Author Topic: Blank (Read 4840 times)

Motorman · « **on:** October 28, 2018, 07:32:35 AM »

Blank

Lauri Malila · « **Reply #1 on:** October 28, 2018, 08:21:05 AM »

There is no such thing as unidirectional carbon veil. Carbon veil has randomly oriented fibers and it will not add much stiffness to your flap.
Get the thinnest carbon UD, like the stuff from Vladimir's models (UA) ur the Dutch ThinSkin and glue it on in +/-45 degrees.
Do you think you can compress it somehow, like between glass plates?
Of not, why don't you make completely new flaps? It's usually quicker and prettier option. L

Curare · « **Reply #2 on:** October 28, 2018, 02:17:33 PM »

It does, but you're not gonna get a 1/2 ounce uni.

The veil everyone uses is OMNIDIRECTIONAL, and as Lauri says, it's not going to add the same stiffeness as a biaxial woven roving does.

Dave Hull · « **Reply #3 on:** October 28, 2018, 08:32:05 PM »

ACP has 2.9 oz per carbon uni material. I didn't check a bunch of sources, but finding lighter material on the shelf might be tough.

https://store.acpsales.com/products/2382/carbon-fiber-uni-web-unidirectional-fiber

The flap layup schedule really needs to be at an angle like the 45 deg that Lauri suggested. And, if you choose uni it needs to have two layers on each side at opposite 45s to pick up both torsional load directions and to have fibers in tension. Just running uni lengthwise along the flap would make it stiff in span-wise bending, but would be pretty useless in torsion, which is what you are probably trying to improve. It wouldn't be much better than just coating the flaps with the epoxy all by itself.

I have cut the flaps off of several planes, leaving the hinge intact on the wing TE side. Made new flaps, and then reinstalled using new half-hinges. Personally, I would go with plain weave E-glass on a 45 deg angle. Probably .58 or .75 oz. per and either pressed or bagged on the bench. You can do both flaps at the same time.

Lots of guys swear by their processes (they vary) using super lightweight carbon veil. I didn't like how much filler it took to prep the material I tried. (This was a material that was recommended to me, but may not be the same as the guys using carbon that are huge proponents.) And sanding thru a bunch of the carbon in order to use less filler and get your final finish seems like 3 steps forward and 2 steps back to me. So, not a fan of this method so far, but I want to try bagging it to see if that will get it to lay down so the carbon stays on the plane and not in the sandpaper. And without a huge pinhole problem, which is a pain.

Good luck with your improvements,

Dave

Curare · « **Reply #4 on:** October 28, 2018, 08:55:41 PM »

Dave, I had a similar experience on my last plane, tried the veil, and found that a) it absorbs epoxy like a sponge, and the surface finish wasn't all that great (even when bagged).

I too found that to get it flatted out I'd blasted through the veil in a number of spots, thereby reducing the 'monocoque' I was expecting it to be.

Overall, structural stiffness didn't change much and it took far more priming and filling that glass cloth normally does.

I'm not sold.

Dave Hull · « **Reply #5 on:** October 28, 2018, 10:14:06 PM »

Hmmm,

Well, then I better not get my hopes up for bagging it, then. It is hard to know if the material itself might be different. But of the planes I have seen under construction, and photos I have seen, it seems pretty routine for guys to sand a good deal of the carbon fiber off. At least with the 1/2 oz. plain weave E-glass it all stays on, so I trust the part structurally.

Did you try a molding sheet in the layup? I have had some good success with racing wings when I cut a thick (.040"?) polyethylene sheet to match the exact planform. After wetting out the cloth, I laid the pre-waxed molding sheet directly over the layup, and then bagged it. You could alternatively use a press on solid parts like flaps if they are not built up. This gives a great finish, but it is going to take whatever resin the thickness and "holiness" of the fabric demands, or else we're back to a starved layup. And lots of post-mold prep prior to painting. If you are bagging, you do not need to pre-calculate the exact resin volume with this method. Just lay a bleed drain (felt strip) around the periphery of the part. I have to remind myself to dial back the vacuum a bit, but when I get that right, the finish is so smooth that if I didn't polish the wax enough, I can see the swirls in the final layup.

