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David, Thank you for the explanations,
At first I flew my Rotary Powered Zenith
200 with a old Rochester two barrels carburator and a low pressure fuel
pump. Never had any problem except for a very rich fuel mixture at altitude and
of course the possibility of carb icing...which never materialized.
Whenever I felt the carb was beginning to ice up, I would go to full throttle
and adopt a full nose up attitude to maximixe heat in the engine compartiment.
After a short time, I would continue flying normaly.
After a while, I switched to a low pressure
EFI system, which I am still flying AND fiddling with after several
years...
So, actually, I am thinking about going
back to carb and low pressure fuel pump. A carb with a fuel leaning
capacity...hum...still thinking...
Thanks again. Yvon
Cournoyer
Yvon, don't tell me you are thinking about switching to EFI?
:-)
Most EFI systems used for rotary aircraft installations work like
this:
The pump gets turned on, and just pumps away as hard as it can at a more
or less constant flow. Pressure is created in the system by the
regulator that is placed after the fuel rail. It works like a thumb over
the hose to create back pressure, and lets the excess fuel flow back to the
tank. So as long as the pump is able to pump just slightly more than the
engine is using, fuel pressure remains constant. As soon as the pump
cannot keep up with what the engine is burning, i.e. the engine is using more
than the pump is pumping, then the fuel pressure very quickly drops and the
engine begins to falter. (ie, once the pressure starts to drop the engine
starts to falter - skip, misfire, run lean, loose power, surge, or just plain
quit).
Normally, the pump puts out several times what the engine needs. As
the pump starts to fail, flow is reduce but pressure remains unchanged for a
while (depending on how fast the pump is failing - in my experience of 1 pump
failure, it failed over the course of a few hours). By the time the flow
is reduced enough that the pressure starts to drop and the engine starts
to falter, the pump is only putting out a fraction of its rated flow. i.e. it
has almost failed completely.
Better to catch it early if possible. I found the return flow meter
useful for that purpose.
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