Power Kite Forum

De-Power Help

Qside - 12-9-2010 at 05:18 PM

So my first de-power arrived this weekend and, of course, the winds sucked. I really wanted to try this bad boy out so I went over to the local fields and set it all up via the instruction book. Just a side note, HQ make great kites but their instructions are sometimes unclear. Anyway, I finally got it in the air and there are a couple things that confused me. Now I didn't get to fly very long because the winds were only 3-5mph with the gusts in the 7-8 range. Now my FB kites I pull the power lines nice and hard to launch, but the instructions had me pulling on the brake lines to launch? I grabbed the Y line just below the red top hat and gave her a few tugs and up she went, but alas when I let go to grab the bar down she went... Second try and held on to the line until she was all the way up in the air and she flew just fine, until I lost wind. Then flipping through the instructions it says to land the kite I'm to grab and steer it down with the black strap which is attached to the red/blue power lines? Ether the lines are reversed on de-powers or they fly completely different then FB, see how I'm confused? Last question, flying in low winds do I want the bar close to me or pushed farther away?

If anyone could enlighten me, It would be appreciated.

Qside - 12-9-2010 at 05:27 PM

I guess I should have read...looked at the picture closer before posting. The outside "power lines" would be the equivalent of the brake lines on a FB. So I'm steering with the brakes? I'm still a little...a lot, confused on how the de-power works.

B-Roc - 12-9-2010 at 06:33 PM

Depowers are set up different from fixed bridles as you discovered. You steer with the rear / brake lines as you also discovered. The bar is where the bar is no matter the winds. Ideally you want the bar around the middle of the depower line always so you can push it out in gusts and pull it in for power but in low winds you don't want the bar constantly pulled in as you will stall the kite.

Play with the trimmer. Even in low winds you may find the kite flies a bit better slightly trimmed... or maybe not - depends on how HQ has it set for a default trim. My pulse flies better slightly trimmed in low winds whereas the eskimo prefers all the trim out in low winds.

Kamikuza - 12-9-2010 at 07:00 PM

Power lines are the front lines that go through the center of the bar and onto your harness via the chicken loop.
Steering on the outside or back lines that look like brake lines :)
Bar moves in and out to trim the kite "on the fly" - Angle of Attack to the wind and "indirectly" controls the power ... 'depower' is a bit of a misnomer IMHO :D
Trim strap provides a more permanent trim position.

Kites are a little easier to understand if you're a plane geek :D

Power developed by a kite is actually lift developed by the kite.
Angle of Attack = 0 ... imagine your hand out the car window, parallel to the ground ... the kite is in a neutral position, wind flows over the kite with the least amount of drag and the least amount of power is developed. Any lift (power) is due only to wind speed and how much like an airfoil the kite is ... kite should remain at the zenith, given sufficient wind.

Angle of Attack is increased by pulling the bar towards you ... imagine you hand out the car window at 45' to the ground ... you feel more power because the kite generating more lift - but also more drag. If you hold the bar in, the wind speed over the kite will (relatively) drop and the kite will stall.

Because of this, we usually trim the kite in with the strap when flying in light winds - it's more difficult to increase the AoA and induce a stall; the kite flies easier in less wind. Like B said, it can be kite dependent ...
To avoid stalls, fly in more wind. Either go out when the wind speed is higher, or move the kite around the sky which increases relative wind speed over the kite.

Usually, you want to be using the bar to gradually alter the AoA until you balance the power (lift) and drag. Which is why the bar should be considered "trim on the fly" not depower :D

Txshooter38 - 12-9-2010 at 07:47 PM

Kamikuza, nicely explained. I did not realize it until you explained it but this must be why I have been getting frustrated with my synergy. I kept adjusting the strap for max power and the winds have been low. I could not understand why the kite kept stalling. This clears that up.

Qside - 12-9-2010 at 09:58 PM

Very good explanation Kamikuza, I think I understand. I don't know where my trim strap was set today but let's say it was set for "max de-power" and my kite was stalling when I kept the bar pull toward me for too long, which it seemed to be doing but I was blaming the wind cause that's what noobs do. Wouldn't adjusting the trim for "more power" stall the kite even with the bar in the neutral position? Also, does de-powering for too long cause stalls?

The way I'm picturing this in my head is the kite as an airplane, when you pull the bar in the airplane climes and when you push the bar out the airplane dives. Or at least the kite angle changes the same way the wing angle would change in that scenario, is that accurate?

Turning is done the same as fixed bridles right? Pulling the right or left side of the bar? Should I be keeping the bar parallel to the ground?

I guess getting out there and playing with it is the best way to learn, but this kite is a lot more intimidating then my FBs and now that I'm attached to it I'd just like to have as much advise as possible. Thanks for all the help!

