pooba

ho there!
how do i apply 2oz cloth to the double curve at the front of a sukhoi su26 cowl? should i just cut lots of thin strips to get around the curves?

Darrinc

My Feedback: (5)

Just cut triangles in to the edge that goes around the curve. There called darts.

Deadstik

My Feedback: (8)

Ditto what Darrin said... all it takes is a small pair of very sharp scissors and cut the "darts" into the wet glass. You don't actually have to cut the "darts" out unless you are trying to be super weight concious...I just cut down one side and have a small overlap. It will not show on the outside of the finished part, and will lay evenly on the inside.

Dan [8D]

newbiepilot

How could it not show, wouldn't there still be a little on the outside? Also, does the cut in the glass weaken the structure. Would making the cowl out of thin strips weaken or strengthen the cowl?
Thanks for the info guys.
I really appreciate it.

KC-135

My Feedback: (3)

Another way is to mix visco-fill or micro ballones in to a thick slurry and fill the lip then lay your glass on top this will give you added strenght when you cut out the front and less cuts to lay your glass.

Darrinc

My Feedback: (5)

Quote: Also, does the cut in the glass weaken the structure.


What is the structure being weakened??? Your making this for a model. The shape gives it strength.

We run single layer carbon cowls on giant scale.

Darrinc

My Feedback: (5)

Your probably trying to do this on a 0/90.

Actually, a round cowl like this should be easy. 2 layers of glasss on the 45 should just bend in. It might take some orintation fuzzing but this is not structural and will not matter.

You must learn to work the fabric, make it go where you want it to. Maybe a slice every 3"-4"

I would rather hear about your failures about getting it to lay down. That kind of info will help everyone!

newbiepilot

If it were for a stuctural part, would the cut lose strength. Also, is it strong or stronger to use cut strips of cloth rather than big pieces of cloth to make the part.
Thanks for the info guys.
I really appreciate it.

Darrinc

My Feedback: (5)

Are you using a male or female tool? If a male then you will have to bodywork the heck out of it anyway.

As long as you overlap each piece there should be no loss of strenght, so what ever is easy for you should work.

newbiepilot

Thanks for the information.

Deadstik

My Feedback: (8)

The cuts will have no effect on the structural strength of the bond. The resin saturated fabric will form one piece as the resin cures and the individual cuts will not show up on the outside of your piece and will appear seamless. As others on this thread have stressed, a lot of times you just have to "work" the resin into the cloth with a dabbing motion rather than brushing it in. With time and technique you will get to the point where you will make very few cuts in a layup. I know from experience that it is possible to layup an entire fuselage side without making a cut at all. Good luck with your project !!


Deadstik [8D]

newbiepilot

So, even if you have overlapped the pieces, the seam won't show up? Can you further explain how to "work" the resin into the cloth?
Thanks for the info.
I really appreciate it.

P.S. Is it like the two pieces are melting together into one piece when you overlap?

RTang

pooba initially sent the post for me as i did not get around to registering until now(he is building an 56" extra 300L and with undoubly need to build a cowl as well). thanks for all the replys guys... and i see this may have been a worth while question asking afterall, rather than plundering ahead.

By the way for this kind of job would you perfer laminating or finishing epoxy resin to do the whole thing (i had tried polyester by the fumes managed to get under my first mold of white foam and 2" parcel tape, reducing my nice foam piece to something i cannot tell what is now[:@]!) However the polyester did not seem to stick to the cellotape, whether it had small amount of wax on or not. Would epoxy resins stick to this kind of membrane?

Is dynel cloth (i think 3oz or so) any good - it is much looser (bigger gaps between the threads and likes the curves better than the 2oz fiberglass cloth). Are we all talking about the same kind of 2oz cloth, and is 2oz similar to 2.5oz? No probles though with the 6 oz. Is there any other methods people prefer as per selection and final layer of cloths?

