This may seem a naive question:

I've read an online kite description that seemed to link it's depower and upwind abilities. It would kind'a make sense on one hand, but it has never been mentioned in anything else I read.

I can't say I notice any more upwind cutting ability or pull when I tried trimming in my Phantom or Access'es front lines when angling upwind.

So, I either misread the implied link; didn't fly the kite(s) correctly; or I'm using the wrong kite?

Upwind ability is more dependant on the kite itself then the kites ability to depower.

Quote:

Originally posted by snobdr Upwind ability is more dependant on the kite itself then the kites ability to depower.

Agreed.

The AoA and the kite profile are the keys to tracking up wind and while you can adjust the AoA of a depowerable (and even the camber of some kites) there are still limits based on how the kite was designed and the profile remains unchanged. Many depowerables are boxy, fat kites with wide / thick leading edges and are relatively inefficient (which is why they are so big compared to a fixed bridle kite of comparable power). Changing the AoA may get you closer to the windows edge and get you upwind better but the design of the kite is still less efficient than it could be if say there was a depowerable race kite.

Yes the overall setting of AOA is your best way to gain large chunks of upwind performance.

However, i will say that if i need to get better upwind performance while riding, i will let the bar out more. When i depower i do notice better upwind performance.

But i guess its a rough/fine tuning issue then... If you want good upwind performance, "rough" tune your kite and lessen your angle of attack. But if you want "better" upwind performance at whatever setting your riding on at the moment, "fine" tune the kite and push the bar a little and it should hike a decent amount more upwind.

Did that make sense for anyone? i feel like i added to many brain ticklers in there

Quote:

Originally posted by flyboy15 However, i will say that if i need to get better upwind performance while riding, i will let the bar out more. When i depower i do notice better upwind performance.

That makes sense because when you pull the bar in you actually move the kite to its slower, less efficient AoA which is what produces the lift. The kite moves faster with the bar out as it maintains a flatter / more efficient profile.

Bar in = less efficiency and more lift. Bar out = more efficiency and less lift.

At least that is how it was explained to me and it makes sense if you refer back to the "hand out the window of a moving car analogy". The hand is very efficient with a slight AoA into the wind and it cuts though the air, but turn it somewhat against the wind and the hand is less efficient and pushes towards the back of the car (which would produce lift if it were a kite moving slower and away from you).

"Course, the "hand outside the car window" is more at a vertical angle when buggying/boarding upwind
- "lift" is translated into more horizontal pull.

Strapping down/in the top/leading edge in could help it cut more in front/ahead of an upwind course
- but giving is "some gas" by pulling in the bar/trailing edge would tend to pull the kite back into the window, away from a more forward, unwind course...

Sounds more like an Art than Science, similar to my NASAwing upwind discourse here.

My head is starting to hurt again....

In general, when you depower a kite, you decrease it's drag and increase it's potential forward velocity. Depowering a kite doesn't necessarily make it less 'lifty' - on the contrary, if the kite can fly faster lift and line tension greatly increase, you move faster, and power is increased.

The formula for aerodynamic (or hydrodynamic lift) is Lift force = p/2 * V^2 * A *Cl where p/2 is mass density of air/2; V^2 is velocity of foil squared; A is area of foil (projected area is more applicable); and Cl is coefficient of lift (Cl is dependent on numerous factors, but is linearly dependent on AOA within the useful range of the kite up until stall).

You can decrease the AOA of the kite, deceasing it's drag and alllowing it to speed up, thereby increasing it's lift a LOT. Do a downturn on your kite high up near the edge of the window and depower it to let it run across the window and you'll see the effect. It'll hold until approach the edge of the window again and you lose that speed in the kite, at which point sheeting in will give you more static pull (and more drag, as the kite starts to sit back in the window further).

krumly

Why would we not fly with the bar out all the time, if theres more speed and power there?

Quote:

Originally posted by snobdr Why would we not fly with the bar out all the time, if theres more speed and power there?

there is a curvilinear relationship in the dynamic system. finding more "usable" power and speed in different parts of the wind window. In a crosswind point of sail not much matters but more power, but with the steepest possible upwind point of sail maintaining system speed is how it works . too much AOA, too much power, the kite falls back deeper into the power zone dragging you with it. getting the kite to point up wind (closer to the edge of the wind window the better) with maintainable system speed . keeping the kite moving with little resistance at the edge of window keeps you moving up wind

maximum "usable" power for upwind riding , not absolute device power. depowering at the edge gives the speed to keep feeding the system . the dynamic system adds up with apparent wind, so more depower is better at the edge for upwind travel .

maybe this helps

The last sentence of my post is key. Once your kite starts approaching the edge of the window, it's gonna slow down. Eventually it'll be parked and it's apparent wind will be the true wind (if you're flying static) or something faster than the true wind if you're moving (which will be dependent on how much friction and other drag your vehicle puts into the equation).

There is an an angle of attack to the apparent wind for a kite at which it will attain it's maximum lift-to-drag ratio. At that point if you increase or decrease the AOA of the kite, your L/D ratio will decrease as will your potential speed.

So yes, decreasing AOA doesn't always increase the L/D and the speed potential. I can have my bows depowered, almost backwinded, that if I drop them into the window, they won't pull very hard. Conversely, I can sheet in and get a lot of downwind pull, but I can't achieve max speed on my skis with it at that high AOA.

I attached a printout from a foil and wing analysis program called XFLR2. It shows a 2D (infinite aspect ratio) CL vs AOA and CL/CD vs AOA for a moerately cambered foil section - a classsic NACA 2415. Probably not used in any specific kite design, but it'll serve to illustrate. Note the linear increase in CL vs AOA up until about 14 degrees, then a mushy stall. Note also the peak for the CL/CD is reached at around 5 degrees. You lower your AOA even more, your CL/CD and total lift decreases and you also start to run the risk of backwinding or losing inlet pressure.

krumly

Here's a another explanation: Generally, you need kite speed for pulling the bar to work like it should. During low speed with the bar pulled, the kite will backstall causing much less power and high drag (aka slow). So in low kite speeds, you will see that the kite will fly better, faster, and probably pull more with the power (bar) out (not stalled).

With high kite speeds, such as when your moving, or doing a jump and your sending the kite over your head, pulling the bar works like it should because the kite has the airspeed it needs.