This is the technique I'd try first on some carbon veil flaps. So the pass/fail grade would be based on:
1. How much weight would this add to the balsa flap? It would be compared to a filled, primed, whatever else weight of the veil and dope guys techniques.
2. How stiff is it torsionally? Again, same comparison basis.
3. Does it avoid all or nearly all pinholes, so as to avoid the fill, prime, sand and PITA of the equivalent dope finish process.

I think my first attempt will be on some Magnum flaps, since that one is ready for some flaps before the airframe can be called done.

Hopefully, some of these issues will help the Motorman decide on his options.

Dave

Target · « **Reply #6 on:** October 28, 2018, 10:35:35 PM »

You guys need to look up Carboline fabric. That is what you should be using instead of mat, especially in that application. Solves a multitude of problems.
But what do I know, LoL…

I'll let you google it, and figure out why I say what I do, or you can just tell me I'm wrong, because I haven't been flying U/C for decades like you all. ;-)

R,
Target

Curare · « **Reply #7 on:** October 28, 2018, 10:43:32 PM »

Dave I use .080 polyester sheets to do my layup, then apply those to the control surfaces. What I found was that it was hard to manage the amount of resin, you can't scrape the veil or it'll turn to fuzz. I found the best way was to roller some resin onto the sheet,
then lay the weave down on it, and gently roller it out to spread the resin, and mop up with toilet roll. Even so i was horrified to see the amount of resin going into the veil. With 3/4oz E glass you can just pour a puddle into the middle of the sheet and work it around, and it flows out nicely. Veil on the other hand if you do that you'll wonder where your puddle went, and it will not flow!

After bagging I'd found that I either had too much resin (which worked out the best finish wise as the veil was sealed) or not enough and the veil would 'float' into the next layer of dope / primer / paint....

The heavy parts were probably 1:4 veil and 3/4 epoxy (a %25 roving content),maybe more, and the dry bits were 50:50. I suspect that the balsa does it's fair share of absorbtion of the epoxy too, which doesn't help.

Applying it to rounded surfaces like a fuselage nearly had me in tears - it has a certain mount of stiffness, and wants to return to a roll or a flat (depending on what you have, mine came rolled up). I found that by the time I'd put down the veil at the front of the plane it was already curling up by the time I'd had the rear 'stuck down'. Faced with a curing epoxy mess and bits of curly-wet CF everywhere I had to get creative to hold it down, and used saran wrap to act as a bandage to hole the veil down until the epoxy cured. Any gains I'd made in getting the balsa to be beatifully flat were pretty much killed off after that, and I sanded a fair amount of the veil off trying to flat the surfaces out again. Needless to say I was upset about it all. I did my wheel pants and cowling with 1/2oz E glass and was instantly reminded how much easier it is to get a nice finish that way. Sure there's some weave to fill, but everything draped down beautifully and damn well stayed where it was put!

I suspect that the reason everyone is happy with the method is that they use dope, and can stick the veil down, (permanently) quick with dope, and rub in any recalcitrant spots before moving on.

I thought I was being smart using epoxy, but boy was I wrong!

Curare · « **Reply #8 on:** October 28, 2018, 10:44:39 PM »

Quote from: Target on October 28, 2018, 10:35:35 PM

You guys need to look up Carboline fabric. That is what you should be using instead of mat, especially in that application. Solves a multitude of problems.
But what do I know, LoL…

I'll let you google it, and figure out why I say what I do, or you can just tell me I'm wrong, because I haven't been flying U/C for decades like you all. ;-)

R,
Target

My DLG (behind me as I type this) is carboline. It's pretty and all but not cheap!

Tim Wescott · « **Reply #9 on:** October 28, 2018, 11:10:39 PM »

Motorman: yes, unidirectional means one direction. This was kind of alluded to, but not pointed out straight out.

Curare would have you believe that veil is omnidirectional, but it's pretty much limited to randomly oriented in TWO dimensions, not even the three we can touch, much less the 11 or 23 or whatever that physicists want us to believe exist.

