Just got back from a week at Key West, the weather wasn't very nice! Scale contests are finished for the year and it is time to get with building. I need to get this Super Cub off the bench so that other projects can start. It is time to think about running the engine and I thought a tach would be nice to set the carb up. On four strokes you don't want the butterfly opening beyond the point where the engine speed no longer increases. It nice to observe the rpm reading after reducing the endpoint to where the rpm just begins to drop. Valach recommends opening the carb 60%., the Roto manual doesn't address this. There are two maneuvers that I was using that require a rapid increase in throttle position, the Chandelle and the Overshoot. During both of these maneuvers I would experience a bog when the throttle was advanced, never noticed this until practicing the maneuvers. I had the butterfly set to full open. I happened across the Valach recommendation by accident and decided to give it a try, I also put a 1 second delay on throttle opening while the throttle closing is full speed. Both of these changes eliminated the bog.
I could not determine what Roto uses to trigger the ignition so I decided to add a Hall sensor and magnets to the engine. I pulled the prop hub and surprised to find it is a straight bore and not tapered. It came off with a little heating with the puller engaged. 1 1/2" pvc pipe was used the make the Hall sensor holder ring as shown in photo below while actual holder was cut off a commercial ignition holder. This is attached with rubberized CA, seems to hold well. 1/8" x 1/16" rare earth magnets were ordered from Amazon and should be here on Wednesday, these will be installed after the hub is reinstalled since heat man damage the magnets. Installing two magnets 180 degrees apart to improve low end resolution. The tach in the Champ drops out at 1000 rpm.
I tested the Roto trigger sensor with a VOM and found a meg ohm resistance between each wire, also checked with a DLE ignition tester and could not get any trigger for both south and north magnets. Proping the engine over with while measuring the voltage found nothing as well. I don't knows what's inside but I sure hope it runs.
ignition
