ferpe
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TF42, Our Engine Project For The Airliners-200

Sat Feb 02, 2013 10:16 pm

   Dear colleagues,   

this is a mail to let you know that our sister department, Airliners.net airframes have secured funding    (from a middle east consortium    ) for our Airliners-200 single aisle airliner    . While they had planned to use available engines (the GTF and Leap class) the market requirements have now forced the project into making a new engine in the 40 klbf class. As our airframe colleagues have not been able to convince    any of the established OEMs to produce a suitable engine they have now turned to us, Airlines.nets engine department, to conceptualize, design and certify a suitable engine    . The parts will later be contract produced by established tier one suppliers and we will final assembly the engine in our MRO facility in Key West Florida    .

The airframe specs are :



As can be seen they are already short on range, the interested airlines want a Transcon, TATL range with margins for unfavorable winds.

The engine requirements they ended up with are (before they ask us to fix their problem  Wow!   )




As our latest engine design goes back to the 1980:ies one must admit that we are in general a bit rusty    (even though we have discussed a lot  ). I have therefore secured some consultancy from industry experts that will come in and help us as we go. The idea is to start the design phase with a classical 2 spool turbofan employing established methods (and learn what is going on ) and see if we can fulfill the spec our airframe team put forward. We will then explore more advanced techniques (like ceramics, gearboxes, 3 spool) to see if this can gets us a better engine as the airframers will certainly run into weight problems (they already have) and ask for more thrust and lower TSFC (they already do) !   


To help with the process we will start with everyone putting forward books, articles etc that are useful for the department refresh  . I will also present our engine design tool that we purchased from the well known company GasTurb software from Dachau Germany.

So dear colleagues we have got a real challenge on our hands    ,

let's get out of those armchairs    and kick some    ,


I count on your participation in this very important project   

your engine department mgr "Ferpe"   

[Edited 2013-02-02 14:28:36]
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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Sat Feb 02, 2013 10:35 pm

Dear collegues, could some cabin experts check the airframe departments ideas about number of seats? I have no ideas about seating etc but we don't want a late surprise that the frame will take even more pax+bags then they say so that payload-range problems we are already in will be even worse  Wow! . We need to know if we shall size the base engine larger then they say already from the beginning    .
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LH707330
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 2:27 am

Ha ha love this! I've always been saying we need a medium-haul 200 seater with overpowered engines....
 
KC135Hydraulics
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 2:31 am

Sounds suspiciously like a 757.
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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 8:14 am

Quoting KC135Hydraulics (Reply 3):
Sounds suspiciously like a 757.

Sure, that is why there is a market and no engine  . More fun to invent an engine together that is not available, also less sensitive to discuss for the experts we have on the forum    . But everyone can contribute, no input is off the mark, this is the chance for us all to learn something about those elusive engines.

As Tom said said when I contacted him, "engines are a black art", time to put a torch into it or a    at least  . Re 757, what about the spec, good enough for this market niche? The airframes department says it will be Al-Li fuselage with CFRP wings.

Re the engine requirements, I have calculated these using my frame model, the values should be good enough to use for an engine design me thinks. The fuel consumption around 0.54 is todays state of the art ie 787 generation so should be doable but as we can see the frame guys already is screaming for more so those advanced discussions have to come. But first we all learn while doing a vanilla first try.


Here some hints where we all can dust of our engine knowledge:

- General and good write-up: Rolls Royce, The Jet engine, you can find it online. The chapter 21 performance is good reading, the formulas are ok but use old units (mm Hg for pressure for instance) therefore check Wikipedia for modern ones http://en.wikiversity.org/wiki/Jet_engine_performance. Don't worry about all those formulas, we will have a software that does all the calculations, see below, it is good to be able to look up a formula to understand en large what factors are involved however.

- A good summary http://en.wikipedia.org/wiki/Turbofans and this article goes into the details with calculations examples. Together with the proposed PC software below you are fine with Wikis different articles.

- I got hold of a copy of a recommended book Cumpsty "Jet engine propulsion". The good thing is it takes one through a design example of a A380 frame with T900, EA7200 size engine with modern values for turbine inlet temps, compressor and turbine efficiency etc and most important of all in what order does one design an engine? He says Top of climb is sizing the engine (design point), cruise is deciding it's fuel efficiency optimization (off design) and one engine out take-off is deciding the top 5 minute turbine temp (also off design work).

He also recommended an excellent PC software http://www.gasturb.de which has a free copy http://www.gasturb.de/software.html where you all can do your own design work. Read the excellent manual for how to run optimization loops, there are many ways to do it. Also the diagram functions explain what happens much better then any textbook, the Wiki + this free copy are good compatriots. I got a full copy after fiddling with the free for a week or so, it allows one to also specify cooling losses and run more then a turbojet or 2 spool turbofan in thermodynamic only mode (no looses etc). Mail the guy at kurzke@gasturb.de for a non commercial personal copy, the price is really good, even my weekly allowance could craft it  .

