"CCred68046" wrote in message
...
The only area where it may be difficult to separate the ground from the
frame is the spark plugs. Even this is not an insurmountable problem; it
is
possible to make a spark plug with two electrodes.

I can agree with your post, I understand the high voltage motors and
generators. The spark plug scenerio would require 2 wires to each plug
and the
plugs would have to be insulated from the block and I can say I've ever
seen
that... Is that the way they are? Now I'm real interested

Yes, there are two wires running to the plugs on some turbines.

I spend considerable time lurking in aircraft hangars. You see all sorts of
odd things done on aircraft systems.

The starting spark on a turbine engine has considerably higher power than a
standard gas engine - It has enough oomph that you can hear the snap of the
spark over the whine of the compressor when it starts up. It has to have
"lot 'o zots" to fire kerosene at the high air velocities in a turbine
engine.

Mark Browne

Yes, there are two wires running to the plugs on some turbines.

I spend considerable time lurking in aircraft hangars. You see all sorts of
odd things done on aircraft systems.

The starting spark on a turbine engine has considerably higher power than a
standard gas engine - It has enough oomph that you can hear the snap of the
spark over the whine of the compressor when it starts up. It has to have
"lot 'o zots" to fire kerosene at the high air velocities in a turbine
engine.

Mark Browne

Thanks for sharing that, I didnt realize turbines were that way. They must have
a huge magneto if you can hear em snap
I have a good friend who is an aircraft mechanic USAF and he told me that on
piston engine aircraft many will have 2 wires per plug but the reason is for
redundancy (in case one fails), they are both hot.

"CCred68046" wrote in message
...
Yes, there are two wires running to the plugs on some turbines.

I spend considerable time lurking in aircraft hangars. You see all sorts
of
odd things done on aircraft systems.

The starting spark on a turbine engine has considerably higher power than
a
standard gas engine - It has enough oomph that you can hear the snap of
the
spark over the whine of the compressor when it starts up. It has to have
"lot 'o zots" to fire kerosene at the high air velocities in a turbine
engine.

Mark Browne

Thanks for sharing that, I didnt realize turbines were that way. They must
have
a huge magneto if you can hear em snap
I have a good friend who is an aircraft mechanic USAF and he told me that
on
piston engine aircraft many will have 2 wires per plug but the reason is
for
redundancy (in case one fails), they are both hot.

You are correct on the light aircraft ignition.

I am interested in the DIY turbine engine hobby so I ask a lot of questions
when I lurk in aircraft technical offices. Some of the old timers have some
interesting things laying around for show and tell.

One of the more curious approaches to generating the high energy required by
turbine engines was the "opposite-polarity system." In this circuit two
electrodes extended into the combustion chamber. Each electrode becomes
alternately charged with positive and negative potential. This allows double
the voltage across the electrode without the corresponding need for higher
voltage insulation in the power leads.

Modern capacitor discharge igniters have made these exotic systems
unnecessary; most modern turbines use an annular ring, single gap igniter.
Some of the exciters on these thing pumps out in excess of 20 Jules
discharges! I have not seen one that uses a magneto, the power source is
either 24v DC or 115/400hz AC so they have a lot of power to play with. The
firing rate is pretty slow, it sounds like about four zaps a second, so they
can build up this monster spark. These ignitions have big bold warning
about the lethal nature of the spark, and after seeing the spark these
things throw, I believe it! As far as redundancy goes, the engines I have
seen use completely separate dual exciters, power leads, and igniters.

Mark Browne