"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
:

My intuition tells me that when you ' loosen the grip' on
the propeller shaft and let the propeller turn freely, it
reduces the drag on the boat. Right or wrong?



It'd be real easy to test. Get one of those plastic props for a small
outboard, put it on a shaft. Pull it loosely behind the boat,
FREEWHEELING, with no load (which produces no work) using a simple fish
weighing scale to measure its drag. Then, lock it to the shaft so it can't
turn and drag it at the same speed, yet again.

Wanna bet the locked prop draggin' through the water creates lots more drag
than the one locked that can't turn?

Take the dingy out for a spin. Run it wide open then drop the engine into
neutral, freewheeling the prop, and see how long it takes to stop dead.
Crank it back up and run it wide open again. This time, leave it in gear
and just pull the safety lanyard making it lock the prop dead still.
Retime how long it takes it to stop. More the drag, the quicker the stop.
You'll find it stops MUCH quicker pulling that STALLED prop through the
water than one FREEWHEELING.

As Lionheart's freewheeling shaft alternator is TURNED ON to produce power
(producing torque on the alternator shaft), it SLOWS the boat as the
alternator SLOWS THE PROP. The heavier it pulls (more torque produced),
the more it slows the boat and prop. Freewheeling props are producing a
minimal amount of torque...and work with no or little load...as load
increases, to the point of being stalled at maximum torque, the drag-
converted-into-torque INCREASES, not decreases!

If you were to spin the prop faster than its drag is capable of, you will
pass through a point of ZERO DRAG just at the point where increasing the
speed of the prop PRODUCES THRUST. So, as prop speed DECREASES, drag
INCREASES! As prop speed INCREASES, it passes through zero drag at the
point where it starts to produce thrust by turning it even faster!

I'm not a physicist, but I play one on Usenet....(c;
Your assignment for tomorrow's class is pages 287 through 312. Do the
workbook exercies on workbook pages 42-43 for turn in. The test will be on
Friday at 2PM.

It might also be a good time to point out that the HELICOPTER rotor CHANGES
DIRECTION as the chopper crashes. It is FORCED in the OPPOSITE direction
from freewheeling to provide DOWNDRAFT to hold the craft aloft by the
engine. As it decends freewheeling, unless you can reverse the pitch of
the rotor, the RISING air through it will make it spin in the opposite
direction.....making it not relevant to any of our discussion here as props
are fixed pitched and already going in the direction of flow caused by
thrust.

Geez....