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sidsel.svein(at)oslo.onli
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 Posted: Fri Feb 22, 2013 6:04 am Post subject: SV: fuel flow and return line status |
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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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clivesutton
Joined: 23 Jan 2013
Posts: 187
Location: KENILWORTH
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| Posted: Fri Feb 22, 2013 7:18 am Post subject: Re: SV: fuel flow and return line status |
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Hello Svein,
I created the original fuel flow SM12209 Modification and asked Ian Rickard to get it 'passed' for use on my TriGear, through the LAA.
I also have a 912S and have been using this MOD since early 2009 - my a/c has completed about 150hrs with it fitted - including about 35hr around France and Italy on one of the Europa Club trips. I have a single FloScan 201A sensor and a Stratomaster Infinity readout unit combination installed.
Over the time of its use I have calibrated it by adjusting the readout units K factor and conclude that it is accurate within about a 5% error. I agree that the flow rates change with engine speed but propose that the average accuracy is quite good enough to keep track of useage and cross-correlate with my two other forms of fuel quantity monitoring, a capacitance fuel probe and the sight-glass tube arrangement - though the latter does not seem to be very useful in the air due to ram-effect air pushing down the fuel level in the tube.
I've fitted my sensor in the ine bwtween the electric boost pump outlet and the mechanical pump inlet.
Clive. 
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raimo.toivio(at)rwm.fi
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| Posted: Fri Feb 22, 2013 9:49 am Post subject: SV: fuel flow and return line status |
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Hi Svein,
Johnsen" <sidsel.svein(at)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
-----Alkuperäinen viesti-----
From: Sidsel & Svein Johnsen
Sent: Friday, February 22, 2013 4:04 PM
To: europa-list(at)matronics.com
Subject: SV: fuel flow and return
line status
Johnsen" <sidsel.svein(at)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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houlihan(at)blueyonder.co
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| Posted: Sun Feb 24, 2013 9:52 am Post subject: SV: fuel flow and return line status |
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Hi Svein.
Looking at your graph you seem to have documentary evidence of high quality aviating including a decent landing ! ! that's very good, I wish I could do decent landings :<)
Tim
On 24 February 2013 17:34, Sidsel & Svein Johnsen <sidsel.svein(at)oslo.online.no (sidsel.svein(at)oslo.online.no)> wrote:
[quote]
From the two replies to my first message, and reading once again Bud Yerly's detailed explanation last fall on how he set up a one-sender unit, I now understand how one sender can be made to work accurately enough to show fuel consumed/remaining. As I indicated in my second message, the reading error at flows outside the normal cruise power evidently are of too short duration to give much error in the flow x time = consumption calculation. The attached illustration shows this clearly, I think (it is fairly accurate to scale).
I therefore regret my earlier statement that 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. In actual fact, this feature is an additional feature to keeping good enough track of fuel consumed (provided that a K-factor has been found that gives true consumption for a typical flight time).
With my two-sender system (one in feed and one in return line), I cannot check that the return line is open unless I somehow disconnect momentarily one of the senders. I have therefore asked Electronics International in which wire I can introduce a push-to-break pushbutton mounted next to the display unit. This return flow check will then become an item in my pre-engine-start checklist.
I will then also be able to inform the List about actual return flows at various power settings and tank levels, for those who share my sometimes too deep interest in the mysteries of our aircraft!
Regards,
Svein
LN-SKJ
[b]
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budyerly(at)msn.com
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| Posted: Wed Feb 27, 2013 7:55 am Post subject: SV: fuel flow and return line status |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Sven,
You're my hero. Excellent work.
Bud
[quote] ---
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