Alan,
To reinforce the point that Frans has made, it's helpful to recognise that
what is often referred to as "alternator failure" is actually failure of the
rectifier/regulator feeding DC to the 12/14 V electrical system (and in the
case of the 914 word according to the Europa circuit diagram, the 2nd
electrical fuel pump).
Failure of the actual alternator, which has permanent magnets rotating
inside the fixed stator, such that both of the 2 independent coils that
supply the ignition modules direct failed, would indeed be extremely rare.
The point made earlier about bypassing the the master switch to provide a
live feed from the battery to the trim switch was a subject of much
discussion back in 1996. Ivan Shaw was insistent that in the event of smoke
in the cockpit caused by a wiring fault, the immediate action would be to
turn off the master switch and land as soon as possible - but the aircraft
could be very difficult to control if they were large forces on the elevator
because the trim could not be adjusted. Similarly, in later years people
have fitted electrical stall warners - and again it would probably be a good
idea to have this system working while attempting a sensible forced landing.
The risk of either circuit (each protected by a very-low-value fuse) causing
a fire during a crash landing I personally believe to be acceptable.
Mike
Dr Mike Gregory
Europa Club Safety Officer
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Frans Veldman
Sent: 11 October 2013 16:31
Subject: Re: Europa-List: Re: Battery questions
--> <frans@privatepilots.nl>
On 10/11/2013 05:11 PM, Alan Carter wrote:
> <alancarteresq@onetel.net>
>
> Hi Frans. I am getting a bit lost here, I think you are saying if my
> Alternator Fails I won't get the spark to keep the engine running,
There are mutiple coils in this alternator. Two are used for the ignition,
the rest for charging the battery.
> I am not sure if this is correct, surely my battery will keep the
> power to the ignition modules for a while.?
No, the ignition coils are not connected to the battery.
> With ref to the mechanical pump I believe some 914 in the world have
> been fitted, there is usually a way to get round cooling, maybe a
> thermal barrier in the gasket, or water jacket,
Why would you go that complicated route if there is a better solution?
> The 914 and the 912 I must say I find it hard to believe there is a
> huge temperature difference under the cowling, why is it so hot.
The 914 has a turbo. A turbo compresses the inlet air. A side effect of
compressing air is that the temperature goes up. The inlet air passes
through the carbs after it has been compressed (and heated!) by the turbo.
So, as the carbs have quite a higher temperature than in the 912, it is not
a good idea to feed them hot fuel as well. The combination of heat and fuel
lead to an increased change of vapor lock and detonation.
Hence the Rotax engineers made a few modifications to the fuel system:
1) The return feed is largely increased. This increases the flow, so the
fuel stays a shorter time in the cowling and heat is transfered away.
2) The mechanical fuel pump (a heat source) is eliminated and replaced by
cool running electrical pumps, that can remain outside of the hot cowling.
3) By changing the location of the fuel pump the fuel hose routing can be
kept much shorter.
Think about it: When the Rotax engineers developed the 914 they had already
their convenient mechanical fuel pumps on the shelf. They sure must have a
good reason to block off the fuel pump connector on the gear housing and
change the whole setup.
It is not wise to revert back to mechanical pumps, especially since there
are no practical problems with the dual electrical pump setup.
Hundreds of airplanes are flying happily around with them.
Frans
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