"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.

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).

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.

BDS

BUT... the initial condition, as stated in the OP, is that the
river(conveyor) is moving at the same
speed as the airplane but in opposite directions. So, with a 30 mph
river(conveyor) and a
20 mph headwind the airspeed would be 50 mph. The plane is moving at 30 mph
in the opposite
direction with respect to the shore(runway). The airplane would then be
travelling upstream at 60 mph
relative to the rivers surface. The only difference between the river
example and the conveyor example is how firmly the airplane is
coupled to the conveyance. The floats/river scenario would require more
thrust to overcome the resistance
than the wheels/conveyor example. Same mathmatics, different numbers. The
floatplane just needs a bigger motor.