Qantas744er
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PW4056 On The 744

Wed Oct 04, 2006 1:27 am

Got a question, the PW4056 has 56,750Lbs of thrust compared to the
GE CF6-80C2B1F ( 58,000Lbs) and the RR RB211-524G (58,000Lbs)

So for operators like CX, SQ, UA etc. does this mean that their 744´s will have
a "longer" takeoff roll than the other two engine types? And this will result in a slower climb rate right?

And for the pilots.. how does it compare, is there a real difference?

Cheers Leo
You live and you die, by the FMA
 
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jetmech
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RE: PW4056 On The 744

Wed Oct 04, 2006 1:43 am

Quoting Qantas744ER (Thread starter):
So for operators like CX

Erm... Do you mean MH Qantas744ER? I am pretty sure CX does not currently have P&W powered 744's, although they will have some P&W powered 747 (744?) freighters in the future.

[Edited 2006-10-03 19:04:45]
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
Avro85
Posts: 236
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RE: PW4056 On The 744

Wed Oct 04, 2006 2:01 am

Quoting Qantas744ER (Thread starter):
So for operators like CX, SQ, UA etc. does this mean that their 744´s will have
a "longer" takeoff roll than the other two engine types? And this will result in a slower climb rate right?

I would rather suspect that the planes with the PW engines will be certified with a smaller MTOW.... I'm not sure  Wink

Chris
 
Qantas744er
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RE: PW4056 On The 744

Wed Oct 04, 2006 2:31 am

Quoting JetMech (Reply 1):
I am pretty sure CX does not currently have P&W powered 744's, although they will have some P&W powered 747 (744?) freighters in the future.

Actually they do.. just check the database... they are all ex SQ planes.

Quoting Avro85 (Reply 2):
I would rather suspect that the planes with the PW engines will be certified with a smaller MTOW.... I'm not sure Wink

Nope because the SQ and CX (ex SQ) 744´s all have the max MTOW for the 744, 875,000Lbs

Cheers Leo
You live and you die, by the FMA
 
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jetmech
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RE: PW4056 On The 744

Wed Oct 04, 2006 2:35 am

Quoting Qantas744ER (Reply 3):
Actually they do.. just check the database... they are all ex SQ planes.

Yep, you are quite right Qantas744ER   . I stand corrected.

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[Edited 2006-10-03 19:39:21]
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: PW4056 On The 744

Wed Oct 04, 2006 2:59 am

Quoting Qantas744ER (Thread starter):
Got a question, the PW4056 has 56,750Lbs of thrust compared to the
GE CF6-80C2B1F ( 58,000Lbs) and the RR RB211-524G (58,000Lbs)

So for operators like CX, SQ, UA etc. does this mean that their 744´s will have
a "longer" takeoff roll than the other two engine types? And this will result in a slower climb rate right?

If all 3 engine types are operated at max rated thrust on respective a/c that weigh the same amount, the Pratt powered a/c will have slightly less performance in all flight regimes. In practice, it is a negligible difference.

Cheers-
 
Qantas744er
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RE: PW4056 On The 744

Wed Oct 04, 2006 3:46 am

Quoting JetMech (Reply 4):
Yep, you are quite right Qantas744ER   . I stand corrected.

No problem.. thats what aviation is all about, righ? Learning new things Big grin

Quoting Essentialpowr (Reply 5):
If all 3 engine types are operated at max rated thrust on respective a/c that weigh the same amount, the Pratt powered a/c will have slightly less performance in all flight regimes. In practice, it is a negligible difference.

Thanks, that pretty much what i wanted to know  Smile

Cheers-
You live and you die, by the FMA
 
Tristarsteve
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RE: PW4056 On The 744

Wed Oct 04, 2006 5:20 am

On a max weight take off out of Hot Singapore, for a 12hr flight our B744 uses reduced power take off. So you would only notice that you have PW engines on really long flights. Up to then everything would be the same, same take off roll at the same thrust, just the PW engine would come up against a limitation a little earlier than a RR or GE engine. Say a 13 hr flight instead of a 13.5 hr flight. So if your route profile does not include ant flights over 13hrs, you would never notice it.
 
