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Here is what we do at Scaled Composites - 11/13/2003 1:09:51 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		Here are some of the techniques that we use here at Scaled Composites. I am a modeller so I have adjusted them for our use. I work a lot so I cannot say how much that I will have time to answer questions, but these are some guide lines.

Buy some Peel-ply and Teflon/mylar tape. Use good epoxy.

As always, experimentation is the key!

Darrin R Cash

< Message edited by Darrinc -- 11/13/2003 5:15:37 PM >
       Post #: 1

Nomex Honeycomb/PVC Foam Panels - 11/13/2003 1:27:54 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		Before I start on the proceedure, the most important point I can make about composite panels is that the panels are far superior in strength compared to the pieces that they are replacing and are not drop in replacements. They key is to cut in lightening holes once the panels are made. Lots of them! I mean a LOT of them. (see FYI note below about Nomex panels that have had massive lighting done)

You want to use full vacuum during the skin and core layups. Bake the Nomex @ 250°F for 4 hrs before it's layed up. (this burns out all of the moisture) Lay the skins up by themselves, apply peel-ply if you have it, it will save a lot of sanding. When you put the laminate together, you will need to come up with a dam material to go around the outside of the plate of the same thickness so that the vacuum does not crush the edges. (plywood or hard balsa will work, wrap it in plasic so that it will not stick)

If you did not peel-ply the bond side, sand ALL of the gloss off of the carbon. Lightly brush on a thin coat of epoxy (just so the panel looks wet, this will take practice on how wet) on the skins for either Nomex or PVC. If useing PVC foam, lightly wet the foam with epoxy, then squeegee on a slurry of epoxy/microballons to fill the cells. Assemble the laminate then place your dam material around the perimeter and bag, then pull full vacuum.

For mounting the panels, you want to sand 1/8" around the edge to be bonded, both sides and glue in panels with Flex CA, making a small fillet around the sanded edge. For firewalls, sand 0.5" around the edges of the engine side, 1/8" around the back side, glue in with Flex CA and tape the front side with 1" tape (carbon or glass) and epoxy. I usually wet out the tape and set it aside until its very tacky then place on firewall, secure with clear tape. (teflon/mylar tape if possible) Engines try to go out of the plane, not into the plane.

FYI : Typically in full scale, the edges of honeycomb are closed out, with a super thick, super dry mixture of micro and epoxy, mix in micro until it will not accept any more micro, then pack the edges. This is typically to heavy for model use, I usually do not do this unless a Nomex panel has been really hogged out with lightning holes. This increases the stiffness by giving the edge a better surface.

I hope this helps!

Darrin R Cash

(in reply to Darrinc)
       Post #: 2

RE: Nomex Honeycomb/PVC Foam Panels - 11/13/2003 1:31:49 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		Mike,

That would of been my old job. Heh heh
Nice to hear from you, it's been a while.

Darrin

(in reply to Darrinc)
       Post #: 3

Closing out wing panels/fuselages - 11/13/2003 2:00:29 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		Before you are lay up your pieces in your molds, place tape 1" around the edges that need to be joined. You are creating a "joggle" The tape thickness should be equal to one layer of your cloth. Wax, then lay up your whole part, right over the tape. (your just building in a step)

Once everything is cured and trimmed, mix up a super thick epoxy/cabocel slurry. (micro will work) Coat the edges and put the molds together. Once cured pull out the bonded pieces and sand the joggle and smooth the joint. Remove ALL of the shine.
Don't worry if there is not a solid edge of your slurry bonding the pieces, it will be fine. Wet out some cloth and cut out a 2" piece on a +-45° bias, wrap that around your joint in the step, put on a 4" wide piece of peel-ply and wet out past the tape 3/8". (this will give a nice transition and fill in the hard edge of the step)

Once cured, pull off your peel-ply and your done, there will be only little bodywork to finish.

Darrin R Cash

< Message edited by Darrinc -- 11/13/2003 7:55:58 PM >

(in reply to Darrinc)
       Post #: 4

Tape is your friend - 11/13/2003 2:45:36 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		When laying up composites, tape is a very powerful tool.

If you have made a full fuselage mold, there is no sense in making seperate molds for individual pieces. You can build the model in steps, tape out trim lines in the mold for the cowl, rudder, hatch or access panels, wax the mold, layup just past the trim lines and cure. Once the main part is removed and trimmed, clean the mold with alchohal, then butt up tape next to the tape that was placed previously, rewax and layup the small pieces. Once cured, trim at lines and have perfect matching parts.

You can get fancy in area's like the hatch, access panels and cowl by adding tape to the thickness of your cloth on the first layup, then trimming on the opposite side of the tape, which will make a step and give your soon to be layed up piece a place to slide into.

Or

Lay up the small pieces first, trim and put back in the mold. Cover the edges with teflon/mylar tape and wax the mold and tape. Layup the main piece, extending onto the tape, cure and trim some distance from the step. Perfect parts every time. (if the step is big, you can put some epoxy/cabosil mix along the edge.

Kind of cool!

