Perry Mick wrote:
Paul:
Here is the twist data from the Hollman book on the Hartzell prop,
blade angle for 200 mph is at 2700 rpm per the book. Assuming 0
aoa at the 0.9 station, the blade is rotated +10 degrees at 200 mph
and 2700 rpm.
r/R radius theta blade ang. theta + Hartz Hartz IVO IVO
200MPH CS rot. aoa CL aoa CL
-------------------------------------------------------------------
0.2 7.8 33.8 57.9 43.8 -14.1 -1.0 -50 -.8 stalled
0.3 11.7 27.7 46.8 37.7 -9.1 -.9 -26 -.8 stalled
0.4 15.6 23.8 38.6 33.8 -4.8 -.3 -18 -.8 stalled
0.5 19.5 20.0 32.6 30.0 -2.6 -.2 -20 -.8 stalled
0.6 23.4 17.5 28.0 27.5 -0.5 0 -8 -.5
0.7 27.3 14.6 24.5 24.6 +0.1 +.15 -4 0
0.8 31.2 12.5 21.8 22.5 +0.7 +.2 -2 +.15
0.9 35.1 9.5 19.5 19.5 0.0 +.1 +.5 +.4
1.0 39.0 17.7
I think they are definitely not putting in the full twist near the hub,
but think we should since we are not designing for a particular plane, and
most homebuilts, especially rotary powered ones, will have less frontal area
as you said.
I agree Perry. That Hartzel segment angle of attack (aoa) looks
awful for 200 mph. I also think we need to rotate it a bit more
than 10 degrees.
I looked it up in Von Doenhoff and plotted the lift coef. for a
66-212 which is a similar airfoil to the one Hartzel used.
Heck if you have a blunt nose it looks like a prop extension
would really pay off big time. No wonder Nemesis goes so fast
with its ten inch prop extension. Gets the root of the prop
out into faster air away from the engine.
BTW I added the IVO data on for grins. I assumed the airfoil
was a 4412 which is similar to a Clark Y.
This is for the IVO prop fully twisted so all of the blade
is at 20 degrees. I don't have a complete IVO blade here so this
is just a guess. I base this IVO max twist guess on the fact that when
the blade is relaxed the tip starts out at near zero degrees.
I am giving it the benefit of the doubt on 20 degrees max twist
at the tip. Unlike a real constant speed prop this is all the
angle of attack you are going to get with an IVO no matter what.
Maybe I should up my bet to a $1000.:-)
Perhaps an IVO equipped airplane could back up at 200 MPH :-) PL
I'll send drawings of what I've got so far later today or tomorrow. I'm
keeping the chord distribution of the Hartzell prop, but not the
straight trailing edge.
Perry J. Mick
Mick Duckt N7XR
http://www.ductedfan.com
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