rblackley

rblackley

Member
I am installing a XO-340 with a fixed pitch propeller. Wondering why my FFK came with a manifold pressure line. What kind of helpfull information can a manifold pressure gauge tell me with this set up? Carb ice? Intake obstruction? Leak? What would an unusually low or high mp in relation to rpm indicate?

Thanks,

Ryan
 
It certainly isn't essential but it is nice to be able to compare power settings if you are interested in how efficient your RV is. It allows you to figure out what power percentage you are running.
 
Or real pilots...

enjoy the beauty, simplicity and low cost of a simple panel not mucked up by another dial.

Technique only.
 
Another advantage is being able to "set" power more quickly by using manifold pressure rather than having to wait for the rpm to stabilize.
 
RPM alone is no indication of how much power the motor is producing. With a manifold pressure gauge, you can tell when the prop is loaded (power) and not just spinning.

For example, if you are at 75% power at 3000 ft you would be at about 2400 rpm and 24" mp. As you climb, for each 1000ft, you lose 1" of mp. If you don't increase your MP and RPM by pushing the throttle in, your % of power will decrease.

If you add the MP and the first two numbers of the tach you can get a close estimate of power produced.............

24+24=48=75%
any combo= 48=75%
45=65%
42=55%

So, as manifold pressure decreases during a climb, the rpm must be increased to maintain % of power.

This chart only works with a fixed pitch prop.
 
I wonder if they go in all the FF kits now becasue so many people are putting in glass panels, and most of the EFIS's come with a MAP sensor - so why not hook it up?

I ordered Van's Manifold, Fuel, and Oil Pressure lines the other day for the -3 project....they are way cheaper than buying raw hose and fittings to build your own. Van must have gotten a bargain....

Paul
 
gasman said:
..
If you add the MP and the first two numbers of the tach you can get a close estimate of power produced.............

24+24=48=75%
any combo= 48=75%
45=65%
42=55%

So, as manifold pressure decreases during a climb, the rpm must be increased to maintain % of power.

This chart only works with a fixed pitch prop.
Click to expand...

Hmmm. Well I would argue it doesn't work very well with any prop, but shouldn't be any different with FP or CS.
 
MP gauge? optional? essential?

FWIW, I am in the same predicament as Ryan.
I've read with fascination since I was 6, about the wonderful gaggle of gages and how the expert airman caresses the controls to make the dials point just so....MP, VOR, DME, TIT, VSI, EGT, CHT, OAT, LMNOP.
....still, I have no real idea what the heck the MP shows or does, or why I would try to hit 70% ( of what?) power....as long as I am flying along.
If I am not going fast enough, I push the black knob in some more. IF it's already in, I don't think I can go faster.
am I wrong?
 
Best to keep it simple unless you really like to look at gauges. Some people do and that's okay also.
"Push the stick (yoke) forward and the houses get bigger. Pull the stick back and they get smaller and then stabilize. Pull the stick all the way back and the houses get smaller and then get bigger again, fast." That's about it. :)
 
flyboy1963 said:
...If I am not going fast enough, I push the black knob in some more. IF it's already in, I don't think I can go faster.
am I wrong?
Click to expand...

If you don't have a blue knob to manage, then yes, the MP is mostly there for entertainment.

Even if you do have a blue knob, the throttle is wide open most of the time (for some of us), so the MP is also mostly there for entertainment. The exception is that changes in MP will indicate induction icing or other performance issues before the tachometer will.
 
gasman said:
Even if they couldn't spell it.

If the FAA required perfict spelling, They would have never given me my lisence............:eek:
Click to expand...

Spelling is important, but it's important to remember there are alternates.
Websters 3rd New International Dictionary (unabridged) states "gauge or gage." Also 2D under gauge reads "gage: Any of various instruments privided with a graduated scale or dial for measuring."
 
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