Russell Kent wrote:

Paul wrote:

Did I forget anything?

Russell Kent replied:

Yeah, density altitude.

Paul responded:

Very good point Russel. There is plenty of evidence that high altitude props
require a higher solidity ratio.

I have no idea what you mean by "solidity ratio."  What I meant was that a given prop is
going to attempt to move a fixed *volume* of air.  Thrust is a measure of the *mass* of
air moved.  So prop thrust has to include the density of the air, i.e. density
altitude.  This implies that a prop running in cold dry air at sea level will generate
more thrust that the exact same prop running in hot humid air on a mountain top.  I
think that this jives with everyone's experience, right?

Russell

Solidity ratio is the area of the blades over the prop disk area.
A four blade prop with the same width blades would have a higher 
Solidity ratio than a two or three blade prop.

Paul Lamar
 
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