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Old 06-18-2021, 01:55 AM   #14 (permalink)
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The energy at the blade-air interface must be lower than that at the road-to-tire interface due to energy loss in the tire, gears, wheel bearings, lower sprocket, chain, upper sprocket, jack-shaft bearings, then the blades themselves.
Sit down and enjoy this moment of enlightenment.

Power is force times velocity.

For the wheels it's simple: The velocity is just the difference in velocity of the wheels and the ground.

For the propeller it is just as simple: The velocity is just the difference in speed between the propeller and... (this is the facepalm moment!) the air!

The propeller doesn't give a hoot about ground speed!

Let's say we wanted to go 10m/s down a 5m/s wind and were transferring 100N of force.

We harvest 100N*10m/s = 1kW at the wheels.

The useful power of our propeller needs to be: 100N*5m/s = 500W.

Ergo (I love that word) we need a total system efficiency of 50%, including all losses, that is very very much not over unity, no magic needed!

Propeller efficiencies can be 82-92% according to the internet.

2016: 128.75L for 1875.00km => 6.87L/100km (34.3MPG US)
2017: 209.14L for 4244.00km => 4.93L/100km (47.7MPG US)
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