Impulse Coupling on Magneto

[Kai Glaesner]

Hello community,

I have a question I think some of you may be able answer: in most(?)
reciprocating engine installations, the left magneto seems to have a impulse
coupling, enabling the magneto to produce a spark strong enough for ignition
even at low (starter cranking) RPM's.

The question: does the coupling alter the ignition _timing_ (e.g. towards
late), too?

I hear this, sometimes, as the main reason why you should put the ignition
shift in the "L"eft position when handpropping the engine and, while doing
so, preventing the right (early igniting) magneto to kick back the prop.

Thanks in advance for the answer....

Best Regards

Kai


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[Paul Sengupta]

"Kai Glaesner" > wrote in message
om...
> Hello community,
>
> I have a question I think some of you may be able answer: in most(?)
> reciprocating engine installations, the left magneto seems to have a
impulse
> coupling, enabling the magneto to produce a spark strong enough for
ignition
> even at low (starter cranking) RPM's.
>
> The question: does the coupling alter the ignition _timing_ (e.g. towards
> late), too?
>
> I hear this, sometimes, as the main reason why you should put the ignition
> shift in the "L"eft position when handpropping the engine and, while doing
> so, preventing the right (early igniting) magneto to kick back the prop.

Yes.

[[email protected]]

Paul Sengupta > wrote:
: > I hear this, sometimes, as the main reason why you should put the ignition
: > shift in the "L"eft position when handpropping the engine and, while doing
: > so, preventing the right (early igniting) magneto to kick back the prop.

: Yes.

... and I believe it's on the order of 5 degrees ATDC. Hand-propping with one
mag set to fire 25 BTDC could ruin your day, although it's fairly unlikely to fire at
such a slow speed.


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[G.R. Patterson III]

Kai Glaesner wrote:
>
> The question: does the coupling alter the ignition _timing_ (e.g. towards
> late), too?

Yes.

> I hear this, sometimes, as the main reason why you should put the ignition
> shift in the "L"eft position when handpropping the engine and, while doing
> so, preventing the right (early igniting) magneto to kick back the prop.

This is correct if the left mag has an impulse coupling and the right does not. It's
unlikely that the right mag will cause kickback, since it will not produce a very
strong spark while handpropping, but it's possible.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

[Dan Thomas]

"G.R. Patterson III" > wrote in message >...
> Kai Glaesner wrote:
> >
> > The question: does the coupling alter the ignition _timing_ (e.g. towards
> > late), too?
>
> Yes.
>
> > I hear this, sometimes, as the main reason why you should put the ignition
> > shift in the "L"eft position when handpropping the engine and, while doing
> > so, preventing the right (early igniting) magneto to kick back the prop.
>
> This is correct if the left mag has an impulse coupling and the right does not. It's
> unlikely that the right mag will cause kickback, since it will not produce a very
> strong spark while handpropping, but it's possible.
>
> George Patterson
> If a man gets into a fight 3,000 miles away from home, he *had* to have
> been looking for it.


My A-65 starts best on Left (impulse) mag only. If I try to
start it on Both, the right one will start firing before the engine
has passed thru 150 RPM or so, and will sometimes kick back and quit.
The mags are 58-year-old Case tractor mags, originally certified for
aircraft use, and still produce a hotter spark than a brand-new Slick.

Dan

[Orval Fairbairn]

In article >,
(Dan Thomas) wrote:

> "G.R. Patterson III" > wrote in message
> >...
> > Kai Glaesner wrote:
> > >
> > > The question: does the coupling alter the ignition _timing_ (e.g. towards
> > > late), too?
> >
> > Yes.
> >
> > > I hear this, sometimes, as the main reason why you should put the
> > > ignition
> > > shift in the "L"eft position when handpropping the engine and, while
> > > doing
> > > so, preventing the right (early igniting) magneto to kick back the prop.
> >
> > This is correct if the left mag has an impulse coupling and the right does
> > not. It's
> > unlikely that the right mag will cause kickback, since it will not produce
> > a very
> > strong spark while handpropping, but it's possible.
> >
> > George Patterson
> > If a man gets into a fight 3,000 miles away from home, he *had* to
> > have
> > been looking for it.
>
>
> My A-65 starts best on Left (impulse) mag only. If I try to
> start it on Both, the right one will start firing before the engine
> has passed thru 150 RPM or so, and will sometimes kick back and quit.
> The mags are 58-year-old Case tractor mags, originally certified for
> aircraft use, and still produce a hotter spark than a brand-new Slick.
>
> Dan

Interesting -- IIRC, the old Case tractor mags became Slicks.