i went and read those posts, good stuff, to me it is clearer than my posts, but i stayed away from all the pendulum effects because frankly I haven't taken the time to do the specific pendulum math and didn't want to make any errors or lose the focus of my explanations. So maybe it is you that has all the answers!

I find it interesting that you also fly gliders too. Having the theory and the practical experience of these manipulations under our belts we seem to be the only people who really have the necessary framework to truly understand the admittedly more complex machinations of kite jumps. Most designers or kiters seem to have different parts of the picture according to their prior knowledge framework, but not the full deal.

At the end of the day though the thing that impresses me the most is that riders with NO understanding at all can evolve near absolutely perfect technique just through training their nervous system in the command and control of kites intuitively through practice.

I seems to be a fact of life that when practical problems get complex, trial and error usually arrives at better solutions than pre-computuation. Kite designs too have certainly arrived at their current format more from tinkering, feedback and discarding poorer designs than any specific vision of exactly what the entire design remit was and how to fully analyze it and derive solutions.

I agree...very important. An understanding of theory can help optimize technique, but it can't replace practice. Sometimes I think that's overlooked in these threads. An explanation of dynamics or theoretical limits doesn't negate the value of practical trial and error.

Cheers,
James

Agree with you JS and Rabidric.

Interesting topic.

The wide helicopter loop is a tricky one, as just like a helicopter blade with engine cut off or autogyro (or like a maple seed), it will obtain a bigger "swept" surface if the speed is higher with the same AOA, thus way lower sink rate (lower swept wing loading).
But just like you say JS - there is a vector loss as a kite is not horisontal like a helicopter blade - and there are other forces (losses) present, like the AOA changing if you still have motion relative to the wind etc.
So very complex, and it might not lead to lower sinkrate Or maybe it will

Rabidric - you mentioned that the drag of the rider would move the Cl for max L/D up near max Cl.
This is of course correct, as the polar will make a shift to the right when introducing more (parasitic) drag - thus max L/D will appear at a higher lift coefficient

But it is IMO not near max Cl !

As, our kites are quite cambered profiles with very large LE diameter, which leads to a very "curved" polar at the top (a very soft stall so to speak, and very curved before the stall).
So eventhough the max L/D moves up at a higher Cl with more "rider" drag - it will not move up to max Cl - but closer which is fine for understanding the principles, agree

Max L/D is far from lowest sinkrate though - many do not know this, as L/D is the "popular" term many have heard about.
Minimum sink rate is obtained at max (L*L*L)/(D*D) so lift coefficient to the power of 3, and drag only squared.
This will lead to minimum sink at a somewhat higher Cl because of the curved polar

If you take very thin airfoils/profiles with a very little LE diameter, both max L/D and min sink and max lift can almost appear at the very same Cl
Because the polar is quite straight all the way up, and at the top also, and then it abruptly breaks
Leading to a very violent stall of course - but incredibly efficient low drag profiles in the "static" state/flight.


My point is, that the rider drag will make the kite airfoil operate at a higher Cl (or AOA) closer to max Cl for max L/D just like you say.
But min. sink will be at an even higher Cl, because of the "blunt" polar.
I think we all know this actually - that we have the kite sheeted way more in when jumping and doing hangtime (not distance) - compared to going upwind where we want max L/D (max upwind angle), and sheet out a bit or a lot.



We all agree that max jump height is finally determined by the apparent airspeed of the kitesurfer, and it can never be exceeded by a 2000m2 huge efficient kite - it can maybe be approaced closer, but never exceeded - and rider weight is not a parameter
Just like JS pointed out in 2007

Peter, Engineer.
(also a glider pilot, hangglider pilot, and R/C glider enthusiast, and designed/calculated many gliders over the years)

Yeah, in my mind's eye , since I don't know the specific polars I just imagine a generic one, which i truncate at min sink, as for conversation Cl(min sink) and Cl(max) are close enough,without putting up pictures and diagrams. I have no real idea of the exact shape of the back part of the polar for kites either, so will take your word for it.

Hey guys who wants to go kiting.........

Great post Peter, but the original question remains. Which kite jumps the highest? It seems you are solving the question "How do you operate a kite to jump the highest" which has to do with Cl, and also solving for max hangtime which involves L and D and best upwind angle L/D but the original question remains unless I miss something.