- There are many NASA reports and sites which helps as well, here is a reference to an ASME contest for a UAV engine that uses Gasturb as the design tool and that reveals a lot of practical numbers http://files.asme.org/IGTI/33208.pdf . It is a small engine however so you need to change some numbers (and some can't be specified in the free copy), put in a massflow of around 1400 lb/sec in the free Gasturb and you come close to the numbers asked for by our framers, with losses I am at 1600lb/s right now for a first cut. Then play with different efficiencies, temps (1700K continuous and 1800 TO (3060 and 3240 R). For RPMs 4000 low spool and 13000 high is a good start, put the compressors at around 0.87 isentropic efficiency and the turbines at 0.9 and have fun!!

For any numbers your don't have just ask in the thread, we will give you advice (if from me be careful, blind leading blind    )

[Edited 2013-02-03 00:31:15]
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Starlionblue
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 8:19 am

Given the current market environment, shouldn't this be the "Airliners-800", "Airliners-8", or even better the "Airliners-888"? 
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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 8:25 am

Quoting Starlionblue (Reply 5):
Given the current market environment, shouldn't this be the "Airliners-800", "Airliners-8", or even better the "Airliners-888"?

Bulls eye Starionblue, as these numbers schemes does not allow simple triple triple stretches (in the short form) the framers decided to go back to the old fashion numbers, the time of the -8 is over comrades they said      

[Edited 2013-02-03 00:32:04]
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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 10:21 am

The first Wikiversity link is a bit funny, on the page you land search for "turbojet" and you get all the relevant entries, the one about "jet engine performance" is the one with all the formulas. As said don't worry about these, the software has them all and happily calculates everything 1000 times while you graaadly get the gist of things  .

Use the page as a reference for terms and principles, you can skip Husk plots, we don't use these.
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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 12:07 pm

To help those who want to play with free Gasturb, here what you do once installed:

1. On start window, choose 2 SPOOL TURBOFAN and Basic thermodynamics/Cycle design.

2. You are now at design point entry screen, put in these numbers:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/TF42freeSWdesignpointscreeninput_zpsa36cab48.jpg and then the Alt (33000), M (0,82), mass flow (1400), efficiencies (0.87 and 0.9) , RPMs (4000 and 13000) and you are good to press DESIGN POINT, voila:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/TF42freeSWdesignpointscreens_zpscd1accf0.jpg

A lot of numbers, not all immediately useful and and understood (therefore just push along with the software and revisit the texts to understand what you see), I have circled the key stuff. Look at the stations tab to understand the station markings (the red arrow shows where most EGT numbers are taken, to far back for our purposes right now, we will use it later):

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Turbofanstations_zpsbfcfd58c.jpg

3. Now play with the possibilities, press for instance Properties@stations, then select what you want to see along the engine stations, for instance these parameters:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/TF42freeSWdesignpointstations_zpsd71ba17a.jpg


Then it might be time to check the other so called off design points (your engine geometry is now defined, now you throttle it for e.g. initial cruise at FL330 or you check the Take off case):

4. Go back to main screen and press "Off-design". At the off design point you can choose your alt and M (we leave it as we want to look at what happens when we throttle back the engine after reaching initial cruise alt, but you could for instance put in 0 ft and M 0 and then our max turbine temp 3260R as a Max limiter under "Controls" to check out the TO 5 min thrust ). Press "Operating line" twice and "No" for more lines (you can do more lines later with eg varying Alt) and then choose what you want to plot, here is one example:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/TF42freeSWoffdesignworkinglinescreen_zpscbfcadbe.jpg

I have plotted how TSFC, Burner temp, OPR and BR change as you throttle the engine at our initial cruise level. Looks like we are pretty OK with TSFC? No, not really, in the sharp version we loose some 20% of our high compressor air for cooling, sets us back to around 0.58 and we now need work (and help from pros) to get to our target   .

As said, check the manual how you can iterate etc, not all functions are there for the free version but many, have fun while fiddling, it's free    .

[Edited 2013-02-03 05:11:24]
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RussianJet
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 12:56 pm

Quoting ferpe (Thread starter):
this is a mail to let you know that our sister department, Airliners.net airframes have secured funding (from a middle east consortium ) for our Airliners-200 single aisle airliner

Please do excuse the naivety, but I have never heard of this. Could we have some basic background on this? Is this a genuine, tangible project, or some kind of paper exercise?
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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 1:05 pm

Quoting RussianJet (Reply 9):
Please do excuse the naivety, but I have never heard of this. Could we have some basic background on this? Is this a genuine, tangible project, or some kind of paper exercise?

It is 100% a fake project to have some fun together and learn about turbofans while inventing one for a fake aircraft. By playing the game you will learn a lot, not only about the facts how a turbofan is made but also a glimse of the internal politics in an aircraft project. Welcome to join the virtual team!
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RussianJet
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 1:12 pm

Quoting ferpe (Reply 10):
It is 100% a fake project to have some fun together and learn about turbofans while inventing one for a fake aircraft

I see. I thought as much, but didn't want to offend anyone if by some miracle there was actually some kind of crazy real plan here.
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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 1:15 pm

Download the software and join the team, you will for certain learn a lot .   
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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 7:06 pm

I have found a really interesting Master thesis, it checks whether Gasturb, the software we are using, is any good for Bombardiers internal use to model the engine OEMs engines. The results from GasTurb 11 was compared to the engine manufacturers data supplied to Bombardier, in general Gasturb predicting within 2% of the real data. Pretty d-mn good, so thought Bombardier as well, so it will do for us as well  :

http://www.google.fr/url?sa=t&rct=j&...1b0u6A&sig2=wDmMpWxJI0ORB7QO_RPBGw

This document has many practical sections but one of the best is the table 3.2, it gives the different efficiency levels of fan, booster, HPC, burner, HPT, LPT, turbine inlet temps etc. This is sensitive data that our experts would probably have had trouble to give us in clear, here we now have it to adopt. My data given above is conservative, it is on the level of engines conceived around 2000.

