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Master switch

Walt Shipley

Active Member
Another builder in my airpark posed an interesting question for which I don't currently have an answer.

He asked if the engine would quit if the master switch was accidentally turned off while the engine was running. I have sent my D180 back to Dynon and don't wish to start my engine. Do anyone of you know the answer to this question?

Walt Shipley
 
No, the engine will not stop when the master switch is turned off. The Rotax dynamo has 3 independent windings, one for each electronic ignition and one for the aircraft electrical system. When the ignition switches are shut off, they short the electronic ignitions to ground, similar to conventional magnetos.
Joe Gores
 
Master Switch

Another builder in my airpark posed an interesting question for which I don't currently have an answer.

He asked if the engine would quit if the master switch was accidentally turned off while the engine was running. I have sent my D180 back to Dynon and don't wish to start my engine. Do anyone of you know the answer to this question?

Walt Shipley

The master switch must be on to supply the starter with electricity from the battery to crank engine for startup. After starting the airplane with a standard Magneto it will run until the fuel is gone with the master switch on or off.
 
Was this question by the OP specific to the RV-12?

I believe it was.

As Joe said, the Rotax 912 ignition is self generating like 'normal' mags so needs no outside power to keep it going once the engine has started.

And yes, you can hand swing a 912 if the battery goes flat in the desert...
 
I can confirm it keeps running. I checked it during my first engine run. I always like to understand the knobology of what I fly.
 
Jerry - Have you (or anyone) actually hand-propped one? I ask because I thought I had read that it would not work because the engine needs to have a high RPM to start, and you have the gear reduction drive in between. On the other hand, the thing sure starts immediately, a countervailing influence.
 
Bill, I attended the UK Rotax guru's 912 heavy maintenance course through work.

He assured us it was possible to hand swing a 912. I'll check my notes at work tomorrow but I think it was around 200rpm engine speed. Given the 2.43:1 gearbox ratio this means it is quite easy to spin the prop fast enough.

That said it isn't the easiest prop to swing through compression but the 912 starts easier than pretty much any other aircraft engine.

Here's a link to an accident report from the UK Air Accidents Investigation Branch (AAIB) concerning 'one that got away':

AAIB G-CCXM

For info purposes, here's Conrad's really helpful Rotax servicing booklet (always check that info is still current via Rotax' own website ;) ):

Conair Sports - 912 Maintenance Info
 
Master Switch - Off

On many Lycoming powered RVs, just turning off the electrical master switch has no effect on anything. The alternator will continue to power the main buss and continue to keep itself energized. To shut down the electrical system (electrical smoke/fire) the alternator field must also be shut down.
 
Checked my notes today from the Rotax course that I attended.

Engine needs 220rpm to produce a spark - and as I mentioned, that is possible by hand given the 2.43:1 gearbox ratio.

Don't believe anyone that says you can't hand swing a 912!
 
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