terrafirma
Super Anarchist
This must of been the Jetskier..! https://www.facebook.com/652246773/videos/10159073663686774/
His behavior confirms your theory..! LOL
Team NYYC
- Thread starter Barnyb
- Start date
His behavior confirms your theory..! LOL
Ex-yachtie
Super Anarchist
Watched AM and LR train while having a swim off the bays this afternoon. I feel better now.Hot and bothered?
Tell us how you really feel Ex...
barfy
Super Anarchist
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Awesome!!! I chased errant cows through deep bush in 28 degrees for three hours. Swim tomorrow..or kill fish
MaxHugen
Super Anarchist
In this Span Squared | North Sails article they illustrate that the 'reflected' span is included in "span" measurement prior to the drag calc. Span in my calcs is sail height, so now I've doubled it before it gets squared. Seems right, the drag distribution is looking far more realistic:
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Board skiff
Super Anarchist
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That North article is good, and it is ultimately span that matters not AR. But end plating one end of a foil will not quadruple the effective aspect ratio. In reality it won’t even double it. See NACA Tech Note 2440, Table 1 for example. http://naca.central.cranfield.ac.uk/reports/1951/naca-tn-2440.pdf
MaxHugen
Super Anarchist
Hmmm... that's from 1951.
North Sails appears to use Span*2 (shown as 'b' below) but there is no specific reference to end-plating of a sail.
Not easy finding anything specific on this topic!
MaxHugen
Super Anarchist
Quite agree, have to recheck the calcs for that. I have equations coming out of my ears! :wacko:
The "Spray" is also a bit suss I think.
Board skiff
Super Anarchist
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Max, it doesn't matter how you calculate AR - whether you use span / mean chord or span^2 / area. It's the same thing once you replace area with span x mean chord.
When you double AR assuming a perfect seal under the sails, you can use 2 x (b/c) or 2 x (b^2/A) or [(2b)^2] / 2A. It all gives the same number.
buckdouger
Anarchist
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Sailbydate
Super Anarchist
It would seem the imminent death of ITUK has been greatly exaggerated.
Good line speed and pretty sharp in manoeuvres too.
Good line speed and pretty sharp in manoeuvres too.
MaxHugen
Super Anarchist
It makes a huge difference when calculating the Di using the equations from @Basiliscus. As per my original query, applying a doubling of the Span before or after squaring is quite crucial for balancing longitudinal forces etc, since I'm calculating these myself.
They are mathematically the same thing. If you are getting different results, then there is an error somewhere in your calculations. Just put some numbers in the three versions I posted above. You should get the exact same AR with either of them.
MaxHugen
Super Anarchist
The equation I'm using is exactly as presented by B - which as he explained, does not use non-dimensional values such as AR, CL, etc:
Di = Lift2 / ( PI * e * 0.5 * Density_Air * Velocity2 * Span2 ) I have changed the Span part to (Span*2)2.
Would be interesting to know how Vortex handles end-plating re Span when calculating Di - to double or not, or use a deduced 'factor' instead?
MaxHugen
Super Anarchist
OK that's just written in a different form, but it's the same thing as calculating cdi first as cdi = cl^2 / PI * e * AR , and then Di = 0.5 * cdi * dens * A * v^2
So using your version, the (span*2)^2 is correct if you want to double the AR.
Vortex does handle end-plating, you have to specify if the wing is on a solid surface, but in addition to that and the AR, it also considers the shape of the planform (which is factored in as 'e' in the other equation). The advantage is that you can input the dimensions of the whole rig (jib and main), so I think it's more accurate than calculating induced drag separately for each sail.