[Edited 2013-02-03 11:50:16]
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Aviaponcho
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 10:37 pm

Fun...
Can i help for the cabin layout?
I was looking at an a310 neo... But it looks like a twin aisle narrowbody
 
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 03, 2013 11:02 pm

Quoting Aviaponcho (Reply 14):

Hmmm. Cross section, parasite drag...

I think the 757-300 is the role model here. Single aisle, 6 abreast, classic but efficient.
It could be made a little wider. LD3 capability would be nice, but that would stretch it a bit. 'Low-profile' LD3, like the A320 family, will do.
I'll do my own airline. With Blackjack. And hookers. In fact, forget the airline.
 
ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Mon Feb 04, 2013 5:15 am

Quoting Aviaponcho (Reply 14):
Fun...
Can i help for the cabin layout?
I was looking at an a310 neo... But it looks like a twin aisle narrowbody

Absolutely! Please help with the seating, seat and isle withes etc.

Quoting francoflier (Reply 15):
I think the 757-300 is the role model here. Single aisle, 6 abreast, classic but efficient.
It could be made a little wider. LD3 capability would be nice, but that would stretch it a bit. 'Low-profile' LD3, like the A320 family, will do.

You are right on the money    , it is also a little wider then the A320/737 crop, 3.90 instead of 3.70 (A320) or 3.54 (737). Arliners,net would not put a 1980/1950 cross section on their shiny new frame would they    We are asking the pax to sit still for up to 8-9 hours, better have some decent seat withs in there. I don't know if 3.90 cuts it, please check otherwise we have to ask the framers to widen the ship further  .

Re cargo, a LD3 would not fit 2 abrest in a SA unless you make it a bit pregnant IMO (and we don't want that do we  ), therefore the A320 LD3 low profile will have to do. How many would one get into such a belly?

[Edited 2013-02-03 21:44:11]
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Aviaponcho
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 05, 2013 10:51 am

Ferpe,
What is the basic layout for Airliner200 ? 220 PAX seems 2 class configuration with a not so qualitative front section ?


A310-300
Juste remembering the A310-300 coming with a perfect 2 LD3 capable cross section is a
77-79 t OEW airplane (depending on TOW), > 5000 Nm with late 70's technologies

It's 46.66 m long and 43.9 m span.

It was a 243 PAX all tourist @34 in 8 abreast or 265 seats @34 9 abreast

Airtransat l'utilise encore : http://media.transattravel.com/airtr..._b2c/flotte/310_300_FR-europe.html

I'm sure it's worth looking at...
Sure you can shave as much as 4-5 t of weight going CFRP wing and new legs, optimised tail section
Sure you can have a 20% fuel burn gain easily
Sure you need something in the 45 klbfs+ range for 150-155 t MTOW maybe less ? for more payloard
What do you thinhk


Airliner 200
Otherwise with 3.9 m Internal (153.5") width you can go 1+4+1 (twinaisle) with 17.5" seat cushion and 17" aisle
See Frequent's Traveller concept here http://fr.slideshare.net/Frequent_Traveller, and 1+2+1 in biz with no excuse me seats
It will allow quick rotation time and cabin product differentiation

Nice to play btw
 
ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 05, 2013 1:15 pm

Quoting aviaponcho (Reply 17):
What is the basic layout for Airliner200 ? 220 PAX seems 2 class configuration with a not so qualitative front section ?

You got all the dimensions in the first table, it is in the first brown section in the middle between the blue thin lines.


Quoting aviaponcho (Reply 17):
Airliner 200
Otherwise with 3.9 m Internal (153.5") width you can go 1+4+1 (twinaisle) with 17.5" seat cushion and 17" aisle
See Frequent's Traveller concept here http://fr.slideshare.net/Frequent_Traveller, and 1+2+1 in biz with no excuse me seats
It will allow quick rotation time and cabin product differentiation

Very interesting, what would it mean in a normal 3+3 in term of seat withs? I will look at what the A300 cross section means in drag etc, give me a day or so, it is an interesting alternative.

Quoting aviaponcho (Reply 17):
Nice to play btw

Absolutely, let's play with the aircraft and the engine, it is more fun that way. Perhaps we will find something REALLY interesting   Wow!

[Edited 2013-02-05 05:22:36]
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Aviaponcho
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 05, 2013 1:43 pm

As Frequent Traveller explained me, there's a max width for triplet seats that is due to the fact that hostess/stewards should be able to reach the third person near the windows without climbing on the first passenger.
So basically airbus 18" triplet (wide seat) for the A320 is near to the max... so staying single aisle the airliners2000 whicjh is 7-8 in wider than the A320 may end up with the same seats but with an aisle "champ elysée style" at >22 in width.

http://avia.superforum.fr/t908-irkut-ms-21#17407 (I don't know If I can link it)

It can be good for turn around time, but I think twin aisle narrowbody can be a good idea.


