Magneto vs TL

[JohnS]

I'm trying to decide between a mag and points type ignition. One thing I wanted to know whether anyone knows of the weight difference between the two. And while we're at it votes for either being more or less reliable than the other.

[leshoman]

I have one of each. The deciding factor is charging the battery, is power readily available at hanger and how much long cross country flying you plan. Battery weight makes conventional ignition sysyem heavier. My conventional ign starts easier than mag system.  I have a 7ah battery and can get about 3 hours flying before recharge

[Dan_]

I'm trying to decide between a mag and points type ignition. One thing I wanted to know whether anyone knows of the weight difference between the two. And while we're at it votes for either being more or less reliable than the other.

The 009 ignition weighs 3.3 lbs.  I weighed it for Steve back in  2001, when he was installing the Leburg electronic ignition which weighs 2.5 lbs.

Both the 009 and mag have points, but the mag is more complicated and the condenser is extremely expensive and hard to find.

The 009 is easy to check and maintain and likely by far the cheapest.

The 009 can be converted to breakerless electronic triggering.

The 009 must have a means to absolutely clamp it down...  The stock VW clamp is apparently not really good enough for aircraft use.


Some one else will have to chime in on what the mags weigh...

[JohnS]

Does one run any better than the other. I know Les Homan has said that the mag starts a little harder. One thing in favor of the conventional is that batteries are getting lighter and light

[leshoman]

I do not notice any differance in operation once started

[Dan_]

I do not notice any differance in operation once started

Les,

Does your mag have an impulse coupler?  

Mags call for a tight plug gap and are known for weaker spark, that is why there are usually 2 mags and 2 plugs per cylinder.  (and tight plug gap)

I had a plane with an O-200 and both mags had impulse.  I made sure they were both dead-nuts timed with each other.

After the first start of the day it would start just barely moving the prop.  

Especially if you killed it with the key, (instead of pulling the mixture to LCO) which I liked to do to often to test the ground wire to the mags.  

It dint have a starter.

[leshoman]

Mag does have impulse drive

[JohnS]

As far as hand propping do I understand correctly.

The impulse coupling heavily retards the spark at low ,hand propping speed, rpm to prevent kick and then drops out and the timing you set takes over.

The 009 ignition is set at TDC or just barely retarded past TDC and then the advance adjusts to somewhere around 20 degrees advanced at full throttle. But the static timing just not be advanced or you run a real risk of a bite when propping.

[s johnson]

I also have flown with both the standard 009 dist. and slick 2220 mag. The 009 and battery combo worked very well for me. My concern was not knowing if the battery would take a memory . Meaning if I flew for 20 minutes for several flying sessions and charged between each flight  followed by other flgts over an hour or so. I did have a volt meter and never had any issues. Just concerned. It was very easy to start. I did have one time of having moisture in the points after a long rain event but was easy to dry out.
The slick mag is what I have now and have had no issues and am very happy with it. I like the fact that it is self contained and not worried about the battery charge. 

Both work well. You will need to adapt the crank for the mag drive though while the dist. is standard for the vw. and cheaper but also needs very little modification.

Scott J.
Slug Musher

[Will Weidner]

I think this is a good time to ask a question that's been bugging me.  The 2220 impulse coupling give 15 degrees of advance.  The -009 centrifugal advance is 28 degrees.  28 degrees is recommended for the VW.  If you use the 2220, are you giving up 13 degrees of advance?  If so, is there a power reduction?  Has anyone who's using the 2220 done the mod described by Weasel (search "weasel" in this forum for a comprehensive description of the modification)?

[Dan_]

As far as hand propping do I understand correctly.

The impulse coupling heavily retards the spark at low ,hand propping speed, rpm to prevent kick and then drops out and the timing you set takes over.

The 009 ignition is set at TDC or just barely retarded past TDC and then the advance adjusts to somewhere around 20 degrees advanced at full throttle. But the static timing just not be advanced or you run a real risk of a bite when propping.

...from the www.

Impulse Coupling
The impulse coupling is an extraordinarily clever mechanical solution to the starting problem. It's a mechanism that's contained within a hub that attaches to the magneto's drive shaft and is driven in turn by the engine. Here's how it works.
When the starter cranks the engine, a spring-loaded flyweight in the magneto drive hub catches on a stationary stop pin mounted on the magneto case. This stops the magneto shaft from turning further. As the engine continues to turn, an impulse spring in the hub is wound up for 25° to 35° of engine rotation (the "lag angle") until a drive lug on the coupling body trips the flyweight, disengaging it from the stop pin. At this point, the wound-up impulse spring "snaps" the magneto through its firing position at a speed much faster than cranking speed.
This has precisely the two effects desired: the ignition timing is retarded (by lag angle of the coupling), and the magneto rotor is turned fast enough to generate a decent spark. Neat trick, eh?
Once the engine starts, centrifugal force causes the spring-loaded flyweights in the impulse coupling to retract so that they no longer catch on the stop pin. When this happens, the engine drives the magneto directly and timing returns to its normal setting of 20° BTDC or whatever.
It's easy to tell whether or not your engine uses impulse couplings. If you hear a loud "snap" when you pull the prop through by hand, and if you hear "snap snap snap" just before your engine stops at shutdown, then you have impulse couplings.
Some installations provide an impulse coupling on both magnetos. Others use an impulse coupling on only one mag, and employ an ignition switch that grounds out the P-lead of the non-impulse mag during the start.
Because impulse couplings have moving parts, they need to be disassembled and inspected carefully during each 500-hour magneto maintenance cycle. In addition, there have been a lot of Airworthiness Directives against impulse couplings in recent years — both Bendix and Slick — and these have to be taken very seriously. An impulse coupling failure in-flight can result in total engine failure, and some failure modes can cause parts of the impulse coupling to drop into the engine gearbox, causing catastrophic destruction of the engine. So be sure your impulse couplings are not worn excessively and that all applicable ADs are complied with.

