Calculations below are all nonsense. You need to do a basic physics course.
Your original calculation of the force on a 25sq.m wing was correct with Cl of 1 was correct - 922N. Actually achieving a Cl of 1 is another matter. I suggest you work on 0.7 for a single wing. A twin wing set up could exceed 1 but at the cost of efficiency.
Here is some reading for you on power:
For a moving boat the relevant relationship from that page about half way down is:
In one dimension, this can be simplified to:
Note that this is the vector product so it has to be the force in the direction of movement.
The air speed is only relevant to producing the force on the wing. From a power perspective it is the force in direction of travel to overcome the drag on the boat in that direction and the velocity through the water.
I was being generous with respect to the speed. I assumed the 5mph or (2.1m/s) was actually in the direction you wanted to travel. If you were wanting to go directly to windward the 5mph drops down to about 3.5mph as VMG. It is inevitable that the average cruising boat spends more time on the wind because the VMG is about half the speed it can do reaching. Also more time is spent running than reaching - even if the boat can exceed windspeed on a reach and tacks downwind its VMG downwind is lower than reaching. So there is not much time that a sailing boat will actually be on its fastest point of sailing.
On 09/01/2016, at 5:41 AM, "taladorwood@yahoo.com.au [harryproa]" <harryproa@yahoogroups.com.au> wrote:
I think I see one of your problems. You are assuming that the boat sailing at a 20˚ angle is going 5 mph. Why are you making that assumption? And then using the boats velocity to determine force? Drag maybe.I was careful just to compare a single force being generated. The velocity of the boat has little (none) relationship to how fast the boat is being accelerated.Force = Mass times Acceleration, not Velocity. In other words Force = Mass times the change in Velocity. So can you see why even with your 5 mph assumption, your math is wrong? 1 N = 1 kg x m/s^2I am also concerned that my hp calculations of the wings lift are wrong^^ Obtaining the lift (force) is easy, 912 kg m/s^2 which is a kilogram-force meter second which multiplied by 9.8 m/s^2 gives Newton meters or Watts directly. So a 912 kilogram-force m/s^2 equals 8,900 watts or 12 hp.I think I was wrong about the 911 n it should have been 8,900 newton meters. Now all the numbers make aproximate physical sense to me and my real world observations.Back to the example, It appears that all of your power calculations are off by a factor of 9.8. Sorry about my contribution to your error.Talador
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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