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Old May 14, 2003, 10:37 AM
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San Diego
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hollow wing lay-up schedule

The staright wing story continues with the lay up of the wing. As I have some 1 oz square weave carbon fabric I plan on just using that to lay up the wing. The fact that this wing is REALLY thin ( less tha 1/2 "! ) I was planning on using three layers of cloth.

1. outside layer at 0 degrees

2. inside layer at 45 degrees

3. innermost layer at 0 degrees, diamond cut to about 60% span

This is then vacuum bagged and then I will screed syntactic foam ( epoxy and microspheres , dry mix ) into each half and close the mold.

The compressive and shear strength of the syntactic mix should take the loads quite easily with the added bonus of utilising the full area of the carbon skins for load transfer.

As I have never layed-up an F5-D wing before, I would appreciate any words of wisdom. thanks.

Bob K
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Old May 14, 2003, 12:44 PM
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San Diego, CA, USA
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hollow wing layup

Hey Bob!

Full carbon on your first part? Man, you're more gutsy than I thought! Actually, your layup schedule sounds pretty good. However, I would suggest using ~1mm balsa or rohacell sheet between the outer two layers of carbon. This way the wing skins are sandwich panels (they will be much stiffer this way). You might also consider laying up some tow along the highpoint to act as a spar cap.

Are you talking about filling the mold with syntactic mix, or just making a thin layer over the skin? Most hollow wings I've seen have balsa ribs and shear webs installed after the skins have been bagged. (I'll attach a picture) Then the two wing halves are joined by running a bead of syntactic mix along the perimeter and over each rib and spar cap. Ribs are placed only at the root and the edges of the ailerons, etc.

I'll also attach a picture of the D99 wing, showing the glass/balsa/glass skins... with carbon spar caps and carbon reinforced ailerons.

My last final is tomorrow... I can't wait to see these molds in person!

-David
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Old May 14, 2003, 01:13 PM
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San Diego
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Oh yeah, full syntactic foam core. Not much point putting any carbon near the center of this wing, it's too thin. By using a syntactic I am theorizing that I can avoid top skin buckling while keeping a really hard wing surface. I'll make up a couple of batches and get a density ( for a reality check! ) measurement.
Just to make sure. But, I am going to have a lot more carbon spanwise than just spar caps would ever have. Oh well, I have enough carbon for a few wings. We might have to "allocate" a wing and have a little experiment with a lot of weight ( and maybe safety gear! )......
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Old May 14, 2003, 01:24 PM
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The Team Ariane guys in Germany used to make their (very thin) F5B wings with carbon/glass skins and a styrofoam core, using the same build sequence you're talking about. It worked really well for them. Who knows... it will be interesting to see how light (what density) you can get the syntactic foam.

One of the coolest things is that, since you made the molds, you can experiment with a bunch of different layups. I've got one in mind, myself.

-David
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Old May 14, 2003, 03:37 PM
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> As I have some 1 oz square weave carbon fabric I plan on just using that to lay up the wing.

1 ounce! OK spill your guts, where did you get that stuff? And did you have to rob a bank?


> This is then vacuum bagged and then I will screed syntactic foam ( epoxy and microspheres , dry mix ) into each half and close the mold.
> The Team Ariane guys in Germany used to make their (very thin) F5B wings with carbon/glass skins and a styrofoam core, using the same build sequence you're talking about. It worked really well for them. Who knows... it will be interesting to see how light (what density) you can get the syntactic foam.


If I understand the proposed syntactic method correctly, Iíll be interested in your weightl. The Ariane foam core mentioned above would probably be about 1 pcf density if it were polystyrene bead foam, or maybe 1.5 Ė 2.0 pcf if it were extruded foam or rohacell equivalent. In the case of your syntactic mix, epoxy resin+hardener mix is 1.13 g/cc (use MGS as example). Thatís equivalent to 70 pcf density. I donít know the density of microballoons but call it 0.3 pcf just as an example. So 100 units of 0.3 pcf microballoons + 2 units of 70 pcf epoxy would yield a mix density of 1.7 pcf. That might be in ballpark weight wise, but Id be very surprised if you could actually mix it anywhere that lean. If the spheres arenít bonded structurally, it would be a weak crumble. Id recommend making a small batch coupon, observe your mix volumes & see how you fair.

I think it would be pretty hard to beat a spar, even hard stock balsa is only 10 pcf & capped with CF because the remaining core is open air. You would have to have sandwich construction G/B/G wing skins though. Hmmm sounds familiar....
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Old May 14, 2003, 05:30 PM
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OK , maybe I am going to have to weigh the carbon, it's pretty thin stuff. But, the scale will tell no lies! I can't divulge my source because , well, it was just some stuff he had laying around from some past job and it's thinner than the usual stuff I have seen. And if I could have gotten anymore ........( Hmmm.... I did'nt try beer, and he does like cigars....)

Your point on the density of epoxy syntactic is well taken. I am banking on the fact that this wing is so-oo thin that the difference in density will not translate into a significant weight penalty. Once again the scale will tell no lies. I am looking at about 12-15 lb./cu.ft. syntactic. And yes, just a balsa spar (end grain) is my fall back technique. End grain balsa is good stuff at the densities we deal with.

It's just attractive to be able to screed in some syntactic and just close up the molds...... We'll see.

