Originally Posted by DynaMeme
For airplanes which have low speed performance requirements there is a concept called ventialted slots or blown flaps. In this case a blower, not a fan, blows air across the leading edge of the wing or flap. THis is done to insure the air flow stays attached -- preventing stalling -- and allowing the aircraft to fly much more slowly and land in shorter distances.
This concept has been experimented with on sailboats. Rigid sail catamrans in particular.
The issue is power requirements. Such a blower on a sailboat would have energy requirements that would be at least as demanding as a motorsailors.
However, boat's such as Cousteau's Alcyone did consider spinning their rigs using power until natural forces took over.
Thanks for the response. The question is not purely theoretical. I'm considering it both for sea cruises and transport and for aircraft to improve fuel efficiency and travel times.
It is known with motorsailers that you could improve fuel efficiency and speed by having the propeller in water operating at the same time you are using the sails.
Because of this fact if you used a fan not blowing over the sails but blowing rearward from the stern, you would likewise get better fuel efficiency and speed.
But it seems to me by placing the fan at the front so that it blew over the sails, the apparent wind speed would be even greater so the fuel savings and speed should be greater than for the fan at the stern.
I don't know how much greater though. Might it even be large enough to match or exceed having a propeller in the water?