*EDIT*

Quote:

"Angle of Attack is increased by pulling the bar towards you ... imagine you hand out the car window at 45' to the ground ... you feel more power because the kite generating more lift - but also more drag. If you hold the bar in, the wind speed over the kite will (relatively) drop and the kite will stall. Because of this, we usually trim the kite in with the strap when flying in light winds - it's more difficult to increase the AoA and induce a stall; the kite flies easier in less wind. Like B said, it can be kite dependent ..."


Re-reading this this makes complete sense. Going into this I knew pulling the bar = more power but flying today in low winds it was stalling the kite, which I didn't realize. However, de-powering seemed to give the kite more power thus partly why I was confused. I knew from flying my FB in low wind the only thing keeping them in the air sometimes was relative wind, so when you said pulling the bar increases power but decreases relative wind it clicked. Low wind + reduced relative wind = making my wife drag the kite back across the field all day because I can't keep it in the air! Thanks!

Qside - 12-9-2010 at 10:25 PM

I'm not sure why this thread got moved to Kites and Acces. from Techniques. Reading the descriptions of the categories I though that was the perfect place...

John Holgate - 13-9-2010 at 04:46 AM

Occasionally I static fly my depower kites (I'm usually in the buggy) but I will pull the bar right in when I'm turning the kite (it will speed up the turn a lot) and then let the bar out which helps the kite speed up back through the window and also lessens the pull. If I feel the kite is about to stall, I'll turn it down - which picks up speed and stops the stall - and back across the window. This will leave your lines crossed - no problems, either down turn the kite at the other end of the window or spin the bar around in a full circle to untwist your lines. There's a video of me flying the Access XT 4m this way in the 'kite reviews' section. My Apex 2's have three knots where the power lines join the leaders on the bar end - if you find it's real sluggish to launch and keeps stalling, move the lines to a knot closer to the bar or you could pull in a bit of trim.

gemini6kl - 13-9-2010 at 05:59 AM

The depower concept is very simple pull the bar in the kite powers up let it out the kite looses power, depower kites use all four lines to control the kite the center lines are the power lines and the two outer line are like brakes line on a FB kite but do a different job because if u look closely they are attached to more than just the trailing edge of the kite, they are also attached to the center of the kite. in low winds ALL depower kites like to have the back lines fairly loose for the kite to fly. Trimming the kite via the trim strap just allows you to adjust how much power or depower u get when u actually pull in the bar. Thats it its a simple concept. again in light winds use the trim strap to give the kite alot of depower so that when u pull in the bar u can steer it but it dosent fall to the ground. As the wind picks up u can now let out the trim strap and enjoy more power form pulling in the bar .

Bladerunner - 13-9-2010 at 06:46 AM

I am confused ?

Your bar throw gives you the SAME amount of depower no matter where your trim stap is. The catch is how your trim strap is set. If your strap is open and you pull in the bar your kite will depower . You can further depower it with the trim strap. Trim the kite so it will stall but not fall back when the bar is trimmed in.

I prefer to not use the term " depower " and say front lines , back lines because as Kami describes things change when the kite is moving from too low of winds into it's proper wind range. It also changes when you are in motion.

I prefer to think Speed ='s power !

Fly on your front lines to fly fast and far into the window. Add back lines to slow the kite and have it sit farther back in the window .

John Holgate - 13-9-2010 at 02:58 PM

Quote:

am confused ? If your strap is open and you pull in the bar your kite will depower . You can further depower it with the trim strap. Trim the kite so it will stall but not fall back when the bar is trimmed in.


Perhaps I'm confused by your terminology here - when I pull the bar in on the Access/Apex I get more power, not less.

Perhaps I should say - pull in the bar and you will increase the angle of attack of the kite hence creating more lift (pull) but also creating more drag (resulting in the kite sitting back a little in the window) In light winds this may stall the kite- too much drag for the lift generated.

Let the bar out - decrease the angle of attack - less lift - less drag - kite will speed up and fly further forward.

Adjust your trim strap to suit the conditions. Have I confused you even more?? LOL!

Spend an hour or two with the kite and you'll soon get the idea. It's probably easier done than said in this case.

Kami's is a good explanation.

Bladerunner - 13-9-2010 at 05:07 PM

YES I always have a hard time explaining things using the term " depower "

When people are using that term they must be referring to the kite at the edge of the window and in motion + above the kites minimum winds. Then yes, Pull in the bar, the kite catches more air + sits back in the window providing more power.

When the wind is below the minimum or the kite is NOT at the edge of the window then those " depower " rules get warped. This is when I prefer to think " speed equals power " concept fit ( in my little mind ) . When you pull in the bar ( power up ) with the kite in the window. Like on a hot launch as an example. The kite will travel to the edge slowly and will not be producing as much power. Push the bar out ( depower ) and the kite will ZOOM across the window giving you HOOJ power boost !


