Do helicopters always makes noise? or are they quiet sometimes?

Question

i was looking outseide. and i saw what seems like a helicopter. its got a whitish yellowish light and a redlight. and it seems to be circling around off in the distance. i live in the city so its probably a police helicopter.

it went across the sky pretty quickly into teh distance and is now circling changing its like from whitish/yellow/ to only a flashink its red light and sometimes both.

but usualy i hear it. why isnt it making noise this time? are some helicopters more quite?

Answer 1

They only make noise when the engines are running.

Otherwise... very quiet.

Answer 2

I've noticed that a helicopters' noise also depends on what it is doing. Different functions mean moving different amounts of air. Moving a lot of air, as with a slow vertical decent, make more noise. Air can be noisy.

Answer 3

There are probably some lines of helicopters that are more or less quite than others.  The biggest thing is what are the conditions for the sound to travel in, that probably has the mos importance for you being able to hear it.

Answer 4

i once ate a cookie that looked like a dinosaur

Answer 5

There can be big differences in the noise signature of different models of helicopters.  A large portion of the excessive or offensive noise generated can be avoided though with proper piloting technique.  For the most part a two bladed main rotor system will be noisier than a four or five bladed main rotor ship.  The fewer the number of blades, the wider the blades have to be, the cord of the blade. A wider blade makes much more noise while descending to land for instance. With collective lowered loosing altitude with speed you get that popping noise that can travel quite a distance. Also a big source of noise on a helicopter is the Tail Rotor.  Some helicopters don't have conventional tail rotor systems, but have an enclosed fan ( Notar ) that ducts air out the sides of the tail boom to maintain directional control and counteract torque. Others use a Fenestron Tail Rotor where the tail rotor is enclosed or surrounded by fairing that generates much less noise than a conventional tail rotor.

Answer 6

Why isnt the my neighbors dog barking? sometimes I can hear it but for some reason as it goes away I cant hear it anymore. And its color seems to change too.

Seriously though, I think a helicopter wont make any sound if its off.

Answer 7

most of the noise is produced by the main rotor and tail rotor blades. the noise from the tail rotor is especially effectively reduced by using the NOTAR system which replaces the tail rotor with jet-like nozzle. generally the smaller helicopters are quiter than the bigger, and the more blades, the better. thus the Jetranger should be noiser than the bell 412. note the typical Huey flapping sound.

Answer 8

always noise

Answer 9

They're quiet when they are turned off

Answer 10

One interesting point is that a gyrocopter makes less noise than an helicopter. It makes me think that the engine exhaust close to the rotor may be the cause. (gyrocopters have free rotating rotors; truly 'rotating wings').

The same can be observed with aircraft: A pusher (engine behind) configuration makes more noise that a tractor (engine in the front) one.