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SV: Rotax fuel flow detection

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sidsel.svein(at)oslo.onli
Guest

Posted: Thu Oct 21, 2010 1:24 am Post subject: SV: Rotax fuel flow detection

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

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Fra: owner-europa-list-server(at)matronics.com

[mailto:owner-europa-list-server(at)matronics.com] På 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

Posted: Thu Oct 21, 2010 4:21 am Post subject: Re: SV: Rotax fuel flow detection

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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_________________
Ira N224XS

sidsel.svein(at)oslo.onli
Guest

Posted: Fri Oct 22, 2010 10:38 am Post subject: SV: Rotax fuel flow detection

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] På 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
Guest

Posted: Sat Oct 23, 2010 3:09 am Post subject: SV: Rotax fuel flow detection

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 



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[mailto:owner-europa-list-server(at)matronics.com] På 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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