Manifold Pressure with FP Prop

[Jesse]

I know traditionally fixed pitch prop planes don't have a manifold pressure gauge, but in the day of digital engine monitors, I think it is getting much more common. I have MAP in my -6A, and when I fly a FP plane without it, it drives me crazy, feeling like I really have no idea of my true power setting. Am I the only one? I think this might make a nice Poll.

[YellowJacket RV9]

I am very glad I have a MP gauge on my FP. My GRT Sport calculates % power which was helpful for break-in and is also helpful when leaning, and for getting a baseline of performance numbers at different power settings.

On another note, was that you in N399DC that gave me a shout-out on Friday with Jax center on my way to Charleston?

Chris

[Kyle Boatright]

Originally Posted by Jesse

I know traditionally fixed pitch prop planes don't have a manifold pressure gauge, but in the day of digital engine monitors, I think it is getting much more common. I have MAP in my -6A, and when I fly a FP plane without it, it drives me crazy, feeling like I really have no idea of my true power setting. Am I the only one? I think this might make a nice Poll.

Same here. I really like having both pieces of information necessary (RPM & MP) to gauge the power setting.

[Jesse]

Originally Posted by YellowJacket RV9

I am very glad I have a MP gauge on my FP. My GRT Sport calculates % power which was helpful for break-in and is also helpful when leaning, and for getting a baseline of performance numbers at different power settings.

On another note, was that you in N399DC that gave me a shout-out on Friday with Jax center on my way to Charleston?

Chris

That was me. I didn't push it with Jax as they were a little slow on the uptake and were a little busy. I love meeting other RV'ers in the air. Next time please stop by X35.

[rightrudder]

Originally Posted by Jesse

I know traditionally fixed pitch prop planes don't have a manifold pressure gauge, but in the day of digital engine monitors, I think it is getting much more common. I have MAP in my -6A, and when I fly a FP plane without it, it drives me crazy, feeling like I really have no idea of my true power setting. Am I the only one? I think this might make a nice Poll.

I never fitted MAP to my -9A with an FP prop, and it doesn't bother me because I've never flown a plane with MAP....except for a -7A with a CS prop I flew in transition training.

If I'm going somewhere, say, more than 50 miles away, I just make sure I'm above 8000' DA and run between 2500 and 2550 rpm at 40-50 degrees F LOP. If I can hit 145-150 KTAS I'm happy; exact power doesn't concern me as long as the engine is not in danger of detonation and everything's running in the right temp range.

[rvbuilder2002]

I rarely look at the tach indication on my fixed pitch RV-6A. Power setting is primarily done based on MP.

[SHIPCHIEF]

I prefer a manifold pressure gage when running a FP prop. My first experience with one was when I bought my T-18. When you are cruising along and begin your decent to your destination, the RPM hardly reduces at all, so the manifold pressure gage is the 'go-to' gage.
In the pattern, the Tachometer is the 'go-to' gage, but once I'm out of the pattern, the faster we go, the more I use the MP gage. It's also helpful when flying cross country in formation with friends.
So I installed one in my RV-8 when I built it. When I install an Engine Monitoring System, I'll get one with an MP gage to figure HP like Chris mentioned.

[vic syracuse]

I've even installed them on the Kitfoxes with 912's. As Scott says---I always use it instead of the RPM gauge.

Vic

[Jesse]

Originally Posted by rvbuilder2002

I rarely look at the tach indication on my fixed pitch RV-6A. Power setting is primarily done based on MP.

That's exactly what was coming to my mind. RPM means very little, just to avoid an over speed in descent. MAP is the more useful gauge.

[Rupester]

I've had an MP gauge with my fixed pitch from the get-go and cannot imagine flying without it. Most important for me is it's use in flying LOP. The % power tables in the GRT system are based on altitude, MAP, and RPM; there is no reflection of lean vs rich operation. Don Rivera indicated at FI 101 that Lycomings "do not like to be run lean above 24" MAP." Sure enough, if you look at at the related Lycoming graph of "Fuel flo vs % Rated Power", it shows that Lyco's are thirstier above 75% power. Not coincidentally, at lower altitudes 24" MAP gets you very close to 75% power.

http://aeroclub-lehavre.e-monsite.co...r-s-manual.pdf (see page 60)

Accordingly, I run LOP at any altitude so long as the MAP is 24" or less. I don't use the % Power indication in my GRT system. At lower altitudes, that means throttling back quite a bit; at higher altitudes, not at all.