I know there are some airfoil experts lurking about - here is the
Question----
First the setup.
I have a Hartzell compact constant speed prop bolted to my mysterious Lyc
IO 320. It is a 70 Inch prop (35 inches on each side of the hub
center) as a result from cutting down an 84 inch prop. Yep, they lopped off 7
inches on each side. Now, the unusual part of this is that the prop shop
in Tucson (AZ) actually did the cut down on usable 84 inch prop blades,
supposedly following Hartzell guidelines. Of course, every other 70 inch
prop user got their prop from Hartzell - carved to the 70 inch length with an
appropriate taper reducing unneeded metal at the tip. Believe me, I
know since I am on blade # 9 and #10 (don't even ask....).
My recent conversation with Hartzell resulted in qualified answers
(qualified by their attorneys) - They had never done any vibration analysis of
the simple cut down prop, only (hmmmmph) the carved, thus tapered, prop.
They could give me no useful information about the performance characteristics
of my specific prop. As a matter of fact, the following was
determined:
Hartzell plans call for the following thickness at certain stations (from
the center):
Station - Thick
Station - Thick
Hartzell 33" - .280" 35" - .120"
Old Prop 33" - .290" 34.5"-.200" damage at the tip, old blade is used
for the "dolt of the week" award.
Current 33" - .342" 35" - .336"
In other words, my prop is about 7/32" fatter at the tip with the same
airfoil as a "carved" prop. I know that more metal carries more
momentum. I know that thin airfoils may be more efficient at near mach 1
airspeeds(?). I know that thicker airfoils are less susceptible to
performance degradation due to contamination. I know that some inner
portion (away from the tip) of the prop does most of the work. I know
that I am fast.
Now the questions.
1. Does my tip, 7 inches inboard of the original hardworking area of
the 84 inch prop, work harder (produce more thrust) than the thinner tapered
airfoil?
2. Is the greater mass of tip metal an advantage or disadvantage?
Why?
3. Does the thicker airfoil increase the drag near the tip or is it
irrelevant?
4. Would altering the tip like some fat wings - angled cut - eliminate
noise and drag?
5. Should I just shup up and keep flying ahead of other 320s?
6. Any I/O 320 experimenter/builder/owner want to come to
KARR on a nice day and swap your normal Hartzell prop with mine, fly it, and
then swap'm back? Huh? Huh? Lunch and safety wire included. Maybe even a
dynamic prop balance - maybe.