Boeing 717 / MD80 question

Cherokee_Cruiser

Cherokee_Cruiser

Bronteroc
Hey guys,
This question is mainly for the 717, although I'm sure it applies to the MD80 as well. I was recently on an Airtran flight on a 717, sitting in 30A. That window seat has no view outside: just the engine. Basically after pushback when the engines started, all throughout taxi, the engines were loud!!! All that while, the engine sound was resonating in the back of the aircraft. But right when power was applied for takeoff, that sound died out, and was replaced by the quiet hum (MUCH quieter) that I'm used to on the 717. Any idea why the aircraft engines are louder when on the ground taxiing to the runway?

Also, I've noticed this is only true when you're sitting in the back of the airplane. Sitting in the middle and up front, there was no loud noise as described.
 
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Sitting in the middle and up front, there was no loud noise as described.

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That's because you are farther away from the engine. /ubbthreads/images/graemlins/grin.gif I avoid at all costs the back seat on a DC-9 variety airplane.
 
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Resonate frequencies.

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The other big factor is all the noise coming through the doors. When power is pushed up the cabin starts pressurizing and the doors seal. This can make a major difference in noise level. Sometimes there is such a gap in the door seals it sounds like the door is open until it pressurizes.
 
I know the 757/767, have a very high pitched whine when idiling, that whine is enough to make me miserable, but when they are at full power they sound much easier to deal with? /ubbthreads/images/graemlins/grin.gif

/ubbthreads/images/graemlins/blush.gifI guess since we are on the subject, why is it that the MD-80 makes a really loud "pop" sound when the engines start, I have noticed that no other airplanes do that/are that loud. Any body know why? /ubbthreads/images/graemlins/spin2.gif
 
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Man, I love that whine!!!

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Yup me too...gotta love these new high ratio bypass engines /ubbthreads/images/graemlins/spin2.gif


Matthew
 
My favorite seat on any aircraft, as a passenger, is right next to the wing and at the window. I love watching the control surfaces being adjusted all through the flight, but I never thought about the obvious - it was a lot louder right next to the engine then anywhere else.

I decided to host a marathon of The Young Ones on a flight to Vegas, for my extremely nervous fellow passenger. He liked the show and it got his mind off everything that worried him. I had the volume turned up all the way on my laptop - and this thing has some awesome stereo speakers - but I could barely hear it! All of a sudden, a passenger behind me tapped me on the shoulder, pretty pissed off, and told me that the show was "Way too loud!"

I was puzzled. How could it be "Way too loud!" when I could barely hear it? ....Yeah, then came my lesson about how sound travels, and when you sit right next to loud things, it's loud. /ubbthreads/images/graemlins/buck.gif The crew was lucky that I didn't stand up and yell, letting them know right then of my phenomenal discovery!

Always love the engines' various sounds during flights. The MD-80 was nice. Has anyone noticed how the Embraer 135 sounds like it's underwater?!

/end of tangent
 
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I decided to host a marathon of The Young Ones on a flight to Vegas

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The Young Ones?! Talk about good obscure British comedy. I approve. /ubbthreads/images/graemlins/grin.gif
 
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/ubbthreads/images/graemlins/blush.gifI guess since we are on the subject, why is it that the MD-80 makes a really loud "pop" sound when the engines start, I have noticed that no other airplanes do that/are that loud. Any body know why?

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I've got about 5,000 hours on the airplane (in the quiet end) and didn't know that. If it's happening consistently and you hear it in the back, I would have to guess it's one of the many valves that open and close during a start cycle.
 
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He may just be refering to light-off....

It's sometimes more pronounced than at other times.

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That's a good point. Probably right. Some engines do go with a pop, particuarly the JT-8 series.

I think you win the prize.

Dave
 
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He may just be refering to light-off....

It's sometimes more pronounced than at other times.

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What exactly is "light off"....is that when the underwing mounted lights retract on MD-80/90 series aircraft?


Matthew
 
Right after you 'introduce' fuel to the engine, it's when combustion begins during the engine start.
 
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I decided to host a marathon of The Young Ones on a flight to Vegas, for my extremely nervous fellow passenger.

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Haven't watched that in a long time. "Rick! I got six pair o' 'ands!" /ubbthreads/images/graemlins/smile.gif
 
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