dual ignition
Posted: Fri Feb 17, 2012 11:02 pm
Mike
I assume you're talking about a Vertex magneto. That alone may not be
more reliable than electronic ignition and may compromise either maximum
power or cruise efficiency. An electrical system utilizing a reasonably
maintained Recombinant Gas (RG) battery and fed by even a single
alternator, setup within the 'Aeroelectric Connection' guidelines, has
two power sources and is probably as reliable as any of our major engine
components or aircraft systems. I added a small John Deere permanent
magnet alternator anyway but full efi requires a few more amps. Some
folks like to use a second battery ;)
Holler if you want to discuss a particular method but in a nutshell it
is difficult to use dual ignition with a magneto and single spark plugs
and I've never seen it done. The polarity reverses from spark to spark.
Fairly easy to do it using a distributor and a MSD8210 coil joiner.
Common in racing vehicles. Redundant sensors, electronics, and coil with
a common distributor and spark plug. Auto spark plugs are extremely
reliable and cheap to replace yearly if you wish. Dozens of EA81 subarus
do this.
More difficult with distributorless ignition but doable.
Can't help you much with the carb other than to suggest that there are
methods of attaching mixture controls to automobile carbs.
I'd suggest that perhaps a 0.8 prop tip speed might be a better design
target for lower noise and higher efficiency. Losses mount rapidly at
higher tip speeds and the SR does not have the problem of trying to put
more power into a small diameter prop like some aircraft.
Some fun eh...
Ken
ps - have I mentioned recently that my opinions are theoretical and not
based on first hand operating experience? :)
Mike Kimball wrote:
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I assume you're talking about a Vertex magneto. That alone may not be
more reliable than electronic ignition and may compromise either maximum
power or cruise efficiency. An electrical system utilizing a reasonably
maintained Recombinant Gas (RG) battery and fed by even a single
alternator, setup within the 'Aeroelectric Connection' guidelines, has
two power sources and is probably as reliable as any of our major engine
components or aircraft systems. I added a small John Deere permanent
magnet alternator anyway but full efi requires a few more amps. Some
folks like to use a second battery ;)
Holler if you want to discuss a particular method but in a nutshell it
is difficult to use dual ignition with a magneto and single spark plugs
and I've never seen it done. The polarity reverses from spark to spark.
Fairly easy to do it using a distributor and a MSD8210 coil joiner.
Common in racing vehicles. Redundant sensors, electronics, and coil with
a common distributor and spark plug. Auto spark plugs are extremely
reliable and cheap to replace yearly if you wish. Dozens of EA81 subarus
do this.
More difficult with distributorless ignition but doable.
Can't help you much with the carb other than to suggest that there are
methods of attaching mixture controls to automobile carbs.
I'd suggest that perhaps a 0.8 prop tip speed might be a better design
target for lower noise and higher efficiency. Losses mount rapidly at
higher tip speeds and the SR does not have the problem of trying to put
more power into a small diameter prop like some aircraft.
Some fun eh...
Ken
ps - have I mentioned recently that my opinions are theoretical and not
based on first hand operating experience? :)
Mike Kimball wrote:
I've got my engine decisions pretty much completed. The only things I have
yet to figure out are which carb and I would like to find a way to have
redundant ignition. My first look at ignition was to put a mag in the
distributor hole. I know I could use dual electronic with a second small
battery for backup but I like the idea of a mag that will run without
external power. I just can't figure out how to have two with a single set
of plug wires. I really don't want to deal with dual plugs.
I was thinking about giving the three bladed in-flight adjustable IVO-Prop
with the electronic constant speed prop governor a try. It's only 26.7
pounds and $2130. Supposed to be good up to 700 HP. Can anyone tell me how
to size and pitch the blades? Here are the ranges possible according to
their website.
30"- 90" or 45" to 105" pitch range
58"-76" diameter
I keep hearing that the biggest blade I can run and have good ground
clearance is what I want. That being the case, then I guess I would go with
the 76" diameter which I think should have plenty of ground clearance in a
level attitude rolling down the runway. What pitch range would I want?
Using a prop tip speed calculator I found on the web a 76" diameter prop
needs to turn 3000 rpm to develop the desired tip speed between .88 and .92
mach to produce maximum thrust. (Only works between about 30-70 deg. F). I
want to limit my max engine rpm to about 5000 rpm so that means I will want
a gear reduction ratio of about 1.7. Then again, I also keep hearing that a
big slow turning prop is what we want on a Super Rebel. Perhaps 76" just
isn't big enough?
Mike Kimball
SR #044
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