Beep beeeep beep STFU!! Alternator question

James331

James331

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James331
Hey guys, so I just noticed after flying today, while on the ground after a .7 flight in 0C - -10C OATs I have that dang beeeep beeeep beeeep slightly tied into RPM very faint in my headset, if I turn the alternator off it doesn't do it anymore, what's the fix for that, other than not turning the alternator on lol


Thanks!
 
Report the bird strike and clean the intake maybe?
 
bluerooster said:
A filter capacitor?
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Thanks!


And to my fellow trolls
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I'm guessing that moisture froze and caused a ground to run amuck. That or the plane was whining for an AOA to be installed.
 
James331 said:
Hey guys, so I just noticed after flying today, while on the ground after a .7 flight in 0C - -10C OATs I have that dang beeeep beeeep beeeep slightly tied into RPM very faint in my headset, if I turn the alternator off it doesn't do it anymore, what's the fix for that, other than not turning the alternator on lol


Thanks!
Click to expand...

Did you change anything to do with the headset jacks? They should be insulated from the airframe; if they're grounded they tend to pick up alternator noise and sometimes strobe whine.

What airplane is it?
 
If a bigger hammer doesn't do the job, you have to call an electrician.
 
Find somebody with an oscilloscope and do a signal trace on your main power bus. If the ripple traces aren't of equal amplitude, you have a failing diode in your alternator. If they are, then you probably have a power wire routed to close to a sensitive RF cable, or a corroded ground. A filter might mask the problem, but it won't solve it. Many alternators come equipped with an RF filter from the factory.
Before ya spend any money, ya might start by cleaning the main airframe and engine mount grounds just on principle.
 
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Sounds like ripple current from the alternator is getting into the aircraft ground. Maybe a bad engine ground? Make sure that the earphone output jacks are isolated one BOTH terminals and have a wire connection back to the electronics ground at the Intercomm output (or whatever............)

If you can't get access to an oscilloscope to check the alternator diode bridge, listen critically to the tone of the noise. If only one of the three phases is out, there will be a new undertone sub-harmonic superimposed on the fundamental alternator whistle. If two phases are out, the whistle will be gone and the only thing left will be a much lower hum.
 
Had a problem recently with one of our 172s. It was reported to me that there was in flight static coming over the radios that made it impossible to communicate with the controllers.

I headed to the airport, fired it up, taxied it around and all the radios and intercom worked just fine. Did a run-up to full power and everything was crystal clear even with every noise inducing item possible turned on.

Decided to take it around the pattern. The *moment* the wheels departed the ground an amazing quantity of really loud static flooded my headset. I messed with the volumes for the radios and the intercom and determined that the noise was coming entirely through the intercom system. Putting the intercom into PILOT OR CREW resolved the noise. Turning off the alternator or any of the electronics made no difference.

On landing the noise immediately stopped as soon as the tires touched the ground again.

It turns out that all of the headset jacks were wired to airframe ground (they shouldn't have been). Correcting that fixed the issue.

Why it worked fine when it was wired that way for at least 5 years then suddenly became a problem? Not sure...
 
Thanks guys!!

I'd imagine the jacks are good, based on the plane having a full panel job done with the last owner, but I'll still start checking connections, I'll also try to listen again, maybe I'll record it and upload it too.

Just thinking if I know anyone who knows anyone with a scope....
 
Sure would be cool if intercoms could silence one mic input at a time in a troubleshooting/maintenance mode and possibly isolate a channel that is acting up.
 
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