The ACP web site seems to be down at the moment -- there's a CF sock material that automatically puts the fiber on a bias. I couldn't tell you what size to order, or if it works, but it may be something to think about.

Howard Rush makes (or has made in the past, I dunno which) flaps which feature a LE tube of carbon fiber on a 45 degree bias, with light balsa flaps glued on. They are reported to be quite rigid -- but, Howard makes his own tubes, and my own research as to what's on the market doesn't cough up anything that really looks good.

Curare · « **Reply #10 on:** October 28, 2018, 11:53:16 PM »

Geez Tim, way to get techical about directions!

I can tell you though that once it all turns to fuzz it is very much a ball of omnidirectional uselessness!

What I can say is that veil, or *tissue* as it's known in the industry is more of a felt than anything. The fibres are long, but don't necessarily go in any specific direction, and cross back and forth over themselves, so not really that structurally strong when looking at it from a purely fibre orientation view.

Chopped strand mat is different in that it's a whole mess of small straight fibres that get connected together in the resin, sort of like having millions of unidirectional fibres, in all directions, which makes it structurally usefull,and 'neutral' (not biased or having any grain).

Woven roving is a bunch of tows (multiple strands running in the same direction) weaved across each other.

Unidirectional rovings are a number tows all facing the same direction, but generally stitched together for ease of laying up.

Carboline is a bit of a mix the tows that would normally make up a weave have been spread out, like a uni, but very thin, and then another set of twos are set at a bias underneath.

Textreme is similar to weave, but the tow instead of being a bundle (roundish in cross section) is flattened out and then the flat tow is weaved together.

Carboline and textreme are useful to us as they contain a very high number of strands for their thickness, which means less resin, and correspondingly less weight for a given layup.

The trade-off is price.

There may be some benefit in considering doing a "Disser" style layup for a flap, where tows are laid in a grillage over the surface to give better torsion resistance, without having to resort to expensive lamintes like carboline or textreme.

Here's a disser wing for reference.

Dave Hull · « **Reply #11 on:** October 29, 2018, 12:56:49 PM »

Thanks for the info on Carboline. From your sample photo, the uniformity seems a little variable. If so, that might make it a little rich when filled. If I had some in hand, I'd sure try it on some flaps!

Dave

http://carboline.info/price

Target · « **Reply #12 on:** October 29, 2018, 01:10:25 PM »

No, the carboline is the opposite of rich when filled. Because it has zero intersections, there will be no excess epoxy used compared to woven cloth. It is SUPER THIN. That is how they make DLG wings that weight 110g, and will still take a full power discus launch.
Additionally, cloth is normally terrible in compression, even carbon, since the fibers are kinked and not straight to begin with.
Hence the use of uni-carbon, when you need stiffness to bending.

It used to be that you would have to use woven fabric to get torsional strength, but now, you can have 45/45 fibers without the dead weight of pooled epoxy at the intersection of the weave, AND without the kinks in the weave, that makes the fibers much weaker in compression.

This is not what you will want to make severe compound curves though, for the very same reason that it works great for wingskins. And it is not easy to distort.
Barry Kennedy of Kennedy Composites is the dealer for the Vladimer carbon sold in the USA. I would suggest a group buy by some that are interested to save money.

R,

Target

TDM · « **Reply #13 on:** November 12, 2018, 06:56:58 AM »

Pretty much any weight of Carboline will add more than sufficient strength (torsional) to your flaps. The problem comes during the finishing process. If you choose the light stuff 25g/m it is quite porous and leaves you with pinholes to fill in. Because of that I would stay with the 40g/m stuff that has little or no pinholes to fill in. You can fill the pin holes with some kind of filler or you can fill them with carbon which is always lighter than any filler and adds to the rigidity of your part.

Speaking of this we should have a Composite applications in the building techniques in this thread.

If you want to use fiberglass weave for stiffening flaps make sure it is a balanced cloth. The .5oz cloth is not balanced, you can use .75 1.2 or 1.6 cloth as those are balanced weave cloths. And there are techniques that keep the nice finish and weight down that should be followed to get light stiff and with nice finish.

