>That's generally correct, but we may disagree on potential consequences.
We can't rely on the pump's CB to trip (a fast-acting fuse is
inappropriate for an inductive device). If a failed regulator were to
supply 7 amps to the pump after the OV trips, it can take up to one hour
to trip the recommended 5A breaker. If we're lucky the pump will fail,
or it may run very hot with fuel inside plus excess pressure to flood
the carbs. <
Not relevent in a system like mine that uses a pressure regulating valve.
> A bad scenario is right after takeoff with both pumps on.
The only indication of a very serious problem may be a panel indication
that the OV has tripped, but not whether one pump is under stress.
Alternatively without an OV device doing us such a favor, the battery
will clamp the volts to that pump, with similar panel indication of a
problem, but not potential engine stoppage at the worst possible time.<
If the OV unit works in such a situation the remaining pump will ensure the
engine continues to run. Subsequently when time permits the pump connected
to the regulator can be switched off. In a high workload situation such as
this it is much better to have the system look after itself allowing the
pilot to concentrate on flying the aircraft. There has already been one
Europa accident where the pilot became distracted and lost control shortly
after take-off. There is no guarantee that a small aircraft battery (13 -
17Ahr) will be able to hold the battery voltage down to acceptable levels.
If there was I am sure that Bob Nuckolls would have limited his design to
just avionics protection. Total electrical failure from a single failure
with the existing system can happen and is critical to engines with just
electrical fuel pumps. By seperating the two sources of power quickly any
single failure is unlikely to cause engine shutdown.
>It's easy to add a circuit to prevent excess volts to the pump while
keeping it safely running off a runaway regulator, <
This means more complication. One voltage control circuit for the pump and
an OV unit for the avionics.
We will obviously have to agree to differ about this. I just wanted to make
it clear to those using the existing Rotax 914 electrical system that there
is a single electrical failure that can cause engine shutdown. If we are
going to bother with twin ignition systems then we should have one level of
redundancy on the electrical system which doesn't rely on immediate pilot
input. How the individual goes about this is up to them but the expertise of
Bob Nuckolls sounds like a good starting point to me.
Nigel Charles
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