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 GEnx Vs. Trent XWB?
 holzmann From United States of America, joined Jan 2011, 510 posts, RR: 0Posted Sat Jan 5 2013 11:18:49 UTC (3 years 4 months 3 weeks 4 hours ago) and read 12760 times:

 I was watching this GEnx promo video on youtube recently: https://www.youtube.com/watch?v=S1ahHWXGx5Y GE talks a lot about the 23:1 pressure ratio of the engine being one of its most advanced features. I decided to look up the same figure for the Trent XWB (wikipedia) and it has an overall pressure ratio of 52:1! From this information, is it safe to assume that RR has somehow leapfrogged GE in some way?
 21 replies: All unread, jump to last
 tdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 78 Reply 1, posted Sat Jan 5 2013 11:46:36 UTC (3 years 4 months 3 weeks 4 hours ago) and read 12752 times:

 Quoting holzmann (Thread starter):From this information, is it safe to assume that RR has somehow leapfrogged GE in some way?

No. 23:1 is the high pressure compressor ratio; it doesn't include the pressure rise from the fan or low pressure compressor ("booster" in GE parlance). Total pressure ratio for a GEnX is about 41:1.

The Trent 1000 is 50:1 according to Rolls (http://www.rolls-royce.com/civil/products/largeaircraft/trent_1000/).

Tom.

 ferpe From France, joined Nov 2010, 2809 posts, RR: 60 Reply 2, posted Sun Jan 6 2013 03:35:56 UTC (3 years 4 months 2 weeks 6 days 12 hours ago) and read 12509 times:

 Quoting tdscanuck (Reply 1):The Trent 1000 is 50:1 according to Rolls (http://www.rolls-royce.com/civil/products/largeaircraft/trent_1000/).

Before one can speak about pressure ratio one must define for what part of the design envelope. The most common ratios are static and top of climb, they differ a lot, typically 40:1 for static and 50:1 for Top of climb. The most reliable static info is available at the ICAO engine emission database where all OEMs were forced to talk about the same thing, unfortunately it only contains info for pollutions around an airfield thus static wet (installed, which is another of those cheat things, uninstalled, ie not in the nacelle, is typically 3% better) data and climb out data, but not top of climb or cruise data (which has yet another sets of OPR, BR, TSFCs etc ).

The TXWB is not yet in the database thus we don't know the static OPR. The T1000 50:1 is top of climb, it's static value is 41 to 44 dependent on version. The TXWB 52:1 is therefore most likely top of climb but I have never seen RR actually state the OPR so that might be a Wikipedia invention. I would expect it slightly higher if top of climb.

 Non French in France
 ferpe From France, joined Nov 2010, 2809 posts, RR: 60 Reply 3, posted Sun Jan 6 2013 05:53:27 UTC (3 years 4 months 2 weeks 6 days 9 hours ago) and read 12456 times:

 Sorry your question was GEnx1 vs TXWB, the GEnx1 has the same static OPRs as the T1000 for the 64k to 70klf versions, ie 41-44, those are most likely bench numbers ie not wet. BTW here the link to the ICAO database http://easa.europa.eu/environment/edb/aircraft-engine-emissions.php[Edited 2013-01-06 05:55:25]
 Non French in France
 ferpe From France, joined Nov 2010, 2809 posts, RR: 60 Reply 4, posted Mon Jan 28 2013 12:31:06 UTC (3 years 3 months 4 weeks 3 hours ago) and read 11415 times:

 Just wanted to add that the ICAO data is from static test bench numbers and they are uninstalled, ie with a test bench inlet. They are not assured to be measured at sea level, for instances the GE data seems to be from 800ft which is their outdoor test site at Peebles Ohio. Wet and dry is augmented or not, allmost all civil turbofan values are dry or non augmented (except for the Tu144 engines which were augmented tubofans). Re the data for the TXWB, it seems that the static OPR should be in the region of 45 if the OPR is 52-53 at top of climb. GEnx OPR is around 50 at top of climb and around 41-43 static, more for the stronger versions, the same for the T1000. All these engines have their engine sizing point at the most demanding part of the flight envelope, top of climb. This is where the engine only delivers some 15-18klbf because of the low air density, they need all the power they can produce to get the frame to it's initial cruise FL of around FL 350 with 300ft/min climb excess power. Thus it is where the engines spins the fastest and therefore has the highest OPR. The turbine inlet temp (TIT) is at it's highest continuous value, some 1700-1800K, the 5 minutes Take Off rating has an even higher TIT (approx 100K more) but the engine does not spin as fast due to the higher air density and higher ambient temp (the TIT limit is reached first), thus the OPR is some 15% lower.
 Non French in France
 JoeCanuck From Canada, joined Dec 2005, 6363 posts, RR: 33 Reply 5, posted Tue Jan 29 2013 23:27:51 UTC (3 years 3 months 3 weeks 5 days 16 hours ago) and read 11126 times:

 Quoting ferpe (Reply 4):

It's always nice to get some un-spun data and explanations about terms which are often bandied about. Learning is good...thanks.

