Ignition switch settings

[Tony Cox]

Here's a question that until yesterday I'd have thought was
obvious.

Cessna-style (and no doubt other) ignition switches have five
settings -- Off/Right/Left/Both/Start. When you're on the "Right"
setting, does it mean you are firing on the right magneto or
does it mean the right magneto is grounded?

[Orval Fairbairn]

In article . com>,
"Tony Cox" > wrote:

> Here's a question that until yesterday I'd have thought was
> obvious.
>
> Cessna-style (and no doubt other) ignition switches have five
> settings -- Off/Right/Left/Both/Start. When you're on the "Right"
> setting, does it mean you are firing on the right magneto or
> does it mean the right magneto is grounded?

Right magneto is "hot" (ungrounded). The "OFF" position grounds both
mags.

[Tony Cox]

On Mar 3, 8:34 am, Orval Fairbairn > wrote:
> In article . com>,
> "Tony Cox" > wrote:
>
> > Here's a question that until yesterday I'd have thought was
> > obvious.
>
> > Cessna-style (and no doubt other) ignition switches have five
> > settings -- Off/Right/Left/Both/Start. When you're on the "Right"
> > setting, does it mean you are firing on the right magneto or
> > does it mean the right magneto is grounded?
>
> Right magneto is "hot" (ungrounded). The "OFF" position grounds both
> mags.

That was my understanding too, but after arguing the
point with two very experienced pilots yesterday, I
wondered how prevalent the contrary view might be.

[[email protected]]

On Mar 3, 11:12 am, "Tony Cox" > wrote:

>
> > Right magneto is "hot" (ungrounded). The "OFF" position grounds both
> > mags.
>
> That was my understanding too, but after arguing the
> point with two very experienced pilots yesterday, I
> wondered how prevalent the contrary view might be.

Most pilots don't understand much about aircraft systems,
and many who have automobile maintenance experience don't understand
magnetos. They make a lot of assumptions and sometimes harbour many
misconceptions. A magneto's primary winding is grounded to kill it, so
when the key is in the R position, the L magneto is grounded, and vice
versa. Even the terminals on back of the switch are labelled R and L
and when the appropriate positions are selected, the other terminal is
grounded. Can confuse someone trying to test the switch itself unless
they know what the principles are.
Another misconception: that the magneto is somehow connected
to the aircraft's electrical system. They're afraid to turn off the
master switch in flight lest it kill the engine.

Dan

[Andrew Sarangan]

On Mar 3, 11:09 am, "Tony Cox" > wrote:
> Here's a question that until yesterday I'd have thought was
> obvious.
>
> Cessna-style (and no doubt other) ignition switches have five
> settings -- Off/Right/Left/Both/Start. When you're on the "Right"
> setting, does it mean you are firing on the right magneto or
> does it mean the right magneto is grounded?

Very good question. If we use the logic that "Both" means both magneto
circuits are open, and "Off" means both magneto circuits are closed,
that would imply that "Right" means the right magneto is open (and
hence firing).

But I am sure an A&P should be able to give a more authoritative
answer.

[Jon Woellhaf]

And I've been trying to learn for years why R is on the left and L is on the
right.

[Peter Dohm]

> > > Right magneto is "hot" (ungrounded). The "OFF" position grounds both
> > > mags.
> >
> > That was my understanding too, but after arguing the
> > point with two very experienced pilots yesterday, I
> > wondered how prevalent the contrary view might be.
>
> Most pilots don't understand much about aircraft systems,
> and many who have automobile maintenance experience don't understand
> magnetos. They make a lot of assumptions and sometimes harbour many
> misconceptions. A magneto's primary winding is grounded to kill it, so
> when the key is in the R position, the L magneto is grounded, and vice
> versa. Even the terminals on back of the switch are labelled R and L
> and when the appropriate positions are selected, the other terminal is
> grounded. Can confuse someone trying to test the switch itself unless
> they know what the principles are.
> Another misconception: that the magneto is somehow connected
> to the aircraft's electrical system. They're afraid to turn off the
> master switch in flight lest it kill the engine.
>
I know from personal experience that a lot of pilots continue to have
serious misconceptions about such things, but it still bothers me. This is
the sort of thing that is part of every run-up, and therefore should have
been part of the aircraft systems knowledge requirement to get the
license--not necessarily the grounding issue, but which magneto actually
fires its set of plugs.

[[email protected]]

On Mar 3, 4:21 pm, "Jon Woellhaf" > wrote:
> And I've been trying to learn for years why R is on the left and L is on the
> right.

