Jet Engines

[EnRoute]

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.

[JA Yawd Bwoy]

I think this belongs in Techinical Talk.

[Maximillian_Jenius]

Originally Posted by EnRoute

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.

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]

MD-80s and 727s actually have turbofans on them (albeit a fairly low bypass turbofan).

[Maximillian_Jenius]

Originally Posted by Dan208B

MD-80s and 727s actually have turbofans on them (albeit a fairly low bypass turbofan).

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!

[Polar742]

Originally Posted by Maximillian_Jenius

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!

Huge I tell ya, huge!!

[Maximillian_Jenius]

Originally Posted by Polar742

Huge I tell ya, huge!!

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!

[Polar742]

Originally Posted by Maximillian_Jenius

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!

I remember the first time I saw one. I thought it was a 757 lowrider.

[tonyw]

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.

[Holocene]

Rolls Royce engines:

http://www.youtube.com/watch?v=_vJliayH6co

[OldTownPilot]

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.

[youngflyer]

Originally Posted by OldTownPilot

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.

Yeah!

[AZBigDog]

Originally Posted by OldTownPilot

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.

Wow... my brain just melted.

[Maximillian_Jenius]

Originally Posted by Polar742

I remember the first time I saw one. I thought it was a 757 lowrider.

yeeeeeup!

[Maximillian_Jenius]

Originally Posted by OldTownPilot

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.

Whoooooa! Check Justin out, he is totally kicking those books ass!

[OldTownPilot]

Yeah, Sorry. But I figured i'd chime in

Engineering is rubbing off on me. Not sure if that is a good thing or not.

[JDE]

I much prefer the sound of the CJ-610's on the 20-series Learjets...those MD-80 engines are too loud!

[OldTownPilot]

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.

[Holocene]

Originally Posted by youngflyer

Yeah!

Hey youngflyer, ever hear 897LP over the radio?

I sometimes rent from Exec at SYR.

[JDE]

Originally Posted by OldTownPilot

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.

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.

[OldTownPilot]

Yep N128LR, white with a green tail and winglets. It came into BHB a few times last summer. Flies 135 out of ABE.

Lear 28 sn 001. It was the plane Neil Armstrong flew to get nearly every time to climb record in existence.

I would stop whatever I was doing just to watch that thing take off. Simply amazing.

[moocowtex]

They need to pass a law that all motors need to sound and smoke like the L-1011 on startup.

[Dan208B]

I feel the need to contribute to the geekness just a little bit more. It's a common misconception the JT8D is a Turbojet. It is a very long narrow engine, which gives it that look. Its nearly identical looking to the actual turbojets on the older 707s and DC-8s. Boeing was a big "fan" (no pun intended) of the JT8D. Offhand, 737-100/200, all the 727s, later model 707s. And of course DC-9s/MD-80s. Im sure there are many more aircraft that use that engine, but it's a very strong, proven engine, and makes quite a noise.

[EvilGN]

another great plane to listen to that has this lower pitched sound is the C-5...large bypass fan on that guy.

[scooter2525]

Originally Posted by Holocene

Rolls Royce engines:

http://www.youtube.com/watch?v=_vJliayH6co

I LOVE that video and it captures the sound of those RR's in sound. It is a VERY distinct and pleasing sound.

I haven't heard any JT8's yet... hopefully in this lifetime.