In low wind for me it works sort of. Front lines to speed the kite up through the window then pull in the bar at the edge to slow the kite + aid in turning.

krumly - 13-9-2010 at 05:54 PM

I've groused about this before and will take the opportunity to do so again: kiter's use the term power with a lot of indiscretion. Power is force x distance / time. Equating line force or force on your harness to power is often used, but it ain't the same thing in a physical sense.

We can increase line tension by flying the kite faster, which is what happens when we let the bar out. Usually this puts the kite into a more optimum lift-to-drag RATIO, which is evident by the fact we can point upwind further. We can also increase line tension by pulling the bar in and increasing lift with a disproportionately large increase in drag. The result is the kite won't point as high, we slow down, and get pulled downwind. If the trim strap is fully let out, when the bar is pulled in we'll likely get a trailing edge stall (angle of attack is too high) and lift is killed while drag is high.

Rider preference may vary and kite or bar limitations will factor in, but as a rough rule, I like the trim strap set so I can have the kite flying it's fastest with bar about 3/4 out, and just starting to backstall when the bar is all the way in. Let the bar out and let the kite run fast between turns. Sheet in a bit to get the trailing edge into play for the turns.

krumly

John Holgate - 13-9-2010 at 05:58 PM

Ah, I see what you're saying now. It depends alot on what we individually think of the term 'depower'.

Ozone used it when they first started marketing the Turbo Bar - "depower through use of brakes" I seem to recall was the term they used. And yes, when static flying with the turbo bar - pull the bar in and often the kite will stall and fall to the ground - hence 'depowering' the kite Too much drag, not enough lift. Mind you, do that at speed in the buggy and the opposite happens. Lift overcomes drag and woohoo!! off we go.

So speed = more lift = more power.

Personally, I view the term 'depower' meaning the ability to change the angle of attack of the kite and 'spill' some power.

I think Kami was spot on when he said it helps if you're a plane geek!! Our kites are, after all, just inflatable wings.

Kamikuza - 13-9-2010 at 06:18 PM

AoA is a result of the relationship between relative line lengths.

Trimming - using the trim strap, using different knots (on the rear lines usually) ... lets call it Static Trimming - alters front to rear line length and thus AoA. The bar gives you the same amount of travel for On-the-fly Trimming within the range of your Static Trim settings and also works by altering the relative line lengths - sheet in, front lines get longer/rear gets shorter = AoA increases. Sheet out, front gets shorter/rear gets longer = AoA decreases.

I believe that most aircraft have a maximum sustained rate of climb, which is a certain speed at a certain AoA. Yes you can go to a higher AoA and climb faster, but you'll be losing air speed and will stall. Diving the plane, pointing the nose down and decreases the AoA will increase your airspeed but you'll lose altitude.

With a kite, you can (kind of) do the same ... gradually sheet in to trim the kite for maximum power without losing kite or board speed (max rate of climb ie. most lift/power) but if your speed drops, you have to sheet out to "nose down" and pick up some air speed for the kite. More airspeed in the kite means you can bang on the depower hard without stalling ... and jump! but only for a short time ... hold it down and depending on the wind speed, you may stall the kite. This is all assuming you haven't changed course - angling your board towards or away from the kite will affect the airspeed of the kite too ...

Or you may not - last night, I forgot to put the donkey dick in before I tried to pull the trim strap ... chicken loop unhooked and left me hanging on to the bar with the kite at the zenith and me unable to take a hand off to pull the CL to my harness ...!

Perhaps sailing would be a more appropriate analogy ... although I think it's best used to describe the effects of relative wind ...

I really must sit down with a paper and pencil and figure out all the relationships between wind speed, direction and what the kite will do when you alter your AoA ... we know that if you're riding and sheet out, the kite will fly further forward in the window and if you sheet in, it'll settle back towards the power zone - but then what :)

IMO whatever is most comfortable ... naturally, the bar will somewhat follow the kite so if kite is perpendicular to the ground, then the bar will want to do the same. But it won't matter if you're holding the bar parallel to the ground. You'll affect the steering a little but you can compensate. Don't waste energy fighting the bar though ;)

krumly - 13-9-2010 at 06:28 PM

Spot on John. The bar setting that provides maximum lift to drag won't pull with so much force if you are standing static with the kite parked at the edge or zenith, but it is the setting that will let the kite fly at the highest speed and will get you moving fastest on th buggy (or board or skis).