I wonder. Maybe because the ancient systems used two toggle
switches labelled "L" and "R" and they were connected to their
respective mags. When you turned off the L switch, you were running on
the R mag. It was self-evident. Our two Citabrias still have this
setup and I bet American Champion is still building them that way.
When Bendix came up with the combination starter/mag switch, the
internal mag-shorting contacts were set up in the same order but now
they had to label them opposite so that you knew which one you were
sparking on.
I'd rather have the toggles in my Jodel but it makes the
airplane so much easier to steal. If you can get in you can go.

Dan

[Travis Marlatte]

"Peter Dohm" > wrote in message
...
>> > > Right magneto is "hot" (ungrounded). The "OFF" position grounds both
>> > > mags.
>> >
>>
> I know from personal experience that a lot of pilots continue to have
> serious misconceptions about such things, but it still bothers me. This
> is
> the sort of thing that is part of every run-up, and therefore should have
> been part of the aircraft systems knowledge requirement to get the
> license--not necessarily the grounding issue, but which magneto actually
> fires its set of plugs.
>
>

I don't get the connection. Why would the licenced pilot need to know which
mag and which set of plugs is firing on Left or Right key position? Know why
the mag check is important and what to watch for during the mag check, yes.

[Tony Cox]

On Mar 3, 5:11 pm, "Travis Marlatte" >
wrote:
>
> I don't get the connection. Why would the licenced pilot need to know which
> mag and which set of plugs is firing on Left or Right key position? Know why
> the mag check is important and what to watch for during the mag check, yes.

Here's one reason (and this scenario initiated the post
in the first place). My 182 failed the run-up yesterday
on the "left" mag. I knew which cylinder it was through
my JPI. But which plug? The upper plug is easy to check, but
the lower requires removal of the lower cowling, which is
a 2-person job to replace.

[Travis Marlatte]

"Jon Woellhaf" > wrote in message
...
> And I've been trying to learn for years why R is on the left and L is on
> the right.
>

My recollection from the last time this was discussed is that the labeles
used to be the other way around so that "L" on the left meant that the left
mag was grounded and, therefore, the right mag was firing. Then, to keep it
more consistent with the "Off" and "Both" labeling, they switched the
labeling but left the right key position which grounded the right mag so
that the left mag was firing now labeled "L"?

Doesn't bother me a bit. If one mag fails an RPM drop, I'm gonna check the
wiring to both any. What is more important to me is that the left key
position has the bottom plugs firing. That's important so that I can pull
the correct plugs the first time to clear an unusually stubborn fouling.

Say, why don't they label them "Off", "B", "T", and "Both"?
-------------------------------
Travis
Lake N3094P
PWK

[Peter Dohm]

> >> > > Right magneto is "hot" (ungrounded). The "OFF" position grounds
both
> >> > > mags.
> >> >
> >>
> > I know from personal experience that a lot of pilots continue to have
> > serious misconceptions about such things, but it still bothers me. This
> > is
> > the sort of thing that is part of every run-up, and therefore should
have
> > been part of the aircraft systems knowledge requirement to get the
> > license--not necessarily the grounding issue, but which magneto actually
> > fires its set of plugs.
> >
> >
>
> I don't get the connection. Why would the licenced pilot need to know
which
> mag and which set of plugs is firing on Left or Right key position? Know
why
> the mag check is important and what to watch for during the mag check,
yes.
>
>
No, but he should know that that the Right mag is hot (firing plugs) and the
Left mag is cold (not firing) when the switch is in the "R" position, and
that the Right mag is cold (not firing) and the Left mag is hot (firing
plugs) when the switch is in the "L" position. That much systems knowledge
would seem usefull for a safe and reasonable Go/NoGo decision prior to
take-off, and also to explain a problem to an efficient manner.

Knowledge of the specifics of how the ignition system works could be very
usefull in the case of "stealing your oun airplane" because you lost the key
at a remote hunting/fishing spot; but I can not imagine that being part of
an accredited licensing test.

Peter

[Peter Dohm]

> > And I've been trying to learn for years why R is on the left and L is on
the
> > right.
>
> I wonder. Maybe because the ancient systems used two toggle
> switches labelled "L" and "R" and they were connected to their
> respective mags. When you turned off the L switch, you were running on
> the R mag. It was self-evident. Our two Citabrias still have this
> setup and I bet American Champion is still building them that way.
> When Bendix came up with the combination starter/mag switch, the
> internal mag-shorting contacts were set up in the same order but now
> they had to label them opposite so that you knew which one you were
> sparking on.
> I'd rather have the toggles in my Jodel but it makes the
> airplane so much easier to steal. If you can get in you can go.
>
Very true. But I've known pilots who thought that might be very usefull if
they lost their key at a remote fishing hole...

