Alternator whine

[On Patrol]

My 160 and I were flying back from Utah and through the noise attenuating headsets I start to hear what is a bearing whine. I thought on the way out one cold morning that I heard a squeal on start up but it went away. In denergizing the field of the alternator it goes away. I do not know if it is the belt or the alternator itself. Any diagnostic suggestions???
Thanks
FMD

 

[cubdriver2]

John, you should talk to Tim, when it comes to whining he has a lot of experence in that field

Glenn

 

[cubamigo]

John, When you were leaving PIA Saturday i was standing near your plane. the first 30 seconds after you started your cub, the alternator was squealing. sounded internal but check the belt to see if it is loose. sounded like a turbine spooling up!

 

[On Patrol]

The belt seems fine as it was the firt thing I checked. The noise is worse on the startup like you said but it does go away to the pont of a whine at higher RPMs in flight can barely be heard over the engine noise.
I will get a better look this weekend.
John

 

[Fortysix12]

Starter still engaged as in not disengaging?

 

[btracy]

John sounds like a bearing showing its first sign of failure. Right after start up the alternator is recharging the battery and pulling a heavy load and putting more pressure on the bearing making it squeal. After the battery is back to a charged state the alternator is not working as hard. Deenergizing it is causing the same symptom.

 

[SteveE]

I sometimes hear a whine in my headset when the alternator is charging hard,, but the noise quits when it stops charging. Some sort of filter probably would fix it,, Plane Power alternator.

 

[On Patrol]

Hi Steve,
No it is an external noise. I have a switch for the field and when it is energized I hear the noise more pronounced like Bill says. It becomes lighter as time goes on but it is different from normal.
I am being told externally that it is a screech on start this past weekend. Probably need to take a close look as the annual is coming up the end of the month.
John

 

[bjh356]

After a quick search for “engine whine” I’m wondering if what started recently (1.5-3 hrs ago) on my cub is related to the alternator. This evenings 1.5 hour flight was to learn/educate about where and why this whine is present. Noise is external to headset. Can turn off all electrical loads and alternator field and noise persists. Tonight the noise did not present until approx 5-10 min into flight. Higher RPMs more pronounced and oddly enough nose high attitude reduces or nearly makes noise go away altogether. Nose down attitude amplifies the “whine”. No visible wear on internal of cowl near ring gear. Alternator belt visibly in tact and unworn (no fraying or chord showing). I have BC400 System with approx 100 hours operation under its belt.
Another potentially related symptom was when I witnessed the system voltage (as shown on Garmin 495) go from 13.9, which is nearly always the charging voltage on my bus go from 13.9 to 13.7 to 14.4 to 13.8 and eventually stabilize back at 13.9. So not directly related to the noise whine but a correlation for those that know more about this potential issue than myself. Can see this jump in my video when nose down to nose high changes

 

[Kid Durango]

This sounds dumb, but I have that sound as well. But I can trace it to the fairing at the wing root. It changes with the air movement, and not the engine. Sounds exactly as yours. I don’t get it all the time. You didn’t say if you have it on the ground, or all the time. If an alternator I would think you would have it anytime engine is running, and it might vary with load.

 

[bjh356]

Not present at startup. Can make the noise go away with reduction of RPM below approximately 2000 or as seen in the video with nose high attitude. Last flight it came about approx 5-10 min after takeoff. Once it comes about, it’s more or less audible at all phases of flight except again that nose high attitude. Approach to landing with low RPM it’s not present. So a high RPM nose low it’s amplified but a nose low, low ROM and nothing. Definitely something new. Thanks for sharing your idea. I’ll be checking wing root fairing just to ensure it’s secure etc.

 

[stewartb]

This sounds dumb, but I have that sound as well. But I can trace it to the fairing at the wing root. It changes with the air movement, and not the engine. Sounds exactly as yours. I don’t get it all the time. You didn’t say if you have it on the ground, or all the time. If an alternator I would think you would have it anytime engine is running, and it might vary with load.

