Evektor SportStar - Magneto Safety Question

[jandras]

Hi all,

I train in a SportStar and have a (probably dumb) safety question. Part of our pre-flight process is hanging the key away from the ignition switch and then rotating the prop until we hear the oil gurgle, rotating it two more revs, and then checking the oil in the sump.

That said, I understand that with a Cessna (e.g. 150), turning the mag switch (ignition key?) kills the mags by grounding them, but the preferred way to kill the engine is by pulling the mixture full out in order to cut off the fuel supply. Evidently this is easier on the engines.

I also understand that before cutting off the fuel to kill the Cessna, part of the shutdown procedure involves making sure that in the OFF position, the magnetos are grounded safe, by quickly turning the mags to OFF and back to BOTH just quick enough to hear the engine start to quit. Evidently, this confirms that you could turn off the engine by turning the mags to OFF if you ever needed to and, just as importantly, ensures that rotating the prop won’t take off your arm by having the engine start because the mags aren’t properly grounded (loose wire, etc.).

So, here are my questions

(1) Is it correct that the SportStar also has magnetos and, if they weren’t grounded, cranking the prop could start the engine?

(2) If so, even though our last flight successfully turned off the engine by grounding the mags, should we be a little bit concerned about our hand-propping technique in order to check the oil?

Thanks!

[FastEddieB]

What engine does your plane have?

[jandras]

It has a Rotax 912.

[drseti]

The SportStar (and other LSAs using the Rotax 912 ULS engine) does not use magnetos for the ignition. Instead, it uses two Ducati capacitive discharge ignition modules. There is no P lead to ground. There is, however, a shutdown procedure your instructor should have taught you, that ensures the ignition modules are working properly (and hence safely).

When you're ready to shut down, close the throttle completely, verifying that the engine is idling smoothly (typically, idle speed should be set for 1700 RPM or so, with the engine hot). Then, turn the key one click to the left, which disables one CD ignition module. Pause there. Note that there is an RPM drop, but the engine still idles smoothly. Next, turn the key one more click to the left. This turns the first CDI unit back on, and the second one off. Pause again. You should still get a smooth idle, at about the same RPM. Having verified both CDIs are functioning properly, you can now do the final click, to "off". The engine will stop abruptly. Don't let this alarm you; it is perfectly normal with a geared engine, and you have a slipper clutch to prevent any damage.

When the engine has stopped, turn off the master switch before you pull the key. Get in the habit of doing this every time. Otherwise, you will some day come back to a dead battery.

[3Dreaming]

The Rotax uses an electronic ignition system that runs off the AC voltage provided by the engine. The engine has to be turning around 240 RPM to make enough voltage for the system to work, so turning it by hand will not produce enough voltage for the engine to start.

[jandras]

Thanks everybody. Very informative!

[jandras]

When the engine has stopped, turn off the master switch before you pull the key. Get in the habit of doing this every time. Otherwise, you will some day come back to a dead battery.

Thanks drseti! If I turned off all of the other switches, but accidentally left the master switch on, what are the hidden loads that will drain the battery? Is it just a solenoid coil, or other stuff too?

[FastEddieB]

Thanks, guys, for saving me a lot off typing!

Back to the Continental/Lycoming/typical aircraft engine questions...

1) I was told we killed the engine with the mixture for two reasons...

First, it left the cylinders free of fuel, making an unintended start less likely, and..

Second, aviation fuel is more corrosive than auto fuel, making it advantageous not to leave any in the cylinders.

2) The "Mag Ground Check" at the end of every flight on an airplane with mags is a good idea. The "p-leads" that ground the mags in the "OFF" position are often incredibly flimsy. Were you not to check for proper grounding, you would never have any idea that a lead was broken and a mag was hot all the time. You might check it on runup on your mag check when you had zero drop on one side, but many pilots might not catch that.

Finally, though there's essentially zero chance of a ROTAX starting from pulling the prop through, its still a good idea to follow all the typical prop handling procedures - cup your hands on the blades, keep your body out of the propeller arc, keep your weight/momentum always moving away from the prop arc - that sort of thing. It will serve you well by building good habits for when you DO fly a "normal" plane, and may save you serious injury if somehow by some freak of nature your ROTAX ever did kick back or start.

[drseti]

If I turned off all of the other switches, but accidentally left the master switch on, what are the hidden loads that will drain the battery? Is it just a solenoid coil, or other stuff too?

Solenoids, yes, but also the electric trim circuit. The LED bar-graph trim indicator doesn't draw much current, but if it's on long enough...

Also, as Eddie points out, it's about building good habits for when you fly other aircraft.

[jnmeade]

Second, aviation fuel is more corrosive than auto fuel, making it advantageous not to leave any in the cylinders.

I'd never heard that av gas is more corrosive than auto fuel, and it surprises me. Can you cite some references supporting that assertion?

[drseti]

Simple. AvGas contains lots of lead. Mogas is lead-free. Lead is a corrosive. Ergo, AvGas is corrosive.

[jnmeade]

Mogas contains all kinds of junk which varies by geographical region and time of year, including possibly ethanol which is quite corrosive.
Rotax gurus tell us we may leave a plane with avgas in the tank but caution us to not let mogas sit in the plane too long without refreshing it for various reasons.
I'd like to see a definitive side-by-side comparison before I'd accept that avgas is more corrosive than mogas.

[drseti]

I just said that lead is corrosive. I never said that mogas didn't contain lots of other junk!

[jnmeade]

You are implying that the other "junk" in mogas is not corrosive.
I'd simply like to see some scientific corroboration other than assertions that avgas with lead is more corrosive than mogas with it's additives and possibly ethanol.

[drseti]

You are implying that the other "junk" in mogas is not corrosive.

Not at all, Jim (although that might possibly be what Eddie was implying; I'll let him speak for himself.) I was merely asserting that I know what lead is, and I know that it's corrosive. Since I'm not really sure what that "other junk" might be, I'm not qualified to evaluate its corrosive properties. (If there's a petroleum engineer lurking here, I'd be delighted to be enlightened.)