Yes, precisely, which is what the thread was actually about.

SSS, I posted a reply to your question, because you obviously didn't understand the need for the "Mags to off/dead cut" check on some aircraft. We may not like the answer, but it is the correct answer.

Of course I understand it, Shy. Been flying the bleedin' things for decades, including a stint as a meat bomber pilot. My point is, it would not be necessary to introduce arcane operating practices if manufacturer's refrained from putting style before function!

MJ. Thank you. And I would agree that switching both off momentarily will (provided both earths are good) pump un burnt fuel down the exhaust with whatever consequence depending on the duration of momentarily. I kill my Continental with two toggle switches, since it once had a Stromberg carb with no mixture control. Using mixture "idle cut" proves nothing and would allow me to shuffle off leaving the mags live if I forget! Perhaps the "stylists" would care to think of numpties like me.

Jan, I'm not squabbling or squibbling but you seem to have taken rapid and undue offence because I asked a technical question! :)

You implied that I thought that the battery provides the power supply to the DCDI modules. It obviously doesn't because we both know full well that on aviation engines the requirement is for fully independent ignition systems.

On the Rotax system, it appears that induction coils and magnets on the engine (not the battery) supply the LT power for the ignition. This is supplied to electronic modules which presumably convert this to HT energy and from there it is fed to the spark plugs.

The reason I asked? Grounding a traditional magneto isn't the same as cutting off the LT power supply to the input side of an electronic module by switching/breaking the circuit with a key operated switch. If it is done via the latter method, there is no point doing a "dead cut" check. All you would have to do is to check for "mag drop" and switch off. This would fit in with the OP's engineer's advice.

BTW, The diagram I mentioned was a simplified picture showing numbered parts of the ignition components. Alongside it was a list of those numbered parts. If I had found a circuit diagram I could perhaps have worked out the answer and wouldn't have needed to ask here.

I've just tried to get an answer from my local aircraft engineer, who helps maintain a couple of Rotax engines. Unfortunately, he wasn't in the hangar.

Forgive me if i'm wrong, but AIUI, the Rotax employs electronic ignition modules. one assumes that these work by disconnecting the power-feed (switching off) Some transistorised (solid-state) stuff doesn't take kindly to shorting -out or open-circuiting..

When using ICO to stop, is the carburettor float-bowl still full of fuel?
If so,it's not much different, strangling the idle -fuel, to switching off the sparks.
Just as a mag-system will show a slight drop when each mag is grounded, both off will produce a sudden and distinctively quiet drop. A very brief transition through that switch-position is all that's required to confirm both mags are grounding-out correctly. under those circumstances,a backfire is unlikely..
Always treat a prop as potentially LIVE and you won't get a free lobotomy.:}

The carb float bowl is still full, ICO just leans the mixture to far too lean to run ie: fresh air.

Nice to do whatever is recommended while you are letting the engine temps stabilise while just parked/running up to the dock or whatever.
Nothing will ensure the Mags won't be live next time you go near the prop.
Meat bombers always have a spare set of mag keys! SSD where have you been?

Rotary magneto switches -

https://encrypted-tbn1.gstatic.com/i...nnS40QWZ3o26jQ

As found on DC3s for example. Admittedly not key-operated. Top centre switch kills both mags at the same time in an emergency.

I've managed to get hold a copy of the Rotax 912 manual. Section 9.4 covers the electrics.

As I suspected, this type of engine doesn't actually have magnetos.

It's a CDI system powered by a generator on the crankshaft (the word magneto doesn't occur anywhere in the manual).

As you suspected, you have found out for yourself what I already told you in #52

Congratulations! There is no need to ask on a forum those questions you can answer for yourself.

And. if I may ask a technical question, what do you mean in #64 by LT power ?

Jan, You seem to have some sort of personal issue anger here. You have received a lot of advice from quite a number of members over the years you have been a member of this forum. It would be nice if you could give something back and discuss genuine questions without sarcasm or anger showing through.

By the way, having read the Rotax manual, I noted that your description of the ignition system wasn't completely accurate and you admitted you weren't sure about it. You should already have the circuit diagram you asked me for. It's in the 912 manual, below the system description.

Regarding your question added in the edit. LT? As you told me to do, look it up for yourself and answer your own question.

In #52 and #54 I offered purely technical replies. Later reactions bewildered me and I answered up to that bewilderment. Everything else I leave up to you, and please spare me your (doubtlessly well meant) recommendations.

I quite disagree. Some of these rotary key switches are notoriously unreliable, and subject to AD's (perhaps you read my earlier hand propping story?)

There are lots of later model Cessnas and Pipers which use toggle or rocker switches for the mags, rather than a key switch - all of their twins. However, I expect that their singles were fitted with key switches just to add one layer of theft deterrent - they are easy to fly!

