why are little jets louder than big jets

SixPapaCharlie

SixPapaCharlie

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I am sitting at Founders Plaza at DFW Airport. I just watched a giant mamma jamma Emirates airplane and a 747 and a handful of 757 take off. However anytime a little regional jet takes off it is twice as loud.
 
They have to work harder..??

I think I can..... I think I can.... :lol:
 
High bypass ratio engines *tend* to be quieter than low bypass. A lot of what you hear is shear from the exhaust mixing with ambient (or freestream), and moving a little air fast (low bypass) creates more shear and is louder than moving a lot of air slower (high bypass), for a given massflow.

Nauga,
and the J52 screechmaker
 
I'm thinking that because of the far smaller outlet of the little jet engines that the sound created contains higher frequencies, a more shrill sound. As opposed to the huge high-bypass engines on the jumbos creating rumbling low frequencies that are less annoying.

Edit: The good doctor beat me to it (I type slowly)...
 
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Zeldman said:
They have to work harder..??

I think I can..... I think I can.... :lol:
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It always feels to me like the jets on the bigger planes struggle more to get the plane airborne than an rj's. Maybe the smaller jets make a higher pitched "whine" that sounds louder :dunno:
 
Aeric said:
I'm thinking that because of the far smaller outlet of the little jet engines that the sound created contains higher frequencies, a more shrill sound. As opposed to the huge high-bypass engines on the jumbos creating rumbling low frequencies that are less annoying.
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That too. :D

Nauga,
constant speed, variable noise
 
Love the smell of jet fuel in the morning,it's always the little guy who makes the most noise.
 
nauga said:
High bypass ratio engines *tend* to be quieter than low bypass. A lot of what you hear is shear from the exhaust mixing with ambient (or freestream), and moving a little air fast (low bypass) creates more shear and is louder than moving a lot of air slower (high bypass), for a given massflow.

Nauga,
and the J52 screechmaker
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Out of curiosity.....why is the Hornet so much louder than the Tomcat?
 
Watch an old school turbo jet take-off. Talk about loud. Advances in technology help with decibal levels too. Blade shapes, cowling shapes, and everything inside.
 
Its not just one thing, noise is a variety of factors. Inlet and outlet length, type of core air diffuser, bypass duct lengths, diameter and RPM of the rotating components, I'd even go as far to say that the design of the fan gearbox plays a roll.
 
Fearless Tower said:
Out of curiosity.....why is the Hornet so much louder than the Tomcat?
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TBH I always thought the F-14A's (TF30) were louder than the Hornet. Didn't have enough time around B/D models (F110) for the noise to leave a lasting impression although they did strike me as pretty loud. Either model has a higher bypass ratio than the F404, by the way, and they all pale in comparison to a J52 or a J79 :D

F-14's (by reports) and TA-4's (J52, personal experience) were almost as loud on the inside as the outside. :eek: :D

Nauga,
who says, "WHAT?"
 
Why are little dogs yappier than big dogs? :D
 
nauga said:
TBH I always thought the F-14A's (TF30) were louder than the Hornet. Didn't have enough time around B/D models (F110) for the noise to leave a lasting impression although they did strike me as pretty loud. Either model has a higher bypass ratio than the F404, by the way, and they all pale in comparison to a J52 or a J79 :D

F-14's (by reports) and TA-4's (J52, personal experience) were almost as loud on the inside as the outside. :eek: :D

Nauga,
who says, "WHAT?"
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Can't say for certain on takeoff, but on approach the Hornet is twice as loud as a Tomcat.

Says the guy who stood OOD on the plane guard back when the CVW had both.
 
Bro....I'm here now. Gate 39, but about to bounce out on this alum shipping tube.
 
Higher pitched whine sounds louder than lower pitch?

Guessing...
 
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bflynn said:
Higher pitched whine sounds louder than lower pitch?

Guessing...
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Pperhaps, close in. I understand that foghorns and whistle buoys have a lower pitch because it carries farther.

Are the noise abatement rules different for larger planes than smaller ones?
 
I like the turbines that 'growl' in the distance...I have never identified which airplanes or engines do that however.
 
Want loud? Listen to a Paris Jet or a Fouga 170, they're downright painful to be near.
 
Let'sgoflying! said:
I like the turbines that 'growl' in the distance...I have never identified which airplanes or engines do that however.
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The first ones I remember were the DC-10s. I CFI'd at Long Beach while the 10s were in precertification flight test, and I remember thinking they sounded more like giant leaf blowers than jets.
 
Fearless Tower said:
Can't say for certain on takeoff, but on approach the Hornet is twice as loud as a Tomcat.

Says the guy who stood OOD on the plane guard back when the CVW had both.
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Hornets are higher pitched, which makes them sound louder even though they're quieter in pure db.

On approach, the 'Cat is comparatively lighter WRT max takeoff weight as well as being optimized for slow flight, so those big engines are near idling, vs the Hornets who keep the power up.
 
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Let'sgoflying! said:
I like the turbines that 'growl' in the distance...I have never identified which airplanes or engines do that however.
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I like the TF34's in the S-3 Viking. They get a sort of resonance in the inlet with power changes so on approach they give a low frequency 'whooooop' with small power changes, noticeably louder than the steady whine from the engine. The airplane sort of 'whooop...whoops' its way down the glideslope and then winds up like a sewing machine on a waveoff. There's a reason they call it the 'War Hoover' :D

Haven't been around A-10's as much but they don't seem to do it. Same engine, different inlet. Different approach technique, too. ;)

Nauga,
who says, "There it is"
 
warthog1984 said:
Hornets are higher pitched, which makes them sound louder even though they're quieter in pure db.



