On Feb 5, 8:56*am, "Brent" wrote:
Sounds like an airboat hovercraft or some other type of propeller driven
ground effect vehicle

Actually it sounds closer to something like a skateboard with as prop motor
and a user on it. you are missing a huge amount of variables and for props,
pitch, density altitude, motors, and at speeds that slow your in the wrong
group because very few things, If Any, in any of these groups fly at that
speed.

And aircraft move slow taxiing because they are not meant to be ground
vehicles they usually have very narrow stances and high centers of gravity
compared to a ground vehicle as soon as they have any kind of airspeed they
want to fly.

Look up an RC or Aeronautical engineering group on usenet or elsewhere. you
need to find design people not pilots

"Flaps_50!" wrote in message

...
On Feb 4, 11:55 am, John Doe wrote: Is there such a calculation/formula? How can you tell what
propeller to use, how fast it should rotate, and how much weight
it can push along the ground?

Specifically... I would like to tell what sort and size of
propeller rotating at what speed, in calm air to push 100 or 200
pounds on smooth and level pavement with zero rolling resistance
to about 20 mph.

20 mph is too fast for taxying. What are you asking about -zero
rolling resistance????

Cheers

To add a little to this: zero rolling resistance means all that has to
be overcome is aerodynamic drag, and one needs to know something about
the shape of what is being moved. Air weighs about 0.08 pounds a cubic
foot, you simply have to decide how long you want to take to get to
whatever speed, that will tell you the force you need. F still equals
mass times accelerations, so then for any diameter prop there is a
certain rotation speed that'll throw aft the required mass of air. The
lower limit on prop diameter will have to do with keeping the tip
speeds sub sonic, the upper limit is related to mechanical factors. I
seem to remember props in general are about 30% efficient, if that
guess is true and you need 1 horsepower delivered you'll need an
engine that produces something over 3.

Why do I feel I'm answering someone's homework question?