TDM · « **Reply #14 on:** November 12, 2018, 07:53:57 AM »

You applied the wrong technique. I bet the flaps are heavy. 1.6 is a good weave it is dense and has little pores and is light enough.
If you want to go in this direction you can get away with the lightest wood you can find and I actually recommend that, C grain is recommended but not necessary if you glass it with 1.6oz glass. The proper way and cheapest way to do this is to stick the glass on Wax paper with 3M, cut to size, wet with a roller and dry with paper towels to remove excess epoxy, vacuum the balsa to remove all dust and throw this in a vacuum bag.
What you did may work only if you used a very dry roller to apply the epoxy otherwise all the pores and the balsa soaked a bunch of epoxy that now goes for the ride and adds no extra strength.
If you have a hot wire cutter you night want to try to laminate foam with 1/32 balsa and glass that for a stiff flaps.

Dave Hull · « **Reply #15 on:** November 12, 2018, 03:24:27 PM »

MM,

You did your basic wet lay up. If you weren't weight challenged as you stated in your first post, then you should have been able to get perfectly acceptable results.

But if you want increased fiber density and/or lower weight you still don't have to bag it, you can press it. The racing guys do this all the time. If you use a controlled amount of resin, then you don't need to worry too much about bleeders, either. For a solid wood part it works great.

The basic idea is to wet everything out over a plastic sheet that won't stick. Fold over the plastic (or use two sheets.) MonoKote backing material works pretty good. Now you essentially have a baggie with a wet part wrapped in glass inside. Squeegie the bubbles and excess resin to the edges of the part. Then put it between a pair of two inch thick urethane foam sheets. We're talking upholstery foam, here. Lay the foam sandwich on a flat bench and put a flat piece of plywood over the whole thing. Add a lot of weight. Or, make a dedicated press and put multiple bolts thru the edges of two plywood sheets. This won't tie up your workbench while you are either prepping the setup or waiting for it to fully cure.

Another opportunity for a flat part like most flaps is to lay it on your perfectly smooth, flat bench (glass pane) and eliminate the lower foam pad since you don't need the pad to conform to the contour of the part.

There are lots of improvements and variations, but laying up composites is not the all-or-nothing proposition some of the gurus will suggest. Yes, we can adopt some of the techniques that commercial fabricators use---but let's get real. How many stunt guys are buying shelf-life limited prepreg and using an autoclave? Or doing automated fiber placement. Right.

If this is all old news to you, then my apologies, and sorry to have added noise to the conversation....

Dave

Target · « **Reply #16 on:** November 12, 2018, 05:27:28 PM »

It is <ALWAYS> easier and more controllable to use more resin than wanted, ensuring a complete wetting out of the fabric, and then remove the excess.
Also, it is never advised to "thin Epoxy" with anything. Using the correct epoxy for laminating is the correct way to do it. MSG, Pro-Set, etc. West Systems if you HAVE to...
If your epoxy is thick due to ambient temperature being low, you want to warm the epoxy just prior to application, 85-90f is good. Removing excess epoxy is the way to control the weight, unless you want to use pre-peg and an autoclave, which is way past most peoples capability.

For you cavemen that don't know anything about vacuum bagging or molding fiberglass, try to keep an open mind, and you might learn some useful techniques. Trust me, some of them are worth learning, even for control line.... Here is a couple-

1. The whole 3M77 light spray and using waxed paper or butcher paper as a carrier so as not to distort the light bias weave is PURE GOLD! and definitely applicable to ALL modeling.
Just spray a super light mist on the pre-smoothed, unwrinkled fabric from about 2' above. Just a dusting. Then lay a smooth layer of your carrier paper on it. It could be waxed paper, butcher paper, something that has a "coating" on it, so that the epoxy will not soak in. Plastic can work as well, but it needs to not wrinkle.
Rub it down gently. After that, the two layers are lightly bonded, and you can cut or gently handle the layers without distorting the weave. GENIOUS!

