I contacted Michael Kobylik at Electroair hoping to gain some insight into ignition timing curves, some history and how they went about certifying their electonic ignition system.
He's not a big forum guy so he gave me the ok to post his response. I'd like to thank him for taking the time both on the phone and providing his response in writing that I have copied below.
Walt-
Thank you for your email. Per our conversation from yesterday, I was finally able to work my way through the pages of posts on the link you shared with me. You had asked me to comment on the discussion, and in particular, whatever information I would be willing to share about our system, development, and how it compares or helps efficiency, etc. So here goes...
Some general comments about the thread on the Van's Air Force site:
1. I agree with "Rocket Bob's" comment on 12/29 about how timing should not be advanced at full power settings. Let's keep that comment in context of aircraft engines in general. Remember, from our perspective, we are supporting a very wide range of engines and flying parameters (more on this in a minute). That dictates to us that ignition timing adjustments should be conservative. There will always be exceptions to the rule, but those exceptions (advancing timing at full power settings for instance) should be made with the kind of knowledge that is gained from data collection (like what you might learn with dyno testing) and with a good understanding of the flight envelope that you want to operate within.
2. Post #105: The advance curve data posted for an Electroair system appears to be from our first generation system, which utilized an RPM curve. That data is no longer accurate for our current generation systems. We no longer use an RPM curve because we found them to not be useful in typical aircraft applications. RPM curves are great tools when you are rapidly accelerating or decelerating engines (like in race applications). But they do not have a real useful application in typical aircraft applications. Load on an aircraft engine is really only varying because of intake manifold pressures.
On a related comment, there also seems to be a theme in this discussion about ignition manufacturer's keeping their advance curves proprietary and secret. Our curve has never been secret, at least as far as I am aware. It is published in our installation manual. I have to admit that I thought it was in a little more obvious place on our website, but it is not (we will correct that in the near future). Here is the link for our installation manual for our certified system:
http://www.electroair.net/pdfs/EIS_41000_Installation_Manual.pdf (the experimental manual did not have this section included - I'll get that updated too). If you go to the beginning, pp 1.1 -1.2, you will find a discussion of electronic ignition systems and our advance curve charted out. Simply put, we advance spark timing two degrees for every inch of manifold pressure below 24" (more on that later too).
3. Post #128: This post caught my eye because it is part of the discussion of a one size fits all ignition system. This post highlights one of the biggest hurdles we have when thinking about ignition systems. In order to make a sensible business case for aircraft ignition systems (magnetos or EI), you have to try and design a system that will cover a very wide range of engine applications. If we didn't, the permutations of ignition systems would almost be endless. Ideally, you would have an ignition system that optimizes itself to a specific engine configuration. This is reasonably easy to do in the automotive world, because you have the numbers. Also easy to imagine that this can be done in the racing world because you are dealing with a vehicle that operates in a narrow envelope, so tuning can be done in the field. In the GA world this is not so easy because the numbers don't exist to make it practical and the operational envelopes are relatively big. So, what you end up with is a compromise. Our system, and timing curve, is not perfect, but it significantly enhances the performance of a wide range of typical aircraft engines. Hence, a system that is nearly a "one size fits all" ignition with big performance improvements.
4. Post #150: This post commented on our system in that we ignore MAP and only look at RPM. Our system only adjusts timing based on MAP. Our original system also had a RPM curve built in (for lower RPMs), but we no longer use a RPM curve. Again, the data that was posted appears to be from a Generation 1 system.
Walt - You had asked me in one of our conversations if I would be willing to share how we arrived at the RPM curve we did. The short answer is sure! We did through Flight Test. Early on, Jeff Rose, the original owner of Electroair, performed a series of flight tests and collected data. Jeff had a created a manual ignition advance control, and for a range of altitudes and flight conditions, determined what an optimal range of ignition timing should be by measuring power drop off. The aircraft was trimmed/leaned for best performance. Plotting out this data lead to a natural curve. Additionally, some factors of safety were added, including the start point for advancing the ignition timing was set to 24" of MAP.
The curve that Jeff developed is a conservative advance curve. Lots of debate could happen about whether or not the curve we choose is the best one, optimal and all of that. I am not going to enter into that debate. There are always engineering compromises when making a system that is not only effective in obtaining performance gains for a wide range of engines, but also safe to use and won't cause any undue stress on the engine. Our curve that Jeff originally developed has been used by Electroair throughout our history. I would point to our track record of the number of systems we have sold and our reliability as a measure that the choices we have made are the correct ones. On a side note, I found out a few years ago that the advance curve that we use is very nearly the same curve that was used by Unison in the '90s for the development of the LASAR system - the magneto system with electronically controlled timing.
It is worth noting that the developments Electroair has made, especially in the experimental world, led directly us to earning a Design Approval and STC from the FAA for our ignition systems. In fact, we just received an STC for our ignition system on 470 and 520 Continental engines. I noted within the Van's thread a comment that someone might be able to "dazzle" the FAA in order to get an STC. We don't have enough time here to dive into that one, but suffice it to say that comment falls short of understanding how the FAA approval process works and what is required to obtain a Design Approval. We have accumulated mountains of data showing and proving that our systems are not only effective, safe and reliable, but can address a big weakness in aircraft power-plants over a wide range of applications.
I hoped I answered at least some of your questions. I'm sure more questions will come up. Please feel free to fire them off to me. Also, feel free to distribute this email as you see appropriate. While our business is clearly changing with earning STCs and expanding into the certified marketplace, we remained committed to supporting our customers that build and operate experimental aircraft. Without those customers, we would have never been able to move our product into the certified world.
Best Regards,
Michael Kobylik
Electroair
517-552-9390
[email protected]