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argnan
03-06-2005, 12:18 PM
What are the superchangers???? The only thing i managed to figure out is that they work like shifts in a car but i am sure that i am wrong!!!
And what the are the magnetos??? When i mess with them i end up losing my engine!!!

stansdds
03-06-2005, 01:30 PM
A supercharger is basically an air compressor. The more air you feed an engine, the more power it can produce. Multi-stage superchargers provide even greater air pressure to the engine at altitude. As you go up in altitude, the lower the air pressure. The supercharger provides air at higher pressure to the engine, so as far as the engine is concerned it is still operating with same amount of oxygen it had with sea level air pressure. This helps keep engine power output constant whether it is at sea level or at altitude.

Some superchargers had more than one stage. In the F4U-1, which had a three stage supercharger, Stage one was used at 5500 feet altitude or lower, stage two needed to be engaged by 7000 feet and stage three at 18,000 feet.

A magneto is the aircraft engine equivalent to the distributor in an automobile engine. Most aircraft engines have two magnetos and the engine will usually continue to run, albeit at a lower rpm and power level, with one magneto off.

SkyChimp
03-06-2005, 04:51 PM
One has to be careful about using "magneto" and "distributor" interchangably. Only in cases where there were dual function units were they the same. On almost all engines of the period, magnetos and distributors were distinctly different. And the vast majority of engines had only one magneto unit - although some single units were double stacked on one drive shaft.

The sole purpose of the magneto was to generate a high-tension electical current. This current was fed to the distributor or distributors. The distributors fed the current to the spark plugs.

For the most part, American twin row radials had one magneto and two distributors (distributors were mounted on the reduction gear case, magneto usually in between them). Almost all R-2800s had a single magneto and two distributors, although SOME (and not very many) had dual funtion magnetos and distributors.

Here is the R-2800-21 engine.

The black thing on the upper center of the reduction gear housing is the magneto. The two tuna-can-shaped things on either side of it are the distributors.

http://www.wpafb.af.mil/museum/engines/eng34.jpg

The V-1710 had a single fixed timing magneto as well, one of the extra large (double sized) units on a single drive shaft. It fed current to the dual distributors.

I believe the Merlin may have had a similar set-up, but I don't have an ignition schematic for that engine and the stuff I've found on the internet is contradictory and misleading, due to the using "magneto" and "distrubutor" interchangably.

Another term that adds to the confusion is "dual ignition." Generally that meant the plane had two spark plugs per cylinder which necessitated a very powerful magneto (generating up to and over 20,000 volts) and multiple distributors.

SkyChimp
03-06-2005, 05:53 PM
Found a schematic of the Merlin. And also checked the manual I forgot I had. This engine had two high tension magnetos.

Bikewer
03-06-2005, 06:50 PM
Some of us are old enough to have driven magneto-fired vehicles, specifically motorcycles. I had a Spanish-made Montessa circa 1970 that had a magneto. No battery at all, which meant at night if you pulled up to a stoplight the lights would die...hehe.
A magneto ignition is fairly simple and reliable, no doubt explaining it's use on military aircraft of the period.

SkyChimp
03-06-2005, 07:58 PM
Let me qualify what I wrote earlier:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>
And the vast majority of engines had only one magneto unit - although some single units were double stacked on one drive shaft.
<HR></BLOCKQUOTE>

That's true of American enegines. I don't know if it's true of all-nation's engines. I don't know what the DB engines used.

DHC2Pilot
03-06-2005, 08:47 PM
The purpose of two magnetos is redundancy....if one fails the engine will continue to run, usually with only a minor drop in RPM. On modern aircraft using dual spark plugs in each cylinder, each magneto would send current to one plug in each cylinder. If one mag dies, then you would still have combustion in all cylinders, however the fuel air mixture would not be as efficiently ignited, thus causing the slight decrease in power.

SkyChimp
03-06-2005, 10:28 PM
Two seperate magnetos MAY provide redundancy, and a safety factor, in case one magneto is lost. But I'm hard pressed to see how.

