On Mon, 16 Aug 2004 at 21:04:45 in message
, Roger Long
wrote:

The three blade prop will be less efficient per unit of area than the two
blade where it counts, near Vx with trees in the windshield. Given a
limitation on length however, the extra blade area of the three blader can
easily offset the efficiency loss by a substantial margin.

Just curious, but how does this fit with the 6 bladed props on the
latest C130s? The Herk has gone from 3 to 4 to 6 bladed props it seems.
Short take off and good climb out is a major requirement for the C130 I
would have thought?

Still curious but how does the extra blade area compensate for a loss of
efficiency? Depends how you define efficiency perhaps? If the 3-blade
prop loses something does the extra blade area restore the efficiency?

Another thought: No matter how many blades there are they are all
subject to exactly the same conditions. There is not a leading blade.
The other blades are in no sense one behind the other. In fact the
rotation of the prop radically changes the velocity vector that actually
meets the blade. The extreme of this is the enclosed fan where the
enclosure markedly reduces tip losses. The fan runs nicely along like
this with a high blade area and little daylight visible through the
disc.

;-)
--
David CL Francis