1. good ratio between min stable Cl and max achievable Cl ( power range)
2. High max Cl (power per sq metre in laymans terms)
3. High aspect ratio gives better l/d when high Cl is being used
4. Curvature allows turns to be made with a bit less drag, and with less adverse variation of pull
5. Moderate aspect ratio makes turning faster, so allows less rider momentum loss in the sending phase, and less time redirecting the kite (where it is typically being less productive) in the air

Compromising between these traits is a convex function, i.e. focus too much on one and the others will all suffer disproportionately in most cases

e.g. 7,7,7,7,7 might be acheivable, but 10,10 in two traits with yield 3,2, or 1 in the others

who knows what the exact blend is, it may be 7,7,7,7,7 or perhaps 8,6,6,8,6 , only trial and error based design evolution will really sort the wheat from the chaff. this has been going on for the last decade.
As i said before , modern Hybrids seem to have it pretty sorted, regarding max boost and float. Even the "high aspect flat kites" aren't all that high aspect, and have decent arc in the tips.

ME! ME!

Among production kites, I suspect the largest Flysurfer Speed that one can manage in particular conditions is the highest and floatiest jumping kite, at least in moderate conditions.

A week or two ago, underestimating wind strength some distance from shore, I flew my 19m Speed when my 9 or 12m inflatable kite would have been sufficient. It was probably blowing between 15 and 20 knots (20 mph +/-), which feels really windy with that kite. Jumps were really high for the conditions.

That leads me back to comments I made earlier in this thread, focusing on minimum sink rate. I think that's far and away the most important parameter. That basically means the biggest, (generally) most efficient kite you can handle, even if the turning characteristics are compromised.

Based on paraglider performance, I estimate the sink rate of an optimally trimmed 19 or 21m Flysurfer Speed with a rider of moderate weight to be a little more than 200 fpm (~2 kts), probably right around 4 feet per second. That being the case, in simplified terms if it takes three seconds to achieve the apex of a jump, then about 12 feet of sink will have occurred by that point. In other words, in that situation the actual jump height would be about 12 feet less than the maximum theoretical height based on an energy calculation for the rider's apparent windspeed at takeoff.

In the case of my recent overpowered 19m Speed ride, if I jumped during a 25 mph gust while riding a bit upwind at 15 mph, my apparent wind at takeoff would have been about 33 mph. If my quick calculation is correct, that would have given me a maximum theoretical jump height of about 35 feet if my mass slowed to 7 mph apparent wind speed at the jump apex. And if it took three seconds to reach that apex, I would have bled off about 12 feet of height via 'sink' while on the way up. That means I would have actually jumped about 23 feet high. That likely isn't far off, and nor are my various assumptions, I think (hope). Some of those jumps felt like 30 feet (and beachgoers guessed likewise) but I have little doubt that 20 feet high feels like 30 feet.

Now, suppose I was flying any good 10m inflatable kite in the same conditions. That kite's quicker turning ability might have allowed me to sustain an extra 1-2 mph of board speed at takeoff compared to my previous example, but that would have only increased my apparent wind by about 0.5 mph +/-, and therefore my theoretical jump height by about one foot.

However, with the same rider weight, that smaller inflatable kite likely has a minimum sink rate of 6-7 feet per second. So, even if it can get the rider to the jump apex a bit quicker, it's likely to bleed off 15-20 feet of jump height via 'sink'. By my best guess, the actual jump height would be more like 15 feet, compared to the big Flysurfer's 23 feet, and there'd be way less hang time.

One more thing: kite trim is really important. Notwithstanding comments somewhere in this thread about mild stall characteristics, any foil or inflatable kite is easy to stall with poor line trim. In particular, front kite lines typically stretch more than rear lines over time. Further, when lines are heavily loaded during a jump, the front lines stretch even more, relative to the rear lines. That all makes it easy to inadvertently over sheet your kite, especially during a jump, causing at least partial aerodynamic stall and lousy jump results.

Cheers,
James

Just 1/2 cent, with no scientific input, about high jumping kite.
The rebel 7m 2007 was a hell of a jumping machine. Why?
- Because it depowered like hell (almost too much) so you could use it in 50 knots
- Because it powered like hell when you pulled the bar
- Because it was super fast flying forward

Down point: no stability and fragile

My current kites are more powerfull and stable, but you can't "over-clock" them like you could with that crazy kite.