Blade Slap...?
Just of late where my office is based we seem to get a lot of 2 blade helis flying at a mid-ish sort of altitude say up to 1200ft, beyond that we see many of the three and four bladers scooting along at around 1600 to 2500 ft, all seems pretty normal but then I have started to realise the two bladers are responsible for my estimate of 70 /80% of the noise generated by Blade Slap.
I have looked into all my books and can only find comments about advancing blades colliding with the tip vortices of the previous blade tip, is that really all that cause this noise, for it only seems to be the two blader ie Jet R and the Robbies, these are alway a slight tad lower than the bigger helis, last week we had a Utility Heli checking the line and I heard it again very loud but it always seems that the slap is heard upon what appears to be a losing of height, or could air density have some affect on this problem?
Peter R-B .