The more off-hand comments I read, the less I'm convinced I understand what de-power actually is ...
I always thought that a kite was considered de-powered if it was parallel to the air flow, such as at zenith with the bar out - thinking of a sail
sheeted out, flapping in the breeze.
Then, due to the differences in design (eg. foil vs LEI) I could understand how X kite could be considered to have "more" de-power the Y kite in such
a situation, say foils creating power in the wind flow due to the 3D shape or whatnot ...
... but then I read guys talk about total de-power on the bar - always thought total de-powered was a kite flagged to safety and falling out of the
sky :puzzled: or massive de-power range, which I guessed is just the ability of the kite to get parallel to the wind like above at any position in the
sky :puzzled:
I been thinking about this a lot since I got the PowerBlast :wee: Nick-san the instructor from Shizuoka says I over-analyze things :Dkteguru - 2-2-2010 at 12:03 AM
In my mind, depower is as you say it.....like a sail, when everything is sheeted out and the bar pushed away the kite flaps at zenith. The power comes
on when you pull the bar in and/or adjust the trip strap. Hence - depowerable kite vs a fixed bridle. You can depower it with the trim strap or the
bar, on the fly.
I think the fact that a foils' shape (an airfoil....hence the name I do believe....'cuz we all know they're not made out of tinfoil, right?) creates a
high and low pressure like a plane wing is just good design. Truth be told, even an LEI will create high pressure overtop and low pressure underneath
because of the big tub up front. Can't remember what that's called but I have flown RC planes with similar wing design.
Just my 2¢ (1.707 yen)rocfighter - 2-2-2010 at 04:53 AM
Kteguru, it almost makes me feel sorry for the ass!!! :DDrewculous - 2-2-2010 at 07:27 AM
Kami... chill out and just fly... doesnt matter how it works... so long as you enjoy the magic :tumble: lol
That is such a great video...BeamerBob - 2-2-2010 at 07:48 AM
I'm like you Kami. I have to understand WHY it works. You have it right on how depower works. Macboy added some correct stuff except I think he had
it backwards about high and low pressure. The high pressure has to be underneath with the faster airflow over the top and down the backside (creating
a vacuum) which causes the kite or wing to lift. Switch them around and the kite falls out of the sky like if you are at the edge of the window and
the wind direction shifts so that it hits the backside of the kite.
With depower it is as has been said, you can change the Angle of Attack of the kite (and with some kites the shape of the kite itself) with both the
trim strap and by letting the bar out.macboy - 2-2-2010 at 11:13 AM
Right you are Bob. Had it backwards (not spending enough time with the RCs these days ; )art_lessing - 2-2-2010 at 11:54 AM
I believe that a wing with low pressure on the bottom is a spoiler..hence the name...it is on cars as lift killersssWELDNGOD - 2-2-2010 at 04:30 PM
Bernoulli's pricipal. google Bernoulli's principle
Yeah I always gotta think a little to accurately remember how Bernoulli's Principle works too
So at zero AoA the kite is as de-powered as it can be and any pull is related to its effectiveness as an airfoil ... by meddling with trim and pulling
on the bar (or not) you increase the AoA and alter the power of the kite for a given position in the sky ... I think I got it
So how do people make claims of "total de-power" then - or are they talking about releasing to safety and implying you get teh same effect at the bar?
Or does the kite just have a really crappy airfoil design?BeamerBob - 2-2-2010 at 06:27 PM
Total depower is a misnomer. If it isn't generating any power, there isn't enough lift to keep it in the sky. The kite can approach totally
depowered where it has very little pull but just enough to keep flying.Kamikuza - 2-2-2010 at 06:34 PM
So, what constitutes a "huge de-power range" - really short rear lines and a long throw bar?WELDNGOD - 2-2-2010 at 06:45 PM
I was under the assumption that it was adjustable to some degreeBeamerBob - 2-2-2010 at 09:25 PM
Quote:
Originally posted by Kamikuza
So, what constitutes a "huge de-power range" - really short rear lines and a long throw bar?
That might be a good way to put it. "Long throw" would be relative to the kites design though. Whatever dimensions take it from very depowered to
full power for the kite per current conditions.
WG, yes it is adjustable with the trim strap as a rough adjustment and bar pull for fine adjustment. I think I got those right. Contribute to fixed
costs and cover variable or ............. Oh wait thats a different subject.Kamikuza - 2-2-2010 at 09:46 PM
So in other words it's all marketing hype krumly - 3-2-2010 at 10:15 AM
From a physics standpoint, we kiters often use 'power' and 'depower' incorrectly. We often talk about force, or line tension in terms of power when
it's really only a part of the equation.
