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Disconnecting Z or more at the tip

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foilholio
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Disconnecting Z or more at the tip

Postby foilholio » Sat Mar 16, 2019 3:16 pm

So I was looking at the FS Race line plan to check exactly what they were doing with their mixer and 3 bridle row design and I saw this.
fsracetip.jpg
fsracetip.jpg (11.29 KiB) Viewed 724 times
So you can see the tip doesn't have any Z for 3 cells, B for 2 and A for 1. Factor that this kite has thin cells compared to some others then would other kites benefit in some way from a similar setup?

So far I have tested the A15 just flying with 1 and 2 Z disconnected and also C. I didn't like C disconnected. I noticed a loss of static power with 1 Z and more with 2 Z, an improvement in L/D and less stall, maybe more power with faster flight. I think 1 Z is better but I will need to test it more.

I have tested on water a few times a Psycho 4 with 1 Z disconnected (of note the Psycho 4 Tip C is at B position, so no real C there). I had a quite noticeable improvement in L/D, reduction in stall, more power flying, faster kite, faster through the turn, more glide in jumps, higher upwind. The kite turned less tight, had slightly lighter bar, little less responsive, had less static power, less peak power jumping. The kite behaved significantly different jumping, and it threw all my timing off. The glide was great, but lack of height not the best but could be just timing related. I found the flying much quicker so I was missing loops at the right spot. I don't usually look at the kite but after a few bad landings I saw that was the problem.

When flying the kite and sheeting it there is a noticeable deflection away at the tip, more so the more the kite is sheeted. I would say about 6 inches near stall, way past that after and in turns. With highly efficient fast flight with peak power the deflection is maybe 1 inch and the kite is quite able to hold it's shape flat in some flight when not sheeted much.

What it seems we have here in some part is an actual antistall device, like what the jetflaps promised but this works :-) Well done Flysurfer. It definitely does something and seems to improve performance in a significant way to be useful. The most noticeable thing to me is the improvement in upwind and power with flying fast, seems to give an actual improvement in lowend and I can see why a race kite would want this, but also maybe anyone chasing the very low end ( ring ring Regis :-) )

How and why does this work? Well I know for a while now that loosening Z more at tip so to prevent over cambering there, improves L/D. If you have no Z this can never cause a problem. It also seems obvious that the tip is free to allow air to flow or bleed back which would prevent a stall, makes a nice oversheeting indicator too. There is precedent in winglets, but also nature where birds have very flexible tip feathers.
eagletipfeathers.jpg
A very cool and interesting development and easy to try out (sorry Ozoners :-) )

What should it be called? I scanned the FS Race page but no mention. Maybe Flexible Tip Technology aka FTT?

I certainly think there is potential and more development to be seen with this. Go try it out.
Last edited by foilholio on Tue Mar 19, 2019 12:12 am, edited 2 times in total.
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Brian H
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Re: Disconnecting Z or more at the tip

Postby Brian H » Sat Mar 16, 2019 4:13 pm

Take a look at Little Cloud paragliders , there wing tips flair out .

foilholio
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Re: Disconnecting Z or more at the tip

Postby foilholio » Sat Mar 16, 2019 4:27 pm

Interesting. Looked a bit like one had winglets like the sonic has. Can definitely see the tip flare on their gliders as in the pic. I think on the Psycho4 it has more of the tip doing it. Would think that paragliding wouldn't hit stall angles as much as kiting.
EZlittlecloudtipflare.jpg
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Re: Disconnecting Z or more at the tip

Postby kitexpert » Sat Mar 16, 2019 10:25 pm

These kind of things should not be overestimated or thought to have essential effect on how kite flies. Real explanations for L/D, performance, agility, stability etc. are much deeper than in the bridles.

As long as kite looks clean and changes AoA reasonably with the bar movement kite is quite close that performance it is capable of. Some fine tuning afterwards is possible, but if some qualities then are improved some are worsened.

Tweaked kite is always inferior to a kite that is designed to be that kite (goal of tweaking) in the first place.

To not have bridles at the wingtips is reasonable because last cell is often so small. Wingtip cell doesn't have a rib at the tip so having bridles there may cause creases etc. because there isn't much structural rigidity there. In PL arcs wingtips have sticks for support but having them in foil kites would have their own problems.

Unbridled wingtips allow two extra cells "for free" in bridle design point of view, that is perhaps 5% advantage.

Thin wingtip with a short chord is a challenge to fit for same pulley ratios than much wider center of the kite has. In VMG wingtip is left unbridled because it is so small, it is just an end to a wing and smooths airflow best it can. If there was Z bridles at the wingtips pulling them normally 1:1 would be too much. Moving last bridles towards center, to wider chord ribs helps.

