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Blended Airfoil 72" vs. 74" (I have the answer, kind-a)

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gmcjetpilot(at)yahoo.com
Guest

Posted: Thu Mar 16, 2006 5:42 am Post subject: Blended Airfoil 72" vs. 74" (I have the answer, kind-a)

I have the answer, I got it from Hartzell. Its prop 

  data on the HC-C2YK/F7666. It is similar but 

  it does show some trends based on dia.

   

  The nod goes to.......

  Climbing (slower speed) =  74"

  Cruise, High speed & higher RPM  =  72"

   

  Bottom line 

  Low speeds 74"

  Higher speeds 72"

   

   

  When I say better, I mean one prop may be 1/8 th of  

  one percent better, to may be 1/2% to 1% more efficient 

  at best for a particular flight condition.

   

  When I say efficency I don't mean performance.

  You may throttle (rpm) back and get more prop efficency 

  but you get less thrust and thus less speed. In 

  general RPM is a big factor on efficency at cruise 

  speeds for any diameter. If you play to the 72" you 

  would climb at a faster speed. Efficency may increase 

  but rate of climb goes down. TINSTAAFL.

   

  If you're a racer, want to go fast the 72" is better.

  In climb at slower speeds the 74" prop is better. 

   

  The 72" seems to always enjoy a slight edge in cruise 

  and even more at higher speeds and RPMs. The 74" 

  seems to alwasy enjoy a slight edge in climb and even 

  more at slower speeds

   

  Better means if you fly side by side at the same RPM 

  one plane may go 1/2 mph faster or climb 50 fpm 

  faster. Slight, not big differences, but differences.

   

   

  What to buy? I like going fast but I like having the extra 

  2" of prop material. At least you have something to trim if 

  there is tip damage, but than if it was 2" smaller dia you 

  might not get the tip damage in the first place?

   

  Sorry can't tell you what to do, but I am leaning to the 74" 

  for more rework material if it was me. The BA prop has the 

  extra 3.5 edge on the HC-C2YK any way, and about 3 mph 

  over the WW RV200 prop, so you can give 1/2 mph away 

  and enjoy that extra 50 fpm climb.   

   

  Specific question email me off line. George

   

   

   

  >From: "Jim Thorne" 

 	  Quote: 	
		  Subject: Blended Airfoil 72" vs. 74" 

Does anyone have any information on pros and cons on choosing a 

  >72" vs. 74" Hartzell blended airfoil prop? Have searched archives and 
	


  >was unable to find any specific information relative to propeller diameter.

 	  Quote: 	
		  

Jim Thorne

7A-QB CHD


	




		

---------------------------------

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truflite(at)yahoo.com
Guest

Posted: Thu Mar 16, 2006 6:50 pm Post subject: Blended Airfoil 72" vs. 74" (I have the answer, kind-a)

George,

I know a lot of alphabets, i.e. ATC,IFR, and so forth,

but what is TINSTAAFL?

Dave

--- gmcjetpilot(at)yahoo.com wrote:

 	  Quote: 	

 <gmcjetpilot(at)yahoo.com>

 I have the answer, I got it from Hartzell. Its prop 

   data on the HC-C2YK/F7666. It is similar but 

   it does show some trends based on dia.

   The nod goes to.......

   Climbing (slower speed) =  74"

   Cruise, High speed & higher RPM  =  72"

   Bottom line 

   Low speeds 74"

   Higher speeds 72"

   When I say better, I mean one prop may be 1/8 th

 of  

   one percent better, to may be 1/2% to 1% more

 efficient 

   at best for a particular flight condition.

   When I say efficency I don't mean performance.

   You may throttle (rpm) back and get more prop

 efficency 

   but you get less thrust and thus less speed. In 

   general RPM is a big factor on efficency at cruise

   speeds for any diameter. If you play to the 72"

 you 

   would climb at a faster speed. Efficency may

 increase 

   but rate of climb goes down. TINSTAAFL.

   If you're a racer, want to go fast the 72" is

 better.

   In climb at slower speeds the 74" prop is better. 

   The 72" seems to always enjoy a slight edge in

 cruise 

   and even more at higher speeds and RPMs. The 74" 

   seems to alwasy enjoy a slight edge in climb and

 even 

   more at slower speeds

   Better means if you fly side by side at the same

 RPM 

   one plane may go 1/2 mph faster or climb 50 fpm 

   faster. Slight, not big differences, but

 differences.

   What to buy? I like going fast but I like having

 the extra 

   2" of prop material. At least you have something

 to trim if 

   there is tip damage, but than if it was 2" smaller

 dia you 

   might not get the tip damage in the first place?

   Sorry can't tell you what to do, but I am leaning

 to the 74" 

   for more rework material if it was me. The BA prop

 has the 

   extra 3.5 edge on the HC-C2YK any way, and about 3

 mph 

   over the WW RV200 prop, so you can give 1/2 mph

 away 

   and enjoy that extra 50 fpm climb.   

   Specific question email me off line. George

   >From: "Jim Thorne" 

 >Subject: Blended Airfoil 72" vs. 74" 

 >

 >

 >Does anyone have any information on pros and cons

 on choosing a 

   >72" vs. 74" Hartzell blended airfoil prop? Have

 searched archives and 

   >was unable to find any specific information

 relative to propeller diameter.

 >

 >Jim Thorne

 >7A-QB CHD

 ---------------------------------

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Vanremog(at)aol.com
Guest

Posted: Thu Mar 16, 2006 7:57 pm Post subject: Blended Airfoil 72" vs. 74" (I have the answer, kind-a)

In a message dated 3/16/2006 6:53:52 P.M. Pacific Standard Time,  

truflite(at)yahoo.com writes:



I know a  lot of alphabets, i.e. ATC,IFR, and so forth,

but what is  TINSTAAFL?



=============================

 

There is no such thing as a free lunch.  



GV (RV-6A  N1GV O-360-A1A, C/S, Flying 777hrs, Silicon Valley, CA)

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rv7a(at)cox.net
Guest

Posted: Fri Mar 17, 2006 6:11 am Post subject: Blended Airfoil 72" vs. 74" (I have the answer, kind-a)

I had to goggle that one.   TINSTAAFL =There ain't no such thing as a free 

lunch.  Do not archive

---

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