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SV: Rotax fuel flow detection

 
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sidsel.svein(at)oslo.onli
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PostPosted: Thu Oct 21, 2010 1:24 am    Post subject: SV: Rotax fuel flow detection Reply with quote

Graeme,

I installed the Electronics International fuel flow instrument with
differential module:
http://www.buy-ei.com/Pages/FP-5P/FP-5P_Details.html

One transducer measures flow to the carbs, another measures the return flow
and the differential module sends the net flow data to the instrument. I
have used it for two years now, VERY pleased with its accuracy (easy
comparison of fuel used shown by the instrument and quantity to top up the
tank again). I have not done any recalibration. User friendly. Easy to
install. I placed one transducer between the engine driven fuel pump and
the right side carb, the other in the return line in the tunnel.

Great instrument for determining fuel efficiency (range) under various
conditions as you fly and showing remaining fuel. Only thing to remember is
to update the fuel quantity in the tank when you start the engine if you
have refueled since last flight - flashing light on the instrument reminds
you to do this.

Regards,
Svein
LN-SKJ
-----Opprinnelig melding-----
Fra: owner-europa-list-server(at)matronics.com
[mailto:owner-europa-list-server(at)matronics.com] P� vegne av graeme bird
Sendt: 21. oktober 2010 10:37
Til: europa-list(at)matronics.com
Emne: Rotax fuel flow detection



Just sorting the fuel system on my new build. I am considering including an
RS type flow sensor for future use but what confuses me on the 912 install
is that some of the fuel comes back which would make the reading useless
unless a return sensor was also fitted. This is the reason my fuel
calculator in my C42 is worse than useless. Any advice appreciated.

--------
Graeme Bird


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rampil



Joined: 04 May 2007
Posts: 870

PostPosted: Thu Oct 21, 2010 4:21 am    Post subject: Re: SV: Rotax fuel flow detection Reply with quote

the return fuel rate in the 912s is tiny.
the 914 is on the other hand a significant fraction of total flow


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sidsel.svein(at)oslo.onli
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PostPosted: Fri Oct 22, 2010 10:38 am    Post subject: SV: Rotax fuel flow detection Reply with quote

Remi,

At first sight, your proposal may look like the obvious solution. With
respect, however, I think it is not to be recommended for 912ULS
installations (I do not know enough about 914 to comment on that engine).

Contrary to what seems to be a common assumption, the return flow through
the restrictor is not insignificant - it is roughly 10 litres per hour (i.e.
roughly half of the net cruise consumption, or roughly 1/3 of the fuel going
to the engine is flowing back to the tank). The reason for this relatively
high surplus circulation is of course to reduce the time the fuel is exposed
to heat before it reaches the carbs, by increasing the flow velocity through
the fuel line. According to the build manual, the return line branches off
at the point farthest from the pump, just before the left side carb
(assuming the fuel line goes from the pump to the right side of the engine
with a short branch off to the right carb, and from there across the back of
the engine to the left carb).

Moving the return line branch-off upstream (closer to the pump) increases
the risk of vapour forming in the fuel lines downstream from this branch-off
point. By how much, I do not know, but maybe it is critical under
unfavourable circumstances. "Maybe's" under the cowling are not nice - - -
- - .

Regards,
Svein
LN-SKJ

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[mailto:owner-europa-list-server(at)matronics.com] P� vegne av Guerner Remi
Sendt: 22. oktober 2010 19:53
Til: Europa-List Digest Server
Emne: Rotax fuel flow detection
Thank you Ian for posting the LAA mod.

I have not installed a fuel flow in my aircraft but if I had to, I would use
the attached schematic which allows measuring the flow to the carbs with a
single sensor, therefore improving accuracy and reliability and reducing
cost.

The same principle can be used for the 914. In that case the single flow
sensor would be installed between the pressure regulator and the carbs.

Remi Guerner
F-PGKL


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sidsel.svein(at)oslo.onli
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PostPosted: Sat Oct 23, 2010 3:09 am    Post subject: SV: Rotax fuel flow detection Reply with quote

Remi,

The Rotax manual shows a principle, not one that is optimal for all actual
installations. Different aircraft will have different under-the-cowl
arrangements, different cool air flows under the cowl, etc. Europa shows
another arrangement, which of course is better but I cannot say by how much
or whether it will matter. The difference in fuel tube length at high vs low
flow velocity is small, and if the tube is placed in a heat shield the
increase in vapour lock risk may be acceptable.

Regards,
Svein

-----Opprinnelig melding-----
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[mailto:owner-europa-list-server(at)matronics.com] P� vegne av Guerner Remi
Sendt: 23. oktober 2010 10:44
Til: Europa-List Digest Server
Emne: Rotax fuel flow detection

Svein,

I basically agree with what you wrote. However my proposed schematic
is very close to the one recommanded (and optionally supplied) by
Rotax in the 912 Install Manual (see attached). This arrangement works on
most LSAs so I do not see why it would not work with the addition of the
fuel flow sensor as propsed.

Regards
Remi Guerner


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