I don't think it would provide any safety margin in the Merlin. I've been looking at the stuff I found on the Merlin (in the Mustangs) and it looks like each cylinder bank had its own magneto, or possibly the seperate magnetos powered seperately the exhaust and intake-side plugs (anyone with specifics on this please chime in). The loss of one magneto would have probably meant a complete failure of the engine. I don't think the Merlin could have run on either just the left or right cylinders, or on one plug per cylinder (at least not for long).

Pratt and Whitney apparently produced a few R-2800s with two magnetos, but most WWII vintage R-2800 engines had only one "dual" magneto and two distributors. The magneto was basically a double stack unit on one shaft (one big, high-output magneto). The loss of the magneto meant complete loss of ignition and, thus, complete engine failure.

Same with the Allison V-1710. It had one large Scintilla "double" magneto (a single big, high-output magneto) and two distributors (one distributor firing the intake-side plugs, and the other firing the exhaust-side plugs). Loss of the magneto would have resulted in total ignition loss and total engine failure.

I don't think the use of two magnetos would have provided much redundancy or safety. (Apparently, neither did Pratt and Whitney.)

First, for it to be redundant, each magneto would have had to provide power to all plugs. I'm not sure that was the case in engines with two magnetos. Back to the Merlin, each magneto appears to have powered a seperate bank of cylinder, or seperate rows of spark plugs. (Again, if some one has specifics on this...) Therefore, the loss of one magneto would have left only one bank of cylinders firing, or only on plug per cylinder firing. I seriously dobt that engine would operate that way.

Second, as stated, the sole purpose of the magneto was to produce high-tension current. The role of either one big magneto (in the case of American engines) or two smaller magnetos would have been exactly the same - to produce enough power to fire all those spark plugs (two in each cylinder in most engines). Pratt and Whitney tests revealed that when one spark plug in each cylinder was lost, detonation quickly set in. In aircraft engines, two plugs were needed to create two flame fronts that were necessary to ignite all that fuel, all at once. P&W found that when one spark plug in a cylinder was lost, the burn time slowed down too much. This slower burn time allowed the unburned mixture ahead of the flame-front to heat up to the point where it ignited uncontrollably - detonation. The loss of function of one plug in each cylinder resulted in detonation that could not be controlled except at the very lowest power setting - and then only for a very short period of time (this may be differnt in civil aircaft that don't possess the high performance engines of fighters)

Two magnetos on one engine would have done one of three things

1) each magneto powered ALL plugs - in which case the loss of one magneto left one operational, but underpowered which was probably unable to provide enough power to created adequate spark.

2) each magneto powered a seperate bank or row or cylinders - in which case the loss of one left half the engine cylinders without ingnition power, and probably an impossible condition to fly in.

3) each magneto powered either the intake-side or exhaust-side plugs - in which case the loss of one magneto would leave only half of each cylinder's flame front firing, leading to detontation and engine failure.

Pratt and Whitney found that mechanical failure of its mechanical magnetos was almost unheard of. It found no benefit in two seperate magnetos - except in cases where there were two sperate magneto/distributor combination units.

In short, its difficult to see any real benefit (or problem) in having two seperate magnetos since the loss of one probably would still result in engine failure.

Additionally, magnetos were tucked away in places that if they were shot up, then other vital components would have been likely damaged was well. In the case of the Merlin and the Allison, the magnetos/magneto was on the back of the engine near the carb and supercharger. If a pilot were unlucky enough to have a magneto shot out, he probably had other damage, too. On the R-2800, a hit to the magneto would porbably have meant hits to the reduction gear, distributors and cylinders. .

JR_Greenhorn
03-07-2005, 12:04 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by stansdds:
Multi-stage superchargers... <HR></BLOCKQUOTE>Most of what you say is accurate, stansdds, but I need to correct you on some terminology. What you are describing is multi-speed superchargers, not multi-stage.
Multi-speed superchargers in the aircraft of that era are simply a centrifugal compressor driven through a gearbox from the engine. With the example of the 3-speed supercharger in the F-4U, there was three gear ratios that could be selected in that supercharger drive gearbox.

In multi-stage supercharger systems, the airflow makes more than one pass through the compressor(s). The F-4U also happens to use a multi-stage supercharging system. In the case of the Corsair, the air first passed through an exhaust-driven turbosupercharger (the first stage). Then, the airflow passed through the 3-speed, gear-driven centrifugal superchager (integrated into the engine), which was the second stage.

