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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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