prop rpm question

On Thu, 26 Jan 2006 at 19:29:21 in message
, Brian Whatcott
wrote:

Hi Brian,

Hi David,

let's forget about jets and recips. Let's imagine a vehicle that is
provided with a constant thrust device.
Then, the faster it goes, the more hose power it provides.
You can take it to the bank


No don't let us forget the basic ideas of propulsion.

A constant thrust device is doing one of two things;

1. Accelerating. In which case it is adding to its kinetic energy
and its power is going into that or

2. It reaches a constant speed against a constant drag and a steady
state occurs..

I presume you are not claiming that a constant thrust motor can generate
infinite power? In that case you would be right!

What do you have in mind as a constant thrust device? Newton's laws are
pretty good and I am not aware of any means of getting around them. They
only need adjustments at velocities and masses far beyond normal
terrestrial transport activities.

It is of course true that the efficiency of propulsion devices does vary
with speed and many other conditions.

--
David CL Francis