BTW i only we can be sure of the internal width of the C919 and the MS21 !

My assumptions for twin aisle above is 17.5 seat width (similar to 787 @9 abreast I think), 1.5" armrest, 17.5" aisle

Ok for cabin length and width.... is length between front of door 1 to aft of door 3 (or 4), what king of exit configuration shall we use ?
 
boacvc10
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 05, 2013 9:24 pm

Quoting ferpe (Thread starter):
his is a mail to let you know that our sister department, Airliners.net airframes have secured funding    (from a middle east consortium    ) for our Airliners-200 single aisle airliner

I'd be interested to help out if the project has a better name! Is "N2XX" type satisfactory? AXXXX is airbus, BXXXX is boeing CRXX, ERXX are taken, and Airliners.net does not lend it self to good abbreviation as ANXXXX as that is taken as well.

Reason: If we are to get top billing as a commercial company at the next big air show (UK, Mid-East*** or Far-East), we need to have a catchy name, and fast, ad-space is limited !
Up, up and Away!
 
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RE: TF42, Our Engine Project For The Airliners-200

Wed Feb 06, 2013 10:53 am

Quoting boacvc10 (Reply 20):
N2XX" type satisfactory?

Absolutely, but I'm just the engine department mgr  cry  , well have to pass it to the framers (ie you all  ) to see if it passes    . If we don't have violent complains in this thread say in a couple of days it is done and dusted    .

[Edited 2013-02-06 02:55:02]
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LH707330
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RE: TF42, Our Engine Project For The Airliners-200

Wed Feb 06, 2013 5:14 pm

Back in its day the A300 was the most efficient people mover, hence the term "continental shovel." I hear LH still misses their capacity on thick routes within Europe. If you gave the legacy carriers a good, light 250 seater with a nice premium option, I bet they'd bite.

If the plan is to go with two aisles, you're adding weight in the width, so I think you have to go 8-across WB or 6-across NB, but not 7.
 
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RE: TF42, Our Engine Project For The Airliners-200

Wed Feb 06, 2013 8:42 pm

You are forgetting the most important detail. Will it be controlled by a yoke or a sidestick?   
 
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RE: TF42, Our Engine Project For The Airliners-200

Wed Feb 06, 2013 9:21 pm

This might be a little risky in terms of R&D, but I would like to propose my unconventional twin-core contra-rotating ducted dual fan engine concept...  http://i32.photobucket.com/albums/d37/Peeto999/TwinPT6.jpg
I anticipate some resistance to this approach, but I'm fairly certain it could work! Kuznetsov NK-93 is the closest equivalent.
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JoeCanuck
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RE: TF42, Our Engine Project For The Airliners-200

Thu Feb 07, 2013 4:57 am

I'm not an engine guy but I like to try wrap my mind around wacky concepts...no matter how out to lunch they may be..so here goes.

How about an engine with contra rotating geared ducted fans? The planet gears are fixed, with one fan attached to the sun gear and one to the rig gear. The fans would spin in opposite directions at different speeds, (I think), which is ok since that might take some harmonics, (and hopefully noise), out of the system. Keeping the fans ducted prevents a lot of noise issues.

I see the thing as a longer, wider CSeries...Al-Li fuse, CFRP wings. It would have to be about the same size as the 757, with gear long enough for some big, fat fans, crazy long wings, maybe folding tips. Maybe even a high wing, so engine size or gear length would never be an issue, and you could keep the fuse height to a minimum to better serve more austere airports...a x2 An-158.
What the...?
 
LH707330
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RE: TF42, Our Engine Project For The Airliners-200

Thu Feb 07, 2013 5:57 am

Quoting JoeCanuck (Reply 25):

How about an engine with contra rotating geared ducted fans?

I reckon that the weight and complexity of this will outweigh any TSFC gains, it's much easier just to have a de-swirl stage in the fan case with one more (or less?) blade than the fan itself.
 
ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Thu Feb 07, 2013 4:57 pm

Quoting wingscrubber (Reply 24):
but I would like to propose my unconventional twin-core contra-rotating ducted dual fan engine concept...

Nice picture but how do you propose that we analyze it's efficiency? The Gasturb software has a number of configs, but not that one         
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bhill
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RE: TF42, Our Engine Project For The Airliners-200

Thu Feb 07, 2013 8:01 pm

Err...."vaned conveyor belts" pushing the air mass in.......

 

Birdstrikes would be a thing of the past......
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JoeCanuck
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RE: TF42, Our Engine Project For The Airliners-200

Fri Feb 08, 2013 12:33 am

Quoting LH707330 (Reply 26):
I reckon that the weight and complexity of this will outweigh any TSFC gains, it's much easier just to have a de-swirl stage in the fan case with one more (or less?) blade than the fan itself.

How about a variable pitch GTF?
What the...?
 
LH707330
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RE: TF42, Our Engine Project For The Airliners-200

Fri Feb 08, 2013 7:11 pm

Quoting JoeCanuck (Reply 29):
How about a variable pitch GTF?

