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 Post subject: Magneto Ignition
PostPosted: Mon Jun 17, 2013 2:19 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 14779
Location: CT
We're all accustomed to breaker point or breakerless ignition systems in our street cars. But some of us may have experience with MAGNETO ignition systems, so let's start a thread about those and zee what we can learn.

Magnetos replace standard ignition systems on hi-performance cars. The magneto actually replaces the coil, distributor, and sometimes the alternator and battery. Why?

Distributor ignition systems are fine within certain limits, but tend to deliver an erratic and weaker spark as engine RPM increases. Distributors all have their own rev limits, above which you begin to experience "point bounce" (with a breaker point distributor), or "spark drift/wander" (with electronic ignition distributors). Either condition will cause the engine to stutter, which effectively limits the top engine rpm available.

The performance of breaker or breakerless distributors (and coils) depends upon how fast the entire system can repeatedly close and open the coil's primary ignition circuit, and how fast the distributor can repeatedly deliver a hot spark to the right plug at the proper instant. Ignition coils also experience extreme heat due to electrical resistance. Heat is the enemy of everything electrical or mechanical, and coils can overheat and break down when asked to operate at extreme engine speeds.

If you wanted to use your engine under redline, a distributor ignition system should be fine. (The redline of some engines is actually determined by the upper performance limits of the ignition system, rather than by the strength of the reciprocating parts). But for extended hi-engine speed applications, Magnetos are the right ignition system to use.

A MAGNETO is actually a generator (or "Dynamo" in many European languages, which is defined as "converting mechanical motion into electrical output"). It creates its own electrical power pulses, by spinning a rotor inside a stator or field windings. Like any generator, the faster you spin it, the more power it makes. The more power it makes, the hotter the spark it delivers.

Racecars which routinely operate above 10,000 rpm exclusively use magnetos instead of coil and distributor ignitions. Those which race in endurance events prefer them too, since they are lighter and simpler than a standard distributor ignition system and are less likely to break down. ("Complexity is the enemy of dependability"). Magnetos have no breaker points or coils to worry about. Many magneto applications (mostly in race cars) don't even have a battery, relying on a bump start, a direct-drive hand crank, or an A/C electrical motor being momentarily attached to the engine drive mechanism ("Gentlemen, let someone start your engine").

Magnetos suffer at low RPM, especially when they're asked to run lights and electrical accessories, such as in exotic Sports/GT cars. The slower they turn, the less current they produce, making them fairly unsuitable for street use. If the battery has been eliminated as well, the magneto is responsible for sending electricity to every electrical feature on the car, once it is running. A magneto at rest produces NO output, so it is not capable of starting a car which doesn't have a battery. Mags also produce such a hot spark, they may cook your spark plugs much faster than common ignition systems. Drag racers can completely melt entire sets of plugs in less than 4 seconds.

Magnetos used to be very common in motorcycles and mopeds, which relied upon YOU supplying the initial input to start the engine. You either kicked the kickstarter on a motorcycle, or you pedaled the bicycle pedals on a moped, which got the engine turning *just* fast enough to make the "mag" put out enough juice to let the engine start. Once it started running, the lights came up bright as you revved the engine, then dimmed again as you backed off the throttle and the rpm dropped.
Everyone has memories of that.

Magnetos are still used today in common lawnmowers and weedwhackers, which require YOUR initial input on the starter pull cord to get the engine and Mag turning.

OK! You've heard about all I know about Magnetos. Let's hear some more comments (or questions) from others who have more (or less) experience with them?

