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Engine break-in with a fixed-pitch prop

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glcasey

Joined: 01 Jul 2007
Posts: 23

Posted: Tue May 13, 2008 4:59 am Post subject: Engine break-in with a fixed-pitch prop

With a fixed-pitch prop you don't have a lot of choice.  The engine power is roughly the rpm times manifold pressure and they can be controlled independently with a constant-speed prop.  If 29 inches and 2700 rpm are 100% power then 75% (the usual suggested by engine rebuilders) would be about 2600 and 23 inches, 2500 and 24 inches, etc.  If you at 3,000 ft you might be able to run at a manifold pressure of 26 inches - 75% power would then be at an rpm of approximately 2250, but I doubt that you can operate there with the fixed prop.  If you can fly at 6,000 ft full throttle and not go over 2500 then you're there, otherwise not.  If your plane is equipped with a manifold pressure gage then you can at least see what you have.  Note that I rounded everything off - it just isn't worth more accuracy than that (in spite of what some engine rebuilders would say).  I suggest just go up and fly it at the highest power comfortable without going over the engine redline; just keep it rich to avoid high temperatures.  There just isn't much else you can do.Gary Casey

[quote]

I have a topped O-360-A1A (180 HP) in an experimental amateur-built that 

is ready for its first flight.  The prop is fixed pitch and I don't have 

a manifold pressure gauge in the panel.  I want to prepare a simple 

table of RPM at various pressure altitudes to yield 65% (117 HP) and 75% 

(135 HP) power so that I can set the power appropriately for the first 

few hours on the engine to set the rings properly.  

I have the Lycoming Operator's Manual (Publication No. 60297-12, 

Revision -6/7th Edition).  I'm trying to decipher Figure 3-17, Sea Level 

and Altitude Performance on Page 3-33.  By my reading it seems like I 

can generate 75% power at less than 2000 RPM up to a pressure altitude 

of about 3000 feet and pull 65% power at 2000 RPM at 7500 feet pressure 

altitude.  That RPM seems way too low to generate those power levels.  

Do any of you have the right power settings for an O-360 180 HP fixed 

pitch set-up?  The prop is a Sensenich 74" diameter and the pitch is 65" 

if I recall correctly (the pitch between climb and cruise).  

Or can someone tell me how to properly interpret the table?  My 

inclination is to run it at 2700 RPM for take-off and then reduce it to 

2500 RPM from then on out and then vary the RPM +/- 100 RPM every half 

hour or so.  I'll be operating at pressure altitudes of between sea 

level and 5000 feet.

Bob

[b]

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_________________
Gary Casey

flyinwithme99(at)yahoo.co
Guest

Posted: Tue May 13, 2008 7:03 am Post subject: Engine break-in with a fixed-pitch prop

Completely agree with Gary.

   

  You could also borrow a prop with a couple extra inches in it for break in purposes if 65" put you in between the cruise and climb category.  Keep take-off performance in mind here...(short strip...etc.)

   

  It is imperative that you apply as much manifold pressure as you can given engine temp and altitude restrictions.  You are not going to hurt the engine running it at red line RPM.  Do not baby the engine.

   

  I have always tried to stay below 5000 feet with fixed pitch combinations and keep a close eye on the temps.



Gary Casey <glcasey(at)adelphia.net> wrote:

   	  Quote: 	
		  With a fixed-pitch prop you don't have a lot of choice.  The engine power is roughly the rpm times manifold pressure and they can be  controlled independently with a constant-speed prop.  If 29 inches and 2700 rpm are 100% power then 75% (the usual suggested by engine rebuilders) would be about 2600 and 23 inches, 2500 and 24 inches, etc.  If you at 3,000 ft you might be able to run at a manifold pressure of 26 inches - 75% power would then be at an rpm of approximately 2250, but I doubt that you can operate there with the fixed prop.  If you can fly at 6,000 ft full throttle and not go over 2500 then you're there, otherwise not.  If your plane is equipped with a manifold pressure gage then you can at least see what you have.  Note that I rounded everything off - it just isn't worth more accuracy than that (in spite of what some engine rebuilders would say).  I suggest just go up and fly it at the highest power comfortable without going over the engine redline; just keep it rich to avoid high temperatures.  There just isn't much else you can do.  Gary Casey

      	  Quote: 	
		    

  I have a topped O-360-A1A (180 HP) in an experimental amateur-built that 

  is ready for its first flight.  The prop is fixed pitch and I don't have 

  a manifold pressure gauge in the panel.  I want to prepare a simple 

  table of RPM at various pressure altitudes to yield 65% (117 HP) and 75% 

  (135 HP) power so that I can set the power appropriately for the first 

   few hours on the engine to set the rings properly.  

  



  I have the Lycoming Operator's Manual (Publication No. 60297-12, 

  Revision -6/7th Edition).  I'm trying to decipher Figure 3-17, Sea Level 

  and Altitude Performance on Page 3-33.  By my reading it seems like I 

  can generate 75% power at less than 2000 RPM up to a pressure altitude 

  of about 3000 feet and pull 65% power at 2000 RPM at 7500 feet pressure 

  altitude.  That RPM seems way too low to generate those power levels.  

  



  Do any of you have the right power settings for an O-360 180 HP fixed 

  pitch set-up?  The prop is a Sensenich 74" diameter and the pitch is 65" 

  if I recall correctly (the pitch between climb and cruise).  

  



  Or can someone tell me how to properly interpret the table?  My 	
	




            [quote][b]

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