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MAGNETO!


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#1 Bob Riebe

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Posted 03 May 2019 - 20:40

When I was a yout, I remember how cool it would be to use one of these in your street car, THEN, I found out how impractical that was. :lol:  :smoking:

 

https://www.enginela...-vertex-magneto



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#2 BRG

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Posted 04 May 2019 - 21:17

I am too young to know about magnetos, and too old to understand electronic ignition.



#3 gruntguru

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Posted 05 May 2019 - 22:57

 . . and nothing has points anymore so we can leave ignition work to others.



#4 Kelpiecross

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Posted 06 May 2019 - 04:42

  Magnetos are still the typical ignition system in lawnmower engines etc.  (at least I think they are). 



#5 BRG

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Posted 06 May 2019 - 19:48

  Magnetos are still the typical ignition system in lawnmower engines etc.  (at least I think they are). 

And in most aircraft piston engines.  Aviation authorities are ultra conservative in the interests of reliability and hence safety, and still consider magnetos tp be preferable to those new fangled coil and points systems.  Let alone the unproven ECUs that have only had a couple of decades and several trillion road miles of use so far.



#6 Bob Riebe

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Posted 07 May 2019 - 00:34

And in most aircraft piston engines.  Aviation authorities are ultra conservative in the interests of reliability and hence safety, and still consider magnetos tp be preferable to those new fangled coil and points systems.  Let alone the unproven ECUs that have only had a couple of decades and several trillion road miles of use so far.

Unlike automobiles when the latest whizz-bang gizmo goes bad and it costs a tow, or a hundred bucks at service station to see what is wrong,   in aircraft people die.

 

When I had my kick-start Honda, getting it, and keeping it,  gong was never a problem, ever.


Edited by Bob Riebe, 07 May 2019 - 00:37.


#7 7MGTEsup

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Posted 07 May 2019 - 15:56

And in most aircraft piston engines.  Aviation authorities are ultra conservative in the interests of reliability and hence safety, and still consider magnetos tp be preferable to those new fangled coil and points systems.  Let alone the unproven ECUs that have only had a couple of decades and several trillion road miles of use so far.

 

But are quite happy with fly by wire controls.....



#8 BRG

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Posted 07 May 2019 - 16:01

Unlike automobiles when the latest whizz-bang gizmo goes bad and it costs a tow, or a hundred bucks at service station to see what is wrong,   in aircraft people die.

 

Indeed.  Which begs the question: is the magneto a more reliable ignition system for the ICE than coil/distributor/points or ECU?  And if the answer is 'yes', why has the automotive industry abandoned it?



#9 7MGTEsup

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Posted 07 May 2019 - 16:05

Indeed.  Which begs the question: is the magneto a more reliable ignition system for the ICE than coil/distributor/points or ECU?  And if the answer is 'yes', why has the automotive industry abandoned it?

 

Because they want to sell you more spare parts?



#10 Charlieman

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Posted 07 May 2019 - 19:29

Indeed.  Which begs the question: is the magneto a more reliable ignition system for the ICE than coil/distributor/points or ECU?  And if the answer is 'yes', why has the automotive industry abandoned it?

Multi cylinder engines? I have never owned a four cylinder lawn mower...

 

RF noise. In the 1970s and earlier, magnetos upset radio and TV reception a lot.

 

Why not have both? In the Edwardian/pre WW1 period, you could buy a car with Delco coil ignition and a magneto. Cadillac?



#11 Kelpiecross

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Posted 09 May 2019 - 04:43

Indeed.  Which begs the question: is the magneto a more reliable ignition system for the ICE than coil/distributor/points or ECU?  And if the answer is 'yes', why has the automotive industry abandoned it?

 

 I don't think there is much mystery  - if the car has a battery for the starter motor, lights etc. it is much simpler to have a non-magneto ignition.  If the plane, vehicle etc. has no battery there is not much choice - it has to be a magneto.   The battery ignition system also works from more-or-less zero revs meaning they are  easier to start - magneto systems are harder to start (need more cranking speed).    


Edited by Kelpiecross, 09 May 2019 - 04:55.


#12 Allan Lupton

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Posted 09 May 2019 - 12:14

Multi cylinder engines? I have never owned a four cylinder lawn mower...

 

RF noise. In the 1970s and earlier, magnetos upset radio and TV reception a lot.

 

Why not have both? In the Edwardian/pre WW1 period, you could buy a car with Delco coil ignition and a magneto. Cadillac?

