Making a kite for a school project

Kitesurfing/Kiteboarding on Liquid H2O

Making a kite for a school project

Postby Snake » December 21st, 2012, 4:02 am

For science fair I was thinking about making a kite. The experiment would be on how the shape of the profile affects the lift to drag ratio and the amount of lift. This means that the kite must auto-zeinth so it can fly on one line to get accurate readings of the lift it creates. Also the kite will need to have its profile easily adjusted. An arc seems to be the best choice.

One small problem though. What airfoil profile should the control be? Two different control profiles could change the results dramaticly. After some thought, I found a soulution. The kite will have no profile. The top and bottom skins will both be flat.

I know what your thinking, an arc with no profile can't possibly work. Well I turns out it does. The yagu on http://2e5.com/ has no profile and it flies well. Thats why I have chosen it to be the kite for this experament. The bottom skin profile can easily be altered with a few floating straps and the bumps can be sewn to create a more airfoil like shape.

I already have the fabric picked out. Black for the bottom and yellow on top. All I have left to do is ask my teacher if this experiment would be acceptable for the science fair.
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Re: Making a kite for a school project

Postby Kamikuza » December 22nd, 2012, 1:19 am

When's the science fair? You're going to have a lot of sewing to do :o

The thing is, kites use a reflex curve in the profile (like a spoiler on the back of a Japanese import :D) to stop it over-flying, I think. Even LEIs have it...

I don't think your experiment as it is, would yield any useful or interesting to anyone other than us results - especially compared to the work involved :o I'm not trying to be a downer on your enthusiasm, I just don't think it's the best way to go about it.

With a wind tunnel, you'd be able to control wind-speed better and eliminate a bunch of variables, and get more accurate lift measurements.
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Re: Making a kite for a school project

Postby Snake » December 22nd, 2012, 2:36 am

Kami, this experiment is not about testing airfoil profiles to see which has the best L/D. It is about how those profiles affect the kite. A real world use for this would be in useing kites to generate electricity. A reflex profile makes the kite more stable and have less drag than a cambered profile. I'm not sure if LEIs have a reflex profile being they don't have a botom skin. If the kite overflys I will simply put in the results that a cambered profile flew poorly. Thats the point of the experiment. The yagu is basicaly a single skin kite with bumps to make it more rigid. The kite could be inverted to test the top skin shape too.
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Re: Making a kite for a school project

Postby Kamikuza » December 22nd, 2012, 3:38 am

If your experiment is only about how they affect the kite, you need to be able to measure it - just saying "it flew poorly" doesn't explain or account for anything, other than your opinion. You've got to be able to relate the changes you make to some measurable differences and show the relationships. Why did it fly poorly - inherent to the design or some external factor like gusty wind? etc

If you're going to generate electricity, you want to maximize static pull and L/D will come into it heavily. As will reflex profiles :D no good having a kite that pulls like a freight train if it's just going to overfly and luff... I think reflex curves, depending on the AoA, actually have more curve than a 'proper' profile - after all, we're after different results from our airfoil. Drag isn't always a bad thing...

That is of course, assuming that you science fair teacher is as hard-ass as mine were :-/

You can see in the image how it 'flicks' back up to the rear. Just cos it's a single skin doesn't mean you can't mess with the curve ;)

Image
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Re: Making a kite for a school project

Postby Snake » December 22nd, 2012, 4:41 am

I see how the top skin is reflex, but being there is no bottom skin the air passed over the bottom of the kite will move in a relitively straight path. By reflex I thought you ment top and bottom skin both having the upward flick. Also, LEIs have ridged tubes suppoting the fabric. Too much reflexness in a soft kite might cause negitive lift in the rear of the kite and cause the AoA to be too high. And yes, I know I can not simply put "the kite flew poorly". I was in a rush since I needed to help a friend with something. I would put some thing like "the lift increased X%, but increased drag Y%. It also made the kite prone to stalling and over flying".
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Re: Making a kite for a school project

Postby Kamikuza » December 22nd, 2012, 9:14 am

How are you going to measure lift and drag?

The tubes support the fabric, but the way the fabric is sewn together determines the shape of the sail. It's pretty neat :)
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Re: Making a kite for a school project

Postby Snake » December 22nd, 2012, 10:40 pm

The measureing the lift and drag will be easy. First I attach a scale to the line and measure the amount of pull. Then I find the slope of the line which is the L/D ratio. Once I know those numbers I can find how much is lift and how much is drag.
Example:
Pull = 50kg
Lift/Drag = 4/1
50kg/5 = 10kg
Lift = 40kg
Drag = 10kg
Lift/Drag = 40kg/10kg

With those numbers I can create percentages to show the differances in the lift and drag
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Re: Making a kite for a school project

Postby aatamian » December 25th, 2012, 11:27 am

What about something like a Peter Lynn Pilot?
http://www.peterlynnkites.com/?attachment_id=1896
http://www.peterlynnkites.co.nz/kites/b ... rafoil.htm

-Easy to adjust the AoA
-Much less sewing and fabric
-Obviously autopilot
-Much simpler shape, in order to understand better which parameter affects its flight
-You can then use it for other experiments, KAP, etc.

Dunno about the patent issue though... But an "open source" sled might do the job.
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