Peter
(It is an amusing thought)

[Don Tuite]

On Sat, 3 Mar 2007 19:11:50 -0600, "Travis Marlatte"
> wrote:

>"Peter Dohm" > wrote in message
...
>>> > > Right magneto is "hot" (ungrounded). The "OFF" position grounds both
>>> > > mags.
>>> >
>>>
>> I know from personal experience that a lot of pilots continue to have
>> serious misconceptions about such things, but it still bothers me. This
>> is
>> the sort of thing that is part of every run-up, and therefore should have
>> been part of the aircraft systems knowledge requirement to get the
>> license--not necessarily the grounding issue, but which magneto actually
>> fires its set of plugs.
>>
>>
>
>I don't get the connection. Why would the licenced pilot need to know which
>mag and which set of plugs is firing on Left or Right key position? Know why
>the mag check is important and what to watch for during the mag check, yes.
>
On the right (or left) looking toward the propeller, or t'other way
round? (And tractor or pusher? And are the mag designations different
on the two engines in a Cessna 337?) Maybe it's time to label mag
switches Port and Starboard, mateys!

Don

[Morgans[_2_]]

> wrote

> I'd rather have the toggles in my Jodel but it makes the
> airplane so much easier to steal. If you can get in you can go.

You could rig up a cover to put over the toggles, with a place to put a
padlock on the cover, as long as it is not a certified plane.

Would altering a plane in that manner be against the rules for certified
planes? It would be in the certified plane's regular certified condition,
while it was being flown, after all!
--
Jim in NC

[Morgans[_2_]]

"Travis Marlatte" > wrote

> Say, why don't they label them "Off", "B", "T", and "Both"?

Excellent suggestion! Why not? It might make too much sense, that way!

One could put an "auxiliary label" on panel next to the "L" and "R" with a
Dyno Label, or with another favorite method, though.
--
Jim in NC

[Jackal24]

"Travis Marlatte" > wrote in
t:

> What is more important to me is that the left
> key position has the bottom plugs firing. That's important so that I
> can pull the correct plugs the first time to clear an unusually
> stubborn fouling.
>

I thought that one mag controlled the top plugs on one side and the bottom
on the other side.

[Blueskies]

"Peter Dohm" > wrote in message ...
: >
: No, but he should know that that the Right mag is hot (firing plugs) and the
: Left mag is cold (not firing) when the switch is in the "R" position, and
: that the Right mag is cold (not firing) and the Left mag is hot (firing
: plugs) when the switch is in the "L" position. That much systems knowledge
: would seem usefull for a safe and reasonable Go/NoGo decision prior to
: take-off, and also to explain a problem to an efficient manner.
:
: Knowledge of the specifics of how the ignition system works could be very
: usefull in the case of "stealing your oun airplane" because you lost the key
: at a remote hunting/fishing spot; but I can not imagine that being part of
: an accredited licensing test.
:
: Peter
:
:

But they sure as heck should know that turning off the master switch will not turn off their engine.

[Jim Macklin]

There are some old engines that did use battery power for
the ignition and in those, the battery master must be on.
But, in general aircraft built in the post WWII period have
two independent magnetos and the battery is used for lights,
starting and radios, etc. Some aircraft had one magneto and
one coil/distributor [like a car], so the AFM/POH should be
read. Also ignition operation should be checked on the
ground as part of the pre or post-flight checklists.



"Blueskies" > wrote in message
t...
|
| "Peter Dohm" > wrote in message
...
| : >
| : No, but he should know that that the Right mag is hot
(firing plugs) and the
| : Left mag is cold (not firing) when the switch is in the
"R" position, and
| : that the Right mag is cold (not firing) and the Left mag
is hot (firing
| : plugs) when the switch is in the "L" position. That
much systems knowledge
| : would seem usefull for a safe and reasonable Go/NoGo
decision prior to
| : take-off, and also to explain a problem to an efficient
manner.
| :
| : Knowledge of the specifics of how the ignition system
works could be very
| : usefull in the case of "stealing your oun airplane"
because you lost the key
| : at a remote hunting/fishing spot; but I can not imagine
that being part of
| : an accredited licensing test.
| :
| : Peter
| :
| :
|
| But they sure as heck should know that turning off the
master switch will not turn off their engine.
|
|

[Blueskies]

"Jim Macklin" > wrote in message ...
: There are some old engines that did use battery power for
: the ignition and in those, the battery master must be on.
: But, in general aircraft built in the post WWII period have
: two independent magnetos and the battery is used for lights,
: starting and radios, etc. Some aircraft had one magneto and
: one coil/distributor [like a car], so the AFM/POH should be
: read. Also ignition operation should be checked on the
: ground as part of the pre or post-flight checklists.
:
:
:

How old are you talking, Jim? Any specifics? Engine, airframe?