Magnetos were used in multi-cylinder aeroplane engines - including more cylinders than any non-aviation application (e.g. P&W's R4360 with 28 cylinders - albeit more than one magneto)

RF noise was as prevalent with coil ignition in the VHF television days, but suppressors were easier to fit than in a magneto system.

Not only could you have both with an independant system for each (e.g. R-R Phantom) but Bosch produced a system which used the same plugs, leads and distributor for either magneto or coil with a driver-controlled switch-over. That gave you the good low-speed spark (mentioned above) for starting and the high-speed power of the magneto.



#13 Lee Nicolle

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Posted 23 May 2019 - 08:54

Magnetos function quite well but as for ultra reliable I dont know. Speedway still uses mags in Sprintcars and Midgets though a few have and do use multispark high intensity ignition. Running on a motor cycle battery.

More than occasionally one goes bad and most carry a spare.

Yet most sedan? type cars use multi spark. Only a few still use a mag.

A mag is very hard on distributor gears,  I have seen a few cams stripped clean, even using a bronze gear on a steel roller cam.

In an engine designed for a mag probably different but on a production based engine a bit suspect. AFAIK Sprinters still use a factory Chev location and interchangeable with a production engine. though the crap they put on the cam, 4 stage oil pump, power steering pump, waterpump and hydraulic wing pump and the fuel pump on the back of the cam. The distributor of whatever type is nearly coincidental.



#14 Charlieman

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Posted 23 May 2019 - 10:55

 I don't think there is much mystery  - if the car has a battery for the starter motor, lights etc. it is much simpler to have a non-magneto ignition.  If the plane, vehicle etc. has no battery there is not much choice - it has to be a magneto.   The battery ignition system also works from more-or-less zero revs meaning they are  easier to start - magneto systems are harder to start (need more cranking speed).    

As we have noted, adoption of the coil ignition system depended on the existence of reliable batteries for road cars. Different considerations existed for racing cars and planes -- consequences of failure, battery vulnerability, battery life and recharging complexity etc. Standard starting procedure for a piston engine plane might be to run and observe on magneto #1 before switching to #2.

 

Magnetos were not the only alternative electrical option. Ford persisted with the trembler coil system on the Model T, even adding a battery option to make starting easier in theory.

 

Why did magnetos persist for so long on racing and sports car engines? I suggest that if you were designing an engine for racing you would incorporate the magneto at the start and that it would trickle down into production variants, rather than being a bolt-on addition. Race duration was also significant. If we jump to the DFV era of F1, early years of coil and transistor ignition, the battery was still a vulnerable component. The battery had to be able to start the engine, drive supplementary startup pumps until the engine was warm and provide ignition for two hours -- without a charging system. Unsurprisingly some cars failed to finish after the battery conked out.



#15 Allan Lupton

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Posted 24 May 2019 - 09:40

Historically coil ignition preceded magneto. Early cars had hot tube ignition and the trembler coil was the next step. Starting from cold was tremendously improved and the concept of timed ignition started there, but the battery capacity was a limiting factor as charging systems were developed later.

So far as I can remember the low-tension magneto was only used in competition and up-market large-engined cars: generated electricity passed through a pair of contacts in the combustion chamber and a spark resulted from mechanically separating of those contacts at the appropriate point. Not sure, being away from my books this week, when the HT mag as we know it replaced LT, but the simpler system it has makes the change seem sensible.



#16 GreenMachine

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Posted 24 May 2019 - 11:36

IIRC, starting a Lycoming in a 172 was both magnetos, pre-takeoff check was to switch to one then the other and check there was no significant rev drop (ie both working ok), then back to both for the rest of the flight.  That was late 60s.



#17 Kelpiecross

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Posted 24 May 2019 - 12:24

IIRC, starting a Lycoming in a 172 was both magnetos, pre-takeoff check was to switch to one then the other and check there was no significant rev drop (ie both working ok), then back to both for the rest of the flight.  That was late 60s.

 

 I saw this  being done in a Chipmunk just before the take off roll started in the early

1960s - the pilot called it "mag drop" -  I think about a 100RPM drop was the limit on one magneto. 



#18 GreenMachine

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Posted 25 May 2019 - 07:38

I was addressing a point above, which implied flight was undertaken on only one of the magnetos.  I should add (in response to another comment above) that the magneto continued long after generators/alternators/batteries were standard fitment, presumably to this day?  I guess this is testament to the innate conservatism of aero engineering, as even after the generator failed, and the battery failed, the plugs would still fire.