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Mystery Vibration - 74 Cherokee 140
Plugs might be clean but the resistor in them can fail or
conduct intermittently, weakening the spark. It won't usually show up during a mag check, but in cruise, if the mags aren't timed exactly the same, the plug that fires first causes a pressure rise in the cylinder that the defective plug now has trouble sparking against. Plugs need to be tested in a pressure-type spark tester, and even then they can act up when hot. Dan |
#12
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Mystery Vibration - 74 Cherokee 140
The Visitor wrote:
: I remember finding some play in the stab on my Seneca. So the shop : replaced the bushings. I am going to look in the tech logs to see if the : bolts were also done. If not, I'll have it done. It's a 83 model. : 125,000 lp tensile strength on those bolts though I believe. Yeah... when I was replacing the bolts/bearings on mine, I did a quick calculation just to make sure. I don't remember the exact numbers, but each one is in double-shear (both sides of the bearing). That's 4 cross-sections of 1/4" to split the load over. Not super-special bolts, either... just regular AN stuff. Anyway, from what I remember, my computation on the shear strength of the bolts concluded that I could pick up the airplane loaded at gross weight by just the tail, and then shake it with 4G's before the bolts would shear.... Now, that doesn't say anything about excess material for corrosion resistance, stress risers due to corrosion, or other strength-reduction due to wear. As long as it's in good shape however, nothing to worry about... just seemed too small. -Cory -- ************************************************** *********************** * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * ************************************************** *********************** |
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Mystery Vibration - 74 Cherokee 140
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#14
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Mystery Vibration - 74 Cherokee 140
Thank you for the comments. They are most reassuring.
I'll "second" that -- thanks for that data, Cory! I've always looked at those stabilator attach points and quickly averted my eyes, cringing. They look soooo small! Of course, take a look at how a 172s wing attaches, and you'll never fly one of those again. Yet they've never had a wing failure. All I can say is: Thank goodness for engineers who can figure this safety stuff out. -- Jay Honeck Iowa City, IA Pathfinder N56993 www.AlexisParkInn.com "Your Aviation Destination" |
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