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

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

Postby foilholio » Wed Nov 09, 2016 12:56 am

Kitexpert your simplistic view that 421 mixers give a linear change to AoA is just wrong. These are soft kites and there is ALWAYS a change to camber, even inflatables alter camber (and arc!), even things with carbon struts alter camber. I even think if you were to look at the relatively rigid wings on commercial airlines, you would see some twist and altering on the mm scale.

Back to topic here and it may have been answered, but why no 631?

Extra pulley and pulley line and the increased bar throw! such that the bar is less effective turning etc.

If you use a WAC you can get even higher ratio, without the pulley too, but higher bar pressure.
Last edited by foilholio on Wed Nov 09, 2016 2:47 pm, edited 1 time in total.

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

Postby jakemoore » Wed Nov 09, 2016 3:05 am

foilholio wrote:........your simplistic view that 421 ...........
NOT CONTSTRUCTIVE

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

Postby jakemoore » Wed Nov 09, 2016 3:08 am

4:2:1 changes camber when there is even spacing of bridle insertion points chord wise. The change in AOA at B is small in every case. Much more interesting to consider a situation where a 3:1 pulley occurs between C and Z, e.g. 6:3:1.

Leading edge is on the left on these plots.
Mixer1.jpg

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

Postby jakemoore » Wed Nov 09, 2016 3:33 am

WAC and Diablo Line Effects
Diablo WAC.png

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

Postby gwicke » Wed Nov 09, 2016 5:00 am

The "harmonic spacing" in the diagram with C at 50% chord seems rare in practice. I'm not aware of any current race kite that puts C forward of 1/3 of chord, and most are rather close to 1/4 chord.

To me, the camber induced by 6:2:1 plus Diablo line would be most interesting. With common row spacings, this should result in a more uniform camber curve than 4:2:1 plus Diablo. Bar pressure would also be a bit lower than 4:2:1 plus diablo.

Downsides of 6:2:1 over 4:2:1 mentioned so far:

- More complicated: Extra block and bit of rope.
- More bar throw needed for changing AOA in gusts when extremely overpowered (C slack).
- More creases at the extremes of trim (possibly on top side when extremely depowered, bottom when sheeted in).

I am honestly a bit doubtful about the creasing issue. If anything, I can only imagine this to matter when extremely depowered. Has this actually been shown to cause issues in practice, or is this more theoretical?

The extra bar throw / slower AOA change when overpowered on the other hand looks like a clear disadvantage. I haven't used my foil in so overpowered conditions yet, so can't comment on how much this matters in practice.

In any case, this is probably one of those questions that are best settled experimentally with two-boat testing, and the answer might depend on the particular kite. If anybody has already done such experiments, I'd be very interested in hearing about them.

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

Postby foilholio » Wed Nov 09, 2016 6:16 am

Jakemoore your Diablo line example is not accurate, both C and Z would be getting pulled at that extreme level. But otherwise you have just proven what I said, that the camber always changes,i.e kitetwit is wrong, no surprises there. You also need to consider that the spacing is not 100% static, the fabric can curve and compress etc, particularly between C and Z.

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

Postby jakemoore » Wed Nov 09, 2016 8:03 am

It looks to me like you could design a kite that had a constant camber: 4:2:1 mixer with a harmonic bridle spacing. I doubt that would be a good kite especially if it had a reflex profile. The current 4:2:1 kites do indeed change camber via the mixer.

The chart is magnified in the Y direction to make the differences visible. e.g for a speed 5 12 M the horizontal axis would be stretched to 3 times the width illustrated here. I also chose straight connecting lines to make the change in camber evident. Clearly the lines do not represent the shape of the airfoil, and the idealized bridle gallery spacing here does not represent a particular brand of kite. The original Speed series was closer to the "harmonic" spacing with B very far forward, while newer kites are closer to even spacing.' Speed 2 had 6:2:1 with B farther forward.

Agree that the effect of the fabric curving and soft profile is going to make the brake boosters look a lot like a fixed bridle race kite with pulled breaks, with the biggest change in curvature toward the rear.

The point is going from 4-2-1 to 6-2-1 changes the total movement of the B gallery by only a few centimeters, an effect that is less meaningful with kites that have the B gallery moved farther to the rear.

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

Postby jakemoore » Wed Nov 09, 2016 8:37 am

gwicke wrote:If anybody has already done such experiments, I'd be very interested in hearing about them.
I did with the speed 1. Could be different today but my findings are that: Movement in B is most useful to steer a depowered kite. Changing B from 2:1 to 3:1 is going have a small effect, mostly on reducing depowered turning. Movement in C and Z are where the money is regarding stability, power and backstall.

If I had the gumption to mod a kite today I would consider:

Adding a Diablo line, possibly in conjunction with shortening C main to create an over stable profile depowered and reduce the exaggerated brake line when powered.

Adding a WAC line, probably in conjunction with shortening B main. The effect is B is fixed to A and not over sheeted while the kite is powered. The movement in B occurs as the kite depowers, increasing B turning while depowered.

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

Postby foilholio » Wed Nov 09, 2016 2:46 pm

If you mean try 421 and 631 on the same kite? Yes I have. 421 is more responsive with less bar throw, the two are not exclusive. 631 offers higher camber, lighter bar pressure. 631 could work for racing.

@Jakemoore I just noticed your mention of 621 and 631, I think what we are talking about is 631, otherwise I would like to know how the setup is different on 631 and 621. Looking back at the OPs post yes what we are discussing is 631 vs 421. Big fail understanding how to write ratios is at hand, I fell into it as well. :roll: :roll:

6Z to 3C to 1B , 6:3:1, 631. etc easy

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

Postby jakemoore » Wed Nov 09, 2016 8:48 pm

I'm not sure there is a convention?

I think of it in terms of fraction of bar travel for a mixer gallery, B,C,Z. Not sure OP, you and I are on the same page there?

4:2:1 I think of Psycho 4 - 1/4 A : 1/2 B : 1/1 A Most of the speed 1 mods were done this way.
6:2:1 I think of Speed 2. - 1/6 B : 1/2 C : 1/1 A
6:3:1 I think of my mod for Speed 1 which differed from most other mods and kites. IMO the gallery spacing worked better with a 3:1 pully between C and Z with that Speed 1.

I assume OP was talking about modding a kite to look more like a more common Speed 2 mixer? I think going 3:1 on C is going to be a more noticeable difference in flight than going 3:1 on B.

I would consider modding to a 3:1 between C and Z for a kite that had a high tendency to go from unstable to backstall, e.g. some of the smaller race kites?


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