Sheeting Foam wings
 

just wondering if you really need to use the vacume bag method to balsa sheet a foam core wing ? i intend to buy 2 x 24 inch foam cores and sheet these with the normal 1.5 mm balsa sheets and use something like skin -it as the glue. thanks.

RE: Sheeting Foam wings
 

You don't have to use a vacumn bag.... I use a press(full wing length) I built years ago to squeeze the skins on under a 6" piece of laminated MDF using 1/4" allthread running through my workbench. Very cumbersome and heavy but it does an good job keeping everything straight and places quite a lot of pressure on the skins. You can even use a good board and stack a lot of weight on top (this is how it was done for years by almost everyone). Books, bricks, blocks approximating the weight of a small car(just kidding) would be about right!

That said... the vacumn bag system is by far the best, but if you are on a budget, there are alternatives that will provide acceptable results.

RE: Sheeting Foam wings
 

Aww come on DMyer, you only need about 500 to 600 pounds of weight on it to do it right! :D You do want to pile quite a bit on it to get a good bond. I used to have a perfectly flat area (very important if you want a straight wing!) marked out on the garage floor, have the lay-up taped together, place a flat 1"x10x5' board on top and then begin adding concrete blocks, cement bags, bricks, pavers, ceramic tile or whatever I could find on top. The board on top helps keep the pressure even, and allows you to distrubute the load better. I used 500 lbs minimum.

I think the press idea is also a great way to do it, but I decided to get a vacuum instead. Either way works fine for attaching the sheeting, and I dare say that you can't tell what method was used when the wing is done.

Have fun,

RE: Sheeting Foam wings
 

Scott are you ready for the race in several weeks :D

RE: Sheeting Foam wings
 

I wish I was. I have some Scorpion kits on order, but the wings are my big hold up. They come from California and won't be here in time. I am however, about to mold the v-tail and the final fuse molds for 428 :D I am on the final polishing of the plugs and will lay up the molds over christmas.

Give 'em hell for me!!

RE: Sheeting Foam wings
 

So you are not coming to the Tangerine, Scott??

RB

RE: Sheeting Foam wings
 

Think about this. A quicky wing has an area of 500 sq/ins. That is 500 on the top surface and 500 on the bottom surface. Total 1,000 sq/ins. I use a vacuum bag set to apply 4 #/sq/in. That is 2,000# pressure on the top and bottom of the wing. Total 4,000#. How many toolboxes, cement blocks, housebricks, books, etc, etc, etc would you have to lift on to the wing to apply that much pressure? I do it all on my worktop with no effort. When it is done I roll up the bag and put it away.

Ed S

RE: Sheeting Foam wings
 

So I would need to park my Dodge Ram 4X4 on top to get similar results?:D:D

RE: Sheeting Foam wings
 

I am afraid not Randy. I told Gary by email, and I hate that I can't be there. This year I am going to have to step back a little, and hope my wife can find a new job so we can get out of this hole, and I can continue to race. I will still hold the events in the spring and fall, but I may not be racing much until next year. I plan to test the composites for 428, and hope in 2009 I can start in the 428 class.

Sorry Mr. WC sir... :D

RE: Sheeting Foam wings
 

ah, no worries Scott. family first for sure. we'll see you next time around for sure...

WC

RE: Sheeting Foam wings
 

Scott, do you have the race date for March race in Mulberry? I will be in Venice March 13 to April 9 and would love to race with you again. Let me know, I will pack up the planes.

RE: Sheeting Foam wings
 

Randy, it should be in that range, I am waiting for the April date from the Markham park guys so that we don't conflict with their event. I will PM you with the final date as soon as I know. ;)

RE: Sheeting Foam wings
 

Randy,
John McDermott and l are coming down. J MAC will fly Q40
and l'm gonna do 424&428. l was wondering about how many entries
do you think will be there????????


Thanks, John G.

RE: Sheeting Foam wings
 

I built my first racer without using a vacuum bag system. It went together O.K..

On later models they are all done with a vacuum bag system. That is the way to do it if you can get the parts. I took some pictures and wrote a how to. See below:


Building a vacuum pump and other construction tips are shown in these forums.

http://www.nmpra.org/phpBB3/viewforum.php?f=12

There is lots of good information there.

