Do I really need to see MAP INHG?

[rileyspoon]

I have the dual Dynon HDX configuration and I have the engine instrumentation on the bottom band of my PFD. The system is configured based on the Van's documentation but one of the items shown to the right of the fuel pressure is for what I assume is manifold pressure. The scale is all green. No yellow or red areas and unless I missed it somewhere, I can't find any reference to it in the Van's documentation or the HDX manual.

Why is it even shown? Nothing in the POH to tell me to do something if it has a specific reading. What parameters represent good or bad? Is there an upper and lower limit? And what actions am I supposed to take for either one? The Dynon pilot user's guide doesn't even show it on the engine band.

If I remove it from the display will Dynon still give me a warning if it is out of bounds? Not that I'll know what to do.

[Mel]

Manifold pressure is handy for setting power. When changing power settings, RPM takes a while to settle down. Once you are used to your airplane, you can adjust power by using MAP much faster.

[Piper J3]

Originally Posted by Mel

Manifold pressure is handy for setting power. When changing power settings, RPM takes a while to settle down. Once you are used to your airplane, you can adjust power by using MAP much faster.

This is Rotax 912 fixed pitch prop. MAP is virtually useless for RV-12 airplane...

[Mel]

Originally Posted by Piper J3

This is Rotax 912 fixed pitch prop. MAP is virtually useless for RV-12 airplane...

You can still set power faster with MAP than with RPM. MAP is definitely useful with F/P prop. I flew my RV-6 with F/P for over 25 years making power adjustments with MAP.

[gasman]

Originally Posted by Piper J3

This is Rotax 912 fixed pitch prop. MAP is virtually useless for RV-12 airplane...

Actually, manifold pressure can tell you if the prop is properly loaded by correct pitch even if it's not a C/S.

[rvbuilder2002]

Originally Posted by Mel

Manifold pressure is handy for setting power. When changing power settings, RPM takes a while to settle down. Once you are used to your airplane, you can adjust power by using MAP much faster.

Originally Posted by Piper J3

This is Rotax 912 fixed pitch prop. MAP is virtually useless for RV-12 airplane...

I disagree for the reason Mel mentioned.
Once you know your airplane and know what MP gives you a typical RPM in cruise you can just set it to that value and not have to move it again.
If you only use RPM to set power, you will be adjusting the throttle multiple times as the airplane accelerates and eventually stabilizes in cruise.

I have an RV-6A with a fixed pitch prop and I almost never look at the tach. reading.


To the OP's original question... do you need a MP indication? No, but it is very useful to have. Even on a fixed pitch airplane.

[David Paule]

If you are descending, it's a useful guide to the increased power due to the thicker air as you descend. It lets you know how far to continue to reduce throttle to keep power constant.

Dave

[Piper J3]

Wow, that’s an eye-opener... Maybe I’m the only one not using MAP for power settings while flying RV-12? I've flown my 12 for 800 hours without looking at MAP. I don’t know anyone else that is actively using MAP in a RV-12. It would be interesting to start a poll and ask the fraternity this question... I don’t see where VAF has ability to create a thread with polling option.

It would be nice to have EMS display % Engine Power based on MAP and RPM. Dynon doesn’t have option for Rotax 912 engine….
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[Amadeus]

Originally Posted by Piper J3

Wow, that’s an eye-opener... Maybe I’m the only one not using MAP for power settings while flying RV-12? I've flown my 12 for 800 hours without looking at MAP. I don’t know anyone else that is actively using MAP in a RV-12. It would be interesting to start a poll and ask the fraternity this question...

Put me in the "always reference manifold pressure" column. The only time I reference the tachometer is when I notice the engine sound change due to density, temperature or throttle creep.

[Mich48041]

I always use manifold pressure to set the throttle, usually at 25" for local flying.
I only look at RPM to make sure that upper and lower limits are not exceeded.