Wing theory

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ap73
ap73
VIC
43 posts
VIC, 43 posts
14 Oct 2021 5:40pm
Hi Brains Trust. I was wondering. Assuming everything else is held constant and only the size of a wing is changed. Will a 3m wing have a wind range twice that of a 6m? For example, if a 6m wing has a comfortable wind range of 8-16 kts then will a 3m of the same design have a comfortable wind range of 16-32 kts. I think spending too long in lockdown has muddled my mind. ?????
mcrt
mcrt
643 posts
643 posts
14 Oct 2021 2:56pm
ap73 said..
Hi Brains Trust. I was wondering. Assuming everything else is held constant and only the size of a wing is changed. Will a 3m wing have a wind range twice that of a 6m? For example, if a 6m wing has a comfortable wind range of 8-16 kts then will a 3m of the same design have a comfortable wind range of 16-32 kts. I think spending too long in lockdown has muddled my mind. ?????




Roughly,yes.
Lift= (WindSpeed x WindSpeed) x Sail Size

So those two sizes would give approximately the same low end power at 8&16 kt.
EDIT: Got the math wrong,it is 3m/11kt

But Wings are very difficult to "scale", meaning that the same design in different sizes is going to behave differently,bigger the gap bigger the difference.

Ps: if you are thinking of a quiver of 2 i would definitely go for a smaller gap, i ride 3.5 and 5m and that is gappy enough for me :)
kobo
kobo
NSW
1111 posts
NSW, 1111 posts
14 Oct 2021 6:17pm
Ooo no sure about that ....double the velocity and the force is 4x not 2x ....it's a squared relationship.
mcrt
mcrt
643 posts
643 posts
14 Oct 2021 3:48pm
kobo said..
Ooo no sure about that ....double the velocity and the force is 4x not 2x ....it's a squared relationship.



I think we are saying thevsame thing.
(WindSpeed x WindSpeed)= Speed squared

What i meant is he will get the same power from a 6m/8kt and a 3m/16kt.
EDIT: got the math wrong,it is 3m/11kt .

In theory,in practice it is not that simple.
Svendson
Svendson
58 posts
58 posts
14 Oct 2021 4:00pm
You got the principle right, but calculated the math wrong. All else equal, scaling just area and calculating wind speed from 6m/8knt, then it will be 3m/11kn. Squared relationship means if you halve the area wind speed increases by sqrt(2), not two.

As noted, all else is not in fact equal. Lift coefficients vary across wing sizes and even across wind ranges for the same wing (pesky flexible lifting generating devices), the rider and the board in the air quickly become the dominant source of drag as apparent wind increases, etc etc.
mcrt
mcrt
643 posts
643 posts
14 Oct 2021 4:09pm
Svendson said..
You got the principle right, but calculated the math wrong. All else equal, scaling just area and calculating wind speed from 6m/8knt, then it will be 3m/11kn. Squared relationship means if you halve the area wind speed increases by sqrt(2), not two.

As noted, all else is not in fact equal. Lift coefficients vary across wing sizes and even across wind ranges for the same wing (pesky flexible lifting generating devices), the rider and the board in the air quickly become the dominant source of drag as apparent wind increases, etc etc.


You are correct :)
ap73
ap73
VIC
43 posts
VIC, 43 posts
15 Oct 2021 11:11am
Thanks, that makes sense
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