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Whining Engine Noise at Takeoff

in 915iS Technical Questions 2 years ago

  • Re: Whining Engine Noise at Takeoff

    by » 2 years ago

    Air bubbles in a pump is called “cavitation” which cause less fuel transfer and that funny noise because the pump is trying to pump air (more noise) vs all fluid (quieter).

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Whining Engine Noise at Takeoff

    by » 2 years ago

    Much of Arizona allows for a slightly higher vapor pressure for auto fuels during the summer months.  Where many states require summer fuel to have an RVP of 7 PSI (similar to Avgas), much or Arizona allows fuels to have an RVP of 9 PSI.  Avgas is always 6-7 PSI.  Also, if this happened when the aircraft still had some of the last winter grade fuel, the RVP of that fuel may have been 11-13 PSI, which would explain this.  

      
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  • Re: Whining Engine Noise at Takeoff

    by » 7 months ago

    --UPDATE--

    I've been using pure AVGAS yet the noise returned several months ago.  This time I did some more dedicated troubleshooting and found the following:

    At full power on takeoff & climb it's nice & quiet.  Once I level off and gain airspeed >100 KIAS the noise appears.  I tested this at different altitudes and power settings--from straight & level cruise (~125 KIAS), I pull up, bleed airspeed and noise goes away below 100.  Level off, and noise comes back >100.  Go into dive and noise seems to get louder. 
     
    So now I'm convinced the noise has something to do with airflow through the cowling and not the fuel/fuel pumps.  Because the noise still sounds like a fuel pump, I replaced the aluminum standoffs that hard-mount the fuel pump housing to the firewall and replaced them with rubber isolators.  This changed nothing.
     
    So my new theory is perhaps it has something to do with airflow around the turbo and/or air filter?  I only think this because it's another hi-pitched frequency source and because the noise is sporadic above 100 KIAS and I don't hear it at high power settings/low airspeeds (e.g. takeoff) I don't think it's the turbo itself.
     
    Has anyone experienced something similar?  Thoughts?  Theories?
     
    -Chris
      
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  • Re: Whining Engine Noise at Takeoff

    by » 7 months ago

    Chris

    Thanks for the update. Just to put the fuel pump thing to bed, does the sound change with one or both pumps running?  

      
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  • Re: Whining Engine Noise at Takeoff

    by » 7 months ago

    It's the same noise regardless.  I tried isolating each one, then both and it made zero difference.  Frustrating!  😕

      
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