On Wednesday 16 July 2003 23:17, Bob Japundza scribbled:
> Yep..the wing tanks have ribs in them and the lightening holes are not =
cut
> out, except for some holes to allow fuel to pass in between the ribs, o=
r
> 'bays' as they're referred to.  Its designed to help keep down sloshing=
,
> but there is still quite a bit of sloshing even when nearly full.

Absolutely.  It's a major problem in a car, and I know from flying that i=
t's=20
an greater problem while being tossed about in the air.  I *never* trust =
or=20
even bother with fuel gauges in small aircraft.  Only once when I first g=
et=20
into the aircraft, before even doing a walk-around check, I look at the f=
uel=20
gauges to know if to call for a fuel truck.


>  There is
> one rib (#2 from the root) which has a trap door to allow fuel to easil=
y
> flow into the first bay but not as easily to flow out, so that in an
> uncoordinated turn while low on fuel the pickup tube doesn't unport, wh=
ich
> would obviously cause the engine to quit.

Do you have any diagrams for this, I had started redesigning a new fuel t=
ank=20
for my (kit)car, but never finished it.  Primary reasons were to have dua=
l=20
in-tank pumps, more fuel capacity, and a proper sump, but I know I'll nee=
d=20
some good baffling to prevent running the pumps dry, which would be very,=
=20
very bad.  I had looked a bit at trap doors on oil pans, but felt=20
uncomfortable with metal scraping metal (all aluminum) inside a fuel tank=
=2E =20
Of course, since I have electric pumps in there, I shouldn't be such a pa=
nsy=20
about it. :-)  If you have any diagrams showing how the trap doors are=20
implemented, I'd love to see them.


>  One problem with the RV's are
> the float-type fuel senders are not very accurate above 1/2 full, due t=
o
> the dihedral of the wing and the location of the senders being attached=
 to
> the root rib.  I've been thinking about putting a second sender on the
> other end, and using a pic to extrapolate fuel level with a table looku=
p
> based on the a/d results of sampling both senders...

If you can get the full range, a PIC lookup-table can very easily compens=
ate=20
for non-linearity.  If you run 2 senders, you'll have to do some in-fligh=
t=20
calibrating, since averaging may always be low ... during sloshing, I can=
=20
imagine situations where one sender would go up while the other would go=20
down, and the average would be correct, but there are other situations wh=
ere=20
both could be lower than actual.  I cannot see how both would ever get hi=
gher=20
=2E.. unless you're inverted :-)


> There are some other
> alternatives, such as capacitance-typ! e senders, but they are inaccura=
te
> due to different fuel densities and temperature changes...

Personally, I feel that using flow-sensors (~3% accuracy) would do an=20
excellent job here.  If EFI, you could also calculate the consumed fuel f=
rom=20
pressure and injector-pulse widths.  And if you use either of these, you=20
could still use an in-tank float-type level sensor with a very very long=20
averaging period to essentially "re-calibrate the fuel-flow" sensor over =
a=20
longer period of time.

BTW, a new/recent wave of "arm-less" fuel senders have hit the market.  A=
 bit=20
more expensive, but I like the idea of not having the swing arm.

Cheers,
-Neil.

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