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MAP Reading WOT@ Take Off Pwr vs. Engine Off

S

supik

Well Known Member
RV10, IO540 standard with 1 slick (fix timing) and 1 mag, 2 blade hartzel, standard cowling

-Just wondering if I should start looking for a leak in the induction system or is this a normal behavior?

1. with the Engine Off ( 0 RPM ): I'm reading 29.8 inHg MAP
2. WOT static pwr at Take Off ( 2700 RPM): reading 28.7 inHg MAP

There is a 0.9 difference in MAP (WOT with engine running vs. engine Off)

Further the pressure at the airfield was 29.94 inHg, so I'm assuming the MAP reading is of by 0.14 ?

Data point: I'm reading 22.9 inHg with WOT at 7400 PA (which seems to be on the lower side when reading other posts ?)

Thanks,
 
You are simply seeing the losses associated with inlet geometry, the filter, throttle blade, etc. It's normal. At zero RPM, there are no losses. In many cases, these losses are overcome (masked, really) by ram pressure due to forward speed. If you were to note the MAP at liftoff, then push the nose over and maintain 1 foot AGL as the airplane accelerated, you should see the MAP climb along with airspeed.
 
supik said:
RV10, IO540 standard with 1 slick (fix timing) and 1 mag, 2 blade hartzel, standard cowling

-Just wondering if I should start looking for a leak in the induction system or is this a normal behavior?

1. with the Engine Off ( 0 RPM ): I'm reading 29.8 inHg MAP
2. WOT static pwr at Take Off ( 2700 RPM): reading 28.7 inHg MAP

There is a 0.9 difference in MAP (WOT with engine running vs. engine Off)

Further the pressure at the airfield was 29.94 inHg, so I'm assuming the MAP reading is of by 0.14 ?

Data point: I'm reading 22.9 inHg with WOT at 7400 PA (which seems to be on the lower side when reading other posts ?)

Thanks,
Click to expand...

Was 29.94 the actual pressure or was it the altimeter setting? The altimeter setting is referenced to sea level. I’m assuming that you are located at the Stefanik airport which has a field elevation of 436’. If 29.94 was the altimeter setting, then the MAP at 0 RPM should be 29.5 (29.94 - .44). Your engine monitor may have a way to offset or calibrate this.
 
Mike, that makes sense..

thanks

Toobuilder said:
You are simply seeing the losses associated with inlet geometry, the filter, throttle blade, etc. It's normal. At zero RPM, there are no losses. In many cases, these losses are overcome (masked, really) by ram pressure due to forward speed. If you were to note the MAP at liftoff, then push the nose over and maintain 1 foot AGL as the airplane accelerated, you should see the MAP climb along with airspeed.
Click to expand...
 
At that time, I was located at LZDB (771 ft Altitude), so the reading should be approx 29.1 inHg if I'm not mistaken. I haven't found anything in the G3X Touch Install Manual about offsetting the MAP reading.

EDIT: Yes, altimeter setting was 29.94 on that day

RV8Squaz said:
Was 29.94 the actual pressure or was it the altimeter setting? The altimeter setting is referenced to sea level. I’m assuming that you are located at the Stefanik airport which has a field elevation of 436’. If 29.94 was the altimeter setting, then the MAP at 0 RPM should be 29.5 (29.94 - .44). Your engine monitor may have a way to offset or calibrate this.
Click to expand...
 
supik said:
At that time, I was located at LZDB (771 ft Altitude), so the reading should be approx 29.1 inHg if I'm not mistaken. I haven't found anything in the G3X Touch Install Manual about offsetting the MAP reading.

EDIT: Yes, altimeter setting was 29.94 on that day
Click to expand...

Igor,

You are correct on both counts. Based on that field elevation and altimeter setting it should have read approximately 29.1, maybe closer to 29.2 (29.94-.77). I didn’t find anything in the Installation manual or the Maintenance manual. That’s surprising. My old VM1000c has that ability. Maybe the G3Xperts might know something.

Jerry
 
Thank you Jerry,

I'll check the issue with the G3Xpert team..

RV8Squaz said:
Igor,

You are correct on both counts. Based on that field elevation and altimeter setting it should have read approximately 29.1, maybe closer to 29.2 (29.94-.77). I didn’t find anything in the Installation manual or the Maintenance manual. That’s surprising. My old VM1000c has that ability. Maybe the G3Xperts might know something.

Jerry
Click to expand...
 
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