ConcordeBoy From , joined Dec 1969, posts, RR: Reply 4, posted (8 years 6 months 4 weeks 1 day 8 hours ago) and read 4636 times:
I've yet to see any official information, but I'd say the latter if I had to venture a guess... since every single PW4090 airline has gone that route, even those who've expressed their desire for more power out of PW.
Lan Chile also comes to mind-- they cancelled their entire 777 ambitions after Pratt's f^ckups with the PW4098's SFC.
could this just be a case of different parameters, eg temp, altitude?? I know some GE engines can be several thousand lbs thrust between different sources and its only due to different standard conditions
TimT From United States of America, joined Jun 2001, 168 posts, RR: 0 Reply 12, posted (8 years 6 months 2 weeks 5 days 15 hours ago) and read 4321 times:
Back in the early days of TWA's 767 powered with JT9D-7R4's TW was having some trouble with top of descent stalls, (pull power back and BOOM). It was rumored around TWA that P&W had certified the engine to 41,000 feet using a test cell certified for 39,000 feet. What we eventually found was the after 2 or 3 HP compressor overhauls that the cases were not as round as they should have been and the compressor blade tip clearance was short on one side and long on the other. And didn't necessarily coincide. After the overhaul procedure was modified to correct the clearance problems, the stalls diminished.
Lightsaber From United States of America, joined Jan 2005, 11951 posts, RR: 100 Reply 13, posted (8 years 6 months 2 weeks 2 days ago) and read 4211 times:
Quoting ConcordeBoy (Thread starter): No airline utilizes (or apparently, is allowed to) the PW4090 at higher than 90,000lbs... hence the artificial MTOW restriction to 648,000lbs for users thereof.
The reason for the pw4090 thrust limit is simple: Emissions. The pw4090 at 90,000lbf of thrust puts out 99.2% of the allowed ICAO NOx emissions. This is the highest certified thrust that Pratt is allowed to sell on the market. You are not allowed to fly into/out of a FAA or JAA airport without meeting ICAO emissions. In other words, the pw4090 is certified for 91,700lbf of thrust in every criteria *except* emissions. But you're not allowed to miss even one certification criteria... Note that the pw4090 has no trouble with the smoke or Carbon monoxide portions of the emissions certification.
The pw4098 has Pratt's 1st generation low emission combustor, the Talon I. This reduced emissions enough that even with the fuel efficiency miss its fine emission wise. Now why hasn't Pratt put a Talon I or Talon II combustor into the pw4090? Cost. The joke in the engine business is that "emissions are forever" as very few engines get recertified emissions due to the large costs involved. One exception is the pw4062 (with a Talon II) as UPS made emissions a criteria in their A300 purchase decision. Also the pw4068 was recertified with the Talon II. (As part of the botched pw4072 thrust increase).)
The one and only exception with a permanent emission waiver was the Concorde.
Gigneil From United States of America, joined Nov 2002, 16313 posts, RR: 87 Reply 14, posted (8 years 6 months 2 weeks 1 day 20 hours ago) and read 4187 times:
Quoting Lightsaber (Reply 13): One exception is the pw4062 (with a Talon II) as UPS made emissions a criteria in their A300 purchase decision. Also the pw4068 was recertified with the Talon II. (As part of the botched pw4072 thrust increase).)
Do you mean the 4156 and the 4168? They're different engines.
Lightsaber From United States of America, joined Jan 2005, 11951 posts, RR: 100 Reply 15, posted (8 years 6 months 2 weeks 1 day 10 hours ago) and read 4139 times:
Quoting Gigneil (Reply 14):
Do you mean the 4156 and the 4168? They're different engines
Gigneil, You are correct that they were sold as 4156 and 4168. I should have only used the 4168, there isn't a 4068! My bad!
Pratt Naming convention #XYZ
#=serier (e.g., 4000)
X=airframer (0=Boeing, 1=airbus, 2=McD)
YZ=thrust in thousands of pounds.
Pratt developed the combustor for the 4156 in a 4062. Why not! And it leaves the combustor certified for the 62k thrust level. I tend to default to calling them the 40XX as that was a bad habit in my old department in Pratt. Mea culpa. We'd refer to each family as the 62k, 68k, 90k, or 98k pw4000. oops. Recall that even if a thrust is an "upthrust" (e.g., the 62k pw4262), all of the lower thrusts become just derates (e.g., the 4156) of that engine family.
Now, technically, the 4156 and 4056/4062 are the EXACT same engine (if a generation 3 build. Earlier builds cannot be upthrusted to 62k, the fan and case aren't built for the stress), just with different interface points and of course computer logic. You can modify a 4056 to a 4156 in minutes for a few hundred bucks worth of parts. (Tubes, electrical connectors, and the Fadac logic chip.) Note: to go to the higher thrust might require different restrictors in the fuel injectors and other trivial parts. (But Pratt charges big $$$ for the higher thrust license and controls that but charging for the fadac logic chip.)
The 4056/4156 to 4062/4262 are all 94" Pratt 4000 series for 747, 767, A300, and MD11
The 4168 is the Pratt 100" diameter fan 4000 series custom for the A330
The 4084/4090 is the Pratt 112" diameter fan 4000 series custom for the 777.
The infamous 4098 kept the 112" fan (kept nacelle geometry) but had a reduced bypass ratio due to a larger core.
Note and appology to those in opperations: I understand you can't be this sloppy with the number. E.g., the mx on a 4156 is on a different schedule than a 4262 even though they are the exact same engine (exception fadac logic, signal connector, fuel connector, and possibly fuel injector restrictors) as they leave the factory! Same exact build of materials except for the parts mentioned.
Lightsaber From United States of America, joined Jan 2005, 11951 posts, RR: 100 Reply 17, posted (8 years 6 months 1 week 4 days 4 hours ago) and read 4016 times:
Quoting Trex8 (Reply 16): thanks for all that great info, what exactly did happen to the 4072??
The Pw4072, at the higher thrust level, had a temperature exceedence out of the compressor surge vents that would have required a nacelle material change and recertification. Due to GE having made some good sales of the CF-6 via lease incentives, Pratt didn't thing the return on a nacelle recertification was there. Also, Pratt was under contractual obligation to have *zero* nacelle modifications from the pw4068 to pw4072... so the plug was pulled.