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Why have most brands settled on 4:2:1 mixers over 6:2:1?

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gwicke
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Why have most brands settled on 4:2:1 mixers over 6:2:1?

Postby gwicke » Sun Nov 06, 2016 7:33 pm

I'm wondering why most brands have settled on 4:2:1 mixers, rather than 6:2:1.

4:2:1 keeps the A-B-C camber constant across the sheeting range.

6:2:1 (as used by Paraavis & other brands in the past) flattens A-B-C when sheeted out, and cambers it more when sheeted in. In theory, I would expect 6:2:1 mixers to result in a wider useful wind range, as the flatter profile at the upper end reduces drag and improves stability, and the deeper profile when sheeted in allows for higher angle of attack & grunt for downwind and underpowered riding.

It doesn't seem likely that this is only about saving one pulley in the B cascade, so which other reasons are there to go with 4:2:1 over 6:2:1?

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Last edited by gwicke on Sun Nov 06, 2016 9:03 pm, edited 2 times in total.

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jakemoore
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Re: 4:2:1 vs. 6:2:1 mixers

Postby jakemoore » Sun Nov 06, 2016 7:43 pm

Front/back chord wise position of the bridle insertion also has something to do with how the kite changes camber as it depowers. So 4:2:1 only has a constant camber if the bridle insertion is spaced harmonically.

Psycho 4 had 4:2:1. But the C and the B were both pretty far back.
Psycho4.jpg
Speed 1 had 3:1 (A and B Fixed)
speed1.jpg
Last edited by jakemoore on Sun Nov 06, 2016 7:50 pm, edited 1 time in total.

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Re: 4:2:1 vs. 6:2:1 mixers

Postby jakemoore » Sun Nov 06, 2016 7:47 pm

Gosh I'd like to see a Psycho4 re-boot with no jet flaps, leading edge stiffeners and Lotus Cloth.

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Re: 4:2:1 vs. 6:2:1 mixers / speed systems

Postby Regis-de-giens » Sun Nov 06, 2016 8:01 pm

concept air Pulsion ? not so far from this requirements, with a thinner airfoil thickness leading to good performance.

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Re: 4:2:1 vs. 6:2:1 mixers

Postby gwicke » Sun Nov 06, 2016 8:05 pm

jakemoore wrote:Front/back chord wise position of the bridle insertion also has something to do with how the kite changes camber as it depowers. So 4:2:1 only has a constant camber if the bridle insertion is spaced harmonically.
Ozone and Fone seem to place the B row slightly closer to A than to C, which should move the location of the main camber along A-B-C slightly forward when sheeting out, and back when sheeting in. Total camber along A-B-C should stay about the same, though. Elf spacing looks rather even.

Flysurfer used the WAC line to change A-B-C camber in the past. Once engaged when sheeted in, this prevented B from shortening any more relative to A. After trying both for a few sessions, I see 6:2:1 mixers as a milder and more predictable alternative, primarily because there is no hard engagement point that needs to be precisely adjusted.
Last edited by gwicke on Sun Nov 06, 2016 8:52 pm, edited 3 times in total.

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Re: 4:2:1 vs. 6:2:1 mixers / speed systems

Postby jakemoore » Sun Nov 06, 2016 8:40 pm

Last time I built a mixer for a kite was with the Speed1 mods and I found the 6:3:1 definitely worked better for that kite. IMO the 4:2:1 created either frontstall or backstall depending on how it was tuned. C was closer to the center chord than for example on Psycho 4. With 6:3:1 and a WAC line I could get a huge range with stable flight. On that Speed 1 I think the main benefit of modding some movement in B was the ability to steer the kite in extremes of depower. The A and B were so close together that moving B did not change the lift much, but you could steer the kite off B with C very slack.

My main point is the mixer has to match the kite. I am guessing moving B farther back and going 4:2:1 gives a bigger change in profile than keeping B forward with a 6:2:1 in part because the profiles are soft. But I'm just an amateur, not a kite expert.

Since then, I have been very happy with the kites as they come out of the bag so not a lot of motivation to do mods. I think the most interesting thing I have seen recently to increase camber powered up is the Diablo Turbo. I've had a desire to try a turbo line, possibly including flattening the mixer when depowered. Alas no time.

(For clarity, my Speed1 mixer had 6:3:1 meaning B moved 1/6 bar movement, C moved 1/3 bar movement and Z moved 1/1 bar movement.)