RE: Sheeting Foam wings
 

Ed, check your concept of force again.

RE: Sheeting Foam wings
 

what i can,t understand is the use of excess weight just to glue 2 surfaces together, surely if too much weight is applied to the soft foam and the soft balsa [ whats going to give ] also where is the glue going to go [ squeezed out ] . when you look at foam there is no penetration of glues to soak into the cells, also goes with balsa wood.

RE: Sheeting Foam wings
 

John G. - I think we have around 20-25 signed up right now, give or take a few. And most the locals don’t pre-register.. we were originally hoping to have around 20-25 "428/422" guys, maybe more? If all our locals did show up, we'd pull about 30 pretty easily. But with the dates being close to Xmas, and the economy still hurting some.... who knows. We’ve got Dub Jett and Jerry Small coming from Texas. We’ve got Tom Scott and Craig Grunkmeyer coming from Ohio. Rusty Vanbaren coming from California. So we’ve got some national travelers headed out, which is cool of those guys coming to support. As well as you guys up in NC making the trip. Dennis O’brien throws a awesome party as well, we’ll announce that at the race.

FWIW…. Back when I started racing quickee, we built foam wing planes. And the wings were both one piece foam cores, and two piece foam cores. We have a piece of steel with a couple handles, it weighs about 65 lbs… and that’s all we used on the two piece foam core wings. The weight was not long enough for the one piece cores, so we just placed a couple gallon paint cans on the ends. Point being… it appears that we used far less weight than everyone else. And rest assured, we never had any balsa skins come lose after flying the model.

The question I have is. When you vacuum bag a set of wing cores. Do you still weight it done? To keep it from twisting? Meaning…. How do you insure that the wing (or wing half) doesn’t twist from the bag shrinking around it?

Randy Bridge

RE: Sheeting Foam wings
 

The object of the exercise is to end up with a true lightweight wing. You asked where will excess glue go? The answer is obvious. Do not apply excess glue to the skins in the first place. When my skins are ready t be applied to the core the glue is barely visible, the balse has a slight damp look to it. There are no shiny (Excess) glue spots on the skin. All excess glue has been squeegeed off. The even vacuum bag pressure will ensure that all of the skin is down tight on the core surface. The pressure I apply does not crush the foam.

If you think the above is nonsense, then slop on the glue, shove it all in the bag, apply the pressure and watch the glue come up through the wood.

Ed S

RE: Sheeting Foam wings
 

High Plains

It seemed simple to me, atmospheric pressure is all around us. If not then please educate me.

Ed S

RE: Sheeting Foam wings
 

Ok guys, I know I am not the sharpest knife in the drawer but I am having trouble visualizing how you are using weights and/or clamps to apply a uniform pressure to a sheeted foam wing. It would make sense to me if anyone said that they put the sheeted wing back in the shucks. That would help apply a uniform pressure to the whole surface, but nobody mentioned that possibility. By the descriptions given, what I visualize is a wing with an airfoil shape laying on a flat surface with a flat board or whatever lying on top. It appears to me that the wing surface would have a very small footprint on both the top and bottom where the pressure would be applied.

I have sheeted foam wings in the past and have always used contact cement, usually a spray adhesive that will not attack foam on the cores and regular old brush on contact cement on the balsa sheet. After it dries past the tacky state, carefully roll it on being careful to position it right the first time because when it touches it sticks and it’s there permanently. No weights necessary, just press it down good to get out the air bubbles.

I think that the downside to using this method is the extra weight added to the wing from the contact cement and I am assuming that you folks are using some kind of epoxy. That would explain the need for weights or vacuum bagging.

When you get to be 70+ and are from the South folks need to speak slowly and distinctly for you to understand. So please type your answers very slow so I can keep up.

Thanks

RE: Sheeting Foam wings
 

You are correct Regent, the wing with all the internal glue, carbon fiber strips, fiberglass pieces and balsa skins are placed back in the shucks (I also add a sheet of wax paper between the shucks and the wing to aid in keeping it from sticking if any glue oozes out) and then add the weight or vacuum to it. If you vacuum it, you will need to add a couple of small weights just to ensure it doesn't move aroud any. I use 5-7 inches of vacuum on my wings and MGS epoxy resins. I also bond the foam cores into one piece, and lay up 2 layers of 2" wide 2oz. fiberglass along the trailing edge and do all the center section additional glassing UNDER the balsa skins.

