Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Tue, 03 Feb 2004 12:52:41 -0500 Message-ID: X-Original-Return-Path: Received: from imo-m02.mx.aol.com ([64.12.136.5] verified) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2973035 for lml@lancaironline.net; Tue, 03 Feb 2004 11:59:26 -0500 Received: from Sky2high@aol.com by imo-m02.mx.aol.com (mail_out_v36_r4.12.) id q.86.459581a (18555) for ; Tue, 3 Feb 2004 11:59:21 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: <86.459581a.2d512d64@aol.com> X-Original-Date: Tue, 3 Feb 2004 11:59:16 EST Subject: Propeller Heads, Help! X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1075827556" X-Mailer: 9.0 for Windows sub 460 -------------------------------1075827556 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit 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. Scott Krueger AKA Grayhawk Sky2high@aol.com II-P N92EX IO320 Aurora, IL (KARR) "...as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns - the ones we don't know we don't know." D. Rumsfeld -------------------------------1075827556 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
I know there are some airfoil experts lurking about - here is the=20 Question----
 
First the setup.
 
I have a Hartzell compact constant speed prop bolted to my mysterious L= yc=20 IO 320.  It is a 70 Inch prop (35 inches on each side of the hub=20 center) as a result from cutting down an 84 inch prop. Yep, they lopped off=20= 7=20 inches on each side.  Now, the unusual part of this is that the prop sh= op=20 in Tucson (AZ) actually did the cut down on usable 84 inch prop blades,= =20 supposedly following Hartzell guidelines. Of course, every other 70 inc= h=20 prop user got their prop from Hartzell - carved to the 70 inch length with a= n=20 appropriate taper reducing unneeded metal at the tip.  Believe me,= I=20 know since I am on blade # 9 and #10 (don't even ask....).
 
My recent conversation with Hartzell resulted in qualified answers=20 (qualified by their attorneys) - They had never done any vibration analysis=20= of=20 the simple cut down prop, only (hmmmmph) the carved, thus tapered, prop.&nbs= p;=20 They could give me no useful information about the performance characteristi= cs=20 of my specific prop.  As a matter of fact, the following was=20 determined:
 
Hartzell plans call for the following thickness at certain stations (fr= om=20 the center):
 
         Station - Thick&n= bsp;=20 Station - Thick
Hartzell   33" - .280"  35" - .120" 
Old Prop 33" - .290" 34.5"-.200" damage at the tip, old blade is u= sed=20 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=20 airfoil as a "carved" prop. I know that more metal carries more=20 momentum.  I know that thin airfoils may be more efficient at near mach= 1=20 airspeeds(?).  I know that thicker airfoils are less susceptible to=20 performance degradation due to contamination.  I know that some inner=20 portion (away from the tip) of the prop does most of the work.  I=20= know=20 that I am fast.
 
Now the questions.
 
1.  Does my tip, 7 inches inboard of the original hardworking area= of=20 the 84 inch prop, work harder (produce more thrust) than the thinner tapered= =20 airfoil?
 
2. Is the greater mass of tip metal an advantage or disadvantage? = =20 Why?
 
3. Does the thicker airfoil increase the drag near the tip or is it=20 irrelevant?
 
4. Would altering the tip like some fat wings - angled cut - eliminate=20 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 t= o=20 KARR on a nice day and swap your normal Hartzell prop with mine, fly it, and= =20 then swap'm back? Huh? Huh? Lunch and safety wire included.  Maybe even= a=20 dynamic prop balance - maybe.
 
 
Scott Krueger=20 AKA Grayhawk
Sky2high@aol.com
II-P N92EX IO320 Aurora, IL=20 (KARR)

"...as we know, there are known knowns; there are things we kn= ow=20 we know. We also know there are known unknowns; that is to say we know there= are=20 some things we do not know. But there are also unknown unknowns - the ones w= e=20 don't know we don't know." D. Rumsfeld
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