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The problem with flysurfer mixers.

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kitexpert
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Re: The problem with flysurfer mixers.

Postby kitexpert » Sun Apr 17, 2016 1:20 pm

"The relation to the % cord that each bridle is attached ,has to
do with the ratio your changing A,B and C with your mixer ; if the ratio doesn't match the % cord
then you get more drag because it introduces wrinkles to the top & bottom surface." -Bille

This is correct in principle. There is only one A, B, C bridle location by the chord versus used mixer that changes AoA without distorting airfoil shape (and not introducing wrinkles to the top and bottom surfaces). In practice it is easier to play with bridle locations than mixer pulling ratios.

However it is more beneficial to have increased camber when sheeting in than to have some added drag, so changing camber is used. This allows to use low cambered airfoils, which are stable and make high depower possible because they have low lift.

"In other words : changing A, B and C with a mixer ,should only affect the AOA, and NOT the camber." -Bille

Main object is to change AoA by bar movement to control power. Mixer (pulleysystem) is the tool to make it possible for foilkites. LEI kites don't need speedsystems because they are rigid, they change AoA just pulling backlines. But still, if struts have attachment points for bridles (like Genetrix) even more control for powering/depower is possible. Cost is added complexity and some line drag.

Camber change is a bonus. It is not same thing than tweaking mixer settings (which is never optimal). Designer can decide how much camber of the airfoil changes (within certain limits) or if it stays the same when sheeting the bar.
Last edited by kitexpert on Sun Apr 17, 2016 1:34 pm, edited 1 time in total.

foilholio
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Re: The problem with flysurfer mixers.

Postby foilholio » Sun Apr 17, 2016 1:44 pm

Bille wrote: When Ya add camber with B and C ; it ain't worth the drag for the return.

80% is the hinge point ; so when you pull on Z at 90 to 100% , your hinge point is
still at C.

Further back than 80% hinge point, will give a higher CL change : but it's at
the expense of More drag. Most flaps on an airplane are at, or near 80% for a reason.

The relation to the % cord that each bridle is attached ,has to
do with the ratio your changing A,B and C with your mixer ; if the ratio doesn't match the % cord
then you get more drag because it introduces wrinkles to the top & bottom surface.
In other words : changing A, B and C with a mixer ,should only affect the AOA, and NOT the camber.
ONLY the Z should affect camber ; and it's best done at 80%.


Bille
All large amounts of camber are going to induce lots of drag. It's for lift that airplanes change their camber, they have big powerful engines to overcome any drag but not a significant way to increase wing area, they can extend the wing a little bit with Fowler flaps and certain LE flaps, but camber is the big changer on lift. With kites it is possible to increase projected area and camber, but it's you and your board that fights the drag.

Cambering B and C are of significant use for kites. As I said I think B has a large effect on control while still being depowered. C has a huge effect on stability. You get into the sewn profile and their is now no limit to where or how you can change camber. You can put it on the very leading edge or trailing edge or the middle. If you read a bit about peterlynn arcs and autozenith this is probably the main factor to produce that effect, I think it may have something to do with leading edge shapes.

There is seemingly a wide range of variability with what cord positions work with what mixer. If you are talking about absolute maximum L/D, where even wrinkles are an issue then very very low almost no camber or AOA is going to what you want. Of importance would be the bridles match the sewn profile. Still you could set for this , I think flysurfer may use that as a base setting where ABCZ are even, and then after it or before many very different things can happen. Like the engagement of a wac and diablo line for extreme camber after the that high L/D profile is reached.

From my limited reading what gives best L/D is near zero camber and AOA. As to what gives the highest lift is camber. For the high camber if you were to position it at the front the change would physically look much the same as just an AOA change. Gradients work well in this world and I would guess some sort of exponential curve starting very minorly at the front proceeding to massively at the end. Of course you only have 4 points on the wing to work with but still some sort of gradual curve or adjustment can be achieved. It is debatable whether foils can change AOA at all and in fact only change camber.

