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Maximum Power Mixture

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fbrewer

Well Known Member
I'm getting ready for the first flight of our new YIO-360-M1B.

When perusing Lycoming Engine Performance Data chart, in the box, it references: "MAXIMUM POWER MIXTURE UNLESS OTHERWISE NOTED".

I'm sure my search skills can improve, but no where in the Lycoming Operating Instructions Manual can I find a definition for "MAXIMUM POWER MIXTURE".

Any idea here I can find the definition?
 
fbrewer said:
I'm getting ready for the first flight of our new YIO-360-M1B.

When perusing Lycoming Engine Performance Data chart, in the box, it references: "MAXIMUM POWER MIXTURE UNLESS OTHERWISE NOTED".

I'm sure my search skills can improve, but no where in the Lycoming Operating Instructions Manual can I find a definition for "MAXIMUM POWER MIXTURE".

Any idea here I can find the definition?
Click to expand...

Leaned to the point where the engine makes its most power. It is usually just rich of peak EGT.

Full rich sacrifices some performance for cooling and detonation margin. Maximum power mixture at low altitudes and high power settings - high manifold pressure/high RPM - is likely to overheat and or detonate.

Ed Holyoke
 
Go here, first chart, distributed by Lycoming:

http://www.vansairforce.com/community/showpost.php?p=1288501&postcount=41

Best power mixture is graphed at 100 to 150 ROP EGT.

Bicyclops said:
Leaned to the point where the engine makes its most power. It is usually just rich of peak EGT.
Click to expand...

Depends on how we define "just".

Max power with any engine is just short of detonation. Trouble is, detonation onset is not based on a fixed FA ratio. It varies with CR, CHT, inlet temperature, octane rating, oil temperature, oil consumption, ignition timing, and a few other things. Given certification conditions (meaning everything max hot) and 20 degree timing, it will detonate near peak EGT at full throttle. Some will detonate at quite a bit less than full throttle

The above referenced chart is general in nature, i.e. pretty safe if you're operating a standard M1B. Might not want to go nearer to peak EGT at max power without an eye glued to the EIS.

See the 540K charts in the same post. The K is considered one of Lyc's most detonation prone, so it is used for test purposes by the FAA and at GAMI. B15 is 2700/28", and a perfect example of max power (the peak in the red curve) just short of detonation onset...which is about a fuzz and a half leaner than 100 ROP.

Full rich sacrifices some performance for cooling and detonation margin.
Click to expand...

Not cooling. Overly rich just means less power, i.e. less heat.
 
Dan,

In order to know if you are ROP, I need to find peak for the given MAP and RPM.

Is it best to find peak from the lean side or the rich side?

Does it matter which side I find peak?

Can I assume that in the few minutes I find peak, before richening to 150 ROP, I will not do any damage to my new YIO-360-M1B?

I am getting ready for our first flight with our new motor.
 
For the first flight just stay at full rich. You will have enough stuff to do and check other than worrying if you are at 150 degrees rich of peak. The extra fuel will be a benefit to mitigate the typical high temps with a new engine. Temper this if you are at high density altitude where leaning to get power makes sense.

After the first few flights, get level at cruise power and then start leaning just a little and watch CHTs. Ease into finding things like peak EGT, GAMI spread and such as the flight test program proceeds.

Carl
 
DanH said:
Go here, first chart, distributed by Lycoming:

http://www.vansairforce.com/community/showpost.php?p=1288501&postcount=41

Best power mixture is graphed at 100 to 150 ROP EGT.



Depends on how we define "just".

Max power with any engine is just short of detonation. Trouble is, detonation onset is not based on a fixed FA ratio. It varies with CR, CHT, inlet temperature, octane rating, oil temperature, oil consumption, ignition timing, and a few other things. Given certification conditions (meaning everything max hot) and 20 degree timing, it will detonate near peak EGT at full throttle. Some will detonate at quite a bit less than full throttle

The above referenced chart is general in nature, i.e. pretty safe if you're operating a standard M1B. Might not want to go nearer to peak EGT at max power without an eye glued to the EIS.

See the 540K charts in the same post. The K is considered one of Lyc's most detonation prone, so it is used for test purposes by the FAA and at GAMI. B15 is 2700/28", and a perfect example of max power (the peak in the red curve) just short of detonation onset...which is about a fuzz and a half leaner than 100 ROP.



Not cooling. Overly rich just means less power, i.e. less heat.
Click to expand...

More scientific definitions for sure. I was being very general. Should have said cooler running or something like that. OP is talking about first flight. Trying to approach "best power" or establishing where peak EGT lies probably isn't the best use of time and attention on early flights or the best for the engine. My first flight was at max RPM, WOT, full rich for a little more than an hour at about 3000' MSL. I circled near the airport in case of... and got most of my break in done. I was showing 600 some odd GPH fuel flow, but all the temperatures were OK so I kept on flying for a while.

Ed Holyoke
 
If it is a new engine from Lycoming, take a look at the run sheets provided with the engine.
 
fbrewer said:
Is it best to find peak from the lean side or the rich side?
Click to expand...

I generally find peak from the lean side, but I won't claim it's "better".

That said, I agree with Carl and Ed. First flights, leave it rich, mind the EIS for limits, and run the snot out of it. Fly 15 minutes, land, celebrate, catch your breath, check for leaks. Rest, relax, then go for an hour. Run WOT, coast a bit to cool when needed, run WOT, repeat.

Can I assume that in the few minutes I find peak, before richening to 150 ROP, I will not do any damage to my new YIO-360-M1B?
Click to expand...

Depends on power setting and temperature. As a practical matter, none of us look for peak at full throttle, while nothing can be hurt with the red knob below 65%.

The fuel injection vendor flow checked the control. It's not likely to be far off the mark. After a few flights, if you want to start power reduction with leaning, or lean in the climb, simply look down at the EGTs shortly after liftoff, at full throttle. Note one of them, doesn't matter which. Climb with everything against the stops until MP drops back to 25 or so. Now pull RPM to 2500. EGTs will drop. Lean until the EGT noted at liftoff rises back to the value you saw then. You're in a safe best power range. If climbing, adjust again from time to time. Glad to help you get fancy later.
 
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