I bet it's too complex/unreliable/susceptible to bird strikes. Let's assume these hurdles can be overcome though, then it gets interesting: assuming a conventional engine is sized for max. takeoff thrust and is thus too large at cruise, you could design a fan that has an optimal alpha on the takeoff roll, which should let you get away with a narrower fan (with a possible noise penalty). When climbing you can have a slightly finer pitch to keep N1 up, and at cruise you can go back to a coarser pitch to reduce ram drag. What I'd like to know is how fixed-pitch fans are optimized in terms of blade alpha (cruise vs. takeoff), and how much efficiency you can gain from varying them. Ideally you get a smaller engine with a 5-minute temp-limited medium-coarse setting for takeoff that is then more efficient at cruise because it's working harder and has less nacelle drag.

Another avenue I'd be interested in exploring is water-cooled HPT blades. My dad used to ask me "if it's such a good idea, why hasn't someone done it?" Maybe someone can help here. Most engines take bleed air from the compressor and use it to cool the blades downstream by pumping the air through the blade. Although it keeps the blade from melting, you lose thrust and SFC by robbing compressed air from the combustion chamber. If you had a small water reservoir in the core that fed the blade cooling tubes and expended the water out the blade holes for 5 minutes during takeoff, you could regain thrust from the lack of bleed and from the pressure rise as you release the superheated water out the back of the blade as steam. The system runs out of water as you're throttling back to climb power and you revert to bleed for cooling. You get more thrust from these three factors:
1. No bleed->more combustion air
2. Higher TIT tolerance (thus more thrust) because the water carries away more heat
3. Increased mass flow and pressure from the steam

Combined, these let you make a smaller engine with its attendant benefits (less weight/nacelle drag, less wing reinforcement, shorter gear (more weight saving), and higher cruise thrust/TSFC). Most takeoffs are derated anyway, so you'd only need it rarely. As far as answering my dad's question, I imagine water pressure would be north of 1000 PSI, which might make it difficult to keep it liquid until expelled into the airstream. If you get steam bubbles, you lose cooling and the blade melts (bad news). I bet there are other problems with the idea, but if we're looking at variable pitch fans and back-to-back turboprops I figured I'd throw this idea in the ring too.
 
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RE: TF42, Our Engine Project For The Airliners-200

Sat Feb 09, 2013 7:09 am

Quoting wingscrubber (Reply 24):

That's definitely out of the box thinking but it is an interesting concept.

Quoting LH707330 (Reply 30):
What I'd like to know is how fixed-pitch fans are optimized in terms of blade alpha (cruise vs. takeoff), and how much efficiency you can gain from varying them

Some turbo props are getting so many blades that they are looking like fans to me;


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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Sat Feb 09, 2013 8:06 am

Quoting JoeCanuck (Reply 29):
How about a variable pitch GTF?

We will start to look at and discuss more exotic ideas but before that lets see how far one can reach the spec with a classical Direct Drive 2 spool turbofan (DDTF) and a rusty (actually new beginner) chief designer fiddling with the excellent software Gasturb. First a table for those like me have problems with the mix of units in the engine world:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Conversiontable_zpsfeed341a.jpg

This makes it easier for everyone to take the data into the units one is used to. Then the engine variant that comes closes to meeting the framers expectation after 2 weeks of fiddling. First the performance and key data:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/TF39data_zps15207907.jpg

As you can see the engine is slightly smaller (9600lbf at the design point, Top of Climb, ToC). I increased the Turbine Inlet Temp, TIT (or Stator Outlet Temp, SOT) T41 which sizes the core. This makes for a smaller, more efficient core and ultimately engine. I also put in the cooling flows and fan/compressor/turbine efficiencies according to the Bomardier study:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Coolingflownumbers_zpsd900e47d.jpg
http://i298.photobucket.com/albums/mm262/ferpe_bucket/Efficiencytable_zps644b1b60.jpg

I kept the bypass ratio at 9 at ToC for now, we will explore what and increased BPR means in terms of TSFC and weight/dimensions in the next step. The nice thing with Gasturb is, it not only helps you with the thermodynamic design but also sketches the engine for you and even gives you the key physical data:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T42GeometryV4_zps8e18a8a7.jpg

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T42maindimensions_zpsd38b68ba.jpg

So what has changed inside the engine? Here the design point screen with the key data circled and then the working line or throttled engine at our initial cruise height of FL330:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/TF39designpoint_zps3e8d3b66.jpg

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T42workinglineFL3500823240RV1_zps938aba7b.jpg

Look at the mass flow table at the left, mass does not vanish it just splits up in core (some 10%) and bypass, you can see the bypass again in the last station. Here the stations in the engine with also shows the cooling flows:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T39stations_zps58249340.jpg

So we have a bare engine (less gearbox and other accessories) that weighs 10klb/4500kg and gives us a cruise TSFC of 0.55, pretty close to what the framers asked for but not there. Look into the data at your pace, there is a lot, but it gradually dawns on one what if all should be good for. Especially the throttle diagram tells what happens with PR, BPR, RPM of the fan etc as one regulates the power of a turbofan at height. Also look in the first table for these values at Start and at 50ft V2 where one has to reach 2.4% climb One Engine Inoperative (OEI) to get certification for a twin.
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RE: TF42, Our Engine Project For The Airliners-200

Sat Feb 09, 2013 9:25 am

Quoting LH707330 (Reply 30):
Another avenue I'd be interested in exploring is water-cooled HPT blades. My dad used to ask me "if it's such a good idea, why hasn't someone done it?" Maybe someone can help here. Most engines take bleed air from the compressor and use it to cool the blades downstream by pumping the air through the blade. Although it keeps the blade from melting, you lose thrust and SFC by robbing compressed air from the combustion chamber. If you had a small water reservoir in the core that fed the blade cooling tubes and expended the water out the blade holes for 5 minutes during takeoff, you could regain thrust from the lack of bleed and from the pressure rise as you release the superheated water out the back of the blade as steam. The system runs out of water as you're throttling back to climb power and you revert to bleed for cooling. You get more thrust from these three factors:
1. No bleed->more combustion air
2. Higher TIT tolerance (thus more thrust) because the water carries away more heat
3. Increased mass flow and pressure from the steam

Although injected slightly further upstream, that's basically what "conventional" water injection does.
 