As far as using adhesives other the lamination epoxy resin systems, I do not trust them. Do a test with identical sections and different adhesive types. I did this with 4 different epoxies, 2 poly glues, 2 alphatics and normal hobby store epoxy. I did them all at the same time, and placed them under the same presure for curing. I then weighed them, and did some flex and fail testing on each sample. All I will say is, I use MGS resin systems for a few very good reasons. ;) Most either melted the foam somewhat or were to flexable or weak. I suggest you do some tests and see what will meet your needs.

Good luck with your project!

RE: Sheeting Foam wings
 

Ed, if you are using 4# over 500 squares by vacuum, then it only takes 2000# of weight to do the same, not 4000#.

RE: Sheeting Foam wings
 

Randy prooved a good point. While using a vacuum bag or ton of weight can help, properly done, must less weight can also lead to successful wings. I've personally used everything from very thin industrial carpet tape, to a vacuum system to sheet wings, and all worked. They each had different advantages/disadvantages to the others, but they all got the job done.

I believe the original question was can it be done without a vacuum bag..and the answer is...yes.

Ed,
If you just pulled a vacuum of 4psi on an empty bag without a wing in it, how much vacuum pressure would it have holding the two sides of the bag together?

RE: Sheeting Foam wings
 

Some kind of oxymoron Gary?

RE: Sheeting Foam wings
 

I've used 3M 77 and southern sorgum without weight or vacuum successfully.[8D] And I've also used them unsuccessfully. :(

Denis

RE: Sheeting Foam wings
 

Bob, yeah...deal with it...I wasn't completely awake yet!

RE: Sheeting Foam wings
 

But it is 500 sq/in both sides of the wing. Maybe it is easier to understand if you visualise the wing suspended in mid air. The bag will collapse all round it, not just on one surface.

Gary,

Have we been here before? With a porous wing in the bag, all of the atmosphere is not removed with the vacuum I apply. If it was the foam would be crushed. If the bag is completely emptied of atmosphere then the total surface area of the bag would be subject to full atmospheric pressure. which is around 14.7#/sq.in. If there is nothing in the bag to "Store" atmosphere as it were the bag will probably collapse completely with a low vacuum setting.

Do you ever wonder why we do not implode? It is because we have atmosphere inside us pushing outwards, with the same pressure as the atmospheric pressure outside of us pushing inwards trying to squash us.

Ed S

RE: Sheeting Foam wings
 

It seems that Scorpion Racing and I are on the same wave length with vacuum bagging. We even use the same epoxy resin. We can prattle on about pressures and in which direction as much as we like.

All I can say is that my bagged wings come out of the bag light, straight, strong and stiff with no glue oozing out of anywhere.

Ed S

RE: Sheeting Foam wings
 

You are right Ed, but the table also pushes up with 2000# also.

I think we did this discussion two years ago.
I guess we are all big gas bags.

RE: Sheeting Foam wings
 

High Plains,

At last we are in agreement.

Ed S

RE: Sheeting Foam wings
 

I no longer sheet wings without vacuum. You can use less resin to get a good bond because the pressure (no matter how you calculate it) is dead ***** even over the entire surface.

RE: Sheeting Foam wings
 

It is actually amazing how little glue actually is used when bonding skins. I mix about 2-OZ of West systems for an entire wing. I squeegee it all off the skins until it is barely visable as wet. I will brush a little back on the leading edge and trailing edge CF and fiberglass(i like a really stiff trailing edge). It is amazing how much ends up back in the cup! To get a good bond I like to lightly sand the cores and skins smooth(vacumn/tack rag the dust). Some people spray the skins with hairspray to prevent the epoxy from penetrating too much and using even less glue.


I have seen many foam core wings post crash bonded from every method descibed in this thread... they all look the same in the can... and delamination is never a problem. Build your wing using whatever method fits your time and budget, go fly, and don't worry about it too much!

