MGL vs Corvair ignition issue


In the past few weeks we had been going over an ignition issue with 650 builder and pilot Shayne McDaniels. His aircraft refused to run well on the points ignition.  He changed the points, went over the system, and even mailed it back to me to have it checked out. Just to be sure, he went over all the other systems on the engine to eliminate the possibility that he was looking at a secondary effect. The plane had been unused on the ground while he was doing some work on it and upgrading things in the panel, and the connection is not immediately apparent that the issue was being directly caused by his MGL disrupting the ignition circuit. Shane is a very experienced builder, and he had received the wiring diagram for the tach hook up from an MGL dealer. This wiring was directly responsable for the erratic ignition. When the connection was removed, the plane instantly ran perfectly. It had been a long goose chase.

Our conversion manual suggests never hooking the tach signal to the ignition. This is for good reason. If you are one of the people choosing to use MGL products, the correct solution is to use a sending unit to count bolts in the flywheel. Dan Weseman as a few sending units for this in his hangar. I am told that MGL even has a sending unit that would perform the same task. Either way, just because a company makes avionics doesn’t mean they understand ignition systems. You might think that they would be very reluctant to suggest a connection that was not tested, but it isn’t the case. I am not singling out MGL. Other companies have also made suggestions for tack signals that proved erroneous. As a builder, the best thing for you to do is choose a system that doesn’t connect to the ignition, (like the Stuart Warner tachs) or only use a system that has been proven over 100s of hours to work with the Corvairs ignition. Grand Rapids, MGL and Dynon are all successfully flying with Corvairs, but none of these are using the tach wiring that the manufacturers first recommended.

The above photo is Shane and Phyllis McDaniels’ 650 at Oshkosh 2011. The fantastic finish work was admired by legions of builders all week. This aircraft was the first amateur built Zenith 650 to be registered with the FAA. When a new model of aircraft comes out and the first one flying is Corvair powered, it speaks a lot about the popularity of the powerplant. This is the aircraft in which the MGL unit was interrupting the ignition.

In our booth at Oshkosh 2011, I stand with three pilots who flew in their Corvair powered Zeniths. From left to right, Shayne McDaniels who flew in a 2,700cc CH 650 from Missouri, Woody Harris in a 2,850cc CH 601B from California, and Andy Elliott in a 3,100cc CH 601B from Arizona. If you add in the time we put on our own 601, you are looking at 1,400 hours of ‘Zenvair’ experience. These aircraft have flown in 40 out of 50 states. We have several dozen other zenith pilots who have written their own chapter in this same story. In the eight years since we pioneered the Corvair/Zenith combination all the development and testing has long been done. Any issue that builders experience today is a case of an aircraft that isn’t of our standard configuration or is having a problem like the MGL tach connection issue.

In the foreground above is Dan Weseman’s Wicked Cleanex. Off his wing, Chris Smith flys the Son Of Cleanex. The photo was taken over a bend in the St. Johns River in North Florida in 2007. Dan’s aircraft used a Grand Rapids system, but Chris’s used an MGL. On the first flight of Chris’s plane, it had a very high oil temp indication, a very serious issue. It made little sense because Chris’s aircraft was a clone of Dan’s, and Dan never had oil temp issues. After investigation the issue was traced to the MGL unit set to read the incorrect value from the VDO sending unit. This type of issue can not happen with a mechanical system.  The MGL is a computer person’s idea of a good instrument. It can use many different sensors, but I prefer systems that are fool-proof and use high quality sensors.  Chris’s plane did not have the ignition tied to the tach, Chris and Dan made a system to have the tach signal come from a sender counting bolts on the flywheel. To be fair, most people who have studied MGL’s products agree that the things they make today are better thought out than the generation of things in Chris’s aircraft, but builders using them are still advised not to use any connection to the corvairs’s ignition system.


In the above 2007 photo, Gordon Alexander’s 3,100cc Pegzair complete and running had just passed its FAA Airworthiness Inspection. To understand something of Gordon’s sense of humor, its N-number is N129LZ. LZ129 was the Hindenburg. Gordon’s airplane was seven years of hard work in the making. Gordon brought the project down on a trailer from Minnesota to our old hangar in Edgewater, where he commenced a savage 14-hours a day for 100 days to finish it. Inspired by his commitment, Gus, Kevin and I each worked to assist him. Gus guided him through covering the fuselage. I built his motor mount, and Kevin did an enormous amount of work ahead of the firewall. It was the first Corvair powered Pegzair ever. This was probably the first corvair powered plane to have an MGL Enigma panel. I do not critique the company without firsthand experience with their products.

Our 701 testbed in the Zenith booth at Sun ‘N Fun 2010.  This aircraft was completed in our shop in 2007. It also has an MGL Enigma panel. In the weeks before the show, Dan Weseman and I worked to upgrade the aircraft with one of his 5th bearings. After Dan installed the bearing, the engine showed a drop in oil pressure. This kind of made sense because of the area of the additional bearing and the fact the engine was equipped with a stock oil pump. Changing to a high volume oil pump required pulling the engine and removing the rear case. After doing so, I was stunned to se the oil pressure was the same. Issue? The MGL sending unit had coincidently failed at the same time as the bearing was installed. I checked the system with a $19 mechanical gauge and found that there was never anything wrong with the oil system. It was $200 in parts and 9 hours of work wasted.

