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#11
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Wow! Ooops, take #3
On Friday, April 3, 2015 at 8:02:11 AM UTC-5, Dave Walsh wrote:
I think it says more about the technical competence of the engine designers; maybe God doesn't like them either? Well, crankshafts don't like to be loaded at their output location other than along the axis of rotation. Put a belt reduction drive on there, and you are applying load perpendicular to that. Interesting dynamics happen with a two cylinder in-line engine with this setup. It is not an easy system to design. Steve Leonard |
#12
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Wow! Ooops, take #3
On Friday, April 3, 2015 at 9:42:40 AM UTC-4, Steve Leonard wrote:
Well, crankshafts don't like to be loaded at their output location other than along the axis of rotation. Put a belt reduction drive on there, and you are applying load perpendicular to that. Interesting dynamics happen with a two cylinder in-line engine with this setup. It is not an easy system to design. Steve Leonard The failure is the prop hub (receiving end of belt reduction), not at the crankshaft. Last round was classic fatigue - nice crystalline structure on broken part. |
#13
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Wow! Ooops, take #3
On Friday, April 3, 2015 at 8:48:59 AM UTC-5, Dave Nadler wrote:
On Friday, April 3, 2015 at 9:42:40 AM UTC-4, Steve Leonard wrote: Well, crankshafts don't like to be loaded at their output location other than along the axis of rotation. Put a belt reduction drive on there, and you are applying load perpendicular to that. Interesting dynamics happen with a two cylinder in-line engine with this setup. It is not an easy system to design. Steve Leonard The failure is the prop hub (receiving end of belt reduction), not at the crankshaft. Last round was classic fatigue - nice crystalline structure on broken part. Same sort of issue. Up and down loading on that shaft due to increasing and decreasing tension because of engine dynamics and the loading going in and out of phase with the prop being in low or high moment of inertia relative to the motion (prop horizontal, low moment of inertia relative to motion created by pushing up and down by the drive belt). Likely source of the fatigue failure. But, as stated before, these are complex systems with lots of interactions. Be interesting to know the crack propagation direction relative to the blades on the prop. |
#14
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Wow! Ooops, take #3
On Thursday, April 2, 2015 at 4:44:59 PM UTC-4, Dave Nadler wrote:
Yikes. http://ad.easa.europa.eu/ad/2015-0052-E Sounds along the lines of this..... http://www.bugatti100p.com/web_docum...lvibration.pdf Sorta long read (the link), but curious to see results from the new AD. |
#15
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Wow! Ooops, take #3
On Friday, April 3, 2015 at 10:44:26 AM UTC-4, Steve Leonard wrote:
On Friday, April 3, 2015 at 8:48:59 AM UTC-5, Dave Nadler wrote: On Friday, April 3, 2015 at 9:42:40 AM UTC-4, Steve Leonard wrote: Well, crankshafts don't like to be loaded at their output location other than along the axis of rotation. Put a belt reduction drive on there, and you are applying load perpendicular to that. Interesting dynamics happen with a two cylinder in-line engine with this setup. It is not an easy system to design. Steve Leonard The failure is the prop hub (receiving end of belt reduction), not at the crankshaft. Last round was classic fatigue - nice crystalline structure on broken part. Same sort of issue. Yep. Up and down loading on that shaft due to increasing and decreasing tension because of engine dynamics and the loading going in and out of phase with the prop being in low or high moment of inertia relative to the motion (prop horizontal, low moment of inertia relative to motion created by pushing up and down by the drive belt). Likely source of the fatigue failure. But, as stated before, these are complex systems with lots of interactions. Be interesting to know the crack propagation direction relative to the blades on the prop. Crack propagation direction wasn't obvious on the broken part I saw. Propagation *appeared* to have started at stress points from inadequate flange radius and/or rough machining marks. Not my area of expertise! See ya, Dave |
#16
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Wow! Ooops, take #3
I have seen a picture of the fracture. Could be a brittle fracture, but
can't say for sure without having seen it live... I am sure Solo will be on to it. Engine apparently was run well within operating limits, had very low time and had the mandatory SB performed (new part failed). |
#17
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Wow! Ooops, take #3
On Friday, April 3, 2015 at 6:02:44 AM UTC-7, John Galloway wrote:
At 07:46 03 April 2015, Tango Whisky wrote: It affects ONLY 2350C engines with non-foldable propellor. That's DG1000T in the first place (which caused the AD) and probably J'S. S-H is not concerned (and I'll use it on my Ventus cM). Also the turbo Antares - or at least the prototype according to this: https://www.youtube.com/watch?v=-mxwvd-ps2A Try buying an Antares 23, they are not even being made. |
#18
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Wow! Ooops, take #3