2. Don't have a vacuum bag "Mylar" and want to get glass down on a flat surface smoothly with a glossy finish? (Like for a small repair or something).
Balsa wood (or other wood, ply, for example) can be sanded smooth and covered with packing tape. Using this piece of wood clamped over your flat stab, or whatever (fuse nose on a profile?) effectively makes a good base for a "press" that Dave mentioned. Epoxy will not stick to packing tape. Depending on how hard you can squeeze the pieces, you can get a good amount of resin to ooze out of the piece, getting closer to the "correct" ratio of fibers to resin. ALSO, the finish will be SHINY and ready to go if you don't HAVE to paint it. And no pinholes. If painting, just scuff and go.
Great for trailing edges on my composite sailplanes, but I'm sure you can see the applications are endless.
Need a wider than 2" piece (packing tape width)? I'm guessing that a fresh piece of monokote could be used the same way, and you all have that sitting around. Please test my theory FIRST before committing to this technique. Don't scratch the monokote on application to the wood, and avoid air bubbles.

Keep learning,
Target

Dave Hull · « **Reply #17 on:** November 12, 2018, 07:49:44 PM »

Now Chris, no reason to start calling us Cavemen---we prefer to be referred to as Neanderthals. That emphasizes the improvements in our brain case volume in the years since we gave up caves for man-caves....

One thing about the resin: it is my understanding that any two part epoxy that has equal mix ratios has been altered by adding filler. The part B catalyst just doesn't require as much volume. So if you are using an equal mix product, it is higher viscosity than it needs to be. For light cloth and fine weave, a thick epoxy is going to be a lot harder to work with. And yes, I have tried various methods of thinning it, but each of these introduces new issues. For example, I found the worst to be using isopropyl alcohol as some had recommended. It really impeded the cure schedule. And I really didn't want the water trapped in the matrix as things tried to cure. Why contaminate your layup? Nobody making aerospace parts does this.

I still recommend the EZ-Lam epoxy, although I have heard good things from trusted sources about West Systems. This has been hashed over before, but again, one of the claims to fame for West Systems is that the cold temp curing is better. This was important for boat shops, which was a primary customer. It is also used substantially in homebuilt aircraft construction.

Dave

Brett Buck · « **Reply #18 on:** November 12, 2018, 10:33:07 PM »

Quote from: Motorman on November 12, 2018, 10:09:48 PM

Really don't need a carrier with 1.6 glass, just pick it up, put it on the wood and brush Zap Zpoxy on it, done. I'm not building the Boeing 360.

You are giving up a tremendous amount of the advantages, or adding much more weight for the same advantages, by not compressing it. Dead space is just that, dead space, the maximum improvement for a given weight will occur when you have either resin or glass (or carbon), and nothing else.

Brett

Target · « **Reply #19 on:** November 12, 2018, 11:38:35 PM »

Quote from: Motorman on November 12, 2018, 10:09:48 PM

Really don't need a carrier with 1.6 glass, just pick it up, put it on the wood and brush Zap Zpoxy on it, done. I'm not building the Boeing 360.

Motorman

Cave-Man ^^^^^^^^^^^^^^^^^

Aren't you the guy that has made composite props before? I thought it was you that did this. If so, I am surprised to hear your response.

Yes, you CAN fiberglass parts static, and get the job done. Just more work and weight doing the filling and sanding. One of the BEST things about composites done in a press or vacuum bag is the finish needs now further work. And if you ask me, that is huge.
Also, especially on a long flat surface, with light-ish glass applied on a bias, it is somewhat wasteful and also easy to distort the fabric unintentionally (or intentionally, as is sometimes done for purpose) and create a mess. Yes, glass is relatively cheap. I'll assume that you might tuck that tip away for if you spring for 1k woven CF.
Dave- The beauty of the Carboline is that it doesn't distort because it isn't woven, and it is already on a carrier. Just cut to exact or slightly oversize and go!

Target · « **Reply #20 on:** November 12, 2018, 11:51:46 PM »

Here is a few pictures of my @ 5th ever vacuum bagged wing.
The paint sprayed on the plastic mylar is very special spray paint called "Krylon", it is extremely hard to find, and expensive, like $3/can.

