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Author Topic: JT9D-7R4  (Read 355 times)

Offline Maxair

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JT9D-7R4
« on: December 08, 2015, 02:15:44 PM »
How is it possible that my 747-300 with the JT9D-7R4 engines are chapter 3 certified but my 747-200s with the exact same engines are only Chapter 2?

Offline Sami

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Re: JT9D-7R4
« Reply #1 on: December 08, 2015, 02:21:11 PM »
It's not only about the engines but also about the airframe. Though for this exact case - can't comment directly (the B747 and all variants and all engines is quite a mess..).

Offline Maxair

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Re: JT9D-7R4
« Reply #2 on: December 08, 2015, 02:46:19 PM »
It has nothing to do with the airframe. The engines produce the noise. Thats why all of the old JT8Ds that were on 737s, DC9s 727s and so on had to be equipped with Hushkits to make them chapter 3 compliant. They didnt change the airframe.

Offline Sami

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Re: JT9D-7R4
« Reply #3 on: December 08, 2015, 02:56:13 PM »
The noise certification is not engine specific, it is aircraft model specific. Each model and even each weight variant in real life has a dedicated certification for the noise ... Even different landing flap settings for some models create different noise levels and may be the deciding factor between level 2 or 3 (the planes are always certified with the "most noisy" flap setting by the way).. So it's most definitely also about the airframe.

But what I originally meant was that it could be that the -200 with those engines is noisier than -300, since it's a slightly different design. Though that's highly unlikely since those two are so similar.

Checking ICAO's database (http://noisedb.stac.aviation-civile.gouv.fr/find.php), I see that all early 747s are grouped together and it's a very longlong list there with all different options and weights. But I'd say that most likely (with a quick look) also the -200 with the 7R4 engines should be chapter 3 (though not a 100% fact).. But I've updated it to the master database (= all future games) now anyway.

Offline Maxair

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Re: JT9D-7R4
« Reply #4 on: December 08, 2015, 03:30:13 PM »
The only reason flap settings have anything to do with noise levels is because they cause drag which requires more power to overcome. More power = more noise. But you already know that. Anyways we can go on about this forever so back to my original post. There is no conceivable reason why the -200 and -300 shouldn't be uniform with regards to chapter 3 certification with the exact same engines equipped.

Offline wapp11

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Re: JT9D-7R4
« Reply #5 on: December 08, 2015, 04:24:05 PM »
The 300, even though being a larger aircraft than the 200, burns less fuel with those same engines. Maybe you should worry about that too!?

Offline alexgv1

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Re: JT9D-7R4
« Reply #6 on: December 08, 2015, 04:30:35 PM »
The only reason flap settings have anything to do with noise levels is because they cause drag which requires more power to overcome. More power = more noise. But you already know that. Anyways we can go on about this forever so back to my original post. There is no conceivable reason why the -200 and -300 shouldn't be uniform with regards to chapter 3 certification with the exact same engines equipped.

You may be surprised to know that most noise on final approach and landing is aerodynamic  from the high lift and drag devices and not the engines (which of course are back from their takeoff power setting).

Hope this helps  :)
CEO of South Where Airlines (SWA|WH)

Offline Maxair

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Re: JT9D-7R4
« Reply #7 on: December 08, 2015, 07:17:33 PM »
No it doesnt help but thanks. Ive lived under the approach path to Rwy 06 at yqm for 35 years. I fly planes myself. I know what im hearing. If an airplane makes so much noise aerodynamically then why did no one hear the Gimli Glider when it descended on that abandoned airfield in 1983? Cmon people. You cant possibly be serious?

Offline Maxair

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Re: JT9D-7R4
« Reply #8 on: December 08, 2015, 07:18:59 PM »
The 300, even though being a larger aircraft than the 200, burns less fuel with those same engines. Maybe you should worry about that too!?


Worry about what exactly?

Offline Sami

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Re: JT9D-7R4
« Reply #9 on: December 08, 2015, 07:35:30 PM »
The 300, even though being a larger aircraft than the 200, burns less fuel with those same engines. Maybe you should worry about that too!?

Again, not about the weight alone (though it's of course a big factor in jets). -300 cruises faster due to various aerodynamic improvements (0.01 mach more; though for aws game play purposes both have the same cruise speed) and those changes also make the plane more fuel efficient. A source quotes 3-5% better climb fuel performance for example, and another source even 10% better cruise fuel performance (which is quite high and I'm not really buying that).