Do you put the heaver cloth on first? and is the resin applied to the cloth - i have heard of putting resin on the mold then rolling the cloth into it. do you do all of the one layer at once - where also is the best position to place the drying resin on cloth. does anybody do both the layers at once since you do not sand the cloth (having minimal amounts of resin and then a filler on the outside final layer to provide the smooth finish here).

I was also thinking of useing this resin as well for my fiberglass bandage in the centre of the wing, since the ca fumes are horrible and it is a white foam core with light balsa sheeting. what weight of cloth and how many layers do you use?

Thanks for replying

Darrinc

My Feedback: (5)

Finishing resin is fine, but if you are going to do more layups then get some good laminating resin. Sounds like you are using a male mold, you must like to do bodywork and add weight. If the male mold is done, then wax it and pull a female tool off of it, then you get a perfect part everytime.

I would use 2 layers of 2oz glass on 45° since this is a 56" plane and will need to be as lite as possible. (it will be stronger than you think)

Wett out the mold then lay in the glass, take a stiff brush and push straight down repeatively on the glass to wett out. Place the second layer and wett out with the brush, then take a paper towel and dab out all the resin you can. Excess resin = weak part

If you do one layer at a time then you must take a lot of time to sand between layers. (remove all the shine!!!)

You should not have to glass the wing, it only adds weight.

newbiepilot

Thanks for all the info guys.
So, when you overlap fiberglass pieces, do they melt into one piece as they cure? Wouldn't there still be a little lump where the overlap is?
Thanks.

davidfee

No, the pieces do not melt together. Yes, there will be a bump where the overlap is. If you are making something in a female mold, then it doesn't matter because the lumps are on the inside where nobody will ever see them. If you are making something on a male mold, then the lumps are on the outside and will need to be sanded down.

-David

newbiepilot

Is there a way to prevent this bump on a male mold? Other than sanding. Without losing too much strength? Also, how much can you sand untill you start wearing the stuctrual support?
Thanks for the info.
I really appreciate it.

Deadstik

My Feedback: (8)

If you are making a cowl using a male mold. then as the other here have said, the bump (joints) would be on the outside and have to be sanded. How far is too far?... You want it to appear one piece and smooth, so you basically have to get it where the overlapped piece has been sanded away. You will probably end up using glazing putty to fill this joint. In your case, I feel the answer is to make as few "overlaps" as possible. 2oz or 3oz cloth can do some really nice things if you just take your time. Since this is for a Sukoi, you may want to try to do the cylinder section first (easy to do in one piece and get it as close to the leading edge as you can. Then cut a doughnut shaped piece to form the leading edge. You pose an interesting problem that I haven't had to deal with as all my molds are female and it is no problem to overlap/cut at any time. Joining the fuse halves together in the mold is the REAL trick. Only took about 12 fuses to get it right!! Anyway... it may be in your best interests to perhaps look at making a female mold. After all, a Sukoi cowling looks like a LOT of pots and pans I've seen so to make a cowling would just require a little of the old thought process. Good luck on your project. By the way, for filling the glass after sanding I use a product called "Icing". It's a glazing putty that is very easy to sand and purchased in an auto paint store.

Deadstik

Darrinc

My Feedback: (5)

You are always worried about strength, so what is the cowl supporting??? The shape gives it strength to hold it's shape, and isn't it just for looks anyway. You could make it out of paper, but that would be harder.

RTang

Thanks for all the replies!

I also see it is gathering more posts and people are finding this info useful too. I will create something about my progress with the Sukhoi's cowl - grrr (school work and my layness!)

But guess what, i've got another question - or rather asking what do you think?

I was thinking of buying some covering soon to get this project done. However, i had get more than 1m of a colour, since it could not fit on that roll. How about covering the cowl with the polyester covering - is the finish good? Does it add 'strength' to a cowl? The covering film is yet to be decided, but i was thinking of oracover, monocoat, easycoat, or solarfilm - weigh, cost and (sufficient) strength are ultimatly the discriminators! What do you think?