Is any of this clear to anyone? Feel free to ask questions.

I found these tables very useful in helping me understand the dynamics of
aircraft speed and prop pitch/twist.  I see what you mean, how the twist
changes more than pitch at low air speeds.  We see that this is because the
root is "dynamic" or changes more dramatically than the tip.  I think you
should have the program calculate the airspeed of the blade parts and not
just the circular speed. (Oh - just noticed that you have now done this..
great minds think alike :-).

I wanted to mention, though, that the tip is far more important than the root
because of its higher velocity and longer moment arm.  For example, an
over-pitched root at say 100 mph will not adversely affect the RPM nearly as
much as an over pitched tip traveling at >500mph...  by a factor on the order
of the square of the difference in airspeed multiplied by the difference in
moment arm!!  A HUGE difference.  Also, because of its slower speed, the root
can tolerate much more over-pitch without stalling (cavitating).  On the
other hand, an underpitched root can still act as a flat plate and create
quite a bit of drag.  (under pitch the tips, and you're in beta).  So, I
still strongly feel that Mr. Ivo is onto the right Idea with changing the tip
and not the root (assuming that technology requires us to change only one or
the other...).

It also seems, according to your table, that underpitching at the root is the
problem with the current IVO props and why they are better on slow airplanes,
as several people have suggested.  Lets take an RV in max cruise for example.
 With a Speed of 190MPH (remember we should use TAS here) the root pitch

from

your table is 75.8 just to avoid causing extra drag, and that dose'nt yet do
anything useful for forward speed.  I think someone mentioned that the new
high-pitch Ivo props still only have a root pitch of 70 deg.

Im just rambling here... cut me off anytime :-)    Does anyone know what the
root pitch of a typical RV cruise prop is?  How about the cruising root pitch
of a C/S?

Dave Leonard

Good post Dave. I know you miss it over here at Christmas time.
At least you have snow :-). Merry Christmas!

I will check my C182 prop although it don't go too fast :-)
 
Paul Lamar
 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org