[harryproa] Re:: Re: Wingmast Stuff

Gary - "the angle off attack along the height of a mast section varies, soft sails easily deal with this through twisting, but a wingmast does not generally twist very much. I could go on at length but suffice to say that there are some big gains to be had here."

My 'solution' to the difference between the apparent and relative wind (twist) is a compromise, but let me explain my conjectures first.

My understanding is that the apparent wind at the base (lower velocity wind) moves forward faster than the upper (higher velocity wind) as the boats speed increases. The mast then sees the apparent wind at different angles going up the mast.

My research indicates that 2 meters above the wave tops there is very little wind gradient. The boat itself though is an impediment to the wind and has to be considered.

For a sailboat with triangular sails this is a huge issue because the majority of the sail area is in the lower, slower air, next to the boat and starting under the 2 meter mark. This is why the tell-tails love to stream upward and probably a major reason why sails are draggy and also determines a boats pointing ability. Triangle shapes are mother natures revenge for giving us the wing.

If I start the wing high enough above the boat, I think it avoids the wind gradient issue / twist problem all together. Of course there is a cost of vortex loss at both ends, but the control and stall issues (a separation stall will spread up the wing) are taken care of and the entire wing can now be set at the appropriate angle.

Gary - " “What would Bert Rutan do ?” :-)"

Burt would build an amphibious airplane.

A Legendary Airplane Designer Hints at His Next Creation