-- 
Paul Lamar ...No rotor no motor.


Paul,

My comparison of efficiency of a 24 inch prop and a 72 inch prop is
comparing a freestream prop to a freestream prop, not a duct.

I explained that this was so we could compare just one factor, the
induced efficiency. In other words, we are concerned for the purpose of
that exercise only with how efficient, in terms of kinetic energy, a
small prop is versus a big prop.

I will get to the issue of duct efficiency and drag in my next post.
There is some very interesting stuff there. It's not just a matter of
the duct having a downside because of drag.

Also, your formatting scrambled all my math, taking out all the minus
signs and some other stuff as well. Anyone trying to work through it
will get nonsense results. Can we put up the math in proper form, in
case someone wants to do their own calculations?


Regards,

Gordon.


You can double check your calculations with the
single verses the twin with this chart as the twin has
more prop area. Note it only helps the climb.

The duct is the problem with its internal skin friction
drag. It is also a 3D problem as the air is whirling
around inside the duct. The density of the air on
the outer inner wall is higher than the density of
the air near the core.

Paul Lamar ...No rotor no motor.

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