Jet Engines

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EnRoute

New Member
I live near the approach/departure of PDX. I had a question that struck me as I was sitting on my front porch watching and listening to the traffic depart the airport. Question? Why is it that on the larger engines which are obviously on the larger A/C have more of a deep, wining, groan when compared to the smaller turbine engines.

My thought is has to do with the amount of bypass air on the larger engines versus the smaller machines. Am I right or am I wrong. Anyone, Anyone.

:confused:
 
EnRoute said:
I live near the approach/departure of PDX. I had a question that struck me as I was sitting on my front porch watching and listening to the traffic depart the airport. Question? Why is it that on the larger engines which are obviously on the larger A/C have more of a deep, wining, groan when compared to the smaller turbine engines.

My thought is has to do with the amount of bypass air on the larger engines versus the smaller machines. Am I right or am I wrong. Anyone, Anyone.

:confused:
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Don''t ya just love that deep whining, blowdryer, groan? Or as I term it the difinitive Rolls Royce sound.

As all RR engines seem to make it, though rarely, I do hear it on the CFM 737 engine.

Another great sound is the turbojets from say an MD-80 or 727 series plane.

They're definitely a "boom, boom" shake ya room kinda sound.

Love it!


On a side note...OMG...a CO 737-900ER just flew over my apt real low on approach.

My god those things are fracking HUGE man huge!
 
Dan208B said:
MD-80s and 727s actually have turbofans on them (albeit a fairly low bypass turbofan).
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Cool. Thanks didn't know that, I took a tour of Allegiant last year at NJC, and the tour guide said they were turbojets.

Either way, they sound great powered up for takeoff!

The more I know! :)
 
Maximillian_Jenius said:
LOL!

Hey, I'm just saying that if like many on this board know the 737's original planes the 100-200 model that 800, but more especially the 900 model are huge, man.

Huge! :D
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I remember the first time I saw one. I thought it was a 757 lowrider. :bandit:
 
Geeks!

It's an engine. It takes air, compresses it, combines it with fuel, burns it, and creates thrust.

Don't get me wrong, I enjoy flying as much as the next guy, but you will never hear me discuss the difference in sounds between various engines...unless one of them is making a noise which makes me think it's going to die on me. If that's the case, I'll be more concerned about other things. :D
 
Alright, The RPM of the engine is limited by not wanting supersonic relative airflow at the fan blade tips. Assuming that the airframes have the same forward velocity, the larger engine diameter has to spin slower. This internal rotation speed determines the frequency of the sound. The faster it spins, the higher pitched it is. Alot of people say an engine it 'big' when it just has a large N1 fan or bypass fan. Thrust is made by high velocity air that exits the turbine section. This bypass layer increases the amount of area that the shearing of the air takes place, a la a shallower shear gradient. This shearing produces the 'sharp' noise that can be VERY loud. Also with a larger fan area you get a higher mass flow rate through the engine, and to produce the same amount of force the average exit velocity of the air can be a lot lower, thus also reducing noise.
 
OldTownPilot said:
Alright, The RPM of the engine is limited by not wanting supersonic relative airflow at the fan blade tips. Assuming that the airframes have the same forward velocity, the larger engine diameter has to spin slower. This internal rotation speed determines the frequency of the sound. The faster it spins, the higher pitched it is. Alot of people say an engine it 'big' when it just has a large N1 fan or bypass fan. Thrust is made by high velocity air that exits the turbine section. This bypass layer increases the amount of area that the shearing of the air takes place, a la a shallower shear gradient. This shearing produces the 'sharp' noise that can be VERY loud. Also with a larger fan area you get a higher mass flow rate through the engine, and to produce the same amount of force the average exit velocity of the air can be a lot lower, thus also reducing noise.
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Yeah! :buck:
 
OldTownPilot said:
Alright, The RPM of the engine is limited by not wanting supersonic relative airflow at the fan blade tips. Assuming that the airframes have the same forward velocity, the larger engine diameter has to spin slower. This internal rotation speed determines the frequency of the sound. The faster it spins, the higher pitched it is. Alot of people say an engine it 'big' when it just has a large N1 fan or bypass fan. Thrust is made by high velocity air that exits the turbine section. This bypass layer increases the amount of area that the shearing of the air takes place, a la a shallower shear gradient. This shearing produces the 'sharp' noise that can be VERY loud. Also with a larger fan area you get a higher mass flow rate through the engine, and to produce the same amount of force the average exit velocity of the air can be a lot lower, thus also reducing noise.
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Wow... my brain just melted. :nana2: :nana2:
 
OldTownPilot said:
Alright, The RPM of the engine is limited by not wanting supersonic relative airflow at the fan blade tips. Assuming that the airframes have the same forward velocity, the larger engine diameter has to spin slower. This internal rotation speed determines the frequency of the sound. The faster it spins, the higher pitched it is. Alot of people say an engine it 'big' when it just has a large N1 fan or bypass fan. Thrust is made by high velocity air that exits the turbine section. This bypass layer increases the amount of area that the shearing of the air takes place, a la a shallower shear gradient. This shearing produces the 'sharp' noise that can be VERY loud. Also with a larger fan area you get a higher mass flow rate through the engine, and to produce the same amount of force the average exit velocity of the air can be a lot lower, thus also reducing noise.
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Whoooooa! Check Justin out, he is totally kicking those books ass! :)
 
I much prefer the sound of the CJ-610's on the 20-series Learjets...those MD-80 engines are too loud! ;)
 
I drove under a departing lear 28 once. I thought my car simultaneously lost all 4 wheels, and the engine lost all its oil while continuing to run. Damn that was loud. Fortunately I saw the airplane before I totally drove off the side of the road.
 
OldTownPilot said:
I drove under a departing lear 28 once. I thought my car simultaneously lost all 4 wheels, and the engine lost all its oil while continuing to run. Damn that was loud. Fortunately I saw the airplane before I totally drove off the side of the road.
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In that case, you saw a rare piece of history! I think there were only 5 Learjet 28's produced...and something like 4 Learjet 29's. I can't remember now, but that's what A.net told me once.
 
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