THANKS to SurferD for bump-starting this thread! :wink:


Attachments:
File comment: Nearly every race car engine is sparked by a Magneto.
Race car engine with Magneto.jpg
Race car engine with Magneto.jpg [ 143.97 KiB | Viewed 7064 times ]
File comment: Until the late 1960s, most motorcycles used batteryless Magnetos for ignition and electrical generation. Electric starters required small batteries, generating a new industry.
Motorcycle Magneto.jpg
Motorcycle Magneto.jpg [ 131.57 KiB | Viewed 7078 times ]
File comment: A/A Fuel Dragsters used Cirello Magnetos in 1965. Many other big company names made Mags, too.
Cirello Mag on Rail Dragster 1964.jpg
Cirello Mag on Rail Dragster 1964.jpg [ 28.93 KiB | Viewed 7080 times ]
File comment: Drag racers exclusively used Magnetos (like this Cirello unit in 1965). A push car bump-started the racer.
Cerillo Magneto 1965.jpg
Cerillo Magneto 1965.jpg [ 526.29 KiB | Viewed 7084 times ]
File comment: This new MSD Pro-Mag 44 produces an amaZing 44 Watts of electrical output, costs only $2300!
MSD Pro-Mag 44.jpg
MSD Pro-Mag 44.jpg [ 5.38 KiB | Viewed 7087 times ]
File comment: Airplanes are the perfect application for magnetos. Weight saving, powerful, reliable output, and someone to pull the prop thru to start it for you! "CONTACT!" literally means you've switched the Mag on.
Aircraft magneto.jpg
Aircraft magneto.jpg [ 152.33 KiB | Viewed 7095 times ]
File comment: Car mags resemble common distributors, but contain their own Dynamo inside. Wires carry self-generated power pulses to spark plugs.
Automotive Mangeto.jpg
Automotive Mangeto.jpg [ 71.89 KiB | Viewed 7098 times ]

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Last edited by Frank T on Mon Jun 17, 2013 3:31 pm, edited 4 times in total.
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 Post subject:
PostPosted: Mon Jun 17, 2013 3:18 pm 
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Location: Orange, CT
So you went and did it!
Applause again.
I'm an aircraft tech and very well versed in magnetos.
Since aircraft stuff has redundant systems there are two mags and both must be timed to work at the same time. It can be a real pain.
I just don't know how the guys in the old days did it on the big radials like the Wright Cyclone or Pratt&Whitney Wasp.


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 Post subject:
PostPosted: Mon Jun 17, 2013 3:44 pm 
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Location: CT
Well, there ya go, buddy ~ 450hp supercharged P&W Wasp powered some of my favorite fabric wing box kites!

And the big Wright double-row 14cyl 800hp Whirlwind was a fantasy maker for me during my biplane interest days.

Both had not only double magnetos, but double plugs available, as well. Two entire systems available at the turn of a switch. Lose power in one, switch to the other. When you're flying mail cross-country and 'airports' didn't mean the same thing as they mean today, you can't afford engine problems.


Attachments:
File comment: P&W Wasp powered many 1930s-40s biplanes. Available up to 450hp, with twin magneto ignition.
P&W 9 cyl Wasp.jpg
P&W 9 cyl Wasp.jpg [ 28.32 KiB | Viewed 7059 times ]
File comment: Twin-Row 14 cylinder twin-Magneto fired R1670.
Aircraft Engine Cutaway.jpg
Aircraft Engine Cutaway.jpg [ 624.38 KiB | Viewed 7062 times ]

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Last edited by Frank T on Mon Jun 17, 2013 6:53 pm, edited 1 time in total.
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 Post subject:
PostPosted: Mon Jun 17, 2013 4:00 pm 
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Location: CT
I've always been fascinated by radial engines, and developed the personal theory that Harley Davidson motorcycle engines were probably copied from them.

HD was developed during the first decade of the 20th century, when the majority of airplane engines were radials. I picture the HD guys just cutting two cylinders off a radial, fitting it sideways into a bike frame and calling it a day.

The HD Twin pistons share a common crank journal, exactly like the old radial engines do. That's what gives a Harley its distinctive 'double thump' sound.


