Thrust
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747 And PW JT9D Questions

Sat Mar 17, 2012 8:42 pm

Hi there.

I had a question regarding the PW JT9Ds and why they were discontinued in favor of the PW 4000s...had they already reached their technical limitations? Also, i'm curious as to how many 747s that carried the original JT9D-3s were retrofitted with the JT9D-7As (I think that was the model...47,900 pounds of thrust vs. 43,000 pounds of thrust). I see a lot of photos of numerous TWA, Pan Am, and United 747s, among many others, that were delivered with the blow-in door JT9D-3s, and by the early 1980s most had been refitted with the upgraded versions...yet I noticed that the 747s that fly for the Iranian Air Force today still feature the original engines. I guess my question is, were virtually all classic 747s retrofitted with the more powerful JT9Ds, or was it varied...I know there were many 707s that were never retrofitted with turbofans vs. the original turbojets, but it seemed like the JT9D-3s were mostly absent on the first 747s by the late 1980s.
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Jetlagged
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RE: 747 And PW JT9D Questions

Sun Mar 18, 2012 1:28 am

My understanding is that once the JT9D-7 went into service, Pratt and Whitney offered JT9D-3 operators a conversion kit to upgrade the less powerful -3 engines to -7 standard. This involved modifications to the combution system and turbines. So the engines weren't changed as such, but upgraded. Perhaps as a military operator the Iranian Air Force weren't interested in the modification. To be honest I was surprised to hear any JT9D-3s were still flying.

The PW4000 has fewer moving parts than the JT9D and is therefore more reliable. Also all engine designs have a growth potential, increasing thrust as developments are made, but there is a limit. To go further you need a new basic design.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
Thrust
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RE: 747 And PW JT9D Questions

Sun Mar 18, 2012 6:37 pm

Yeah...if you look up the Iranian Air Force, you'll still see the signature blow-in doors of the JT9D-3...they are still flying the 747s TWA sold to them back in 1975....I'm surprised those jets can even stay in one piece anymore...the other reason I might suspect the JT9D-7s never got retrofitted on them would be the breakdown in relations between the U.S. and Iran.
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VC-10
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RE: 747 And PW JT9D Questions

Mon Mar 19, 2012 12:12 am

The blow-in doors may be a red herring. The blow-in doors disappeared as a result of the introduction of a redesigned nose cowl that was part of a noise reduction mod. I remember discussing it on this board at the turn of the century
 
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747classic
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RE: 747 And PW JT9D Questions

Mon Mar 19, 2012 1:58 pm

The blow-in doors installed on the early 747-100 and 200's are mostly deleted after the introduction of new nose cowls , called "quiet or fixed lip "nacelles.

For stage 2 or later stage 3 Far 36 Noise certification fixed lip nacelles had to be installed.
See for the difference in noise levels of a B747-100/JT9D-7(W) with blow-in door nacelles installed and the same aircraft/engine combination with fixed lip nacelles installed, here :
http://www.flightglobal.com/pdfarchive/view/1974/1974%20-%201086.html


AFAIK both nacelles can still be used on all subtypes of the first JT-9D series, produced under Type Certificate Certificate E20EA and the installed nacelle type is not an indicator for the installed subtype of JT-9D engine on that aircraft.
Also an JT9D nacelle intermix is allowed, according the 747 type certificate- note 6.

[Edited 2012-03-19 07:00:10]
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
Qantas744er
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RE: 747 And PW JT9D Questions

Mon Mar 19, 2012 8:34 pm

BA's first 747-136's had the JT9-3 and when the newer -136's started coming in with the JT9-7A they purchased a conversion kit from PW.

All engines were eventually modified to the -7A standard, however significant differences remained.

For this reason BA painted -7A and -7CA (converted) on all of the motors so the mechs knew what they would be dealing with before opening the cowling.
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MarkC
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RE: 747 And PW JT9D Questions

Mon Mar 19, 2012 10:10 pm

The -7 conversion also brought a noise reduction benefit. Because the aircraft could gain altitude faster, it was less noisy from the ground as it was further (higher) away.
 
