just cut it to adequate length for a panel (allowing for excess for the sealing system on the open end where the wing will slide in), fold it in half the long way, tape one of the ends permanently (I think I used Scotch packing tape -- substantial and about 2" wide), tape the long side permanently also. The remaining end will be closed with the sealing system. I have had the setup for more than 10 years doing at least one set of cores (wings, stab, and rudder) per year -- the first few years I was sharing it with another builder so there were some double amounts. I found that the hum/vibration of the pump could make it want to creep -- I put a piece of carpet pad foam under it and that took care of it. It is designed for continuous run -- because of cooler temps where I build (overnight especially) I usually let it go for two nights/days. It doesn't seem to over heat the pump. The nylon bagging material is re-usable (many times). One tip for the fitting that connects the bag to the pump -- I reinforced the hole (in the bag) with a square of duct tape on each side (inside and out) where the fitting goes through -- I use the same fitting for wing bags as for stab and rudder bags so it's getting moved whach could stress the material aroung the entrance hole.

Bag on a flat surface; bag the wings separately with the shucks oriented the same (up and down) as when they were cut; use enough weight to keep the whole package from becoming a banana... I use particle board roughly the same size as the panel for stabs and two rectangular "sheets" of 1/2" aluminum on the wing -- together they cover most of the wing panel -- probably overkill. Check the leading edge and trailing edge for straightness, release the vacuum and adjust if necessary.

I line the offcuts with waxed paper (a few pieces of magic tape) to catch any seepeage of epoxy. Tape the whole sandwich on the ends -- four places -- to make it easier to handle going in the bag (keeping alignment).

I thin the West Systems epoxy (fast hardener) with at least 80% isopropyl -- denatured alcohol would be best -- thin the epoxy with almost as much alcohol as epoxy. Brush it on. The wood will soak it up to the point that it looks like the wood is just damp. It goes back to the foam with the vacuum. The strip cut out between the aileron and wing for facing after sheeting is the "proof" strip. pulling by the two 1/2" wide strips of sheeting will always rip the foam apart but the foams stays stuck to the wood -- that's the best you can do.

I would suggest a practice run with materials that don't matter -- 6" to 12" square of white styrofoam sliced to provide a surface or two to apply some sheeting between -- try different methods of applying the epoxy -- in addition to the method I use, some like to screed it out with a notched credit card type of trowel.

If you have more questions either pmail me or lay them out on the thread. I recommend it highly!

Good luck with it!
Tom

Thanks for the info, Tom. I was hoping to hear that sort of news.

I plan to try using polyurethane glue this time, I was never completely satisfied with my results using epoxy and weight on the shucks. Is there anything wrong with putting the shucks inside the bag as well and applying pressure to the outside of the shucks/skins/core assembly instead of the skins/core alone? Seems it would be easier to keep things lined up that way. Practice runs will definitely happen, with some scraps I won't cry over.

I also plan to begin to cut my own cores this winter, it should be a very educational buiding season this year... I am sure there will be (many) more questions as I go.


Mark

Hey, that gives me an idea...Screen it out! I was planning on rolling the epoxy onto the cores given I don't want glue on the sheeting where ever there is a hole (and there's a lot of them!) What if I laid screening material onto the core to act as a mask then rolled on the epoxy? I'd like to use no more than 10 grams of glue for both skins if that's possible.

The shucks (is it shucks or chucks? Bob Noll was saying chucks in his Perfect Wings video) will be pressed by vacuum as shown.

Scott,

In Terry Brox's page he is using something like 9g of glue, but I think that is per skin.

http://www.mackrc.net/patternwings2/index.htm

Honestly, is this a place to scrimp? If I double up on Terry's glue amounts, I will add 36g to my entire plane weight of 10+lb. But I will be sure of the bond and will not be risking a failure for the sake of 36g (1.27oz). Seems like a false economy to me...Just my $0.02 on it.


Mark

This is my 6th set of wings and I haven't had one come apart yet so I must be overbuilding them!

I'm building an electric Patriot and my goal is 10 lbs ready to fly. To meet that goal, it requires 250 gm panels ready to cover. If they fail then so be it, I found the limit! This is an experiment all the way.

Fair enough. I have never been that concerned with those last few grams myself. Check Terry's page, he definitely was using 9g per wing panel, I just don't recall if that did both skins or one. If you want to try it, the PU glues are lighter than epoxy...


