RE: Seeker Wing Mold

RE: Seeker Wing Mold
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RE: Seeker Wing Mold - 8/16/2004 1:11:08 PM

daven

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First impressions were very good, but this wing probably won't see the sky. My trailing edge is just not strong enough. When I cleaned up the Rohacell at the TE by sanding it down, I made it too thin (and also sanded through the glass on the inside). On the next one, I need to sand the rohacell down before glassing and putting it in the bag. I'm also thinking about maybe an additional layer of glass on the inside of the sandwich full length to help stiffen it up some.

The carbon hinges seemed ok, not great, but definately useable. Where I had some problems was the outboard end of the aileron just isn't strong enough. I can grab it and move it up and down to easily. I'll skip Carbon their on the next one, and use up the roll of kevlar tape that I had been using on my tails.

Another learning mistake was the fitting of the aileron spar wood. I must have been a little sleepy when I make the measurements because they were only glued to the bottom of the wing with a 1/16" gap between the wood and the top of the wing. This was part of the reason why the ailerons were a little wobbly. The main spar fit was very good.

Just for fun, I drilled out the front wing hold down blocks, and that was perfect.

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Post #: 51

RE: Seeker Wing Mold - 8/16/2004 1:14:34 PM

daven

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Just for fun, I put the wing on the scale.

I was expecting a 20 oz wing and was suprised it came in at 17.8 oz. Still about 2 oz heavy, but I know I can shave that.

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Post #: 52

RE: Seeker Wing Mold - 8/16/2004 4:53:05 PM

daven

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I would like to get the rohacell form fitted perfect in the mold, so I don't have to trim it later. However, I am concerned that when the bag starts sucking everything into place, whats to stop the rohacell from moving slightly and being off center?

When You have the breather on top, its tough to see for sure whats going on in there?

I tore a Neme-Q Plus Aileron apart this morning, and it looks like Terence uses some sort of fabric as his hinge material. Not Glass, but some slick looking fabric. I am going to check with him and see what it is. There was carbon fabric on his aileron, but not on the hinge line. Hes aileron was much sturdier than mine.

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Post #: 53

RE: Seeker Wing Mold - 8/16/2004 5:14:48 PM

garys

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Dave,
The rohacell should stick well enough to the outer skin to keep it from shifting as the vacuum is pulled. It's really not a major issue if it does shift slightly anyways. You could also use small 1/4" wide strips of masking tape in aobut 4 to 6 places around the perimeter, holding the rohacell in position, which I believe is what Chuck Bridge does.
Terrence uses some type of nylon that he found. It's really tough, but not nearly as difficult to cut as kevlar cloth can be.
GS

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Post #: 54

RE: Seeker Wing Mold - 8/16/2004 7:09:52 PM

daven

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I believe Randy E. told me that it is the same stuff that is used inside of Suit Coats. I just don't know the name of it so I can ask the wife if she'll pick some up at the fabric store.

The tape idea sounds good, but how do you get the tape to stick to resin filled fiberglass?

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Post #: 55

RE: Seeker Wing Mold - 8/16/2004 7:27:54 PM

PylonWorld

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Some people are actually using the woven Peel-Ply in the hinges. It sounds like the wrong thing to do, but I've been told that because it is sandwiched between the inner and outer fiberglass layers in the hinge relief cutout, it doesn't separate. I have not tried it yet. Peel-Ply is a form of Dacron.

A 2 oz bias piece of glass cloth on the hinge line between the 1.4 oz outer layer and the .7 inner layer makes for nice hinges that are plenty stiff, but also flexible enough.

If you have the skin core material so that it comes close to the edges, but not beyond, the overlapping fiberglass will keep things in place as you pull the vacuum. At least it does when using balsa. I have limited experience with Rohacell.

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Post #: 56

RE: Seeker Wing Mold - 8/16/2004 7:33:43 PM

Marco Vergara

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Dave, it would be better ( stiffer) if you lay up 2 plys of 0.7 oz cloth insted of one 1.4 oz ply on the outside layer of the wing.
To get a stiffer aileron you can ad a strip of 1.4 oz cloth to the aileron surface and don´t forget to ad a spar made of balsa or aluminium tubing inside the aileron.
The skin inge can be made with a strip of peel ply.

Marco

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Post #: 57

RE: Seeker Wing Mold - 8/16/2004 7:42:20 PM

garys

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Dave,
My understanding about taping the rohacell in place is that the pieces are long enough to go beyond the glass, onto the mold itself (where it's dry). After everythings layed up and cured, the tape is simply trimmed with the excess glass and effectively disappears. I remember Chuck holding up a wing in the sun and showing me where you could just see a piece of tape at the trailing edge. Jim Allen uses 1/20" balsa for the skins, and hasn't had any issues with the skins sliding out of position, even without taping them.
GS

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Post #: 58

RE: Seeker Wing Mold - 8/16/2004 8:23:25 PM

daven

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I get it now Gary, but that would mean I would need to lay up the .7 glass on the rohacell in the mold again. That really didn't work well because the rohacell moves up and down in the mold as you lay it up, and the glass doesn't like to stick to the rohacell to begin with, so I ended up using much more laminating resin than I wanted to.

What I'm starting to wonder about, is doing this with one more step. Before putting the glass on the inside of the rohacell, just bag it before that step so the rohacell is flat in the mold (Stuck to the outher layer of glass and resin). Than I could trim up the excess rohacell and then glass the inside and bag again.