RE: Sheeting Foam wings
 

I was thinking there are some with a little too much atmosphere trapped inside. Don't get any on ya!:D

RE: Sheeting Foam wings
 

Guys I really appreciate this discussion even if it's old hat for some of you. It has had my mind working on how I can do this myself with what is available and I understand all the practices you have shared.
I came up with a question on the ride home tonight about what you guys put under the skin...some use fiberglass tape and others carbon tow. My question is are all of these laid in a straight tip to tip line like a spar? Does anyone or is there anything to gain from running an X across the wing for torsion stiffness? I look forward to your answers.:eek:

RE: Sheeting Foam wings
 

Vic, can't say that I built a lot, but the two or three old Formula one wings I built were carbon tow running spanwise, about the high point of the airfoil, between the sheeting and the cores.

And they were built without a vacuum pump, and it was my dumb thumbs that did them in, not wings folding or delaminating!

RE: Sheeting Foam wings
 

I have used .007'' x 1/2'' wide carbon strips for spars. I have heard others in the forums question the need for this, and I suspect that they may have a point, but have not had the guts to leave them out. Making an X may increase torsionsal stiffness, but the sheeting makes them plenty stiff enough.

If you use the CF spars, make a shallow groove for them to sit in, or you will get a 1/2'' wide bump running the length of the wing. What I do is make a sanding block that is about 2'' wide and has a 1/2'' wide strip of 80grit sandpaper glued to it. Use double sided tape to attach a straight edge to the core so that when you put the sanding block against it, the 1/2'' strip is positioned where you want the spar to go.

Now sand the entire span until the sandpaper cuts to the maximum depth.

RE: Sheeting Foam wings
 

If you put a carbon strip on your wing, put it on the bottom side of the wing.
Since racing stresses on the wing are mostly positive, the bottom is where you will
gain the strength. Imagine pushing a string and you can see that adding it
to the top is not much help. If you are sheeting the wing as 1 piece, full span,
most folks cut a v shaped piece of fiberglass cloth (or 2, with the first one bigger
than the 2nd) and put this between the core and skin. On the bigger one, make it
about 14" wide at the l.e. and 6" at the t.e.. Probably about 8 and 5" for the 2nd one.
Cut this cloth on the bias (so that the fibers are running 45 degrees to the span) to
get the most strength. If you have room for extra weight and want a really stiff
wing, add a layer of 3/4 ounce cloth, full span and chord, between the skin and core.
brad

RE: Sheeting Foam wings
 

Hey Vic, I use a strip of .007 x 1/2" wide 48" long carbon fiber on top & bottom at the max thickness of the wing as a spar. I also use 2 strips of 2oz fiberglass cloth 2" wide x 52" long and 1 strip of 2oz fiberglass cloth 1" wide x 52" long on the trailing edge to create a very stiff and sharp TE, and to stiffen the ailerons up some (The glass allows me to sand it sharper than balsa or plywood, and it is very stiff with the MGS resin.) . I also add a few pieces of 2 oz fiberglass cloth in the center section (under the balsa skins) as added insurance against flex and wing mounting, the same as most people do on top of the skins. I do all of this under the skins so that the outer balsa wood shell is smooth, as I like to leave the balsa natural looking and clear glass it with .5 oz cloth and just do some trim and lettering for decorations.

I think torsional stiffness is fine due to the core and balsa contact being constant. The only way it would flex would be if you cut out pieces of foam or the glue was missing in areas. I also had more flexable wings when I used poly glue or that ZAP laminating resin. West system was stiffer, but melted to foam a little bit more than I liked.

But as they say, ... your results may vary!

RE: Sheeting Foam wings
 

Excellent info! Thanks guys.

I thought you guys might get a good laugh out of this repair I did on my Predator a while back. A few pc of carbon, gorilla glue, balsa, and a fiberglass patch. It looked like the unibrain for a while but worked just fine.[sm=bananahead.gif]

RE: Sheeting Foam wings
 

Actualy this is not the case. For a wing to fold the top skin/spar has to compress. It is far more difficult to compress material than it is to stretch it and cause failure.

Ed S.