AFP - measuring fuel flow using pressure

rv8ch · #1 09-30-2012, 05:05 AM

The Airflow Performance manual talks about using pressure at the flow divider as a way of measuring fuel flow, which seems to me a bit simpler than the floscan 201 or redcube FT-60 turbine systems. Has anyone successfully used this pressure method? I've extracted the page below.

Thanks!

rzbill · #2 09-30-2012, 05:40 AM

Mickey,
It is my understanding that the vast majority of "steam panel" fuel flow gages (think classic Mooney or Arrow for instance) are pressure gages that use the ports you describe.

Walt · #3 09-30-2012, 05:45 AM

Using pressure calibrated to fuel flow is not a very precise method of actually measuring FF. This method is used in some certified AC and you
could probably find a pressure gauge out there somewhere that is calibrated in FF.

However, you give up some of the great benefits a FF computer can provide such as:

Fuel to destination
Fuel reserve at destination
MPG
Fuel used
Fuel remaining
Time to empty
Horse power/% power

Radomir · #4 09-30-2012, 07:26 AM

The FF gauge on the Beech Bonanza works off of fuel pressure. It is not very precise (it can be off by 2 gal in cruise) and therefore is pretty useless... I guess back in the day it was better than nothing, but as Walt points out the electronic gauges that work off of the fuel flow sender are much more accurate and provide additional features.

SHIPCHIEF · #5 09-30-2012, 11:16 AM

Measuring pressure drop across an orifice is a very accurate way to measure flow.
However, no one seems to have a computer controlled display which has all the bells & whistles we like, that is based on the pressure output from the fuel flow devider. It's the computer that allows calibration, and does all the math so you can keep the E6B at home.
Too bad, it would eliminate 4 fittings and 2 hose connections (if it were a transducer screwed straight into the flow devider)

Walt · #6 09-30-2012, 11:37 AM

Quote:

Originally Posted by SHIPCHIEF

Measuring pressure drop across an orifice is a very accurate way to measure flow.
However, no one seems to have a computer controlled display which has all the bells & whistles we like, that is based on the pressure output from the fuel flow devider. It's the computer that allows calibration, and does all the math so you can keep the E6B at home.
Too bad, it would eliminate 4 fittings and 2 hose connections (if it were a transducer screwed straight into the flow devider)

This is not really pressure across an orifice system, its just fuel pressure. A clogged nozzle for example will show an "increase" in flow because
the pressure increased with the clogged nozzle, in reality the "flow" actually decreased.

SHIPCHIEF · #7 09-30-2012, 12:07 PM

Agreed. I didn't think of that.

Wayne Gillispie · #8 09-30-2012, 02:04 PM

Quote:

Originally Posted by Walt

This is not really pressure across an orifice system, its just fuel pressure. A clogged nozzle for example will show an "increase" in flow because
the pressure increased with the clogged nozzle, in reality the "flow" actually decreased.

Even worse with a FI line breakage, you will indicate lower FF.

I love my FT-60. FF on takeoff= 25.5-26gph. I set max alarm at 27 and will warn me of a fuel leak from tunnel mounted red cube forward(with boost pum on). Another good reason to keep your red cube there on the -10.