Freaking Noisy Aircraft - What can be done?

[kach22i]

Boeing makes 'quiet' advances
Noise-reduction efforts pay off at remote airfield in Montana

By JAMES WALLACE
SEATTLE POST-INTELLIGENCER AEROSPACE REPORTER
http://seattlepi.nwsource.com/business/236095_quietjet11.html

During tests at the Glasgow site with a 777 in 2001, Boeing found that two engines equipped with chevrons made no more noise than a single engine without the chevron.

Photo Caption:

Technology being tested on this Boeing 777 in Montana is expected to find its way into 787s, due to enter service in 2008, and the 747 Advanced. (August 11, 2005)

Credit: James Wallace/Seattle Post-Intelligencer

Well, NASA ain't all a bunch of drunk'n screw ups after all.

[masraum]

Interesting. Unfortunately, I suspect that it'll be a long time before I get to ride in one of the new quiet planes.

[Joeaksa]

The new series of planes are very quiet. I am flying the first Challenger 605 out on the market and during the test flights we watched at the factory you could not hear them 20-30 seconds after takeoff.

Compare that with a DC-9 or Lear 20 series...

[GO DAWG GO]

For what it worth,


It creates an out of phase sound wave distribution. Sound waves travel in concetric rings in phase and are disturbed or attenuated by the geometrical edges of the by pass nacelle trailing edge. Actually simple physics.

Bob

[Aerkuld]

I wonder if that would work with exhaust tail pipes too?

[BlueSideUp]

The noise from a jet is caused by the high velocity/high temperature air exiting the tailpipe and shearing with the surrounding air. By surrounding the core air (high temperature/high velocity) with the fan bypass air (lower temperature/velocity) on a high bypass engine you cut the noise and increase the efficiency significantly. The efficiency increases as a result of accelerating a lot more air and a lower rate.

The newer engines are using the chevron technology on their core tailpipes but I think this will be the first application on the fan. You can see it on the larger version of the CRJ, an adaptation on the Challenger jet Joe flies.

Here's the CF34-3 used on the Challenger 605. A similar version is also used on the CRJ-100/200. The 605 uses a CF34-3B and the RJs use either the -3A1 or the 3B1. The 3B and 3B1 are rated at 8,729lbs of thrust and 9,220 lbs in an emergency.



The CF34-8C1 is on the larger CRJ700 and has 13,790lbs.



When they went to the even larger CF34-8C5 for the CRJ900 the chevrons were necessary on the tailpipes to cut down the noise. This engine is rated at 14,225lbs of thrust.



Before you think Joe should hot rod his 605 remember it weighs nearly half as much as the CRJ900. I'm sure it performs pretty well with what it has!