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holzmann
Topic Author
Posts: 599
Joined: Mon Jan 17, 2011 3:43 pm

### GEnx Vs. Trent XWB?

I was watching this GEnx promo video on youtube recently:

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?

tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

### RE: GEnx Vs. Trent XWB?

 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
Posts: 2667
Joined: Tue Nov 30, 2010 7:44 am

### RE: GEnx Vs. Trent XWB?

 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.

ferpe
Posts: 2667
Joined: Tue Nov 30, 2010 7:44 am

### RE: GEnx Vs. Trent XWB?

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]

ferpe
Posts: 2667
Joined: Tue Nov 30, 2010 7:44 am

### RE: GEnx Vs. Trent XWB?

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.

JoeCanuck
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Joined: Mon Dec 19, 2005 3:30 am

### RE: GEnx Vs. Trent XWB?

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

ferpe
Posts: 2667
Joined: Tue Nov 30, 2010 7:44 am

### RE: GEnx Vs. Trent XWB?

 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  .

JoeCanuck
Posts: 4704
Joined: Mon Dec 19, 2005 3:30 am

### RE: GEnx Vs. Trent XWB?

 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.

ferpe
Posts: 2667
Joined: Tue Nov 30, 2010 7:44 am

### RE: GEnx Vs. Trent XWB?

 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.

Pihero
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Joined: Mon Jan 31, 2005 5:11 am

### RE: GEnx Vs. Trent XWB?

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.

tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

### RE: GEnx Vs. Trent XWB?

 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.

Posts: 1572
Joined: Fri Feb 22, 2008 7:42 pm

### RE: GEnx Vs. Trent XWB?

I use the superior method of understanding engine technology called "Ask Lightsaber"
Ferpe can use whatever units he wants. I still use cubits myself.

Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

### RE: GEnx Vs. Trent XWB?

... and I'm sure your radio altimeter gives fathoms under the keel, right ?

Starlionblue
Posts: 21137
Joined: Fri Feb 27, 2004 9:54 pm

### RE: GEnx Vs. Trent XWB?

 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?

tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

### RE: GEnx Vs. Trent XWB?

 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
Posts: 6319
Joined: Wed May 08, 2002 4:06 pm

### RE: GEnx Vs. Trent XWB?

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.

Starlionblue
Posts: 21137
Joined: Fri Feb 27, 2004 9:54 pm

### RE: GEnx Vs. Trent XWB?

 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]

CARST
Posts: 1587
Joined: Tue Jul 25, 2006 11:00 pm

### RE: GEnx Vs. Trent XWB?

 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
Posts: 4704
Joined: Mon Dec 19, 2005 3:30 am

### RE: GEnx Vs. Trent XWB?

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

ferpe
Posts: 2667
Joined: Tue Nov 30, 2010 7:44 am

### RE: GEnx Vs. Trent XWB?

 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

Posts: 1572
Joined: Fri Feb 22, 2008 7:42 pm

### RE: GEnx Vs. Trent XWB?

I hear the 7810 will be able to do 2700 leagues.

JoeCanuck
Posts: 4704
Joined: Mon Dec 19, 2005 3:30 am

### RE: GEnx Vs. Trent XWB?

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

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