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Sheeting foam cores - 1/4/2003 3:12:39 AM   
Vince


 

Posts: 1650
Joined: 2/2/2002
From: Nederland, Tx.
Status: offline 		[QUOTE]Originally posted by wildblueyawner
Hi all,

Will the expansion of the poly glues (Probond, Gorilla, etc) tend to lift the sheeting of a non-bagged wing? [/QUOTE]

If you leave too much glue behind, it conceivably could lift the sheeting of a non bagged wing. The key is scraping it almost all the way off to where all you have is a sheen of Probond. Mist the core with water and apply the sheeting with the glue on it. I usually pull tape around the leading and trailing edges to pull them down tight against the core, then I weight the entire core down.

Vince

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       Post #: 26

Sheeting foam cores - 1/4/2003 5:08:54 AM   
ml3456-RCU


 

Posts: 558
Joined: 10/18/2002
From: Darien, IL, USA
Status: offline 		Vince, Joe

Thanks, sounds like the way to go.

Good bye to edge gluing!!

Mark

(in reply to Dennismate)
       Post #: 27

warp with Probond? - 1/6/2003 1:16:02 AM   
patternwannabee


 

Posts: 244
Joined: 10/8/2002
From: Mars, PA, USA
Status: online 		I've been attaching wing sheeting with Probond polyU in a vacuum bag and have come across a problem:

After removing the wings from the bag and letting them dry a little, a warp appears along the trailing edge.

I wonder if anyone else has come across this problem.

First, I true the edges of the 1/16" contest balsa sheeting, tape together tightly, mist the balsa, or the cores, apply the adhesive, scrape thin, place on the cores, insert in bag, place bag on bottom cradle, pull vacuum, weight the wing/bag on top of the cradle lightly with sandbags, then wait about 10-24 hrs.

When I remove from the bag, initially, the trailing edges are straight and true as can be, but after about 20 min, a warp develops.

I'm thinking that the moisture I use to activate the glue is swelling the wood, and that the glue is cures while the wood is expanded. When the wood has a chance to dry out, it shrinks.

I'm currently doing some experiments with polyU in a vacuum bag.

Has anyone else had this experience or any thoughts? I've already ruined a couple of wings.

(in reply to Dennismate)
       Post #: 28

Bagging - 1/6/2003 1:25:13 AM   
ProfLooney



Posts: 2415
Joined: 1/18/2002
From: Moline, IL, USA
Status: offline 		Patternwannabe I have a question and that is I dont vacuum bag dont know first thig about it or why ayone would do it, but my question is why the moisture? When using Probond you do not need any moisture for it to kick off. I am thinking that the moisture sitting in the bag for that long of time could be causing your problems. I have sheeted several cores before I found out foam hates me so I have never used it for anything but a funfly plane and i dont even build them anymore. but I have never had a problem from releasing or warping on the core.

I tape my sheeting together add my probond to the core set it in bottom cradle glue top add sheeting add top cradle and weight down and havent had a problem before. What does wing bagging do that would give different results? just curious as I always hear about bagging but see no advantage to it.

Joe

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       Post #: 29

Sheeting foam cores - 1/6/2003 2:38:50 AM   
Flyin Woodbutcher


 

Posts: 836
Joined: 12/16/2002
From: Ashland, VA, USA
Status: offline 		The advantage to vacuum bagging is the pressure that can be exerted upon the balsa onto the foam. The bagging forms the balsa to the leading and trailing edges for a tight fit.I am not sure what the psi is when vac bagging. Maybe someone else has these no. and more info.

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       Post #: 30

Why Vacuum bag - 1/6/2003 2:50:17 AM   
patternwannabee


 

Posts: 244
Joined: 10/8/2002
From: Mars, PA, USA
Status: online 		ProftLooney,

A few years ago, I tried ProBond for the first time, and without a bag. Perhaps the surface I used to let the cores sit on wasn't totally flat, perhaps the cores weren't completely aligned to the cradles, perhaps the foaming action wasn't enough, but I did detect a few spots where the sheeting was not attached to the foam core. I may have used about 50-60 lbs. to weight the stuff down. Any more than that, and I was worried that my table would not take the weight, and I would have to do that on my basement floor. My basement floor is not straight.

I have heard anywhere from upwards of 100 lbs to 200 lbs as a good weight for setting on top of foam cores for sheeting. As I delve into bigger and bigger planes, the weight to be used, also goes up. For instance, for a wing of 1000 sq in, or 500 sq in for a single wing panel, 500 lbs on top of that would equal 1 lb/sq in. That's a lot of cinder blocks. That plus you have to somehow ensure the distribution of that weight is even over the whole surface. My vacuum setup will maintain a selectable vacuum anywhere between 5-25 in hg which is about 2.5-12.5 lbs/sq in. Of course, white foam won't withstand the higher vacuums. However if I were to vacuum a wing at 7 lbs/sq in, getting the same pressure on the wing with weights would require 2800 lbs. I don't have that many cinder blocks.

One problem I no longer have is getting the sheeting to adhere to the foam core close to the leading edge, especially if there was a lot of curvature close to the LE. With a vacuum bag, it's a snap.

