We have a mono which means fuel quantity measuring devices will indicate
differently
depending on whether the aircraft is in level flight attitude or ground
attitude. Adds a bit of complexity to the problem!
We rely most on the fuel computer built into our GRT EIS and EFIS. This has two
separate FlowScan transducers, one for in and one for return. It has proven
to be accurate, probably within 1/2 gallon. It's hard to know how accurate it
is, since it is difficult to measure fuel quantity accurately with a sight
gauge.
We have a sight gauge positioned on the rear wall of the cockpit module and
connected
to the port side tank water drain. This is calibrated for ground attitude
and we use it when refueling. We compare it to the fuel computer. Due to
it's location, it is not visible in flight.
Andrew Sarangan suggested an alternative to a sight gauge. We don't know what
the
current status of this novel idea is. Here is the thread:
http://forums.matronics.com/viewtopic.php?t=103987&highlight=fuel+level
In flight we use two differential pressure sensors, one on each tank drain. The
transducers are Freescale MPXV4006DP. They output 0-5 volts which our EIS
accepts
as aux inputs. Our GRT EFIS has a tank calibration table so we account
for the shape of the tank there and we did that calibration in level flight
attitude.
We have each sensor calibrated from 0 - 3 gal. So each will show the
amount of fuel in its 3 gal side. When both are at 3 gal, we then display both
sensors as having 6 gal and they change together. When we have less than
6 gal on board, we just add the amount each shows. We ignore the fuel quantity
indications from these sensors when on the ground!
This system works pretty well. We are confident enough to use fuel out of the
port tank until no more than 1 gallon remains. We then switch to the stbd tank
and complete the flight. Of course when low on fuel, we monitor the fuel
computer
and the differential fuel pressure closely.
Ira, we found that with a forward facing tank vent on the belly of the aircraft,
there is enough ram air pressure that we had to use differential transducers
connected to the tank vent. We tried differential sensors vented to ambient
pressure and found large errors.
Jim & Heather
N241BW
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=439702#439702
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