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Re: Europa-List: Re: Rotax 914 - how to avoid an overboost?

Subject: Re: Europa-List: Re: Rotax 914 - how to avoid an overboost?
From: Frans Veldman <frans@privatepilots.nl>
Date: Wed, 18 Jul 2012 00:21:54

On 07/17/2012 05:39 PM, PHILLIPS I wrote:

> I decided early on in my wiring to make sure that the waist gate servo
> and ECU always had power, So I have wired it direct bi passing the
> battery contactor,

Just like some people like the stall warner, the trim servo, and some
other bunch of "recommended execptions" bypassing the master switch?
My thought here is that everything could be essential in some stage of
the flight, but then what is the meaning of the master switch if half
the ship is bypassing it?
I want the master switch do exactly what it is supposed to do, to power
down the ship completely. If I want to retain power on the TCU, the
stall warner, the trim servo, or whatever, I just don't power down. Am I
missing something here?

You have already experienced how such an exception can turn against you.
Everything that is wired apart from the master switch can be forgotten
to be switched on, and can fail just as easily as the master switch. In
an unavoidable crash situation, where you have to land in hostile
terrain, it is highly desirable that you can power down the electrical
system with just one switch, without having to think (or worry) about
all the exceptions which are bypassing the master switch and keep their
sparking abilities when ripping the fuel tank is a possibility.

> It has a klixon CB that is always pulled after shutdown,

These things are not supposed to be used as a switch (please read the
manufacturer technical manual). They will fail, much sooner than an
ordinary switch, if you regularly pull them. There is a quite
complicated mechanism behind these things and repeated use will wear
them out quickly. So, there again, it might turn against you.

I never quite understood why folks want to bypass the master switch.
What is the reason behing it?

Is it just me thinking like this about the purpose of the master switch?

Frans



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