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Is there really a need for a circuit breaker for the hydraulic pump relays on
a 320/360? Let me explain....
I'm using the EXP2 bus from Control Vision (NOT Vision Microsystems) for my
power distribution system. This device uses polyswitches instead of circuit
breakers and has a 40 amp capacity. The hydraulic pump itself will not be on
this device, and will instead be connected via a stand-alone 50 amp breaker.
Further, Control Vision recommends that pitot heat not be connected to their
device, and that a stand-alone circuit breaker be used for that as well. I
could connect the pump relays to either the EXP2 bus or to a stand-alone
breaker, but for the following aesthetic reason I want to connect it to the
EXP2 bus.
The aesthetic problem is that the EXP2 bus indicator module only leaves room
for 4 circuit breakers on the tilted 360 electrical sub panel. (I could
always put another breaker elsewhere, I suppose, but it would look weird...)
I'd like to use these for a 50 amp hydraulic pump breaker, a 40 amp breaker
for the EXP2 bus itself, a smaller one (20 amps?) for pitot heat, and an even
smaller one for electric trim (in case of a runaway trim -- I'd catch it
before it went hard over and pull the breaker....maybe).
I know I need to protect the wiring to the pump relays, and this is what the
EXP2 bus provides. However, I'd plan on connecting the pump relays to a
circuit that is always active when the master switch is on. This means that
I will have no means of turning off power to the flap relays in flight, short
of turning off the master switch.
I don't see a real problem here. To do a manual gear deployment test I would
pull the 50 amp pump breaker, but a relay will be powered on as soon as I use
the hydraulic bypass (dump) valve. So what? It's an intermittent-duty
relay, but is this a problem? (I have the Bosch relays recommended by Bill
Rumburg and others. I THINK it's an intermittent duty relay but I'm not
sure.) How long would the relays have to be powered on before I run into a
problem? In a real emergency where I have to disconnect the pump for some
reason (like, it won't shut off) would I really need to pull the relay
breaker?
A final thought. I can give up the breaker on the electric trim system in
favor of the pump relay. What's the likelihood of actually catching a
runaway trim and pulling the breaker before you're already at full trim? How
likely is the trim system to fail hard-over? Most importantly, is the
320/360 controllable with full trim? (I suspect I'm opening a Pandora's box
here. Dive on in, guys!)
Thanks in advance.
- Rob Wolf
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LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
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Please send your photos and drawings to marvkaye@olsusa.com.
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