No one is saying that the key switch is a great design, or superior to the independent toggle switches, it's just the way about 100,000 very popular aircraft were built. With good maintenance, AND PROPER GROUND CHECKS, they work fine, so what's wrong with that?

Exhausts can be damaged by mags off and on at high power, so don't do that. But I have never heard of exhaust damage at idle, so what's the problem? A necessary check, with no downside, appropriate for 100,000 or so planes. 'Seems worth training and conducting to me.....

Since they are not very secure in that just about any key of approximately the right size will operate them, I'm sticking to my 'motor car' theory. A lot of 1950s spam can marketing was based on the concept of 'motor car of the skies'. ;)

Shaggy sheep driver
 

In my role as an LAA inspector I have yet to encounter any aircraft constructed from spam cans ( or any other food storage device ).

Could you please illuminate me as to the type of aircraft you are referring to ?

A and C. How did you spend long enough in GA to become such an inspector without coming across the expression 'spam can', which I have never found anyone but a not-aviation person not to understand. Or were you just posturing?

There is another type of 'spam can' that railway enthusiasts will know about, by the way.

SSD
 

Spam Can A derisive term used to discribe a metal stressed skin aircraft.

The term is one used in British aviation to deride those products who they don't consider " real aircraft". This backward facing attitude resulted in the demise of the British aviation ( and motorcycle ) industry's when they failed to make use of advancing technology to produce products that were relevant to a modernizing market.

[B]Example[B] last mass produced British designed light aircraft engine.... Gypsy Major ......... Can trace its roots back to about 1914.

Engine that most of this thread is about......Rotax, a modern and very efficient engine..... Built in Austria.

Hmmm, A and C, sort of... But "spam cans" don't use Rotaxes.


Its not a backwards facing term, its a term of derision aimed at aircraft that are flying cars (and probably have rotary mag switches ;) ). People who use the term don't think they are proper aircraft.

http://www.pilotfriend.com/training/...g/eurostar.htm


Is this a spam can I wonder? Its metal, got a Rotax 912 and has separate toggle ignition switches...

Obviously, A&C, you are not a Monty Python fan.

Spam was, in the second world war, the only meat whichwas universally readily available......it was everywhere,incorporated into virtually any and every meat meal. It was the generic, go anywhere, use for everything,universal meat.........It's tin ,popular folklore adopted, as a synonym for a robust, one size fits all, substitutes for any other type
do anything, go anywhere aeroplane.

Perhaps it's the British sense of humour. As I see it, it's an affectionate term for an old faithful that's always there,readyand waiting.

OK, it's bland and mediocre, but consistent and reliable.

OK?

Okay, so we've drifted to discussing spam cans again, because the reality of a live mag check having merit with a key type ignition switch has been established, so instead of accepting this, some would like to divert attention away from a rather narrow minded point of view....

I have visited the Spam Museum, and there is nothing to do with GA aircraft in there (they do have a Spam truck though, I got the toy).

Austin, Minnesota - Wikipedia, the free encyclopedia

Spam Can is not a term used in North American aviation, other than to respond to UK posts. The can for spam is a very useful item, purposely designed to have usefulness beyond containing the meat. (flat sides). I have seen Japanese toys made from recycled spam cans from not long after WW2 (they put the printed side on the inside of the toy). Resourceful people. So I guess those who use the term, equate the can to the plane?

So the spam is the contents of the can [plane]?

I have flown many aircraft which were very certainly not spam cans. Their common traits were fun to fly, nostalgic, and requiring (thus developing) greater pilot skill. But they were all very much less utilitarian, quickly repairable and long life durable than the metal planes I have come to also like.

So for both the planes I own, I have chosen all metal, with key switches, and been very pleased with them both.

Very true, but parked beside another theft candidate with only two mag switches, the key plane will still be stolen last! :D That's all I care about!

Cessna 162 Skycatcher - Wikipedia, the free encyclopedia

And then, I understand that the engine was changed to an O-200 because of market preference? (I don't know much about them, 'never flown one). I bet they had a key switch though! :E

One of things I really enjoy about GA flying is the opportunity to experience many types of planes, and design philosophies. Each have their own pluses and minuses, because every plane is a compromise. We learn to operate them as they were designed and understood, so even the operations can be different, and yes, something which is right for one plane, might be less than good for another - this is why we take familiarization training!

Having flown about 80 types of GA aircraft, I'm getting there. I am learning the nuances. I listen to others who know more than I about a type or system, and try to glean the best from it. So, when I fly the Tiger Moth, I'll check the petrol, fill the oil, and I won't return two mag switches to "on" with the prop turning, and the fuel on. But the key switch planes... I'll be "live mag" checking.....