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Piston Engine Power Problem  
User currently offlinemawingho From Hong Kong, joined Jul 2012, 41 posts, RR: 0
Posted (2 years 3 weeks 1 day 8 hours ago) and read 4241 times:

I have a question regarding to the Engine.

Is the magneto used to give power to the spark plug and then ignite the mixture and cause combustion which move the piston engine, and then the engine provide the power to the alternator and finally product electricity to the bus bar and all equipments?

Is this the case? How the magneto provide power?

Even if the alternator fail and the battery exhausted, all electical equipments would be lost.
Is the engine will still continue to function normally?

18 replies: All unread, jump to last
 
User currently offlineLarshjort From Denmark, joined Dec 2007, 1444 posts, RR: 0
Reply 1, posted (2 years 3 weeks 1 day 7 hours ago) and read 4232 times:

Quoting mawingho (Thread starter):
Even if the alternator fail and the battery exhausted, all electical equipments would be lost.
Is the engine will still continue to function normally?

The magneto is driven by the accessory gearbox on the engine and generates the power by itself.

Look at this wiki page

http://en.wikipedia.org/wiki/Ignition_system#Magneto_systems

The advantage of the magneto is that it operates independantly of the aircrafts elevtrical system. Most GA engines have 2 magnetos, with each magneto supplying 1 sparkplug in each cylinder.

/Lars



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
User currently offlineMender From United Kingdom, joined Feb 2004, 240 posts, RR: 0
Reply 2, posted (2 years 3 weeks 1 day 7 hours ago) and read 4219 times:

To be as fail safe as possible the magneto is designed to be permantly live. I.E. to stop the engine you have to ground the low tension coil (this is done via the ignition switch). Therefore if the switch fails or the wire from the magneto was to break, the magneto will remain live and the engine will continue to run (you'd have to cut off the fuel supply to stop it).

There is also a type of magneto called an impulse magneto. This provides enough energy to create a spark with very, very little engine rotation/slow cranking speed.

Have a look at this http://www204.pair.com/bbg46/FM%20Ma...Impulse%20Couplings%2843-48%29.pdf


User currently offlinerfields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 32
Reply 3, posted (2 years 3 weeks 1 day 6 hours ago) and read 4185 times:

In several forms of auto racing - magnetos are used rather than alternators, generators, distributors, etc. They even use magentos with fuel injection.

They are used in auto racing because (1) it saves weight, (2) it saves complexity, & (3) they are less likely to fail in adverse conditions.

I would think the same reasons would apply to small aircraft aviation.


User currently offlinerwessel From United States of America, joined Jan 2007, 2338 posts, RR: 2
Reply 4, posted (2 years 3 weeks 1 day 5 hours ago) and read 4159 times:
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A magneto is basically a somewhat oddly designed generator - it's optimized to produce brief pulses of fairly high voltage, suitable for causing a sparkplug to, ahem, spark.

It's driven by the engine in some way, and it generates electricity when being turned. No different in principal than a generator or alternator being run by the engine (although the drive system for magnetos tends to be more integral with the engine).

And it's nothing specific to aviation millions of small engines use magnetos, because they're cheap and reliable. Lawnmowers, snowblowers, small generators...


User currently offline113312 From United States of America, joined Apr 2005, 571 posts, RR: 1
Reply 5, posted (2 years 3 weeks 1 day 3 hours ago) and read 4124 times:

Gasoline lawn mower engines use magnetos too. Generator, coil (step up transformer) and distributor all in one.

User currently offlineKELPkid From United States of America, joined Nov 2005, 6370 posts, RR: 3
Reply 6, posted (2 years 3 weeks 23 hours ago) and read 4017 times:

Quoting Mender (Reply 2):
To be as fail safe as possible the magneto is designed to be permantly live. I.E. to stop the engine you have to ground the low tension coil (this is done via the ignition switch). Therefore if the switch fails or the wire from the magneto was to break, the magneto will remain live and the engine will continue to run (you'd have to cut off the fuel supply to stop it).

You usually shut off a piston aviation engine with the mixture. If you shut down with the mag switch, you risk leaving a cylinder filled with a stoichiometric mixture. If there's a broken p-lead in a mag, and someone turns a prop on the engine, it could kick over and fire up.



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineMender From United Kingdom, joined Feb 2004, 240 posts, RR: 0
Reply 7, posted (2 years 3 weeks 13 hours ago) and read 3883 times:

Quoting KELPkid (Reply 6):
You usually shut off a piston aviation engine with the mixture. If you shut down with the mag switch, you risk leaving a cylinder filled with a stoichiometric mixture. If there's a broken p-lead in a mag, and someone turns a prop on the engine, it could kick over and fire u

When readback what I've written it looks like I meant in normal operation you turn off the ignition switch to stop the engine like you would in a car and of course this is not correct.

I was trying to being brief and explain a significant difference between a magneto ignition system and the sort of system that involves a battery and coil like you have on a car and I've ended up being very unclear.

Thanks for correcting me.


User currently offlinestealthz From Australia, joined Feb 2005, 5688 posts, RR: 44
Reply 8, posted (2 years 3 weeks 9 hours ago) and read 3827 times:
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Quoting rfields5421 (Reply 3):
They are used in auto racing because

Really, been involved in many levels of motor sport for 40+ years, only magnetos I have seen have been on a few historic racers and some drag racers.



If your camera sends text messages, that could explain why your photos are rubbish!
User currently offlinerfields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 32
Reply 9, posted (2 years 3 weeks 8 hours ago) and read 3822 times:

Sprint cars, midgets and some late models.

