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Composite racing wing - 2/21/2002 7:20:49 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		I have never used Rohacell, but anything that has porous surface needs to be filled in this manner. I built a 22.5lbs 33% Extra 300SX out of Divinycell last summer, so I have gained a lot of experiance with this material.

After rereading your process, you should be able to use just the 2oz glass and your carbon reinforcements and balsa, you could use even lighter considering I am using 1.4oz glass on my 35% Extra wings.

Make sure you have the glass oriented the same (45°) on your laminate, or on a hot sunny day you will learn what thermal expansion is the hard way. You can add layers all you want, but put them in the same orientation.

Like this:

2oz@45° / 2oz@90° / balsa / 2oz@90° / 2oz@45°

These layers will heat and cool the same and will not twist the piece as the day goes on.

Darrin C

(in reply to Mluvara)
       Post #: 51

Sorry - 2/21/2002 7:39:25 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		I don't mean to keep posting, but I teach a composites class and I am just trying to help by throwing out some different ideas.

We use Meguires Molds release wax which is very paint friendly and after waxing the mold about seven times, we directly paint the mold with Lustercoat, or some other laquer based paint. Your first couple of pieces might not be perfect, so I would wax the mold a few extra times, but the more you use the mold the better it will release.

We let the painted mold cure for at least two days, then do our layup by painting on a thin layer of epoxy then laying our cloth down, pushing the cloth gently into the epoxy with a small brush and getting out any air pockets. When the piece is cured and popped out of the mold, we have a perfectly painted piece with NO pinholes.

Just a thought,

Darrin C

(in reply to Mluvara)
       Post #: 52

Composite racing wing - 2/21/2002 8:14:05 AM   
Mluvara



Posts: 1425
Joined: 1/14/2002
From: San Jose, CA, USA
Status: offline 		I really appreciate your commens Darrin... It's nice to chat with people about "shop talk" on these things.

I have been trying to get away from PVA for awhile. Bought some wax to try on the Tsunami stab. That mold has been well waxed, so the part should pop out ok. However, the wax that I used did not like the primer. I had to mist it on or it would get dots where the paint pulled away from it (not sure what the term is), but basically it looked incompatible. We'll see how it goes when I pop it out of the mold.

Believe it or not, I only used the 4oz on the inside (I think it was 4, could be 3) because I ran out of 2oz. My layup was:

primer/2oz/balsa/4oz (plus carbon in some areas)

Do you think 1/32 would be too thin?

What do you use to close up the molds? what type of material?

What do you make your molds out of? I hear a lot about tooling resins.

Michael

(in reply to Mluvara)
       Post #: 53

Composite racing wing - 2/21/2002 9:05:08 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		The wax we us is Meguiars Mirror Glaze No.8

What direction are you laying up your glass? I would suspect you are running the weave at a 45° from the mold, this will give you the torional strength and keep the wing from twisting.

Well, the engineer I work with wants me, after I make some Nomex honeycomb wings, to use 1/16" balsa as the core material, but that sounds thin to me on a 35% wing that will be taking some massive amount of G's. But he has done the math and assures me that it will work. (It's not his $1000 engine if it fails)

I would stick with the 1/16" and would use 5-7lb contest balsa, because you might run into problems with not enough skin thickness for buckling strength if you use a thinner material.

Main thing I would do at this point is to figure out a way to seal the balsa, especially the endgrain balsa. Balsa absorbs in the direction of it's grain so a light resin layup will have the possibility of having the resin sucked up by the balsa and leaving dry spots in the glass.


What do you use to close up the molds? what type of material?

Do you mean once the halves are bolted? I run 1" glass tape saturated in a epoxy/microballon mix.

I have made my molds like you have, simply because I do not have any of the tooling resins, I would like to try them in the future.

One trick I have learned is after you lay down a couple of layers of glass, mix dry sand or sawdust, 8 parts to 1 part epoxy and spread out a 3/8" layer of this slurry, then put the same amount of glass layers on top. Just a cheap and easy way to build thickness. If it is a large part, lay cut pieces of conduit in the slurry then glass over them, this keeps the mold from twisting and adds strength.


If you look in the aerodynamics/scratch build section, Ollie and several others have made molds and can offer other ideas too. We are all learning so no one has all the answers.

Regards,

Darrin C

(in reply to Mluvara)
       Post #: 54

Composite racing wing - 2/21/2002 10:31:15 AM   
Mluvara



Posts: 1425
Joined: 1/14/2002
From: San Jose, CA, USA
Status: offline 		Actually, on the glass (blushing), I just ran it lengthwise.

[QUOTE]What do you use to close up the molds? what type of material?

Do you mean once the halves are bolted? I run 1" glass tape saturated in a epoxy/microballon mix.[/QUOTE]

Well, I meant on molds where it is basically impossible to put tape in there unless the ends are open (like my mold). What type of "splooge" - material mixed with the epoxy to give it strength do you use on the joint?

I'm going to do some thinking on the next wing. Definitely didn't need the 3 or 4 ounce on the inside. I'm going to have to get some more 1.4 or 2 oz as I'm out. I have a roll of 3/4oz that's lasted me a few years. I must have had 70 yards on it at once time, but it's got no strength for this application. Just good for finishing.

Michael

< Message edited by Mluvara -- Feb 21 2002 5:42AM >

(in reply to Mluvara)
       Post #: 55

Composite racing wing - 2/21/2002 10:33:42 AM   
Mluvara



Posts: 1425
Joined: 1/14/2002
From: San Jose, CA, USA
Status: offline 		Photo of wing from today. landing gear cutout started and hinge line cut away on bottom of wing.

