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#21
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Engine stumble, Any thoughts?
allowing the fuel mixture to collapse before the new lower
velocity swirl pattern establishes itself... It is a lean stumble in my book.. Does anyone have a Cessna that does this? or might it be specific to the Piper/Beech installations? I have never encountered it on my 172M - and I lean a lot. |
#22
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Engine stumble, Any thoughts?
On 6 Dec 2005 04:22:14 -0800, "Denny" wrote:
snip for length, not content Now, if you go full rich mixture for a second, before retarding the throttle, they do not stumble... If you are leaned out and reduce throttle at a normal rate they will burble for a second... If you have been well trained, like my airplane has managed to make me, you instinctively know to just how fast you can creep the throttle back through that magic point so there is no stumble when leaned... Am a flat-lander that hasn't done a lot of hot/high TO's & L's. 99% of my pattern-to-approach-to-land has been full rich. When learning to properly manage a TIO-540, lean mixture was typically used during descent to help keep temps up/rate of change down, but any power reduction was relatively gradual-and the mixture knobs went to the panel entering the pattern. Have time working on/flying in a bunch of carb-d Pipers, but the Apache is one that I missed out on. My own pet theory, based on a life time of building - and breaking - engines is that there is a point where reducing angle of the throttle plate (butterfly), too rapidly and therefore reducing the air velocity rapidly, where the existing swirl pattern within the intake manifold collapses, allowing the fuel mixture to collapse before the new lower velocity swirl pattern establishes itself... It is a lean stumble in my book.. I'd buy into that one. Still flat-ass amazes me that a tractor carburetor works as well as it does. Have been around a bunch of Archers that stumbled on power reduction going downhill. Again, mixture ususally full rich, and what I would consider to be a relatively gradual power reduction. Screwed around with a couple of them with regard to playing with the mixture, engine relatively hot/cool, messed with plugs, timing, etc. Were company airplanes not a customer's, so really wasn't sticking it to anybody, just curious. Regards; TC |
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