Mark

I've always used poly in the past, applying to the skins (first with a notched CC, then a foam roller to get a very thin even coat.) This wing will be different though since the glue has to be applied to the core.

On this project, I tried applying the poly to the foam on the tail surfaces and found it difficult to tell if I had enough or too much. With epoxy, I'm thinking I can apply it heavy and then soak up the excess with toilet paper before applying the skins.

Everything I've read about vacuum bagging said you can get away with less glue. We'll see!

Oh, and more thing about poly and vacuum bagging. I read you shouldn't combine the two since poly requires humidity to 'kick'. In a vacuum, you are removing the catalyst. I read this after I built the last set of wings but fortunately never had a problem. I don't think the partial vacuum we use is enough to stop the curing process.

You should certainly be able to use less glue, with the extremely even pressure application and high force levels involved.

That is a good question, if the vacuum will cause issues or not. Where I live is very low ambient humidity, so I plan to mist the parts before joining, anyway. Hopefully, the local application of moisture will be enough to kick off the glue. Terry Brox shows that he sprays a mist into the air and then waves the core through that mist and that is enough to kick off the glue. He sure can't be picking up much moisture with that method and is seems to work for him. Ah well, even if my first set turn out like garbage, I will post that result as well.


Mark

[quote]ORIGINAL: mmattockx

Is there anything wrong with putting the shucks inside the bag as well and applying pressure to the outside of the shucks/skins/core assembly instead of the skins/core alone? Seems it would be easier to keep things lined up that way.

When I have vacuum bagged wings or anything else, I have put the whole shebang in the bag. Putting some vertical witness marks on the edges of the whole foam sandwich will help with alignment when it is crunch time -- 2 on each end and maybe three on the sides. Do the marks without the balsa sheeting so you can be sure the foam pieces are really lined up. If you cut your own wings, put the marks on before cutting, then you really have good references.

I have only limited experience with poly glue -- none using it for vacuum bagging. The Terry Brox site makes it look like a viable solution.

Cutting tapered foam wing panels poses some interesting problems. That can take some "trial and improvement" and a substantial amount of large pieces of foam turned into smaller pieces... Once you get a system figured out it can be a very good thing.

Good Luck, Tom

Mark,

Here are a couple things that work well for me during bagging:

1) I apply epoxy (proSet with slow hardener...thinnest around and doesn't need additional thinning) to pre-sealed skins.
2) I bag the wing core plus skins directly....I use the husk or shuck as holder only. I wouldn't want to compress the whole husk but it would work okay.
3) I Line the outside of the skin with paper towels....creates a vacuum path and presses the bag more completely and perfectly
4) Had to build a larger bag from the stock they offer in the kit by taping pieces together, but leaving one side open for sealing after assembly
5) I tried using the seal material they sent in the kit but didn't care much for it....too hard to remove. I came up with a simple alternative that's truly reusable....Plumber's putty
6) 500 sq inch panel will weigh in at approximately 9 ozs ready for finish...ailerons cut and finished, servo mount in and tube socket in.
7) I have used carbon veil under the skin and it works fine but I've found it isn't realy necessary for the loads the wings carry. Adds about 3/4-1 ozs due to excess epoxy mostly
8) The amount of vacuum that works best for me is around 6-8 in Hg. I keep the vent path clear always. If a scrap piece of plastic gets sucked up in the vent, vacuum is sufficient to crush the foam like a pancake...don't ask how I know.

Having created all kinds of contraptions in the past 35+ years of model building to build foam wings (presses, cantilevered clam shell devices, cement blocks, etc), vacuum bagging is the simplest method yet and the techniques are well worth learning. Good luck and if something needs more explaining, contact me directly

Matt Kebabjian

PS- Perhaps I may save you some aggravation on foam cutting by giving you my source....Lazslo Horvath in PA cuts the best foam bar none. Started using his foam panels about 5-6 years ago and have been impressed with his accuracy and precision

Great info Matt, thanks! (Did you notice I incorporated your vertical webs on the wing socket? Haven't given up entirely on the false rib though!)

My experiment didn't go so well. The cores absorbed the resin like a sponge! I never had time to remove excess. The toilet paper did not pull any resin from the core. 54 grams of glue on one panel [:@] This puts me at 10 oz before LE and caps; workable, but disappointing.

