Howdy... Maybe this is true for all helis, but I was somewhat surprised today that my C8 is fairly quiet as it climbs to a new altitude, but when I level off with AH, the prop noise gets a LOT lounder. I can initiate another climb, and the sound immediately gets much quieter, but then level off again at a new height, and the loundness returns... Is this normal? Just the way the mechanics of air-to-prop work? Thanks for your thoughts... Best, Ben
Now that is a real brain teaser! I look forward to reading the answers because this falls squarely under the sentiment of my office sign that reads: There has been an alarming increasein the number of topics about which I know absolutely nothing. Andy.
Hmm. My tentative analysis: Climbing moves the prop blades into "still" air, whereas hovering, each blade is coming around into turbulent air stirred up by the other side of the prop. The resulting turbulence results in larger amplitude compression and rarefaction waves, aka noise. Andy.
I agree with Andy. Clean air vs dirty air. Same with full size helicopters. Quieter blades a bit hidden usually due to engine noise.
Hmmmm..... Blade-vortex interaction (BVI) noise BVI occurs when a rotor blade passes within a close proximity of the shed tip vortices from a previous blade. This causes a rapid, impulsive change in the loading on the blade resulting in the generation of highly directional impulsive loading noise. BVI noise can occur on either the advancing or retreating side of the rotor disk and its directivity is characterized by the precise orientation of the interaction. In general, advancing side BVI noise is directed down and forward while retreating-side BVIs cause noise that is directed down and rearward. It has been shown that the main parameters governing the strength of a BVI are the distance between the blade and the vortex, the vortex strength at the time of the interaction, and how parallel or oblique the interaction is (Hardin 1987, Malovrh 2005).
Nice. Amazing what you can find with Mrs. Google's assistance and on Wikipedia (you can even find lies about me on Wikipedia. ) Andy.