DrieStone

Comment Threads

• GregLondon commented on Directly downwind faster than the wind - part 3
  If you take energy from the forward motion of the cart (ie using the wheels to generate energy) to power the propellers then you will lose more energy than you gain. Yep. But once the propeller starts spinning, the tailwind can start pushing on the prop and speed you up. If the prop doesn't spin, the wind can't push on it. If it takes X number of (energy units) to spin the prop, but that then allows the wind to push you and introduce (Y) energy units into the sytem, and Y greater than X, then you'll go faster than...
• GregLondon commented on Directly downwind faster than the wind - part 3
  I uploaded another rev. It fixed a couple of typos. And I added a "bonus section" which is just add on info for folks who may be interested in it. The bonus section contains a flip-chart animation of the yoyo pulled by a rope with a parachute on teh end. It also contains an idea I've been pondering for making a sail-barge version. Mostly I just wanted to see if I could figure out a way to open and close the sails in a rigid manner. I think that part works. Scaling it to a workable vehicle might be a...
• dny commented on Directly downwind faster than the wind - part 3
  Re: Three questions for cart enthusiasts: Couldn't you just block the wind coming from the front and making the fan turn backwards? Then it would cease to be a factor. Here's an amateurish diagram I drew of what I'm talking about. The wind shield would have to be bigger, so it could cover the entire front of the fan and direct the air from the back down. This would have the added advantage of acting as both a sail from the back and a wing/needle from the front....
• davefoc commented on Directly downwind faster than the wind - part 3
  Hi folks, there has been a long discussion going on at the JREF forum about this. Personally, I have almost zero doubt that it is possible and that it has been demonstrated. There is a fairly simple plausible explanation available. My cut at that: Energy can be recovered by extracting it from the rotation of the axle driven by the wheels. In the normal situation this will slow the card down to something less than the wind speed when energy is extracted from the rotation of the axle. However that available energy can be used to spin a propeller to...
• ian9toes commented on Directly downwind faster than the wind - part 3
  This would have to come down to the efficiency of the propeller versus the drag of the wheels and bearings and pulley etcetera. So my comment is only on how to increase that efficiency. I'm talking about the cart with the big swivelling funnel and the exhaust leading out the back. What about having the exhaust go straight down, so when there is relative tail wind no wind can go up the exhaust and turn the prop the wrong way. In actual fact no wind would ever go up the exhaust as the swiveling top section is greater than the...