Some multi-stage supercharger systems had a dual-impeller centrifugal supercharger. The airflow was primarily compressed in one side of the impeller, then passed through the other side for further compression.



It's worth mentioning that in some multi-speed superchargers, a higher "gear" could be used below the required altitude to overboost the engine for War Emergency Power. This WEP rating was usually accomanied by an allowable time interval (such as 15 min). After the engine had been overboosted in such a manner, an engine overhaul was required after the plane landed.



In drag racing circles, the venerable Hemi engines often wear dual magnetos. In such circles, it is often said that magnetos increase spark energy with rpm, while coil-driven distributor ignitions loose spark energy with increasing rpm. Of course, as was mentioned before, in small engines, the magento often includes a lighting coil that supplies auxilary current for lights and such on the vehicle. Usually, the magneto on these engines doesn't provide enough power to supply the electrical system, and lights will dim--the engine may even struggle to idle. Simply increasing the idle rpm will remedy that problem. Distributor-based ignition systems don't usually suffer from that characteristic in land vehicle applications.

Wizzleteets
03-07-2005, 09:39 AM
I believe I can clear up the magneto issue a little. Each cylinder in the engine has two spark plugs. One spark plug fires off the left magneto, the other off of the right. Now, it is true when both mags are working properly, the engine produces more power(because there is double the "spark" in the engine providing a more complete burning of the combustion charge). However, if one mag fails, the engine will continue to run if only at slightly reduced power (or greatly reduced power depending on how much "boost" the engine is running with at the time of failure) due to the fact the each cylinder only has one spark plug firing. Therefore, the reason for two magnetos is simple: more horsepower and redundancy. Piston aircraft engines today operate on this exact same system.

kSetuni
03-07-2005, 10:35 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Wizzleteets:
I believe I can clear up the magneto issue a little. Each cylinder in the engine has two spark plugs. One spark plug fires off the left magneto, the other off of the right. Now, it is true when both mags are working properly, the engine produces more power(because there is double the "spark" in the engine providing a more complete burning of the combustion charge). However, if one mag fails, the engine will continue to run if only at slightly reduced power (or greatly reduced power depending on how much "boost" the engine is running with at the time of failure) due to the fact the each cylinder only has one spark plug firing. Therefore, the reason for two magnetos is simple: more horsepower and redundancy. Piston aircraft engines today operate on this exact same system. <HR></BLOCKQUOTE>

Exactly. Also dont forget that even though an engine may have only one Mag installed, its very likely that its a DUAL Mag, running off the same drive but tottally seperate after that. I have been looking for solid verification on facts since first reading this thread.

However based on memory from when I worked on an R-2800 in A&P school, it had a dual mag installed. Also remember that the main advantage of a magneto over a coil or other type of system is that its self sustaining and requires no outside power source to operate, as long as the drive is spinning.

The safety factor is tremendous with dual mag systems, and even more so when they are on seperate drives so that a drive shaft failure doesnt take out both ignition sources. With each mag powering one plug in each cyloinder you never have to worry about a magneto failing and causing you to loose several cylinders.

I am still looking for the hard evidence, pictures showing 2 plugs in each cylinder of the 2800 adn may have to drive to Wright Patterson AFB museum to look closely at the engines they have on display from this era and show some pictures.

S.M.

SkyChimp
03-07-2005, 06:21 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by ShadowMech73:
I am still looking for the hard evidence, pictures showing 2 plugs in each cylinder of the 2800 adn may have to drive to Wright Patterson AFB museum to look closely at the engines they have on display from this era and show some pictures.

S.M. <HR></BLOCKQUOTE>

You don't need to. I've got Graham White's "R-2800: Pratt & Whitney's Dependable Masterpiece." It has schematics, cutaways and photos of the R-2800's ignition system. I'll try and scan some relevant pages and post them.

The R-2800 indeed had a "daul" magneto. "Dual" in that it fed current to two seperate distributors and both plugs in each cylinder. But it was still one magneto and if it failed, it failed completely and all power was lost.

