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Hi Al,
interesting!!
Next chance I have I will try to find out more
about this (reasoning for use of fuses over CB's in this
helicopter).
I don't really buy the "repair after trip" -reason
as the result is the same.
Whatever caused the fuse or CB to trip, it should
be repaired. What really happens is that the fuse is replaced - if it doesn't
trip immediately, no one will look any deeper into it, than a
"look" (unfortunately...), .... until it trips again.
A lot of trips can be caused by changing
environment (heat, humidity, etc.) that bring the conditions for over current
just to the trip point, but will not under normal conditions.
However I am no specialist, not even building
anything at this time - so, I will try to find out for this specific application
(AS350B3)
Thomas
PS: First thing I am going to do is to consult the
Maintenance/Repair manual....
----- Original Message -----
Sent: Saturday, February 17, 2007 6:10
PM
Subject: [FlyRotary] CBs and fuses
Eurocopter Factory Instructors are
VERY COMPETENT in Eurocopter Helicopter Systems!!
There is absolutely NO doubt that he
knows the difference between fuses and breakers and WHY either one would be
used.
Thomas;
Certainly not
impugning the competence of the flight instructors; just suggesting the design
engineers may have other reasons than cost. One may be
reliability. The reliability of CBs goes down significantly after they
have experienced a ‘trip’. I recall reading one experts opinion that a
CB should be replaced after a ‘trip’. Yeah; seems extreme. The
modern philosophy of circuit design is to design for fault tolerance, so a
fault; once causing the protection device to open, is left for repair when you
land.
The key for using
fuses is fault tolerant circuit design and proper selection and sizing of
fuses. Having done this; studies suggest that the fuse offers higher
reliability and lower cost.
There certainly
reasons for either CBs or fuses, and I have both in my plane. For my
flight critical circuits I opted for simple, fault tolerance and fuses.
I wouldn’t argue with someone making a different choice.
FWIW,
Al
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