I painted the mylars in a hurry one afternoon, about an hour or two including the masking and waiting for the paint to dry. So, I'm being sarcastic, it was not much effort, and the results are beautiful.
Because this plane is a sloper for high wind, no attempt to save weight was made, but the paint result is roughly the same if you do try to save weight. The top two pics are the painted mylars.
Next pics are the 4oz glass and 1/2oz glass layer being applied to the mylars. The paint transfers into the epoxy layup. Then I simply cut around the outside edge of the .014" thick mylar, to free it from the glass, and keep the glass and epoxy on the painted mylar. THIS is where you use a wallpaper roller and a paper towel to remove the excess epoxy, if you are building light. The wallpaper roller is good even if you aren't worried about weight, because it spreads the fibers and makes less voids for epoxy to fill needlessly.
After that, it gets vacuumed for a day or two. My vacuum pump is home made from a refrigerator compressor (High dollar!!- NOT!).
After that, when cured and or post cured with some heat, you peel back the mylar (otherwise known as Xmas morning!) and see your result.
All with NO SANDING!!!

R,
Target

Dave Hull · « **Reply #21 on:** November 13, 2018, 02:15:24 AM »

Nice job on the color.

Yeah, the mylar face sheet really is the bee's knees. If you are going for a nice finish, it can save a ton of work, as long as you don't starve the layup. And, it will work in a press or with vacuum bagging. I recall my first bagging attempt on a CL Goodyear racer wing. Too much vac pressure and it starved the layup. Can you say pinholes.......?

Using face sheets gets you close to the finish quality of a female mold. But you have to ensure it is flat/straight using good techniques.

Dave

TDM · « **Reply #22 on:** November 13, 2018, 08:35:26 AM »

Target that brings up memories from some 8 years ago at least. My first DLG was bagged with Kevlar skins and the panels where in the 56g range.

Target · « **Reply #23 on:** November 13, 2018, 09:04:32 AM »

Yep, there are definitely applications for C/L that we can all use, if we want to.
The other thing i will say, is that a $100 gallon of "real epoxy", like mgs or pro set or ez-lam will last a really long time, if you'll just spend about $40 more dollars on some support gear. A $20 harbor freight gram scale, and a stack of dixie cups, stir sticks, foam rollers and paper plates. I routinely mix perfect batches of mgs epoxy as small as 1.4 grams when i need to make small repairs to my glider fleet. And it always cures!

R,
Target

Dave Hull · « **Reply #24 on:** November 13, 2018, 05:58:17 PM »

I'd go for smaller epoxy kits and keep your stock fresher. There is a shelf life and the properties do go away--and after that it won't cure reliably. Freshness is important.

Dave

Target · « **Reply #25 on:** November 13, 2018, 07:15:16 PM »

I'm having pretty good luck so far.
IMO, the way to go is get a pair or three guys to go in on a gallon, then split it up. The cost is much better usually. Aircraft Spruce has the MGS.
I have a @ 10-12 year old stash of West Systems, and a 5yr old stash of mgs. They both work as expected, although the WS hardener is darkened.
But I'm in SoCal and my shop stays above 50 and below 90 most of the time.
I keep the gallon closed and periodically fill up clear squeeze bottles with resin and hardener. And it's not very humid here. That helps.

Brent Williams · « **Reply #26 on:** November 14, 2018, 11:17:34 AM »

Quote from: Motorman on November 14, 2018, 08:55:33 AM

Is there a glider forum somewhere on the interweb?

Chris will give some specific links, but www.rcgroups.com has tons of info on lightweight composite construction techniques.

Target · « **Reply #27 on:** November 14, 2018, 08:32:15 PM »

Quote from: Motorman on November 14, 2018, 08:55:33 AM

Is there a glider forum somewhere on the interweb?

Handlaunch forum on RCG-
https://www.rcgroups.com/hand-launch-96/

For all intents and purposes, hand launch today does mean discus launch, but DL is relatively young. A guy up in the PNW discovered it when his arm was too sore from javelin launching all day.

