A recent good thread on alternator failures got me to thinking about how often we see people posting about aircraft or component problems, and folks contributing their ideas on the solution or potential reason for the issue. I find it interesting that people are frequently willing to accept ideas when, in fact, very little detail has been brought out on the actual reason for the problem. In failure analysis terms, we rarely get down to ?Root Cause? ? and that is what we really need to do if we want to solve problems, especially safety problems.
I?ll use the ever-popular alternator failure as an example, and hope that I don?t offend anyone (because this is a generic discussion ? the thread I mentioned above started out with a very clear finding by the author that the problem was a broken pin on a connector). ?My alternator failed? is a common first statement. Sometimes, what a person really means is that they are no longer getting charging voltage on their main bus. Sometimes, they know exactly what happened, but it still comes across as ?the alternator failed?. I have seen a lot of ?I no longer get charging voltage on the bus? failures, and an equally large number of root causes. Sometimes, the Voltage Reg failed (due to heat, vibration, etc). Sometimes, the bearings are shot (which could be due to side load, vibration, poor quality to begin with). I have seen wiring failures of course (either main feed or the excitation leads, wire breaks, bad crimps, fatigue breaks due to vibration?). Sometimes the alternator case casting fractures ? that?s a good one! The ears break off, or the bearing structure fails. Shorted windings happen, but are rarer. OK ? how about bracket failures ? I have seen bolt-holes wallowed out, broken mounts, and mounts that have FALLEN OFF THE ENGINE BOSS! Adjustment arms get loose, loosening the belt, or allowing the alternator to move around and cause one of the above-mentioned vibration failures. And of course, sometimes an airplane has a short or open wire between the alternator and the main bus ? nothing to do with the alternator, but ?no charging? is the end result.
The point with this long but non-exhaustive list is simple ? you need to understand the root cause of a failure before you can fix it. And imprecise definitions of the failure don?t help anyone else if they are trying to build (or maintain) their airplane. It also doesn?t help the various manufacturers of alternators, as rumors about an unreliable product are usually false, and can cause people to choose something else for incorrect reasons. RV?ers tend to use a wide variety of alternators ? from the rebuilt ND auto units to custom-modified and cherry-picked high quality units sold at ?almost-certified? prices. The interesting thing is that without exception, there are folks that have had extremely good results with any of the choices ? and others that have had extremely bad results with any of the choices. But unless you look at the root cause of the failure, you can?t really make an informed decision on which way to go.
To be honest, most ?alternator failures? I have looked at have not been then fault of the alternator! Voltage regulators that get too hot and badly aligned (or loose) mounts have topped the list over the years. Too much tension on the belt can really eat things up, and too little can lead to voltage sag. Connections and strain relief are the other biggies. None of which are truly ?alternator failures? ? rather, they can be traced back to installation problems. Again?.root cause.
If you really want to help the community grow and develop more reliable installations, tracing back to the actual problem is invaluable ? and not doing so will send many people off on wild goose chases. Determining Root Cause is sometimes difficult, but extremely valuable if you really want to fix your problems ? and help others avoid them!
Paul
I?ll use the ever-popular alternator failure as an example, and hope that I don?t offend anyone (because this is a generic discussion ? the thread I mentioned above started out with a very clear finding by the author that the problem was a broken pin on a connector). ?My alternator failed? is a common first statement. Sometimes, what a person really means is that they are no longer getting charging voltage on their main bus. Sometimes, they know exactly what happened, but it still comes across as ?the alternator failed?. I have seen a lot of ?I no longer get charging voltage on the bus? failures, and an equally large number of root causes. Sometimes, the Voltage Reg failed (due to heat, vibration, etc). Sometimes, the bearings are shot (which could be due to side load, vibration, poor quality to begin with). I have seen wiring failures of course (either main feed or the excitation leads, wire breaks, bad crimps, fatigue breaks due to vibration?). Sometimes the alternator case casting fractures ? that?s a good one! The ears break off, or the bearing structure fails. Shorted windings happen, but are rarer. OK ? how about bracket failures ? I have seen bolt-holes wallowed out, broken mounts, and mounts that have FALLEN OFF THE ENGINE BOSS! Adjustment arms get loose, loosening the belt, or allowing the alternator to move around and cause one of the above-mentioned vibration failures. And of course, sometimes an airplane has a short or open wire between the alternator and the main bus ? nothing to do with the alternator, but ?no charging? is the end result.
The point with this long but non-exhaustive list is simple ? you need to understand the root cause of a failure before you can fix it. And imprecise definitions of the failure don?t help anyone else if they are trying to build (or maintain) their airplane. It also doesn?t help the various manufacturers of alternators, as rumors about an unreliable product are usually false, and can cause people to choose something else for incorrect reasons. RV?ers tend to use a wide variety of alternators ? from the rebuilt ND auto units to custom-modified and cherry-picked high quality units sold at ?almost-certified? prices. The interesting thing is that without exception, there are folks that have had extremely good results with any of the choices ? and others that have had extremely bad results with any of the choices. But unless you look at the root cause of the failure, you can?t really make an informed decision on which way to go.
To be honest, most ?alternator failures? I have looked at have not been then fault of the alternator! Voltage regulators that get too hot and badly aligned (or loose) mounts have topped the list over the years. Too much tension on the belt can really eat things up, and too little can lead to voltage sag. Connections and strain relief are the other biggies. None of which are truly ?alternator failures? ? rather, they can be traced back to installation problems. Again?.root cause.
If you really want to help the community grow and develop more reliable installations, tracing back to the actual problem is invaluable ? and not doing so will send many people off on wild goose chases. Determining Root Cause is sometimes difficult, but extremely valuable if you really want to fix your problems ? and help others avoid them!
Paul
Same with using the proper nuts......firewall forward, etc. If you never read the Internet forums during the building process, you might never know!