Power is force x velocity, or work per unit of time, or energy per unit of time. Standing static with the kite pulling hard on you is generating a
force, but not providing any power with respect to you or the kite (you're not moving nor is the kite).
Now, you can use that force to get the kite and yourself moving and generate power (on skis, buggy, being lofted, whatever). The power developed by
the kite is it's total aerodynamic force (pretty much, but not exactly equal to the line tension) x it's velocity across the window (apparent wind).
Power developed at the kiter is line tension x your velocity.
Depower should refer to the 'useful' range between minimum and maximum power that can be developed for a given windspeed. Power can be developed by
flying a slower kite at higher angle of attack - what we normally call 'grunt.' Power can also be developed by flying faster at lower angles of
attack - what is usually associated with a 'lifty' racekite. Maximum power will be developed at the angle of attack where the lift to drag ratio for
the kite is at it's highest.
The low power end is achieved by slowing the kite down and minimizing angle of attack - low line force x low kite speed = low power. Like BB said,
at some point the kite doesn't develop enough force (lift) to offset the weight of kite +lines, and it falls out of the sky. That's what a lot of
manufacturers call 100% depower - sort of a misnomer. This isn't necessarily at zero angle of attack - it's at whatever angle of atttack for a given
windspeed that the kite can't develop lift greater than its weight.
Bows have great depower range. For that matter, so do C-Quads and Revolutions. Arcs too, and that can be extended even further with front briding.
Those are what I have experience with.
krumlyKamikuza - 12-2-2010 at 12:30 AM
That actually makes sense to me
So now then ... trim a la the trim strap. It's sole function is to make sure that when we pull the bar in all the way or ride unhooked ( as if) the kite is not going to back-stall on us?BeamerBob - 12-2-2010 at 08:45 AM
:bigok: :wee:Jack1988 - 14-2-2010 at 11:56 AM
im a noob to depower but i was under the impression that 100percent depower wasnt actually the kite crumpling and falling from the sky, but if you
push the bar forward all the way in a silly wind, it will depower the kite just so its not hauling you all over the place? and you can relax for a
minute?
But depower only actually works if you have enough wind for it?
If you want to land you fly to trhe side and land at theedge of the window? or just pull the safety?acampbell - 14-2-2010 at 12:32 PM
Someone here once said something like the only way to de-power a kite is to put it in the bag and lock it in your car.
Yeah, when the angle of attack is such that it is not developing lift, it is "de-powered", but even hold up a piece of plywood in a silly wind and you
can get yarded.
It's not that you need enough wind for de-power to work right (besides enough to launch in the first place), but the kite needs enough apparent wind,
and this happens when you are in motion on/ in your vehicle of choice. When flying static, if you get it to work by speeding through the window, the
joy is over in a moment when you get to the other edge of the window. When you are in motion with the kite, the kite never gets fully to to the edge
of the window.
In fact flying static with a de-power often causes confusion, especially in light wind, because pulling in on the bar to "power up" just kills the
kite in a back stall. Pushing the bar out gets the kite flying again and lets it built up speed, and with it, power. So everything seems backwards.
Put yourself in motion with the kite however and you will have an "ah ha!" moment.Jack1988 - 14-2-2010 at 01:31 PM
aha :D i will have to experience this when i actually get on my board. I know what ya mean, my first flight earlier in like no wind static, seemed
like pulling the bar was depowering the kite, but now you say that it will be different in motion thats sweet.tridude - 14-2-2010 at 05:29 PM
cruisen down the road stick your hand out the window, parallel to the ground=bar out..................raise the finger tips 45 degrees=bar
in................also check out the flysurfer mixer test thread which shows how the wing reacts to bar
inputs.........................................Kamikuza - 14-2-2010 at 06:15 PM
Was that mixer thread here or at the Foilzone?tridude - 14-2-2010 at 06:33 PM
Interesting ... that all makes sense too BeamerBob - 15-2-2010 at 09:50 AM
Don, I wish I had seen that a year ago, and your talk of mixer tests and minus b and minus c stuff would've made much more sense. It's crystal clear
after watching that.tridude - 16-2-2010 at 07:27 AM
actually I learned the mixer test from talking with Powerzone but yes the videos are awesome if you own a Flysurfer but a bit timid on
trimming.................use a sharpee and mark your start point, the rest is easy. The Pulse 2and Speed 2s with the stopper balls make the mixer test
even easier (instead of loosening a fig 8 knot)..........
back on thread, as mentioned as your trucking along and the kite stalls, trim in just a tad and that should have the kite flying optimum..............