User currently offlinestealthz From Australia, joined Feb 2005, 5688 posts, RR: 44
Reply 10, posted (2 years 2 weeks 6 days 22 hours ago) and read 3689 times:
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rfields, I stand corrected then,

Spent a lot of years working in, officiating at and watching motorsport but very little of that time at shorter speedway type races!

Cheers



If your camera sends text messages, that could explain why your photos are rubbish!
User currently offlinerfields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 32
Reply 11, posted (2 years 2 weeks 6 days 21 hours ago) and read 3673 times:

20+ years around, working with, managing quarter and half mile dirt tracks, along with working on a lot of cars.

I do love sprints - and the Chili Bowl Nationals indoors in Tulsa in January with over 250 midgets is something everyone should see at least once.

I should have mentioned that most of the cars which run magnetos do not have batteries or starters.


User currently offlinedkswim From United States of America, joined Sep 2010, 30 posts, RR: 0
Reply 12, posted (2 years 2 weeks 6 days 17 hours ago) and read 3634 times:

also used in racing applications beacuse as the engine spins faster it produces more energy at the plug, coil type used in most automotive looses emergy the faster the engine spins

User currently offlineAquila3 From Italy, joined Nov 2010, 259 posts, RR: 0
Reply 13, posted (2 years 2 weeks 6 days 3 hours ago) and read 3504 times:

I believe it fits the definition of the ignition system of many classic motorcycles, notably the Piaggio Vespa, (and yes, it is the same Piaggio that you are thinking about...)
The Magneto is a very simple generator built inside the motor flywheel, that works also as a cooling fan and hosts inside the breaker contact as well.
The legend says that the Vespa engine (the original two stroke one) is of Aeronautical derivation.. Its reliability sure is a proof of it. I believe DKW also had something similar, but I never had my hands on them.



chi vola vale chi vale vola chi non vola è un vile
User currently offlinenomadd22 From United States of America, joined Feb 2008, 1846 posts, RR: 0
Reply 14, posted (2 years 2 weeks 6 days 3 hours ago) and read 3500 times:

Quoting rfields5421 (Reply 11):
I should have mentioned that most of the cars which run magnetos do not have batteries or starters.

There's something to be said for not having a several hundred amp power source in the wreckage after a crash. Intrinsically safe diesels go one step further and are completely electricity free.



Andy Goetsch
User currently offlineKELPkid From United States of America, joined Nov 2005, 6370 posts, RR: 3
Reply 15, posted (2 years 2 weeks 6 days 2 hours ago) and read 3473 times:

Quoting nomadd22 (Reply 14):
There's something to be said for not having a several hundred amp power source in the wreckage after a crash. Intrinsically safe diesels go one step further and are completely electricity free.

In fact, when a gasoline engine continues to run after shutoff (due to an accumulation of unburt carbon deposits in the engine), it is called "diesleling"   You hardly see that in new engines because computers won't let things get that bad...



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineprebennorholm From Denmark, joined Mar 2000, 6417 posts, RR: 54
Reply 16, posted (2 years 2 weeks 5 days 22 hours ago) and read 3396 times:

Quoting Aquila3 (Reply 13):
I believe it fits the definition of the ignition system of many classic motorcycles, notably the Piaggio Vespa, (and yes, it is the same Piaggio that you are thinking about...)

Thanks for bringing back good memories with my 1964 Piaggio Vespa Grand Luxe. How I hate myself for selling it in 1967, but it was the only way to finance my first car.

Quoting Aquila3 (Reply 13):
The Magneto is a very simple generator built inside the motor flywheel, that works also as a cooling fan and hosts inside the breaker contact as well.

That's exactly how it was. And to balance the flywheel there was one more magneto which produced power for the headlight and the horn. Variable frequency AC, the sound of the horn varied with the engine rpm, in idle it was barely hearable.

Quoting Aquila3 (Reply 13):
The legend says that the Vespa engine (the original two stroke one) is of Aeronautical derivation..

I have heard that the Vespa engine was originally designed for a ground power unit for some Piaggio WW2 fighter plane.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlinercair1 From United States of America, joined Oct 2009, 1317 posts, RR: 52
Reply 17, posted (2 years 2 weeks 5 days 17 hours ago) and read 3350 times:
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Quoting nomadd22 (Reply 14):
There's something to be said for not having a several hundred amp power source in the wreckage after a crash. Intrinsically safe diesels go one step further and are completely electricity free.

This is one thing that scares the bejeebes out of fire fighters like me in the newer hybrid and electric vehicles. There is a TON of energy in there that can be liberated in interesting ways. Yes - I know there is that energy in the gas tank too - but it is easier to recognize and manage.

One of the first things we do in a car crash - on a conventional car - is cut the battery cables.
Hybrid and EV - then throw in a dozen airbags - do you really want to cut that roof off to get to the people?



rcair1
User currently offlineMender From United Kingdom, joined Feb 2004, 240 posts, RR: 0
Reply 18, posted (2 years 2 weeks 5 days 14 hours ago) and read 3310 times:

Quoting nomadd22 (Reply 14):
There's something to be said for not having a several hundred amp power source in the wreckage after a crash. Intrinsically safe diesels go one step further and are completely electricity free.

?????

Unless the magneto is turning it's not going to produce any power at all, unlike the battery for the starter motor. Also, although you can throw a match into a puddle of diesel and it will put the match out, once diesel (vapour) is ignited it burns ferociously. I wouldn't consider it to be much safer than Avgas.


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