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Re: 4:2:1 vs. 6:2:1 mixers / speed systems

Postby kitexpert » Sun Nov 06, 2016 9:34 pm

jakemoore wrote: But I'm just an amateur, not a kite expert.
But you write like a one :idea: You have built a mixer, you understand pulley ratios and the meaning of line row locations. There is not much more there...

4:2:1 has become the standard because it is simple and works well. It makes possible to change AoA of the foil kite as much as it is usually needed and it allows to increase the camber at higher AoA. You can say 6:2:1 changes camber more, pulling less B, but this can be understood as well lesser AoA change in that region. Here of course line row locations must be known for understanding what happens.
Regis-de-giens wrote:concept air Pulsion ? not so far from this requirements, with a thinner airfoil thickness leading to good performance.
I don't see P4 and Pulsion very similar kites at all. P4 is very technical kite with jet flaps, inner structures and triple depower, especially with biggest changing PA than any kite. Pulsion is a light weight kite with simple construction.

It would be nice to know what is the airfoil thickness (%) in Pulsion, could you Regis ask Benoit? It shouldn't be so very secret design knowledge :)

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Re: 4:2:1 vs. 6:2:1 mixers / speed systems

Postby gwicke » Sun Nov 06, 2016 10:26 pm

kitexpert wrote:4:2:1 has become the standard because it is simple and works well. It makes possible to change AoA of the foil kite as much as it is usually needed and it allows to increase the camber at higher AoA.
AOA I agree with, but camber I'm not convinced about. My understanding is that the only substantive camber changes with a 4:2:1 mixer and close-to-even row spacing (current race kites) would be initiated by Z, especially with the Diablo line. This cambers the back of the foil more (B-C-Z), but keeps A-B-C substantially unchanged.
kitexpert wrote:You can say 6:2:1 changes camber more, pulling less B, but this can be understood as well lesser AoA change in that region. Here of course line row locations must be known for understanding what happens.
Slower AOA change along A-B is a good point, especially in very overpowered conditions with C and Z slack. A 50% larger bar stroke would be needed to cause the same A-B AOA change, compared to 4:2:1. However, at least some of this larger gust depower throw should be compensated by a flatter profile & thus less drag and power with 6:2:1, which would let the kite adjust its position in the window more quickly. Positioning B slightly closer to A (as done by Ozone and Fone) should also improve gust response in very overpowered conditions.

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Re: Why have most brands settled on 4:2:1 mixers over 6:2:1?

Postby socommk23 » Mon Nov 07, 2016 9:17 am

Keeping a flat wing profile is also a consideration for kite manufacturers. IN a world of double trailing edge cells, and cordwise ballooning, creasing the surface will induce unwanted drag. A fixed profile wing is designed to be slippery, anything that deviates from that design, ie leading edge profile hence the batons holding its aerodynamic shape, will be undesirable. A 6:2:1 will miss shape the skin and create drag.

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Re: Why have most brands settled on 4:2:1 mixers over 6:2:1?

Postby kitexpert » Mon Nov 07, 2016 12:18 pm

gwicke wrote:My understanding is that the only substantive camber changes with a 4:2:1
I'm not sure I understand what do you mean "substantive camber change", but there is just different pulling ratios (between the mixers) and different line row locations. 4:2:1 mixer is a linear one, so if line rows are located similarly (evenly from A), there will be no camber change when AoA changes. But if line row locations are chosen uneven manner it is possible to control camber when AoA changes.

Keeping line rows close to even spaces from each other is more reasonable than having them unevenly. Both for less drag and some structural reasons. Here 4:2:1 is better, and it is simpler too.
gwicke wrote:Slower AOA change along A-B is a good point, especially in very overpowered conditions with C and Z slack.
When overpowered and sheeted out foil kite flies very much on A lines only. Then only chosen airfoil defines how much camber there is. Usually it is quite low ("flat profile"), otherwise depower and stability are not available. I have test flied some of my kites with A line bridles only, it is the ultimate test for kite stability and depower.

Usually line rows are located a bit further from A than mixer pulling ratio would suggest. Then there is some more camber when sheeted in, which is useful (more power, later backstall). Exception is brakes, which can be at 95%, so they are pulled more than "should", again having more effect/camber (last 5% of the kite will follow).

Diablo line does this even more when it engages at the final part of the sheeting in. If kite tolerates it (no backstall) no doubt it is useful, especially at downwind legs.

If line rows are located evenly (for 4:2:1) then it is decided just AoA change is enough to power the kite. If lines B-C were located closer to A than pulling ratio demands, kite would decrease its camber at higher AoA - not a very good idea.


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