[Stubby]

Tony Cox wrote:
> Here's a question that until yesterday I'd have thought was
> obvious.
>
> Cessna-style (and no doubt other) ignition switches have five
> settings -- Off/Right/Left/Both/Start. When you're on the "Right"
> setting, does it mean you are firing on the right magneto or
> does it mean the right magneto is grounded?
>
Is this covered in the plane's POH?

[Tony Cox]

On Mar 4, 8:55 am, Stubby >
wrote:
> Tony Cox wrote:
> > Here's a question that until yesterday I'd have thought was
> > obvious.
>
> > Cessna-style (and no doubt other) ignition switches have five
> > settings -- Off/Right/Left/Both/Start. When you're on the "Right"
> > setting, does it mean you are firing on the right magneto or
> > does it mean the right magneto is grounded?
>
> Is this covered in the plane's POH?

Good question. It isn't. It isn't covered in the
shop manual either.

[Orval Fairbairn]

In article >,
"Travis Marlatte" > wrote:

> "Peter Dohm" > wrote in message
> ...
> >> > > Right magneto is "hot" (ungrounded). The "OFF" position grounds both
> >> > > mags.
> >> >
> >>
> > I know from personal experience that a lot of pilots continue to have
> > serious misconceptions about such things, but it still bothers me. This
> > is
> > the sort of thing that is part of every run-up, and therefore should have
> > been part of the aircraft systems knowledge requirement to get the
> > license--not necessarily the grounding issue, but which magneto actually
> > fires its set of plugs.
> >
> >
>
> I don't get the connection. Why would the licenced pilot need to know which
> mag and which set of plugs is firing on Left or Right key position? Know why
> the mag check is important and what to watch for during the mag check, yes.

So you can tell which mag has the problem -- ehether it is plugs,
harness or the magneto itself. Sometimes it is just a fouled plug; other
times it is a dirty cigarette; other times it is a loose harness
connection. Learn it and use it!

[Travis Marlatte]

"Orval Fairbairn" > wrote in message
...
> In article >,
> "Travis Marlatte" > wrote:
>
>> "Peter Dohm" > wrote in message
>> ...
>> >> > > Right magneto is "hot" (ungrounded). The "OFF" position grounds
>> >> > > both
>> >> > > mags.
>> >> >
>> >>
>> > I know from personal experience that a lot of pilots continue to have
>> > serious misconceptions about such things, but it still bothers me.
>> > This
>> > is
>> > the sort of thing that is part of every run-up, and therefore should
>> > have
>> > been part of the aircraft systems knowledge requirement to get the
>> > license--not necessarily the grounding issue, but which magneto
>> > actually
>> > fires its set of plugs.
>> >
>> >
>>
>> I don't get the connection. Why would the licenced pilot need to know
>> which
>> mag and which set of plugs is firing on Left or Right key position? Know
>> why
>> the mag check is important and what to watch for during the mag check,
>> yes.
>
> So you can tell which mag has the problem -- ehether it is plugs,
> harness or the magneto itself. Sometimes it is just a fouled plug; other
> times it is a dirty cigarette; other times it is a loose harness
> connection. Learn it and use it!


You and Peter seem pretty set on this and I don't quite understand why.
Here's two scenarios I'm thinking about:

1) I do a mag check and notice that I don't get an RPM drop on the Left (or
Right) position. So I taxi over to the garage and I say to the guy, I says,
"Say! I think I may have a broken P-lead. Do you have time to fix it while I
go get some lunch?"

2) I do a mag check and notice that the engine runs rough on the Left (or
Right) position. So I taxi over to the garage and I say to the guy, I says,
"Say! I think I may have a fouled plug that I couldn't clear with leaning.
Do you have time to fix it while I go get some lunch?"

