[QUOTE=Chronos]
Which means that, for the same amount of energy expenditure, it’ll be slower. If someone’s propelling a bike at top speed, that means that that person is working as hard as e can to move the bike, so you can’t just say e could make up for the less efficient drive by working harder.
[/QUOTE]
'e could if 'e was Chuck Norris, mate.
It would be somthing like one of the variable pitch windmills they had on farms a hundred years ago. They didn’t rip apart in severe wind, so were used more in an open prarie type setting like Kansas. They’re not exactly what I discribed, but would give you an idea of the spring setup.
My response:
A propeller doesn’t make it slower. It moves the bike forward less efficiently. You then must provide more leg energy into pedaling to go the same speed you did when all the forward motion was provided by the tire.
Was to this:
However, I don’t agree that mounting a rider driven propeller to the back of a bicycle will make it slower.
[QUOTE=Harmonious Discord]
No for the question. A fan providing thrust in air, is less efficient at transferring power than the tire on asphalt.
Now here’s a variation that could provide bonus power for the rider. Replace the spokes on the rear tire with fan blades. The wind blowing from the correct side of the bike would reduce the need for energy provided by the rider. Wind from the wrong direction would require more energy supplied by the rider. Wind from the front or rear would not transfer power by the fan.
There is a fix to make the wind useful from both sides and most importantly prevent the opposite situation. . Make the blades moveable with stop pegs and springs. The blades will switch to the needed position when the wind hits them. You now have added thrust from the left or right side.
[/QUOTE]
It would have to be quite a considerable wind, otherwise, what’s actually going to be happening is that some of the work done by the rider is expended byt the fan blades in driving the air through the fan.
[QUOTE=Mangetout]
It would have to be quite a considerable wind, otherwise, what’s actually going to be happening is that some of the work done by the rider is expended byt the fan blades in driving the air through the fan.
[/QUOTE]
The correct variable pitch fan blades should fix it. There are drawbacks, and if this was all hashed out, it wouldn’t be something to experiment with. I didn’t say it was always going to be practical in aiding the rider, just sometimes.
While I can see that windmill wheels would, in principle, work, wouldn’t it be easier to just stick a mast and sail on the bike, and tack it like a sailboat?
[QUOTE=FRDE]
Fan boats work fine, so I don’t see why a pedal powered ‘fan bicycle’ should not work, with the right design it could even be amphibious 
[/QUOTE]
Because of Newton’s second (?) law. Every action provides an equal and opposite reaction. The water “pushes back” harder than air does, because it’s more dense and more viscous.
Unless you were joking, in which case I was whooshed…
[QUOTE=Chronos]
While I can see that windmill wheels would, in principle, work, wouldn’t it be easier to just stick a mast and sail on the bike, and tack it like a sailboat?
[/QUOTE]
Balancing a 2-wheel vehicle with a sail would be tricky. But it’s pretty simple to do with a tricycle.
[QUOTE=Chronos]
While I can see that windmill wheels would, in principle, work, wouldn’t it be easier to just stick a mast and sail on the bike, and tack it like a sailboat?
[/QUOTE]
The sail would make balancing a bitch even on a windless day. You’ld have to deal with rigging, and tack back and forth, becuse the sail would hinder movement against the wind. You would have to counter balance by leaning way out like on a windglider. in even a small wind so pedaling is out completely. The blades in the wheel don’t have the problems of the sail. It would look silly.
Many literaries have dreamed of a sailing covered wagon or a ship on wheels.
[QUOTE=Pygmy Rugger]
Because of Newton’s second (?) law. Every action provides an equal and opposite reaction. The water “pushes back” harder than air does, because it’s more dense and more viscous.
Unless you were joking, in which case I was whooshed…
[/QUOTE]
No I was not entirely joking, an Everglades Fan Boat is pretty much the same as a push bike with a fan on the back.
[QUOTE=FRDE]
No I was not entirely joking, an Everglades Fan Boat is pretty much the same as a push bike with a fan on the back.
[/QUOTE]
In this case, though, the method of propulsion is chosen because a conventional screw propeller (which I think would still be more efficient) would foul with weeds or be damaged in very shallow water.
[QUOTE=Mangetout]
In this case, though, the method of propulsion is chosen because a conventional screw propeller (which I think would still be more efficient) would foul with weeds or be damaged in very shallow water.
[/QUOTE]
Exactly !
[QUOTE=Chronos]
While I can see that windmill wheels would, in principle, work, wouldn’t it be easier to just stick a mast and sail on the bike, and tack it like a sailboat?
[/QUOTE]
Ooo! And then you could land airplanes on it!
As I noted before the (single person, flying start) human powered boat record is a fanboat:
pic:
http://www.humanpoweredboats.com/Photos/HydrofoilHPBs/Decavitator.gif
YouTube video:
The main page is gone, but you can do search on decavitator for info.
Brian
[QUOTE=Cervaise]
Ooo! And then you could land airplanes on it!
[/QUOTE]
Unless it’s on a treadmill, of course…
[QUOTE=Harmonious Discord]
The blades in the wheel don’t have the problems of the sail.
[/QUOTE]
Why not?
In fact, the spoke-sails have the problem that they’re constantly changing their forward speed relative to the ground [a point on the rim of the wheel is at rest once per revolution, and is going at twice the overall bike speed once per revolution]. This means that the effective wind direction the spoke-sails see is constantly changing, so they would have to be constantly changing angle to be maximally effective.
People, you’re forgetting the primary benefit - using the spinning blades to mow down pedestrians.
[QUOTE=Chronos]
While I can see that windmill wheels would, in principle, work, wouldn’t it be easier to just stick a mast and sail on the bike, and tack it like a sailboat?
[/QUOTE]
You’d need much wider bikeways, though. Or at least known, predictable wind directions.