Posted for "Matt Hapgood" <hapgoodm94@alum.darden.edu>:

Scott,

How does a fuel flow sensor/totalizer work with a return line in the engines
you mention below??

Thanks,

Matt

ps.  in my electronic fuel injected engine I had some major problems when I
first started flying (lucky not to have gotten seriously dead).  Rather than
return fuel to the header tank, it was being returned to a small (1 quart)
reservoir to recirculate fuel.  Well, sometimes the fuel would get too hot
and the engine would stumble big time.  We troubleshot for weeks, suspecting
bad fuel pumps, restrictions in the fuel line... eventually I figured it
out, and now I return fuel to the header tank

___________

Continental engines, such as the IO 360G, utilize a fuel system where
excess
fuel at the throttle body is returned to the tank from whence it  came.


[Pardon my butting in, but I thought I'd toss in my 2c.  Depending on the fuel flow instrument you'll probably have 2 flow transducers.... one in the feed line and one in the return.  (These transducers need to be plumbed in between the fuel selector and the fuel rail.)  The instrument will either do the math internally (like the EAU in the Chelton Flight System) or it will have a black box that does the math (like the Electronics Int'l FP-5.)  The return flow is deducted from the feed flow and actual consumption is reported on the instrument.

On Ted Noel's IVP we have both the EI instrument and a CFS system.  Initially we were going to display fuel flow only on the EI instrument, but later decided to display it on the EAU & EFIS as well.  Initially, and at the advice of both manufacturers, we simply paralleled the transducer signals to the inputs on both instruments.  Unfortunately this didn't work, as the transducers are solid state devices and simply splitting the signals between the two instruments caused the biasing of the transducers to be screwed up... we would get flow data out of the EAU but the EI instrument showed nothing (the transducers came with the EI instrument.)  After much fiddling and with the assistance of the folks at EI and Greg Toman from Grand Rapids Technology (who actually manufactures the EAU for Chelton) we came up with a small splitter circuit that provided the proper biasing to the transducers and output discrete and duplicate signals to both instruments.  This little circuit (4 transistors and a dozen resistors) was built into the EI black box and I'd be happy to share the details with anyone who cares.

Sorry if I've given you more info than you wanted, but since the subject came up....

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