Garmin GI 275 EIS %HP

[Tom 4536]

I’ve been flying with a friend in his 252 with a new GI 275 engine monitor. When cruising lean of peak the EIS %HP does not change as fuel flow is changed. Is this an oversight by Garmin or are we doing something wrong? The Garmin Pilot Guide (Ver. H) does not mention that we have to tell the EIS that we are LOP.

The JPI 900 in my 231 requires that I tell it I am LOP to get the correct %HP.

Thank you.

[carusoam]

All engine monitors go through this challenge early in their existence…

 

When LOP… the %bhp is an easy calculation based on a FF reading…

When ROP… the same is true based on an air flow calculation…

Since we don’t have an airflow sensor yet…. A form of look up table gets used…. Using RPM and MP….

 

If your EIS doesn’t know you are LOP, how will it know to reference FF for the calculation?

 

To find the procedure… reading the manual might be helpful….  It’s Big G, so the manual may be missing some detail…
 

To find somebody familiar with the Big G manuals….  Find Skip….  
 

PP thoughts only, not a big G guy…

Best regards,

-a-
 

 

[PT20J]

If it works like the G3X, there are no pilot inputs. The inputs to the algorithm are manifold pressure, rpm, and fuel flow. When setting it up you tell it whether the engine is a Lycoming or Continental, normally aspirated or turbocharged, the max rated power and rpm, and manifold pressure for rated power if turbocharged.

Garmin doesn't publish the algorithm, but I can guess how it might work. Given the manifold pressure and rpm would allow approximation of sea level power at best power mixture for a generic engine. This could be adjusted for density altitude for a normally aspirated engine. A generic specific fuel consumption curve would allow using the fuel flow to account for mixture setting.

George Braly (APS, GAMI) developed an algorithm -- I think it may have been for the G1000, but my memory is fuzzy on that -- and it was supposed to be kept proprietary. Maybe that's the algorithm being used. Perhaps someone else remembers.

Skip