[Dan_]

I think this is a good time to ask a question that's been bugging me.  The 2220 impulse coupling give 15 degrees of advance.  The -009 centrifugal advance is 28 degrees.  28 degrees is recommended for the VW.  If you use the 2220, are you giving up 13 degrees of advance?  If so, is there a power reduction?  Has anyone who's using the 2220 done the mod described by Weasel (search "weasel" in this forum for a comprehensive description of the modification)?

Here is the above referenced msg from Weasel... http://www.eaglersnest.com/forum/index.php/topic,61.msg156.html#msg156

[MrG]

Here is my 2 cents 
I also have used both 
Mag = we do know the mag i have was off a power unit in Vietnam in 1964 (brand new - never used)  At first it worked well but condensor had dried out and magnets did need re zaping and was very erratic, so we gave up on it  and went electronic

Dissy - http://www.simonbbc.com/distributors/4cyl-standard-electronic/bosch-powerspark-electronic-distributor-vw-camper
I bought one of these which we flown the DE on and happy with it - it does have mechanical advance 
( 30deg ) which we cut back to 15 - set timing at 28deg max advance @3000rpm  works a treat - starts well 
and just about to order one of these http://www.ntin.net/jhardy/GenniPod.html
The Cub i fly also has a certified version of one of the Wind genies and never had to charge a battery 

If the Mag did work i may of stuck it out with it - after flying the Cub the Genni pod and dissy was a no brainier 
turn key no battery charger

[weasel]

I think this is a good time to ask a question that's been bugging me.  The 2220 impulse coupling give 15 degrees of advance.  The -009 centrifugal advance is 28 degrees.  28 degrees is recommended for the VW.  If you use the 2220, are you giving up 13 degrees of advance?  If so, is there a power reduction?  Has anyone who's using the 2220 done the mod described by Weasel (search "weasel" in this forum for a comprehensive description of the modification)?

Will,

The Impulse coupling does NOT give you advance. It only retards the timing for starting.  

Most people including some of the VW conversion manufactures set the timing to ~28 degrees and then let the impulse coupling retard the timing to ~13 degrees BTDC for starting. This is why they recommend "grab the blade with both hands and deliberately swing the prop as hard as you can".  

If you modify the magneto or buy the correct lag angle impulse couple, the timing will be at TDC for starting and with the fuel/air mixture right, it will crank with your finger pushing it past tdc.

[Aerodude45]

Probably just reiterating...

During starting the impulse coupler is engaged. When the impulse coupler is engaged, it causes the spark to ignite AFTER when it otherwise would have by whatever the lag angle for the specific magneto is. So, if you have a magneto with 15 degrees of lag and you time it, by simply pulling the prop by hand, to fire at TDC, then the advance angle with the engine running will be 15 degrees.

When the engine is running, you want the spark to occur early because it takes time for ignition to occur, and the engine is rotating quickly enough that peak pressure would be reached much later than TDC. When you're starting the engine, you want the spark to occur right at TDC. If it's timed earlier, when the piston is still moving through the compression cycle, the piston may be forced BACKWARDS, causing the finger-smashing "kickback".

The consensus for the 1/2 vw is that 26-28 degrees BTDC is the best advance angle for the running engine.  A different advance angle would alter performance. Different RPMs require different advance angles for optimum efficiency, but impulse couplers allow for 1 angle. Generally, that angle is optimized for cruise power. So if you time your mag to give you an advance angle of less than 26 degrees BTDC, the engine will be more efficient at LOWER RPMs and vice versa.

In order to achieve 26-28 degrees with a magneto that has 15 degrees of lag you would have to set it to spark at 11-13 degrees BTDC when pulling the prop through by hand. That's awfully early, and will tend to force the engine backwards, pushing the prop into your fingers.

The posted mentioned above includes good instructions on how to modify a magneto for the desired lag angle. Just be sure to MEASURE the EXISTING lag angle BEFORE grinding anything. The magneto I got from Casler was already set to 26 degrees of lag, but was still placarded for 15 degrees.

To measure advance angle, simply mark where the mag drive sits before being rotated. Then rotate the mag through and mark where it "snaps". Measure the angle between the two with your protractor.