Author Topic: Carbon Fiber or Fiberglass Prepreg directly over foam (Read 14412 times)

Steve Berry · « **on:** May 05, 2017, 01:45:08 PM »

Has anyone had much success, or even tried, carbon fiber or fiberglass prepreg directly over foam wings, fuselages, or other parts? I know it would be a little more hassle than sheeting with balsa, but much stiffer and perhaps lighter. Before shelling out funds for trying it myself, I'd like to know if anyone has tried it, with success, and if you would ever do it again?

Phil Krankowski · « **Reply #1 on:** May 05, 2017, 02:08:50 PM »

Competition hand launch gliders ate built this way.
Also called
Discus Launch Gliders
DLG
HLG

No personal experience though, other than owning a 1m glider built in this manner with a "bluecore" wing. It is glass with carbon tow diagonally wrapped and "live" hinges formed by one skin. While I am not a fan of live hinges it works rather well.

https://hobbyking.com/en_us/hobbykingtm-1-0m-mini-dlg-v2-composite-1000mm-arf.html

There are lots of examples and how-to's regarding building 1.5m competition gliders. I would expect building a wing for CL to be rather similar.

Phil

Lauri Malila · « **Reply #2 on:** May 05, 2017, 03:43:00 PM »

It's getting pretty common in free flight, so it will be commonly accepted in control line in about 30..40 years time.
These structures are so much better in allmost every aspect.
Usually they have a cnc milled Rohacell core squeezed together with carbon in a metal mold.
At the moment I pay about 1000$ for a pair of wings, but as the hype goes goes away, the prices will go down.
In cl, it would be perfect technology for flaps, stabs etc. Not necessarily for wing and fuselage. L

Avaiojet · « **Reply #3 on:** May 05, 2017, 06:23:06 PM »

Some interesting work.

Steve Helmick · « **Reply #4 on:** May 05, 2017, 08:01:14 PM »

How hot does the autoclave need to get to activate prepreg? And how much temperature can various types of foam take before they turn useless? Wondering what range of temperature we could work with. I know how Howard came up with his homemade "autoclave", but I don't know if he used any foam in it.

Steve

Lauri Malila · « **Reply #5 on:** May 06, 2017, 12:10:03 AM »

Why would it have to be prepreg? There was some issues with thin higher modulus fibres, they can be difficult to handle when dry. But also, they are useless for wing skins.
The only prepreg I can find usefull is the Thinskin from creativecompositetechnologies.com
But today you can buy really nice UD- and wowen cloths starting from 16g/sq.m that are really easy to handle. Especially the flat-tow types.

L

Howard Rush · « **Reply #6 on:** May 06, 2017, 08:43:11 PM »

I've done this. It's hard to beat balsa over polystyrene foam for stunt wings. Be sure to calculate weight before setting out on this path.

Brett Buck · « **Reply #7 on:** May 07, 2017, 11:18:17 AM »

Quote from: Howard Rush on May 06, 2017, 08:43:11 PM

I've done this. It's hard to beat balsa over polystyrene foam for stunt wings. Be sure to calculate weight before setting out on this path.

I did that calculation, too, and you are right, it's really hard to beat balsa and foam, even when you include the additional silkspan, filler, and paint that you might not have to have otherwise. I would probably do it anyway, if it weren't for the "cnc milled Rohacell core squeezed together with carbon in a metal mold." aspect. I imagine I could get a acceptable rohacell foam core, but the metal mold is clearly beyond the capabilities of building in a bedroom.

