Wompoo Build Log - Page 30 - RC Groups
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Jan 12, 2013, 04:35 AM
Entropy is happening!
Jim.Thompson's Avatar

Almost done.

The first half is almost done.

As can be seen in the second picture, I tried laying some core material up to the wing root arris like described previously. I let this go off and sanded it approximately flush. The I added glass/resin to the root face. I employed some plastic cloth to act as a surface binder, which worked ok due to the surfact tension between in and the wet laminate.

I am reasonably confident I will find voids later under the gel coat. The penalty in finding a void in one of these inaccessable spots is that they are very hard to repair. The gel coat may look ok for one or two pulls, but then punch through and provide a nice key into which the part can stick like nothing else!
Guess how I know?

I removed the air port plug and replaced it with a ball of plasticene for safety. There was developing the increasing chance of gluing the threaded plug in. This way, I glassed over the plasticene and will grind it back to expose if after completion. I also did the same with the small diameter incidence pin. This also made the layup around these orifices a bit easier.

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Jan 12, 2013, 06:08 PM
Entropy is happening!
Jim.Thompson's Avatar

Voids in the layup!

I still managed to get some voids in my layup around the wing fillets!

I'm even starting to imagine how I could employ vacuum on the mould layup to deal with this persistent, and potentially damaging problem! Maybe I could cable tie the puckered up plastic sheet around the joiner & incidence pin mandrels and air port? Doesn't sound easy though!
I do them in several session, so the bag could be removed between.

In the first picture, I have removed the pins and picked out the plasticene from the air port threaded part. After grinding down excess layup over the brass fitting, that is.


edit: On further reflection, I don't think that bag idea would be too hard. The air port is simply filled with plasticene so it is no problem just let the bag pass over it.
A template could be cut for the two drill guide mandrels. The plastic is passed over these. Then I could use plastic washers (or metal ones for that matter), with some acrylic grout to seal the plastic around the pins. The rest is self explanatory. I might be giving it a go.
Last edited by Jim.Thompson; Jan 12, 2013 at 06:13 PM. Reason: See edit.
Jan 13, 2013, 02:45 AM
608 km/h!
josh18's Avatar
Hey Jim, i have found for stubborn areas that wont stay stuck down while curing, I use a thick layer of splooge (internal or external radius) and leave it till it starts to tack off but will still bleed through the layers a bit. Then the tackyness will stick the fabric and if you work it will still bleed through and stick over laying layers too. This is with 6oz glass mind you, I dont know how it would go with thick cloth though.
Looking great BTW!
Also, I dont know any more about the TR stuff than what that peice you put up says. Sounds just like frekote to me though.
Cheers mate
Jan 13, 2013, 03:21 AM
Entropy is happening!
Jim.Thompson's Avatar
That's a good trick Josh.

I'm wondering if I should build the wing moulds with open roots and make separate root moulds. I see that there are two threads here on the forums describing how to do it, but I cannot follow it exactly.
Also, I don't know the pro's and con's of doing it that compared to moulding the root half depth with each half of the wing mould. Like I did with my plank.

One of the slight problems with doing them with included roots is getting the vacuum bag to press will down into the inside corner of the root/skin right angle.
I put some tow in there to provide a slight radius, but there is alway some doubt about it fully compressing that section.

Jan 14, 2013, 12:20 AM
608 km/h!
josh18's Avatar
Hey jim, I dont think youll have a problem with the closed roots. I have some sections like that in my scorcher tail sections. I use a bead of splooge, and also some carbon tow as its a high stress area. I put these down before I lay any cloth and I've never had an issue. It should work for full size wings too I would say.
Jan 14, 2013, 12:52 AM
Entropy is happening!
Jim.Thompson's Avatar
Originally Posted by josh18
Hey jim, I dont think youll have a problem with the closed roots. I have some sections like that in my scorcher tail sections. I use a bead of splooge, and also some carbon tow as its a high stress area. I put these down before I lay any cloth and I've never had an issue. It should work for full size wings too I would say.
Thanks Josh. I did it on the "Circa" (moulded plank), and I'm building a second set just now actually. I works ok. But I'm still curious as to the how's and why's of the open ended moulded wing construction method. The only two threads that I have read extensively on moulded wings use this open ended construction technique. Maybe I'm missing something that is much easier. I don't know.

I bought some 40 x 40 x 1.6 mm steel RHS this morning for the mould backing frames. We have had some rain, so welding will be safe again in my environment. I did some the other day and started a small grass fire! Many fires already around our parched country.
The steel backing will be built as as to allow free sliding clamps to be positioned anywhere along the length of the mould. (Ref: See Adam's thread) I'll use threaded rod and 20 x 20 RHS for the clamps. Alternatively, if there is some suitable hardwood around, I'll use that for the clamp faces. The threaded rod will have welded handles to make for fast hand clamping and assembly. The nuts will be either welded to the bottom RHS, or if they are timber, the rod will screw into "T" nuts on the bottom. No more fussing with nuts and washers with sticky resin covered gloves while epoxy is going off in high summer temps etc.

I plan to strip the parting board off the fuse mould tonight or tomorrow and start the second half layup.