This time around, I pinned the wing to the shuck through the root and tip once everything was lined up. This made it easy to get the vacuum setup and not worry about anything shifting.

For bagging material, I used 4mil plastic. At one point, I let the vacuum get a little excessive and pop! The bag failed at the wing socket. Nice safety valve! A piece of duct tape and I was back in business. 6 in Hg is where I left it to cure.

When bagging "to the table", make sure you have plenty of bagging material draping the assembly. If not, the excess sheeting overhanging the core will get folded over. I knew this from prior experiences and so I tape the perimeter of the sheeting to reinforce. I still had a few spots where the L/E skin folded, but it trimmed up fine.

This was the first and last time I'll use epoxy for sheeting...poly just works better (at least for me!)

Just got the second wing glued up. You can see where the L/E folded over again. Looks worse than it is since it will trim up just fine.

Scott,

The 6 mil thick stock of nylon film they offer in the kit is superior for this type of work. Nylon is several times stronger and stiffer than polyethylene bag material and conforms better on flat surfaces such as wings. However, the polyethylene is better when laminating fuselages since it conforms to the shape better. You should be able to buy nylon film from various sources

I like the granite table top you show. For wing lamination where the husks are doing the laminating, it's the best arrangement you can have. I use plate glass....same difference

If epoxy (or other adhesive) is applied to the foam first, the foam will soak it up like a sponge. I don't do it that way. The balsa is first sealed with plain jane hairspray and after a couple hours drying time, I apply epoxy directly to the balsa. A typical 500 sq in panel (top and bottom sheets) will take around 1 oz total. A cheapie sponge roller works well to distribute evenly but lightly. You should barely feel the epoxy after you are done...practically dry but its there. Bagging really puts the load on it so the epoxy comes back out. Must treat the foam with a tack rag to remove any dust

Did you remember to install the tube in the socket when forming the wing mount with subspars? The tube serves as mold to the socket. Subspars extended a couple inches past the end of the socket? Also, did you add 4" square 1 oz glass cloth top and bottom where the socket ends? That's to redistribute the stress riser at the end of the socket.

The aileron cutout facing in the wing, should be extended in a couple inches towards the root. Again to eliminate the stress riser at the inboard side of the cutout. I've seen panels crack over time at the aileron cutout.

I started using 1/4"x1/8" carbon tubing as the aileron horn mount several years ago and have been very pleased with the result. The hole for the horn is already there and perfectly aligned. I use 6-32 bolts for horns (normally not the hardened variety); never use all-thread in this critical application. Vibration will fatigue all thread. If electric power, then not a problem.

Matt

I applied the glue the cores because of the perforation job. My thinking was less surface area, less glue. Didn't work out...live and learn.

I got most of your other points covered. I did use a 1/2" wide .070 CF laminate 'spar' top and bottom to carry the load beyond the end wing tube rib.

Next wing I'll stop playing and do it right! Thanks for sharing your ideas.

Edit: That should be .007 CF laminate.

Matt,

In your words.....
"I started using 1/4"x1/8" carbon tubing as the aileron horn mount several years ago and have been very pleased with the result. The hole for the horn is already there and perfectly aligned. I use 6-32 bolts for horns (normally not the hardened variety); never use all-thread in this critical application. Vibration will fatigue all thread. If electric power, then not a problem. "

Can you elaborate on this? Sounds very interesting.


Thanks,
Mark

Scott, did you mean .070" thick carbon or .007"? The latter is plenty strong

I like the idea of screen material as a mask of sort to reduce epoxy amount. I think I'll try it next time, except on the balsa. Thanks for the tip

Matt

Mark, prepare the hole in the aileron as though it were to accept dowel stock. Substitute the carbon tubing for the wood dowel. BTW, carbon tubing sands a bit easier than wooden dowels, to smoother overall surface.

I typically will countesink the top side of the carbon to accept a flat head 6-32. Threading the carbon tube is straight forward, except the threads have relatively little strength. Or you may just drill out the hole a bit and simply glue the bolt in. I prefer threading and gluing but it's a minor issue. Screw the bolt in from the top until head is bottomed and flush with the top surface.

After the epoxy cures, I bend the bolt forward such that the clevis axis is on the hinge line. I have a bunch of short horns that don't get the hole anywhere near the hinge line so this is necessary for my set-up.

