Dg_pilot From United States of America, joined Sep 1999, 856 posts, RR: 3 Posted (10 years 10 months 2 days 19 hours ago) and read 704 times:
Whenever I switch a mag off for one reason or another, what "actually"
happens? The engine loses some RPM, but what exactly happens as far as the
timing, firing, and total power produced..and why?
Shaun3000 From United States of America, joined Mar 2002, 445 posts, RR: 0 Reply 2, posted (10 years 10 months 2 days 18 hours ago) and read 687 times:
I'll use a 172 as an example. 172s have four cylinders. Each cylinder has two spark plugs, one for each mag. So you have a total of 8 sparkplugs. So when you have both mags on, you have both spark plugs firing, giving you more even ignition thus an increased RPM. When you turn one mag off, then you only have one spark plug firing in each cylinder which decreases the RPM as the fuel isn't burning as evenly which reduces power.
As I understand it, that is how it works. If I messed something up, please feel free to correct me.
FlightSimFreak From United States of America, joined Oct 2000, 720 posts, RR: 0 Reply 3, posted (10 years 10 months 2 days 15 hours ago) and read 666 times:
The engine will not stop if one mag is bad and you turn off the other. The engine still has at least one other cylinder, unless you are running a lawnmower engine, which only has one mag. The engine will become very rough and grumbly, but will not die.
Flyf15 From , joined Dec 1969, posts, RR: Reply 4, posted (10 years 10 months 2 days 13 hours ago) and read 661 times:
Flightsimfreak, an engine (such as what is found on a 172) only has two mags. The magneto is what produces the electrical charge firing the spark in the spark plugs. If a mag has gone out, all spark plugs on that mag will no longer function.
Sinlock From United States of America, joined Dec 2000, 1532 posts, RR: 3 Reply 5, posted (10 years 10 months 2 days 12 hours ago) and read 652 times:
F15, Thanks for the help.
FlightSimFreak,
I would think that I know what I'm talking about.
Being the fact that I work on a fleet of aircraft including 5 C-152s, 3 C-172s, 2 PA-23s, a C-421,and a B-18.
Cosync From Mexico, joined Nov 2001, 556 posts, RR: 0 Reply 6, posted (10 years 10 months 2 days 9 hours ago) and read 636 times:
its ok flightsim freak.
u rae a lil wrong but u do know more than the average bear. hehe.
but he is a mechanic so he does no his stuff. there are 2 mags for each cylinder u see and when u switch mags its changing all of the mags for each cylinder.
Vc10 From United Kingdom, joined Nov 2001, 1382 posts, RR: 17 Reply 7, posted (10 years 10 months 2 days 1 hour ago) and read 623 times:
I think you are all correct because of the following :-
1] If the selected Magneto itself is unserviceable then the engine will stop
2] However if the selected Mag is OK, but there is a fault with one of it's associated plugs or harness then the engine will run rough as one of it's piston's is not working.
That is my opinion, but feel free to shoot me down
Cosync From Mexico, joined Nov 2001, 556 posts, RR: 0 Reply 8, posted (10 years 10 months 1 day 23 hours ago) and read 616 times:
nah look.
each cylinder has 2 spark plugs. and each spark plug in the cylinders is connected to a different magneto. so in case one mag fails u have another to keep some engine power rather than none.
FlightSimFreak From United States of America, joined Oct 2000, 720 posts, RR: 0 Reply 10, posted (10 years 10 months 1 day 14 hours ago) and read 587 times:
People seem to think that I know nothing about aviation because of my username... I've been flying for a while now, and I have 55 hours in a Beech Skipper. Also, I've had a broken spark plug in my previous car before, it was not generating a spark, but the engine did not die. That's why I said what I said. I find it hard to believe that an engine would fail if one cylinder was not firing.
FlightSimFreak From United States of America, joined Oct 2000, 720 posts, RR: 0 Reply 11, posted (10 years 10 months 1 day 13 hours ago) and read 586 times:
You are correct... I was thinking in terms of one spark plug, not the mags. Sorry about that, honest mix up.
Dg_pilot From United States of America, joined Sep 1999, 856 posts, RR: 3 Reply 13, posted (10 years 10 months 18 hours ago) and read 558 times:
I already knew that each magneto provided spark to its respective set of spark plugs, but why exactly does it run rough and so on? Is it because the fuel is not being burned as efficiently or what? Any idea how much total power is lost when running on one mag? I've ran on one mag in flight before due to a rough engine, and there seemed to be just a little power loss.
MagicMan_841 From Canada, joined Jan 2002, 182 posts, RR: 0 Reply 15, posted (10 years 9 months 4 weeks 1 day 21 hours ago) and read 524 times:
The magnetos use engine rotation to power the spark plugs.
If you turn it on OFF the spark plugs will stop firing and the engine will quit.
If you put it on LEFT or RIGHT, one of the two spark plugs per cylinder will stop firing, but the other will still do sparks, thus explaining the small loss of RPM.
Why two spark plugs per cylinders ?? -- best firing and security.
If you turn in on OFF and it doesn't stop, there's a problem with the electric system (that's why you check the OFF position during the engine shutdown checklist and also during run-up)
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