Brett

Lauri Malila · « **Reply #8 on:** May 07, 2017, 11:33:08 AM »

Sure, you don't need the metal molds to get the job well done, especially with stunt wings. With some imagination you can manage with a styrofoam mold, just like making those wrap around l.e's and turtle decks, some thick Mylar sheet and a vacuum pump.
But there is really no point in a stunt wing with carbon skin because of thickness. The optimal skin would be too thinfor handling. But in thinner parts, like stabs and flaps for example, that's another thing.
In free flight, the demands are much higher because of thinner sections, both for shape accuracy and strenght/stiffness. L

Igor Burger · « **Reply #9 on:** May 07, 2017, 12:05:28 PM »

We tried carbon, but the problem with carbon is that fibers are too thick, so the layer of cloth from such fibers comes also too thick and thus heavy. If you do the math, you will see that balsa or even rohacell or herex are strong enough and they need only some kind of "stabilization" to be straight and not to fold under load, means only thin layer of somthing rigid, but it does not need thick carbon. So solution was rohacell + thin glass which can be 1/4 of cabon cloth thickness since glass fibers can be much thinner. Wings come empty without ribs, only with 1 or 2 foam spars. They are with color from mold, so without any filler, sanding ane next color or dope layers, but they still come little heavier than soft foam, balsa, paper and color.

pmackenzie · « **Reply #10 on:** May 07, 2017, 04:19:43 PM »

There is light carbon cloth out there that is just as light as glass. Sees a lot of use in DLG, carbon parts are no heavier than glass ones.

26 gsm carboline is almost the same as 3/4 ounce glass cloth.
20 gsm carboweave is about the same as 0.6 ounce glass

http://carboline.info/
http://www.carbontow.com/carboweave-products.html

There is also Textreme spread tow and Samurai in slightly heavier weights.
http://shop1.r-g.de/en/list/Fibre-reinforcements/Carbon-fibre

But not sure F2B models will benefit as much as the thinner wings of gliders, and the cost differential is pretty big.
Control surfaces would be a good application, they could be made much stiffer with carbon.

Pat MacKenzie

Brett Buck · « **Reply #11 on:** May 07, 2017, 06:53:22 PM »

Quote from: Lauri Malila on May 07, 2017, 11:33:08 AM

Sure, you don't need the metal molds to get the job well done, especially with stunt wings. With some imagination you can manage with a styrofoam mold, just like making those wrap around l.e's and turtle decks, some thick Mylar sheet and a vacuum pump.
But there is really no point in a stunt wing with carbon skin because of thickness. The optimal skin would be too thinfor handling. But in thinner parts, like stabs and flaps for example, that's another thing.
In free flight, the demands are much higher because of thinner sections, both for shape accuracy and strenght/stiffness. L

I am already using double-covered graphite for the stab - one at the bond line with the foam (where I can squeeze out the excess glue - which is the essence of the weight problem) and over the balsa, with dope per usual. But I did the same sort of figuring and came to mostly the same conclusion - the ideal thickness was unreasonably thin, considering the need to take a finish and to stand a few dings into motel doors, etc, and a usable thickness was way too heavy.

Brett

Lauri Malila · « **Reply #12 on:** May 08, 2017, 09:30:40 AM »

Igor,

I may well regret this as you have kind of proven that your wing is good enough, but I'd like to see a decent mainspar with good caps (hardwood or carbon) and a nice shear web in it.
Earlier generation Sharks had some kind of foam ribs and shear web and they had a bad habit of falling apart in use. But maybe engine vibration made a difference.
Regardless of the thickness that gives shape stability, spar should take care of bending and skin of torsion.
A good spar would also make it easier with possible take-apart construction.
Replacing the skin foam with good balsa would save some weight.
I think Yuriy & Andrey use 1,3..1,5 balsa with 50g glass on both sides.

