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.
2 Replies to “MGL vs Corvair ignition issue”
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 LinkedIn.com 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.”
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