Noiseless helicopters are PROBABLY in the military inventories of the USA, RUSSIA,
ISRAEL and China but they are NOT telling! Germany, the United Kingdom, Japan,
Canada, France and few others have the CAPABILITY but no particular military reason
to create them other than for simple COMMERCIAL reasons.
A truly silent chopper uses advanced V-shape blade design, blade ducting to prevent
vortex expansion outside of the immediate blade area, and ACTIVE noise cancellation.
One chopper I was nearby during a film shoot was a modified MBB (Daimler of Germany)
that was CUSTOM done for film industry clients where the local audio environment was
REQUIRED to be recorded during aerial shooting (that's an unusual request!).
It TRULY was quiet, no louder than a Honda Civic car at high idle...in other words
I could hear people talk amongst themselves very clearly and hear a simple dull
whup whup whup even 30 feet (10 metres) away!
The pilot said it was the EXTREMELY LARGE V-blade design and ultra low-RPM's
using an advanced blade management software system which kept the blade tips
from going supersonic (they were just under mach 1). All i can say is that it was
way quiet relative to a normal helicopter.
edit on 2012/7/24 by StargateSG7 because: spelling