I had that in my -12. It was a whistle from air passing over the float rudder retract tube, which had been in place for some time. Not easy to find. No idea why it started when it did.

 

[bjh356]

Took N8086D out after work for ~1HR. Before flight I gave cowl, baffling and engine compartment another thorough visual for any mechanical wear or loose bits. Even taped over the float retract tube and checked wing roots for security. I’m definitely gaining confidence that there is something amiss with the BC400 system. I’ll have to get the exact number that the system has been installed on the plane but I’d guess around the 100 hr mark. Like new if you were to ask me.


I did as many controlled and intentional videos I could think of with B and C and others around the airfield here in Juneau’s input.


As you will tell from my links, the voltage is far from steady through all phases of my 1hr test flight. I’ve never seen anything other than 13.9 on my Garmin 496 until the other day when this whine came about. How sensitive and accurate the readout is on the 495, is anybody’s guess but I’d say it’s telling me something in conjunction with the whine.


Why the whine decreases during a climb, couldn’t tell you that either. Whine continues to be manageable with reduction in RPMs below approx ~2000 or with a climb attitude.


Why the whine isn’t present from startup through entirety of flight I don’t know either. I’d say this last flight whine wasn’t as persistent as my previous 1.5 hour flight on 20Aug23 but still very much noticed.


Without further ado:


https://youtu.be/8TfRf0_O1Ys
https://youtu.be/IbPXTU2IBrA
https://youtu.be/Cnsmu0_BWA0
https://youtu.be/11_gG_WNvyM
https://youtu.be/7NYU7qFa3mo

 

[stewartb]

I’m curious about your voltage. I have two B&C alternators and LR-14 regulators and both run at 14.4v. I’ve never seen a variation up or down greater than .1 volt.

No actual aircraft instrument for volts or amps?

 

[bjh356]

stewartb

Thanks for following up. As for an instrument strictly dedicated to the function of voltage/amperage, no. I have an ammeter connected direct to battery and the Garmin 496 with Voltage selected as one of the data fields (top R in all my previously shared youtube videos). Garmin voltage is bus voltage readout.

At this point in time, I am going off my experience and exposure to this configuration since installation. BC400-2 alternator and BC201-1 Regulator with ~100 hours operation. From the start, reading on Garmin495 has been 13.9 with the occasional, as you mentioned, drift of .1 volt. So, my troubleshooting self is trying to tell me to K.I.S.S. Whine began when the voltage reading on my 495 began to jump around. I do have a Fluke Oscilloscope that I could connect directly to the battery and set for logging during another flight if that in fact adds any value to the isolation of the issue. I'd really like to be confident that it was alternator/regulator/battery before digging in on anything. I'm not certain it is mechanical or a whistle from airflow (could be wrong...). Coworker of mine who is rather smart was asking about health of my battery. Was indicating that a highly resistive battery would cause a potential issue where alternator doesn't have anywhere for its output to go. I didn't exactly follow but I certainly trust him when it comes to things related to electrical systems.

 

[wireweinie]

While the whine is present, pull the field breaker. Noise stay or go? Re seat that breaker then pull the output breaker. Noise stay or go?

Web

 

[stewartb]

I’d still rule out airframe noise. Steep turns, slow flight, uncoordinated flight, etc. To see if different air flow makes a repeatable difference. I don’t see a correlation between the sound and the voltage. Maybe turn the master off and see if it changes? Get a small megaphone and use it to isolate the sound origin, like to an instrument or interior panel? That’s how I isolated my noise to the float rudder tube. Just tossing out ideas. Good luck!

 

[Kid Durango]

I’m still not convinced you don’t have an airflow issue. Based on your videos, I hear your issue mostly with airspeed. It’s not super specific to what speed, but appears around 80. Everything you’ve done shows it disappears when you slow. Have you varied your engine rpm’s on video with out changing airspeed? You mentioned it, but I haven’t seen you post it, or at least I don’t think I’ve missed it. Secondly, I’ve had alternator issues, and removing it for testing was easy. Food for thought. Very frustrating.

