Which Lightspeed?

[Rick6a]

Guys,

Make this easy on me. I am out of my depth in such matters and dazzling me with arcane trivia will only serve to confuse. I've seen this type of question go way off on a tangent with wordy responses that lose me after the second paragraph.

As background, I am a recreational VFR pilot and cross country accounts for roughly 20% of my flying. I posed this question to Van's support several days ago and have yet to receive a response.

Item: I am going to install a Van's ordered XIO-360MIB and want to install a Lightspeed ignition system to replace one magneto. Van's offers two Lightspeed options, the Plasma II and the Plasma III and the price differential is around $275. Is the extra cost of the Plasma III really worth the premium or would I be perfectly happy ordering the Plasma II and save some serious money in the bargain?

[Ron Lee]

I chose the III because of the improved spark IIRC. If in doubt, call them and talk to Klaus.

[db1yg]

Rick,

I also chose the PIII unit for my 9a. The PIII unit has a longer duration spark than the PII and LS says this contributes to better fuel efficiency or higher hp.


Cheers,

db

[n2prise]

I have the Plasma III with the front-mounted direct crank sensor. The timing will ALWAYS be correct. The direct crank sensor, the ring gear comes with two magnets permanently installed in it at the precise timing location needed.

And yes, the fuel economy is better. I cruise up high with an ECI 160 HP O-320-D1A equivalent engine. I get 160 MPH true air speed with a Hartzell CS prop at 12,000~13,000 feet, burning around 5.5 to 6 gallons per hour of 100LL fuel.

Jerry K. Thorne
East Ridge, TN
RV-9A, N2PZ

[RV7Factory]

I spoke to Klaus and crew at OSH about this very issue, and he said exactly what you've already been told above, but added that the spark advance is different between the two.

This came from the FAQs on Lightspeed's web site.

What is the difference between the Plasma II Plus and the Plasma III system?

• All Plasma systems are high energy Capacitor Discharge type systems. They are more accurate due to their faster voltage rise time and provide a hotter spark from a smaller and lighter coil when compared to the typical inductive type ignition system.
  
  The Plasma II series is a single spark system which has a fixed spark duration at all rpm.
  
  The Plasma III has a dual output stage which provides a continuous spark for about 20 degrees of crankshaft rotation at all rpm. Extensive flight testing with cockpit variable spark duration showed maximum performance gain with an un-interrupted 20 degree spark.

BTW... I'm fairly certain I am going to go with the III. Good luck!

[Captain Avgas]

OK Rick, I'll give you the plain vanilla facts and you can read the following thread as well which has lots of info. http://www.vansairforce.com/communit...ad.php?t=16721

1. In THEORY the Plasma III SHOULD give slightly better engine performance than the Plasma II, particularly when running Lean of Peak when a longer duration spark would be beneficial to ignite the more stubborn mixture.

2. In REALITY no-one has been able to discern a quantifiable difference in favour of the Plasma III under real flight conditions. Walt Aronow is the only person I know who has the LS Plasma II on one side and the LS Plasma III on the other side. In the above thread he reports that with Iridium fine wire plugs all around he finds he gets smoother engine running on the Plasma II than the Plasma III when he switches backwards and forwards between the two systems in flight (and that's a pretty definitive and practical test).

3. The downside of the Plasma III (apart from price) is that the longer duration spark erodes the plugs faster and stresses the high tension wires and coils more. Thus reliability is reduced. Very few purchasers of the Plasma III understand that.

4. The crank sensor has less failures than the Hall Effect sensor, but is a bit more trouble to instal.


So the bottom line is this. No-one who has been able to compare both systems directly has been able to report any performance improvement with the LS Plasma III (in fact the opposite has been true). And the Plasma III is DEFINITELY not as reliable as the Plasma II.

If you prize engine reliability above all, then the Plasma II would be the choice. It has been around for a long time and is a very mature product with an excellent history. The panel is still out on the Plasma III.

In the meanwhile builders continue to buy the Plasma III model due to what might be called the 'Spinal Tap' theory ie. a bigger number must be better. You might remember in Spinal Tap that the guy was raving on about his amp being the best because the volume knob went up to eleven.

[RV7Factory]

Great info Bob, thanks!!!

[Rick6a]

You might remember in Spinal Tap that the guy was raving on about his amp being the best because the volume knob went up to eleven.

Thanks guys for all the insights. My DNA tend towards the Spinal Tap theory when making purchases. I've learned the hard way that sometimes less is more. Bob....your explanation was particularily concise, easily understandable and compelling. Thanks to all for helping me make a decision.

[Captain Avgas]

Originally Posted by Rick6a

Thanks to all for helping me make a decision.

Glad to be of help Rick. I spoke face to face with both Klaus Savier of LightSpeed and Bart Lalonde of Aerosport and had in-depth discussions with both of them on this very subject before I ordered my engine with the Plasma II on one side and an impulse coupled mag on the other.

It's the Experimental category but I am reluctant to be too "experimental" when it comes to FWF matters. I fly IFR (occasionally at night) so I view the engine as a life support system. For that reason I won't opt for anything FWF that don't have a proven track record over MANY years. That was the reason I also crossed the EMAG off my list. I love all the latest and greatest gadgets coming onto the market...but when it comes to FWF I am not inclined to be a beta tester.

Cheers Bob

[the_other_dougreeves]

Originally Posted by Captain Avgas

Glad to be of help Rick. I spoke face to face with both Klaus Savier of LightSpeed and Bart Lalonde of Aerosport and had in-depth discussions with both of them on this very subject before I ordered my engine with the Plasma II on one side and an impulse coupled mag on the other.

It's the Experimental category but I am reluctant to be too "experimental" when it comes to FWF matters. I fly IFR (occasionally at night) so I view the engine as a life support system. For that reason I won't opt for anything FWF that don't have a proven track record over MANY years. That was the reason I also crossed the EMAG off my list. I love all the latest and greatest gadgets coming onto the market...but when it comes to FWF I am not inclined to be a beta tester.

Cheers Bob

Interesting. I look at LSE (or EI in general) as a way of providing dissimilar redundancy for the engine. We all know that mags normally sit there and work just fine, but when they fail, it's sometimes without warning. Mags and EI have different methods of failure, different MTBF, etc. I like dissimilar reliability and, for that reason, really don't want two EI of the same type.

Most of the LSE failures that I have heard of are from the Hall Effect sensor failing. Going with the crank sensor seems like a PITA, but if it's more reliable, then I'll take it.

I think EI has a pretty good track record in general (use mine every day to drive to work), and the LSE systems' failure modes are pretty well understood. EMAG/PMAG are well conceived systems, but have had some teething problems with their software. I like LSE because of the lack of software / hard-coded spark advance map. Perhaps not as flexible as LSE, but it seems to be more reliable at the moment. However, it does not have the level of redundancy that a PMAG has.

TODR