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Author Topic: Kite Turning Mechanics/Aerodynamics Question  (Read 1113 times)
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JB
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« on: June 29, 2012, 09:29 PM »

So when line tension increases symetrically on both wings, the kite flies with a higher velocity.  But when you asymetrically increase tension on one wing, or decrease tension on the other, the kite will yaw in the direction of the wing with the highest tension.  That means that in a turn, the wing that has the most tension will be traveling the slowest and the wing that has the least tension will be traveling the fastest.  This doesn't make sense, considering that when symetric tension on both wings is higher, both wings travel faster. 

Can someonme please explain to me, why the aerodynamic properties of the kites airfoils reverse as soon as asymetrical tension is applied.

Thanks
« Last Edit: June 29, 2012, 09:34 PM by JB » Logged
mikenchico
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« Reply #1 on: June 29, 2012, 11:31 PM »

It's like a horse, when you pull on the "Kite Faerie" on the right it will slow down causing the kite to turn right because faeries are a bit obstinate and will resist your beckoning.

Seriously though a thread on why a kite flys could go dozens of pages and has, while no consensus has ever been reached.

But during a turn the angles of the wings come into play, changing the angle causes one wingtip to washout and also causes a higher pressure against the keel on one side which instigates the turn. Hopefully somebody can put it in better words, I'll just stick with the "Kite Faerie" thing   Wink

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Steve
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« Reply #2 on: June 29, 2012, 11:51 PM »

Thanks Mike. Saved me from having to post that.


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mikenchico
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« Reply #3 on: June 30, 2012, 12:48 AM »

Thanks Mike. Saved me from having to post that.

Well I did blatantly steal that from you   Wink 

If you didn't know, that IS Steve's explaination of how kites fly, I've only borrowed it.

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Will Sturdy
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« Reply #4 on: June 30, 2012, 04:31 AM »

My theory is that the center of lateral resistance is closer to the tail of the kite. When one side is pulled closer, the kite is at an angle relative to the wind and thus there is some lateral pressure, causing it to turn.

The expected direction of turning does occur when the kite is stalled, which is what tricks like the axel are based off of.

Another theory is that the lift generated by the panels increases as they are brought closer to perpendicular to the wind. That would mean that the left two panels on each half of the sail would create more drive when the right line is pulled and vice-versa. That theory falls apart because of kites like the mirage though. Their sail shape would produce the opposite effect and they turn extremely well the same way other kites do.

It's an interesting question, for sure Undecided
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Tmadz
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« Reply #5 on: June 30, 2012, 06:37 AM »

Where's Chilese when you need him?

You're over thinking it. It's just force (mass x speed) on the sails. The path of least resistance causes the air to pass over that side of the sail and it turns in the direction where more force is applied building up and not released. Don't confuse distance with force. The stronger (turn direction) side moves slower because you're still holding more force in the sail. Let's skip lateral force, surface area, etc and keep it to the basics.

Everyone knows that if you're lines aren't even your kite flies like crap. It's the even application of force on both sides of the sail that causes it to fly in a straight line. When you pump your lines to get the kite to the top of the window, you're increasing force by pulling it towards you, filling the sail with more air than was moving into it at the speed of the wind and that force releasing through the bottom of the sail.

Let's simplify, becasue I don't want this to turn into a kite makers forum on design and measurments and all of that stuff yet (jk guys  Wink)

Balance a pencil on your finger. It has to be in the middle of the pencil where force is applied to both sides equally. If you move the pencil over to one side it will fall off in that direction. That's becasue gravity is exerting force on the mass of the pencil. The heavier side has more force and it pulls that direction.

Kites are the same, but you're adding more factors to the equation. Stunt kites are designed to collect air and flow it through the bottom of the sail becasue the bottom is bigger and force is decreased when the air can spread out over a larger area. On a push turn you're releasing the sail on that side and the kite goes the other direction. When you do a pull turn you're actually loading more force onto that side and it will turn in that direction because the other side has less force or force is released. All tricks are based on application and release of force. That's why they always cry slack, slack, slack. When you pull on one side you don't want any opposing force on the other side so it will turn where you want it.

I gotta stop here because we're just scratching the surface of aeronautical physics. I try not to think about it when I fly. I hope this helps.
« Last Edit: June 30, 2012, 10:39 AM by Tmadz » Logged
JB
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« Reply #6 on: June 30, 2012, 07:05 AM »

I think it helps..  Thank you..


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Tmadz
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« Reply #7 on: June 30, 2012, 07:15 AM »

The only way I can think to have you do a hands on experiment is to fill your kitchen sink with water and use small bowls. Tupperware or disposable preferably. You want something light. Put the bowls on the bottom of the sink and pull them up to the top. Now experiment by tilting or angling the bowls and pulling them up. You'll feel the difference in the force applied and where the bowl will want to move.

I used to love watching Mr Wizard.
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chilese
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« Reply #8 on: June 30, 2012, 12:05 PM »

I hate thinking on a Saturday.

When a sport kite is flying in a straight line, all the forward forces come

off the trailing edges (think shaken up bottle of soda).

When a kite is turned, some of the exhaust (forward) forces flow over

the spine onto the far side where they in turn spill off both the far

leading edge and far trailing edge.

As an example, let's assume 10% exhaust forces flow sideways during a turn.

Near side forward forces = 100-10 = 90%

Far side forward forces = 100-10 + .9*(10) = 99%

Near side side losses = 10%

Far side side losses = 11%

Total forward forces before turn = 100 + 100 = 200

Total forces during turn = 90 + 99 + 11 = 200

So the far side should go "forward" faster causing the turn AND,

the far side side losses should actually cause the kite to slide a bit

perpendicular to the turn. Note that the near side side losses do NOT

contribute to the sideways motion of the kite as they are recovered

by the far side sail and redistributed. So only 1% of the near side side

losses contributes to the sideways motion while all of the far side side

losses directly effect the sideways motion.

Wow, I wonder if that's true.

Remember, I was just guessing on the 10% part, but the math should

still be the same with a different number.  Smiley

Sorry for using the word side so many times.

I still prefer Steve's Kite Faerie explanation.  Smiley
« Last Edit: June 30, 2012, 12:39 PM by chilese » Logged

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JB
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« Reply #9 on: June 30, 2012, 12:52 PM »

Chilese,

Thanks for that post.  Will definately sit down and try to absorb that info.

Sorry to ask you to think on a Saturday.   Wink

Have a goodun
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chilese
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« Reply #10 on: June 30, 2012, 06:22 PM »

I should point out that those numbers are percentages of the force coming

off the back of the wing.

The actual numbers (thrust) would be lower than the initial as there is a

side component rolling off the far side leading edge. If we assume the same

start as before, then 5.5% of the initial thrust is lost to sideways motion and

the remaining 94.5% is distributed by a ratio of the numbers previously given.
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Stardragon
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« Reply #11 on: June 30, 2012, 09:22 PM »

I used to as a kid and still as an adult just stick my hand out of the window when driving and angle it.  Varying the angle varies how fast it rises and sinks as well as which direction it wants to go.

Ron
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