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flyfisher

Shutting down engine after flight

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Hi all,Largely because of Fly I have started having flying lessons.In shutting down the engine of a Cessna 172 or Grumman AA5 we are taught to turn the ignition key quickly to the off position, then immediately back to 'both' once it is clear the engine falters, before finally letting the engine die by pulling the mixture to the fully-leaned position.I've tried this with the Fly2 Cessna and the engines dies once the key is turned to the off position even momentarily.Does this happen to all flyers and,if so,does anyone have ideas as to how it could be corrected?:-wave

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Gee, this must be a new procedure during pre-flight. I always checked the left magneto, the right magnito and both magnitos for rpm drop--never turning the switch to off.tony

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Tony, I do believe the question pertained to shutting down the engine and not to pre-flight prior to takeoff.My experience with the Cessna was to turn the key to the off position and leave it there. That was the pocedure some 30 years ago when I took flight lessons. That certainly could have changed since!!:-outta

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G'day Tony, It's a safety issue!The "Kill switch test" prior to shutdown is to confirm that the magneto switches are actually working!!!! ie earthing the primary winding.You don't switch manetos ON. You switch magnetos OFF. (the function of the switch is to enable the magneto to be switched OFF )If you were to remove the switch and wiring from the instrument panel and throw it away :-eek the engine would still start because the magnetos are LIVE. A wire is run from the primary winding through the magneto switch to earth. When the magneto switch is ON the circuit is open. When the switch is OFF the circuit is closed. If you simply shut down by closing the throttle and pulling the mixture to cut-off the engine will stop. You MUST then switch off the magnetos. (for safety purposes )BUT BUT How can you be sure that the primary winding of the magneto is actually earthed. The switch may be faulty ( it does happen ) or the wiring may be disconnected/broken/open circuited ?? in which case the magneto would still be LIVE and a dangerous situation exists. The sure way to check that the switches are actually functioning correctly is to switch both magnetos OFF and check that the engine dies and then switch them ON again before the engine completely stops and check that the engine bursts back into life.Cheers,Roger

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G'day Flyfisher,Same here. As soon as the mags are off the engine is complely dead. There is no wind down stage. I know of no cure for this.My only suggestion is to do your magneto "Kill test" whilst flying (if you're brave or stupid enough :-lol). It works perfectly then because airflow keeps the prop revolving slowly so as soon as you switch the magnetoes ON the engine bursts back into life.Unfortunately it cannot be performed at shutdown due to the instant stopping of the engine.Cheers,Roger

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Roger and Wayne. Again, I agree with how an engine works. I accumulated over 300 hours in a number of crafts and, yet, the shutdown procedure was to simply pull the mixture lever out until the engine ran out of fuel. Then Turn the egnition switch off. Never during my instruction was I told to momentarily turn it back on to check for a live switch condition. In fact, during the pre-flight check, the pilot always assumes that the prop may start, so he carefully pushes the prop as if it were live. tony

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G'day Tony,Sorry Tony I wasn't meaning to lecture you (I'm a retired teacher and it shows :-) ) , just explaining WHY such checks may be done. I agree that most pilots probably don't do it, probably more widely used as a maintenance practice to specifically check out the switch servicabilty on each 100 hourly inspection.It is because of this magneto switch "uncertainty" that the old addage of "always treat a prop as if it were LIVE" exists, just checking the switches are OFF isn't good enough ( unless you know the switches are serviceable ... oh oh going round in circles :-) ) Also keep in mind that one of the magnetos is connected via an impulse coupling so that no matter how slowly you turn a prop a dirty big spring will release and rapidly spin the magneto to produce a spark. A zealous instructor may however, for perceived safety reasons, reccommend the procedure as best practice.It's simply a confidence test; nothing more nothing less. There is no operational necessity for it. Cheers,Roger

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Hi RogerIn Austria we are teaching this check during engine shutdown. (for the reason you described)Harald

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G'day Harald, Thanks for the input. Many people on the forum who did some flying a fair while ago haven't been exposed to this practice. It looks as if engine shutdown procedure has changed over the years.Cheers,Roger

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Hi RodgerHave you ever flown a Diamond Katana ? This Aircraft, made near Vienna, is very popular in Austria flight-schools.It has no mixture control, so you shut it down with the ignition key just like you do with your car.So these people learn a very different concept.Harald

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G'day Harald,No mate, I'm strictly a maintenance guy. Ive done a considerable amount of engine running but never had the wheels off the ground. :-) It's a lot safer that way :-lolWhat engine does the Diamond Katana use. It sounds like it might be based on an automotive engine? Does it use Magneto's?? Just curious as I haven't heard of an aircraft engine that shuts down by switching off ignition.Is it some derivitive of Rotax?Cheers,Roger

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Yes, the Katanas started out using the Rotax 912, although a model is now available with a Continental IO-240.Chris WallaceOttawa, Canada

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Donny AKA ShalomarFly 2 ROCKS!!!Speaking of the Katana, it's available from the Avsim library for FLY 2. Big download, but a nice bird for VFR with custom cockpit.Back to the subject: This was the first I heard of the mags off test. My father was a real world Cherokee/Aztec among others pilot and I took some lessons years ago. Makes sense why though.Best Regards, Donny:-wave

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Hi RogerYes, it is Rotax Engine (912 or 914). The model with the Continental 240 is not very popular in Austria due to the high fuel prices.The Katana has magnetos and the magneto-check is performed like in any other aircraft. The only difference is, that it does not have a lever for leaning.Harald

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G'day Harald,Rotax gained much of their R & D from motorcycle GP racing if my memory serves me correctly. I would expect the Rotax would have to have some form of mixture control for the aircraft engine due to the changes in air density with altitude. Possibly a bellows controlled AMC built into the carburrettor.?? About six months ago I was browsing (dreaming) in a boat shop and noticed a twin engine (twin screws) speed boat and it had Rotax engines. It appears that the Rotax engines are very versatile. :-) Cheers,Roger

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G'day Flyfisher,I was just messing around with the Jabiru and tried the Magneto switch kill test. YOU HAVE TO BE QUICK but it does work. Don't wait for the engine rpm to start falling, switch the magneto back on IMMEDIATELY after switching it off. Idling at 800 rpm the engine falls to between 400 and 700 rpm (depends on how rapidly you operate the switch ) and then picks up and climbs back up to 800.Take too long to get the switch back ON and the engine will die. But it's NOT instantaneous; about 0.1 sec (guess)I went and retried the Cessna and it is possible but a fair bit harder to achieve. Can't explain why as the Jabiru uses the Cessna code.Cheers,Roger

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Donny AKA ShalomarFly 2 ROCKS!!!Did you make a custom electrical system? The Cessna panel reads "low voltage" till engine start. Normally that light should stay off unless tested till some time after alternator failure. Also, during cranking the alternator produces enough juice to keep the battery charged. Maybe higher voltage or lower load is a factor in the difference. I made a report on the Cessna in the wicki topic FLY 2 Bugs.Best Regards, Donny

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