I'll start scanning.

SkyChimp
03-07-2005, 06:49 PM
Here's info on the R-2800

http://members.cox.net/us.fighters/page1.jpg
http://members.cox.net/us.fighters/page2.jpg
http://members.cox.net/us.fighters/page3.jpg
http://members.cox.net/us.fighters/page4.jpg
http://members.cox.net/us.fighters/page5.jpg
http://members.cox.net/us.fighters/page6.jpg
http://members.cox.net/us.fighters/page7.jpg
http://members.cox.net/us.fighters/page8.jpg

I've got similar stuff on the Allison, V-1710. But I'm not going to scan that. Imagine the same system on the R-2800 applied to a V engine and that would be pretty accurate for the V-1710.

kSetuni
03-07-2005, 09:16 PM
Some good info Skychimp. Good reading.

Dual magentos dont mean one magneto powering 2 distributors. A dual magneto is in fact 2 seperate independant magnetos that are contained in a single case and attach to a single accesory gearbox point. They share a common drive shaft. In other dual magnetos, the distributors are also built into the unit.

From the first page posted " therefore if that one magneto failed, the entire ignition system was shutdown and as a consequence the engine. However it should be pointed out that DRIVE FAILURE of the R-2800's dual magneto was almsot unheard of" I used caps for the improtant part the drive failure. This is obviously what the previous line was referring to if the mageneto failed it killed the engine. If one side of the dual mag failed internally (not a drive shaft failure) the other side would continue working and provide an ignition source for the engine. However obviosuly if the drive shaft failed, then neither side of the dual mag would be turning and would therefore provide no tension (power) source for the distributors to take to the spark plugs.

Further evidence and clarification of this is provided in the second picture posted. You will notice in the Bosch cutaway that it shows a coil on one side then the coil cover on the other. Obviosuly there is another coil under the opposite side cover, jsut as there would be a cover over the shown coil. If you look at the internal components you can almsot clearly see the components from both mags and how they are driven by the common shaft. This shows the 2 separate magentos and how they are installed in a common case connected to the common shaft. If you held a single mag in your hand and then compared the internal components to one side of a dual mag, you would have the same components. Also you will notice that there is no reason for 2 coils, in the picture except for each one to be used for one side. (by side I am referrring to each seperate magneto within the common case)

Very interesting and I would love to have books like you have for their historical sence. When I went to the Wright Patt AFB museum in Dayton Ohio with 2 other experienced A&P freinds of mine recently. We were most shocked and interested in the cutaway engines they had, (liek the Jumo engine for the ME 262 and the rocket engine for the Komet in addition to the radials) and compared them to what we currently work on, and had studied in and worked on in school. It was like walking through time to see engines, that for their day were cutting edge, and to see how the problems they had encountered were solved and became standard parts for more modern engines. It was simply amazing.

SkyChimp
03-08-2005, 06:56 PM
Good stuff, Shadow, thanks. That same book has some pictures and cut-a-ways of the GE combo mag/distributor. If I get time, I'll scan then and post them, too.

Someone here on this board was a airplane mechanic in Alaska and took some extremely good. color, high quality photos, at my request, of some R-2800 magnetos in various states of repair. I'll see if I still have those. Wish I could remember who that was http://forums.ubi.com/images/smilies/blink.gif

Targ
03-08-2005, 10:13 PM
That was me http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif
MAG PICTURES (http://simjunkie.com/mag.html)
The idea of an R-2800 having one mag is hard to believe. It is a duel mag config in a single housing.
Kind of a trick question, both answers would be correct but the single mag reference would be the more correct answer http://forums.ubi.com/images/smilies/53.gif
So, even though it operates with a left and right it is still only a single unit, lol.
The reason for the single mag design is that the seperate mag design was not efficient enough and failed to create the needed spark for the plugs, causing massive fouling and improper engine efficency at medium and higher altitudes. In regards to how many spark plugs each cylinder has, 36 per engine or two per cylinder.

JR_Greenhorn
03-08-2005, 10:49 PM
Almost off-topic, but is there anything in the air that can match the Hughes H-4 Hercules for spark plug count? Wasp Majors have two plugs per cylinder also, don't they?

