Embarrassing ROTAX Ignition Question

[FastEddieB]

I know, I know, the only bad question is the one your don't ask, but...

 

I'm fuzzy on one important thing:

 

With a failed alternator and a completely dead battery...will the engine continue to run?

 

In one place - my Sky Arrow POH - in the EMERGENCY section it says that with a failed alternator the battery can provide power to this, that, the other, and the ignition for 30'.

 

In another place - the ROTAX Owner's Manual - it says that each ignition has its own source of power and that they're independent of "outside power".

 

So, which is it?

 

BTW, I think when we had issues with the Sky Arrow I ferried, we tried switching off both the Alternator and the Battery at the same time (on the ground) - and the engine didn't miss a beat. I know now that's frowned upon, but it did not seem to have any ill effect.

[chanik]

Depends why the alternator failed, but the CDIs are not connected to the ALT or battery at all. Both ignition systems have INDEPENDENT pickup coils for triggering and for power to the multi-pole magnetic flywheel spinning in the back of the engine. If something mechanical is broken back there then everything could go dead but that isn't likely. More likely is a dead Ducati regulator on the alternator pickup coils. So the engine will run with no alternator or battery.

[Tom Baker]

Like Kurt said it is a seperate system. On 2 of the post on the stator for the power generation system there are a second set of windings for the ignition. The engine needs to be turning about 240 RPM to make enough electricity for the ignition system to work. The ignition system actually works off of the A/C electricity. It is not converted to D/C. Tom

[Ed Cesnalis]

I have toggles for master switches. on 2 occasions i closed the alternator switch when retracting flaps on take off and didn't notice till my battery went stone dead.

 

on the 2nd occasion I was at 12,500 and climbing over high terrain.

 

the good news is that the engine continued to run as normal. the heads up that alerted me was a tach reading of 3,500 rpm when 5,000+ was correct.

 

been there, done that, it works

[airhound]

All---I know different systems, but generally sounds similiar to Lyc/Cont...broken Mag P-leads//Hot-Mag situation.

[FastEddieB]

Thanks, guys.

 

I think you all confirmed what I surmised from the ROTAX description and diagrams: each CDI ignition has its own tiny generator that functions independently of anything else.

 

To have ignition dependent on a single alternator/voltage regulator and battery would seem risky, especially given the fragility of some of the parts involved (esp. the voltage regulator).

 

But its easy to be confused, especially given the warning in my POH about only having ignition for 30' with a failed "GEN". I know at least one other person who was led to believe that a totally dead electrical system would lead to loss of ignition*.

 

...but generally sounds similiar to Lyc/Cont...broken Mag P-leads//Hot-Mag situation.

 

Not sure what that means. Magnetos are rather different animals. But I guess the similarity is that either system is independent of outside power, which is as it should be.

 

 

*Now that would seem to be the case with the Diamond TwinStar with the original diesel engines. There was one that had dual engine failure de to low voltage caused by raising the gear on a plane that had been jumpstarted and had very weak batteries. Not a good scenario. I know diesels don't have ignitions, per se', but they still required power for some parts of their FADEC engine management system.

[FastEddieB]

Another Sky Arrow pilot forward me this NTSB report:

 

http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20090608X51809&ntsbno=ERA09IA326&akey=1

 

I assume the main fuse in the CT is different, so much does not apply.

 

The relevant text is:

 

"Electrical power for the engine ignition system was provided by magnetos, and ignition system operation was independent of the airplane electrical system; once the engine was running, the position of the master switch would not affect engine operation."

 

That confirms the conclusion here, though I think the word "magnetos" is technically incorrect.

 

But what's curious is this:

 

"When the student cycled the master switch to the "OFF" position, and then back to the "ON" position, the engine ceased operation."

 

This is an odd accident, in that the main fuse being intermittent, leading to overvoltage, leading to a burned avionics fan, leading to a shutting down of electrical power, none of this should have stopped the engine. I'm wondering if the student accidentally shut of the Ignition switches, which in a Sky Arrow are two independent toggle switches on the panel, and located just above the Master switches:

 

[Mike]

If my ignition switches were in any way a risk of being switched off i would have covers on them like these below , i used to have them on my skyranger but with the ct key type switch there not needed ...

 

Mike

 

 

Another Sky Arrow pilot forward me this NTSB report:

 

http://www.ntsb.gov/...A09IA326&akey=1

 

I assume the main fuse in the CT is different, so much does not apply.

 

The relevant text is:

 

"Electrical power for the engine ignition system was provided by magnetos, and ignition system operation was independent of the airplane electrical system; once the engine was running, the position of the master switch would not affect engine operation."

 

That confirms the conclusion here, though I think the word "magnetos" is technically incorrect.

 

But what's curious is this:

 

"When the student cycled the master switch to the "OFF" position, and then back to the "ON" position, the engine ceased operation."

 

This is an odd accident, in that the main fuse being intermittent, leading to overvoltage, leading to a burned avionics fan, leading to a shutting down of electrical power, none of this should have stopped the engine. I'm wondering if the student accidentally shut of the Ignition switches, which in a Sky Arrow are two independent toggle switches on the panel, and located just above the Master switches:

 

[FastEddieB]

If my ignition switches were in any way a risk of being switched off i would have covers on them like these below , i used to have them on my skyranger but with the ct key type switch there not needed ...

 

Mike

 

Obviously a valid concern, but...

 

...you can't see from the photo that these toggle have to be pulled out before they can be thrown. Clearly designed to prevent an accidental incident.

 

I'd say if the student did turn them off, he did so accidentally - and neither a two-step switch nor a cover can prevent that.

 

But from a human interface perspective, maybe they shouldn't be so close to the master - and that's not the only interface problem the Sky Arrow has - the carb heat and canopy latch are in fairly close proximity and are exactly the same shape!

[Jim]

If anyone is tempted to pull the bat and gen breakers while the engine is running, I'd recommend not doing it. If you just have to do it, I'd first pull *all* of the other breakers and turn everything off. Disconnecting a battery from a generator on a running engine can cause huge voltage transients.

[Mike]

I think you are thinking the wrong way round Eddie .... i had the switch covers fitted so when the ignition is ON you would have to physically lift the covers from the switch to turn them OFF so you couldn't accidentally brush against them and turn them off while accessing another switch etc ..someone wouldn't be able to accidentally lift a cover to turn a switch off

 

 

Mike

 

 

Obviously a valid concern, but...

 

...you can't see from the photo that these toggle have to be pulled out before they can be thrown. Clearly designed to prevent an accidental incident.

 

I'd say if the student did turn them off, he did so accidentally - and neither a two-step switch nor a cover can prevent that.

 

But from a human interface perspective, maybe they shouldn't be so close to the master - and that's not the only interface problem the Sky Arrow has - the carb heat and canopy latch are in fairly close proximity and are exactly the same shape!

[FastEddieB]

I think you are thinking the wrong way round Eddie ..you couldn't accidentally brush against them and turn them off while accessing another switch etc ..someone wouldn't be able to accidentally lift a cover to turn a switch off

 

 

Mike

 

I understand.

 

But there's no way my switches could be accidentally "brushed" off - you must definitely pull the switches out before they will move.

 

I still think this "two motion" arrangement is roughly equivalent to having to lift a cover first.