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Avalanche

Sun Jun 12 2011, 11:38AM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I hope you don't think I was being serious with the overunity comment

Sorry, it's the photo with troll face on it that made me do it!

magnet18

Sun Jun 12 2011, 01:40PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

Avalanche wrote ...

I hope you don't think I was being serious with the overunity comment

Sorry, it's the photo with troll face on it that made me do it!

whew, good, I was worried...

Electroholic

Mon Jun 13 2011, 04:09AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

ConKbot of Doom wrote ...

YNPyM

faster than wind vehicle.

judging by the troll face, do you not believe its possible to travel DDWFTTW?

Avalanche

Mon Jun 13 2011, 05:09PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

My immediate answer would be no, but a quick google search found several discussions on other forums - but nothing conclusive so I'm going to stick with my original answer unless anyone can prove otherwise. Of course if you add the troll face into the mix, then suddenly anything becomes possible

Having said that, it all depends upon whether or not we're bringing duty cycle into the equation - if you were stationary for a while and storing up energy from a wind turbine, then you could use that wind energy to propel yourself down stream faster that the wind, so yes

Fraggle

Mon Jun 13 2011, 05:18PM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

magnet18 wrote ...

I think it has more to do with the static friction thing, softer tires will roll and form more, so instead of breaking the static friction they maintain it longer.
Friction Graph

In fact there is no contribution from either dynamic or static friction as the tyres don`t slide (probably :o) so no work is done against them. It is `rolling resistance` that is reduced by over-inflating the tyres as they deform less.

edit: I think I replied to the wrong person there but you get the idea

Ash Small

Mon Jun 13 2011, 05:53PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Fraggle wrote ...

.
In fact there is no contribution from either dynamic or static friction as the tyres don`t slide (probably :o) so no work is done against them. It is `rolling resistance` that is reduced by over-inflating the tyres as they deform less.

edit: I think I replied to the wrong person there but you get the idea

Also, the radius (diameter) of the tyre is greater, which increases fuel consumption, due to effectively 'gearing up' the tranmission (further distance travelled for the same engine RPM)

As an aside, I read in a motorcycle magazine several years ago that a tyre can transmit the most power when it is slipping 15% (ie greatest acceleration)

magnet18

Mon Jun 13 2011, 09:04PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

gear ratios are like transformer ratios, you go farther with less torque, or you don't go as far but get more torque. Pin=Pout
When you're accelerating you use the least fuel if you have plenty of torque, if youre driving along at a constant speed you want the most distance, because the torque is not needed.

@ fraggle, there's static friction involved, what do you think keeps the tires from spinning in place, and when they do spin, you loose energy, so the tire with the highest point of static friction is the best.

And it's tIre.

Ash Small

Mon Jun 13 2011, 09:35PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

magnet18 wrote ...

.
And it's tIre.

"tyre â€“ tire: In American and Canadian English, tire is used to refer to 'to fatigue' and the inflated rim of a wheel. In British and other forms of English, tire means 'to fatigue' and tyre is the inflated rim of a wheel."

-from Wikipedea.

Fraggle

Mon Jun 13 2011, 09:43PM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

Yes but they aren`t supposed to spin in normal operation, that`s the beauty of wheels - no losses at the interface, just losses deforming the wheels and at the axle.

ConKbot of Doom

Tue Jun 14 2011, 12:49PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

[quote]

ConKbot of Doom wrote ...

faster than wind vehicle.

judging by the troll face, do you not believe its possible to travel DDWFTTW?
[/quote1308055152]
Nope, makes perfect sense how they do it, its just usually the propeller hooked the wheel thing is tongue in cheek etc, so its funny to see something actually using it.

Vehicle moving at 30mph and wind at 30 mph would have a zero net airspeed, the propeller slows the air moving at 30mph ground speed to a 0mph ground speed and makes a high pressure zone behind the prop which moves the vehicle along. In an ideal (lossless) system, the thrust of air moving backwards should provide the same energy that the wheels take, so any energy from the wind is added to the system. Make your driveline and prop efficient enough, and you can have your own physics troll vehicle too. The propeller just acts as an impedance transformer from high airspeed of the vehicle to the low airspeed of the wind.

A water cooling system for solar cells to increase their efficiency in the summer that ran off the waste heat in the water seems cyclical and not feasible too, but no reason a sterling couldnt run a fan which keeps its cool side cool.

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