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RE: TF42, Our Engine Project For The Airliners-200

Sat Feb 09, 2013 2:16 pm

Quoting ferpe (Reply 32):

We will start to look at and discuss more exotic ideas but before that lets see how far one can reach the spec with a classical Direct Drive 2 spool turbofan (DDTF) and a rusty (actually new beginner) chief designer fiddling with the excellent software Gasturb.

Have at it, Maestro. Great thread.

I wonder, even with more exotic materials research, if we're getting close to the point of diminishing returns for the two spool, (and probably 3 spool as well), designs. Since no engine can be 100% efficient, there is always room for improvement but my thumbnail sketch interpretation of your data so far, indicates to me that we may be running out of room for many more significant efficiency gains, at the very least without affecting reliability.
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RE: TF42, Our Engine Project For The Airliners-200

Sat Feb 09, 2013 9:09 pm

In the post above I put in the wrong throttle diagram for Top of Climb and the beginning of cruise, here the correct one:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T42FL330M082workingline_zps68320119.jpg

Here one can also see the N1 low spool RPM as LPT relative corrected speed. Note that at this FL the cruise point of the engine is close to the max continuous RPM (94%). GE and CFM engines use N1 as the primary parameter for setting the thrust level of the engine (ie the relative RPM in % of low spool with has the fan, booster and LPT), RR and PW uses the ratio of the total pressure over the engine. You have this ratio as P5/P2 in the mission table (the first engine table in my last post). This is the ratio of pressure after the turbine compared to the inlet just before the fan. Sometimes the rear sensor can sit further back is a so called P7 location (PW). The P5/P2 system takes account of the real engine situation, ie what happens including density changes, the N1 principle is a more indirect thrust indication but easier for many Pilots to understand.

One thing that I finally understood when trying to optimize the TF42 to a lower TSFC ie higher efficiency, was why engine OEMs say they need to adapt the engine to the aircraft, e.g. RR is not to keen on retrofitting an existing engine to another aircraft. To understand why we need to look at how the main components of an engine is matched to achieve what one want. The most important seems to be to match the compressors characteristics to the mission profile (the turbines are less critical in their characteristics). The area of engine design which shows these characteristics are the compressor maps. If we start with the high compressor map one can see the following:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T42FL330M082HPCmapworkingline_zps06b527b6.jpg

The design point is at the N = 1 or 100% RPM line (the lines which start vertically and bend left), one can also see the cruise point in the compressor map, it is at N = 0,95 for the HPC (unfortunately I did hide this line "relative corrected N2" in the mission table). The map is made from CFD analysis of the compressor and then verified with bench trials of test compressors driven by an electrical motor. The map we see in the picture is a scaled and repositioned standard map in Gasturb designed to be typical of such maps but not an actual engine map for eg TF42. It does show the principals and we see a couple of interesting things;

- The engine only uses the working line part of a map, the map is an area map however so we can see how the line should be ideally placed. The map is done as a quasi 3D mountain so we can see where the compressor has it's max efficiency (the top of the mountain, you also see the height curves = efficiency curves). The axis are pressure ratio and relative corrected airflow. The latter means one map can represent all speeds and altitudes as all factual airflows are transposed to the static sea-level case.

- The working line placement and the placement of the different mission working points in the map is not a happening, the engine design is massaged until the line and the different points like ToC and Cruise are placed in areas for maximum mission efficiency. Therefore the ToC=max continuous is just past the compressor optimum but not to far down the other side. When you then throttle back to the cruise range (around N= 0,95) it will fall into the area where the compressor has it's highest efficiency (0.86), ie it consumes the least energy from the turbine for a given compression ratio. You spend very little time at TO, more at climb and longest at cruise. Therefore you prioritize cruise to get the sweet spot of the compressor and the others will have to do with more compromised positions.

- We can also see that the working line stays within the map, it does not cross the red surge line like the booster map does:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T42FL330M082IPCmapworkingline_zps6ab4e857.jpg

Was this a real case I would have to put a bleed port behind the booster in the duct to the HPC to get the line to come down from the surge line at low throttle settings. As the line is not at all lined up with the compressor characteristics the bleed port and other actions would definitely be needed, I haven't yet figured out what to do however. Boosters are tricky as they sit on the same shaft as the Fan but at a fraction of the optimum radius. The Fans tips are placed at optimum speed of around M1.1, it then follows that the boosters blades are far of their optimum speed. A booster therefore does not produce much pressure ratio per stage and also has problems with efficiency. This is where GTFs or triple spools come in to fix that, more of later.

