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Rider weight versus foil classification (wind range)

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Dave K
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Rider weight versus foil classification (wind range)

Postby Dave K » Mon Apr 16, 2018 9:39 am

I’m really just trying to better understand the effect of rider weight on all these expanding foil sizes/categories. Seems like there is more of a blurred line between free ride kite foils and smaller SUP/surf foils, and line gets even more blurred by the effect of rider weight. Would a smaller size sup/surf foil really be the full equivalent of a free ride kite foil for someone closer to 100 kg versus someone closer to 60 kg

I’m around 90 kg and ride an RRD H-flight, which is actually a wee bit smaller than the standard Hoverglide a fellow 68 kg rider uses. If I got a bigger foil (Shinn P, Impulse, Flight 150, etc) am I really forced to ride slower and/or in lighter winds than my lightweight friend on the Hoverglide? Do shape/profile differences of the larger foils have a big impact? What size kite foil are you bigger free-riders on? Thanks for any input

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Re: Rider weight versus foil classification (wind range)

Postby slowboat » Mon Apr 16, 2018 10:21 am

I don't think rider weight (within reasonable weights) impacts the performance of a foil as much as other factors such as wing aspect ratio, thickness, camber, fuse length, etc.

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Re: Rider weight versus foil classification (wind range)

Postby Dave K » Mon Apr 16, 2018 12:14 pm

slowboat wrote:
Mon Apr 16, 2018 10:21 am
I don't think rider weight (within reasonable weights) impacts the performance of a foil as much as other factors such as wing aspect ratio, thickness, camber, fuse length, etc.
I get your point, but do the shape/set-up factors change that much from large kite free ride to small SUP/surf, that a big weight change has little impact? Not quite believing that. What is the stall and top speed difference for a 60 kg person versus a 100 kg person on the same foil, for different foil types? Anyone/manufacturer tried to seriously quantify that?

Zeeko makes different size versions of the Spitfire. I assume a big part of that is rider weight. Lift does a 110, 150, 170 range. But your average “starter” foil is a one size fits all.

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Re: Rider weight versus foil classification (wind range)

Postby slowboat » Mon Apr 16, 2018 12:54 pm

Dave K wrote:
Mon Apr 16, 2018 12:14 pm
slowboat wrote:
Mon Apr 16, 2018 10:21 am
I don't think rider weight (within reasonable weights) impacts the performance of a foil as much as other factors such as wing aspect ratio, thickness, camber, fuse length, etc.
I get your point, but do the shape/set-up factors change that much from large kite free ride to small SUP/surf, that a big weight change has little impact? Not quite believing that. What is the stall and top speed difference for a 60 kg person versus a 100 kg person on the same foil, for different foil types? Anyone/manufacturer tried to seriously quantify that?

Zeeko makes different size versions of the Spitfire. I assume a big part of that is rider weight. Lift does a 110, 150, 170 range. But your average “starter” foil is a one size fits all.
I think your questions are reasonable but you are leaving out the variable of kite size. For a given foil in given conditions, a heavier rider will use a larger kite which will help decrease the effect of body weight on foil "performance".

For SUP foiling, body weight is a much larger (and possibly dominant) factor.

Having said all that, I don't think there is much quantification going on out there at all besides dubious claims of max speed and some claims on minimum speed.

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Re: Rider weight versus foil classification (wind range)

Postby Sandras » Mon Apr 16, 2018 1:18 pm

Explaining why the weight of the rider has smaller influence on the HF compared to a twin tip or compared to other parameters of the wing is technically very interesting.
I believe It will involve angles of attack, L/D vs AoA etc...

The heavier you are, the more angle of attack you need to have. This will work volumes on your lift, while drag will be little increased

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Re: Rider weight versus foil classification (wind range)

Postby BWD » Mon Apr 16, 2018 1:34 pm

Riding at higher angle of attack means closer to stall.
Especially with more weight because the weight means higher surface loading.
So I think the variable to focus on is speed.
For heavier weight, a given foil has to make more lift to take off.
To make more lift, it has to go faster.
It’s similar with airplanes, heavier/full plane uses more of the runway to take off, and is going faster by hw time it leaves the ground.
The ultimate top end may depend more on the specific design of the foil, but somewhat as noted before, if you are using a bigger kite and applying more force to drive a given foil, you will be going faster, most of the time.
Of course there are many other variables that will
come into play as well. But the basic principle of more weight=>more speed to lift should hold.

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Sandras
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Re: Rider weight versus foil classification (wind range)

Postby Sandras » Mon Apr 16, 2018 1:56 pm

BWD wrote:
Mon Apr 16, 2018 1:34 pm
To make more lift, it has to go faster.
How will he go faster?
And what determines the speed?
Does drag play a role in this equation?

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Re: Rider weight versus foil classification (wind range)

Postby Foil » Mon Apr 16, 2018 2:23 pm

There are 5 of us all using the same wings masts stabs from Moses, some of us have a few wings to choose from but very close in sizes, apart from two of us who now have the Onga surf wing kit as well,however when we are all using the standard moses kit the only variable is our weights, Kat is the lightest (being a female) I am guessing quite light.
our largest rider-Wayne, is robustly built and wears xxxxL T shirts on his 6ft frame,the only difference we have noticed is that the lighter you are the smaller the kite you may choose, but unlike when using a Twintip the difference is minimal, if lightweight kat is using a 8mtr then the heavier blokes can also either use similar or go up one size, and wayne who is twice kats size may use only one kite size up or 2 at the most. all this with exactly the same front wings the 550 and standard stabilizer.
What is very different is when the Moses 633 Onda set up is on the water, this changes our choice of kite size, I will now choose 1 or 2 kite sizes smaller than I would for the standard wing set up, the massive lift and crazy low stall speed allow this, so because of this people who are not up to the standard of a pro racer can easily enjoy stylish carving and turns without the fear of being splattered all over the surface of the water, which is the reason why my flying gybes came along in fine style very quickly once I bought one.

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Re: Rider weight versus foil classification (wind range)

Postby BWD » Mon Apr 16, 2018 5:28 pm

Sandras wrote:
Mon Apr 16, 2018 1:56 pm
BWD wrote:
Mon Apr 16, 2018 1:34 pm
To make more lift, it has to go faster.
How will he go faster?
And what determines the speed?
Does drag play a role in this equation?
At any reasonable small angle of attack, a foil will make a certain amount of lift at any given speed.
If the speed is not enough to cause the foil to make lift force greater than the rider+gear weight, the foil will not lift the rider, he will keep going on the surface.
Once the speed is reached that produces enough lift, the foil will lift, without any extra back foot pressure/angle change.
For a heavier rider, the speed is higher.
Think about the airplane example....

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Re: Rider weight versus foil classification (wind range)

Postby Sandras » Mon Apr 16, 2018 6:15 pm

OK, you omit that the kite carries a part of riders weight but this is not my point.

My thinking is the following and please correct me as I may be wrong:

What determines the steady speed in foiling mode?
The vector sum of forward pulling forces will equal the drag.
As we see in the previous graph, there is a big area where the cd remains almost constant while cl increases a lot.
Therefore, a heavier rider just needs a bit higher angle of attack at the same speed. (as long as he does pass the cd apex)

Wings with fatter leading edge have longer area where cd is constant. (greater usable angle of attack range)

This is the explanation the op was looking for.


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