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< Message edited by Mluvara -- Feb 21 2002 5:39AM >

(in reply to Mluvara)
       Post #: 56

Composite racing wing - 2/21/2002 10:35:37 AM   
Mluvara



Posts: 1425
Joined: 1/14/2002
From: San Jose, CA, USA
Status: offline 		Shot of airplane from above.

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(in reply to Mluvara)
       Post #: 57

Composite racing wing - 2/21/2002 10:37:23 AM   
Mluvara



Posts: 1425
Joined: 1/14/2002
From: San Jose, CA, USA
Status: offline 		Another perspective.

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(in reply to Mluvara)
       Post #: 58

GREAT JOB - 2/21/2002 10:52:14 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		Well, I meant on molds where it is basically impossible to put tape in there unless the ends are open (like my mold). What type of "splooge" - material mixed with the epoxy to give it strength do you use on the joint?


I do not know off hand since mine have always been open on the ends, but I will makes some phone calls tommorow and find you a answer. I would imagine that you will be adding some milled fiberglass to the epoxy to keep the seam from being brittle and cracking and some Colloidal Silica to make it a gel so that it does not run.

Let me know if you need any lightweight panels for your project. I make really light weight firewalls, landing gear plates, servo trays, ect...


The pictures are great and you should really be proud of the work you've done!!!!!!!!!!!!!!!!!!!!!!!!!!

Regard's,

Darrin C

< Message edited by Darrinc -- Feb 21 2002 6:02AM >

(in reply to Mluvara)
       Post #: 59

Composite racing wing - 2/21/2002 11:30:15 AM   
Mluvara



Posts: 1425
Joined: 1/14/2002
From: San Jose, CA, USA
Status: offline 		I used milled fiber and cabosil as my joint. Worked good as far as I can tell...

I would be interested in light weight stuff to use for ribs, etc. Like landing gear uprights.

Thanks for all the nice comments. I just take things a step at a time and move it to the next level. This wing weighed (gulp) like 2 lbs, 6 oz with the heavy lg mounts, etc in it. My balsa/foam equivalent was 1 lb 10oz. My target for the next wing will be 1 lb 10 or lighter. It shouldn't be hard to do. This wing was a feasibilty "study" so to speak and my brother got a free wing out of it for himself. Not a bad deal. I think it will be easy to cut the weight down now.

Michael

(in reply to Mluvara)
       Post #: 60

More... - 2/21/2002 12:11:28 PM   
Mike James



Posts: 2438
Joined: 1/19/2002
From: Anchorage, AK, USA
Status: offline 		Great information on this thread, and the photos make everything much more obvious. Keep us informed!


_____________________________

Mike James
RC Design and Building - www.nextcraft.com

(in reply to Mluvara)
       Post #: 61

Re: Next up - 2/22/2002 6:21:40 PM   
AV8TOR


 

Posts: 427
Joined: 12/28/2001
From: Mount Vernon, OH, USA
Status: offline 		[QUOTE]Originally posted by Mluvara
Next for layup is the fuse and tail. These molds have been prepped with mold release and then primer was sprayed on so that it comes out of the mold ready to sand. [/QUOTE]

Mluvara, first off that’s for replying to my thread on glassing over foam wings and pointing me to this thread. I am sure many will get a better understanding from your posts. I run a Model Shop for Industrial Design Product Development and I just finished 3 molds for my 25% Edge 540 and I have some questions for you. Why do you prefer to add primer to the mold before laying up parts? It’s the same amount of work as spraying the body? Are you spraying this over the wax parting or over PVA? Can you describe your splitter plate please? When I CNC machine my plugs I cut them in halves (very easy with CNC) and when you lay-up the first mold half you have a flat parting line? I have never tried the glass stabilizer before but I like it. Do you add any ribs or foam to the inside? I usually vacuum-bag over foam for this. Thanks again.

(in reply to Mluvara)
       Post #: 62

Composite racing wing - 2/22/2002 11:30:28 PM   
Mluvara



Posts: 1425
Joined: 1/14/2002
From: San Jose, CA, USA
Status: offline 		Hi Av8tor,

I'm somewhat an amateur at molding. Started making parts a few years ago and progressed over time to what you see here.

I like to use a "gel coat", primer, or something to reduce pinholes when molding. I find that I get better results and it's just been a habit. A lot of places paint or put a gel coat of some sort on in the mold. I've just followed suit.

I have been using PVA as my main mold release and are trying some other waxes now as PVA tends to give a lot of imperfections. After I apply the mold release (whatever it is), I spray on the primer, let it dry, and then do my layup.

Man, I'd love to CNC all my molds! Mine are all hand-made.

For a splitter plate, it tends to be what I have around the garage. I have generally used wood shelving with a smooth surface on it, or it can be plastic, or metal. It is hard to make sure that they are perfectly flat and I do get some good parting lines, but not perfect. Works for my type of usage I guess. Basically, I make a cutout of the profile of the wing or fuselage, drop it into the splitter plate, center it where I want the parting line, and then use clay to fill in the voids.

On the composite stab, I put a main spar (just endgrain balsa) and then maybe a 1/8" balsa center rib and some stringers or wood near the hinge line. What I put near the hingeline depends on whether or not it is skin-hinged or going to be conventionally hinged. Other than that, it's hollow.

I'm going to finish the stab shown in the pictures tomorrow and possibly lay up another wing or fuse this weekend. More photos to come...

Michael

(in reply to Mluvara)
       Post #: 63

Composite racing wing - 2/23/2002 3:33:08 A