- Finally the fan map:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T42FL330M082Fanmapworkingline_zps08b3867e.jpg

Here 2 things are important, the cruise efficiency (at N = 0,90 - 0,93 ) and low noise at TO power (N = 0,91). The latter means a fan pressure ratio not very much higher then 1.6 (for low speed on the bypass mass flow). For cruise and ToC efficiency I had to put ToC at 1.8 (speed line N = 1,0 in the map), when that resulted in TO PR of 1.69 it was acceptable. We see that ToC is down at the 0.88 efficiency curve and I don't quite hit the 0.92 island at cruise. Here there would be more work required to get the last % of TSFC.

With the above I have tried to show what I have found during my fiddling with Gasturb, the program has several well designed methods for findings these optimums, it has been mainly the designers capability that has been the problem here  Wow! . I am happy however as I now know what the engine guys are talking about when they say they have to tune the engine to the frame  .

[Edited 2013-02-09 13:29:57]
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RE: TF42, Our Engine Project For The Airliners-200

Sun Feb 10, 2013 9:48 am

Quoting rwessel (Reply 33):
Although injected slightly further upstream, that's basically what "conventional" water injection does.

Problem with that water injection is it results in poor combustion and consequently smoke, which is bad news these days.
 
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RE: TF42, Our Engine Project For The Airliners-200

Mon Feb 11, 2013 7:55 am

Before we move to more advanced architectures I did try to reach our TSFC cruise goal by increasing the BPR from 9 to 10 and then 11 at the design point, Top of Climb. For 10 there was a small improvement down to 0.544 at mid cruise weight:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/TF38dataBPR10_zps3120b256.jpg

As can be seen a lot of data changes, eg the ToC BPR is locked at 10 which has as consequence that the static BPR goes to 10.84. This is close to the BPR for the LeapX for A320neo which is said to have BPR 11 (it is probably static as GE normally don't give ToC data). I also ran BPR 11 at ToC but then the TSFC backed up again. This is probably because you need to reoptimize the core to gain from BPR 11. BPR 11 raises the propulsive efficiency but might lower the thermal efficiency unless one reoptimizes the core for this higher load on the low pressure turbine. This improvement in efficiency is also on a pure engine basis. On frame level we need to trade that against the increase in OEW and an increase in drag from the larger nacelle as the fan dia increases (look in the dimensions tables for T42 BPR9 above and BPR10 below).

Here the table for our BPR10 engine variant, the weight goes up 1200lb and the engine dia goes from 94'' to 98'':

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T42BPR10V4maindimensions_zpsc07fb24b.jpg

This makes for 2400lb/1100kg on a frame basis for our two holer before we start to count the nacelle effects. 1100kg is 1/3 of our average fuel flow per hour (TSFC*thrust*2 engines) of 3200kg/hour so we loose some 150nm because of this weight increase before we count the drag increase. A quick check shows that this is really marginal as we gain trip duration (11 hours) * the TSFC diff (0.556-0.544=0.012) * cruise thrust (2*6500lbf) = 1700kg. These 1700kg gain shall be weighted against the 1200kg heavier engines and heavier and larger nacelles. As the frame does not always flies for 11 hours but often shorter trips of perhaps half max duration the gain in fuel burn is halved but the weight and drag increase remains and we are better off with a BPR 9 engine.

The above shall show some of the principal trades around propulsive efficiency vs engine size and weight. For a given engine size the BPR can increase without these negative effects if we can make a higher performing core as the fan stays the same but less air goes through the core ie we have higher BPR and therefore higher propulsive efficiency without weight and drag increase. This is the reason the LeapX for A320 has an optimum BPR of 11, we can rest assured CFM knows how to calculate these kind of trades together with Airbus  .

This is also what CFM has been working on with Boeing for the 737MAX, they have increased the core efficiency to the max via component tuning and shrunk it's size in terms of mass flow as far as possible so that they get the maximum BPR and thus overall efficiency inside the 69'' fan dia restriction the MAX poses.

As we now have two tables with a lot of data we can compare let me comment on two rows, Gross thrust (just below our Net thrust) and Specific thrust (2 rows further down). An engines thrust is the net difference of generated momentum (air mass flow * air speed ) minus the momentum of the air we travel in (aircraft speed * intake massflow ). The Gross thrust is the momentum the engine generates and the Net thrust then what is left to drive the aircraft forward. This is easily seen in the static case where we gain all Gross thrust as Net. This loss in Net thrust with speed is also called Lapse or Lapse ratio. Look at the lapse at our V2 point just after takeoff, we are down at 31.9klbf for our BPR9 engine and 30.6 for our BPR10 engine, loss of thrust with speed increases with higher BPR.

The Specific thrust is the net difference in speed between incoming air and outgoing, thus it tells us how close we are to optimum propulsive efficiency as this is max when the outgoing air has the same speed as incoming (we don't have any thrust momentum then but the propulsive efficiency formula does not care about the absolute amount of thrust, just it's efficient creation  Wow!  ). This is why the specific thrust is the best measure of propulsive efficiency, better then BPR which is only an indirect indication of propulsive efficiency level. The specific thrust of those propfan ships we see up-threat is sure to be low  .