Have a play with

https://www.grc.nasa.gov/www/k-12/airplane/foil3.html

you will need to have java https://java.com/en/download/ access the "configure java" through the start menu search box, under security tab, edit site list and add https://www.grc.nasa.gov as an exemption. I have to reload the page after allowing the app in firefox. Fucking complicated and I would love to know who to blame lol.

It's not meant to be 100% accurate. But playing around with it the maximum L/D I can get is about 18.5. The wing has very little AOA and a little negative camber. Then increase AoA and the lift increases 4.5x with L/D at 6. Then increase camber a lot and reduce AOA a bit and lift goes to 10x with L/D at 3. The high camber profile looks like a hollow profile on a foil kite. Highly unstable but very powerful and won't go upwind. Despite the app only being educational, the lift changes with camber are similar to what I would say I experience, with lift about doubling when I tune for a good amount of camber. Not so sure about the negative camber having the best L/D but it may do as it's some where around flat that going upwind is the best. The camber used is quite a constant curve, and even though AOA is needed to get the lift setting to maximum with high camber, the front of wing looks like it has no or even negative AOA. Which is much how foils look like with this type of camber but with more curving to the rear of the wing depending on the mixer, settings and attachment placement,as you are trying to highlight.

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Re: The problem with flysurfer mixers.

Postby foilholio » Sun Apr 17, 2016 1:48 pm

kitexpert wrote:However it is more beneficial to have increased camber when sheeting in than to have some added drag, so changing camber is used. This allows to use low cambered airfoils, which are stable and make high depower possible because they have low lift.
This is a good point. Using a more stable profile but perhaps lower performance so the depower is more user friendly but gaining back some performance when the bridles are remixed.
kitexpert wrote:LEI kites don't need speedsystems because they are rigid, they change AoA just pulling backlines. But still, if struts have attachment points for bridles (like Genetrix) even more control for powering/depower is possible. Cost is added complexity and some line drag.
I think some use of pulleys on leis could be classed as a mixer, mainly thinking about pulleys used on the LE from my memory. I definitely think more bridles will help leis perform better, mainly on the TE as the lack of support there causes them to arc more and lose projected area. The problem with lei designers is they overdo fucking everything. Adding more bridles and attachment points will just compound the problem. First they need to adopt good aerospace engineering and design closer to the minimum needed. Requires restraint and thinking, I doubt some of them have it. Even flysurfer over does things a bit, but the LEI rider looks at a flysurfer kite and can't believe even how lightly constructed they are. The simple problem is if you have a 300kg component like a front line throwing a 2000kg pigtail or bridle line in doesn't make the system suddenly 2000kg.

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Re: The problem with flysurfer mixers.

Postby kitexpert » Sun Apr 17, 2016 2:07 pm

"There is seemingly a wide range of variability with what cord positions work with what mixer." -foilholio

Yes, many things work. For example Pansh has B very far back, it is pulled "too little" with 1:4 ratio. This means AoA changes less than normally. On the other hand Z is (of course) pulled 1:1, so "underpulled" B can be taken for adding camber of the airfoil.

"Using a more stable profile but perhaps low performance so the depower is more user friendly but gaining back some performance when the bridles are remixed." -foilholio

It is not possible to make depowerable foilkite with high cambered airfoil:

1. it would generate too much lift even at low AoA (like paragliders)
2. it would be too unstable at low AoA, front collapsing

In practical kiting high lift is important. There is limited use for extreme L/D when depowered if kite just sits at the edge of the window. If kiter can take the power of the kite (without going downwind) best upwind performance is usually achieved when fully sheeted in. This is true for example with Speeds.

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Re: The problem with flysurfer mixers.