I had a quick look at the Coefficients of Thermal Expansion here: http://www.engineeringtoolbox.com/li...ents-d_95.html
It seems that the Coefficient of vinylester is close to steel. However, epox is significantly different!
Maybe I should not use it for the epoxy wing moulds? I did on the previous plank moulds, and several other builders have reported using it on threads posted here, without apparent problems.
Last edited by Jim.Thompson; Jan 14, 2013 at 04:30 AM. Reason: See edit.
Jan 14, 2013, 04:35 AM
Entropy is happening!
Jim.Thompson's Avatar

Drag Spars etc.

I'm thinking ahead about what to use for the drag spars and the control surface LE spars for the wings.
One idea I have is to cut some blue foam sheet into approx. 5 -6 mm thick sheets. Then bag some diagonally cut 185 gsm glass onto it. When cured, cut it into strips to suit the depth required.

I also have some very nice biaxially sleeving from Soler Composites. Previously, I used some of this over drinking straws, but I didn't like the lack of continuity.
Maybe there is something more suitable to use with this socking?

Jan 14, 2013, 06:18 AM
608 km/h!
josh18's Avatar
Hey Jim, what do you mean by lack of continuity? I have used the drinking staw/ sock method and couldnt think of a better or easier way to do drag spars. You can also cut some scrap cloth (6oz glass) on a bias into one inch strips and with some 3m spray roll it up like a cigarette. I like this way better than spiral wrapping as its easier and much neater. For fatter straws get some maccas ones! Carbon sock spars over foam noodle make really strong main shear webs too and save major time in a build.
Oh, and the other great thing about noodle/straws/sock is that size is not critical as it squashes down to the right size when you close the mould. You also dont need any splooge so it should be lighter and also stronger.
Cheers mate
Jan 14, 2013, 04:25 PM
Entropy is happening!
Jim.Thompson's Avatar
Originally Posted by josh18
Hey Jim, what do you mean by lack of continuity? .................Josh
Just that the straws are not continuous! I think I got around this problem last time I tried it by using something as a mandrel on which to thread the straws, which was removed when cured. Something like a carbon or fibreglass rod etc. I might try that again.

As for the main spars, where do you find the foam noodle? Harware stores? I have resisted the idea of using them with biaxial sleeving for main spars to date. Mainly because, in my visualisation of them in use, the effective shear web is curved. It seems to me that the most effective (stength/weight ratio etc.) shape for the shear web(s) is vertical to the imposed loads. Does this make sense?
That's why, to date at least, I have chosen end grain balsa for the main spar.

Last edited by Jim.Thompson; Jan 14, 2013 at 04:32 PM. Reason: spelling.
Jan 14, 2013, 07:06 PM
Just fly it!
wyowindworks's Avatar
The foam noodles are called "Backer Rod" or "Caulk Backer Rod". Most hardware stores in the US have them.
Jan 14, 2013, 07:26 PM
608 km/h!
josh18's Avatar
Hey Jim, I just squeeze one straw into the end of the next until I have the length I want. I think you are making things much harder than they need to be by curing the spars before putting them into the wing. If they are cured they need to be accurately sized and splooge is needed to fill the air gaps, this then tends to squeeze out and foul your wiper area! I make my spars with cloth or sock dry, then CA the ends into the mould where I want them (just a few drops) Upon closing the mould I wet the spars out with a brush and just close the whole thing up. As long as you know your straws/ noodle is slightly oversized for between the skins, you will need no splooge for the join. The straws just stay inside the spars.
As for the mainspar, I have only done one like this, but with 2 layers of carbon sock it seemed easily as stiff as a balsa shear web. Timbuck, Kevin Bennet, Avb and the others have all done this way with great success.
Last edited by josh18; Jan 14, 2013 at 07:35 PM.
Jan 14, 2013, 09:02 PM
Certifiable User
killercando's Avatar
This thread is great and the cool/simple tips just keep coming. I had heard of using drinking staws but couldn't see how they would work and backer rod for me will be even easier to get ahold of. Thanks. I love the name and looks of your ship Jim. I wish I had something useful to contribute but until then I will keep Lurking. Lee
Jan 14, 2013, 11:11 PM
Auzzie built planks
timbuck's Avatar
Both warheads 30 and 60 , windburner , shmicko , scratcho , scorcher , gizmo
And plenty more planes done this way.
And to top it off....spencers kinetics are done like this. Worlds fastest planes.
Quick , simple , economic ( use left over cloth to wrap).
They can be done heavy or light..depending on need.
I use different size straws for controls and TE spar. You don't want the straws to completely squish.
You want the size to be just touching so sheer loads will be spread better and you end up with stiffer controls.
From Woolworth....you can get white very skinny home brand straws.
Also colored 5mm...if you need to go that small. theY've foam noodle we get is called... " gap filling rod "....yellow and red packet , MORODAY
Is the brand name. Come in 6mm , 10 , 15 , 25....


Latest blog entry: More colours
Jan 15, 2013, 01:02 AM
Entropy is happening!
Jim.Thompson's Avatar
That's all good Adam, Josh and Tim. And thanks for the comments Lee.
I'll use the drinking straws again. Also chase up some Moraday foam caulking strips.

You don't have a bigger copy of the full wing that you posted above by any chance do you?
I'd like to look a bit more closely at the detail if possible.
Last edited by Jim.Thompson; Jan 15, 2013 at 01:03 AM. Reason: Correction.
Jan 15, 2013, 01:35 AM
608 km/h!
josh18's Avatar
Hey Jim I copied them from the scorcher thread and i think thats why they are so small.
Heres a link to that page but you might find some other info in there too.
Cheers mate

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