AboutPaul Soderman Expertise Aeronautics, Fluid Mechanics, Aeroacoustics, Noise Control, Muffler Design, Wind Tunnel Research.... I know nothing about India - do not ask about schools, jobs, application requirements, career choices, etc. for India. Please, no text message verbiage; I prefer full words in full sentences. Thanks.
Experience 38 years as research engineer at NASA
Publications AIAA, NASA
Education/Credentials B.S. and M.S. Aeronautical Engineering - U. of Washington
Graduate work Standford U.
Awards and Honors AIAA Associate Fellow (American Institute of Aeronautics and Astronautics)
Question QUESTION: Where noises come from when an airplane passes above us in sky? Are they most come from engines or they are for moving through in different densities of air? And different engines make different noises or not?
ANSWER: Mehrdad
The primary source of aircraft noise is the propulsion system. For a jet engine that would include the jet exhaust noise and the inlet fan noise. A propeller makes a different sound. Near to landing, noise can also be heard from the airframe components such as flaps, ailerons, landing gear, etc. Aircraft sound does pass through a range of air densities, but that has virtually no effect on the noise levels. Different engines make different noises.
Paul
---------- FOLLOW-UP ----------
QUESTION: Hello dear Paul
Altogether, how much changes we have in frequencies from rise to landing? Are these changes huge or they are epsilon that we could waive them? I mean could we say that for example several same 747 with same speeds have a known same range of noise frequencies in different airports?
Thanks
Answer There is usually a large difference in acoustic spectra between takeoff and landing because takeoff requires full engine throttle which generates strong jet noise whereas landing requires much less throttle. On landing the fan noise and airframe noise tend to become important.
Yes, you could assume that different 747's at the same speed and distance have similar spectra. This ignores differences due to weight or weather or flap setting for example, but it gives you an approximate spectrum for that aircraft. You should be aware, however, that there is a family of 747 aircraft with several different configurations that have been developed over the years.
Perhaps if I knew what you are trying to accomplish I could be more helpful.
Paul