Since I set up the vacuum system, I've used it for a lot more than just sheeting wings. It's also great for laminating parts. If I had to laminate a long 1/32" ply doubler (say 20" or so) to a fuse side, for instance, getting good adhesion would require a lot of clamping force. Getting even adhesion, I'm not sure exactly how. With a vacuum bag, it's a no-brainer.

I think you're right about the moisture in the bag that whole time. When I finish the experiments, I'll post the results here if you're interested.

One other reason why I use a vacuum bag (probably the main motivating force) is that it's another toy to play with. That makes my hobby that much more complicated and gives me more justification to spend more money and more time on it.

(in reply to Dennismate)
       Post #: 31

bagging - 1/6/2003 2:57:24 AM   
ProfLooney



Posts: 2415
Joined: 1/18/2002
From: Moline, IL, USA
Status: offline 		OK I understand now kinda same thing they do when they are laminating furniture with vineer. Like I said foam hates me so I dont use it anymore. the largest wing I did it with was a 98" ws cloud dancer and hadnt had any problems just using the cradles thats why I was curious the difference.

Joe

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       Post #: 32

Sheeting foam cores - 1/6/2003 4:13:55 AM   
patternwannabee


 

Posts: 244
Joined: 10/8/2002
From: Mars, PA, USA
Status: online 		ProftLooney,

I'm sorry I hadn't read your earlier post carefully. As to why I add the moisture, I guess I'm still in the experimental phase. I had read in a couple of posts that moisture is what kicks it off and that just a swipe with a damp rag or a misting was necessary. I had also heard that it wasn't necessary, that ambient moisture in the air was enough. My basement is pretty dry and since I do most of my building in the winter, I added the moisture just to be safe. Guess I won't be doing that any more.

As to your experience and probably most other peoples experiences with cores working just fine in their cradles, maybe it's some bad technique I'm using, but after trying the vacuum thing, it works for me.

Now only if I could get rid of the warps....

Albert

(in reply to Dennismate)
       Post #: 33

Sheeting foam cores - 1/6/2003 4:35:56 AM   
GW



Posts: 540
Joined: 2/28/2002
From: Guntersville, AL, USA
Status: offline 		To fix the bow:

Slightly moisten the sheeting of the finished core. Both sides

Place back in the shucks on a flat surface.

elevate one end 1/16" so that the bow is reversed the other direction from its natural state it was in.

Warm the room up nicely and keep it there for 24 hrs.
Remove and look at the beutimus straight wing.

In a little bit, you may still notice a slight bow coming back,
If so, "STOP LOOKING AT IT" because it is not going away now.

I have had several people notice slight bows in wing panels, and swear that will make a pattern wing unflyable. HOGWASH!

One of the best flying planes I ever had was a Vortex from RC City

If you laid a ruler along the TE of the wings, there was a 1/8" or better gap about halfway down the ruler on both panels ( I did not build these by the way) . Bought the plane that way, because the guy didn't like the bow in the wings.
Guess what, did not matter one bit. At least not to me , but I am not a primadona flier either, I'm sure a world class FAI pilot might be able to notice so problems, but most of us will not!!

Now a warp,(washin-washout) thats another story, if the incidence is different from the root to the tip, That you must fix!!
Use the same method as above. over and over again till it is right.


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       Post #: 34

RE: Sheeting foam cores - 5/26/2004 11:26:15 AM   
wildblueyawner


 

Posts: 197
Joined: 2/16/2002
From: Covina, CA,
Status: offline
quote:

If you decide to use S. sorghum make sure to seal the inside part of the skin with Balsarite or equivalent
foxx - Which type of Balsarite? One is for fabric covering, the other for films.

Anyone - Can Pro-Bond or Sorghum be used to bond balsa sheeting to the high-density "hard" foams such as pink, blue, Rohacell, etc?

(in reply to foxx)
       Post #: 35

RE: Sheeting foam cores - 5/26/2004 3:22:23 PM   
Deadeye



Posts: 3878
Joined: 7/16/2002
From: Conrad, MT, USA
Status: offline 		I have read this thread thoroughly. I'm about to sheet my first project, a Byron's Cap 21. A very experienced foam core sheeter in our club recommended cutting off the LE, and sheeting up to it, wait for it to dry, and glue a new LE to the wing, sand to shape. He said this eliminates the LE sheeting problem, and he is using ProBond. Do you guys utilize that method?

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       Post #: 36

RE: Sheeting foam cores - 5/28/2004 7:21:11 AM   
patternwannabee


 

Posts: 244
Joined: 10/8/2002
From: Mars, PA, USA
Status: online 		Deadeye,

In most plans I've seen, the foam core templates do not include a shaped LE. Most cores are shy of the LE by 1/4 to 3/8".

I myself have not tried sheeting a core that includes the LE. I imagine this would be very difficult to do correctly. I agree with your friend and would do the same if your foam core has a shaped LE.

(in reply to Deadeye)
       Post #: 37

RE: Sheeting foam cores - 6/5/2004 2:09:56 AM   
Mrbmp


 

Posts: 23
Joined: 1/12/2003
From: Childersburg, AL, USA
Status: offline
quote:

I am not sure what the psi is when vac bagging. Maybe someone else has these no. and more info.


Up to 14.7 PSI at sea level if you have a good enough vacuum pump.
you can calculate it if you have a vacuum guage, roughly .5 psi per inch hg.

(in reply to patternwannabee)
       Post #: 38

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