Trent 700 engine whine

[BTyyj]

Hi,

I have heard this on a lot of planes, but I find it is most distinctive on the Trent 700 A330. If anyone could answer what this sound is. It is almost like a hum or whine as the engines power up. I have searched all over the internet. I have heard somewhere that the sound is from the turbine blades breaking the sound barrier, although I am not certain about validity of that statement.

If you are not sure what sound I am talking about, listen at 0:40 on this video:

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

Thanks in advance

[iflyforpie]

It's the baby in 32B....

After that, the first howl is the bleeds (at 0:46). They dump some of the high pressure air from the compressor to reduce back pressure so the engine can accelerate without stalling.

As it is spooling up, that whisle sound is the core exhaust coming out through the turbine and/or diffuser. The whisle is a characteristically RR sound (pretty much any of their jets). Just listen to Back in the USSR.

The fan blades breaking the sound barrier is the low buzz saw sound you hear throughout the takeoff roll. All wide chord RR engines make that noise. I actually found the RB211-535s on the 757s to be the loudest.

[righthandman]

Well regardless of what the origin(s) of the sound is/are... when the brain tells the hand to advance the power levers forward and the ear picks up these sounds, it makes the muscles responsible for generating a smile come to life.

[palebird]

You guys are pathetic. There is nothing breaking the sound barrier in a jet engine..if there is then the engine and it's design are a complete failure..know what you are talking about before making statements like that..

[linecrew]

The whistle is a characteristically RR sound (pretty much any of their jets). Just listen to Back in the USSR.

FYI, the landing plane sound in "Back in the USSR" is actually from Rolls Royce Dart turboprop and not from a pure jet engine.

[gustind]

There is nothing breaking the sound barrier in a jet engine..if there is then the engine and it's design are a complete failure...

+1, the speed at intake is only about 0.4 Mach if I remember correctly. That being said, the air passing around them will (but shouldn't do to the twist in the blades).

[bezerker]

From RR:

"The tip of the fan blades can be travelling at speeds of over 1000mph"

http://www.rolls-royce.com/Images/gastu ... 2-4977.pdf

[Snagmaster E]

From RR:

"The tip of the fan blades can be travelling at speeds of over 1000mph"

http://www.rolls-royce.com/Images/gastu ... 2-4977.pdf

Proverbial egg in the face! Nice find bezerker.

I think some people should brush up on their turbine theory.

[Bede]

fan diameter = 97.4", fan RPM = 3000 RPM
speed = 97.4 inches*pi*3000 RPM
= 9.2 x 10e6 inches/minute
= 868 mph
> mach 1

The air flow within a jet never exceeds mach 1, but that doesn't mean the blades don't. I think even a C185 prop approaches the speed of sound.

[GoinNowhereFast]

The C185 float plane prop goes supersonic at the tips. That's why the thing is so danm loud, 2850rpm on takeoff.
I was talking to the the test pilot who did the STC in the US for the MT prop on the 185, and he said the primary reason for doing the STC was to reduce the tip speed and thus the noise. In his own words "the tips are going horribly supersonic".

[iflyforpie]

Yes, on a cold day my 206 prop will break the sound barrier. 2850 RPM but not quite as bad as the long prop on a 185.

The blades of a fan aren't any different. Generally you want to avoid supersonic flow because of the inefficiencies involved. Also, airflow in a duct doesn't stay supersonic for long before the shock waves slow it down, but that doesn't mean supersonic airflow is impossible. The reason why the newer fan blades are contoured is for better supersonic performance of the tips.

[Siddley Hawker]

The C185 float plane prop goes supersonic at the tips.

The Noorduyn was there first. And the round engine sounds better too.

[iflyforpie]

The C185 float plane prop goes supersonic at the tips.

The Noorduyn was there first. And the round engine sounds better too.

When I was at SAIT, we rolled out the 185 with its IO-520 and the Harvard with its R-1340 to do runs. With each at power, you couldn't even hear the Harvard...

[North Shore]

I see your 'Trent 700s' and raise you two R2800s...

[GoinNowhereFast]

I'm gonna call cheater! There's no way a jet can compare with the classic radial in terms of the pleasant sound produced.

[all_ramped_up]

I'm gonna call cheater! There's no way a jet can compare with the classic radial in terms of the pleasant sound produced.

The rumble and roar from the R-1820s on the Firecats when they're on the roll is one of my favourites.

[Siddley Hawker]

Nice one NS. Those short stacks sure snap.

[The Old Fogducker]

North Shore ... this will be my first season away from sitting on the patio at the Tanker Base watching a Bomb Group takeoff on a dispatch .... I'll miss it. Hopefully my LOA is only one season ..... I'm not quite ready to hang up my headset yet. Thanks for posting.

OFD

[Big Bus Mech]

That 215 was nice but props are for boats. Running and climbing into my flame proof suit

Nothing beats the RB211-22b on a cold YMX morning, its the whole package you get the whine and a smoke show!

[iflyforpie]

For jets, my favorite was the RR Nene in the CT-133. Sounds like the world's largest subwoofer on startup, and then to hear and feel the roar and crackle of the exhaust at full power was just awesome. Noise abatement shnoise abatement.

But nothing beats the beautiful sound of a round engine. Especially the four R-2800s of a DC-6 passing low overhead Skaha beach after taking off 16. Watch out for oil and retardant.

[BTyyj]

Thanks for the replies from everyone. Personally, my favorite is the initial sound of a Trent 700, but most of those aircraft types people have posted I haven't seen yet. Hopefully I will be able to see them some day.

[sidestick stirrer]

Well, I just have to jump in here and say MY favourite engine sound-by far-is the J79 in the Starfighter. Sure, it sounds like a Hoover on the start until it catches its breath but, from then on, there is no other engine yet made that sounds so much like it has a soul and is a living, breathing entity all on its own.
Much like an old steam engine breathing and wheezing away while idling, the J79 makes a plethora of different sounds, most of them not heard from any other engine.
My second favourite would have to be the GE90's on the Boeing 777 which are only audible from the pointy end during the start and the rundown at the end of the flight, thanks to the incredibly-noisy equipment cooling airflow and high-transonic Mach cruise speeds.
They start with an extremely-low frequency beat that slowly rises into the range that is detectable to the human ear but by that time, our entire bodies can sense the subtle vibration as the enormous assembly starts rotating and accelerating. This sound, very-slowly rising in pitch but not volume, brings a smile to everyone on the flightdeck and is known as " waking the sleeping giants", quite an appropriate observation to those who have experienced it.
On the shutdown, having spun away without complaint or hiccup for around sixteen hours nonstop on our longest leg while drinking their way through one hundred thousand kilos of Jet A, give or take a tonne or two , they would reverse the process, and-if one lingered in the quiet of the hurriedly-vacated flightdeck for a moment to listen-they expired with an audible, almost-contented sounding sigh.
Then, as previously mentioned in a similar thread, there is the unique airstarter on the earlier JT3D-powered DC-8's, not the -63 series with different ducting.