L

Istvan Travnik · « **Reply #13 on:** May 08, 2017, 05:32:10 PM »

Dear Steve Berry,
here is the complete answer to your post:
http://stunthanger.com/smf/building-techniques/the-bluefoam-model-or-how-to-build-a-stunt-plane-without-a-bit-of-balsa/
I started to work with "bluefoam" (Roofmate) since early '80s, and never return to balsa, in F2B
Regards: Istvan (Steven)

Igor Burger · « **Reply #14 on:** May 11, 2017, 01:48:08 PM »

Quote from: Lauri Malila on May 08, 2017, 09:30:40 AM

Igor,

I may well regret this as you have kind of proven that your wing is good enough, but I'd like to see a decent mainspar with good caps (hardwood or carbon) and a nice shear web in it.
Earlier generation Sharks had some kind of foam ribs and shear web and they had a bad habit of falling apart in use. But maybe engine vibration made a difference.
Regardless of the thickness that gives shape stability, spar should take care of bending and skin of torsion.
A good spar would also make it easier with possible take-apart construction.
Replacing the skin foam with good balsa would save some weight.
I think Yuriy & Andrey use 1,3..1,5 balsa with 50g glass on both sides.

L

That wing is stressed skin construction, so the spar is only for "connecting" both sides and keep them stable on place, it does not contribute to load strength directly. That works well if both sides of wing are glued together, such a wing is like a rock. But you are right it is nightmare if you want take apart model. I had hard time to design connectors on my model for Australia which can properly distribute load from screws to the skin. It would be much much easier with main spar, that is true. Pictures show mounting, it looks complicated, but all is milled, no problems with making so many pieces :- ))

Balsa will be for sure better, we use rohacell or herex because we do not have good source for balsa of proper density and because it is much less work with foam plate and safer result, not because of any technical advantage :- ))

Istvan Travnik · « **Reply #15 on:** May 11, 2017, 04:05:16 PM »

Bože moj...
I will take a look into the wing, as you allow that, next weekend in Hradec Králové...

Avaiojet · « **Reply #16 on:** May 13, 2017, 07:25:04 AM »

Quote from: Steve Berry on May 05, 2017, 01:45:08 PM

Has anyone had much success, or even tried, carbon fiber or fiberglass prepreg directly over foam wings, fuselages, or other parts? I know it would be a little more hassle than sheeting with balsa, but much stiffer and perhaps lighter. Before shelling out funds for trying it myself, I'd like to know if anyone has tried it, with success, and if you would ever do it again?

Steve,

I may have posted just about the same question in another Thread some time ago.

One of the replies were that I airbrush the look of CF. Not all that bad a reply actually with my background and expertise in using the tool.

I did reach out to R/C and glider guys and I did get one good reply. This e-mail is dated 4/10/17.

The modeler seems to know what he's talking about. One never knows.

Just keep in mind these are NOT my words. It's a "copy and paste."

Wouldn't want to get negative "Fake News" replies for words I never said.

CB
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If you have the white foam it cannot be done. The white foam will collapse during the vacuum bagging process. You need closed cell foam like the blue or pink foam. There are other exotic foam like Divinycell or the Rohacell PMI foams. Be mindful as the surface finish will not be perfect if you are shooting for appearance points. If you want surface finish then Hollow molding in female molds is the only way to get perfect results every time. Here is Hollow molding video on how is it made https://www.youtube.com/watch?v=JMK_DewbPFo and you can follow this Tom as he has a bunch of videos with several construction techniques videos.

The technique you are referring to is vacuum bagging a wing where you use a Millar piece of plastic to put the carbon on it then you wrap it around the wing and put in a vacuum bag overnight to cure.

Look at this What you see at the beginning of the video is the Kevlar that is already placed on the top of the Millar sheet which is the white piece of plastic material https://store.acpsales.com/products/2295/pet-polyester-film. The Mylar film is cut 1/8 short of the LE. I n a CL wing with high curvature on the LE I have no experience with that. You might want to try one picece Mylar wrapping it TE around the LE back to the TE and hold it with tape in place to help with insertion in the vacuum bag.

There are a bunch of light skin materials look for Carboweave CW30 CW45 or also search for Textreme which is a little heavier but gets the job done. However I would try my luck on some light 1.6oz/sqyd balanced before you use the carbon fiber.

