Hello Bob,
The diagram on page 25-11 was developed for the 914 installation after Andy
had an incident on a demonstration ride where the handling pilot switched
OFF the number one fuel pump instead of switching ON the number two pump
during the pre-landing checks. Because the 914 has no mechanical pump, it
all went very tense for short time. There was a Rotax recommendation to
connect one pump directly to the output of the alternator, and the circuit
was revised to do this downstream of the 30 Amp Slow Blow fuse that was
incorporated on the firewall side to protect the cable feeding the bus bar.
This pump has its own 5 Amp circuit breaker, before the switch connecting
the alternator to the bus bar.
This arrangement, together with the number two pump (labelled "secondary
fuel pump" on page 25-11) connected to the main bus bar, allows you to
switch on the battery master (whether you use a solenoid or a direct switch)
and carry out any actions such as programming your GPS without running
either pump. When you are ready to start, the number two pump can be
switched on briefly to check it can supply pressure. The alternator feed
switch should be closed before the engine is started, because it is not
recommended that the alternator should run without a connection to the
battery, and this will automatically switch on the number one pump. If you
wish to be able to isolate the number one pump when the engine is running, I
would recommend a pullable circuit breaker rather than adding a switch,
since you wouldn't normally wish to do this (OK, OK, some people may wish to
even out the wear on the pumps, but they could do this by switching the
electrical connections every annual rather than adding an extra circuit
component).
Ivan Shaw originally asked for the trim circuit to be arranged so that it
could be operated in the event of a dead stick landing after the master
switch had been turned off. This therefore required a feed direct from the
battery rather than downstream of the isolator/master, together with its own
fuse and switch. If you do not wish to have this feature, the trim circuit
could be fed off the main bus. Again, there should be a fuse to protect the
wiring and a switch to isolate the circuit in the event of a trim runaway.
Hope this helps
Mike
Europa Club Safety Officer
Europaphiles,
This is the question I had for Andy. Perhaps some of you folks who have
completed a 914 installation can help.
I am completing the electrical wiring. I have some questions about wiring
in the two fuel pumps and the trim system.
The diagram on page 25-11 shows a single fuel pump being fed from right from
the load side of the Main alternator through a 30 Amp Slow Blow fuse and
simple 5 Amp breaker. None of your electrical diagrams show the wiring for
electrical fuel pump #2 for the 914.
My aircraft has the battery isolator solenoid fitted.
My panel, as wired by Gulf Coast Avionics, has a 35 Amp circuit breaker in
the electrically equivalent location of the 30 Amp Slow Blow Fuse.
They have pump #1 being being supplied from the Line side of the main
circuit breaker, thence through a 5 Amp circuit breaker and to the pump. I
believe this is the electrical equivalent of the circuit for pump 1.
Presently, the only way to shut off pump #1 is to pull the circuit breaker.
Should pump #1 go through a switched breaker rather
than a simple breaker?
Pump #2 is presently supplied from the Load side of the main circuit
breaker, thence through a switched 5 Amp circuit breaker and to the pump.
Is this correct? Is this OK? Or, should it also be supplied from the Line
side of the main circuit breaker?
Your diagram (25-11 again) states that the trim should be fed directly from
the battery if the battery isolator solenoid is fitted. Should it be fed
---From the hot side of the solenoid or from the load side of the solenoid?
The trim wiring, as supplied by GCA, is fed from the Load side of the main
circuit breaker and no switch is provided. I do plan to add a switch to the
trim circuit. I need to know from where it should be supplied.
I hope this is clear. If not, let me know and I'll try to provide a better
description.
Good building all,
Bob Borger
Europa Kit #A221 N914XL, XS Mono, 914, Airmaster C/S
http://forum.okhuijsen.org/N914XL
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