EssentialPowr
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RE: PW4056 On The 744

Wed Oct 04, 2006 5:46 am

Quoting TristarSteve (Reply 7):
On a max weight take off out of Hot Singapore, for a 12hr flight our B744 uses reduced power take off. So you would only notice that you have PW engines on really long flights. Up to then everything would be the same, same take off roll at the same thrust, just the PW engine would come up against a limitation a little earlier than a RR or GE engine. Say a 13 hr flight instead of a 13.5 hr flight. So if your route profile does not include ant flights over 13hrs, you would never notice it.

This is a more than a bit confusing. If the a/c and take off weight weights are the same, and all 3 engines are operated at max rated thrust as provided above, the Pratt powered a/c has less performance. What diff does the 13 vs 13.5 hr flight distinction mean? If the engines have the same SFC, then the Pratt w/ less thrust has MORE range.
 
Avro85
Posts: 236
Joined: Sat Jun 11, 2005 4:35 am

RE: PW4056 On The 744

Wed Oct 04, 2006 6:36 am

Quoting Qantas744ER (Reply 3):
Nope because the SQ and CX (ex SQ) 744´s all have the max MTOW for the 744, 875,000Lbs

OK thanks for clarifying. Sorry for the mistake ...

Chris
 
Tristarsteve
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RE: PW4056 On The 744

Wed Oct 04, 2006 11:28 pm

Quoting EssentialPowr (Reply 8):
What diff does the 13 vs 13.5 hr flight distinction mean?

OK, sorry finding it difficult to explain.
At the same weight on the same runway at the same OAT all three engine types would have a similar take off thrust requirement. As one of these factors increases then the PW engined aircraft will reach its linits before the others.
For example for a max zero fuel weight departure on the same runway, the PW engine aircraft would be able to carry less fuel than the other two. This would make its planned mission shorter, or for the same mission it would have to offload payload in able to take the required fuel.
On the B744 out of SIN for LON with max zero fuel weight, this would not be noticed as we use derated thrust.
You would need a longer mission, or a shorter runway to notice the restriction.
 
PhilSquares
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RE: PW4056 On The 744

Thu Oct 05, 2006 12:29 am

Just to throw this in, the RR powered aircraft are substantially heavier, so they won't have the same fuel, the RR are also slightly heavier than the PW, so again, the fuel won't be the same.

In reality, there is no discernible difference. The difference in thrust is neglible.
Fly fast, live slow
 
EssentialPowr
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RE: PW4056 On The 744

Thu Oct 05, 2006 2:12 am

Quoting Tristarsteve (Reply 10):
As one of these factors increases then the PW engined aircraft will reach its linits before the others.

I agree.

Quoting Tristarsteve (Reply 10):
For example for a max zero fuel weight departure on the same runway, the PW engine aircraft would be able to carry less fuel than the other two. This would make its planned mission shorter, or for the same mission it would have to offload payload in able to take the required fuel.

Negative. Same a/c remember, certified to the same weights, same day, but different engines? The MZFW won't be limiting. If there was a runway or climb limitation in which max rated thrust was required, then the Pratt powered a/c would be penalized with a runway or climb limit, which would lower MGTOW with a reduction in either payload or gas.

You stated (I copied it from my post):

Quoting EssentialPowr (Reply 8):
On a max weight take off out of Hot Singapore, for a 12hr flight our B744 uses reduced power take off. So you would only notice that you have PW engines on really long flights.

Therefore, no runway or climb limit is assumed by that statement. I assumed a max rated thrust t/o, then, and assumed equal SFCs. Since the pratt powered a/c is producing less thrust at equal SFCs as the other types, it uses less fuel for takeoff and climb. For equal MGTOWs (again, exact same a/c), that reduced fuel burn in climb translates to more range for the Pratt powered a/c, b/c it burned less gas in the t/o and climb regimes, and we can assume that cruise thrust is equal for all 3 types.

Make sense?

[Edited 2006-10-04 19:15:24]

[Edited 2006-10-04 19:16:14]

[Edited 2006-10-04 19:18:42]

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