Hi Everyone.

I know Engines are bound to make noise but what is it that gives Jet Engines there characteristic Whistle and High Pitched Sound?

It only ever seems to happen when they're relatively far away i.e. 1000 ft or more. Maybe its the normal sound of the engine, but quieter so it whistles. Sorry I cant be more detailed, or certain.

Anyway, I love the sound of the high pitched whine/whistle/cry of a jet engine, so if anyone can find a clip of it, please tell me.

How about that is the sound wave the blades make when whirling through the air. The tone being dependant on the speed. That's my thought anyway...


http://www.meanrabbit.com/wavhtml/airwave.htm

http://www.turbosquid.com/FullPreview/Inde...ion/FullPreview

http://www.rcexchange.com/html/sound-3.html

Kind of an odd-ball thought, but the doppler effect would make the sound even more high pitched than it really is, adding to the whine (assuming it's in flight and moving towards you).

Hey SF3aviatrix that is a nice sound website, I downloaded some of those sound files and use them on startup and shut down on my pc. Really good stuff! Thanks a lot!

What makes jet engines whistle?

A pretty girl engine. LOL !!

Funny, I always thought it was the leprechauns inside the combustion chamber!

Leprechauns only whistle when they don't know the words.

Would the blades also have anything to do with the "growling" effect that you get on takeoff particularly with RR and GE variants? Is it the blade vibration that creates that?

I believe the sounds of an engine are uniquely generated by engine speed, compressor and turbine section pressures both in flow and back pressure, number of turbine blades, configuration of tailpipe, and the plane's location relative to the listener among others. And yes, the vibration of every part of the engine would contribute to the sound. After all, sound is nothing but vibration.

It's all music though.

I fly a 727...the JT8D doesn't so much whistle as scream like a mother f***er...but that's just me.

The whine, whistle, roar, whatever is a combination of the turbines, compressors, and the combustion of the fuel in the chamber. Higher bypass (turbofan) engines will have that "growl" because there is a higher percentage of air flowing around the "action" of the engine itself, supermechanical blah, blah, blah, and it's not so bloody loud as the (usually) lower bypass turbojets, such as the JT8D or JT3D.

Leprauchans always know the words...I don't know how...but they do. It's a fact of life...just go with me on this one. Engines, however, can NEVER freaking remember CRAP! Thusly, they whistle. They also hum, rumble, roar, and occasionally shreik. When they shreik, you have to throw something at them...try money. Everyone loves money...$10s and $20s.

LOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOL!!!!

from what i've read is that the sound comes from the deference in speed of the blades from the center to the tips. Thats what creates some of the sound.

And as for the wistling its always there and the reason for not hearing when your close is that its taken over by the deeper sounds. the reason you can hear it from further away is that high pitch sounds can travel longer distances so the low sound can cover the wistling nose.

srry for missed spelling.

im gonna have to correct you here, pitch as you are calling it is really frequency. As you know whales communicate with low freq sounds and as such they can talk from over 10 or so miles away(they can also hear good). Low freq(low pitch) sounds travel further. The reason you hear the while more from affar is low frequency sounds loose energy quicker(might not be audible to you but still there) whereas high freq sounds pack more punch for a given range(thats why F-16 and 15's idle is almost more loud and annoying than full mil power(not AB).

Ahh, informative post there, McChord. I have a few questions myself on high bypass turbofans, and rather than start a new thread, figured i'd toss them in here.

In regards to the B757 and the RB-211's or PW2037's mounted on them, why does she ahve that patented "whirring" sound. Anyone who's ever been around 757's should know what i'm talkin about, u can always tell when one takes off by this particular "whirr" i speak off. U can even hear it clearly inside the plane, i can at least. Anyone have thoughts on that?

Also, i'm kinda having a hard time wrapping my mind around the process of derating engines. What all goes into that, and how is it done? And one more thing, does anyone have a way of portraying to the layperson like myself a way of understand "pounds of thrust"? What exactly does 55,000lbs of thrust mean?

The amount of weight the engine can pull, in this case 55,000lbs. Although this 110,000lbs (both enignes combined) of thrust does not equal the weight of the aircraft- hows that work? Well the engines only have to pull the aircraft forwards enough for lift to occur. Once this happens the wings take a large share of the weight. Examples of higher thrust to weight ratios is the space shuttle. It's engines (im not sure of the exact rating) pump out enough thrust to throw that thing vertical, meaning that the thrust is higher than weight of the aircraft ahhh i mean spacecraft.

i know this from heart, about 600-660,000lb thrust for all the main engines combined, and each booster puts out 1,000,000lb a piece giving about 2.6 millionlb of thrust on takeoff. This is however nothing compared to the Saturn V's main's which pumped out something like 7,000,000lb of thrust on takeoff eating 40,000 gallons of fuel a minute(compare that to an F-16 engine which burns something like 132 gallons a minute at sea level afterburning.

As for why the 757 RR engines make that growling buzzsaw sound, I'm no expert on engines but i would say its a combination of the full nacelle type, the shape and density of the fan blades, how much play there is in them, the number of compressor stages, the bypass ratio. The list could go on, the P&W powered versions sound about 90% identical to C-17's(90% engine similarity). Also the tips of the blades are usually going supersonic but since pressure has a direct influence on the speed of sound its not "breaking" the sound barrier even though the tips may be moving at 800mph. The sound is especially influenced by the chord of the blades and how many there are. The more blades there are the more it sounds like a buzzsaw in general, which is why the GE 110/115B and RR A380 Trents are so quite, that and the fan is massive compared to the core, the wide chord blades dont have to turn as fast to get the same thrust. If they had conventional blades they would have a really loud horrible buzzing sound.

That's correct. Depending on the diameter of the fan, the blade tips go supersonic. They can reach speeds up to 500 m/s!!! So they produce this typical 'roaring buzzsaw' sound (as they break the sound barrier).
You can hear it easily on CFM engines (e.g. on A340-200/300)

I can't remember where I found that information. Perhaps somebody has a source for that topic?

Its from the compressor. Stand near an F27 without ear defenders and you will need a hos !

Wha ?

Sweet, thanks alot, Eric. I'm less of an idiot now than a few days ago, if only slightly

I think it happens when you pinch their boobs.

Dude...nothing can whistle when you pinch their boobs. Do you know how difficult that is? No way...

Nothing sounds as good as an MD80 or a DC-9! Whenever I see videos of them, the sound of the engines get stuck in my head, the MD80 and DC-9 are like no other. You can actually hear the engines drop and rise in throttle in those classics during aprroach, and can hear the idle, as well as the many differant tones, and sounds of the engines. That is why I like the MD80 so much-becuse of the great sound. Well, it's 11:28PM, time to hit the sack, good night everyone, and have a good night, good bye!

Ladies & Gentlemen, I hope you enjoyed your flight, thank you for flying A Wake Air, have a good night.

Thought I'de like to make a little joke, my mood is lifted.

Well correct me if Im wrong but I think the sudden suction of hundreds of pounds of air causes the wind to whistle moving at such sudden speeds.
-Aspiring Pilot

Does anyone know why the 757 makes that sort of grunting noise on take-off?

Dan

Here is an interesting video on jet engine operation. Good sound. Watch the graphics on the right side during run.


http://www.rolls-royce.com/education/schoo...ey02/flash.html

Nice animation, Magnum, thanks alot for the link...good stuff.

ahh sorry must of missed it when i was skim reading it

Dan