Wynn Robins · « **Reply #17 on:** May 15, 2017, 06:16:37 PM »

actually with the new spread tow carbons available you can get way better weight to strength distribution than balsa over foam

Latest DLG wings weigh 98grams (3.45ounces) and they are 1500mm long (59inches) complete with prefaced ailerons, Kevlar hinges, paint and full gloss finish.

Cores are Rohacell with Carbon main spars.

I see vacuum bagging mentioned - most production DLG wings and made in aluminium moulds. The cores are a fraction of deeper than the mould so when the moulds are closed and clamped - the skins and forced onto the foam and pressed solid. - excess epoxy is squeezed out into relief channels in the moulds and trimmed off later.

heaps of new tech that can be used in CL - if people had the money to do it.

Wynn Robins · « **Reply #18 on:** May 15, 2017, 06:17:53 PM »

Igor,
have you looked at CW20 or CW40 carbon?

TDM · « **Reply #19 on:** May 16, 2017, 08:07:32 AM »

Finally we are coming to more current build techniques. The glider continuity is years ahead of our technologies. Windy and Dave where making the "carbon wing" in the past in Aluminium molds but the layout used in those wings was still using outdated materials.
Here is some work I was involved in the past few years.
https://www.rcgroups.com/forums/showthread.php?2660658-Evolution-%28EVO%29-3-1-removable-wings-and-tails
https://www.rcgroups.com/forums/showthread.php?1800565-Evolution-3-the-E-Pluribus-Unum-DLG-group-build-log
https://www.rcgroups.com/forums/showthread.php?1083322-Build-Log-Evolution#post12709618

Yes there is a verry posibile way to make a 560sq inch model well under 1500g maybe even under 1400g and without even braking a suet. My wings are 56g per pannel the fuselage is 35g, hec the whole model is 265g including the radio.

I definitely see this starting to move in to our community.

Carboweave CW20 is the best material to use on wing skins. Also rather than using XPS which is cheap but not so good Roahcell is a far better option. The reason for that is because the fiberglass is not as durable as the Carbons is and also it lacks the stiffness that the carbon wing adds, I am talking about the holding the model by your helper etc.

You want to use at minimum closed cell foam AKA XPS. The white expanded foam as is open cell will collapse in the bagging process.

Howard Rush · « **Reply #20 on:** May 17, 2017, 12:49:52 AM »

Dorin, good to hear from you again. I hope this means you'll be flying some stunt.

TDM · « **Reply #21 on:** May 17, 2017, 06:28:22 AM »

Quote from: Howard Rush on May 06, 2017, 08:43:11 PM

I've done this. It's hard to beat balsa over polystyrene foam for stunt wings. Be sure to calculate weight before setting out on this path.

Howard you are completely wrong on this one. The main concern should be surface finish quality rather than weight.
You can make a finished stab for a 60-90 size model in under 50g and i am talking everything included. 1mm round spars (BP Hobbies) and CW20 or CW30 skin in a bag will be super light. Depending on spar layout there can be variations in the surface finish. With Mylar backing you will get a decent finish except perhaps around the LE and TE area which can definitely be sanded off blended in and painted. If you decide to go with the flat unidirectional carbon there will be a raised surface around the spar area.

For a wing hollow molded skins are the way to go. Thin surfaces (flaps elevator rudder) can be done with the solid core vacuum bagging DLG like molding techniques. You could do the wings like that but you have to core the wing after you bag the skin on the wing.

And you need some good quality epoxy.

https://www.rcgroups.com/composites-fabrication-210/ Tons of information here if you use the search button.

TDM · « **Reply #22 on:** May 17, 2017, 06:30:46 AM »

Quote from: Steve Helmick on May 05, 2017, 08:01:14 PM

How hot does the autoclave need to get to activate prepreg? And how much temperature can various types of foam take before they turn useless? Wondering what range of temperature we could work with. I know how Howard came up with his homemade "autoclave", but I don't know if he used any foam in it. Steve

If you use the right resin you do not need an autoclave. No one I know uses autoclaves in the modeling world. At most you use post-cure.

