Hi Elvis
On (23 Aug 97) Elvis Hargrove wrote to Charles Bowman...
 EH> That's all well and wonderful if that was all that could go wrong....
 EH> That's fer SURE though why TWO of them are required on acft engines.
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Logic gets to be a victim of narrow experience.
Magnetos are fine in principle thanks to simplicity and reliability. Lawn
mowers and small motor cycles owe a lot to these. The evolution of the same
principle to provide headlamp power and battery charging when batteries are
provided, was a nice step. These suffer gross abuse often. The
tolerance of hosing and neglect reflects much credit on the designers and
makers.
Two maggies for aero engines, is a neat bit of logic: on running up before
flight the ability to test and verify the dual, fully redundant sets of spark
plugs and ignition leads and magnetos gives mighty assurance that the flight
may proceed with a working engine. A pity that the pilots cannot be so
convincingly tested before flight.
Having two sets of gear does not mean that the gear is bound to be 
nreliable,
it means that the function is so darned vital that redundancy is paid for.
Redundancy [belt braces plus piece of string, to hold up the pants] is a
calculated element of good design. Generating station turbines each have
several lube oil pumps: like, one is shaft driven, a second is AC motor 
riven
and a third is DC [battery] driven. Not because oil pumps are prone to fail
but because a 300 ton turbine at 3600rpm is an imminent disaster, if the lube
oil stops flowing.
Show me an aero engine with just one source of engine ignition, then show me
the railroad station!!
Show me a HOMEPOWER equipped house, but show me where you keep the candles
too......
Cheers....ALEC
... How an engineer writes a programme: Start by debugging an empty file.
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