Darrin r cash

< Message edited by Darrinc -- 11/13/2003 3:50:59 AM >

(in reply to Darrinc)
       Post #: 5

Placing Core material on curved surfaces - 11/13/2003 3:03:58 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		When placing core material on curved surfaces, lay-up the first skin with peel-ply on top. Once cured, remove the peel-ply and install your core. (PVC can be heated so that it conforms) Sharpen the end of a 1" tube and cut into the core, pop out the little piece of core and CA it back in place onto the first skin. Put in enough "hard points" so that the core stays in place.

When ready to bond in the core, lightly wet the first skin, place in the core, layup the inner skin*, then bag.


* I perfer to wet out the cloth and let it sit until it gets very tacky before placing it on the core. This gets the resin near B-Stage and keeps the resin from running down the core.

Darrin R Cash

(in reply to Darrinc)
       Post #: 6

New Thinking - 11/13/2003 3:39:47 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		Composites allow us to tailor a part in a n'th degree micro level. We can manipulate the feel of the skin just where we touch it, (eg. adding a grid network with uni) and the strength of the skin (eg. adding extra layers or core material) to only where we need.

We are in control with composites. The opposite is using balsa and plywood which has the same strength and feel through out the entire piece, weither we need it or not. Directly replacing traditional materials will be heavier, you need to think about what the piece was doing.

Coreing a flat panel makes perfect sense, but how about a constant curved piece like a fuselage? Does not the shape give rigidity and strength naturally, even with a single skin of carbon?

The reason for adding core material is to increase strength/stiffness to a particular place. To make a 1D skin into a 2D skin where it needs it...

Places that have high stress like landing gear mounts and wing tubes need extra thickness, but we must transfer that stress gently. When using a core material for spot strength, the edges of the core need to be tapered, about a 1 to 4 ratio is a good starting point.

Working with composites requires new thinking, somewhere between a artist and a detective. We tend to not look at our parts so detailed because our old methods used flat sides and little curves which required little thought. With our new world of curved pieces, just stand back and just look at the shape of your piece.

It will tell you what it needs.

Just something to think about.

Darrin R Cash

(in reply to Darrinc)
       Post #: 7

Finishing a plug or a mold - 11/14/2003 9:04:49 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		When finishing a plug or a mold you can mix up a very, very very dry mixture of epoxy and micro balloons and cover the entire piece. It will not spread, so you will have to pack it on. Place your peel-ply over the mixture and massage the mix so that it becomes evenly spread out. The peel-ply should be drawing out some of the resin. If you can, bag the part and draw some vacuum, it doesn't need to be full vacuum. After this is cured, it should sand like butter with no pin holes.

Also we use a primer called PolyPrimer, it has a very high solids content, is flexible enough for composite work and sands well.

Darrin

< Message edited by Darrinc -- 11/14/2003 9:08:56 AM >

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       Post #: 8

Building a light weight foam wing - 11/22/2003 5:20:10 PM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		This for a one piece wing, but it also works for plug in wings. Just cut the extra uni at the root, put it down first, then the full piece of uni.

To prep the wing core, draw a line 0.5" behind the max thick point at the tip to a point 1.5" down from max thick point at the root and 4" from the root. Inside these lines, cut bays out of the foam, just leaving 3/8" ribs.

For the spar, try to order the 0.007" thick Uni in 6" wide pieces. Cut uni to length of one wing, then cut uni lengthwise in half, you should have two pieces. Cut the two pieces from tip to opposite tip making four triangles. Lay the uni on the foam about 3" from the tip, thin end at the tip. This should leave about 3" overhang onto the next wing. Mark all of this onto the foam.

When your ready to put on your 8lb density, 1/16 contest balsa, wing sheeting, have the foam cores already epoxied together and in the foam cradles with your sheeting already trimmed. On the area that you marked on the cores for the uni spar, lightly brush a thin film of resin over the marked area's. (lightly!!! just so that it looks shiny) Wet out your uni thoughly, but not soaking, then place your uni spars in the marked out area's, overlaping in the center. Then apply Probond onto the foam for the rest of the sheeting.

Put the top foam cradle on, you might want to put waxed paper between the cradle and the wing so nothing will get stuck, and stack all the books and weights that you have on top. I mean all of them!!!

The next day you will have a incrediblly light, stiff wing. It is well worth the time. Cut out the ailerons, put in a hard point for the control horn, cap them with balsa, shape them, and then your done.

Start there, once you get that process down, we can work on building you a really light wing.

First things first.

< Message edited by Darrinc -- 11/22/2003 10:49:33 PM >

_____________________________

"Make everything like your going to make the front page of NASA Tech Briefs"
Go Team Orange! Darrin R Cash

(in reply to Darrinc)
       Post #: 9

RE: Building a light weight foam wing - 11/22/2003 11:25:25 PM   
ColinM


 

Posts: 162
Joined: 11/7/2003
From: Cambridge, UNITED KINGDOM
Status: offline 		Darrin, interesting information. Any chance you can post any photro's to reinforce and explain your points?

