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Disconnecting Z or more at the tip

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bohme
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Re: Disconnecting Z or more at the tip

Postby bohme » Tue Mar 19, 2019 10:54 am

The best lift distribution is not necessarily 'elliptical'
Try google "bell shaped lift distribution". Unloading the tips can reduce induced resistance.

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Re: Disconnecting Z or more at the tip

Postby foilholio » Tue Mar 19, 2019 2:59 pm

Interesting thanks for that. There is some quite complex articles on the subject. I was thinking of airplane wing washout when I started with this and before with letting Z out at the tips. I just read that reduced lift at the tips can have a quite dramatic effected on induced drag. I can confirm this is my experience so far. Obviously rigid wings don't have the structural limits of foils. As I was reading to have negative lift on the tips or even the end 1/3 of the half span, having negative lift on a foil is not going to work. I am wondering now that many foils use B at the tips to pull on an A position, which should reduce lift maybe, but then would increase the ratio and with it camber. My general experience is the tip is always over cambered because of the shorter cord. I think cambering the tip offers great benefits to turning, but runs completely opposite to this bell curve. Some long time ago I was told or read it is bad to camber the center of the kite over the tips. This info is counter to this bell curve and even the elliptical model. I can only guess it is in relation to turning.

My further testing with Pyscho 4 , I definitely feel a great improvement to L/D and stall. The stall point seems to move quite a few inches in on the bar. The Pyscho 4 is quite a stally kite. I would think there seems a compound benefit because as it can hold a higher AoA it can also seem to flatten it's PA more, maybe contributing more power. I am still not used to the jumps with it, might need to adjust the trim some.

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Re: Disconnecting Z or more at the tip

Postby kitexpert » Tue Mar 19, 2019 4:46 pm

bohme wrote:"bell shaped lift distribution"
I didn't google but something like that?


Image

Hansen Design
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Re: Disconnecting Z or more at the tip

Postby Hansen Design » Tue Mar 19, 2019 5:12 pm

I have made a number of RA foils with reduced or no bridling at the tips to allow them to self-align reducing drag and tip tuck.

kitexpert
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Re: Disconnecting Z or more at the tip

Postby kitexpert » Tue Mar 19, 2019 8:09 pm

Hansen Design wrote:
Tue Mar 19, 2019 5:12 pm
I have made a number of RA foils with reduced or no bridling at the tips to allow them to self-align reducing drag and tip tuck.
Interesting to hear as always :wink: Was there any drawbacks noticed? Wingtips without bridles make some sense but I haven't take it further than one cell.

For sure there is room for experimenting with this idea also.

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Re: Disconnecting Z or more at the tip

Postby Hansen Design » Tue Mar 19, 2019 8:48 pm

For the limited design brief, none. It is a worthy improvement.

kitexpert
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Re: Disconnecting Z or more at the tip

Postby kitexpert » Tue Mar 19, 2019 9:33 pm

Hansen Design wrote:
Tue Mar 19, 2019 8:48 pm
For the limited design brief, none. It is a worthy improvement.
Ok, good to hear. I'll make some designs with moderate cell counts and sizes and perhaps complete one if it looks promising...

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Re: Disconnecting Z or more at the tip

Postby foilholio » Tue Mar 19, 2019 10:26 pm

You should google it Kitexpert. It is not that the kite is bell shaped but the lift distribution. The largest lift is at the center with little, none or negative lift at the tips or actually more than the tips. If you don't support the LE of the kite like with an A bridle it will most likely increase AOA and lift, which has been my experience.

If I think about this a bit more, this will work with not against the vortexes created and would then make sense that it has less drag. The last third from center also makes sense with reference to vortexes.

kitexpert
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Re: Disconnecting Z or more at the tip

Postby kitexpert » Tue Mar 19, 2019 10:47 pm

foilholio wrote:
Tue Mar 19, 2019 10:26 pm
You should google it Kitexpert. It is not that the kite is bell shaped but the lift distribution. The largest lift is at the center with little, none or negative lift at the tips or actually more than the tips. If you don't support the LE of the kite like with an A bridle it will most likely increase AOA and lift, which has been my experience.

If I think about this a bit more, this will work with not against the vortexes created and would then make sense that it has less drag. The last third from center also makes sense with reference to vortexes.
Yes I did it and of course I know what it meant. Actually many of my kites have been like that by lift distribution because I've used airfoils morphed to small or even negative camber in wingtips.

I was designing that one a bit tongue in cheek attitude, but I don't know if it is so bad or wrong. It looks a bit weird though. If there is no bridle support at the wingtips they will turn up any way, this can be seen in all FS kites which have it. In practice I am a bit worried if two last cells without bridles is too much, will they keep their shape or not.

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Re: Disconnecting Z or more at the tip

Postby foilholio » Wed Mar 20, 2019 4:30 pm

I had guessed you were part joking as with other kite mock up pics you post. Unsupporting the LE of the last 2 cells on the A15 causes it to turn up and degrade performance. If the end cell/s were turned up and designed more like winglets then maybe they would hold shape better and also infer winglet benefits.

I tested the A15 on water with no 1 Z a few times and I am not noticing the same benefit change as the Psycho 4. Because I have extended Z so much at the tip already the kite has Z slack for a lot of it's AoA increase. Z can still engage at higher AoA giving more power and tighter turn. It would seem like this much of the benefit of disconnecting can be had while limiting the negative. The kite did have a large reduction in stall with no 1 Z though. I also think because of the 3 split bridle there, disconnecting the tip would shorten the next bridle in effectively, so I would need to lengthen it. Also the ABCZ positions are quite different than the Psyscho4. So more adjusting and testing I think.


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