Postby foilholio » Sun Apr 17, 2016 2:21 pm

I think your last point is interesting. More experienced kite flyers can fly a faster high L/D kite in the window more and generate more lift than a static high lift kite. It's one reasons I dislike inflatables as they "mostly" have fat LE and can't be flown fast. As to going upwind it all depends on wind speed, more wind the less you need to sheet in. In fact it gets easier going upwind as the wind speed increases and then it gets worse. The same for sining or flying the kite in the window there is an optimum speed and sheeting amount. Best explained in graphs like this
induced vs parasitic drag.gif
induced vs parasitic drag.gif (5.58 KiB) Viewed 776 times
basically as the speed picks up, through flying or just the wind, you need less AOA or camber to get the same lift so the drag is less. Works to the point the exponential increase in your other drag exceeds the improvements generating lift. Then you should switch to a smaller kite lol! It is also why small kites can start relatively so early and have so much power as it is much easier to generate lift in higher speeds with their thinner profiles helping them do that.
Last edited by foilholio on Sun Apr 17, 2016 2:32 pm, edited 1 time in total.

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Re: The problem with flysurfer mixers.

Postby kitexpert » Sun Apr 17, 2016 2:32 pm

"I think some use of pulleys on leis could be classed as a mixer, mainly thinking about pulleys used on the LE from my memory." -foilholio

For my knowledge Genetrix is the only one which has compareable speedsystem with foilkites (Supported profile system). Normally used pulleys in LE mainly balance loads.

I find usual "pulleyfear" for bad bar feel a bit funny, because backlines don't have any pulleys in LEI's. To feel frontline pulleys to the bar is not very easy to believe. And where is same kite with and without pulleys?

LE pulleys allow some more twisting for kite. It may help turning. Pulleyless systems are stiffer and simple. I have both kind of kites and I see pulleys reasonable.

My last point is based on years of experince. When kiter needs to sheet out to get better upwind angle it is because he can not take the pull which kite gives.

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Re: The problem with flysurfer mixers.

Postby foilholio » Sun Apr 17, 2016 2:43 pm

Flysurfer is doing some interesting bridle and pulley stuff on inflatables. I will have a look at genetrix. Some of the pulley function on a mixer could be considered balancing loads between A and Z, but they are not setup as proper load balancing as on leis. I definitely remember pulleys on a LE which would function somewhat like a mixer. Obviously not viewed in that light though.

Some lei models have had pulleys on the back lines. but most do not.

Thinking about it a bit more you should get the optimum upwind angle while the kite is at it's minimum drag speed. The other day I was trying to keep up with a hydrofoil and I found slowing down while I keeping the kite flying allowed me to point higher. Of course he was still going faster but after he fell off I overtook him lol. As to max VMG that is probably matching the board speed to the kites minimum drag speed.

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Re: The problem with flysurfer mixers.

Postby Bille » Tue Apr 19, 2016 7:01 pm

foilholio wrote: ...

Thinking about it a bit more you should get the optimum upwind angle while the kite is at it's minimum drag speed.
...
As to max VMG that is probably matching the board speed to the kites minimum drag speed.
For VMG, I like the second one ; (matching board AND kite) !! :thumb:

Using the same kite on water, land, and snow ; there is a HUGE difference in VMG, because
of the different drag profiles for each .
Best up-wind machine i ever used with a buggy , was a 2M, Rev-II , in 30mph wind ; but
i doubt it would work for squat, on water ?

Bille
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Re: The problem with flysurfer mixers.

Postby foilholio » Wed Apr 20, 2016 1:50 am

The peterlynn C quad is much the same. It couldn't float but in shallow enough water could be relaunched. You would need to add flotation which equals more drag. You could add a thin inflatable tube only for relaunching but maybe it wouldn't catch the wind well. On normal inflatables I wonder how thin the inflatable LE can be made with extreme amounts of bridling say every 6 inches or less. Maybe adding angled tips like on the cloud would allow such tubes to relaunch, maybe even negatively curved tips.
cquad1.jpg
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Bille
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Re: The problem with flysurfer mixers.

Postby Bille » Thu Apr 21, 2016 4:55 pm

Dang ; he's about to tell me , exactly how it is !! :lol:
Last edited by Bille on Fri Apr 22, 2016 6:35 am, edited 1 time in total.


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