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Another DIY foil

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kostantin
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Re: Another DIY foil

Postby kostantin » Sun Jan 07, 2018 6:57 am

Hi,

was a little lazy the last days. At the present I have finished two set of wing mockups and the stabilizer. All parts are glued on thick wood plates and today I will start to make the surface finish of all three mockups The slight ghosting you see on the picture is so little, you can hardly feel it.

Goal is to have all molds laminated by Sunday next week.
Below one half of the stabilizer.


Image

TomW
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Re: Another DIY foil

Postby TomW » Sun Jan 07, 2018 3:20 pm

I get it now. You are making full plug for the mold, to make the mold out of composite. From your previous posts, you will make mold out of composite in order to be more stable and withstand heat curing.

I thought you were going to make the mold directly...
I tried a test to make a mold directly out of pla on Fdm machine. I made a small dish form on a block. Then vbagged some glass directly on to the mold. Used some car wax as release. Didn't even sand the pla mold at all. The mold withstood the pressures and it turned out fine.

Be interesting to see your results
DSC_0001.JPG

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kostantin
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Re: Another DIY foil

Postby kostantin » Sun Jan 07, 2018 4:10 pm

Hi,

I was thinking about an opensource foil in the last days. Means every one is doing what he knows best.

As a starting point STL for wings and stabilizer. We all have to agree to a span, depth, profile. I would manage this part. This would cover this year for sure.
If you have access to a CNC, mill it. Should you have the chance to print, do so. You will get the code, let us know how it turned out.

Fuselage, mast next year. There will be another winter for all of us, hopefully :-)

I am thinking about a construction that every one should be able to handle. Means, no canard, race or wave, but something that hits the nail for most riders.

There is so little fun in these days, lets see if we can have some serious fun here.

Let me know what you think

tks

Kosta

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Re: Another DIY foil

Postby thewindego » Sun Jan 07, 2018 4:46 pm

That is a great idea. I have the 3d printer and good skills for epoxy etc.

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Re: Another DIY foil

Postby opie » Sun Jan 07, 2018 4:59 pm

TomW wrote:
Sun Jan 07, 2018 3:20 pm


I tried a test to make a mold directly out of pla on Fdm machine. I made a small dish form on a block. Then vbagged some glass directly on to the mold. Used some car wax as release. Didn't even sand the pla mold at all. The mold withstood the pressures and it turned out fine.

DSC_0001.JPG
Tom, is that mold solid PLA?

Awesome thread, love the new printer tips from Kosta and the plug-in. Thanks

TomW
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Re: Another DIY foil

Postby TomW » Sun Jan 07, 2018 6:10 pm

The " mold" I made is pla with 15% hex infill and Fast presets. 65c build platform and 225c extrusion temperature. Plenty strong, epoxy had no effect on the pla.

TomW
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Re: Another DIY foil

Postby TomW » Mon Jan 08, 2018 9:57 am

Kosta,

I think the Open HF is a great idea. Carbon and composite tech is very affordable and available online globally, and 3D printing is now in reach of many hobbyists.

I would like 3 wings: "fast recreational cruiser", " allround Freeriding ", and " slow speed/ stable wing ".

I would also like to have STEP file so it could be modified in CAD for different fuselage attachment.

BTW, I tested DevCad wing mold for a few hours. It's not that hard to figure out. It's really fast and gives a lot of control. I did struggle with the wing tip - it didn't look refined enough. Any " tips" ( ha-ha). The visualisations and visual analysis tools are weak though...

On the subject of tip twist. I measured my Moses 550 with a digital angle meter and it has 1.8 degrees twist at tip, measured about 50mm from actual tip, and it starts twisting about halfway out along the span. It is twisted "down" at LE, reducing AoA and potentially reducing stall at tips. My reading says it is to induce " wing root stall" closer to fuselage first. I'm assuming this is to improve stability in stall moment. what do you know about this?

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Re: Another DIY foil

Postby thewindego » Mon Jan 08, 2018 4:42 pm

Hi TomW

Thats interesting about how the tip aoa is setup on that foil. Can you deduce what the profile is? Seems eppler 817 type foils are optimized for hydrofoiling but that is only what I read...no hands on experience. The devcad wing really is a nice tool and would make life easy. I may bite the bullet and purchase.

Cheers

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kostantin
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Re: Another DIY foil

Postby kostantin » Mon Jan 08, 2018 4:52 pm

Greetings,

bad news first devcad exports only as STL. I tried every thing to import it into every thing on the software market. No way, to many triangles. My english is not good enough to explain this problem. For all other guys reading this thread a quick and dirty explantion. Your construct a 3d ball in a software. To get a printer printing this ball you have to convert it into a stl file. The software puts a mesh of thound's triangles around this ball. The more triangles the higher the printing resolution, the bigger the file. This works only in one direction without problems. *step->stl, but not the other way around.

Tom, if you like to add holes or plates for mounting, you need to upload the file into tinkercad. Have fun over there ;-) It took me days to understand this. It looks more like something made for kids then a serious platform. But everything can be done and it is very percise. After you have downloaded the file you nee netfabb to inspect and repair it. In 50% you have mesh errors.

This -1.8° twist sounds a lot to me. Mine have less then -1° I guess, when the tip comes off the water, you gonna fall anyway, because the the air will be sucked down all the way. All those high tech profiles are laminar profiles. When you fly with a glider in the rain you will find rain drops on the wing. No matter how fast you fly, the drops remain. Those drops disturb the performance highly. The drops are in the laminar area. You will get rid of them only if you manage the glider back into the sun, not with flying faster. From knowing to guessing, if you have such an amount of twist you carry a totall of 100mm wingarea that does not do anything then producing drag and doubtless no lift.

Quick and dirty again for those guys and galls not to much into arerodynamics. Take you car for a ride, open the window. Drive 50km/hour put your hand out horizontaly. When you turn your hand negative you feel a force bending your hand to the road. AoA positive your hand tends to the sky. The faster you go, the bigger the forces. I would say, as little twist as possible gets the max performance out of a wing. There is also a static problem. High performance profiles are thin, around 7-8% thick. If you have a lot of twist, the water tries to put torque forces on the tip. The faster you go the bigger the the torque.

tks

Kosta

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Re: Another DIY foil

Postby BWD » Mon Jan 08, 2018 5:36 pm

About the washout/reduced AOA at tips: Since the foil is almost always ridden heeled a bit to windward, you really don't want your lift distribution to be unbalanced when the inevitable tip stall/breach/ventilation happens. It could possibly cause a capsize/hinge motion crash, the kind that send the wingtip at you.
The washout angle helps the tip not stall first, and helps make a lift distribution that lessens the pressure towards the tips so fluctuations out there don't hit you as hard.
With this design feature I think it's easier than it would be otherwise to ride with a bit of wing tip out of the water when heeled.
Done right washout could help with L/D also, again related to lift distribution, tip vortices etc.
I'm no engineer but that is what I have read in the past, seems plausible.


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