Bolt bending should be done very carefully as to not overstress the threads. I use a 1" long piece of aluminum threaded coupling stock from ACE hardware, thread that onto the bolt nearly all the way, and use the coupler as handle to start the bend. Just a little here, then move the coupler up a little and bend a bit more, and so on, until I am satisfied with the curve in the bolt and things align correctly.

I prefer using coupling stock as the handle rather than pliers. Much easier to control the bend with finger pressure, and doesn't bugger the threads

Hopefully thats clear. If not, let me know

Matt

Very clear. Thank you for the informative solution.

-mark

Could you tell more about the vacuum pump you use?

Gast MOA-V113-AE 1/16HP, 24in Hg, 0.5 CFM, continuous duty.

I got it off EBay a couple years ago for $70. cstsales.com sells them new for $246

Scott Smith,

I see you hollowed out the foam on your wing before sheeting it. Did it leave "dents" on the wing after vaccum bagging it due to the pressure applied where there's no foam under the skins ?

Thanks
Albert

The sheeting looks perfect. There is no indication that there is anything other than a solid core underneath. I don't know if the results would be the same bagging just the wing.

All those holes added up to over 250 sq in that wouldn’t be getting glue...that was the purpose in theory anyway. But since I couldn't control how much resin got applied to the core (I rolled it on with a lightly loaded 1/4 in foam roller), I ended up using more than double the amount of glue had I applied it to the entire sealed skin as Matt suggested. All those holes only removed 18 grams per core.

My panel weight (in grams) during construction were as follows:

Core 132
Slots and socket cut 124
3/32 Ribs 132
Socket/Root rib 160
Holes 142
Sheeting 280

The sheeting weighed a total of 88 grams and the CF laminate and a couple pieces of FG cloth were about 5 grams, leaving 45 grams added from glue.

I believe my foam may have been on the heavy side as well. A friend has some Black Magic cores that weighed in less than 100 grams out of the box. I’m guessing Lazslo Horvath mentioned above supplies Mike??? Anyone have a contact?

Scott,

Les Horvath's email is [email protected]. He will use whatever foam density you want from around 3/4 pound up. He always recommends about 1 1/2 pound density for our use and that works well.

I found a very short supply of 0.4 pound density a couple years ago and he cut several sets of cores (wings and stabs) per my design airfoil and planform. He is extremely well informed and does work for the full scale crowd as well. Also does special work for airfoil investigators like Selig. He is the real deal. A little cantakerous sometimes but will work with you.

On honeycombing a core, the way you laminated the cores by pressing the husks, you shouldn't have seen any evidence of the holes. Had you applied pressure directly to the cores, there would have been indents at the holes, giving the wing a golf ball look. That isn't a bad thing necessarily.... a little more drag but just as much additional lift. Would have been tougher to cover tho. It's an idea I have played with some and should pursue further in this age of constant speed. I don't believe I will see enough negatives to worry about... it will just look a bit different.

The few times I honeycombed, I reduced the core weight by about 45%. I leave behind about 5/16" ribs in geodesic pattern and in general leave the root area alone especially around the socket and the servo cutout. It's a good technique to master. If there's interest I can explain how I do it.

Matt

I just noticed this thread and wanted to chime in here. First, yes, that is 9 grams per skin for a total of 18 to 20 grams per wing. Remember, with Polyurethane glues, you want both skins to be equal with glue volume. More on one skin than the other can cause a warp. Also, the key to the success of such a small amount of glue, is lots of weight. Even with vacumn bagging, I would still use a couple hundred pounds of weight on a stable, flat surface to insure a straight wing. I now use 1100lbs of weight on the Symphony wings I build. Lance Van Nostrand had a picture of it in the K Factor a few months back. In regards to misting the cores, it does not take much to kick off the activation. I prefer the "mist in the air and wave" method as it is easier for me to control the amount of "moisture" that is applied. Once again, too much on one side than the other can cause a warp. Wood and water can be a sensitive combination. When I wave the core through, I immediately place the sheet and the core together so I dont loose the "humidity" I introduced to glue activation. As my tutorial explains more of my theories, it has worked well so far. Knock on wood. LOL I am glad to see this type of thread (thought I have been out of town and can't always check the puter), this is an excellent source for people to express their expriences. Good luck with the build, and Thanks for including me in your discussion. I hope my tutorial has helped. Terry