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5.3.3 Precision of Fuel Flow
The highest precision is achieved with normal RPM during cruise flight (Fuel
consumption between 10 and 20 l/h). In the extreme corners of the RPM range, e.g.
during full throttle or idle, the precision is slightly less. Below a fuel consumption of 5
litres/h the precision is rather low, therefore the
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MFD
does not indicate a fuel
consumption below 5 litres/h. It always assumes a minimum fuel consumption of 5
litres/h, even when the engine idles.
5.3.4 Fuel Flow with Engines with Fuel Flow-Back System
Certain engine configurations not only have a fuel line from tank to engine, but fuel
which is not consumed by the engine is transported back from engine to tank.
5.3.5 Measuring with
two
flow senders (engines with fuel flow back system)
Because the back-flow can be a significant portion of the fuel pumped to the engine,
the
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MFD
can be used with a second fuel flow sender. The
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MFD
measures the fuel flow from tank to engine and also from engine back to tank. Both
values let the
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MFD
calculate the actual fuel consumption.
In SET-Mode 37 the
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MFD
can be programmed, whether the aircraft uses a
single fuel line (tank to engine, setting 1WAY) or a fuel flow back system (setting
2WAY).
Even when two senders are used, the fuel flow can be calibrated as described in
section 5.3.6
WARNING!
Because two fuel flow senders are used with engines with fuel
flow-back configuration, possible measuring
errors could duplicate
.
Therefore the
precision is lower
than with only a single fuel line in 1-way
configurations and we do not recommend to use two flow senders.
5.3.6
Recommended
: Measuring with
one
fuel flow sender (engines with fuel flow
back system)
There is a second way of measuring the fuel consumption of engines with a fuel flow
back system. This works with engines, where the fuel line is split to two carburettors
AFTER the fuel line which leads back to the tank (e.g. some Rotax 912 and 912 S
versions). Because it can be assumed that both carburettors receive approximately the
same amount of fuel, only the fuel consumption of one carburettor is measured and
then doubled.
The calibration factor in SET-Mode 3 must be set to double the indicated fuel flow. A
setting of approx. 140-170 has shown to be right in various tests
The measuring method must be set to 1WAY in SET-Mode 38.
