Leaning & temps

[pilot716]

When leaning at cruise I usually bring the mixture back to run between 12 & 12.5gph which keeps our temps in the 1340ish range or slightly higher on cylinder 2. On a recent trip I actuall leaned back to 11.0, sure the temps went up but not over 1400. What do most of you use as a maximum? If you go by the poh most of the power combinations actually show 9.8 gph or less, I can almost guarantee my temps would be over 1400 at those settings..opinions...thanks,

Mark

PS..I am using a JPI monitor.

[Cruiser]

How are you setting MP and RPM? What is your reason for limiting EGT? What are the CHTs?

[Becca]

Quote: pilot716

When leaning at cruise I usually bring the mixture back to run between 12 & 12.5gph which keeps our temps in the 1340ish range or slightly higher on cylinder 2. On a recent trip I actuall leaned back to 11.0, sure the temps went up but not over 1400. What do most of you use as a maximum? If you go by the poh most of the power combinations actually show 9.8 gph or less, I can almost guarantee my temps would be over 1400 at those settings..opinions...thanks,

Mark

PS..I am using a JPI monitor.

[201er]

Peak is the maximum...

[pilot716]

That definitely helps, I have read all the ROP LOP arguments but really wanted to get better fuel economy with out overheating the cylinders. Thanks for the info. I have a long flight on Friday and will use the JPI book. Thanks

[pilot716]

Quote: Cruiser

How are you setting MP and RPM? What is your reason for limiting EGT? What are the CHTs?

[jetdriven]

For example, the last flight we did was ~25 LOP and the hottest CHT was #4 at 310.

 

FF was 9.3 GPH so the % of power was in the 71% range.

 

 

[Becca]

Quote: Becca

You are probably en route to creating another storm of a million emails on lean of peak and rich of peak.

But before we go there, let's talk about the basics.

Its a curve, so you are full rich - then you lean lean lean, and the EGT temperatures will rise until you get to some maximum value (because you are providing less fuel for cooling), and then you lean beyond that, and now you are using air for cooling, and the temperatures start dropping again from the peak.  So what you should do is you should lean slowly, watching your EGT until it gets to peak.

[Cabanaboy]

Great Article on EGT:

http://www.alcorinc.com/PDF/EGT_Nutshell_06_14_2010.pdf

 

[carusoam]

Cabana,

Nice read.  According to Alcor,  over heated exhaust valves cause pre ignition that leads to detonation.  This can occur in a few minutes time.

To avoid over heated exhaust valves, identify peak EGT for your engine at 65% power.  Keep you EGT below this value, and you will avoid the ill effects of detonation.

It was nice to see that Alcor gave a position on ROP / LOP.  It does not matter on the method, as long as the EGT is kept below this critical point.

Other interesting statements include dollars saved by LOP ops.  Max power is 100 d ROP.  Best efficiency is at peak.  LOP efficiency increases only because the airplane is going slower, less drag.

Overall, know your critical 65% EGT and stay below it.

You have to love the simplicity of the Alcor EGT system.  It is similar to a crystal radio. No power required....

Best regards,

-a-

[jetdriven]

I disagree.  Minimum BSFC occurs ~15-50 LOP.  Thats lb of fuel per HP per hour.  Flying slower is more efficient.  Flying lean of leak is more efficient combined with flying slower.  Still, you cannot get the same NMPG flying slower ROP than the same speed LOP. 

 

Re: hot exhaust valves.  I would like to see a single data point referring to hot exhaust valves as a trigger for preigniton. I can see a burned valve feather edge glowing hot, but not a proper exhaust valve.   Detonation is the premature lighting of fuel due to exceeding the coimpression-ignition (octane) resistance of the fuel.  Preignition is caused by a hot spot in the chamber. 

Re: 65% power EGT.   Our peak EGT at 65% used to be ~1590 at 65% power.  Now, with 25 degrees timing, its 1500.  So, for all the naysayers out there saying we are harming the engine, the exaust enjoys 90 degree cooler temps.  More horsepower too.  Of course that heat now goes to the cylinder fins.  That is still manangeable. 

Lycoming recommends peak at 75% power and below.  We use LOP up to 10.0 GPH, which is 75% power. 