Northwest727
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RE: 747 And PW JT9D Questions

Tue Mar 20, 2012 12:15 pm

Quoting VC-10 (Reply 3):

I was thinking that the cowl design had nothing to do with the type of engine, but wasn't sure. The redesigned intakes appeared around the mid 1970s, after the -7 made its debut but just before the tougher noise regulations went into effect (1978, I believe). Thanks for clearing this up.

Quoting 747classic (Reply 4):

Thanks for that chart. What's incredible is that the BAC 1-11 and its Speys, which everyone makes fun of for its noise, is actually quieter than the 747-100 with the JT9D-7W's. The only thing louder than it are low-bypass JT3Ds and the JT4A turbojet!
 
B747FE
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RE: 747 And PW JT9D Questions

Wed Mar 21, 2012 3:29 am

Quoting Thrust (Thread starter):
why they were discontinued in favor of the PW 4000s

As jetlagged said, it was at the limit of it's potential.
The last -7R engines were significantly different when compared with the -3's: Improved fan/case, compressor (from the -7Q on it had 16 stages), combustion chamber & turbine blades (single crystal), different materials, different seals.
Sub-systems were also greatly improved, especially the compressor control, fuel metering and case cooling systems.
From a throttle bar in the cockpit, turbine reversers and water injection to an electronic engine control. The list goes on.

Quoting Thrust (Thread starter):
how many 747s that carried the original JT9D-3s were retrofitted with the JT9D-7As

Probably most of them had there original -3 engines upgraded to -7 and subsequent upratings to -7A, F & J.
Most of the -7A's I saw were originally built as -3.

Quoting 747classic (Reply 4):
AFAIK both nacelles can still be used on all subtypes of the first JT-9D series, produced under Type Certificate Certificate E20EA and the installed nacelle type is not an indicator for the installed subtype of JT-9D engine on that aircraft.

  

Regards,
B747FE.
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Thrust
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RE: 747 And PW JT9D Questions

Fri Apr 20, 2012 5:43 pm

So the blow-in doors were not to help the engine suck in more air?
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DocLightning
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RE: 747 And PW JT9D Questions

Sat Apr 21, 2012 4:53 pm

Quoting Thrust (Reply 9):

So the blow-in doors were not to help the engine suck in more air?

AFAIK, they were. But they also made more noise. The new cowl had both the benefit of better airflow and quieter noise.
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113312
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RE: 747 And PW JT9D Questions

Sun Apr 22, 2012 12:19 pm

Later -200 models had -7Q, -7R and -70A versions of the JT-9D to name a few. However, all of the JT-9 are conventional hydromechanical fuel control unit engines while the later PW series powerplants feature FADEC (Full authority digital electronic control) . These assist in accurate power settings, efficiency, and observance of limits which aid in service life.
 
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747classic
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RE: 747 And PW JT9D Questions

Thu Apr 26, 2012 1:34 pm

Quoting 113312 (Reply 11):
Later -200 models had -7Q, -7R and -70A versions of the JT-9D to name a few. However, all of the JT-9 are conventional hydromechanical fuel control unit engines while the later PW series powerplants feature FADEC (Full authority digital electronic control) . These assist in accurate power settings, efficiency, and observance of limits which aid in service life.

To be exact : The installed JT9D-7R (R for Rosati, the lead engineer of P&W) series on late 747-200 and all 747-300 series were still conventional controlled, but had also a supervisory EEC (electronic engine control) for more accurate pwr settings and limit observance. This was a sort of "in between solution" before the appearance of the FADEC on the PW4000 series.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
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Jetlagged
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RE: 747 And PW JT9D Questions

Sat Apr 28, 2012 3:11 pm

Quoting 747classic (Reply 12):
To be exact : The installed JT9D-7R (R for Rosati, the lead engineer of P&W) series on late 747-200 and all 747-300 series were still conventional controlled, but had also a supervisory EEC (electronic engine control) for more accurate pwr settings and limit observance. This was a sort of "in between solution" before the appearance of the FADEC on the PW4000 series.

I thought it was called the 7R because the previous version was the 7Q. More puzzling to me was why the version lettering jumped from 7J to 7Q.
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