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Low RPM Harmful ?

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n1cxo320(at)salidaco.com
Guest

Posted: Mon May 22, 2006 8:11 am Post subject: Low RPM Harmful ?

At our EAA Chapter meeting the gossip turned to cruise rpm settings. One 

pilot, who I had thought was fairly knowledgeable, said that low rpm 

settings (say 2000 or so) for an extended time would harm the valves.



I can't see his logic and didn't have the opportunity at the meeting to 

question him further about his statement. My relatively uninformed view 

is that his idea isn't on track.



Opinions from engine experts would be welcome.

low pass

Joined: 10 Jan 2006
Posts: 32
Location: Houston

Posted: Mon May 22, 2006 1:43 pm Post subject: Re: Low RPM Harmful ?

 	  n1cxo320(at)salidaco.com wrote: 	
		  At our EAA Chapter meeting the gossip turned to cruise rpm settings. One 

pilot, who I had thought was fairly knowledgeable, said that low rpm 

settings (say 2000 or so) for an extended time would harm the valves.



I can't see his logic and didn't have the opportunity at the meeting to 

question him further about his statement. My relatively uninformed view 

is that his idea isn't on track.



Opinions from engine experts would be welcome. 	


I'm not an expert, but I would think he had it reversed.  Higher RPM will cause greater dynamic loads on the valve train and other moving parts.  Valves contact the seat when the cylinder is under compression, transferring very little load anywhere except the inside of the cylinder.



Lower rpm would be easier on the moving parts, but the cumbustion chamber will see higher pressures longer.  This results in higher cylinder pressure and greater blowby (if sealing is an issue).



2 cents



Bryan

Houston

LessDragProd(at)aol.com
Guest

Posted: Mon May 22, 2006 8:17 pm Post subject: Low RPM Harmful ?

If all else fails, read the manual.

 

For the engine side of the system:

Figure 3-17 & 3-19 are similar for the IO-540-C & -D engines.

 

Minimum RPM & Maximum MP continuous power settings are 1800 RPM (at)  25" MP to 

2200 RPM (at) 29" MP.

 

For the propeller side of the system:

MT Propeller engineering says these engine power settings are  acceptable 

with the RV-10 MT Propeller.

Does anyone know what is acceptable for the RV-10 Hartzell propeller?

 

Regards,

Jim Ayers

 

In a message dated 05/22/2006 9:24:59 AM Pacific Daylight Time,  

n1cxo320(at)salidaco.com writes:






At our EAA Chapter meeting the gossip  turned to cruise rpm settings. One 

pilot, who I had thought was fairly  knowledgeable, said that low rpm 

settings (say 2000 or so) for an extended  time would harm the valves.



I can't see his logic and didn't have the  opportunity at the meeting to 

question him further about his statement. My  relatively uninformed view 

is that his idea isn't on  track.



Opinions from engine experts would be  welcome.

cjensen(at)dts9000.com
Guest

Posted: Tue May 23, 2006 6:10 am Post subject: Low RPM Harmful ?

Bryan,



Intuition is a strong force....that's often wrong.  While the argument

of engine life v. operating will not be settled soon, primarily because

there is no one single answer, Aviation Consumer did a 'study' of the

issue and canvassed many of the engine builders and over haulers and

looked at, in detail, peak cylinder pressures and other issues of

running at high v. low rpm.  



In short, the consensus was running at higher rpm and higher hp output

equated well with engine life for a variety of reasons, but upper most

among them was stress on the engine.  The worst power configuration was

low rpm, high power output.  As rpm went up, stress was reduced.  The

cylinder wear from more linear feet of piston travel was also

counter-intuitive.  The cylinder wear was more a function of peak

pressures, which were lower at higher rpm; hence higher rpm operations

reduced cylinder wear.



We always need to remember, 'for every complex question, there is a

simple answer---that's wrong.'



Chuck Jensen

I slept at a Holiday Inn last night.



[quote] --

gmcjetpilot(at)yahoo.com
Guest

Posted: Tue May 23, 2006 6:38 am Post subject: Low RPM Harmful ?

Great question. With gas prices what they are flying at low power is 

a great idea. The idea of saving wear on the engine not so much. 

  

I am no expert but Lycoming is, and here is a key reprint (article) 

from Lycomings Flyer publication.

   

  http://www.lycoming.textron.com/main.jsp?bodyPage=support/publications/keyReprints/operation/lowPowerLowRPM.html

   

  Bottom line engine parameters should be within limits (for my O360A1A):

  CHT: 280-400F* 

Oil Temp: 185-210F*

   

  *(These are all personal limits, 190F OT is what I like to see; much lower 

than this you are not buring off the water from conbustion fully and it stays 

in your crank case. 300F CHT is as cold as I like to see. Below that you 

can get more lead deposits.)

   

   

  See your manual for proper limits.