Targ
03-08-2005, 11:11 PM
I dunno, maybe the Connie?

JR_Greenhorn
03-08-2005, 11:18 PM
H-4 had eight R-4360s. (You've got to like a guy who always uses the biggest dam engines he can get his hands on.)

Was it four R-3350s the Connie had?
What do the Wrights have for ignition?

Targ
03-08-2005, 11:51 PM
I looked in the spitfire maintenence manual and the merlin (45M, 50M, and 55M) had two magnetos.
Early models of the Merlin had a starting magneto switch but later models did not provide one, instead they used a booster coil switch wich had to be pushed in while cranking the engine and was released once started.
The first pdf image is pilots notes and the second is from section 6: Electrical and radio Installations-Maintenance.
PILOT'S NOTES (http://simjunkie.com/images/IMG.pdf)
ELECTRICAL (http://simjunkie.com/images/IMG1.pdf)
Notice section III. and V. of the pilots notes.

kSetuni
03-09-2005, 07:49 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Targ:
That was me http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif
http://simjunkie.com/mag.html
The idea of an R-2800 having one mag is hard to believe. It is a duel mag config in a single housing.
Kind of a trick question, both answers would be correct but the single mag reference would be the more correct answer http://forums.ubi.com/images/smilies/53.gif
So, even though it operates with a left and right it is still only a single unit, lol.
The reason for the single mag design is that the seperate mag design was not efficient enough and failed to create the needed spark for the plugs, causing massive fouling and improper engine efficency at medium and higher altitudes. In regards to how many spark plugs each cylinder has, 36 per engine or two per cylinder. <HR></BLOCKQUOTE>

Actually if you are talking aircraft engines, with anyone that knows about engines and their components, the Dual magneto reference is the most and only correct reference. If you talk about a dual magneto to anyone that works on them, they will know exactly what you are talking about. If you talk about a 2 magneto installation the same is also true. A single magneto is just that, a single magento with no other magneto to select. The Dual magento still retains the ability to choose one side or the other.

On what do you base your statement that they used a Dual (using correct terminology not the single mag as you referenced) mag setup because the single mag design was not as efficient to create the needed spark? I have never heard of this being the case. A dual magento is not more or less powerful when compared to a single magento with the same specifications. Keep in mind the only thing that makes a dual mag different is that both seperate magnetos are housed in the same case. They dont work togther to create additional power. They are independant and you could cut the case in half, except for the common drive shaft and have 2 seperate fully functioning magnetos.

Often times dual magnetos are used instead of 2 seperate installations because the engine manufacturer only has one acessory pad to mount the magneto on instead of 2. It could be space requirements, or other considerations such as that that dictate a dual magneto installation instead of the two magento installation. Having a dual magneto available as an option aids in the overall engine design.

The reasons for 2 spark plugs increasing efficiency is completly correct. If redundancy was not a consideration, then designers could have used a higher capacity magneto and had all plugs operated by that magneto. Instead there is always 2 power sources available for the spark plugs. Whether its a 2 magneto installion, or if its accomplished by a Dual Magneto.

S.M.

Targ
03-09-2005, 08:53 PM
You did see the pictures correct? Than you must have noticed that the R-2800 magneto has four coils. As to why the design? Skychimp has all ready posted the reason why and I have expanded on it.
If you are ever in Alaska look me up and I will give you the tour of the hanger and engine shops.
PS: A R-2800 has one magneto, sorry.

Targ
03-09-2005, 09:01 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by JR_Greenhorn:
Almost off-topic, but is there anything in the air that can match the Hughes H-4 Hercules for spark plug count? Wasp Majors have two plugs per cylinder also, don't they? <HR></BLOCKQUOTE>
I found an engine with more plugs than the ones on the spruce goose. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif
Lycoming made a prototype engine called (I think) the XR7550 that was a four row engine, but had 36 cylinders per engine and 72 plugs per engine. The engine had something like 4400 horse power or about 1/2 horsepower per sqauare inch http://forums.ubi.com/groupee_common/emoticons/icon_eek.gif

kSetuni
03-09-2005, 11:21 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Targ:
PS: A R-2800 has one magneto, sorry. <HR></BLOCKQUOTE>

Yes I know the R-2800 has one mag. Its a Dual magneto installation. Reread through the previous portions of this thread and you will understand the difference as its been clearly explained. I spent some time working on one including timing the mag. If you look at the engine manual that sky chimp provided, it even verifies this my clearly calling it a Dual mag.

