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Engine Power reading on G3X screen

design4p

Active Member
Hello,

I would be pleased if anyone could assist. I have a full suite of Garmin avionics including 2 G3X screens.

I understand that the Engine Power requires inputs from the RPM, manifold pressure, and fuel flow sensors.

However, when the on "Take Off" or "Climb" with the engine full rich the Engine Power indicates a rating of well over 100% and then settles down to below 100% when the RPM is reduced. In cruise, when I Lean the engine to "Lean of Peak" the Engine Power reduces further to a value that is expected ie 65%.

My fuel usage (flow) is accurate with comparing G3X fuel used and tank dip stick.

Is this normal or is there something not quite right?

Any assistance would be appreciated.

Regards John
 
In my experience the %power algorithms give an indication of power produced and are never completely accurate. Have you tried tuning the data table?
 
Percent Power Configuration Suggestions

Good morning, John.

You are correct on the required inputs for Engine Power to be calculated and displayed in your system (Section 35.4.32.29 of the Installation Manual). In that section, we also discuss setting up the correct maximum rated power and RPM for your engine. I believe you have a Lycoming IO-390 in your -14, correct? This engine has a few variants which could be 200hp-215hp. Would you mind checking to see that the power and RPM are both set up correctly per your specific variant?

I also noticed that you have had this issue for a while (MAP with engine power well over 100%). If you verify that the settings are correct and are still seeing issues, sending data logs and a screen capture of your engine power configuration page to [email protected] would be the best way for us to assist you further.

Blue skies,
Brian
 
Good morning, John.

You are correct on the required inputs for Engine Power to be calculated and displayed in your system (Section 35.4.32.29 of the Installation Manual). In that section, we also discuss setting up the correct maximum rated power and RPM for your engine. I believe you have a Lycoming IO-390 in your -14, correct? This engine has a few variants which could be 200hp-215hp. Would you mind checking to see that the power and RPM are both set up correctly per your specific variant?

I also noticed that you have had this issue for a while (MAP with engine power well over 100%). If you verify that the settings are correct and are still seeing issues, sending data logs and a screen capture of your engine power configuration page to [email protected] would be the best way for us to assist you further.

Blue skies,
Brian

I am hoping G3xpert can improve the answer to the original question by answering the following. I have a 10:1 compression engine, raised from 8.5:1 Theory says the increase in compression ratio from 8.5 to 10 should increase thermal efficiency by a factor of

(1-1/10^[x-1]) / (1-1/8.5^[x-1])

where x is the specific heat ratio (around 1.3 at common exhaust gas temperatures, which gives about a 5% bump in efficiency). Whatever that bump is—call it y%—my question is, when flying on the lean side, where HP is a function of fuel flow, can I assume that HP is y% higher than the HP associated with the %power that you report on the G3X, which I assume is based on fuel flow?
 
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