Modern Engines & Ignition Systems

[rizzz]

I have a Bendix D2000 dual magneto directly driven from the crankshaft on the back of my VW:



They don’t make these dual mags anymore though, you can only buy them refubished now, so if I were to build one now from scratch I’d probably put a single mag on the back and probably would not bother with a secondary. The new mags are very reliable and secondary igition on a VW is always a bit of fiddling, unless you put it on the distributor which means you’d have to make blisters in the cowl in case of a Sonex.

[lutorm]

And yes, I remove my cowls after EVERY flight in prep for the next preflight.

I guess your plane isn't parked outside...

[daleandee]

The point is simply that everything has a failure mode. Nothing is perfect. There are tradeoffs for everything. Just because something can fail does not automatically make it a liability. For anything mechanical, having a backup is the wisest choice of all.

This is very true! The point I was after is that if it can be improved, then it must be. To illustrate: many moons ago I was training a student in a Challenger with a 503 Rotax. Those engines, especially the ignition systems, are not known for failure ... at least not both at once. Yet it happened to me and my student. It seems that the glue Rotax was using on the stator coils to hold the small end plates on would sometimes fail over time with exposure to heat. One of the coil plates came loose, got caught in the flywheel and came around like a knife blade and took out all the wiring for both ignitions. Was a dead stick slip into a muddy field landing. Researching this event I only found one other case of it happening. Is that acceptable? Perhaps the reason the issue wasn't more wide spread was that after the first failure Rotax stepped up and addressed the problem by changing the glue and manufacturing process.

If one wants a dual ignition, the Aerovee magnetrons seem quite good as the stupid-simple, self-contained, system.

They are a great idea but they do fail. I've seen it happen. The other concern is that we see builder's using splicers to put better plug leads on them in an effort to quiet the noise. After all they are designed for mowers and can be a bit noisy in the electrical system. Adding splicers is not something I would do as it still leaves part of the old wire, adds two more failure points to each HT lead for a total of eight, combines wires of different core & resistance, and has more places where moisture and dirt can enter.

It would be quite easy to replace the fixed-time secondary ignition with an aftermarket electronic ignition system. The only hardware needed would be to replace the trigger magnet with a toothed trigger wheel since you can keep the existing coils.

The toothed trigger of even a lobed cam lode is a good idea. Many auto distributors use such a set up.

On the other hand, a Sonex isn't really a traveling machine, so I'm not sure it's worth the complexity.

I know a couple of folks that use the Sonex for traveling. Not so much for commuting but there have been a lot of miles put under Sonex wings! To me it wouldn't matter whether I'm a mile or a thousand miles from a landing strip ... I want as much reliability as I can get.

I have a Bendix D2000 dual magneto directly driven from the crankshaft on the back of my VW:

This discussion wasn't aimed at the Aerovee but at other ignitions and options as described here.

Primarily I was curious as to the thoughts of others as to whether they would fly behind a single plug ignition system and if so, what would it look like. We have a vast number of different engines being used from the AeroVee, Revmaster, Hummel, Corvair, Viking, Jabiru, etc and these all have different ignition systems and some are very different.

If you were designing a modern ignition system for your engine what might be the approach you would use? Would you use coil on plug technology? An approach like Electroair or SDS systems? Or are you of the old magneto tried and true approach?

Again this is not about making the current offerings from any company look inadequate but rather trying to see what builders would like to see coming along in the near future.

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
166.7 hours / Status - Flying
Member # 109 - Florida Sonex Association
https://www.youtube.com/watch?v=1VP7UYEqQ-g

[SNX1508]

I would say that my experience contradicts that. When I lost the trigger magnet the engine would not start. The engine turned over good and fast, battery was fully charged but it would not fire. Maybe the earlier aerovees had a different starter?

Well Keith, your sample size is one. Yes, maybe your engine won't start on the magnetrons alone. But that does not mean that ALL AeroVee engines won't start on magnetrons alone. Yes, the early AeroVee engines did use a different starter, but I've started them with the current SkyTec starter on magnetrons alone, so it can be done.

I know of 3 Sonex owners with AeroVee engines that had visited my hangar during my aircraft building project. All 3 of their engines lost the magnet for the secondary ignition trigger, and all 3 of them were unable to start the engine using only the primary ignition/mags.

My secondary trigger magnet was not lost but rather it lost its magnetism and still had to be replaced. I could however start the engine using only the primary mags, but I had just taken the charger off of the battery and it was for sure fully charged.

The "sample size" would however be greater than one.