TDM · « **Reply #23 on:** May 17, 2017, 07:07:21 AM »

Quote from: Wynn Robins on May 15, 2017, 06:16:37 PM

actually with the new spread tow carbons available you can get way better weight to strength distribution than balsa over foam

Latest DLG wings weigh 98grams (3.45ounces) and they are 1500mm long (59inches) complete with prefaced ailerons, Kevlar hinges, paint and full gloss finish.

Cores are Rohacell with Carbon main spars.

I see vacuum bagging mentioned - most production DLG wings and made in aluminium moulds. The cores are a fraction of deeper than the mould so when the moulds are closed and clamped - the skins and forced onto the foam and pressed solid. - excess epoxy is squeezed out into relief channels in the moulds and trimmed off later.

heaps of new tech that can be used in CL - if people had the money to do it.

Yes that is called compression molding. They use Rohacell 31IGF for the core material which is cut .03in oversize and it is compressed brute force in the mold. I do then in the Evolution3.1 already. I have more wing area and a take apart system in the model. The panel weight is around 55g for a wing panel that is much larger tan a CL 60-90 size horizontal (and by the way i have the hinge attached finish and painting done). Excess resin is not squeezed out at all as there is no excess resin. What you see squeezed out it called splurge which is a filler material we mix up to fill in the voids around the LE and TE.

Guise welcome to the Revolution. I spent years trying to get where I am at now.

Yes you have to spend heaps of money to do compression molding but it is not the best for CL applications. The DLG world went to compression molding because is easier to produce but most important reason is because is easy to repair. DLG have a bunch of carnage and midair collisions, and when they meet in the air things get dinged smashed etc. We usually cut the bad area out add a piece of aluminium tape on top of it, continue flying and repair when we return home. Another reason for not using the compression molding techniques in a CL model is surface finish. In time the foam pushes against the wing skin and becomes looking like it gets goose bumps over time.
Since we do not worry to much about mid air collisions a much more suitable for CL application is the hollow molding technique. You do not need the aluminium molds for this technique. You can use the classic gel-coat fiberglass molds for that.

Howard Rush · « **Reply #24 on:** May 17, 2017, 11:00:01 AM »

Quote from: Traian Dorin Morosanu on May 17, 2017, 06:30:46 AM

No one I know uses autoclaves in the modeling world.

I know one guy.

TDM · « **Reply #25 on:** May 17, 2017, 11:30:33 AM »

Quote from: Howard Rush on May 17, 2017, 11:00:01 AM

I know one guy.

It may be, but no one I know does that at home. Autoclaves are not cheap. Anywise it is better to change resin that works without autoclaves.

Howard Rush · « **Reply #26 on:** May 17, 2017, 12:19:02 PM »

Quote from: Traian Dorin Morosanu on May 17, 2017, 11:30:33 AM

It may be, but no one I know does that at home. Autoclaves are not cheap. Anywise it is better to change resin that works without autoclaves.

The problem is that aerospace prepreg takes 250 or 350 degrees F.

Lauri Malila · « **Reply #27 on:** May 17, 2017, 03:47:30 PM »

Are our toys aerospace? No.
As far as I know, aerospace composite structures are usually quite average, when it comes to optimizing the structures, or at least finding the most optimal fibers and resins. To get the materials aviation approved is a bureucratic hell and companies don't want to go through it with every new material.
I would say that the finest state-of-art composites allready exist in aeromodelling categories. It's very hard to think of more complex structural engineering that what is in free flight gliders, for example. I think that's where you should look for new ideas, not aerospace. L

Target · « **Reply #28 on:** May 22, 2017, 08:28:07 PM »

I still intend to vacuum bag a wing, fuse and tail for a stunter...
I'll core out the wing panels on the second one. First will be a trial run and proof of concept with a solid core wing and external bellcrank.
MGS Epoxy or bust.

