REFLECTOR: Fuel flow - RG sump

[Pat Shea]

Hi Al,

Were your 1/4" forward strake fuel lines open or did
you close them off for this test?

It sounds like we have the same fuel/vent line sizing,
so I wonder why my sump started to drain at 25GPH with
a similar amount of fuel in the strakes? 

Possibilities:

-I was in a cruise climb attitude leaving the forward
strake 1/4" fuel lines un-ported. 

-You've got more head pressure at the sump.

-I've got a slight vacuum acting on my strake fuel in
flight. My 3/8" exiting vent line hose a forward
facing angle cut.

-My fuel lines are more restrictive.

-I was seeing things...

Pat

--- Al Gietzen <ALVentures at cox.net> wrote:

> While I had the fuel line open for servicing the
> filter; I made some
> measurements of fuel flow yesterday to get a better
> handle on flow rate from
> strake to sump.  The strakes had about 6 gals each
> side at the start.  I
> first pumped fuel out of the sump with one of dual
> FI pumps (before the
> pressure regulator, no back pressure).  Timed flow
> for 2 1/2 gals was 3
> minutes, 15 seconds – which is a flow of 45 gph. 
> The sump low fuel level
> light did not go on.
> 
>  
> 
> At first I thought, “Great, that’s a very good
> rate.”  But I now apologize
> for my impatience because it could be that the sump
> level was slowly
> dropping to the level of the float switch, and that
> over a longer period of
> time the light may have come on.  However,
> estimating that there is ½ gal,
> or less, above the low level switch, this would
> still indicate that the flow
> rate from both strakes to the sump was about 35 gph,
> or better.  (Stock vent
> system including sump vent, sump tank down close to
> fuselage bottom, 3/8”
> lines from strakes.)
> 
>  
> 
> I then made the same measurement with both pumps on;
> and, as expected the
> rate doubled.  The sump light came on about 15-20
> seconds after starting the
> pumps.  All I inferred from this was that the first
> test was probably close
> to the upper limit – and I went on to other tasks. 
> My engine will never
> burn more than 22-23 gph.  35 gph should be good to
> over 400 hp.
> 
>  
> 
> I was pleased to note that there was only a very
> small amount of what looked
> like dirty lint in the filter after about 7 hours of
> engine operation –
> first servicing from newly built strakes and sump.
> 
>  
> 
> FWIW,
> 
>  
> 
> Al 




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