Ron Swinden wrote:
>Graham Singleton rightly made the point that we should not lightly alter a
>design that has served well for a long time but, in the case of the problems
>experienced by Pete Kember I think we should not lightly dismiss the fact
>that he was left trundling across the Irish sea not knowing his true fuel
>state because water got into the system. Leaving out the filter from the vent
>line would put the system back in line with the original specification but
>would also allow water to flow into the petrol tank, a bit worrying really???
> Luckily I spoke to Andy this pm. He was unhappy about changing a system
>that had served him well (on his Long eze) for 11years during which he has
>many times flown thru heavy rain and never had water problems with his fuel.
> He mentioned that his system has a small hole drilled in the back of his
>vent pipe to ensure that, if the kamilkarzi bee comes along the vent
>continues to work thru the back hole simple init???? He is including
>directions for modifying the vent pipes in his latest update of operating
>instructions I believe. After thinking about it I suggested that because of
>the back hole air must flow, at some considerable speed into the front
>facing hole of the vent and out of the back one, If water goes in with the
>air it will almost certainly I suggest run round the outside of the bend and
>leave by the back entry so to speak. If this is so then this would explain
>why Andy never has had water problems. Andy agreed that it seemed a likely
>explanation and as he was going to recomend the back exit hole in the vents
>anyway think that we just may have a system that does all we want without
>electonics after all.
>Anyway I am happy to try it and I believe it should work well. Richard was
>unhappy about the effect of the pitch attitude on the accuracy of the guage.
>Surely a few seconds level flight is a small price to pay for an accurate
>assesment of the fuel state of the aeroplane. I intend to fit a gascolator
>in place of the petrol filter. It has a top tapping intended for use with a
>primer, as I do not have or need a primer I shall connect my level guage to
>it, unless I (or any of you) can think of a good reason not to. Hope that
>the above gives you some thing to think about. Please let me have your
>comments/questions Ron S No 33.
The long Eze is a completely different case where (as far as I know)
the tank is higher than the carb, or at least much nearer the same
level than it is on the Europa. Suction is not such a problem, if
at all. It is this suction combined with the sight gauge on the main
line which causes us problems. Is Andy's sight gauge in his long
eze drawn off the main line to the engine in a suction type of
environment? This is the crucial element.
Consider this extreme case in the Europa:
Low fuel level, high pitch angle & high power setting (hense fuel
flow): Even with no obstruction in any vent, if the horizontal level
in the tank falls below the level of the tee off to the sight gauge
then the fuel will prefer to be drawn from the sight gauge rather
than the tank....
It may be possible, I don't know, it depends on exactly where the
tee to the gauge is, how small a restricted orifice is Etc. The
higher the tee relative to the tank the easier it could occur,
during aerobatics perhaps. Of course it is likely that this
phenomenon would only be temporary and there would be sufficient
fuel in the float bowls to keep the engine running while a bubble
is run through the system. However a lowered level in the float
bowl with any needle type carb means a leaner mixture - even if you
didn't notice it immediately, it could damage your engine.
In principle I have no objection to sight gauges, there's nothing
like solid state systems, though there is bound to be a pitch
problem in this particular case. Suction problems would be avoided
if the gauge was drawn from anywhere other than the main line.
Electrical gauges are not the be all and end all, it appears, for
example, that capacitance type gauges can be significantly affected
by different types of fuel, there can be up to a 10% difference in
reading between Avgas & Mogas. This is one reason why, as stated
before, we have also installed a mechanical gauge.
Equally, with the vents, a hole may or may not cure some of the
problems, but won't, in my view, a) necessarily stop rain getting in
and b) it certainly won't stop fuel pissing all over the fuselage in
certain circumstances. Venting out of the bottom will prevent a)
and make no mess with b).
Regards
-------------------------------------------------------
Richard Meredith-Hardy TEL + 44 (0)1462 834776
rmh@flymicro.win-uk.net FAX + 44 (0)1462 732668
CIS: 100071,2422
Check out the British Microlight Aircraft Association at
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