MikeAdminI feel the need for light speed
18 April 2021
For what seems like the life of the plane I have been fighting issues with my light speed electronic ignition system.
Quick tutorial – the FAA mandated back in the 1950s that aircraft engines must have two independent sources of ignition (spark). This is accomplished by having two sparkplugs for each cylinder – in my horizontally opposed engine this means a top and a bottom.
The traditional method of timing and creating the spark is through the use of a Magneto that is mechanically connected to the engine. These systems are great and reliable – though they do require significant maintenance one major advantage is they will continue to work even when all electrical power is lost – since they have a self-contained generator. But since they are mechanically timed to the motor they are unable to adjust the timing of the ignition spark based on power output, or manifold pressure. Electronic ignition systems are able to compensate for these varying conditions and provide 10-20% more power and fuel savings. But the down side is they require power to operate – meaning if all electrical power – the alternator and the battery died then then engine wouldn’t receive a spark and thus would stop running.
In N95VT we attempted to get the best of both worlds by having both an electrical system and a mechanical system. In our case the lower sparkplugs are connected to the mechanical magneto and the upper sparkplugs are connected to an electronic ignition system. This has worked well and the redundancy has been appreciated as on numerous occasions I have had the electronic system fail. In every case the cause of the failure was due to a connector coming off. Specifically either the spark plug wire or the timing wire that send the signal to the coil.
This is normally recognized in the airplane by a small drop in performance and a spike in EGT temperature as the affected cylinder has less complete combustion and more ‘fire’ happens in the exhaust. This has been a recurring issue which I have tried to fix by going in and reattaching the wires or replacing the bonnet connector on the timing wire.
Speaking with the system designer Klaus after returning from Georgia when the issue occurred three times each time after being in flight for about 2 hours I decided to add a support behind the coil that supplies spark to the #1&2 cylinders since they have been the only cylinders to exhibit this issue. To do this I built a support to hold the timing wire forward and added a clamp to an existing fuel line support to hold the sparkplug cable.
I thought this had solved the issue but after a few hours of flying on Saturday I had an EGT spike on #5&6 when I went flying Sunday. After removing the cowel and examining the engine I wasn’t 100% sure I was able to identify the issue but believe the ground wire associated with the timing of this coil was lose.
After speaking with Kevin who also has the light speed system on one of his airplanes I decided to build brackets to support the other 2 coils, replace the timing wire connectors and add RTV to the connectors to help “glue” them in place.
Next step will be to test fly it with these modifications. If this isn’t successful I believe the next logical step will be to mechanically connect the timing wires to the coils with a screw. This will require drilling into the bonnet fitting on the coil but we will cross that bridge when we come to it.
4-25-21
Flew for about 1.5 in pretty rough air and the engine seemed to have no issues.
