REFLECTOR: new electronic ign.

[Alex Balic]

Jim-
That is exactly why mags are used on racing engines, because at high RPM
they generate a ton of power, more than an electronic unit can... problem is
at 2500 rpm, they are pretty weak. I am interested that yours can throw a 1"
spark - I don't have my formula handy, but at sea level, dry air, I would
think that it would require several thousand volts- do they use a capacitor
in the high altitude units? I though that they were just better insulated to
prevent internal arcing at altitude..... I suppose that if there is enough
spring tension on that impulse coupler that it could simulate momentarily,
several thousand RPM though........ I have been a grounding source for a
magneto in the past, it wasn't a fun experience that I want to repeat, but
once again, it happened when the coupler tripped, and the speed could have
been pretty high....

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Jim Agnew
Sent: Saturday, July 17, 2004 9:11 PM
To: Velocity Aircraft Owners and Builders list
Subject: RE: REFLECTOR: new electronic ign.


Scott,

I have Bendix high altitude mags on my IO-360 and if you
turn the prop by hand the impulse coupled mag will throw a
3/4-1" spark so I doubt if .035" would bother them.

On AA Fuel dragsters the cylinders are filled with an
almost liquid mixture and they use mags to fire it!! and at
10K+ RPM.  The problem with mags is their lack of automatic
spark advance that gives the electronic ignitions an
advantage.  They solved this in cars in the 40s so this
isn't exactly a new development.

BTW it is said that the mags on those dragsters at top RPMs
produce a spark of 42 AMPS so if you think that mags have a
weak spark at high rpms you are wrong.  The mag output is
weak at low rpms and increases as rpms increase.

Jim

--- Scott Derrick <scott at tnstaafl.net> wrote:
> WHile there may be mags with a good spark, you won't find
> one on an
> airplane.   THe spark is absolutly lousy.
>
> I gap the plugs on my one slick mag at 18, I gap my plugs
> on my lightspeed
> at 35.  Hmmm.. WHy?  Reason is the mags are so weak any
> larger gap will
> just arc across the points in the mag instead of the
> plug.  The lightspeed
> on the other hand has a very hot spark that can jum the
> 35 gap with ease.
>
> I can run my engine on one mag and loose, minimum 25%
> power, closer to
> 35%, I can run on the lightspeed and loose at the most
> 10%, probably
> closer to 5%.
>
> WHen I do a mag check I drop 75 rpm when running on the
> mag, I drop less
> than 10 rpm when shutting the mag off.
>
> Mags suck in all respects except one, they don't need any
> external power.
>
> Mags fail all the time and have very short lives. The TBF
> for a well
> designd EI is longer than the life of the plane.
>
> Scott
>
> > Mags do not have a lousy spark. They need two spark
> plugs per cylinder
> > because it is too big to combust properly with only one
> ignition point,
> > especially a 540. And you need two ignition units
> because anything can
> > and will eventually fail. Electronic units fail
> instantly instead of
> > running rough like an old style mag.  bg
> >
> > -----Original Message-----
> > From: reflector-bounces at tvbf.org
> [mailto:reflector-bounces at tvbf.org] On
> > Behalf Of Scott Derrick
> > Sent: Saturday, July 17, 2004 10:15 AM
> > To: Velocity Aircraft Owners and Builders list
> > Subject: Re: REFLECTOR: new electronic ign.
> >
> >> Try and remember: you do not have two mags because
> they give better
> >> ignition that way - they give lousy ignition the day
> you install them,
> >> and go downhill from there. You have two mags because
> one of them is
> >> *certain* to fail. One electronic unit provides better
> ignition (saves
> > a
> >
> > While I agree that mags are much more failure prone
> than an EI and that
> > one of the reasons for two is redundency in case of
> failure.
> >
> > Mags have a lousy spark and you will not get full power
> with just one.
> > two are required.  Even with EI's two plugs will
> provide a more complete
> > burn and more power than one.
> >
> > Scott
> >
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=====
James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying
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