If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
Vibration Testing
I've come across a marvelously cheap vibration sensor that I want to convert
into an engine vibration instrument for a Kitplanes article. The electronics for me is relatively trivial...the mechanics of vibration are a little harder to fathom. From a mechanical engineering point of view on a horizontally opposed engine, there are (as with most things) three axes of freedom -- fore and aft, side to side, and up and down (longitudinal, lateral, vertical). The sensor I have reads two axes, and my hit is that fore-aft is the least interesting vibration mode of the engine. The question is whether to have a two-channel meter (which complexes up both the design AND the panel space), a single meter switchable between lateral and vertical) or a single meter with the two axes summed together. Comments and thoughts from the technonerds amongst us appreciated. (It has nothing, repeat NOTHING to do with the fact that such a meter might have detected a crack in that cylinder WAY BEFORE it departed the engine on the way home from Oshkosh {;-) ) Jim Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#2
|
|||
|
|||
Thirty years ago I worked for a company by the name of IRD Mechanalysis.
Their business was vibration detection, monitoring and analysis for preventive maintenance of heavy machinery. At that time they were a subsidiary of H H Robinson Company, a construction company based in Pittsburgh PA. We built our own crystal-transducers to work with the monitoring equipment. I never worked in the analysis end of the business, so I cannot tell you where the frequencies indicating "good" and "bad" lie. Each device is different. A problem with each component was indicated by a different frequency. The only aviation use I am aware of was to dynamically balance props. Jim Weir wrote: I've come across a marvelously cheap vibration sensor that I want to convert into an engine vibration instrument for a Kitplanes article. The electronics for me is relatively trivial...the mechanics of vibration are a little harder to fathom. From a mechanical engineering point of view on a horizontally opposed engine, there are (as with most things) three axes of freedom -- fore and aft, side to side, and up and down (longitudinal, lateral, vertical). The sensor I have reads two axes, and my hit is that fore-aft is the least interesting vibration mode of the engine. The question is whether to have a two-channel meter (which complexes up both the design AND the panel space), a single meter switchable between lateral and vertical) or a single meter with the two axes summed together. Comments and thoughts from the technonerds amongst us appreciated. (It has nothing, repeat NOTHING to do with the fact that such a meter might have detected a crack in that cylinder WAY BEFORE it departed the engine on the way home from Oshkosh {;-) ) Jim Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#3
|
|||
|
|||
john smith writes:
Thirty years ago I worked for a company by the name of IRD Mechanalysis. Their business was vibration detection, monitoring and analysis for preventive maintenance of heavy machinery. I remember them. We used it on pumps. Here "pump" mean 17-stage centrifugal with a 800 HP motor that runs on 3-phase 4160vac. As I recall, it took a fair amount of training to interpret the results. -- A host is a host from coast to & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 |
#4
|
|||
|
|||
"Jim Weir" wrote in message ... Comments and thoughts from the technonerds amongst us appreciated. I suppose it depends what you're going to do with the data. If it's just an idiot sensor that something is going wrong with the engine, probably a sum of the total vibration would be best. If you're trying to test something, two meters would be better than one (either summed or switched). Frankly I kindof detest switched meters. I replaced that kludge in the navion with individual fuel gauges. Seems like the hifi apps should have some stereo vu-meters available, I know you used to be able to get a stereo bar graph led display at RadioSnack a few years back. |
#5
|
|||
|
|||
In article ,
Jim Weir wrote: I've come across a marvelously cheap vibration sensor that I want to convert into an engine vibration instrument for a Kitplanes article. If you really wanted to try to diagnose problems with it you should try to couple it to RPM. Then you could measure vibration in terms of the order relative to the moving parts. If you could include the phase of the crankshaft you could probably spit out enough information to do a dynamic prop balance on a serial port. Alternatively you might be able to infer RPM by doing an FFT on the raw data. That would be a neat party trick. As far as mounting it seems like getting it as far forward as possible (where you should see the largest magnitudes) would be good. And if you only get 2 axes then I'd go with your idea and ignore push/pull and keep side/side and up/down. -- Ben Jackson http://www.ben.com/ |
#6
|
|||
|
|||
I don't think serial ports need dynamic prop balancing.
