AngelAirways
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767 RR Vs PW/GE Fuel Burn

Sat Sep 01, 2007 12:43 am

HI

I was looking at the SFC for an RB211-524H and it is around 0.58. Meanwhile the PW4060 and CF6-80C2 are in the 0.35 region.

I am perplexed at why the RB211 has a much higher SFC, and how this affects overall Aircraft fuel burn on a 767. I know SFC for an engine and Fuel Burn for an aircraft do not quite correlate directly.

Can anyone help??
 
speedracer1407
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RE: 767 RR Vs PW/GE Fuel Burn

Sat Sep 01, 2007 1:33 am

I don't know what your source is, but the last time I looked at a spec sheet comparing various engine performances, those are exactly the numbers I saw. But look closely; on mine, there's a superscript "2" next to all of RR's SFCs, and a scroll to the bottom indicates that RR's numbers reflect SFC at cruise power, where everyone else's reflects SFC at maximum power. That likely accounts for the difference, as I doubt the RB211 actaully has nearly double the SFC of its competitors.
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zeke
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RE: 767 RR Vs PW/GE Fuel Burn

Sat Sep 01, 2007 2:13 am

Quoting Angelairways (Thread starter):
Can anyone help??

The problem is you are comparing the cruise TSFC of one engine to the takeoff TSFC of another, most high bypass engine around at the moment have a TSFC of 0.3-0.4 at takeoff, and 0.5-0.6 in cruise.

During takeoff the thrust being produced is higher, so even with a lower TSFC than cruise, the amount of fuel being consumed is greater.

When comparing engines, you also need to take into account the mass of the engine, the speed and altitude of the aircraft as this will effect the efficiency of the engine.

RB211-524H-T - TSFC is closer to 0.56 in cruise, generating 11,813 lb thrust at 35,000 ft, M0.80
PW4060 - TSFC is closer to 0.58 in cruise, generating 12,000 lb thrust at 35,000 ft, M0.80
CF6-80C2B6 - TSFC is closer to 0.564 in cruise , generating 12,000 lb thrust at 35,000 ft, M0.80

RB211-524H-T - TSFC is closer to 0.35 at takeoff
PW4060 - TSFC is closer to 0.365 at takeoff
CF6-80C2B6 - TSFC is closer to 0.348 at takeoff

RB211-524H-T - dry weight 9,470 lb
PW4060 - dry weight 9,213 lb
CF6-80C2B6 - dry weight 9,670 lb

The RB211-524H-T (60,600 lb), PW4060 (60,000 lb), and CF6-80C2B6 (60,800 lb) are all 60 klb engines used on the 763ER.

Looking at the numbers above the CF6 and RB211 are fairly close, with PW having the to carry about an extra 900 lb for the engines alone over a CF6, and more fuel efficient.

The part of the equation that we do not know, is the purchase price and maintenance costs for the engines. With jet fuel today at 2.055 US$/US gal (todays quote from IATA) it would still be possible to put a pair of PW power plants on a 763ER and still come out with a overall lower cost of ownership over the lower fuel burning competitors.

[Edited 2007-08-31 19:14:42]
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jetmech
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RE: 767 RR Vs PW/GE Fuel Burn

Sat Sep 01, 2007 1:30 pm

Quoting Angelairways (Thread starter):
I am perplexed at why the RB211 has a much higher SFC, and how this affects overall Aircraft fuel burn on a 767. I know SFC for an engine and Fuel Burn for an aircraft do not quite correlate directly.

The best thing is that you are actually perplexed and seeking an explanation for the discrepancy. A certain member that spams on A'net posts such numbers as "fact", despite the SFC's being at two completely different phases of flight.

Quoting Zeke (Reply 2):
RB211-524H-T - TSFC is closer to 0.56 in cruise, generating 11,813 lb thrust at 35,000 ft, M0.80
PW4060 - TSFC is closer to 0.58 in cruise, generating 12,000 lb thrust at 35,000 ft, M0.80
CF6-80C2B6 - TSFC is closer to 0.564 in cruise , generating 12,000 lb thrust at 35,000 ft, M0.80

RB211-524H-T - TSFC is closer to 0.35 at takeoff
PW4060 - TSFC is closer to 0.365 at takeoff
CF6-80C2B6 - TSFC is closer to 0.348 at takeoff

I always knew that the RR was much closer to the GE and P&W despite the vain efforts of a certain A'net troll!

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
baroque
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RE: 767 RR Vs PW/GE Fuel Burn

Sat Sep 01, 2007 6:52 pm

Quoting Zeke (Reply 2):
The problem is you are comparing the cruise TSFC of one engine to the takeoff TSFC of another, most high bypass engine around at the moment have a TSFC of 0.3-0.4 at takeoff, and 0.5-0.6 in cruise.



Quoting Zeke (Reply 2):
Looking at the numbers above the CF6 and RB211 are fairly close, with PW having the to carry about an extra 900 lb for the engines alone over a CF6, and more fuel efficient.

Great post Zeke, but is the para about weights correct? On your data, I would have thought the PW was carrying less weight rather than more?????
 
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zeke
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RE: 767 RR Vs PW/GE Fuel Burn

Sat Sep 01, 2007 7:32 pm

Quoting Baroque (Reply 4):
I would have thought the PW was carrying less weight rather than more?????

Just had a look at the TCDS for the PW4060, it is actually heavier than my other reference indicated it is 9,420 lb, CF6 is the same, cannot check the RB211 TCDS as RR being UK certified includes more into their empty engine mass than the FAA (the TCDS says 12,540 lb).
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
Tristarsteve
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RE: 767 RR Vs PW/GE Fuel Burn

Sat Sep 01, 2007 8:05 pm

Quoting Zeke (Reply 5):
cannot check the RB211 TCDS as RR being UK certified includes more into their empty engine mass than the FAA (the TCDS says 12,540 lb).

Remember that the RB211-524 includes the thrust reverser in the basic engine. There are no C ducts on an RB211.
 
AngelAirways
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RE: 767 RR Vs PW/GE Fuel Burn

Sun Sep 02, 2007 2:18 am

Thanks everyone for the replies

I knew that there's something fishy about the figures I saw published (shock horror they were in a PW booklet  Smile) in that it wasn't an "apples with apples" comparison.

Much more clear now. Thanks again.

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