S.M.

JR_Greenhorn
03-09-2005, 11:38 PM
http://www.aviation-history.com/engines/xr-7755.jpg
http://www.people.virginia.edu/~rjr/engines/redpaul.JPG I was just digging for information on that one last week, and I didn't even think about it now.

It's an interesting engine by default, owing to it's record-breaking size.

On one site, they say:
"There were nine overhead camshafts which could be shifted axially for METO power in one position and cruise at the other."

What does METO stand for? I don't care for FLA's or even TLA's.



What a nightmare it would have been to design an installation for this engine. Five feet in diameter and ten feet long makes it quite ungainly. It looks to be liquid-cooled, so you'd have the engines massive frontal area as well as the radiator to deal with.

http://www.people.virginia.edu/~rjr/engines/

Bluedog72
03-10-2005, 09:12 AM
This is just a flat out guess, but would METO be Military/Emergency/Take Off ?

Interesting thread guys.

PE_Mosor
03-10-2005, 02:45 PM
METO = Maximum Except Take Off


Actually Corsair didn't had any exhaust drive supercharger, exhaust gases were simply dumped overboard. For engine charging it used two-stage, two-speed engine driven supercharger with intercooler (actually two) between stages.
Then why we have three positions for supercharger in game?
Because of way it worked. First stage (or main stage) was driven, via a set of gears, at fixed ratio to crankshaft speed, and it always worked, provided engine was running. On other hand second stage (or auxiliary stage) was also engine driven but thru small transmission box with two speeds and neutral. For low altitudes only main stage was used, and auxiliary was in neutral (in game position 1). For intermediate altitudes auxiliray stage was in low gear (position 2 in game), and for high altitudes it was in high gear (position 3 in game). Similar system was used by Wildcat and Hellcat.

SkyChimp
03-10-2005, 07:20 PM
Targ!! Thanks for those.

My understanding is that the "dual" magneto was called a "dual" because it powered a dual ignition system (ie. two distributors and two plugs per cylinger).

What's your take on that?

BTW, a few models of R-2800 DID have two seperate magnetos. GE made a magneto/distributor comb loosely called a "turtle back" (due to its shape). They sat where the distributors normally sit, except that there was no seperate magneto between then. I've got some pcitures of them and I'll try and scan them.

ZG77_Lignite
03-10-2005, 10:20 PM
Mosar, thanks for that. I haven't actually seen that explained so clearly before. Much appreciated.

P.S. Interesting thread fellas, almost like the old days.

kSetuni
03-17-2005, 08:05 PM
We were having a quiet night at work, so I decided to go through my toolbox and I found an Aircraft Technical Dictionary, published by the Federal Aviation Administration. I decided just for grins to see if they had a dual magneto listed and here is the result:

"Dual Magneto: Actually a single magneto housing which holds one rotating permanent magnet and one cam, with two sets of breaker points, two condensers, two coils, and two distributors. Sometimes aditional sets of components are installed, but always in pairs. For all practical purposes, this constitutes two ignition systems."

Kind of interesting to read what the U.S. authority over aviation defines the dual magneto.

S.M.

Targ
03-17-2005, 08:48 PM
R2800 magneto has 4 coils. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

SkyChimp
03-17-2005, 09:12 PM
Thanks for that Shadow. That's a pretty clear description of a dual magneto. It should be noted, however, that the majority of WWII R2800s had a double type magneto and two seperate distributors.

Targ, wouldn't it depend on the type of magneto? The 2 major types used on R-2800s during WWII were the Bendix-Scintilla and the Bosch. I don't have a cut-away of the Bendix, but I do the Bosch and it has just 2 coils, one on either side. Maybe the more common Bendix has 4?

The other major ignition system used, although not as extensivley used as the Bendix or the Bosch magnetos, was the use of 2 GE combination magneto/distibutors.