Making Airplanes Quieter
by Kelly McEntire
March 30, 2001
Have you ever been near an airport and listened
as the jets take off or been under one as it roared into the air
at takeoff. It is extremely loud. How would you like to be one of
the lucky ones whose house is right at the end of an airport runway?
They get to hear this noise all the time. Many people who live near
the airport are getting tired of all that noise, so they complain
to the government. The government is trying to help them out by
asking us at NASA to fix the problem by making jet's quieter.
Jets are powered by jet engines. The technical
name for a jet engine is a Gas Turbine Engine. They make a jet plane
fly by generating thrust. Thrust is generated by sucking air into
the opening of the engine, then heating it to 1000's of degrees
with jet fuel, and then shooting it out the back of the engine hundreds
of time faster than it went in.
Unfortunately, moving all this air through the
engine is very noisy. The first step in making jet engines quieter
is to understand why they are noisy and what parts are making the
most noise. It is easy to tell that the engine is making a whole
bunch of noise, but it isn't easy to tell what part is causing it.
We investigate this problem by building a small part of the engine
so that this part gets isolated from the other parts. We then test
it to see how much noise it generates. We do this with each major
part of the engine. Once we understand what causes the noise, we
can then begin the task of designing the new part to correct the
cause of the problem and thus make the engine run more quietly.
We also investigate ways to make an engine burn
less jet fuel and to burn it cleaner so we have less air pollution.
More people are flying and more packages are flying than ever before.
Small increases in engine efficiency can mean huge savings in jet
fuel. The same is true for decreasing air pollution.