Attachments:
File comment: Radial engines had all connecting rods joined on a single crankshaft journal.
Radial 9 cyl.jpg
Radial 9 cyl.jpg [ 16.51 KiB | Viewed 7052 times ]
File comment: Direct parentage of the HD Twin to the old aircraft Radials.
HD V-Twin.jpg
HD V-Twin.jpg [ 32.9 KiB | Viewed 7052 times ]
File comment: I mean, just LOOK at this old HD and tell me if an aircraft radial engine doesn't come to mind?
EARLY HD ENGINE.jpg
EARLY HD ENGINE.jpg [ 32.67 KiB | Viewed 7056 times ]

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 Post subject:
PostPosted: Mon Jun 17, 2013 6:51 pm 
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We really appreciate technical discussions on this website, so if you have some Magneto experience or technical wisdom, we'd certainly enjoy it if you'd share it with us. I haven't had my hands on a Magneto in 25 years, so if you can update anything I said, please do?

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 Post subject:
PostPosted: Mon Jun 17, 2013 7:16 pm 
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Joined: Sat Jun 01, 2013 5:38 pm
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Location: Orange, CT
Always happy to give a bump!
I believe you're correct about the Harley V.
The giveaway is the aforementioned comon crank same as many of the old radials.
The radials were more balanced when running so they sound smoother.
If you ever heard a missing/misfiring radial you would swear it was a bike driving by.


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 Post subject:
PostPosted: Mon Jun 17, 2013 7:30 pm 
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I used to hang around Syracuse University a lot. For some reason, their Mechanical Engineering dept had a garage full of old radials which the students perpetually tore down, miked, and re-assembled. After each teardown they had to run the engine to prove they had done it correctly. They had stub propellers on them and were all on stands. That's where I learned the merits of the radials. They had one 4-row Russian 28 cyl cutaway exhibit engine with an electric drive motor hooked up to make it turn over at/abt 200rpm. You could get diZZy watching everything move in there.
I have often bought flights in WACO UPF-7 biplanes for Christmas presents, just because I think it's the very best thing a person can do with 30 minutes (unless he knows Angelina Jolie).
Is there any good flying weather where you are?

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 Post subject:
PostPosted: Mon Jun 17, 2013 7:52 pm 
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Location: Orange, CT
I'm in Orange and Bridgeport airfield (oddly located in Stratford) is a decent place to go.
I have seen many cutaways of all kinds of weird engines.
The Air Force Museum in Dayton, OH has many examples.
The New England Air Museum does too but not on the same scale.
Of course the Smithsonian Air and Space is the ultimate.
I'm still amazed by the complexity of the early aviation recip engines.
It was all designed and manufactured without computers and a lot of it was trial and error.
I used to run up engines after rebuild.
It was awesome that something I fixed actually worked LOL.
I also worked doing turbine engine testing but they were kind of lifeless "terminators" compared to the "living" recips.
Just to clarify, I no longer work in aviation but it's still a passion of mine.


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 Post subject:
PostPosted: Mon Jun 17, 2013 7:57 pm 
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In case no one noticed, the R1670 Frank showed has a built in centrifugal supercharger below the carb.


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 Post subject:
PostPosted: Mon Jun 17, 2013 8:25 pm 
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We need to revitaliZe the thread on superchargers vs blowers, too. It sounds as if I've finally found someone who knows the technical difference btwn them.

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 Post subject:
PostPosted: Mon Jun 17, 2013 8:32 pm 
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Frank T wrote:
We need to revitaliZe the thread on superchargers vs blowers, too. It sounds as if I've finally found someone who knows the technical difference btwn them.

Good idea, most people don't even know how a turbo system works.
Forced induction is a mystery to most car guys.


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 Post subject:
PostPosted: Mon Jun 17, 2013 11:26 pm 
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Lead on ~ you have our attention!
We have a thread already on here someplace, in which we disagree about the difference btwn a true supercharger and a blower. I'll try to find it tmrw ~ too tired to see tonight.

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 Post subject:
PostPosted: Tue Jun 18, 2013 8:57 am 
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Here's a link to our SECOND discussion about superchargers and blowers. Still searching for the initial discussion link.

http://forums.ctzcc.com/viewtopic.php?t=7258

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 Post subject:
PostPosted: Tue Jun 18, 2013 4:11 pm 
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I'll read through it.


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