 

[Shadrach]

dupe...

[Shadrach]

Quote: CABANABOY

Great Article on EGT:

http://www.alcorinc.com/PDF/EGT_Nutshell_06_14_2010.pdf

 

[Cruiser]

The Alcor article is interesting but much simplified in its explainations. They clearly discourage LOP operations. The graphs while accurate are misleading. There is no comparision of fuel consumption at the same power settings.

Here is an easy test that everyone can do. Do this at 65% power because everyone agrees that you cannot hurt your engine at 65% power or below. Set up your engine to run 65% power ROP. Record the EGT, CHT, fuel flow, airspeed and anything else you want to compare. Then setup your engine to run 65% power LOP (for the Lycoming 360 this is 8.6 gph) and record the same parameters. You can see for yourself the difference in the two operating methods.  

[jetdriven]

 

"or cruise, using the Figure 10 dial presentation, all one needs to remember is to lean to peak EGT for best fuel

economy unless this puts the EGT into the yellow arc, in which case the mixture should be enriched sufficiently to keep the
EGT in the green." 

 

 

LOP or ROP?  Richen her up until the EGT is in the green.  Never mind them CHT's, they are in the green at 450F.   No problem! 

NO discussion of BSFC.  It is the greatest around ~15 LOP to 50 LOP.  You don't have greater range because you are flying slower while LOP. You also fly farther because BSFC is greater. IE more shaft HP per lb/hr of fuel.  

 

In  the photo.... Where is the 50F LOP data?    its missing!

 

[pilot716]

If CHT is more important than EGT why do they make the comparison using EGT and never really mention CHT? Regardless I am going to try and use the method in the JPI book to first manually lean so I know exactly how to do it then I will try the autolean procedure.

[carusoam]

JetD,

Any idea why the timing was changed to 20d to begin with? (I read the bulletin)

25 seems to be win-win all around for you.  The only "il-effect" is slightly higher CHTs?

It seems that Lycoming wrote the change for everyone to allow use of 80 octane fuel, fixed pitch props, un-instrumented engines, poor baffling, and uncaring operators.

Lycoming seems to be unable to help down to the level of special interest groups.  They can only handle information for everyone or no information at all.

Keep fighting the good fight.

Best regards,

-a-

 

[Shadrach]

Quote: pilot716

If CHT is more important than EGT why do they make the comparison using EGT and never really mention CHT? Regardless I am going to try and use the method in the JPI book to first manually lean so I know exactly how to do it then I will try the autolean procedure.

[carusoam]

The Alcor article is an ancient sales tool for there ancient EGT guage.  Their intent seems to be, bring people out of the dark and into the light.

Not so much deliver them an engineering degree in propulsion.  BSFC would be too much for the intended audience.

Their audience doesn't have EGT guages, never mind digital ones with electronic FF.

Best regards,

-a-

[Becca]

Quote: carusoam

JetD,

Any idea why the timing was changed to 20d to begin with? (I read the bulletin)

25 seems to be win-win all around for you.  The only "il-effect" is slightly higher CHTs?

It seems that Lycoming wrote the change for everyone to allow use of 80 octane fuel, fixed pitch props, un-instrumented engines, poor baffling, and uncaring operators.

Lycoming seems to be unable to help down to the level of special interest groups.  They can only handle information for everyone or no information at all.

Keep fighting the good fight.

Best regards,

-a-

 

[Becca]

Quote: carusoam

The Alcor article is an ancient sales tool for there ancient EGT guage.  Their intent seems to be, bring people out of the dark and into the light.

Not so much deliver them an engineering degree in propulsion.  BSFC would be too much for the intended audience.

Their audience doesn't have EGT guages, never mind digital ones with electronic FF.

Best regards,

-a-

[Shadrach]

Quote: carusoam

The Alcor article is an ancient sales tool for there ancient EGT guage.  Their intent seems to be, bring people out of the dark and into the light.

Not so much deliver them an engineering degree in propulsion.  BSFC would be too much for the intended audience.

Their audience doesn't have EGT guages, never mind digital ones with electronic FF.

Best regards,

-a-