Primarily for general aviation discussion, but other aviation topics are also welcome.
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By matthew_w100
#1810081
On this topic, can anyone explain why I stop my car engine by turning off the ignition, but I have to stop my plane engine by cutting the fuel and waiting while it drains the carb?
By Boxkite
#1810084
matthew_w100 wrote:On this topic, can anyone explain why I stop my car engine by turning off the ignition, but I have to stop my plane engine by cutting the fuel and waiting while it drains the carb?


It doesn't drain the carb.

Hang on a minute, what engine Matthew?
Last edited by Boxkite on Sat Nov 21, 2020 1:43 pm, edited 1 time in total.
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By skydriller
#1810089
matthew_w100 wrote:On this topic, can anyone explain why I stop my car engine by turning off the ignition, but I have to stop my plane engine by cutting the fuel and waiting while it drains the carb?


Good question (but dont think its a carb thing) Ive never thought about it because I drove tractors from a young age and thay have a similar pull to stop... so I just do it that way...

Regards, SD..
By johnm
#1810090
An aeroplane engine will spin down slowly and with the mags off fuel will simply explode in the cylinders and exhaust which is not a great idea.
matthew_w100 liked this
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By matthew_w100
#1810095
johnm wrote:An aeroplane engine will spin down slowly and with the mags off fuel will simply explode in the cylinders and exhaust which is not a great idea.



I think John has it - Rotax are often stopped by the ignition. Certainly in flexwings.

But we come full circle. That's exactly what you are doing with a mag dead cut!
By johnm
#1810096
I've seen a Rotax :D but all my flying has been behind Lycoming or Continental
By Boxkite
#1810097
johnm wrote:An aeroplane engine will spin down slowly and with the mags off fuel will simply explode in the cylinders and exhaust which is not a great idea.

What exactly would cause the fuel to explode in the cylinders John?
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By Miscellaneous
#1810099
matthew_w100 wrote:That's exactly what you are doing with a mag dead cut!

I think the risk is not so much switching the mags off, as it's switching them back on immediately.

johnm wrote:I've seen a Rotax :D but all my flying has been behind Lycoming or Continental

See if you can observe one being shut down. You'll discover they don't spin down slowly. In fact they don't spin down at all. They just stop. :wink:
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By skydriller
#1810101
johnm wrote:An aeroplane engine will spin down slowly and with the mags off fuel will simply explode in the cylinders and exhaust which is not a great idea.


How without the spark from the plugs if the magneto is off... diesel is different as its compression , hence the pull to stop on a tractor... what obvious thing am I missing?
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By matthew_w100
#1810105
skydriller wrote:
johnm wrote:An aeroplane engine will spin down slowly and with the mags off fuel will simply explode in the cylinders and exhaust which is not a great idea.


How without the spark from the plugs if the magneto is off... diesel is different as its compression , hence the pull to stop on a tractor... what obvious thing am I missing?


Huge inertia of the prop is what I was guessing. Much more than the flywheel on a car engine.

Rotaxes do stop violently - it feels quit horrid, rocking the whole plane. Less inertia in a wooden/plastic prop, and (possibly?) higher compression.
By Boxkite
#1810106
matthew_w100 wrote:On this topic, can anyone explain why I stop my car engine by turning off the ignition, but I have to stop my plane engine by cutting the fuel and waiting while it drains the carb?

What engine are you talking about Matthew?
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By matthew_w100
#1810107
Lycoming O320 (in a Beagle Pup) always cut off the fuel to shut down.

Rotax 912S (in a P&M Blade flexwing) switch off the mags to shut down. There is no mixture control, so no option!