Wed Jul 29, 2020 10:07 pm
#1787029
Having owned a couple of 912 UL engines over the past 18 years I have come to understand the following:
1. The oil level doesn't always show on the dip stick until it is gurgled.
2. Whilst the 912 doesn't usually burn oil between oil changes, this all changed on my first engine. It would burn about 120ml per hour, so gurgling was the only way of accurately assessing how much oil to add between flights until I finally got fed up and replaced the engine.
3. A 912 will fire if two conditions are satisfied:
a. the high voltage capacitor in the ignition has sufficient charge to generate a spark. This cannot occur immediately; it would take several prop movements at a ‘quicker’ speed causing the flywheel magnets to pass the charging coils a sufficient number of times. There are multiple magnets in the flywheel, and it rotates about 1.5 times faster than the prop.
b. one of the poles of the flywheel passes a trigger coil with sufficient instantaneous speed to generate trigger pulse with sufficient amplitude to trigger the ignition.
4. There is a failure mode of the 912 ignition modules where the kill circuit stops working. This is usually detected when the engine cannot be stopped by switching off both ignition modules. It is however possible that the failure could be temperature related meaning that the failure could be present on a cold engine but not on a hot engine. I have not seen this myself; I have only witnessed this as a hard fault. i.e. it is faulty all the time.
5. Whilst it is unlikely that hand propping a 912 will result in a start it is definitely possible. Take a look at this:
1. The oil level doesn't always show on the dip stick until it is gurgled.
2. Whilst the 912 doesn't usually burn oil between oil changes, this all changed on my first engine. It would burn about 120ml per hour, so gurgling was the only way of accurately assessing how much oil to add between flights until I finally got fed up and replaced the engine.
3. A 912 will fire if two conditions are satisfied:
a. the high voltage capacitor in the ignition has sufficient charge to generate a spark. This cannot occur immediately; it would take several prop movements at a ‘quicker’ speed causing the flywheel magnets to pass the charging coils a sufficient number of times. There are multiple magnets in the flywheel, and it rotates about 1.5 times faster than the prop.
b. one of the poles of the flywheel passes a trigger coil with sufficient instantaneous speed to generate trigger pulse with sufficient amplitude to trigger the ignition.
4. There is a failure mode of the 912 ignition modules where the kill circuit stops working. This is usually detected when the engine cannot be stopped by switching off both ignition modules. It is however possible that the failure could be temperature related meaning that the failure could be present on a cold engine but not on a hot engine. I have not seen this myself; I have only witnessed this as a hard fault. i.e. it is faulty all the time.
5. Whilst it is unlikely that hand propping a 912 will result in a start it is definitely possible. Take a look at this: