YoungDon From United States of America, joined May 2001, 303 posts, RR: 0 Posted (9 years 11 months 2 weeks 1 day 12 hours ago) and read 6383 times:
Hello all,
Does anyone know where I can find a database of specific fuel economies (cruise) for heavy jet engines. Any help in this topic would be greatly appreciated.
Prebennorholm From Denmark, joined Mar 2000, 5810 posts, RR: 56 Reply 1, posted (9 years 11 months 2 weeks 11 hours ago) and read 6344 times:
I doubt that you can find such data.
Specific fuel consumption (SFC) is dependant upon a few factors, even in "cruise".
At what altitude are we cruising, 25,000 or 40,000 feet?
Are we heavy, full payload and full tanks for a long journey, or are we light, little payload and coming near our destination? There will be an enormous difference in the induced drag on the wing, and therefore also on the actual power setting.
Mach number?
The same engine can have very different SFC's at various conditions.
I think that the best data are found on the manufacturers' webs, rolls-royce.com, CFM56.com etc. When they tell a SFC, then it is probably the SFC at the most favourable conditions for the specific engine type, which can vary a lot among different engine types.
Always keep your number of landings equal to your number of take-offs, Preben Norholm
EssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 2, posted (9 years 11 months 2 weeks 8 hours ago) and read 6330 times:
1. Baloney. AW&ST publishes a Source Book every year that has SFCs listed for every engine and dash number. Read the footnotes in the intro that define the parameters; it can be back ordered from their website.
2. SFC is lbs of fuel burned/lb of thrust produced, or the reciprocal of this if you prefer. Note the math; SFC is totally independent of a/c configuration, so the comment:
"Are we heavy, full payload and full tanks for a long journey, or are we light, little payload and coming near our destination? There will be an enormous difference in the induced drag on the wing, and therefore also on the actual power setting."
has nothing to do with it. Fuel burn per unit distance may vary with the above scenario, but SFC will not vary significantly for an engine in the flight regime.
YoungDon From United States of America, joined May 2001, 303 posts, RR: 0 Reply 3, posted (9 years 11 months 1 week 6 days 9 hours ago) and read 6287 times:
Thx for the responses.
What is an AW&ST Source Book and where can I get one? I know that SFC is hard to find, but I didn't know it was this hard!!
FDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 44 Reply 4, posted (9 years 11 months 1 week 6 days 9 hours ago) and read 6286 times:
Essential Power
I love getting the AWAST Sourcebook every year. It's a great bonus included in the regular subscription price. I love poring through all the statistics.
In regard to this post though, I found an interesting difference between GE, RR and PW.
GE and Pratt publish their SFC based on T/O thrust while Rolls uses cruise thrust.
I don't have one handy at the moment but if memory serves me, GE and Pratt SFC's are considerably lower than Rolls. I would have instinctively though that SFC at cruise would be lower than T/O. What's your take on this?
Delta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 9 Reply 5, posted (9 years 11 months 1 week 6 days 8 hours ago) and read 6284 times:
FDXmech....I would guess that the lower SFC at T/O thrust is due to higher thermal efficiency as the engine is running hotter. But it can't be maintained at this condition continuously, while the cruise thrust can. This is also consistent with culture -- the US cmpanies like to show the best of their product, while the Brits tend to be more conservative.
I'm not a powerplant expert, so don't take this to the bank. It's an interesting question, I'm curious what others think.
EssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 6, posted (9 years 11 months 1 week 6 days 7 hours ago) and read 6278 times:
Nice question FDXmech! I recycled my most recent Source Book, so I can't evaluate specific values...BUT-
For a given core, the hotter the EGT, the higher the SFC. For the trend stated above, my guess is that Rolls chooses to run its engine closer to its cruise temp limit than GE or Pratt choose to run theirs with respect to takeoff limits...Certainly and "apples and oranges" at best, with the converse being engine life.
Gotta love the decisions, decisions, decisions in this industry...
SAS23 From , joined Dec 1969, posts, RR: Reply 7, posted (9 years 11 months 1 week 5 days 15 hours ago) and read 6245 times:
Don't forget that the RR engines are triple spool, whilst the GE/PW ones are generally dual spool. This means that the RR engines should have better sfc.
Dynkrisolo From United States of America, joined Feb 2001, 1813 posts, RR: 8 Reply 8, posted (9 years 11 months 1 week 5 days 9 hours ago) and read 6234 times:
Absolute nonsense. RR engines do not have better SFC. In terms of fuel consumption, RR is no. 3 in nearly all competition except on the A330.
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