Thanks

(in reply to Darrinc)
       Post #: 10

RE: Building a light weight foam wing - 11/23/2003 2:14:13 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		These are tips from past projects. I should be laying up some hollow core carbon wings in a couple of weeks, which should show the tapeing, the joggle and the closeout. I'll try to get some pics. I just have to finish sanding the molds. I hate sanding!!!

I just learned how to filament wind. You don't want to try that at home!

If your standing in front of your mold with these tips printed out and in your hand. It should not be that difficult to figure out.

They are fast processes that add strength and simplify. Everyone wants that perfect seam when they pull the final part from the molds, so they tape from the inside, this is not a proper structural way to do this process and forces you to make heavier skins.

If you wrap from the outside of the part you prevent the pieces from doing what they naturally want to do, pull apart. You have also just added a layer to the piece in a critical area, especially with wing leading edges. You just increased the strength of the D-tube, this allows you to use less core for structural integrity and therefore reduces overall weight with the same or improved strength.

It's simple if you think about it.

< Message edited by Darrinc -- 11/22/2003 6:23:00 PM >

_____________________________

"Make everything like your going to make the front page of NASA Tech Briefs"
Go Team Orange! Darrin R Cash

(in reply to ColinM)
       Post #: 11

RE: Building a light weight foam wing - 5/26/2004 10:17:29 AM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		I know I have not added anything in a while. I been very busy. But here is probably the best tip I could give anyone learning composites.

Pick up the phone!

I know it sounds too easy, but it works. The companies that makes the epoxy/cloth/core material that we use pay people to help people use there products, and as a added benefit they may direct you to a product that works better than the one you thought to use. They typically have guides that they can send you on proper uses of there products. These are not bibles, so keep with the experimenting. If you figure out a new way to use their product, share that with them.

Don't talk to the sales staff because their not going to make big money off of you so they won't be that helpful, so spend your time with the technical staff. Heck, ask if anyone there is a modeler. If you find someone you don't like to talk with, ask to speak to someone else. It is in the companies interest to help, the more people interested and educated, the more the industry grows.

I just went to SAMPE in Longbeach and I'm amazed about all of the modelling that I ended up talking about.

< Message edited by Darrinc -- 5/26/2004 2:18:59 AM >

_____________________________

"Make everything like your going to make the front page of NASA Tech Briefs"
Go Team Orange! Darrin R Cash

(in reply to Darrinc)
       Post #: 12

RE: Here is what we do at Scaled Composites - 5/28/2004 11:23:11 AM   
Magne


 

Posts: 333
Joined: 3/7/2004
From: Moss, NORWAY
Status: offline 		Thank you, Darrin.
Lots of VERY useful information and ideas.

"Start there, once you get that process down, we can work on building you a really light wing. " (Post #13)

I have been making some wings not to dissimilar to what you describe here, basically consisting of hot wire cut foam ribs. Good weight saving.
Could you please describe your method for making "really light wings"??
Thanks,
Magne

(in reply to Darrinc)
       Post #: 13

RE: Here is what we do at Scaled Composites - 5/28/2004 6:23:08 PM   
Darrinc



Posts: 1028
Joined: 1/22/2002
From: Piqua, OH, USA
Status: offline 		To make really light wing you need a vacuum pump. Here is one layup methods that I use and it requires molds.

The best way that I have found to make my molds is to make up a solid foamcore wing and glass/paint it, do not cut out the aileron. Pull a mold off of that and have about a 2" flange around for the BST. (Bag Seal Tape)

If you are going to do skin hinging like a Composite Arf, you will want to put some thin kevlar where the hinge is.

The lay up is 3/4oz glass, 1/8" contest balsa,(2) 3" wide uni strips tapered to nothing to look like a long triangle, 1/4"x1/2" light balsa planks for "ribs". ( and 3/4oz glass, optional) The spar is 1lb white foam cut to shape, and tapered from 3" at root to 1" at tip

Pre cut and glue the sheeting so that it lays down in the mold. Spray the sheeting lightly with water and vacuum bag the balsa into shape in the mold. Let dry under bag for a day. Afterwards I would place sheeting in cradles until put in mold. Doing this prestresses the balsa and make it more rigid.


Then wet out the mold and place the glass and squeegee the heck out of it. (I would even dab it with paper towels so that it is very dry) Once this gets to B-stage (really tacky) lay in your sheeting.

If you have peel-ply, wet out your uni on a table (put down plastic, once wet out, put another piece of plasic over it and squeegee the heck out of it. You'll be able to see if there are any dry spots) Place in mold an just lay peel-ply over uni and vacuum bag.

Once cured, dry fit spar and CA in the ribs. Now your ready to glue in the spar and do your close out.

You can add another layer of 3/4oz glass on the inside after placing the ribs, but that would be tough to do lightly. Remember to put peel-ply where the spar goes! I would try the plastic trick and maybe pull off on side of plastic and dab with paper towel before laying in mold. Let resin get to b-stage before putting in mold. (this keep the balsa from soaking up the resin)

Let me know how yours comes out!!!

< Message edited by Darrinc -- 5/28/2004 10:32:08 AM >

_____________________________

"Make everything like your going to make the front page of NASA Tech Briefs"
Go Team Orange! Darrin R Cash

(in reply to Magne)