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#1
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Shutting down engine Question
Perhaps this doesn't matter much for a non-turbocharged engine,
but an instructor says that it is best to idle the engine at 1,000 RPM for a few moments before Mixtu Idle Cut-Off at that RPM to shut down. The POH says throttle full aft, then mixture cut-off to shut down. Which is best? |
#2
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"Lisa" wrote in message ...
Perhaps this doesn't matter much for a non-turbocharged engine, but an instructor says that it is best to idle the engine at 1,000 RPM for a few moments before Mixtu Idle Cut-Off at that RPM to shut down. I doubt 1000 RPM is an idle setting for most piston aircraft engines. Probably best to avoid confusing the issue by not using the word "idle" when you don't really mean having the throttle set to idle. With that out of the way, I don't see any compelling reason to run a non-turbo engine prior to shutdown. I suppose that if you also lean the mixture, you might get rid of some plug fouling, but if you're having trouble with plug fouling, you can better address the issue operationally by making sure the engine is leaned during taxi. Obviously, with a turbocharger, allowing the engine to run prior to shutdown is a good way to help circulate engine oil through the turbo and allow it to cool down more gradually, and without cooking the oil. AFAIK, whether you do this at 1000 RPM or at idle is less important than whether you do it at all. But with a non-turbo engine, I don't see why idling or running the engine at 1000 RPM would be beneficial, as a general rule of thumb (allowing for the possibility of some particular instance where it might be useful). What reason does this instructor to which you refer give for running the engine at 1000 RPM prior to shutdown? Also, what does "a few moments" mean? To me, that's less than five seconds, which I can't imagine would make a difference in any case. Pete |
#3
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Peter Duniho wrote:
What reason does this instructor to which you refer give for running the engine at 1000 RPM prior to shutdown? Also, what does "a few moments" mean? To me, that's less than five seconds, which I can't imagine would make a difference in any case. Some engines seem to shake a whole lot less on shutdown when set to 1000 RPM. Hilton |
#4
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"Hilton" wrote in message
ink.net... Some engines seem to shake a whole lot less on shutdown when set to 1000 RPM. Then the instruction should be to *set* engine power 1000 RPM before shutting down. Telling a pilot to run the engine at 1000 RPM before shutting down is ambiguous and could (probably will) lead to the pilot simply reducing RPM before pulling the mixture, after running the engine at 1000 RPM. Especially if the instruction is to run the engine at 1000 RPM "for a few moments" (which would clearly imply to reduce RPM again before actually shutting the engine down). Pete |
#5
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Peter Duniho wrote:
Hilton wrote: Some engines seem to shake a whole lot less on shutdown when set to 1000 RPM. Then the instruction should be to *set* engine power 1000 RPM before shutting down. Telling a pilot to run the engine at 1000 RPM before shutting down is ambiguous and could (probably will) lead to the pilot simply reducing RPM before pulling the mixture, after running the engine at 1000 RPM. Especially if the instruction is to run the engine at 1000 RPM "for a few moments" (which would clearly imply to reduce RPM again before actually shutting the engine down). Quoting the full sentence: "...an instructor says that it is best to idle the engine at 1,000 RPM for a few moments before Mixtu Idle Cut-Off at that RPM to shut down." So the CFI wanted Lisa to shutdown "...at that RPM" and this does not "...clearly imply to reduce RPM". Hope that clarifies it. Hilton Hilton |
#6
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"Hilton" wrote in message
ink.net... [...] So the CFI wanted Lisa to shutdown "...at that RPM" and this does not "...clearly imply to reduce RPM". It does to me. "A few moments before" could even be reasonably interpreted as "run the engine at 1000 RPM for any period of time, but make sure there are a few moments between reducing engine speed and shutdown". Hope that clarifies it. I think you're pretty foolish to think that the original instruction was not ambiguous. The fact that we're even having this discussion proves that it is. Pete |
#7
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On Tue, 30 Mar 2004 21:38:31 -0500, Lisa wrote:
Perhaps this doesn't matter much for a non-turbocharged engine, but an instructor says that it is best to idle the engine at 1,000 RPM for a few moments before Mixtu Idle Cut-Off at that RPM to shut down. The POH says throttle full aft, then mixture cut-off to shut down. Which is best? On hot days, the O-300 in the 'Hawk tends to diesel on after you pull the mixture. Opening the throttle a little makes it stop. Don |
#8
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Don Tuite wrote in message . ..
On hot days, the O-300 in the 'Hawk tends to diesel on after you pull the mixture. Opening the throttle a little makes it stop. Don, Sounds like you have a fuel leak into the manifold. Pulling the mixture to cutoff should, well, cut off the fuel flow. This could be something in your carb, or might be a leak in your primer system. Either way, it shouldn't continue to run after you've cut off the fuel supply. That's an indication of a problem in the fuel system. John Galban=====N4BQ (PA28-180) |
#9
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John Galban wrote:
Don Tuite wrote in message . .. On hot days, the O-300 in the 'Hawk tends to diesel on after you pull the mixture. Opening the throttle a little makes it stop. Don, Sounds like you have a fuel leak into the manifold. Pulling the mixture to cutoff should, well, cut off the fuel flow. This could be something in your carb, or might be a leak in your primer system. Either way, it shouldn't continue to run after you've cut off the fuel supply. That's an indication of a problem in the fuel system. John Galban=====N4BQ (PA28-180) Concur. Our O-300 has never dieseled. We do have a problem with fouled bottom plugs though. I never thought it was related to shutdown procedure until this thread, but now I will consider it. Always thought it was too much priming. -- Frank....H |
#10
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This is the procedure we use on our O-320 and have had noticeably smoother
and quicker starts since we started it: RPM - 1200 Lean for maximum RPM rise. (Don't worry, no amount of leaning will hurt the engine at this low power) Run 20 seconds Throttle - Quickly to Idle Mixture - Idle Cut Off Switches - OFF Leaning for all ground operations is vital to keep the mags clear on this engine. On startup and after exiting the active runway, set RPM to 1000 and lean slowly for maximum RPM rise. This will often be about 100. Lean slightly past until RPM just starts to fall. If the engine runs a hair rough, that's OK. It will be lean enough that it will start to stumble and quit if you try to run it faster than about 1300. This means you can't accidentally take off with it leaned. Since we started doing this, I have only had to clear a mag a couple of times in two years. Speaking of idle. Lubrication is poor on startup and especially critical in this engine. The parts most susceptible to damage are the camshaft and lifters. It is counter intuitive but, due to the valve train dynamics, the stresses become less the faster the engine turns. Running at minimum idle while it "warms up" actually is harder on the parts most likely to wear. As soon as the oil pressure gets into the green, set the RPM to 1000 and lean. Keep the RPM at 1100 on the ground whenever this will not require rolling use of the brakes. RPM over 1000 also gets combustion temperature high enough to scavenge lead deposits and reduce plug fouling. -- Roger Long |
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