Terry L. Cooper
SNX #1508
Tail Wheel
AeroVee #0736
N296SX
2005 construction hours, and was completed in October 2016
http://www.mykitlog.com/SNX1508
First engine run: https://www.youtube.com/watch?v=K9wP77I ... e=youtu.be
FAA Inspected & Airworthiness Certificate issued 11/4/2016
Sport ASEL endorsement on 8/9/2017
Tailwheel endorsement on 9/7/2017
Sonex #1508 N296SX first flight on 11/29/2017

[n982sx]

Well Keith, your sample size is one

I can add two more to that sample size making it now six.

Mine and another local Sonex builder's trigger magnets let loose and neither of ours would start without the electronic ignition. Mine went almost 400 hours before coming out. My friends lasted a little more than 100 hours. Not starting is usually the only symptom of a missing trigger magnet.

I'm not complaining really, it is an elegantly simple solution for timing. Just pointing out that from the many Aerovee owners I know running 100LL, cold starting with mags only is iffy. It might be easier with mogas and lower compression however.

I like the idea of peening the magnet in place. I have done that before on other things and it works well. I wish I had thought to do it.

[GordonTurner]

An important consideration in comparing the aerovee and Corvair ignitions is that the six cylinder Corvair will run reasonably smoothly and produce good power on five cylinders. Typically four cylinder engines run extremely rough and as a result produce little useable power with one cylinder out.

Therefore having a secondary ignition source but only one set of plugs on the Corvair means risking the loss of a cylinder but hedging against a complete loss of ignition.

On the aerovee, both scenarios need to be addressed.

Gordon

[WaiexN143NM]

Hi all,
If any one is looking for Corvair parts to complete engines, the zenith aircraft website has a classified section, I've seen probably a dozen postings over the last 2 years. Other places would be eBay, or barnstormer's. and of course the main few Corvair guru's and their companies.
Www.zenair.com
WaiexN143NM
Michael

[wlarson861]

I lost a trigger magnet about 260 miles from home after over 400 hours on the engine.

[daleandee]

An important consideration in comparing the aerovee and Corvair ignitions is that the six cylinder Corvair will run reasonably smoothly and produce good power on five cylinders. Typically four cylinder engines run extremely rough and as a result produce little useable power with one cylinder out.

Quite an excellent point! The other part of this is that the Corvair (or Jabiru 3300) gives the Sonex plenty of power that increases performance but also enhances safety. Perhaps that isn't readily apparent but more power (especially on tail draggers) can sometimes get you out of a bad landing scenario and into a go around quickly (yes - I have experience with this). More power can get you high above the ground faster (my instructor taught me, "get as high as you can as quick as you can"). With 120 HP the airplanes will out climb it glide rate. But more to Gordon's point ... the bigger engines not only have more power overall, but because the power comes from more cylinders the loss of a cylinder means less of a loss power-wise. This isn't true if you lose a valve of course because pumping pressure being wrongly distributed can cause greater loss but that's another subject.

With this air frame powered by an 80 HP engine any loss or reduction in power could entail an unscheduled landing in a hurry on inhospitable terrain. Thus the argument that the ignition systems must be as bullet proof as is possible. The recent news of a number of trigger magnets coming loose is not comforting and it's good to see that the company has addressed this concern. Still, I believe that moving to a toothed gear (as mentioned earlier) with a reliable electronic ignition sensor might be considered as it seems to me to be a better approach.

Another concern with the dual plugs in VW heads (as reported here) are that the quality of the heads and the threads for the plugs are sometimes not quite up to aircraft engine standards. Other have noted recently that the recommended spark plugs are being hit by the pistons and it was suggested to grind a relief in the piston tops. I can't help but marvel at such statements as that seems to me to miss the point and not direct the fix at the source of the problem. Other suggested "stacking" more than one washer under the plug but again that doesn't address the main issue.

Some builder's do fly single ignition on VW heads. Certainly that eliminates a lot of concerns but as Gordon pointed out it introduces a pretty good liability if a cylinder is lost. Would I fly a single ignition VW conversion? Yes I would ... but I must insist there are a few caveats that go with that ...

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
166.7 hours / Status - Flying
Member # 109 - Florida Sonex Association
https://www.youtube.com/watch?v=1VP7UYEqQ-g

[lutorm]

Other have noted recently that the recommended spark plugs are being hit by the pistons and it was suggested to grind a relief in the piston tops. I can't help but marvel at such statements as that seems to me to miss the point and not direct the fix at the source of the problem.

To be fair, putting a relief in the piston tops is my solution to the problem given the heads that I have. Of course getting new heads, that supposedly have better quality control, would be a better "fix", but if it comes to buying a new set of heads vs cutting a little dish in the pistons when I'll have them mounted in the mill anyway, I'm going to go for the latter.

I don't think anyone suggested that dishing the pistons was a desirable option to solving the underlying quality problem. It does in any case not have anything to do with whether the engine is modern or what ignition system it has, just with quality control of low-volume fabrication.