mawingho
Topic Author
Posts: 41
Joined: Sun Jul 22, 2012 4:23 pm

Piston Engine Power Problem

Sun Jul 29, 2012 2:38 pm

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?
 
User avatar
larshjort
Posts: 1434
Joined: Wed Dec 19, 2007 6:54 pm

RE: Piston Engine Power Problem

Sun Jul 29, 2012 2:52 pm

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,
 
Mender
Posts: 249
Joined: Wed Feb 04, 2004 9:36 am

RE: Piston Engine Power Problem

Sun Jul 29, 2012 3:08 pm

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
 
rfields5421
Posts: 5859
Joined: Thu Jul 19, 2007 12:45 am

RE: Piston Engine Power Problem

Sun Jul 29, 2012 4:32 pm

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.
 
rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

RE: Piston Engine Power Problem

Sun Jul 29, 2012 5:28 pm

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...
 
113312
Posts: 643
Joined: Sat Apr 16, 2005 9:09 am

RE: Piston Engine Power Problem

Sun Jul 29, 2012 6:56 pm

Gasoline lawn mower engines use magnetos too. Generator, coil (step up transformer) and distributor all in one.
 
KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

RE: Piston Engine Power Problem

Sun Jul 29, 2012 11:16 pm

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 :-)
 
Mender
Posts: 249
Joined: Wed Feb 04, 2004 9:36 am

RE: Piston Engine Power Problem

Mon Jul 30, 2012 9:01 am

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.
 
Stealthz
Posts: 5550
Joined: Wed Feb 02, 2005 11:43 am

RE: Piston Engine Power Problem

Mon Jul 30, 2012 1:21 pm

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!
 
rfields5421
Posts: 5859
Joined: Thu Jul 19, 2007 12:45 am

RE: Piston Engine Power Problem

Mon Jul 30, 2012 1:39 pm

Sprint cars, midgets and some late models.
 
Stealthz
Posts: 5550
Joined: Wed Feb 02, 2005 11:43 am

RE: Piston Engine Power Problem

Tue Jul 31, 2012 12:33 am

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!
 
rfields5421
Posts: 5859
Joined: Thu Jul 19, 2007 12:45 am

RE: Piston Engine Power Problem

Tue Jul 31, 2012 1:30 am

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.
 
dkswim
Posts: 29
Joined: Thu Sep 09, 2010 9:28 am

RE: Piston Engine Power Problem

Tue Jul 31, 2012 5:23 am

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 avatar
Aquila3
Posts: 521
Joined: Sun Nov 14, 2010 3:18 pm

RE: Piston Engine Power Problem

Tue Jul 31, 2012 7:07 pm

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
 
nomadd22
Posts: 1566
Joined: Fri Feb 22, 2008 7:42 pm

RE: Piston Engine Power Problem

Tue Jul 31, 2012 7:29 pm

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.
Anon
 
KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

RE: Piston Engine Power Problem

Tue Jul 31, 2012 8:29 pm

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 :-)
 
prebennorholm
Posts: 6562
Joined: Tue Mar 21, 2000 6:25 am

RE: Piston Engine Power Problem

Wed Aug 01, 2012 12:32 am

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
 
rcair1
Crew
Posts: 1144
Joined: Wed Oct 28, 2009 8:39 pm

RE: Piston Engine Power Problem

Wed Aug 01, 2012 4:44 am

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
 
Mender
Posts: 249
Joined: Wed Feb 04, 2004 9:36 am

RE: Piston Engine Power Problem

Wed Aug 01, 2012 8:38 am

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.

Who is online

Users browsing this forum: Max Q, TailDragging and 1 guest

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos