Dennis
You have to be clear on the difference between a propeller and a turbine. A turbine collects energy while a propeller delivers energy.
In the cart the propeller is driven by the wheels. The propeller is pulling air back through its disc as soon as the cart starts to move.
This is no different to an aircraft moving forward with a tail wind. The ground speed is airspeed plus wind speed. Just because there is a tail wind does not mean the airflow reverses through the propeller.
As long as the air is moving in the same direction as the cart it can make up for the losses in the drive train and propeller.
The best overall efficiency is around 80% so 4X windspeed is possible. At slow speed the efficiency is lower - more like 65%. So if you want a self starting cart then something around 2.5X windspeed is possible.
It is much harder to do this on water. The prop has to be very large and there are much greater losses in the water turbine required to collect the energy than wheels on a smooth surface.
The system is just reverse gearing to sailing directly upwind into the wind using an air turbine and water propeller.
Rick
On 30/08/2010, at 8:48 PM, Dennis Cox wrote:
This has nothing to do with our Proa's, and I'm have no desire to use one... but curiosity is getting the better of me...I just got my Sailing World Magazine and on page 18 it describes a propeller driven land yacht that succeeded in going directly down wind... at THREE TIMES wind speed. Exactly how is this done?(1) I mean at some point as you accelerate down wind, your apparent wind is zero. How do you accelerate on past this with no energy coming into the system.(2) Once up to speed, all energy is being generated solely based on the apparent wind you are creating. Basically it sounds like a perpetual motion machine... which is impossible.SO HOW CAN THIS HAPPEN?
Rick Willoughby
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0419 104 821
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