I don't understand how this car works.

Quote:

With wind directly behind your sails there is zero force from that wind at the wind vel/speed.

And due to the design of the props here, the wind is never directly behind the 'sails' - even when it is directly behind the vehicle. Do you not understand this?

Cycloptichorn

JB, is there any practical use for such a vehicle design, or is this just an academic exercise?

So what is the point of this hoax?

The mistake is to imagine it works like a sail, ...

> Isn't the basic issue that it is lift that is driving a landsailer
> so the apparent wind speed across the sail increases as the roll
> speed increases and the "boat" keeps accelerating until one kind of
> drag or another exceeds the power from lift?

Yes. The basic sailing performance relationship is:

Vb = Vt * sin(gamma - beta) /sin(beta)
Vb: yacht speed
Vt: true wind speed
gamma: course sailed relative to true wind (gamma = 0 is straight
into the wind)
beta: apparent wind angle, measured between course over the ground
and the apparent wind vector

The closer the yacht can sail to the apparent wind (small beta), the
faster it goes. A typical beta for an efficient landyacht is on the
order of 14 degrees, which yields a maximum boat-speed ratio of 4
times the true wind, and a maximum Vmg downwind of 2.5 times the true
wind.

Beta, in turn, depends on the lift/drag ratio (actually the inverse -
the drag/lift ratio) of everything exposed to the air, and the lift/
drag ratio of the tires.

beta = arctan(aero_drag/aero_lift) + arctan(tire_drag/tire_lift)

Landyacht performance is all about reducing the aerodynamic drag in
all its forms.

Cheers,

Tom Speer

Apparently, I need to start a new thread titled "I don't understand how this iceboat works"

So, the wheels replace a boat's keel, or an iceboat's runners.

The wheels spin the propeller not to provide thrust out the back of the machine, but to keep the blades of the propeller angled correctly against the "apparent wind" at the leading edge of the propeller? The thrust is provided because the apparent wind creates lift against the propeller blades?

The key component isn't apparent wind across the hood of the vehicle, but the apparent wind at the leading edge of the propeller.

The answer (in my way of looking at the problem) is that the propeller pushing back against the tailwind interacts with the tailwind. In this way the tailwind can do work (through action/reaction) on the propeller and the cart can "extract" energy from the tailwind (remember a key part of the system is the ground doing work on the wheels).

Quote:

The wheels spin the propeller not to provide thrust out the back of the machine, but to keep the blades of the propeller angled correctly against the "apparent wind" at the leading edge of the propeller? The thrust is provided because the apparent wind creates lift against the propeller blades?

Here's where I don't have time to carefully answer -- I'll get to you later, but currently you'll just say I'm full of crap when I answer this: The wheels DO spin the prop to provide thrust just like a regular old propeller AND they operate just like a sail on a broad reach. There's no conflict in that statement ... it's that most folks (even most sailors) don't realize that a sail isn't alway acting as a turbine but is often acting as a prop.

I don't see how the thrust from it acting as a propeller can be any greater than the drag created by the wheels

and that's because you are as wrong on the following point as you are on the ice-boats:

If you'll give up your hard headed wrongness on the point of the ice-boats and the point of the distance, we'll be done here and you can go on your merry way on the correct side of this brainteaser.