N2EC

I recently saw a Composite ARF Extra 330L and the model was just fantastic. While looking at the model closely, was curious on two aspects. One, what is the brown colour material they use as the sandwich core. Also, how many layers of cloth and what weight of cloth is used for the wings and the fuselage.

Second was how do they get the ailerons so perfect with the hinges installed. I have seen wings being molded but would be really inerested to see photos of how the ailerons and elevators are cut from the wing after molding and then finished and attached to the wing.

Also, photos also showed that they use some sort of an auto clave for making their models..wow!!

Jack

tommyboy1229

I am interested in this also. I have a set of wings from a crashed Eurosport. Some aspects of the construction leave a little to be desired but other areas are very impressive such as the hinging. This is an original set of wings and they have since improved the design. I'm not sure how they cut the bottom of the elevon but it is very clean, and the skin on the bottom of the leading edge of the elevon slides into the bottom of the trailing edge of the wing. I'm not sure if the leading edge support on the elevon is a little smaller than necessary, so that when it is cut it fits into the wing, or if it's just the way it's cut or the geometry that makes it work. I'm not sure what that brown foam is, but i'm curious about this also. It appears that there is a very light layer of glass on each side of the foam. Really light like 1.4 oz.

Any one else know what this stuff is? Chime in.

Thanks,
Tom

Mike James

Composite ARF (one of my favorite manufacturers!) says on their site that the material is foam, but they don't elaborate on what kind of foam. (glass/foam/glass, vacuum molded with heat) If you download some of their instruction manuals, there's more information on the construction than what's "out front" on their site.

I got some close-up photos of their flap and aileron hinging, which I think is the best in the business, on Bob Violett's new "BobCat Composite". (made by Composite ARF to BVM's specs) They're at http://homepage.mac.com/mikejames/rc..._jets2004.html

N2EC

Mike,

Blessed by Bob Viollet eh...some of your projects look wonderful...I would want to in future work on a project employing similar construction for the wings...could the experts offer some light with photos....like a step by step sort of thing...

Jack

Mike James

You can buy a video called "Building Hollow Composite Aircraft Structures", which shows the whole process, from making the molds, to pulling wings from them, at http://www.soaringstuff.com/hollow.html

These are very strong... glider wings that can take 40 Gs.

In a couple of weeks, we'll be doing the molds for the wings on my "Eliminator 2" sport jet, and that will be photo documented on my site, at http://www.nextcraft.com/j47_sportjet01.html

It's a great way to go. With wing (or other) molds, you can:

• Change the overall skin construction method whenever you like
• Change the internal structure whenever you like
• Change the size, shape, and hinging method of the control surfaces whenever you like
• Prime or paint parts in the mold, resulting in a very smooth finish

Lots of advantages.

N2EC

on hunting further on the methods used by Composite ARF...one it seems that they employ aramid as the sandwich material and second they do not use a autoclave...they use someth9ing which is like a hot table...basically..I think that their molds have some heating element built into it...to heat during curing...while the vacum is on...

does this appear to be possible....Mike what are your views...

Jack

Mike James

There are MANY of us that would love to know, but if I said much more, I'd be guessing. They are cautious about protecting their specific methods, and since they're so good, I don't blame them.

Heat is certainly helpful, as is vacuum. Their methods, whatever they are, seem to be ideal. And... It's worth stating that probably every plane is not built exactly the same way. They may use foam as the sandwhich material on some parts, an Aramid fabric on another, and glass/balsa/glass on others. Having spoken to several Composite ARF owners, and inspected some of their aircraft, I find differing opinions.

tommyboy1229

I don't think that the brown looking foam core material that Jack was asking about is any kind of Aramid. It looks like a thin layer of the type of foam they use in flower arrangements or a polyurethane. It is very brittle by itself and it does not appear that it soaks up very much resin.

Mike wrote: They are cautious about protecting their specific methods, and since they're so good, I don't blame them.


I don't blame them either, but most of us share our methods, which is great for everyone. It is also a well known that many manufacturers from overseas of many different products not only use other manufacturers specific methods but copy the entire product exactly. ( I am in no way insinuating that composite ARF does this.)

