Cycloptichorn wrote:No - drag on the wheels should match thrust from the propeller + thrust from the sail in a perfect world...
If drag on the wheels = propeller thrust + wind thrust, then the thing would never accelerate. Propeller thrust + wind thrust would never overcome the drag.
I really don't believe that this is true. Take the example of an iceboat. It clearly overcomes the drag in order to accelerate. It does so by using the stiff keel of the runners to cancel out some of the force vectors while harvesting others, and the sail-suck effect does the rest.
This is the exact same thing! Except the nature of the propeller means that you can face any direction you want, and still have your sail tacking the wind.
Watch the video that I linked above - even if you don't believe it's going faster then the wind straight downwind, it's clearly accelerating.
Into the wind is trivial. Wind blows on wind vanes, wind vanes turn, transfers power to the axle.
You could do this with direct power transfer, or you could convert to electricity first, then run an electric motor.
Your speed is limited by the size of the wind mill you have attached to your vehicle. Bigger windmill = more power.
I'm saying that I don't believe it when they say it will run steadily at 2.85 times the average wind speed.
So, the car is now moving at equal speed to the wind (from directly behind) and the wheels are turning. Your contention seems to be that there's no way that the force of the wheels turning could possibly provide more thrust out of the propeller then it slows down thrust due to increased drag on the wheels.
But it does in fact do this - because the spinning propeller tips actually provide an angled surface for the wind to push against, as well as the additional thrust due to air which is pushed backwards by them - at least, if I understand this thing right.
Like I said, peep the videos - the thing clearly accelerates.
Quote:I'm saying that I don't believe it when they say it will run steadily at 2.85 times the average wind speed.
This is a complex argument, so it's important to be accurate. The creators did not claim that it would run steadily at 2.85x the wind speed; they claimed that this was the TOP velocity it hit, the absolute peak.
-- the spinning rotor is a propeller, not a turbine
-- the wheels provide the torque to turn the rotor (always).
-- the rotor does not provide the torque to turn the wheels (ever).
-- it will take off from a standing start on it's own.
-- we sometimes push it up to speed to save time during testing
-- there's no "null point' at windspeed.
-- It will maintain it's speed well above wind speed indefinitely
-- By design, this particular one works best when aimed directly downwind.
-- One can be built to go faster than the wind in any direction
-- A simple gearing change will cause it to go upwind rather than down
These are the two claims I have trouble believing.
Unfortunately, much of the room is out of the frame. It would be trivial to place a fan at the base of the treadmill during the initial exposition, and have it blowing up the treadmill for the rest of the demonstration.
Hi folks. I'm one of the two primary designer/builders of the craft in question.