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Wings only project

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mcfly777
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Wings only project

Postby mcfly777 » Thu Nov 03, 2016 3:13 am

Hello
I am a beginner foiler, bought a used Liquid Force Foil Fish and now I have the itch. I have seen many high-end foils at the beach, and rode one one day, and loved the speed of it. But instead of building everything, I thought I'd build initially the wing and stab for my existing mast/fuselage and see how it goes.

As background, I am not an engineer. I live in the SF Bay Area and ride in between 12-20 knots usually. Been kiting for ~4 years.

I bought a software for foil design, and came up with the following wing:
- front wing area ~ 660 cm2 (root chord 12.5cm, tip chord 7 cm, span 66.5 cm)
- stab area ~ 180 cm2 @ -3 degrees
- foil profile Eppler 817
- Anhedral 5 degrees for front wing
- small vertical front wing tips

Assuming salt water at 60F as the flow field, I get a total lift of 411 lbs at 5 m/s (sorry the mixture of metric and English units, but this is what the software gives me). The system is stable at a trim angle of 3.08. Lift coefficient 0.388, drag coeff 0.0167, lift/drag ratio 23.16

So assuming (that's a huge assumption) that this system works, it's time to build it. My plan here is the following
- Design using a CAD program. I use Fusion 360.
- 3D print the wing in sections (slightly scaled down to compensate for next step). I designed "rods" to connect the parts just to make it stable when applying carbon.
- Lay carbon fiber (maybe with Kevlar) over it using vacuum bagging technique
- Ride

I have so many questions I don't even know where to start, but here it goes
1) Does the design seem rideable? Obviously I will need to adjust the read stab angle, but does anything here raise red flags?
2) Do I need this much front wing area? I'd rather have it smaller (shorter chord). In the simulation, at 10 m/s (~20 knots) it generates 1650 lbs of lift.
2) Does the building part make sense? I have a reasonably equipped workshop, but I opted to use 3D printing to make this faster and less expensive.

See below for the design. I am now printing the first full size wing to see how it looks, and ordered all the vacuum bagging parts/supplies.

Thanks so much for your contributions, I am learning a lot by just reading your posts.

Leo
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downunder
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Re: Wings only project

Postby downunder » Thu Nov 03, 2016 3:55 am

Man,

this is awesome :)

I have a question for all 3D wing printers out there: you guys realise that epoxy does not stick to the printed parts? :( The way to treat ABS before glassing is a naked flame, and that applied to so thin wing is a...

Hence, if not flame treated the mechanical bond might delam in no time. Yep, sanding helps a bit, but still a mechanical with different shear strength props. Ie, twist the wing and bond breaks, you could hear it cracking and delaminating. Hate to say, only my opinion.

Thoughts?

mcfly777
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Re: Wings only project

Postby mcfly777 » Thu Nov 03, 2016 4:15 am

thanks Downunder. Yes I was thinking about the potential bonding issues between epoxy and the plastic. I have options. My intent is to not use ABS but to use either PLA or PETG.
Leo

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Re: Wings only project

Postby downunder » Thu Nov 03, 2016 4:29 am

Np
Test the bonding heaps. PE plastic does not stick to epoxy at all. No flaming on PE and might even distort when epoxy curing.

D.

mcfly777
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Re: Wings only project

Postby mcfly777 » Thu Nov 03, 2016 4:46 am

Ok.
PLA is actually a polyester. So that's out.
PET also out for the same reason
ABS you have to work on the surface and will get a "good" bond but not outstanding (plus it's a pain to print)

I'll look for additional materials.

For reference see the chart below I found
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plummet
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Re: Wings only project

Postby plummet » Thu Nov 03, 2016 6:15 am

Cool looks like you have it sorted. my research suggests you may want around a 600cm2 surface area. Rear stab 60% the dimensions of front wing.
Vac bag a couple of layers of carbon over top of your 3d printed wing shapes and it will be sweet.

If you have 3d printing capability why not print and try several designs?

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Re: Wings only project

Postby tkettlepoint » Thu Nov 03, 2016 11:58 am

unless you use polyester resin. there might be a bonding problem also on PLA. I know I have fixed a lot of surf boards and tried epoxy over the polyester board is it just a pain in the butt

just my 2 cents.

terrie


but hell if it works let me know maybe I can print wings too.

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Re: Wings only project

Postby Bigdog » Thu Nov 03, 2016 2:11 pm

If you printed little holes in the wing to act as keys for the epoxy it would hold I think.

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Re: Wings only project

Postby Blackrat » Thu Nov 03, 2016 4:24 pm

if your carbon layup is sufficient then it doesnt matter if it delams , all my wings are hollow with an 'I' beam shearweb to join the skins

mcfly777
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Re: Wings only project

Postby mcfly777 » Thu Nov 03, 2016 5:44 pm

Update. Printed the "root" section of the wing and one midsection. They fit together nicely, and to my surprise are quite strong even at 20% infill (I plan to print at 80% for the final wing). I have to work on my settings some more...but I'm leaning toward using ABS as there is some bond between ABS and epoxy, and it's definitely easier to sand. I also looked into the flaming technique, I can do that as well.
plummet wrote:Cool looks like you have it sorted. my research suggests you may want around a 600cm2 surface area. Rear stab 60% the dimensions of front wing.
I wish I had it sorted :) I'll make the rear wing first since it's smaller and I can use fewer materials until I get it right. Right now the front wing is 650, and the stab is 180. Right now the longitudinal stability report says it's stable, see below. I read somewhere that the area of the stab was 1/3 of the front wing. I wish I could understand this software a bit better.
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Vac bag a couple of layers of carbon over top of your 3d printed wing shapes and it will be sweet.
Are only 2 layers enough? I was planning for 3 at least. Any opinions on using Kevlar (or even S-glass?)
If you have 3d printing capability why not print and try several designs?
Indeed that's the plan. Problem is that unfortunately, the printer is too small to print the entire front wing at once. In fact, I have to print it in 5 sections. Each section takes about 6h to print. But you're right, it's cheap to print.
tkettlepoint wrote:unless you use polyester resin. there might be a bonding problem also on PLA. I know I have fixed a lot of surfboards and tried epoxy over the polyester board is it just a pain in the butt
Thanks. I'll do some research on PE resins.
Bigdog wrote:If you printed little holes in the wing to act as keys for the epoxy it would hold I think.
I can definitely do that, not hard to implement into the design.
Blackrat wrote:if your carbon layup is sufficient then it doesnt matter if it delams , all my wings are hollow with an 'I' beam shearweb to join the skins
Thanks. Do you have any images for me to see how this looks? Might be one option also.

Also, does anyone know the approximate pull of a 9m kite (in hp or kW) when cruising at 15 knots? The are estimates of the power requirement at speed. Of course this ignores the wind drag above the water, which can be very substantial.

Leo


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