On approach, the 'Cat is comparatively lighter WRT max takeoff weight as well as being optimized for slow flight, so those big engines are near idling, vs the Hornets who keep the power up.
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That makes sense.
 
I was line crew at OSH when they had the Concorde there. As it spooled up for takeoff we stood just off to the side of the runway about 50 feet from the wing tip to watch for FOD, people etc.
It must have been noisy because I could not hear anything. The guy next to me was waving his arms, hooting and hollering. I could not hear him. What was interesting is that it made your internal organs vibrate. Your chest just buzzed on the inside. Quite a demonstration of resonance.
 
warthog1984 said:
Hornets are higher pitched, which makes them sound louder even though they're quieter in pure db.

On approach, the 'Cat is comparatively lighter WRT max takeoff weight as well as being optimized for slow flight, so those big engines are near idling, vs the Hornets who keep the power up.
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No carrier based aircraft should ever be "near idling" during the approach.....you need the motors spooled up in order to have both good power response (we go up and down on glideslope with the left hand/throttle) as well as acceptable waveoff/bolter capability, especially with really poorly performing and slow spooling motors like the Tomcat had. More aerodynamically efficient airframes like the Tomcat and T-45 use/used things like speedbrakes open to artificially drive the power requirement higher while still being able to fly a ~3.5 degree glideslope. One thing the Tomcat did have, which might contribute to it being quieter, was Direct Lift Control (DLC), which allowed the pilot at least in theory, to keep the throttles steadier while dumping lift via DLC vs chopping the throttles. Or maybe it was just different intake aerodynamics......most of the noise you hear on approach is coming from the fan, not from the tailpipe. What you will hear with the Hornet is typically louder multiple throttle corrections to correct glideslope deviations. Power down to correct a climb, power back up above what is required to maintain glideslope to stop the descent, and then back to your "neutral power setting" that will then hold glideslope. These are very rapid throttle movements, but the effect is a lot of little surges of power and the fan speeds changing quite frequently and I'd imagine creating more noise. That being said, a lot of us use a minor amount of "Hornet DLC" in close, to avoid bringing the power back too far, which would get you severely underpowered after entering the "burble".......ie you waggle the wings really gently and rapidly, which kills some lift (tiny little wings), without actually inducing a lineup problem, and all the while you are able to keep the motors spooled up and ready to respond if you start to settle. Hopefully that babbling paragraph of run on sentences made some sense :)
 
35 AoA said:
That being said, a lot of us use a minor amount of "Hornet DLC" in close [...] ie you waggle the wings really gently and rapidly, which kills some lift (tiny little wings), without actually inducing a lineup problem...
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The A-6 community says "You're welcome." ;)

Nauga,
and his flaperon popup
 
Is that why MD-80s sound so freaking loud compared to similar sized A319/737s?
 
35 AoA said:
No carrier based aircraft should ever be "near idling" during the approach.....you need the motors spooled up in order to have both good power response (we go up and down on glideslope with the left hand/throttle) as well as acceptable waveoff/bolter capability, especially with really poorly performing and slow spooling motors like the Tomcat had. More aerodynamically efficient airframes like the Tomcat and T-45 use/used things like speedbrakes open to artificially drive the power requirement higher while still being able to fly a ~3.5 degree glideslope. One thing the Tomcat did have, which might contribute to it being quieter, was Direct Lift Control (DLC), which allowed the pilot at least in theory, to keep the throttles steadier while dumping lift via DLC vs chopping the throttles. Or maybe it was just different intake aerodynamics......most of the noise you hear on approach is coming from the fan, not from the tailpipe. What you will hear with the Hornet is typically louder multiple throttle corrections to correct glideslope deviations. Power down to correct a climb, power back up above what is required to maintain glideslope to stop the descent, and then back to your "neutral power setting" that will then hold glideslope. These are very rapid throttle movements, but the effect is a lot of little surges of power and the fan speeds changing quite frequently and I'd imagine creating more noise. That being said, a lot of us use a minor amount of "Hornet DLC" in close, to avoid bringing the power back too far, which would get you severely underpowered after entering the "burble".......ie you waggle the wings really gently and rapidly, which kills some lift (tiny little wings), without actually inducing a lineup problem, and all the while you are able to keep the motors spooled up and ready to respond if you start to settle. Hopefully that babbling paragraph of run on sentences made some sense :)
Click to expand...

If you don't have 40%, you don't stand a chance.
 
labbadabba said:
Is that why MD-80s sound so freaking loud compared to similar sized A319/737s?
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The JT8 is older than the engines on the new 737's and A32x. But still, the -200 series JT8 like on the MD-8x is probably quieter than the straight JT8's like we run on the DC9 (and now 727). Even in the cockpit, you have to basically yet at each other at times to get the checklist done.
 
Shepherd said:
If you don't have 40%, you don't stand a chance.
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40%? RPM? :hairraise:

thats like 25% below ground idle haha. I agree, you are toast. Actually, from the LSO platform, you can very quickly hear when a guy "shuts em down" and it is scary if that quiet lasts for even a potato. More than that, and you probably bought yourself a waveoff.......there is absolutely no room for ever going near idle, no matter how high you are.
 
Threadjack

Do turbine blades break the sound barrier?
 
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