"Towards a Silent Aircraft" lecture notes
Posted Mon Mar 7, 2005 2:32 pm UTC
The Ohio State University College of Engineering Distinguished Lecture Series, "Toward a Silent
Aircraft" was presented on 3/4/05 to approximately 55 people . Dr. Edward M.Greitzer
indicated aircraft noise is a global problem and if it can be affectively addressed will improve
quality of life and provide economic gain.
"The Silent Aircraft Initiative" a three year project combining people and resources from
MIT, Cambridge, industry (such as Boeing and Rolls Royce) and government.
Dr. Greitzer, MIT, began by defining the goal of silent aircraft as aircraft that can't be heard
outside the perimeter of the airport. Such an undertaking requires the involvement and genuine
cooperation of aircraft manufacturers, university engineering scholars, communities, pilots and
It's not practical, nor perhaps even feasible, to retrofit older aircraft. Therefore engineering
schools will have to work with manufacturers and communities to "sell" silent aircraft
There has been considerable reduction in aircraft noise. Pre-1980s aircraft are far noisier than
The proposed aircraft wing and body configuration for a silent aircraft is the Boeing blended wing
body design. Mounting engines on top of the wings, instead of under wings, and integrating the
engines into the plane's body redirects the noise skyward and uses the actual aircraft body as a
sound shield eliminating ground focused engine noise. The project is studying other ways to lessen
noise, including variable nozzle engine design, which allows pilots to adapt engines for optimum
noise-reduction efficiency at take-off, cruising, and landing. Controlled descent or
"smarter-flying" by pilots can also reduce noise.
Additionally, "drag" produces much noise when aircraft are landing. Systems of perforated
spoilers are being tested to determine optimum balance between stopping the plane and noise
The bottom line is that a "silent aircraft" is about 20 years away. And even if created
today, it would be years before it could be mass-produced and used.
More information is available at http://silentaircraft.org/
In a related matter: Continuous Descent Approach (CDA)
Dr. Greitzer briefly mentioned a procedural change being tested that may help reduce aircraft noise.
It's called Continuous Descent Approach or CDA. Dr. Grietzer mentioned CDA would be tested next
month at an airport in England.
Some background on CDA:
CDA keeps aircraft at cruise altitude until they are close to the airport at
which point they make an even and continuous descent to the runway. Doing
so reduces noise between 4-6 decibels by eliminating noisy engine thrusts
as aircraft level out using a stepped descent.
In a two week trial last Sept. at Louisville Regional Airport, 126 UPS evening flights were tested.
It was found air traffic controllers could handle about 12-14 flights per night using the CDA
procedure. These tests confirmed the procedure can reduced aircraft noise exposure for those on the
ground. More work remains before CDA approaches become standard practice. The operational
procedures must be refined and worked out for airports with heavy aircraft volume and diversity of
aircraft types. The FAA, some airport and airlines are evaluating CDA appropriateness for nighttime
flights. The project is being funded by Congress as one of ten being conducted for the Partnership
for Air Transportation Noise and Emission Reduction.
CDA overview http://www.newscientist.com/article.ns?id=dn4395
CDA will be tested in Sacramento in 5/05
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