 

[bjh356]

wireweinie

I have a youtube video above where I pull the field and whine still persists. As for output breaker, I have an Alternator switch but the 60A breaker is not one that can be manipulated easily.

 

[bjh356]

Kid Durango

Thanks. Definitely trying to avoid tunnel vision which I seem to be heading towards with this Voltage reading on the 496 getting lots of my attention. In one instance I totally hear you on the airflow/noise relationship, but I cannot ignore the wandering voltage for some reason. As for reducing RPMs while maintaining airspeed, the closest I have is when I was taking a peak at some brown critters in a creek bed. Low RPM, altitude maintained, and likely airspeed maintained throughout. None of those gauges are in view but this is what you are looking for.

https://youtube.com/shorts/dg5APcXwO3o?feature=share

I definitely can make the noise go away immediately when RPMs are reduced regardless of airspeed decrease/increase. One would assume that RPM decrease, and airspeed increase would maintain the whine, which is not the case from past two flights. So.... airflow in that case does not seem to be a part of the equation.

 

[bjh356]

How about this question. Would system voltage jumping around regardless of noise/whine, airspeed, maneuvering characteristics be a concern on a modern-day B and C charging system? When yes, isn't that enough?

 

[wireweinie]

How about this question. Would system voltage jumping around regardless of noise/whine, airspeed, maneuvering characteristics be a concern on a modern-day B and C charging system? When yes, isn't that enough?

You have two separate problems. If the alternator was off and you still had noise, it's not the alternator. But you do have charging system issues. Bad connections or possibly a bad regulator will give you your unstable voltages.

Web

 

[bjh356]

wireweinie

Thoughts on the following? I remove tension from alt belt and stow clear from alternator and flywheel. Go for flight, observe symptom. This could be a step in the right direction to isolating the culprit, correct? Noise still present, not an alternator related issue...? No noise, then more confidence in possibly alt bearing/etc as contributing factor?

 

[stewartb]

If it's an RPM related alternator squeal you should be able to demonstrate it on the ground.

 

[BC12D-4-85]

I'd get a piece of hose and stick to ear in flight. Plug the other ear. Move the open end around the cockpit, door, windows, wing root, panel, under panel, floor. See if it's localized or everywhere. Remove the alt belt and see if that stops it. Exorcism may be indicated.

Gary

 

[bjh356]

stewardb

10-4. No ability to replicate noise on the ground to date. Taxi, runup, etc, no squeal. Same for approach to landing and takeoff. Squeal/whine only noted once airborne and only after a certain duration of flight. For example, last night's flight. Taxi- no symptom. Take off- no symptom. First 8 min of climb out and cruise- no symptom. Only after straight and level for 8 or so min and then it shows up. The only input that seems within my control to present the noise is when > 2000 RPM and descending. < 2000 RPM and descending noise abates.

P.S. Really appreciate the knowledge base that I get to tap into here on SuperCub.org and why I'll keep coming back!

 

[BC12D-4-85]

If it's a bearing or bushing that's talking that may take time to heat up/loose clearance/get noisy. What turns besides the engine? Alternator, mag gears, mags, oil pump, tach drive if mechanical. Not sure what else.

Gary

 

[wireweinie]

wireweinie

Thoughts on the following? I remove tension from alt belt and stow clear from alternator and flywheel. Go for flight, observe symptom. This could be a step in the right direction to isolating the culprit, correct? Noise still present, not an alternator related issue...? No noise, then more confidence in possibly alt bearing/etc as contributing factor?

That will work.

Web

 

[bjh356]

Well, all it took was removal of the alt belt for me to ID the noise maker. Turns out the windscreen is the culprit. I had previously pressed in various locations during previous troubleshooting efforts but apparently not in the correct spot. It’s a vibration and I’ve buttoned that issue up. Now…for the unstable voltage. Next step I think I need to take and rule out is my battery. Approx 5 year old battery. Need a suitable one to swap for a quick troubleshooting feedback step I think.

 

[stewartb]

https://bandc.com/wp-content/uploads/2020/05/bc201-1-trouble_RevA.pdf