Tiger Tiger.
You are absolutely correct - I was not meaning any disrespect to Ivor, who is clearly a highly intellient gentleman. There is a lot of good information on his site and obviously he has developed his ideas with lots of empirical testing.
But I'm afraid some of his conclusions are based on wrong assumptions...
I am aware that I now need to explain why I say that - and yes that will require some effort on my part! But I don't want to hijack this thread either.
Briefly - his assumption on the operating alpha (angle of attack) of soft sails is not accurate - it is based on a misunderstanding of the apparent wind vs true wind. He says that all sails are stalled and the operating alpha is at least 35 degrees. That is demonstrably not true (and I would happily take anyone out on my sailing boat to demonstrate)
Ivor's recomendations for downwind sailing do not follow the method used in full size wingsails where the sail is still set up for a low alpha and lift is still produced as well as drag. This condition is hard to visualize but is shown here
www.omerwingsail.com/driving-force/The use he makes of the airfoil data is a little rudimentary - calculating Lift coefficients and angle of attack from wind tunnel data requires careful attention to the reynolds number of the wing and also a correction for aspect ratio. These formulas are in the public domain.
Many of the aerodynamic interactions between the sail and the trim vane are directly affected by the position of the pivot point for the sail, which (as far as I can see) is not given on the site. In aircraft design this point is analogous to the centre of gravity.
I want to re-iterate that I mean no disrespect to the gentleman, but I just wished to point out that the site is not definitive and I would use it with appropriate caution.
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Topic: Wing Ray design (Read 5902 times)