 What the...?
 ferpe From France, joined Nov 2010, 2809 posts, RR: 60 Reply 6, posted Wed Jan 30 2013 00:36:46 UTC (3 years 3 months 3 weeks 5 days 15 hours ago) and read 11106 times:

 Quoting JoeCanuck (Reply 5):Learning is good...thanks.

I could help here as I am trying to understand engines at the moment and bought a book about the fundamentals (Jet Propulsion by Cumpsty after recommendation here). I will actually start a thread about the design trades of a Turbofan like the GEnx or TXWB, got some who is in the know to chip in as well. Right now preparing, when we all have gone through the basics in this thread we will be much better discussion partners and we can go into the details why this and that. A recent posting in a A350-1000 thread showed me I understand very little about engines, has to change  .

 Non French in France
 JoeCanuck From Canada, joined Dec 2005, 6363 posts, RR: 33 Reply 7, posted Wed Jan 30 2013 01:46:12 UTC (3 years 3 months 3 weeks 5 days 14 hours ago) and read 11083 times:

 Quoting ferpe (Reply 6):I could help here as I am trying to understand engines at the moment and bought a book about the fundamentals (Jet Propulsion by Cumpsty after recommendation here).

Excellent...you get to study all night and we get to ask stuff like, 'what's that pointy thing do...?". I thank you in advance for you patience.

 What the...?
 ferpe From France, joined Nov 2010, 2809 posts, RR: 60 Reply 8, posted Wed Jan 30 2013 02:36:07 UTC (3 years 3 months 3 weeks 5 days 13 hours ago) and read 11066 times:

 Quoting JoeCanuck (Reply 7): 'what's that pointy thing do...?"

Well there will be even better guys then me answering these things...., I think it will make engine discussions more interesting.

 Non French in France
 Pihero From France, joined Jan 2005, 5174 posts, RR: 78 Reply 9, posted Wed Jan 30 2013 04:50:58 UTC (3 years 3 months 3 weeks 5 days 11 hours ago) and read 11029 times:

 Ferpe, Thanks for the explanations. One criticism, though : could you stop these uses of strange units as : klbf ? So much more understandable - and technically right - to use kN in this case. On the subject of books, one I have is the "Jet Engine" published by Rolls-Royce . I have the 2004 version and it's quite informative without going too much into maths developments.
 Contrail designer
 tdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 78 Reply 10, posted Wed Jan 30 2013 06:28:51 UTC (3 years 3 months 3 weeks 5 days 9 hours ago) and read 10994 times:

 Quoting Pihero (Reply 9):One criticism, though : could you stop these uses of strange units as : klbf ?

Unfortunately, engines are one of the last great bastions of stupid units. Although I'm all in favour of metric units, in the context of this discussion, klbf isn't actually strange.

Tom.

 nomadd22 From United States of America, joined Feb 2008, 2142 posts, RR: 0 Reply 11, posted Thu Jan 31 2013 10:05:52 UTC (3 years 3 months 3 weeks 4 days 5 hours ago) and read 10759 times:

 I use the superior method of understanding engine technology called "Ask Lightsaber" Ferpe can use whatever units he wants. I still use cubits myself.
 Anon
 Pihero From France, joined Jan 2005, 5174 posts, RR: 78 Reply 12, posted Thu Jan 31 2013 10:54:32 UTC (3 years 3 months 3 weeks 4 days 4 hours ago) and read 10744 times:

 ... and I'm sure your radio altimeter gives fathoms under the keel, right ?
 Contrail designer
 Starlionblue From Greenland, joined Feb 2004, 17654 posts, RR: 65 Reply 13, posted Thu Jan 31 2013 16:38:01 UTC (3 years 3 months 3 weeks 3 days 23 hours ago) and read 10646 times:

 Quoting Pihero (Reply 9):On the subject of books, one I have is the "Jet Engine" published by Rolls-Royce . I have the 2004 version and it's quite informative without going too much into maths developments.

Second that book. It is fantastic and a layman like me can follow along given the abundance of pretty pictures and drawings. Note that it cannot be ordered from Amazon. I got mine directly from Key Publishing as specified here. http://www.rolls-royce.com/about/publications/jet_engine_book/

 Quoting tdscanuck (Reply 10):Unfortunately, engines are one of the last great bastions of stupid units.

Along with the United States, Myanmar and Liberia?

