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Unexpected telltale results

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JS
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Unexpected telltale results

Postby JS » Fri Aug 23, 2013 6:06 am

I've put telltales on some of my kites... on the top surface, just forward of the trailing edge, to detect early stages of aerodynamic stall.

I'm surprised to discover how often they abruptly flutter erratically, indicating that airflow has become detached from the top kite surface well before reaching the trailing edge, even when the kite otherwise appears and feels to be performing normally. Under such circumstances the kite is not stalling completely, but it's losing effectiveness. It can happen during the upstroke of a "sine", or immediately following a turn, and during other circumstances too.

Since this discovery I'm more attuned to my kite control, now more aware of invisible aerodynamics. Also, I'm surprised telltales aren't utilized by more kiters; most competitive sailors find them indispensable.

Cheers,
James

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Re: Unexpected telltale results

Postby Toby » Fri Aug 23, 2013 6:12 am

Do you have a picture of it?

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Re: Unexpected telltale results

Postby El Rudo » Fri Aug 23, 2013 7:48 am

Great to see JS, more kiters should be interested in how their kites really work. You might also have noticed that the air hardly ever flows parallel to the chord, most of the time it's slanted. Think of how a central strut can impair the flow on the luff side!
The flow detachment you mention is exactly the reason why Ocean Rodeo (and some foil kites) kites have venturi slots across the best part of the TE. It allows you to power up more, with quite a few benefits over non vented kites.

At 220lbs I think I need it!

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Re: Unexpected telltale results

Postby Tiago1973 » Fri Aug 23, 2013 8:35 am

JS wrote: Also, I'm surprised telltales aren't utilized by more kiters; most competitive sailors find them indispensable.


but how could you saw those little things 20 meters away from bellow?

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Re: Unexpected telltale results

Postby Kite2Heaven » Fri Aug 23, 2013 11:19 am

JS - you were fooled by associating the WORD aerodynamic ;)

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Re: Unexpected telltale results

Postby eree » Fri Aug 23, 2013 8:47 pm

El Rudo wrote:Great to see JS, more kiters should be interested in how their kites really work. You might also have noticed that the air hardly ever flows parallel to the chord, most of the time it's slanted. Think of how a central strut can impair the flow on the luff side!
The flow detachment you mention is exactly the reason why Ocean Rodeo (and some foil kites) kites have venturi slots across the best part of the TE. It allows you to power up more, with quite a few benefits over non vented kites.
At 220lbs I think I need it!

oh, so that is why so many world cup races are won by the kiters riding ocean rodeo kites! :bravo:

impressive...

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Re: Unexpected telltale results

Postby Bille » Fri Aug 23, 2013 9:52 pm

eree wrote:...
oh, so that is why so many world cup races are won by the kiters riding ocean rodeo kites! :bravo:

impressive...


I "Thought" you were a Core Guy ; so , why Ya pushing rodeo now ? :o
THAT'S A JOKE !! :D

Bille

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Re: Unexpected telltale results

Postby MikeYQM » Fri Aug 23, 2013 10:35 pm

Telltales near the trailing egde would be deceptive. A kite, similar to an airplane wing has a point where the smooth laminar flow of air seperates and becomes turbulent. The Separation Point always exists and as a stall condition nears, that point moves forward. Only when you teach the critical angle of attack (by reducing airflow or increasing angle of attack/sheeting in too far) does the separation point move forward enough to create a full stall. Its very possible to fly near stall, where there is some turbulent air over the kite but still enough laminar flow to create lift, which is likely what you are seeing. Each kites airfoil is different. I would gradualy move the telltales forward by testing when they flutter according to a full stall. Only then will you get an indication of the critical angle of attack.

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Re: Unexpected telltale results

Postby tautologies » Fri Aug 23, 2013 10:42 pm

eree wrote:oh, so that is why so many world cup races are won by the kiters riding ocean rodeo kites! :bravo:

impressive...


jesus dude whats up with the constant sarcasm?

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Re: Unexpected telltale results

Postby tautologies » Fri Aug 23, 2013 10:47 pm

El Rudo wrote:Great to see JS, more kiters should be interested in how their kites really work. You might also have noticed that the air hardly ever flows parallel to the chord, most of the time it's slanted. Think of how a central strut can impair the flow on the luff side!


I agree interesting topic JS.

Do you think the flow would be more parallel if the canopy section where flatter?

The flow detachment you mention is exactly the reason why Ocean Rodeo (and some foil kites) kites have venturi slots across the best part of the TE. It allows you to power up more, with quite a few benefits over non vented kites.


I've always wondered about the slots..do they actually work? Intuitively it makes little sense to me, but intuition and science is not the same :-)


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