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Old Jul 22, 2012, 10:33 PM
Team Hong Kong F3K
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Sam,

I cannot remember the weight off the top of my head, but it is not a loose weave cloth. It is the same 3K as in this photo:


The mentioned test was done between skins with no foam in between, to see how the skin itself reacts to delamination. We have also done some testing on different foams, there's a foam I mentioned earlier that has all the grains along the Z-axis, and we have made some tails with it for testing so far. Weight drop for a Horizontal tail along is 1g+ by switching to this foam, and is overall stiffer, and very resistant to hanger rash. The downside is, after hot-wire cutting creates a layer of skin over this foam which is very hard to bond to, and early test tails done suffered in delamination issues. We fixed this in later test tails by sanding off the new skin before bagging, and bond strength improved immensely, but is too labour intensive and very easy to damage during that process. We are now waiting for august to test this foam by CNC-milling methods to see whether it will be a realistic option in the future.

Yes, Rohacell is sure nice, and I've been debating whether to use that or stick to XPS in our (future) solid mould projects. Steaming, repairability, and cost is really urging me to stick to XPS though...

Thomas
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Old Jul 22, 2012, 11:00 PM
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I thought the same thing Sam did about the 3k cloth. The stuff we use at work is 3k and it comes out to 5.7oz/yd^2! On top of that it takes more resin than you'd expect to saturate, making it even heavier.

Don't forget that the core is slightly compressed in solid core molding. That means that if you steam out a dent in an XPS wing, it's going to return to its original size and shape, not the size it was after being compressed in the mold.
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Old Jul 23, 2012, 08:02 AM
Team Hong Kong F3K
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Absolutely right, it is for sure overbuilt. We tried some other doublers, but found that it required an extra layer of 80gram STF on both the top and bottom of the blade-side wingtip to let it resist any creasing. We figured it will be safer and simpler to err on the side of reliability, and installed 3K tip reinforcements. An extra piece of STF on the tip after blade installation is no longer necessary, and I am very happy with the current wing weight.

Good point on the solid core moulding, IIRC guys are milling their cores 0.4mm 'thicker' than design, so may be noticeable if steamed. We will have to do further testing later on to determine what substrate to use. Rohacell is sure cool and blingy though!!

Please keep the suggestions coming guys! Everything helps
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Last edited by ThomasLee; Jul 23, 2012 at 08:11 AM.
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Old Jul 23, 2012, 08:24 AM
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So with the Vlad carbon do you have any kind of tip doubler?

I'm hoping to get into solid core molding next year for my own models. I will likely use Hi-load 40 or 60 just for the cost reduction. Rohacell is dang expensive.
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Old Jul 23, 2012, 08:33 AM
Team Hong Kong F3K
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Yeap, they do. In fact, all our wings will have the 3K tip doubler until the next 'improvement'.
All roots have glass doublers that reach past the servo linkage 'tunnel's' as well.

Man that's for sure, a set of XPS cores is really just a couple bucks in raw material, I'd say Rohacell is at least 10X that going from memory.
Are you milling the Hi-Load?
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Old Jul 23, 2012, 08:40 AM
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I too am considering the 3K cloth for reasons you mention Thomas, as I'm having some creasing on the wing tips with thinner cloth. I noticed however that the primary reason for this creasing is poor launching-it wasn't a problem until I was flying off a crappy field and doing funky things to the wing tip in the process.

For some weight references, using a 1K carbon (2.4oz) in a tail mount results in a 0.8g part after trimming. The same part made with the 3K carbon results in a 1.3g part after trimming. If you have some 1K cloth, there is a noticeable difference between that and the spread tows as the 1K is thicker, so more resistant to compressive forces. Some models get by with regular kevlar doublers as well but recommend patches when installing tip blades.
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Old Jul 23, 2012, 08:47 AM
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Tom, I have another method in mind that I'm 99% sure will work, though I'd like to test first. It doesn't require the need for a CNC, but may be more work per wing. To my knowledge, nobody is currently making molded wings this way.
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Old Jul 23, 2012, 09:21 AM
G_T
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Thomas,

You might try using unicarbon oriented parallel to the spar, in a similar cut pattern to the existing tip doubler in post 466. It will be lighter and the stiffness is in the specific required direction. Do not use HM carbon for the job. You want a moderately low modulus uni for this application as you want toughness rather than stiffness. The bias Kevlar you are already using ties it all together and transfers load progressively to the spars.

Gerald
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Old Jul 23, 2012, 09:41 AM
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On my last wing I used uni at about a 30 degree angle to the spar and it feels very solid. The wing hasn't been flown much, though, so durability really hasn't been tested.
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Old Jul 23, 2012, 10:29 AM
Team Hong Kong F3K
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NOOOOO stupid stupid ^^%YWE%$as&

I realize..... I'm just sold out of the TS-D6011 servos yesterday and don't have anything to put in the wings right now!! Oh boy.....guess I need to wait for the next batch...
Not my brightest day!
And I was hoping to get to fly it this weekend...guess not!
Time for bed &^$@
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Old Jul 24, 2012, 06:28 AM
Team Hong Kong F3K
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OK, So I decided to do a 3-in-pod installation in light of having my usual wing mounted TS-D6011 running out. I will be using the awesome JR DS385's in the pod.

Power's out... continue working in sunlight....
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Old Jul 24, 2012, 10:28 AM
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Quote:
Originally Posted by ThomasLee View Post
OK, So I decided to do a 3-in-pod installation in light of having my usual wing mounted TS-D6011 running out. I will be using the awesome JR DS385's in the pod.

Power's out... continue working in sunlight....
go ahead boy, 3-in-pod is great! I like it very much!
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Old Jul 24, 2012, 11:27 AM
Team Hong Kong F3K
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I haven't tried 1K yet, but have a roll so that may be possible to try. What weight uni would you recommend Gerald? Don't have any uni yet, though I could easily order some in my next order to r-g.

Brandon, that sounds interesting, hope to see something of it soon! Is it complicated?

Robust, it should help lower the AUW a bit too!

Waiting for vertical to cure, and also made the bolt hardpoints in the horizontal.Wing is essentially done, just need to install the 2 horns and blade. After that, all I need to do is the vertical/boom reinforcing cloth,drill the hole in the fuselage for the linkages, install servos, and run linkages to finish.
Honestly a very fast build, especially with the 3-in-the-pod. Was hoping to spend much more time on it, but with power being on/off, the typhoon, and work, I wasn't able to spend as much time as I hoped on it today and yesterday. It will still be ready to fly at this weekend's event though, probably one of my lightest builds (i hope!!!!)
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Old Jul 24, 2012, 11:48 AM
G_T
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Something around 100gsm most likely. I forget exactly what uni we used on our Edge and Zone bagged wings. HM is likely not the best choice as it is more brittle. I'd go with IM or lower modulus.

Gerald
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Old Jul 24, 2012, 11:49 AM
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I just can't get over how good that looks! I'm amazed at the finish quality! After I've got a couple wings built for myself I think I'm going to save up for some of that carbon. It looks SOOOO SEXY! I just wish my wings turned out as good as yours!

As for the uni tip doubler, it's pretty simple. I'm planning to slip into my work today (even though it's a holiday here) and while I'm there I'll try to remember to take a pic of that wing tip. Even though it's super thin (zone foil on high AR planform) it feels very solid. Part of that is also because I put a very generous fillet of chopped carbon around the peg.

Brandon
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