   

   

  also

   

  http://www.lycoming.textron.com/main.jsp?bodyPage=support/publications/keyReprints/operation/leaningEngines.html

   

  http://www.lycoming.textron.com/main.jsp?bodyPage=support/publications/keyReprints/operation/properLeaning.html

   

  http://www.lycoming.textron.com/main.jsp?bodyPage=support/publications/keyReprints/operation/powerSettings.html

   

   

  You also have to watch prop limits. In my case I have a no 2000-2500rpm

continuous ops stay out range. I could fly at 1950 rpm but that is not 

quite enough get up an go for me. However is I was circling and going for 

endurance I could go 1900 RPM. IT is all about percent power. For my 

RV-7 the best L/D is down in the 100mph range, so for a real slow flight 

of say 120-140 mph it does not take much power. The gas burn is very 

low. I think more in percent power and not RPM alone. Bottom line 

RPM is part of the power equation and thus ECON. I don't worry about 

wear. A Lyc can be flown at 2,700 rpm all day. The reason is GAS.

   

  Cheers George   

   

   

   

  >From: "John Fasching" <n1cxo320(at)salidaco.com>

 	  Quote: 	
		  

At our EAA Chapter meeting the gossip turned to cruise rpm settings. 

One pilot, who I had thought was fairly knowledgeable, said that low rpm 

settings (say 2000 or so) for an extended time would harm the valves.



I can't see his logic and didn't have the opportunity at the meeting to 

question him further about his statement. My relatively uninformed view 

is that his idea isn't on track.



Opinions from engine experts would be welcome.


	


 __________________________________________________

highflight1(at)gmail.com
Guest

Posted: Tue May 23, 2006 9:28 am Post subject: Low RPM Harmful ?

All engines are engineered to operate at peak levels for their

designed purpose. Operating at anything other than at those peak levels

(over OR under) introduces various non-desireable effects on the engine.



RPM, if operated within the engines limits (even at upper limits) is not a

"stressor" to the engine. Operating at low RPMs and at high torque loads is

low pass

Joined: 10 Jan 2006
Posts: 32
Location: Houston

Posted: Tue May 23, 2006 10:09 am Post subject: Re: Low RPM Harmful ?

 	  highflight1(at)gmail.com wrote: 	
		  All engines are engineered to operate at peak levels for their

designed purpose. Operating at anything other than at those peak levels

(over OR under) introduces various non-desireable effects on the engine.



RPM, if operated within the engines limits (even at upper limits) is not a

"stressor" to the engine. Operating at low RPMs and at high torque loads is 	
Excellent discussion topic.  



But a couple of points to make:



1.  RPM certainly is a factor to a mechanical device.  That's why there's a red line.  Reaching the red line limit is not a limit like the sound barrier.  One is closer to the damaging effects ove rover speed at 2600 than they are at 2500.



2.  The are many factors in recip engine life/wear.  Some involve *driving* components (pistons, rods, crank...), and some involve *driven* components (valve train, accessory devices...).  To say low rpm ops cause the most damage is not absolute, any more than saying high rpm ops will cause the most damage.



Personally, these (Lycomings) have such short stroke already, I don't feel too comfortable with extended low rpm ops.  Aside from OEM limits, I don't like operating below 2300 or oversquare in any instance.  95 % of my time is spent 2350 to 2400 rpm.  General - yes.  But it's just my thing.



another 2 cents



Bryan

Gary.A.Sobek

Joined: 09 Jan 2006
Posts: 217
Location: SoCAL USA

Posted: Tue May 23, 2006 4:13 pm Post subject: Low RPM Harmful ?

So you are telling me that the way I have been operating my engine for the 

past 8.75 years is not good for it and it will not make it past 1,000 hours?

I typically cruse at full throttle 2,300 RPM.  If I can run over square, I 

do.  One of my favorite power settings is 2,100 RPM 22 inches MAP with a 6 

GPH fuel burn.

My engine has over 5,000 hours since new and over 1,850 in the RV.

Gary A. Sobek

"My Sanity" RV-6 N157GS O-320 Hartzell,

1,850 + Flying Hours So. CA, USA

http://SoCAL_WVAF.rvproject.com

----Original Message Follows----

highflight1(at)gmail.com wrote:

 > All engines are engineered to operate at peak levels for their

 > designed purpose. Operating at anything other than at those peak levels

 > (over OR under) introduces various non-desireable effects on the engine.

 >

 > RPM, if operated within the engines limits (even at upper limits) is not 

a

 > "stressor" to the engine. Operating at low RPMs and at high torque loads 

is

cjensen(at)dts9000.com
Guest

Posted: Wed May 24, 2006 10:28 am Post subject: Low RPM Harmful ?

Any Technical Counselor or other qualified individual in the Florida

area that would be interested in doing a pre-buy inspection of an RV?

Contact me off line if you would.



Thanks,

Chuck Jensen

Do Not Archive

Ollie Washburn

Joined: 10 Jan 2006
Posts: 56
Location: Central Florida

Posted: Wed May 24, 2006 11:18 am Post subject: Low RPM Harmful ?

Check  http://eaa1236.loveslanding.com/

One of them might.

Ollie



---

_________________
Ollie RV6-A & Rans S7S
Central FL

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