Very probably braking effect for last Z bridle reaches wingtip well enough in VMG. For mid AR kites with wider wingtips having no Z at the wingtips wouldn't be a good idea because turning speed would suffer.

foilholio
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Re: Disconnecting Z or more at the tip

Postby foilholio » Sun Mar 17, 2019 12:43 am

Turning speed is not everything, this seems to fly through the turn faster but not as tight. Main beneficial effect from this would be reduced stall and improved L/D.

No need for overestimation or estimation at all, this can be tested quite easily, well on kites with LCLs that is, just disconnect the Z tip bridle and maybe the C if it's near the last third.

The VMG mixer setup is not so straight forward, it pulls on A at the tips and B more at the tips.

I think for mid AR this is quite applicable and maybe even for low AR. The desired flight qualities are obviously a factor, but this expands them in a direction. Strange the industries obsession with turning. Slower turning kites are just fine and infact desirable by some of the best in the sport.

Interesting you raise PL Arcs, they had unsupported tip TE and I think that flared a bit.

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Re: Disconnecting Z or more at the tip

Postby kitexpert » Sun Mar 17, 2019 12:16 pm

foilholio wrote:
Sun Mar 17, 2019 12:43 am
The VMG mixer setup is not so straight forward, it pulls on A at the tips and B more at the tips.
Yes, that is because of tips have so small chord in VMG, pulling A reduces pull of B and Z relatively. Pulling A very probably help kite to turn faster.
foilholio wrote:
Sun Mar 17, 2019 12:43 am
I think for mid AR this is quite applicable and maybe even for low AR. The desired flight qualities are obviously a factor, but this expands them in a direction. Strange the industries obsession with turning. Slower turning kites are just fine and infact desirable by some of the best in the sport.
Like I wrote that does not sound reasonable. Low-mid AR kites have that much chord at the wingtips it is not a problem to pull them at normal pulley ratios, it just help these kite turn faster.

Most people like kites that react and turn fast, especially big majority who has used to LEI's feel slowness of foil kites a problem.
foilholio wrote:
Sun Mar 17, 2019 12:43 am
Interesting you raise PL Arcs, they had unsupported tip TE and I think that flared a bit.
IDK what this means, wingtip sticks in Arcs go from LE to TE, wingtip is tensioned and rigid.

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Re: Disconnecting Z or more at the tip

Postby foilholio » Sun Mar 17, 2019 2:26 pm

Some did and didn't, the very popular Venom 1 and 2 I was thinking of didn't.
venomtip.JPG
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jakemoore
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Re: Disconnecting Z or more at the tip

Postby jakemoore » Sun Mar 17, 2019 3:47 pm

There was a time when open cell fixed bridle race kites advertised inboard braking. I think for example Ozone Razor. Maybe this is an extension of the same idea?

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Re: Disconnecting Z or more at the tip

Postby kitexpert » Sun Mar 17, 2019 8:25 pm

foilholio wrote:
Sun Mar 17, 2019 2:26 pm
Some did and didn't, the very popular Venom 1 and 2 I was thinking of didn't.

venomtip.JPG
Ok, I didn't remeber that. Since Chargers came I've using only them and quite rarely. Actually I was out with 12m Charger couple of weeks ago and I have to say it is not competitive kite in general. It goes fast though and loops ok, but for example auto-zenith needs constant guiding it doesn't fly straight for a second when park and ride. Feeling compared to a LEI is wobbly, not precise.

Idea why VMG don't have bridles at the wingtips is they don't need it.

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Re: Disconnecting Z or more at the tip

Postby foilholio » Tue Mar 19, 2019 12:10 am

Arcs have lost most of their advantages as other kites improved more.

The width of the cells is something I alluded to. I would think it is something affecting how well the cells can hold without bridle support. I did some measuring of images on the net so a bit approximate. The span of cells of Race 18m at 3 unsupported z cells is 24.5cm, while A15 18m with 1 Z is 36.5cm, Psycho4 15 with 1 Z is 35.5cm and Soul 18m which currently has 1 Z at 17.5cm. I would guess from the Soul and the Race that around 20cm unsupported is considered ok by Flysurfer. I would think the lower AR kites with thicker cells could support a slightly wider gap. In that regard I don't think the 2 cells on the Mid AR like Psycho4 or A15 is pushing it. But you could bring it to slightly below 20cm by moving the attachment to next to the last cell.

That all said I definitely think some of the advantage to disconnecting the tip cell is that it can flex. How much and where is a big question.


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