Why do props sometimes spin backwards after shutting down?

Re: Why do props sometimes spin backwards after shutting dow

PhilosopherPilot said:
As it was said in an earlier post, it can actually run backwards for a second or two upon shutdown of a hot engine. I've seen it. I've seen my dad's old POS car do it too, though you couldn't actually "see" it in that case, but it was the same thing. Hot spots and a little extra fuel...
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It is called dieseling or running the engine like a diesel engine that doesen't have spark plugs.
 
Re: Why do props sometimes spin backwards after shutting dow

Boris Badenov said:
This is true. Spinning a TPE331 backwards is a no-no and will get your hand slapped by the CP who is training you. Add to this that the -10s on an MU-2-60 spin the opposite direction from the -6s on a -36 and then ask me how I know. "Spin it TOWARDS THE BOOTS...<under breath> idiot".

I think maybe they're talking about pistons, though...
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Thanks, it's one of those things I heard from an old A&P and filed away without much more evidence, but it sounded reasonable. Yeah, I know they're referring to piston engines, but I was struck by mini's comment.
 
Re: Why do props sometimes spin backwards after shutting dow

Ever drive down the freeway and look at the wheels on a car? If the driver lets off the gas all of the sudden the wheels look like their going backwards....

Same dealio here.

RD
 
Re: Why do props sometimes spin backwards after shutting dow

As a quick aside, the only time you'll see the stroboscopic effect on wheels or props or what have you is with artificial light running off AC power (60hz) - The sun doesn't flicker.
 
Re: Why do props sometimes spin backwards after shutting dow

averyrm said:
As a quick aside, the only time you'll see the stroboscopic effect on wheels or props or what have you is with artificial light running off AC power (60hz) - The sun doesn't flicker.
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Wow... wrong wrong wrong... and you need to get out and drive more. We all have a refresh rate in our eyes as to how we see things. We don't see thing infinitely fast and hence why you don't see a big black prop in front of you at 2700RPM. You see the average over a given time period.

Think of it this way, say you could see at an interval of 1000 rpms. At 1100 RPM you would see a misty prop but since it's going a bit faster than you can see you only catch it when it comes around every 1/1000min, but it's going faster and you see it as if it's going forward.

If it's 900 RPM it would look as it's going backwards as you would expect to see it right in front of you but it hasn't gotten there yet. Next second, same thing, so on and so on. It looks like its going backwards but it's going forwards.

Just an example, a bad one, but hopefully some of you click onto the conversation.

I loved the rubber band comment.
 
Re: Why do props sometimes spin backwards after shutting dow

ProudPilot said:
Think of it this way, say you could see at an interval of 1000 rpms. At 1100 RPM you would see a misty prop but since it's going a bit faster than you can see you only catch it when it comes around every 1/1000min, but it's going faster and you see it as if it's going forward.
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Are? .... Are you saying it's possible to overclock me noggin?
 
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