DLG's are crazy light, and strong for what they do. That being said, they are super fragile every other way. They are amazing pieces of engineering.
You could probably make a DLG work for C/L, but the vibration from a .09 would definitely be a problem. E power might be OK. And at 8oz for the airframe with battery servos and rx used as intended, they certainly are not crash worthy at all. You normally could shorten the tail boom if you wanted to. Tail pieces weight between 6 and 12g for each piece!

RCG Composites forum
https://www.rcgroups.com/composites-fabrication-210/

Happy hunting, MM!

Ken Culbertson · « **Reply #28 on:** November 15, 2018, 07:42:43 PM »

This is as good a thread as any to post some basic questions. First, what is "Bagging". Everybody throws the word around like we all know what it is! Second, where do we get carbon fiber for covering flaps, etc.

Sometimes it is better to ask a stupid question than it is to remain stupid!

Thanks - Ken

Target · « **Reply #29 on:** November 15, 2018, 08:08:37 PM »

Bagging is short for vacuum bagging. By taking the pressure out of a sealed bag, the atmospheric pressure outside then presses from 360* all around it.
It is very similar to diving deep underwater, you feel the weight on you.

About the most vacuum you can pull is 28", and there is about 1/2psi equivalent per inch of vacuum.
So, if you pull a 20" vacuum (my home grown fridge compressor can pull at least that, more like 25-26") then you will get the effect of putting 10psi on a surface.
So if you have a 500 sq inch wing, and you want to load it with the equivalent of a 20" vacuum, but with weights, you will just need to put 5,000 pounds on top of that sucker. I hope your workbench is strong....
Or, just use a vacuum pump and bag, and just enough weight in the foam beds to keep it straight. For white foam, you can only use a couple inches of vacuum. My experience is that white foam crushes at about 2psi, or 4-5" of vacuum.
But most blue foam, Dow hi-load, or Owens-Corning"Foamular" 150 or 250, cannot be crushed in a vacuum bag. Foamular 150 is 15PSI crush strength foam, 250 is 25 psi, etc. The structural foams go all the way up to 100 psi. The stronger they are, the heavier they are, since they are denser.

You are probably thinking that the blue foams might be too heavy for control line wings. I don't know if this is true or not, but you wouldn't have to leave much foam behind after vacuum bagging carbon skins on the blue foam. You could core it out to about 1/8" thick I would think and it would likely be stronger than white foam with balsa skins. Plus you won't have to add any appreciable finish to it.

I hope to get some time to cut some cores and test a vacuum bagged wing. Been super busy at work though!

Target · « **Reply #30 on:** November 15, 2018, 08:15:43 PM »

Quote from: Ken Culbertson on November 15, 2018, 07:42:43 PM

This is as good a thread as any to post some basic questions. First, what is "Bagging". Everybody throws the word around like we all know what it is! Second, where do we get carbon fiber for covering flaps, etc.

Sometimes it is better to ask a stupid question than it is to remain stupid!

Thanks - Ken

The Carboline I have been told is cheapest at HyperFlight in the UK.

If it were me, I would get some balanced 1.6oz or 2oz, and some 4oz fiberglass, go in 1/4 on a gallon of MGS epoxy, and start experimenting a little before making the investment in carbon, especially the expensive carboline.

3k (5.9oz/sq yard) CF fabric can be had for fairly cheap, but it is likely heavier than what you would use in most applications. But strong!

R,
Target

Brent Williams · « **Reply #31 on:** November 15, 2018, 08:29:07 PM »

Quote from: Target on November 15, 2018, 08:08:37 PM

You are probably thinking that the blue foams might be too heavy for control line wings. I don't know if this is true or not, but you wouldn't have to leave much foam behind after vacuum bagging carbon skins on the blue foam. You could core it out to about 1/8" thick I would think and it would likely be stronger than white foam with balsa skins. Plus you won't have to add any appreciable finish to it.

I hope to get some time to cut some cores and test a vacuum bagged wing. Been super busy at work though!