Now, if I happened to be out on a lake somewhere and had a fouled plug that
wouldn't clear, I'd walk over to my tackle box, see, and pull out the green,
spotted jitter bug. 'Cause when I'm desperate for dinner, that's what I
always use. In the morning, I'd pull all four of the lower plugs because by
the time I translated left or right for top or bottom on the left or right
side, I'd... well, I'd rather be fishing and, chances are, it's one of the
lower plugs.

-------------------------------
Travis
Lake N3094P
PWK

[[email protected]]

On Mar 4, 12:53 am, Jackal24 > wrote:
> "Travis Marlatte" > wrote . net:
>
> > What is more important to me is that the left
> > key position has the bottom plugs firing. That's important so that I
> > can pull the correct plugs the first time to clear an unusually
> > stubborn fouling.
>
> I thought that one mag controlled the top plugs on one side and the bottom
> on the other side.

Yup, on Lycoming. Continental, at least on the smaller engines,
will have the right mag firing the top plugs and the left firing the
bottom. The impulse mag (right) fires the top plugs, since they're
less likely to get wet with oil or fuel.

Dan

[Morgans[_2_]]

> wrote
>
> Yup, on Lycoming. Continental, at least on the smaller engines,
> will have the right mag firing the top plugs and the left firing the
> bottom. The impulse mag (right) fires the top plugs, since they're
> less likely to get wet with oil or fuel.

I think you mis-interpreted his comments. He said (at least I think he
said) that one mag fires the top plugs on the left cylinders and the same
mag fires the bottom plugs on the right side cylinders.
--
Jim in NC

[[email protected]]

On Mar 5, 11:04 am, "Morgans" > wrote:
> > wrote
>
>
>
> > Yup, on Lycoming. Continental, at least on the smaller engines,
> > will have the right mag firing the top plugs and the left firing the
> > bottom. The impulse mag (right) fires the top plugs, since they're
> > less likely to get wet with oil or fuel.
>
> I think you mis-interpreted his comments. He said (at least I think he
> said) that one mag fires the top plugs on the left cylinders and the same
> mag fires the bottom plugs on the right side cylinders.
> --
> Jim in NC

No, that's what I meant. On the Lycoming the left mag fires the
bottom left-side plugs and right top-side plugs. The RH mag fires the
top LH and bottom RH plugs. Continental's smaller engines have the
mags firing all the top or all the bottom plugs, and the larger
engines are arranged like Lycomings.

Dan

[DL]

On my "larger Continental" the left mag fires top plugs on left side and
bottom plugs on right side. Vice versa for right mag.
DL
> wrote in message
ps.com...
> On Mar 5, 11:04 am, "Morgans" > wrote:
>> > wrote
>>
>>
>>>
> No, that's what I meant. On the Lycoming the left mag fires the
> bottom left-side plugs and right top-side plugs. The RH mag fires the
> top LH and bottom RH plugs. Continental's smaller engines have the
> mags firing all the top or all the bottom plugs, and the larger
> engines are arranged like Lycomings.
>
> Dan
>

[Stan Prevost[_1_]]

> wrote in message
ps.com...
>
> No, that's what I meant. On the Lycoming the left mag fires the
> bottom left-side plugs and right top-side plugs. The RH mag fires the
> top LH and bottom RH plugs. Continental's smaller engines have the
> mags firing all the top or all the bottom plugs, and the larger
> engines are arranged like Lycomings.
>

Haven't followed the whole thread, but on my Lycoming, the left mag fires
all top plugs (TIO540-AH1A).

San

[Morgans[_2_]]

> wrote

> No, that's what I meant. On the Lycoming the left mag fires the
> bottom left-side plugs and right top-side plugs. The RH mag fires the
> top LH and bottom RH plugs. Continental's smaller engines have the
> mags firing all the top or all the bottom plugs, and the larger
> engines are arranged like Lycomings.

How 'bout that. I misinterpreted what _you_ meant.
--
Jim in NC

[Orval Fairbairn]

In article >,
"Morgans" > wrote:

> > wrote
>
> > No, that's what I meant. On the Lycoming the left mag fires the
> > bottom left-side plugs and right top-side plugs. The RH mag fires the
> > top LH and bottom RH plugs. Continental's smaller engines have the
> > mags firing all the top or all the bottom plugs, and the larger
> > engines are arranged like Lycomings.
>
> How 'bout that. I misinterpreted what _you_ meant.

On my O-435 Lycoming the Right mag fires the top right and bottom left;
the Left mag fires top left and bottom right.

This arrangement is standard per Lycoming Overhaul manual for both 4-
qnd 6-cylinder engines.