Does anyone know if simple Krylon paint used with MGS will hold up to glow fuel?
If not, electric is my friend. It's my friend anyway, but it would be even more so.

R,
Chris

Avaiojet · « **Reply #29 on:** May 23, 2017, 06:01:07 AM »

Quote from: Chris Behm on May 22, 2017, 08:28:07 PM

I still intend to vacuum bag a wing, fuse and tail for a stunter...
I'll core out the wing panels on the second one. First will be a trial run and proof of concept with a solid core wing and external bellcrank.
MGS Epoxy or bust.

Does anyone know if simple Krylon paint used with MGS will hold up to glow fuel?
If not, electric is my friend. It's my friend anyway, but it would be even more so.

R,
Chris

Chris,

Would you be sheeting with CF?

Regardless of the sheeting material, afterwards, there's no reason you cannot hot wire out the inside possibly leaving a vertical foam spar. Or two.

I have a foam wings in the works for my biplane stunt pusher, model has no name yet.

The wings will have a 1/8" vertical spar at the high point of the airfoil from the root to the tip. This means the entire front of the foam wing will have to be removed and replaced for the spar.

When this wing is sheeted, the inside will be hot wired and hollowed leaving a vertical foam spar forward of the trailing edge.

Others have built foam wings this way with success so it's not something I made up.

Keep in mind I'm sheeting with 1/16" balsa, not CF and I will not be vacuum bagging.

CB

TDM · « **Reply #30 on:** May 23, 2017, 09:27:00 AM »

Chris MGS is the best resin you can possibly have. Make sure you mix the right ratio on a gram scale.
Here are some things that may help you to have good success:

NO WHITE FOAM unless you want this

Get Mylar .014 for the bagging process. Do not expect to have super LE since the Mylar is usually cut 1/4 is short of the LE (it does not like tight turns) there will be 2 Mylar pieces one on top one n bottom.
For the LE let the bag push the material against the foam and plan to do some filling and blending with MGS and micro-balloons mix after the bagging process. Most of the surface should come out nice and smooth from the bagging process.
There is a video above on how to make DLG wings follow it to the letter.
Plan to finish the LE after bagging
I would add a 1.5mm carbon rod for spar top and bottom (BP hobbies sels them for 2$ a piece)
Core the wing after you bag the part.
Get ALL THE DUST OFF THE CORE !!!!

Optional but i would do this anywise. I would bagg the flaps and the wing in one shot.
To create the hinge you can sandwich a piece of Kevlar (the Kevlar becomes the hinge) between two pieces of balsa and attach that between the flaps and wing cores. You then blend this balsa Kevlar sandwich block to the wing and flaps. After you bag the skins (wing + Flaps). Use a Exacto knife to cut the V in the flaps TE for a hinge. Fix the LE and you are done.

The skins are at 45 degrees bias to control torsion. If ou use CW60 it has 3 layers+- 45 and one uni. If you use that for skin then you do not need a spar as the uni will work as a spar.
CW30 is best compromise. Fiberglass 1.6oz balanced cloth is cheap and good for practice and for making the first parts but is is bad for dent prevention. Apart from the
extra strength or carbon it is very good on dent prevention from normal handling etc. So consider to use it for wing #3 and thereafter.

Good luck

TDM · « **Reply #31 on:** May 23, 2017, 09:33:09 AM »

One more thing for this technique. If you plan to make a profile fuselage you can use this technique to make the fuse and to make your life easy you can sharpen the top and bottom of the fuse so the Mylar will form nicely around the fuse shape if it doesn't have tight turns.

TDM · « **Reply #32 on:** May 23, 2017, 09:49:50 AM »

A better video
[youtube=425,350]https://youtu.be/tW3fEWBZGrU[/youtube]

Target · « **Reply #33 on:** May 23, 2017, 07:25:15 PM »

I've already bagged a handful of sailplane parts with great success; the only possible questions I have are with the internal bell crank and hinging, but I have some plans for that....
Thanks for the encouragement.
R,
Chris