The aero/structural changes in larger planes can make big differences. I remember when MD-11 first came out it did not meet the performance targerts but several PIPs (performance improvement packages) regained the promised perf.figures and the aerodynamic and weight tweaks improved the fuel consumption very much (something like 5% at least, cannot remember exactly anymore).


No it doesnt help but thanks. Ive lived under the approach path to Rwy 06 at yqm for 35 years. I fly planes myself. I know what im hearing.

Well, what can I say. I fly planes myself. And I sure hope I know what I hear too.. (glup)  ;D  And I've researched a bit about this noise certification stuff for the purposes of modelling it to the sim too (though not my strongest area).. It's not about the engines alone like I already pointed about (the jet engine for a modern airliner is at about 40-50% power when on final approach, vs. about 85-105% power on takeoff). But in regards to your original message, see my earlier reply in this thread:

Checking ICAO's database (http://noisedb.stac.aviation-civile.gouv.fr/find.php), I see that all early 747s are grouped together and it's a very longlong list there with all different options and weights. But I'd say that most likely (with a quick look) also the -200 with the 7R4 engines should be chapter 3 (though not a 100% fact).. But I've updated it to the master database (= all future games) now anyway.


More about the aerodynamic noise of aircraft:
http://flyquietoak.com/_source/pdf/Tab%202b%20PDF%20links/aircraft_noise_fundamentals.pdf
Quote
The noise generated by an aircraft flight is quite complex. The sound sources can be described in four broad categories:  jet noise (the mixing of high velocity exhaust gases with ambient air), combustor noise (the noise associated with the rapid oxidation of jet fuel and the associated release of energy), turbomachinery noise (often noticed as an aircraft is coming towards you), and aerodynamic noise (the noise associated with rapid air movement over the airframe and control surfaces). New technologies in modern aircraft have achieved significant reductions in jet noise and combustor noise. Turbomachinery noise has also been reduced in newer aircraft. Aerodynamic noise is a current area of acoustic research to reduce aircraft noise. As jet noise, combustor noise and turbomachinery noise are reduced, aerodynamic noise may remain as the major noise source on aircraft of the future. 


http://adg.stanford.edu/aa241/noise/noise.html
Quote
Non-propulsive noise

In addition to the engine noise, the shear of the boundary layer and unsteady vortex shedding from landing gear, landing gear doors, and other separated flows as well as flap edge flows contribute a significant part of the acoustic energy, especially for large aircraft on approach.
« Last Edit: December 08, 2015, 07:51:26 PM by sami »

Offline Maxair

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Re: JT9D-7R4
« Reply #10 on: December 08, 2015, 10:39:01 PM »
Obviously anytime air passes over a surface at very high speeds it creates sound. Theres no disputing that fact. But noise regulations were created because the turbojets and early version turbofan engines were very loud and were a nuisance around large busy airports. Noise abatement procedures were created to curb noise around airports near residential areas by limiting throttle settings and climb-out procedures. While i agree that as future generations of the Hi bypass ratio engines get quieter and quieter that the aerodynamic noise could potentially be the most significant source of noise pollution, i am pretty confident that in the early to late 80s it was not the major issue. Having said all that, my post was about the -200 and -300 discrepancy and if that will be addressed in the future then im happy with that.

Offline alexgv1

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Re: JT9D-7R4
« Reply #11 on: December 09, 2015, 12:32:10 AM »
I fly planes myself.

If you fly planes yourself then you might notice a shed load of noise next time you put the gear down (even at idle)... but yeah that's beside the 747 argument.

Obviously anytime air passes over a surface at very high speeds it creates sound. Theres no disputing that fact. But noise regulations were created because the turbojets and early version turbofan engines were very loud and were a nuisance around large busy airports. Noise abatement procedures were created to curb noise around airports near residential areas by limiting throttle settings and climb-out procedures. While i agree that as future generations of the Hi bypass ratio engines get quieter and quieter that the aerodynamic noise could potentially be the most significant source of noise pollution, i am pretty confident that in the early to late 80s it was not the major issue. Having said all that, my post was about the -200 and -300 discrepancy and if that will be addressed in the future then im happy with that.

The older aircraft and engines were louder hence the throttle cutback or noise abatement departure procedures were adopted, however the latest focus in aerospace engineering is on reducing airframe noise as turbofan engines are so mature now that they can't reduce the noise much more without changing how we propel our aircraft.

Happy to help   8)
CEO of South Where Airlines (SWA|WH)

 

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