Brantel
Well Known Member
So a few weeks ago I was on a nice smooth solo flight and I started noticing a noise that I am not used to hearing.
The noise sounds sort of like a high pitched whine similar to alternator noise.
First I have ruled out the alternator (electrical noise, not bearings). I can hear it without the headsets on. I have also turned off the alternator in flight and the noise remains.
On several flights after first noticing it, I noticed that the volume of this noise appeared to change on different flights. Weird....
So on my last flight I accidently discovered that the noise volume is directly related to how much I open the cabin heat flapper thingy.
If it is closed, the noise almost goes completely away.
If I open it, it increases in volume up to 100% volume when the gets to about 50% open.
If I open the door more than 50% it starts to reduce the volume of the noise.
One theory I have is that it is some sort of air flow noise that is causing something to resonate and the different volume is due to the changes in airflow thru my heat system. (standard Van's with a Robbin's Wings heat muff and a standard stainless heat valve that dumps to the lower cowl when closed)
Another theory is that the angle of the heat valve door is reflecting the noise to my ears when at the proper angle making it sound louder at a certain spot.
Any ideas on what the source of the noise could be?
For context: I have a mechanical fuel pump, 2 Pmags, and a PCU5000X prop governor on my accessory case and that is it. The engine is a bone stock narrow deck carbed O-360.
The noise sounds sort of like a high pitched whine similar to alternator noise.
First I have ruled out the alternator (electrical noise, not bearings). I can hear it without the headsets on. I have also turned off the alternator in flight and the noise remains.
On several flights after first noticing it, I noticed that the volume of this noise appeared to change on different flights. Weird....
So on my last flight I accidently discovered that the noise volume is directly related to how much I open the cabin heat flapper thingy.
If it is closed, the noise almost goes completely away.
If I open it, it increases in volume up to 100% volume when the gets to about 50% open.
If I open the door more than 50% it starts to reduce the volume of the noise.
One theory I have is that it is some sort of air flow noise that is causing something to resonate and the different volume is due to the changes in airflow thru my heat system. (standard Van's with a Robbin's Wings heat muff and a standard stainless heat valve that dumps to the lower cowl when closed)
Another theory is that the angle of the heat valve door is reflecting the noise to my ears when at the proper angle making it sound louder at a certain spot.
Any ideas on what the source of the noise could be?
For context: I have a mechanical fuel pump, 2 Pmags, and a PCU5000X prop governor on my accessory case and that is it. The engine is a bone stock narrow deck carbed O-360.
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