How much could a kite's condition/bridles add to drag?

[geopeck]

I just got back from a light wind (12ish knots) session with my f-one bandit dos 14m. It's a pretty great kite, but heavy, thick LE and the fabric is far from crisp and has some patches.

The bridles on it are extra long, about 7 feet past the wingtips (the original bar came with different length lines, I fly it with standard lines and added 7/64s amsteel TE lines to even it up). So there's way more thick bridle material up there than any other kite I've ever seen, and then I added a little more. It is also generally worn about the leading edge, and has a few patches like I mentioned.

I know that light wind performance gets hard to judge because small variations in the wind make big differences, but it seems like it used to perform better. It still pulls incredibly hard once it's at the edge of the window but it seems like it's a little more difficult to force it there and it's speed going back through the window appears slower. Anyone want to offer an educated opinion on whether this could be happening due to increased drag on the kite, and would the effects be more noticable in light wind?

[TheJoe]

A lot more than you think. If you want to test it just do this simple test. Get a set of short line extensions say 3m. Fly a kite in its sweet spot with out the extension and then with them. You will feel a difference in bar pressure. The increase in bar pressure is from an increase in drag this is why people think longer lines give a kite more power.

Just so you understand a little better about the line lengths and power. A kite get its power from its shape and size compared to the wind and lift it generates. It does not matter if you have 10m or 30m lines. With 20kts of wind your kite will generate the same amount of lift regardless of line length. The big difference with longer lines is the amount of drag you have and how much deeper the kite sits in the window. This generates more bar pressure and is why people think long lines give you more power. Now you can generate more apparent wind with longer lines and you could have higher winds further off the water but that is a different discussion all together.

As a tip you might want move your amsteel pigtails to your bar at the bar if they are long and not just a few inch's. If the kite is really old as it kinda sounds it all so might be that your canopy is very stretched and it is not as efficient as it once was.

[WildDuke]

Very interesting statement about the relevance between line lengths and bar pressure! Hmmm... Makes sense. I have always gone for the longest lines I can get, but I've also been complaint how bar pressure on the kites that I fly are too hard. Hmmm maybe they weren't meant to be flow with such long lines.... Interesting thought!

[WildDuke]

Ahhh sorry for the grammar in my last post, bloody iPhone spellchecker!

[Kamikuza]

The increase in bar pressure is from an increase in drag this is why people think longer lines give a kite more power.

Intuitively I disagree - while bar pressure may increase (although I doubt it will be significant) with extensions or longer lines, the benefit you glean from having longer lines is the increased time the kite spends developing power while moving. The distance traveled by the kite and the time available for it to accelerate is significant as line length increases... and would positively outweigh any drag.

Parked'n'riding, I agree that there is minimal difference between line lengths, assuming the 'wind gradient' is negligible... IIRC that's a few knots between 20 and 30m and barely worth considering.

Of course... I could be wrong

Oh, the thing you may notice as bar pressure is simply the amount of time you have to hang onto the bar waiting for the kite to respond and get around the turn...

[TheJoe]

The increase in bar pressure is from an increase in drag this is why people think longer lines give a kite more power.

Intuitively I disagree - while bar pressure may increase (although I doubt it will be significant) with extensions or longer lines, the benefit you glean from having longer lines is the increased time the kite spends developing power while moving. The distance traveled by the kite and the time available for it to accelerate is significant as line length increases... and would positively outweigh any drag.

Parked'n'riding, I agree that there is minimal difference between line lengths, assuming the 'wind gradient' is negligible... IIRC that's a few knots between 20 and 30m and barely worth considering.

Of course... I could be wrong

Oh, the thing you may notice as bar pressure is simply the amount of time you have to hang onto the bar waiting for the kite to respond and get around the turn...

You can all ways test it your self . You can generate more apparent wind with longer lines this is true and it is better for lighter wind. How ever it does not change the power of the kite just the efficiency.

How many times have you heard longer lines for light wind? What about the opposite " I got short lines so I can handle more wind." Same difference short lines less drag kite less bar pressure. Now don't think it is the drag of the lines as much as it is how deep the kite sits.

There is more to it but I'm trying to keep it simple. One it goes against all the marketing BS kite companies spit out, and two I'm just not that good at explaining things. I had a hard time understanding it at first but after spending a lot of time with different line lengths and really flying the kite I started to understand all the different forces that effect the kite and the power it generates.

[Kamikuza]

I thought longer/shorter lines was more about time for the kite to accelerate and the subsequent Vmax per stroke and gain in apparent wind...?

Think I understand your bar pressure though - I went surfing around and found some real math for control line model airplanes that calculated drag on the lines (too hard for me!) and a NASA kite model applet... changing line length didn't *seem* to alter drag but DID alter tension the lines were under...

[geopeck]

This is interesting, thanks for the replies - what are your opinions about increased drag due to micro-wear on the leading edge and canopy vs. it's brand new condition. I have definitely been forced to self launch and land this kite quite a bit and it's visible when inspecting the LE closely. Or would you guess that changes in flying characteristics are just due to canopy deformation?

[Hansen Design]

Geopeck:
Some excellent questions!
Couple things to consider about longer or larger diameter flying lines:
1) Longer or larger diameter flying lines do increase drag. As a result a kite will sit deeper in the window.
2) A side effect of longer or larger diameter lines is the reduced AOA (de-powering) caused by the increased catenary (sagging) in the front power lines. This can create a problem at the edge of the window where there is less tension on the lines and even more catenary as a result. Some more efficient kites may try to tumble out at the edge as a result.
3) Longer lines are less responsive as you need more bar movement to remove the catenary in the rear lines before any steering input is made. This is also a problem at the edge of the window.
Leading edge and canopy wear:
1) Leading edge micro-wear will not have much of an effect on performance.
2) Canopy wear which normally presents as increased stretch and distortion can either make a kite more or less powerful depending on the kite design, panel orientation and reinforcing. If it results in increased shape (bagging out) the kite will sit back more and be more powerful but less efficient. If it results in a loss in profile shape, the kite will lose power and most likely (but not always) efficiency.

Generally speaking, an older substantially worn kite will not go upwind as well as when new.
Cheers!

increased drag due to micro-wear on the leading edge and canopy vs. it's brand new condition.

[edt]

1) Longer or larger diameter flying lines do increase drag. As a result a kite will sit deeper in the window.

I dont think this is true. Remember the kite can't "see" the lines sag. So for instance:




Kite a and kite b have the same angle of attack. While it is true that the lines sag, the kite can't "see" this sag all it sees is 1) angle of the line 2) tension in the line

Kite a is not deeper in the wind window than kite b. And if mattered how strong the pull on the lines were then a kite would sit deeper in the window with a fat rider than a slender rider. While a fat rider might put the kite deeper in the wind window this is a matter of him wanting more grunt a deliberate choice, not a characteristic of the kite under load. The performance of the kite depends not on the length of the line but on the characteristics of the kite and how it is being flown not line length.

I can remember thinking at one time that line length mattered for where the kite was in the window but right now it seems to me that it doesn't matter.

The reason for longer lines in light wind is the wind gradient.