REFLECTOR: Fuel flow - RG sump

Al Gietzen ALVentures at cox.net
Thu Jul 6 17:38:59 CDT 2006


 

Hi Al,

 

Were your 1/4" forward strake fuel lines open or did

you close them off for this test?

 

Pat;

 

The forward lines from strake to sump are 3/8” per the manual.  On the right
side I have a ¼” line behind the wheel well (per my manual, circa 1997).
After testing and finding that there was less than 1 quart trapped behind
the wheel well in level attitude; I did not put in the ¼” line on the left
side.  (Later the fitting on the sump tank for that line became my FI return
line.)  So 3 lines were open for yesterdays measurement. – a 3/8” line from
the left, and a 3/8” and a ¼” from the right.  The 1/4” line only
contributes about 15% to the flow.

 

The vent lines from strakes and sump are ¼”.

 

Possibilities:

 

-I was in a cruise climb attitude leaving the forward

strake 1/4" fuel lines un-ported. 

 

I think this is unlikely.  The forward lines (they are 3/8”, right?) are
just in front of the wheel well which is a lot closer to the back of the
tank than the front.  It seems that the head there would be more in climb
than when level, even with only 5-6 gallons in the tank – just guessing.

 

-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.

 

This could be.  What lines are you using? My recollection (which could
easily be wrong) of the photo of your lines seemed like you had more
flexible fuel hose.  The solid al line has about .3” i.d, whereas the
typical 3/8” fuel hose is ¼”.

 

Do you have a low point in your strake vent line that could have fuel in it?

 

BTW; you’re welcome to fly to Ramona anytime and we can compare systems.
I’d enjoy meeting you and seeing your plane.

 

Al 

 

 

--- 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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