Jack, It is very possible that they use some sort of heat built into the mold. I would think that this would be more to speed up the molding process than anything else. These guys do make a bunch of different aircraft.

Goggles

My Feedback: (4)

Check out this link: [link=http://www.arthobby.pl/extra/presentation.html]art hobby[/link].

If you look closely at the available pictures of the internal structures you can see it closely looks like the same material that is in a CA plane. They state they use a product called Herex in their sandwich construction.

SCALECRAFT

My Feedback: (13)

Hi All

The foam that is used in the sandwhich composite configuration is the type Aircraft Spruce and supply offers in thier 2003-2004 catalog, page 36.

The selections that you have are Urethane foam, Divinycell foam, or Last-A-Foam. It is the exact same stuff the Fiberclassics P-51 used. You have a choice of desity.

This should get you guys on the right track.

These cannot be hot wired due to hazardous fumes.

Their online catalog should the same stuff.

Good luck

steve

Goggles

My Feedback: (4)

What kind of paint do you use to get such a nice finish?

tommyboy1229

When painting in the mold, the finish of the mold surface is what gives you such a nice finish.

Tom

Darrinc

My Feedback: (5)

I own the 2.6 Yak, and I would like to start this by saying that I would be hard pressed to layup a plane as nice as this Comp-Arf. It completely blew the minds of the engineers at Scaled Composites.

He is my take on what their process's are, this is pure speculation so take it with a grain of salt.

Materials:
A non silicon, paintable mold release.
Colored gel coat.
Low temp, 3oz fiberglass prepreg, 60% resin content.
Low temp, film adhesive.
Klegcell H100.
Cabosil.
Microballoons.
Comparable resin for wet layup.


or

Dry cloth with a resin transfer setup. (this would be cheaper, but more difficult to setup)


Molds are released then baked, this garrenties that the release has flashed off. The molded are then painted with the colored gell coats and left to almost cure. While the gell coat is very green, hard corners are filled with (I've seen it done both way on my plane) either microballoon or Cabosil/resin. The prepreg is layed in and debulked. (this allows you to get the cloth down tight and gives you some room to manuver the film adhesive without disrupting the outer layer of glass) Next the film ahesive is added and is only debulked if needed.

The klegcell can be ther****rmed, so it is probably cut to shape and formed in a different area. You put the foam in a oven at ~350° for a few minutes, then pull it out and placed in a mold and allowed to cool. It will hold it shape with all of it's material properties. This can be held in place with CA or by having location pins or plates on the mold.

This process is then done in reverse after the foam is placed in the mold. I don't see any sanding marks, so I'm not sure when and how the internal pieces are installed. Then the mold is then bagged, baked and then trimmed. I would imagine that there are jigs to locate the few secondary structural pieces and are reinforced with microballoons. In my opinion, a piece of glass should be place over the joint. The two halves then are put together with microballoons as the gap filler and a tape placed over.

Just a guess.

Goggles

My Feedback: (4)

I've been using a grey primer in my molds and they come out nice and glossy but I was wanting to know what kind of white paint is being used for such a nice finish?

Thanks.

Darrinc

My Feedback: (5)

It's gel coat, a thick epoxy based paint.

Roberto B.

The core used in C. arf models is Herex with a density of 75 kg/mq.
The paint is just a two part industrial grade polyurethane paint.

Bye

Roberto

Darrinc

My Feedback: (5)

Roberto,

Are they getting there foam custom cut? With the Herex ET, the thinnest you can get it is 3mm.

Roberto B.

Not at all.

For my works, I get the 1.2 and 2 mm. Herex here:

http://www.core-and-more.de/airex_c70.0.html?&L=

and look for the C 70.75.

Great service and good prices. Thanks to my friend SchiBru!

Bye
Roberto

Darrinc

My Feedback: (5)

Thanks Roberto!

RCSCALEGUY

I have a question the skin on top with the gel coat say has damage. What is the best way to repair, traditional methods like microlite and or use of Fiberpoxy. That bond to this stuff, I don't want to scuff or sand as I don't want the foam to get damaged. If anyone has repaired a crack or something let me know your process. Thanks.