This model applies to this thread discussion. Istvan Travnik has this innovative, blue foam, carbon and fiberglass cloth method. It's not a vacuum bagged build. If one had a good supply of a low viscosity epoxy, this method would be a fun way to experiment with different designs very quickly.
https://stunthanger.com/smf/building-techniques/the-bluefoam-model-or-how-to-build-a-stunt-plane-without-a-bit-of-balsa/

Lauri Malila · « **Reply #32 on:** November 16, 2018, 09:39:39 AM »

One problem with Carboline, that may increase cost, is that for a good result you need to use both +/- and -/+ 45° products. Unless of course that width of roll is enough for a flap, or you do it from 2 pieces with some overlap.
We learned that in quite expensive and time consuming way in free flight

Other thing maybe worth noting is that it really shouldn't be sanded at all. If you want to paint it nicely, it's still a good idea to cover it with thin tissue and dope and continue finishing from there. L

Curare · « **Reply #33 on:** December 17, 2018, 06:22:49 PM »

Quote from: Lauri Malila on November 16, 2018, 09:39:39 AM

One problem with Carboline, that may increase cost, is that for a good result you need to use both +/- and -/+ 45° products. Unless of course that width of roll is enough for a flap, or you do it from 2 pieces with some overlap.
We learned that in quite expensive and time consuming way in free flight
Other thing maybe worth noting is that it really shouldn't be sanded at all. If you want to paint it nicely, it's still a good idea to cover it with thin tissue and dope and continue finishing from there. L

Lauri, why do need, to use both +/- and +/-45°?

Lauri Malila · « **Reply #34 on:** December 17, 2018, 11:39:24 PM »

Quote from: Curare on December 17, 2018, 06:22:49 PM

Lauri, why do need, to use both +/- and +/-45°?

Because for symmetric behaviour under stress you need a symmetric fiber layout.
It's impostant in thin and long things like glider wings and I'm quite sure in our flaps, too.
L

Target · « **Reply #35 on:** December 18, 2018, 09:41:16 AM »

With vacuum bagging, you actually save time. There's no sanding to finish.
That's once you have the equipment and materials to do the job.
There's nothing worse in my opinion than having to sand large areas of fiberglass. Makes me itchy just thinking about it!

Target · « **Reply #36 on:** December 18, 2018, 09:43:38 AM »

Quote from: Lauri Malila on December 17, 2018, 11:39:24 PM

Because for symmetric behaviour under stress you need a symmetric fiber layout.
It's impostant in thin and long things like glider wings and I'm quite sure in our flaps, too.
L

Absolutely. Definitely would apply to flaps. Almost the same as dlg flapperons, since they both are driven from the root.

Dave Hull · « **Reply #37 on:** December 18, 2018, 01:31:54 PM »

Except that the difference here with flaps as compared to a wing, is that the flaps are supported by the wing via the hinges. Whatever bending is happening to the wing will be enforced on the flap. The TE of the wing ought to be stiffer in bending than a reinforced flap. If you do analysis, that will be one of the constraints. And since it is a torque tube it is the +/-45 orientation that is more important. So if you want to minimize weight, and keep maximum torsional stiffness use the +/-45 layer(s) depending on how you get this. (ie. two layers of unidirectional, or one layer of balanced cloth applied on a 45 bias.)

I suppose the next part of this discussion will be that someone wants the flap to stiffen up the back of the wing "...to take advantage of the stiffness that can be built into the flaps." That is a valid discussion, but you are going to need to upgrade your hinge stiffness to make much progress there.

Dave

Target · « **Reply #38 on:** December 18, 2018, 05:22:01 PM »

The wing stiffness being discussed is somewhat laughable to me. While C/L planes do pull hard corners, with the wings as thick and low AR as the are, if they aren't stiff in bending and torsion at the @ 55mph they are going, I'd say you're doing something wrong.
I know it all matters, and all the give a structure has adds to problems, but it seems like a relatively easy task, compared to a 7-8% thick wing that takes a winch launch at 40g's or more, with a wicked zoom at the end.