Friends;
Below is a picture of my favorite tach for the Corvair, the Stewart Warner 82636. I have used this tach for almost 15 years. We had one in our Pietenpol and also had one in our Zenith 601XL. I just bought another for our Wagabond. It has a number of features that make it attractive to Corvair builders. It isn’t cheap at $120, but I do find it to be a good value.
The most important consideration for any tach in an aircraft is that it does not interfere with the ignition system. This tach does not have that issue because it was designed to work with diesel engines which don’t have ignition systems. It works by counting the teeth on the flywheel with a small sensor. This is a very clever tach, and it can accurately read any amount of teeth from 60 to 255. The ring gear we use has 135 teeth. The tach has 8 tiny switches that set it for a specific amount of teeth. It comes with very good instructions that explain this. It takes only 2 or 3 minutes to set. Because it was intended for industrial diesels, the full sweep is 3,500 rpm, a useful range for many flight engines. The Tach is available from a number of places on line, I just bought ours from Summitracing.com.
Note: Under no circumstances should builders hook up tachometers to the ignition system directly. If you do this with a traditional gas engine/ignition tach, you are in danger of potentially grounding out the ignition if the tach shorts. I have seen people set these up with 1/2 amp quick blow fuses in the signal line, but I think it is banking a lot on a little fuse. MGL, a glass cockpit company has given builders false information saying that their glass panels can be directly hooked to the Corvair without issue. Don’t believe this, they sell panels, they are based in South Africa, they wouldn’t know a Corvair if it bit them on the tail feathers. If you are thinking of using a glass panel let us know and we will put you in touch with a builder who has one successfully flying.
Since we started promoting the use of this tach it has become the choise of a lot of pilots. At least 25 of the fleet of Corvair powered planes use one. occasionally one of these builders will report having an issue with getting their tach to correctly read the teeth. contrary to what you might first expect, the issue often turns out to be having the sender too close to the teeth, not too far away. .060″ generally works, but if it doesn’t, move toward .125″ instead of going closer. Once set, my experience is that this unit works flawlessly.
The Corvair has flown with every kind of tach you can imagine. Bernard Pietenpol showed people how to adapt mechanical aircraft tachs; We have used a number of different diesel tachs; and virtually every popular glass panel from Dynon to Grand Rapids to MGL. (These later units have required the signal to be buffered to prevent the unit from messing up the ignition and giving a poor signal). If you want to use one of the Glass panels, good, builders have figured out how to make each of them work. For troglodytes that still like gauges with needles, the 82636 is still my first choice.
In the next week or so, I will put up a few updates on the new Wagabond panel, a dirt simple Day/VFR basic stick and rudder arrangement with a minimum of simple engine gauges. It has about $700 in parts in it. Builder interested in a very simple traditional panel can use it as a model for their own.-ww