Svein,
I am just a dumb builder who has learned the hard way and only knows
what has worked in my shop. And like you guys, with no time to work on
my own projects.
You can never beat an Electronics International flow meter system. I
have one, and it is superb. No adjustments right out of the box.
Regarding the flow of the return:
I did a bench check of the FS02 return line years ago and found that is
flows at 4 oz per minute so about two gallons per hour at a pressure of
about 2 PSI with a full tank (as the head pressure resists the return).
Non scientific measuring cups and hoses used. In fact it was
practically Rube Goldberg at its best.
There is no way to get a single FF sender to be accurate over all power
ranges but you can get pretty darned close.
My experience with the setup of a single FF sender on a 912 engine with
only a single fuel flow sensor and a restricted return is as follows:
GRT has the fuel flow instruction in their manual starting in section
7.5 for the EIS.
What I do in the shop is the following:
I disconnect the fuel line from the engine, and use a hose extension
draining into a gallon can with a valve to also check the fuel pressure.
Like you, I set it up initially only checking the flow out of the main
line and verify the accuracy and adjust as necessary according to the
manual. Usually it is pretty good...
I then hook the fuel lines back up.
I run the pump with engine off and the return line disconnected and
measure the flow rate. With no other restrictions other than fuel in
the tank and the FS02, it is just about three-four gallons per hour.
One method I tried was to run the engine and measure the return, the tee
pressure should be about 3-4 PSI and the return past the FSO2 installed
in a tightly fitting1/4 inch fuel line, drops the return flow by about
half. But running engines on the ground and dripping fuel around is
stupid, so I don't do that any more.
The GRT manual has you adjust from flight experience the FLOCAL up until
your flow is more accurate, if I recall it is a value between 100-150.
What the GRT folks told me to do was to note your fuel burn in flight
via fill up and stopwatch to get your approximate fuel flow as it is
much safer without fuel lines and props turning on the ground...
Simply increase the FLOCAL and fly again to check it out. Adjusting as
you go, and adjusting, and adjusting, and adjusting.
Being a lazy old guy, I fly during test at cruise power and set the
FLOCAL until I get about 5.5 GPH at about 3000 MSL and 5000 RPM at 20-25
inches MP.
Then adjust while enjoying cross country flights.
For those with two flow meters, I have found the GRT 4000 with FF return
to work as advertised. As accurate as the EI system I have.
I, like you Svein, am spoiled by my Electronics International Flowscan,
it is a great piece of equipment, and I am glad to see other
manufacturers now making similar equipment that is less tedious than the
GRT above.
Regards,
Bud
----- Original Message -----
From: Sidsel & Svein Johnsen<mailto:sidsel.svein@oslo.online.no>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Monday, August 08, 2011 1:46 AM
Subject: SV: Europa-List: FlowScan Problems
Bud,
I am one of the very many who greatly appreciate the knowledge you
share with the Europa community and all the time you spend to help us
out when a problem occurs. Your last posting puzzled me, however,
because I have a different experience:
You write:
>Again, Grand Rapids is the expert on the 2000 models years,
programming and setup. I just know it will work fine with one Floscan
>on a 912S (where the small amount of fuel through the return line with
orifice is not counted) when ordered direct from GRT with >the fuel flow
option.
I have a 912ULS, GRT EIS with fuel flow option and installed the
Floscan that was supplied by GRT in the fuel line (I do not have the
model number at hand, but for this discussion it is not important).
After calibration of the flow reading, I found to my big surprise that
the return flow through the orifice was in the 10 litres range (roughly
4 gallons) per hours. As the return flow varies with the fuel pressure
(and therefore to some extent depends on the engine RPM), I did not wish
to base my "consumption reading" on an unknown return flow to be
subtracted. I therefore first installed a shut-off valve in the return
line (mounted on the tunnel side, to be operated during flight) for
short-period reading of flow during my test flights, to determine
consumption and most economical speed. Later, I have replaced it with
Electronics International's fuel totalizer, which has a flow pickup both
in the feed and the return line - superb instrument. I was very
surprised that the return flow is this high (at least in my
installation, where I think I have the restrictor with the correct
orifice installed!), but concluded that the reason is the very low
viscosity in gasoline compared to for example water. It of course makes
sense to have a significant return flow, as the objective is to flush
through the fuel system forward of the firewall with "cold" fuel,
especially on the ground when idling or taxiing, when the consumption
flow is very low, to reduce the risk of vapor lock. Kind
regards,SveinLN-SKJ
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