Hi Svein,
Johnsen" <sidsel.svein@oslo.online.no>
I fail to understand
how one flow transducer in the supply line to a
Rotax 912-type engine can
measure the engine's consumption, PROVIDED that
the return line is OPEN.
it can, if it is located AFTER a returnline
T-connection.
A fuel line after and before a transducer must be
straight about 100 mm.
I agree you, it is hard to understand how it
should work alone between the el and mec pumps (if
the return line is really open).
Look at an attachment. This set up works
perfectly - very accurate. If I read (Flight Data
Systems FC-10) I have used 47,8 liters, I will
refuel just that amount less couple of deciliters
(I have adjusted a K-factor such a way that it is
a bit on a safer side).
BTW I calibrated it during the several flights
with Kim Prout when he was he last spring.
Cheers and see you,
Raimo
OH-XRT
-----Alkuper=E4inen viesti-----
From: Sidsel & Svein Johnsen
Sent: Friday, February 22, 2013 4:04 PM
Subject: SV: Europa-List: fuel flow and return
line status
Johnsen" <sidsel.svein@oslo.online.no>
I fail to understand (one of my inherent
characteristics, some might say!)
how one flow transducer in the supply line to a
Rotax 912-type engine can
measure the engine's consumption, PROVIDED that
the return line is OPEN.
As has been covered on this List previously, the
return flow through the
factory-supplied restrictor is substantial - as it
should be, to serve the
intended purpose.
Adjusting the K-factor to compensate for the
return flow will give correct
net flow (= consumption) at only ONE specific flow
rate: The flow rate at
which the K-factor has been calibrated.
If the instrument also has a zero offset
adjustment (which the E.I.
instrument does not have), one flow transducer in
the supply line would
work, PROVIDED that the return rate is constant,
regardless of the fuel
pressure and flow rate past the return line
off-take - which it is not.
The K-factor is only a multiplier, telling the
electronic logic how much
fuel is going through with each full rotation of
the flow transducer's
paddle wheel. It cannot cause any flow
subtraction to compensate for the
returned fuel (even if the return flow rate were
constant). If plotted in a
graph, the flow rate vs. transducer output is
always a straight line going
through zero, where the K-factor sets the line's
inclination.
For my 912 ULS, I have GRT's digital engine
monitoring system (great!),
which has one fuel flow input channel. I could
therefore read the total
flow going to the engine. No way of telling how
much went to the carbs and
how much returned to the tank, however. Only then
did I realize how much
fueI is actually returned. I fitted a shut-off
valve in the return line
(NOT recommended - may be bad if you forget to
re-open!!) to determine the
consumption of the engine at various power
settings during the test flying
period, for fuel range calculations. The valve
was subsequently removed,
and I fitted the E.I. instrument with two flow
sensors and the associated
differential module (which subtracts
electronically the return flow count
---From the supply count).
In my opinion, one single transducer will serve
only one useful purpose:
With the engine stopped and the electric feed pump
running, one can check
that the return line is open ............
The E.I. with two transducers and diff. module
shows zero flow (only net
flow is displayed) when priming the engine with
the electric pump before
start. Total flow is returned.
Regards,
Svein
LN-SKJ
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