Bill Freeman wrote:

As to the "off design point"  it is basically that the twist distribution
is a compromise.  The best twist distribution for cruise is not best
for climb and vice versa.  Variable pitch helps a LOT but you still
have some significant compromises.   But,  with a wide enough chord and
forgiving airfoil, I think we can get some pretty darned good performance.
Even with the poor L/D near transonic the rest of the blade is working
well and the thrust is very good.  It is amazing how much screwing
around with the chord and pitch distribution you can do and still
have only modest ups and downs in cruise thrust.  You can sure
wreck the low and mid range pretty easily, tho.  If you are interested
I can send you selected sets of thrust vs airspeed data with the
effeciency also.  Incredibly boring at first, but after a while you can
start to compare various blade forms and twist distributions and see
the performance gains or losses.  The plot of thrust vs airspeed
for different chords was for just one RPM & HP point, one altitude
and one twist distribution.   Change any one and you get a whole
new family of curves.  Finding the sweet spot is the trick.  A prop
is like an airplane - "a collection of compromises flying in close
formation".

I haven't really done any structural calcs on the blades, should get on
that since I have the thrust distribution curves.  You appear to have
captured the radial loads, I'll get on the bending loads in the next week
or so.

Have a nice trip.

Bill

I am interested Bill even if it is a whole book of charts.
200 HP would be a common point as would 180 HP.

Thanks.

Paul Lamar
 
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