Bob K
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Old May 14, 2003, 07:47 PM
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I have a wing from a Sliver Y2K here and it's less than .400" thick at the center. Uses what I would call standard hollow molded construction. Full carbon will look nice but it's pretty heavy. The lightest woven cloth I've seen is about 2.5oz/yd^2. Unidirectional can be had in lighter wieghts.

What kind of weight for a finished wing are you shooting for? What is the wing area?

Greg
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Old May 14, 2003, 09:02 PM
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Quote:
Originally posted by Bob K
I am banking on the fact that this wing is so-oo thin that the difference in density will not translate into a significant weight penalty. Once again the scale will tell no lies. I am looking at about 12-15 lb./cu.ft. syntactic. Bob K
Some other possible techiques are:

- you pour expanding urethane based foam into each mold half. Depending on a bunch of variables it might have a density of say 2 pcf. This would then have to be milled & sanded flush with the mold flanges & bonded together. Adhesion to the skin would be good, the core would be reasonably strong but messsy, messy

- you get cnc (meaning hot wire) cut foam cores which get inserted in between the skins, wet layup all-in-one. The dimensional control is pretty good from my experience & you can choose from a variety of foams & density
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Old May 14, 2003, 11:09 PM
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Quote:
Originally posted by ptxman
- you get cnc (meaning hot wire) cut foam cores which get inserted in between the skins, wet layup all-in-one. The dimensional control is pretty good from my experience & you can choose from a variety of foams & density
This is essentially the technique employed by the Ariane guys (back in the day). They bagged oversized half-cores into each mold half, then cut the foam flush with the part line... then glued the halves together. Detail pics can be seen here: http://www.delago.de/ariane/EBauV7.htm

As an example, here's a sample picture from the Ariane website:



The new Ariane planes, built by Carbon-Vertrieb, are made with the more "standard" hollow molding methods.

-David
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Old May 15, 2003, 12:05 AM
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The two part expanding foam generally tends not to be as uniform in density as we would like. Since your mold is based off a single tapered planform, a CNC'd core would probably be the safer bet. I have not done this process to a complete wing but I'm sure either way will be an interesting experience.
The basic lay up schedule I have done for F5D wings has been:
*outer layer- two layers .75oz glass 45 bias; actuall cut in halves and they overlap each other across the center for doublers in the center in an oblong oval pattern to 30% span.
*next layer- .75oz D tube full span
*doublers along aileron span; can be carbon or glass 45 bias.
*rohacell foam or balsa sheet; cut outs at hinge line and spar caps. I'll usually bag this layer and then come back to sharpen trailing edge and insert uni carbon spar caps.
*inner layer another whole layer of .75oz glass and any other doublers or extra material needed around bolt area, etc.. Bag.
* trim edges, make sheer webs and sub sheer web, put any tubes or wood for ailerons (closing them out), glue down sheer webs and other stuff on one mold half with thick CA, run bead of micro balloons around edges and on top of sheer webs for proper joining squish and close her up.
My first wings out of a new mold usually come out too overbuilt and heavy and I take out material to fine tune it or add it to areas that need it more.
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Old May 15, 2003, 02:35 AM
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Bob,
I couldn't sleep so I just weighed a new D99 wing (no servos or anything). It weighs 104.5 grams, so you should be shooting for 100g or less for your wing. The D99 wing is a bit overbuilt, mainly for cosmetic purposes. People don't like to pay >$200 for a plane that has pinholes in it.

-David
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Old May 15, 2003, 07:19 AM
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Regensburg, Germany
Joined Apr 2003
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Hi!
The layup for my selfmade F5B championship models (Twister, Raketenwurm, Eisvogel) is:

outer layer: 25 g/m≤ 45 degree angle
carbon D-Box or full carbon 93 g/m≤ 45 degree angle
0,8 mm balsa
inner layer: 25 g/m≤ 45 degree angle

The spar is high-module carbon fibre (up to 55 rovings per half)!

The wing of my Twister (160 cm span) weighs 290 g including 2 servos and complete cables! You never can destroy this wing in the air whatever maneuver you are flying!

Ciao, Marcus
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Old May 15, 2003, 08:23 AM
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Joined Jul 2002
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MR. M Koch,
Where do you get your balsa? I make F5D wings and can't find light enough balsa. I gues you use 10x100cm balsa and it weight's under 10g each am I right? I did Avionik copy with that exact layup (but 80 carbon D-box and 1mm balsa) and it weights 140g ready to fly with two 9g servos.

/Antti
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Old May 15, 2003, 09:06 AM
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Regensburg, Germany
Joined Apr 2003
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Hi Antti!
Im getting my balsa directly from a balsa sawmill here in germany! He cuts the balsa in that shape and size i want to have! Normally a 10 x 1000 x 0,8 mm balsa weighs about 6-9 g before i use the filler (Clou Schnellschliffgrund)!

Ciao, Marcus
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Old May 15, 2003, 09:38 AM
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San Diego
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Well, the scale tells no lies ( unlike people ;-) . My carbon cloth is 5 oz/sq.yd. /170g/m2 :-( So much for using that.

BUT, I have a whole 18" wide roll of 3/4 oz glass , so I guess I'll be going with that. I can always pull tows out of the 5oz carbon and use it for spar caps.

I would like to thank everyone for sharing their lay-up schedules. In these few posts, there are countless hours invested.

Cheers

Bob K
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