You guys sure know how to complex up a bonehead simple idea, don'cha? {;-) Jim (Ben Jackson) shared these priceless pearls of wisdom: If you could include the phase of the -crankshaft you could probably spit out enough information to do a dynamic -prop balance on a serial port. Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#7
|
|||
|
|||
Forgot to add that
- the detection boxes were single channel - the transducers were moved to each axis and the data collected - the detection boxes had a built in strobe circuit to independently measure RPM Ben Jackson wrote: In article , Jim Weir wrote: I've come across a marvelously cheap vibration sensor that I want to convert into an engine vibration instrument for a Kitplanes article. If you really wanted to try to diagnose problems with it you should try to couple it to RPM. Then you could measure vibration in terms of the order relative to the moving parts. If you could include the phase of the crankshaft you could probably spit out enough information to do a dynamic prop balance on a serial port. Alternatively you might be able to infer RPM by doing an FFT on the raw data. That would be a neat party trick. As far as mounting it seems like getting it as far forward as possible (where you should see the largest magnitudes) would be good. And if you only get 2 axes then I'd go with your idea and ignore push/pull and keep side/side and up/down. |
#8
|
|||
|
|||
john smith wrote: Forgot to add that - the detection boxes were single channel - the transducers were moved to each axis and the data collected - the detection boxes had a built in strobe circuit to independently measure RPM Ben Jackson wrote: In article , Jim Weir wrote: I've come across a marvelously cheap vibration sensor that I want to convert into an engine vibration instrument for a Kitplanes article. If you really wanted to try to diagnose problems with it you should try to couple it to RPM. Then you could measure vibration in terms of the order relative to the moving parts. If you could include the phase of the crankshaft you could probably spit out enough information to do a dynamic prop balance on a serial port. Alternatively you might be able to infer RPM by doing an FFT on the raw data. That would be a neat party trick. As far as mounting it seems like getting it as far forward as possible (where you should see the largest magnitudes) would be good. And if you only get 2 axes then I'd go with your idea and ignore push/pull and keep side/side and up/down. Weeel--kinda depends on whether you got a heavy metal prop, or a piece'o tree mounted in the prop flange---the gyroscopic inertia of that 40# hunka 'luminum kinda resists vibrating--I think the assend of the engine would kinda describe a jitterbug motion around the nose of the crank.--If the prop is balanced, then a "new" vibration introduced into the system would probably be detected easier with a rear mounted pickup...'Course a wood prop & a front cylinder goin bad might change the scenario somewhat. Y'all run a test & let me know!! |
#9
|
|||
|
|||
Jim Weir wrote: The sensor I have reads two axes, and my hit is that fore-aft is the least interesting vibration mode of the engine. The question is whether to have a two-channel meter (which complexes up both the design AND the panel space), a single meter switchable between lateral and vertical) or a single meter with the two axes summed together. My take is that summing the two axes would be perfectly acceptable. I agree that fore-and-aft is unlikely to produce any interesting results. In fact, I'd bet that any mechanical problem would show up as an increase in lateral vibration. Vertical vibration would tend to occur only just before things come apart, IMO. George Patterson If a man gets into a fight 3,000 miles away from home, he *had* to have been looking for it. |
#10
|
|||
|
|||
Jim if the sensors are that cheap why not just use two mounted 90 degrees
apart. If its analog output you could just sum the two together to get ~total vibration or convert to digital feed a cheap microprocessor chip and display all three. Logging all three channels would let you post process the data all you want and would not be all that difficult. John Jim Weir wrote: I've come across a marvelously cheap vibration sensor that I want to convert |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Vibration Testing | Jim Weir | Home Built | 20 | October 10th 04 07:22 AM |
Testing Stick Ribs | Bob Hoover | Home Built | 3 | October 3rd 04 02:30 AM |
Survey - 3 blade prop conversion- Cockpit vibration, happy or not | Fly | Owning | 20 | June 30th 04 05:32 PM |
Stupid question about flight testing and "the envelope" | Scott Ferrin | Military Aviation | 12 | January 7th 04 03:56 AM |
Torsional Vibration Testing | B2431 | Home Built | 8 | July 25th 03 07:15 AM |