I like that idea. For the ride-on version we could take the same approach we use on sailplanes - just a simple piece of yarn.
Yes, the link isn't too difficult. I wondered about mounting a sail (more like a light but inflexible air rudder) above the rear wheel, but offset enough to add a gear train to turn the wheel, gearing down its motion so that the presumably fairly flappy movement of the rudder would only turn the wheel a little. A yarn connection would presumably be fine too, and its attachment allows gearing in similar manner. The problem I have with it is that pesky reversal of the wind. The rudder principle requires that it is being generally pushed one way - reverse the wind direction as the cart outpaces the wind, and it would tend to jacknife one way or the other. I've been trying to imagine a fully rotating wheel or other self-righting system, but so far can't fix it. The only solution I can think of at the moment is to manually set it by changing the location of the rudder's axle wrt its area (tricky) or only engaging the system at faster than wind speeds. Idiots might then still question whether it got to windspeed by itself and DIRECTLY downwind, but once past it, you could maintain that and also have a mechanism that keeps it self-directing downwind. There's also a bit of a complication that the best wheel for the job is in the turbulent air of the prop end, so maybe a rudder or sail at the front would be better, with yarn to the rear wheel steering mech. Can you think of a way for it to automatically reverse with the prevailing wind?
Hello John,
well, if one wants to have such a cart that can travel DWFTW at some greater angle instead of directly, then yes, it would be a problem. But then, i think that a certain amount of "non-directness" should be possible already, if it isn't too big.
Hi Chris, I think you may have misunderstood, or at least posted the wrong quote. The problem I was describing is that of a rudder trying to keep the cart DDW, not, as you seem to have described, being able to drive in different directions with respect to the wind. I don't have the experience or knowledge to even begin to work that out, but presumably one needs to change the machine significantly, probably rotating the whole prop axis, sometimes changing it from a prop to a turbine, etc., etc. I can well imagine it being a new sport in 5-10 years though. People will sit on anything and go fast!
As for Michaels question of braking the cart, what about a magnetic brake? <snip> Or the straight and simple way that bicycles brake
As others have said, I can't see the need for complex solutions, other than for style-weirdness. If going for the latter, sure, you could even generate electricity from the wind to power the electric brake!
For braking: even for a pure DDWFTTW vehicle meant only for demonstrating the principle, if it's carrying a person I think there should be a means of disengaging the transmission between prop and wheels.
Ah, you're no fun!
As humber reminded us a while back, you don't want to get sucked into the propeller.
But seriously, yes, I agree. There should also, of course, be a cage round the prop, and the rider should have protective clothing and helmet, and perhaps be strapped into a roll cage...especially if this sport becomes combined with storm chasing!
If the prop stays connected (as in the small cart), you have double work when applying the brake: you'd not only be dissipating the kinetic energy of cart + driver, you'd be fighting the thrust from the prop.
Yes, I didn't think of that. Like braking in your car while still with the drive engaged (although with a fluid clutch).
Simply disengaging the prop would apply a braking force: the prop would slow down, then start turning the other way like a turbine, which in itself would slow down the cart.
Surely not much, once its disengaged? It won't act as a brake to the rest of the mechanism if it's disconnected, although changing its momentum would absorb some energy. Above windspeed, once disengaged it will tend to be turned the same way by whatever headwind there is. Then, as the cart slows to below windspeed by general losses [ETA: the headwind!] or a mechanical brake, it will reverse direction (being turned like a turbine in the tailwind - but a disconnected turbine doesn't do much). You would have to drive it faster that way to act as an air brake, and not from the wheels, or you're just back to acceleration mode....I think...
[ETA: yes, the wheels are going the wrong way! - maybe a mechanical reverse gear? - or is there something like Dan's variable gear that reverses also?]
Maybe the variable pitch idea would be better than I first thought, and worth a try (didn't someone already have that on an earlier one?). It can give gradual or maximum acceleration, be trimmed for top speed, and altered again to gradually reduce thrust or gradually reverse it, and finally be set at infinite pitch again at rest, not to mention demonstrating reverse! Maybe its only drawback is that it is complicated - its action changing at different windspeeds, as well as the mechanical complication.
