"BDS" wrote in message
m...

"Michael Ware" wrote

Yes, but an airplane isn't propelled by its feet.

This is where everyone who seems to think that the airplane will fly is
getting confused.

The method of propulsion doesn't matter. You can drive an airplane down
the
runway by driving its wheels just like a car and it will still reach
takeoff
airspeed and fly briefly. The propeller is only important once you are
airborne, because you need something to pull you through the air.

And all this time, I thought it was the propellor that made the airplane
move across the ground. I stand corrected.

The bottom line is this - you cannot take off without first moving across
the ground unless the wind (airmass movement relative to the ground) is
blowing hard enough to give you sufficient airspeed to fly without moving.
In this case, once you take off your airspeed will immediately begin to
decrease unless you are using a prop to pull you through the air, or a
tether to hold you there (relative to the ground).

What do you mean, 'unless you are using a prop to pull you through the air'?
How does your airplane work?

Example - a floatplane is sitting in a river that is moving at 30 mph
(hey,
it's a fast river!). There is also a wind blowing down the river at 20
mph.

If the floatplane is anchored and facing into the wind, it has an airspeed
of 20 mph. If you release the anchor and use enough engine power to get
the
plane going through the water upstream at 30 mph you will be standing
still
with reference to the shore, and your airspeed will be 20 mph. If the
river
was flowing at a rate in excess of the maximum speed of your airplane,
then
you could never move forward going upstream with reference to the shore,
and
your airspeed would never exceed 20 mph, even at full throttle. If you
fully understand this then you would know that you could shut your engine
down, face downstream, and take off and fly briefly.

This is not an anology. With the wheels turning on the treadmill, friction
(and thus the force exerted) are negligible. The force exerted by the
running water on the floats is much greater.

BDS