On Thursday, April 2, 2015 at 2:44:59 PM UTC-6, Dave Nadler wrote:
Yikes. http://ad.easa.europa.eu/ad/2015-0052-E Based on Mr Nadler's description, failure more or less inevitable. Too small a radius will reduce the part's fatigue limit by somewhere between one third and one half roughly speaking. A 90 degree non-radius would result in a more or less infinite reduction in the fatigue limit (which is the stress on a part below which it should have an infinite fatigue life; in the real world all sorts of things reduce this limit, as we are seeing). Rough machining can be even more insidious. Each piece of rough machining that you can see by eye is more or less the same as an already existing early fatigue crack. Its root radius at a microscopic level is effectively infinite with a corresponding reduction in the fatigue limit. Very bad news especially when it happens at a designed in place of inherently high stress. All they had to do was to add some hard chromium plate on any wear surface that ran around the radius and failure would have been even earlier. Pretty basic stuff. For it to have been repeated, as seems to have happened after a known problem, amounts to extreme carelessness. |
#19
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Wow! Ooops, take #3
On Friday, April 3, 2015 at 5:25:34 PM UTC-4, howard banks wrote:
On Thursday, April 2, 2015 at 2:44:59 PM UTC-6, Dave Nadler wrote: Yikes. http://ad.easa.europa.eu/ad/2015-0052-E Based on Mr Nadler's description, failure more or less inevitable. Too small a radius will reduce the part's fatigue limit by somewhere between one third and one half roughly speaking. A 90 degree non-radius would result in a more or less infinite reduction in the fatigue limit (which is the stress on a part below which it should have an infinite fatigue life; in the real world all sorts of things reduce this limit, as we are seeing). Rough machining can be even more insidious. Each piece of rough machining that you can see by eye is more or less the same as an already existing early fatigue crack. Its root radius at a microscopic level is effectively infinite with a corresponding reduction in the fatigue limit. Very bad news especially when it happens at a designed in place of inherently high stress. All they had to do was to add some hard chromium plate on any wear surface that ran around the radius and failure would have been even earlier. Pretty basic stuff. For it to have been repeated, as seems to have happened after a known problem, amounts to extreme carelessness. To be clear: The failed part I examined in fall 2013 was a "take #2" part. The part was redesigned for "take #3", "resolving" the 2013 AD. The new "take #3" part failed, leading to the most recent AD. I have no idea what the failure of "take #3" looks like... It is a bit surprising that 3 iterations of this part have failed... But it is not an easy problem! Hope that is clear, Best Regards, Dave |
#20
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Wow! Ooops, take #3
On Friday, April 3, 2015 at 5:34:23 PM UTC-4, Dave Nadler wrote:
On Friday, April 3, 2015 at 5:25:34 PM UTC-4, howard banks wrote: On Thursday, April 2, 2015 at 2:44:59 PM UTC-6, Dave Nadler wrote: Yikes. http://ad.easa.europa.eu/ad/2015-0052-E Based on Mr Nadler's description, failure more or less inevitable. Too small a radius will reduce the part's fatigue limit by somewhere between one third and one half roughly speaking. A 90 degree non-radius would result in a more or less infinite reduction in the fatigue limit (which is the stress on a part below which it should have an infinite fatigue life; in the real world all sorts of things reduce this limit, as we are seeing). Rough machining can be even more insidious. Each piece of rough machining that you can see by eye is more or less the same as an already existing early fatigue crack. Its root radius at a microscopic level is effectively infinite with a corresponding reduction in the fatigue limit. Very bad news especially when it happens at a designed in place of inherently high stress. All they had to do was to add some hard chromium plate on any wear surface that ran around the radius and failure would have been even earlier. Pretty basic stuff. For it to have been repeated, as seems to have happened after a known problem, amounts to extreme carelessness. To be clear: The failed part I examined in fall 2013 was a "take #2" part. The part was redesigned for "take #3", "resolving" the 2013 AD. The new "take #3" part failed, leading to the most recent AD. I have no idea what the failure of "take #3" looks like... It is a bit surprising that 3 iterations of this part have failed... But it is not an easy problem! Hope that is clear, Best Regards, Dave I'm NOT an "ME", I'm a field service guy with a "ME" background (as well as spending a lot of time fixing "good enough bits" on many different types of machines.....). My link before was to show that there are quite a few factors to consider (not that anyone here know all the facts or can direct the final decision). Just pointing out that some failures have been hit before, thus a research can find a suitable resolution. "Thus that ignore history are doomed to fail in the same manner"..... or close to that.... |
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