How does power output behave when climbing with constant RPM, MAP and mixture

[Kriekos]

Hi everyone,

The titel basically says it all. I have this question: "Standard atmosphere climbing at constant RPM and MAP and with constant mixture setting, the power output of a piston engine will..."

I have an idea but I am also getting different opinions.

Anybody wants to wager in with his opinion?

Thanks in advance!

Grtz,
Kriekos

[Alex Whittingham]

Is it possible to climb with constant RPM, mixture and MAP?

[Genghis the Engineer]

Presumably by judicious tweaking of throttle at the very least during the climb you might get close.

G

[awair]

I think it’s asking about the inevitable reduction of MAP with altitude, and the increasing relative richness of the mixture?

Is this a multiple choice question?

[EXDAC]

Originally Posted by Kriekos

Anybody wants to wager in with his opinion?

If rpm, mp, and mixture remain constant then the power will remain constant. What does "climbing" have to do with the specified scenario? Are you, perhaps, proposing a turbo normalized engine?

[PFD]

Originally Posted by Kriekos

Hi everyone,

The titel basically says it all. I have this question: "Standard atmosphere climbing at constant RPM and MAP and with constant mixture setting, the power output of a piston engine will..."

If turbocharged then power drops as wastegate closes increasing exhaust back pressure, and reducing volumetric efficiency.

If it is a normally aspirated engine, at constant MAP (achieved by opening the throttle as you climb) then power increases because exhaust back pressure reduces as you climb. This only works if you climb at a MAP lower than static pressure, and then only up to full throttle, which would be called Full Throttle height.

We need to know the type of engine to answer correctly.

[Alex Whittingham]

I think this may derive from some very odd ATPL questions which don't set the scenario properly, I'd be interested to hear what the OP is driving at. I wonder if the reference to constant mixture setting means 'don't touch the knob', or does it mean 'leaning the engine appropriately as air density decreases to maintain a constant air:fuel mass ratio'? Probably the former, I would guess. CSE's old piston engine performance notes are likely to blame here, several challengable statements that were never tested under the old syllabus but are now being plucked verbatim by the examiners, and being looked at closely for the first time.