Pull the bar in flying static and what seems like additional 'power' is just increased line force. Do it while you're zooming the kite and you will get a momentary increase in force and acceleration ('boost'), but the power will not be sustained. If it was, you wouldn't come back down like a rock!

krumly

Qside - 13-9-2010 at 10:31 PM

OK so lets see if I got this, keep in mind I'm talking about static flying here. Flying in a low wind condition means I need to keep the kite moving through the window in order to keep it in the air. In order to do this I need to minimize drag and keep the leading edge and trailing edge about equal distance from me. Pulling the bar towards me (sheeting in??), changes the AoA in such a way that the kite "catches" more of the wind and gives you a grunty pull (power). In low wind conditions this will slow down the kite, low wind + slow kite = kite on the ground. In higher winds is does the same thing but less speed is more acceptable and you get a quick boost in lift/power without the kite stalling and falling. So the stronger the winds the longer you can keep the bar pulled in/sheeted in without a stall?

In my low wind situation do I want to pull the trim all the way in (red ball all the way towards me) to get that low drag effect?

Kamikuza - 13-9-2010 at 10:43 PM

Yes to all.
Go easy on steering input in light wind, keep away from the edges of the wind window (ie. don't try to turn at right angles to the wind) and turn down towards the ground (down loop) to make use of gravity to speed the kite up.
Yes, probably. Depends on the kite but the lower the AoA, the quicker it will accelerate and generate apparent wind - wind speed over the kite by it's movement through the air.

Light wind is not much fun though eh ...

krumly - 14-9-2010 at 09:18 AM

I agree with Kamikuza. One point to add is if you trim the kite in too far, particularly in light winds, you can get a leading edge stall, or 'luff.' The kite develops so little lift that it can't support itself. Or it may even invert, where the leading edge gets backwinded on the top and the kite flips, and top becomes bottom.

The attached pic shows some lift-to-drag vs angle of attack graphs for a simple airfoil family. It is a 2D foil analysis only, so doesn't fully apply to a 3D wing or specific kite, but it may be illuminating. Lift-to-drag ratio is one of the chief indicators of a foil section's performance; the higher it is, the faster the foil can fly and the more lift it can attain.

Note how all the foils in the graph have peak lift-to-drag around 5-7 degrees angle of attack. Go either side of this and you are off peak - drag is increasing disproportionately to lift.

Other foil sections may have different curves, with a wider or sharper peak, a higher or lower peak, or with the peak shifted left or right to a different angle of attack. But all will have an optimum angle of attack where you get the most lift with the least drag. With some modifications and complications, this applies to your 3D wing or kite as well. There is an angle of attack where your kite will attain it's greatest speed relative to the true windspeed, and where you will go fastest on your buggy, board, whatever.

Fixed bridle kites are set to an optimum angle of attack and camber. This is altered slightly as the brakes modify the trailing edge of the foil. Some fixed bridle kites have an angle of attack and camber adjustment at the kite bridles that can be changed when the kite is on the ground, but not on the fly. Depower kites allow the angle of attack and/or camber of the entire kite be adjusted on the fly through the complex interrelationship between the rigging and kite canopy.

NACA-X418-Lift-to-Drag-Graph.jpg - 141kB

Bladerunner - 14-9-2010 at 04:30 PM

I think that Kami and Krumly are saying that shortening the strap completely is often too much. I fly in low wind a lot and find about 80% tight is best for me in those conditions. I go to 50 / 50 as soon as possible and often just leave it there ? Rip' and Roland always take my kites and open it up right away so it depends a bit on style !

rocfighter - 14-9-2010 at 04:48 PM

This has been a great thread. I very tentitively flew Pokitetrash's Phantom15m this summer for a few minutes. And now Just what I said would happen has happened and I'm asking about Depower. A lot of my questions were answered with out even asking them.
Thanks again guys. Dave

Kamikuza - 14-9-2010 at 05:16 PM

I think it depends how much of a hauler on the bar you are ... being a big fat lump, I tend to whale away on the bar and spent a lot of time stalling the kite. I'm getting better though :D and trimming the strap in can limit the adverse input I have on the kite. I blame the harness too - when I'm in the right position and my arms are straight, the bar is still sheeted in a long way ...

Great points Krumly!

I found the same with the arcs - about 3/4 pulled was good in light wind. The Speed only needs an inch or two though but I reckon it has a lot of trim at the strap ... the 'bow has like 3 inches, the Speed about 5 ...!

Midgaar - 16-9-2010 at 05:41 PM

Qside - 16-9-2010 at 06:01 PM

Thank you all very much for the advice! Not much wind around here lately but I had to get out there and try again so today in a consistent 5-6 mph wind I had her flying. Thanks to all your advice I went from being able to keep her in the air for 30 seconds to 30 minutes. In fact, the only time she came down was when I crashed her do to learning the turning radius of a larger kite. Even in low winds she had no problem pulled me across the field when I pulling in the bar during a sweep across the window.

:wee: