DC-9s/MD-80s louder than others?

Question

Is it just me or are the DC-9 and MD-80 louder than most other jets (from the outside). It seems that whenever other planes fly over you can't really hear them from inside, but the MD-80 shakes the entire house. Is it something to do with the engines?

Answer 1

DC-9 are older airplanes, and although the MD-80 are recent incarnations, they may well still be 20 years old or more. As such they are equipped with low bypass tubofans (with a bypass ratio around 1; to be compared with the bypass ratio of 5.5 for the CFM56-7 that equips the most recent 737) and normally, the largest bypass ratio engine will tend to be the quietest for the same amount of thrust.

Note that the most recent variants of the DC-9 family (the MD90) uses higher bypass turbofan; conversly older 737 relied to the same type of rather noisy engines as the original DC-9.

Answer 2

they (particularly the dc-9) are older so they have older engines. Older engines tend to be louder than newer engines of the same size and power.

Answer 3

Yes, the DC-9 and MD-80 are generally louder than other aircraft types.  This is because they are older generation aircraft.  The DC-9 was originally developed in the 1960s, while the MD-80 went into production in the early-1980s.  Because they are older, they use an older generation engine.  Both use the Pratt & Whitney JT8D engine, which was also used to power the Boeing 727 and the 737-100/200.  However, the MD-80 uses the JT8D-200, which is a newer, and much larger version of the powerplant.  Despite this, the MD-80 is noticeably louder compared to newer aircraft types, such as the Boeing 717 (which is the most recent variant of the original DC-9 design), Airbus A320, and Boeing 737NG series (737-600/700/800/900).  It is also worth noting that the DC-9-30s, -40s, and -50s that are still used in large numbers at Northwest Airlines have been modified to comply with Stage III noise regulations.  This was accomplished by installing hushkits on the engines to reduce noise levels.  But even though they have hushkits, the are still quite loud in comparison to newer generation aircraft.  On a side note, other aircraft that had hushkits installed in great numbers are the Boeing 727-200, 737-200, and BAC 1-11.

Answer 4

ya think?