Marco, yep the two layers of .7 on the outside would be stronger. I just hate using that thin stuff, the 1.4 oz goes down real easy and still gave a Very nice painted finish when it came out of the mold (even with PVA). I saw that Chuck uses the aluminum tubing in his ailerons as spar, and Terrence uses balsa and a bit of resin.

As to removing the rohacell over the hinge line, from the wings I've torn apart, I don't see that this is being done. The rohacell is moving with the glass hinge.

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Post #: 59

RE: Seeker Wing Mold - 8/16/2004 8:29:54 PM

Randy Etken

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Dave
The product I use on my R-200 for elevator and aileron hinges is from Jo-Ann Fabrics, 100% polyester off white sunline @ $2.99 a yard. Works good as it stays somewhat flexible. When I have used it with only 3/4oz fiberglass over a foam and balsa it is not stiff enough, need to added strip of 3oz.

Randy

< Message edited by Randy Etken -- 8/16/2004 8:42:44 PM >

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Post #: 60

RE: Seeker Wing Mold - 8/16/2004 11:03:54 PM

PylonWorld

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quote:

ORIGINAL: daven

...

As to removing the rohacell over the hinge line, from the wings I've torn apart, I don't see that this is being done. The rohacell is moving with the glass hinge.

All of Lyle Larson's products have the Rohacell removed for a gap of about 1/4" at the hinge line. Including the Dago Red, Vendetta, and the Bird of Prey. Jerry Small's Sidewinder and Quickie have balsa skins and have a relief area cut out and beveled on the hinge line. The V-Max has Rohacell skins and has a relief area cut and beveled on the hinge line.

All of the above also have a corresponding area cut out on the bottom so that gap sealing tape will slide under the front of the ailerons.

If the skin material is not relieved in some way on the hinge, you are flexing the skin. A relief area controls where the flex occurs.

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Post #: 61

RE: Seeker Wing Mold - 8/16/2004 11:42:22 PM

daven

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I guess I didn't do a very good disection. I just checked a Neme and a vortex, and both of them have removed a rough 1/8" gap of the rohacell/balsa on the top skin.

Obviously on the bottom you have to slit the skin so that it can move. The neme just uses an angled cut and no tape, I planned on doing it like the Vortex with just a small 1/16" gap and then run tape into the gap and attach to the aileron.

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Post #: 62

RE: Seeker Wing Mold - 8/17/2004 1:17:51 AM

PylonWorld

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An 1/8" or so gap is enough. To get the cloth to lay down properly, you want to bevel the edges on the inside. I use a 1/4" gap, because some epoxy stays in the hinge line adjacent to the skin material. I wind up with about 1/8"-3/16" of "live" hinge. It also depends on the cloth recipe that you are using. If you use additional cloth like Kevlar or Kevlar mat, the gap needs to be a little bigger than 1/8".

On the subjects I mentioned, the bottom skin has material removed prior to lay up where the slot will be cut later on. By beveling the edges of the material in the bottom slot prior to lay up, the gap seal tape will slide into the slot better. You could bevel the inside after the slot is cut, but that will weaken the bottom skin right in front of the aileron.

BTW, I use CF mat or .007 CF laminate on the insides of the ailerons/elevators. I think the mat yields a stiffer control surface, but adds a tiny bit more weight. CF 2.4 oz cloth is probably optimal. It is important to have the top and bottom skins of the control surface joined at their front with balsa or a tube to get enough strength. On a tail you can just use a bead of glue, but on a wing the space is too big. I've started using CF hollow rods because I feel like the bond is better than aluminum, and the CF tubes are stronger and stiffer than balsa in that application. It does ad $5 or so to the cost of the wing, but that is minimal compared to the benefit.

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Post #: 63

RE: Seeker Wing Mold - 8/17/2004 3:53:20 AM

Mluvara

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Dave,

I remove a 1/4" strip of the core material where the hinge goes and bevel it. On the lower hinge surface, I use a piece of trim tape on the mold to make the indent in the wing where I want the wiper to go.

As far as the undersize core moving when you bag things, it should be a non issue. I actually start evacuating the bag and if I need to move it, I can stop the pump, readjust, and then start things up again. This is all while some vacuum is in the bag. It helps to keep everthing in its place.

I had to look for the old Tsunami composite threads here on RCU (man, has it been that long???), but this one will give you an idea. Granted, I have changed a lot of how I do things, but the basics are the same.

http://www.rcuniverse.com/forum/Tsunami_%2D_composites%2C_part_3/m_229716/tm.htm

Michael

< Message edited by Mluvara -- 8/16/2004 7:58:11 PM >

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Post #: 64

RE: Seeker Wing Mold - 9/30/2004 7:34:07 PM

daven

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Its been over a month since I pulled the first wing. Work has been crazy with travel, and I just haven't had much time to do anything. I spent the past few weeks cleaning up the molds.

When I pulled the first wing, a few edges of the mold chipped loose and stuck to the wing. It was a bit more work filling these voids than I expected. First I cleaned the molds, than I filled with EverCoat "Easy Sand". I then sanded with 400 grit, than 600, than 1000, and finally 1500. After this, I checked the voids again, and refilled. This was followed by the series of sanding above. Of course, with all this sanding, additional pinholes opened up in the fiberglass mold. I needed to fill them and sand, and repeat. It took me quite a bit of time to get everything filled in and sanded smooth.

After this, I applied a series of coats of Rubbing Compound on a buffing wheel attached to my drill. After that, I went down to Polishing compound with the same buffing wheel.

When that was done, I proceeded to buff the mold with 5 more coats of Dolphin Wax.

I can see why alot of people are using the Aluminum molds at this point

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