 "There are no stupid questions, but there are a lot of inquisitive idiots."
 tdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 78 Reply 14, posted Thu Jan 31 2013 19:12:48 UTC (3 years 3 months 3 weeks 3 days 20 hours ago) and read 10617 times:

 Quoting Pihero (Reply 12):... and I'm sure your radio altimeter gives fathoms under the keel, right ?

My car gets 40 rods to the hogshead and that's the way I likes it.

 Quoting Starlionblue (Reply 13):Quoting tdscanuck (Reply 10): Unfortunately, engines are one of the last great bastions of stupid units. Along with the United States, Myanmar and Liberia?

I once heard a RR engineer actually use slugs...a part of me died that day.

Tom.

 LMP737 From United States of America, joined May 2002, 5065 posts, RR: 16 Reply 15, posted Fri Feb 1 2013 01:33:44 UTC (3 years 3 months 3 weeks 3 days 14 hours ago) and read 10566 times:

 You can work on the accesories on the Trent by opeing the fan cowls. On the Gen-ex you have to open the T/R.
 Never take financial advice from co-workers.
 Starlionblue From Greenland, joined Feb 2004, 17654 posts, RR: 65 Reply 16, posted Fri Feb 1 2013 03:37:54 UTC (3 years 3 months 3 weeks 3 days 12 hours ago) and read 10528 times:

 Quoting tdscanuck (Reply 14):I once heard a RR engineer actually use slugs...a part of me died that day.

It gets better. Wikipedia has the following insight. With sources no less!

The slug is a unit of mass associated with Imperial units. It is a mass that accelerates by 1 ft/s2 when a force of one pound-force (lbF) is exerted on it.

The blob is the inch version of the slug (1 blob = 1 lbf·s2/in = 12 slugs)[1] or equivalent to 175.126 kg. This unit is also called slinch (a portmanteau of the words slug and inch).[8][9] Slang terms are slugette,[10] and a snail.[11]

 "There are no stupid questions, but there are a lot of inquisitive idiots."
 CARST From Germany, joined Jul 2006, 1184 posts, RR: 2 Reply 17, posted Fri Feb 1 2013 03:40:17 UTC (3 years 3 months 3 weeks 3 days 12 hours ago) and read 10527 times:

 Quoting tdscanuck (Reply 14):I once heard a RR engineer actually use slugs...a part of me died that day.

Okay I really had to look this up at Wikipedia. You have a crazy system over there...

Quote:
The slug is a unit of mass associated with Imperial units. It is a mass that accelerates by 1 ft/s2 when a force of one pound-force (lbF) is exerted on it.

It makes sense, kind of, as long as you stay inside the imperial system. Going from one size to another one is the more problematic thing.

 Quoting tdscanuck (Reply 14):My car gets 40 rods to the hogshead and that's the way I likes it.

I read that as "my car gets 201.17 meter to a barrel of 238.48 liter and ..." and I had no idea what you meant until I googled it and came up with the explanation. I know that episode and it is funny in German, too, but I would have never linked it to that sentence of yours. ^^

It would be great for a.net to have an automatic unit translator, like the function of decrypting 2-letter-airline-codes and 3-letter-airport-codes, so it would show the metric unit over the imperial unit and the other way round. Or you guys just switch over to our devilish system like Grandpa Simpson said. ^^

 JoeCanuck From Canada, joined Dec 2005, 6363 posts, RR: 33 Reply 18, posted Fri Feb 1 2013 11:08:53 UTC (3 years 3 months 3 weeks 3 days 4 hours ago) and read 10421 times:

 Quoting Starlionblue (Reply 16):

I tried to get through that then everything went grey and I woke up in an alley.

 What the...?
 ferpe From France, joined Nov 2010, 2809 posts, RR: 60 Reply 19, posted Fri Feb 1 2013 11:44:14 UTC (3 years 3 months 3 weeks 3 days 4 hours ago) and read 10403 times:

 Quoting JoeCanuck (Reply 18):I tried to get through that then everything went grey and I woke up in an alley.

Don't panic guys, well get a thread with both ways of measuring present, weather the slug, rod or fathoms makes into the text is more doubtful..., but the Rankine will

 Non French in France
 nomadd22 From United States of America, joined Feb 2008, 2142 posts, RR: 0 Reply 20, posted Fri Feb 1 2013 12:08:32 UTC (3 years 3 months 3 weeks 3 days 3 hours ago) and read 10396 times:

 I hear the 7810 will be able to do 2700 leagues.
 Anon
 JoeCanuck From Canada, joined Dec 2005, 6363 posts, RR: 33 Reply 21, posted Fri Feb 1 2013 12:30:24 UTC (3 years 3 months 3 weeks 3 days 3 hours ago) and read 10379 times:

 I wonder if it can make the Kesel run in less than 12 parsecs.
 What the...?
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