Paul,

 

>> I think the flaw in that argument is the GPH per HP for a specific regime (ROP versus LOP) as your specific fuel consumption will change depending on that setting.  Your HP should be directly proportional to RPM and MP at any mixture. I think I'm correct in that last statement regardless of whether the engine is ROP or LOP.<<

 

That has been a nearly universal understanding by pilots for decades.  But it turns out not to be accurate.

 

TRUE when ROP.

 

Not true when LOP.

 

ROP - - horsepower is controlled by mass air flow through the engine.  The MAF is primarily a function of  MP, RPM, and induction air temperature.  There are second order effects.

 

LOP  - -  horsepower is controlled by  fuel flow.     [ VERY much like a pure turbine engine (which always is “LEAN of PEAK” ) .   The “throttle” is really just a fuel flow lever.]

 

If you are  ROP and you add 1 gph,  you get almost no change in HP.

 

LOP - - if you add 1 gph in fuel flow you get about  14 to 15  additional Hp, depending on the engine configuration.

 

Regards,  George

 

PS.  We teach a class that covers all of this - -  www.advancedpilot.com

 

 

 

 

 

 

I think the flaw in that argument is the GPH per HP for a specific regime (ROP versus LOP) as your specific fuel consumption will change depending on that setting.  Your HP should be directly proportional to RPM and MP at any mixture. I think I'm correct in that last statement regardless of whether the engine is ROP or LOP.  When I ran the TSIO-520NB with GAMI the procedure would be to bump up the MP to keep the desired HP (65%, 70% or whatever you choose).   You have to bring the MP back up as the fuel flow drops off.    So, I would pick your desired power setting for LOP ops (say 65% for talking purposes) and get the MP and RPM for that power setting.   When you go LOP work towards bringing the MP back up to maintain your target power.  That is what I recall for the GAMIs so I would be interested if that might be what was being taught more recently.  As I said in an earlier posting, the only problem with high altitude turbo ops LOP was the need to bump up the MP to keep the wastegate from bootstrapping.  Others may need higher MP for pressurization but I never experienced that in the twin.  Hope that all makes sense.