I mentioned this on a discussion group, and immediately found out that MGL has many ‘friends’ on the net. If you read the MGL site, the founder in South Africa has a lot to say which suggests computers and software may be a much larger passion of his than airplanes or flying. This resonates with a lot of high-tech computer people on the net, who are very quick to respond to any comment made about MGL, even if they have never met him, nor flown behind any of his products, or completed a homebuilt. One of my primary issues with MGL was they were selling a fuel flow sending unit that was made out of cheap plastic. The owner of the 701 had installed one, something that made me reluctant to use the plane at all. To any A&P, aeronautical engineer or experienced builder, selling a barbed plastic fitting in a main fuel line is indefensible. Most of the tech Computer people didn’t understand why this was an issue. The division on this is a good illustration of the two different mind sets between the groups.

People whose day job is in the IT world would be hard pressed to think of a person in their field who lost their life on the job. Yet, most mechanics and aviation professionals know several people who were killed in planes. Three of the four mentors in Grace’s flying were Ken Terry, Bob Bean, and Phil Schact. They were all killed in planes in the last 4 years. Phil, along with Bill Hess burned to death in Bills RV-8. Things I don’t know about computers are not likely to physically harm me. There are many things I try to share about practical aircraft construction that are bitter lessons, things people I knew and loved paid dearly for.

Most people know that I am a troglodyte who like mechanical gauges. I fully understand that I am a in a dwindling minority group. Most builders today like elaborate technology. It isn’t for me, but I fully accept that it is something that typical builders want. My only point is if you are in the latter group, you need to understand the issues associated with applying this stuff to your corvair powered plane, and you need to understand that the information you can trust will at times be contrary to the avionics peoples’ recomendations. Because I went to Embry-Riddle and I have worked with experimentals as a day job for more than 20 years, I personally know more avionics engineers than 98% of the people who will read this. If you work outside of aviation, let me teach you something: Most mechanics can fly a plane; Most pilots can change plugs or tires; Most ATC guys can navigate; Most dispatchers can forecast weather; Most linemen can start and taxi a turbo prop; Most glider pilots can hand prop a plane, and so on. As a general rule, people in aviation have an interest that exceeds their job description. While there are obviously plenty of avionics guys who know how to fly, build, navigate, or what ever, most people who work in aviation would gladly tell you that many avionics people think of the rest of the aircraft as a support system for the panel.

While this all may sound like mean poke at avionics guys, there is a very serious point here. If you are new to homebuilding you need to fully understand that avionics guys as a rule have the least appreciation for the bigger picture of things, in our specific case here, why shorting out the ignition on the noisy thing that makes the fan on the front turn might be bad. 

 One of my pet peeves about this is simple to explain; If we went to Shane McDaniel’s home airport and asked 10 aviators who were around and watched him spend many frustrating hours working on his plane what they thought the problem was, I am sure that 9 out of 10 of them would freely offer “the problem is that he has an old car engine in his plane.” There is little I can do to counter such misconceptions, and realistically, public relations for conversion engines isn’t a goal of mine. I don’t care what other homebuilders think of Corvairs. My only concern is getting reliable information to the builders who have chosen the Corvair as the engine that best fits their personal goals in aviation.


2 Replies to “MGL vs Corvair ignition issue”

  1. I know this was written over 4 years ago, but I am just reading it now. You wrote:

    “People whose day job is in the IT world would be hard pressed to think of a person in their field who lost their life on the job. Yet, most mechanics and aviation professionals know several people who were killed in planes. Three of the four mentors in Grace’s flying were Ken Terry, Bob Bean, and Phil Schact. They were all killed in planes in the last 4 years. Phil, along with Bill Hess burned to death in Bills RV-8. Things I don’t know about computers are not likely to physically harm me. There are many things I try to share about practical aircraft construction that are bitter lessons, things people I knew and loved paid dearly for.”

    I manage an IT department for a marketing agency (that’s right, I work in the belly of the beast). But I am with you on this. Once (after have a few beers – or at least that is my excuse) I wrote an anti-technology, anti-“social media” (which is anything but) rant on my business account. Someone went directly to the owner of our business and told him how unprofessional it was and how bad it looked to our clients. I was forced into pulling it down and writing a retraction.

    But I know how technology can take over a person’s attention, even in small subtle ways. I got into aviation first with no instruments (hang gliding), then minimal (in gliding 2-33’s and my 1-26) When I first started looking into homebuilt’s and saw glass panels and NO steam gauges I was a bit taken aback and my reaction was “but what happens if/when this is a problem with … the device, the electrics, the system…” and the answer was ‘well there is a second screen and you can just switch functions’ or something like that. Although I have softened my position a bit, but I found this:
    “The fatal crash rate of TAA is almost twice that of aircraft with steam gauges, but it doesn’t have to be.”

    1. I think a lot of the difference in the accident rate are also attributable to on paper the pilots had the same ratings, but they likely had two entirely different generations of instruction, from people with very different standards of training

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