[Edited 2013-02-11 00:40:20]
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JoeCanuck
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RE: TF42, Our Engine Project For The Airliners-200

Mon Feb 11, 2013 9:29 am

Quoting ferpe (Reply 37):
The Specific thrust is the net difference in speed between incoming air and outgoing, thus it tells us how close we are to optimum propulsive efficiency as this is max when the outgoing air has the same speed as incoming (we don't have any thrust momentum then but the propulsive efficiency formula does not care about the absolute amount of thrust, just it's efficient creation Wow! ). This is why the specific thrust is the best measure of propulsive efficiency, better then BPR which is only an indirect indication of propulsive efficiency level. The specific thrust of those propfan ships we see up-threat is sure to be low

I find this bit especially interesting...and somewhat counter intuitive. Does specific thrust include the bypass air and the core flow? I assume Specific Thrust can never be zero but it would seem to me that at some point, (I'm guessing cruise due to the thinner air and higher aircraft speeds), the core will provide a greater proportion of total thrust than the fan.
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RE: TF42, Our Engine Project For The Airliners-200

Mon Feb 11, 2013 11:05 am

Quoting JoeCanuck (Reply 38):
I find this bit especially interesting...and somewhat counter intuitive. Does specific thrust include the bypass air and the core flow?

The scientific definition of specific thrust is the total net thrust divided by the total mass flow, thus both core and bypass mass flows (and the minute added fuel mass flow) and thrusts are counted. This is exactly the same as the difference in the average bypass+core air speed and the aircraft speed (if we ignore the fuel mass). I find this definition easier to grasp as the more formal one, and one can think of it like:

- to get any thrust the air mass going into the engine has to be accelerated somehow (the air mass stays the same, no mass disappears, it just changes speed).

- The specific thrust describes how much we accelerate the air mass. If we accelerate little we need lost of air mass to drive an aircraft (low specific thrust), if we accelerate a lot (e.g. Concorde engines) we need less mass of air to achieve the net thrust to drive the frame and the lapse is less.

- Now the gain in accelerating the air a lot is that we have thrust left at high speed (Concorde accelerating to M2), the flip side is that it is less efficient if the frame is an airliner flying at M 0.82.


Thus the specific thrust tells us the excess speed of the air leaving the engine  Wow! , the less the more efficient (if we can rally the air mass needed to get to our necessary thrust level).

[Edited 2013-02-11 03:18:36]
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RE: TF42, Our Engine Project For The Airliners-200

Mon Feb 11, 2013 2:17 pm

Quoting ferpe (Reply 39):

- The specific thrust describes how much we accelerate the air mass. If we accelerate little we need lost of air mass to drive an aircraft (low specific thrust), if we accelerate a lot (e.g. Concorde engines) we need less mass of air to achieve the net thrust to drive the frame and the lapse is less.

Just to keep things clear in my head, we're talking mass over time, right? Using your Concorde example, it's engine if afterburner is rated at about the same thrust as one 757 engine, so as I understand it, they both would be pushing about the same mass of air over time but the RB111 moves the air slowly and the Concorde engines move the air significantly more quickly.

I seem to recall someone mentioning that the efficiency differences partly exist because the force required increase air mass moved by moving twice the air at the same speed is doubled while moving twice the air by doubling the velocity of the air is the force squared.

Quoting ferpe (Reply 39):
Thus the specific thrust tells us the excess speed of the air leaving the engine Wow! , the less the more efficient (if we can rally the air mass needed to get to our necessary thrust level).

So sorts out what I've seen before about bypass flow, and why BPR isn't necessarily the most accurate way to calculate engine efficiency, since one can have a smaller fan spinning faster, or a larger fan spinning more slowly....both bypassing the same mass of air over time but the smaller one moving the air faster.

This is how Rolls says they are going to keep the same size fan and BPR on the -1000 XWB engine as the less powerful -900 engine, by spinning the -1000 fan faster.

So with the TF42, (and I presume the Leap as well), are we bumping up against materials, (or other), limits for size and temp of the core, and as a result, efficiency?
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ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Mon Feb 11, 2013 6:11 pm

Quoting JoeCanuck (Reply 40):
Just to keep things clear in my head, we're talking mass over time, right?

Instant time, ie lb/s or kg/s is the unit for mass flow.

Quoting JoeCanuck (Reply 40):
Using your Concorde example, it's engine if afterburner is rated at about the same thrust as one 757 engine, so as I understand it, they both would be pushing about the same mass of air over time but the RB111 moves the air slowly and the Concorde engines move the air significantly more quickly.

They have the same thrust therefore their product massflow in lb/s * speed in ft/s would be the same, the Olympus in the Concorde push a small mass fast and the 757 PW2000 push a large mass slowly. They both have the same thrust but they differ widely in specific thrust, the Olympus having high spec thrust and the PW2000 low.

Quoting JoeCanuck (Reply 40):
So with the TF42, (and I presume the Leap as well), are we bumping up against materials, (or other), limits for size and temp of the core, and as a result, efficiency?

Yes we are to some extent, there is still potential left but the low hanging fruit is gone. Kurzke, the ex MTU chief performance guy and the maker of the Gasturb program has made a paper about it: http://mtu-rzeszow.com/en/technologi..._maximum_thermal_efficiency_en.pdf

As can be seen beyond 40 and especially 1800K at cruise there is not much more to gain by higher temperatures. For pressure ratio you do gain a bit up to 60 but then no more. This is not the same as RR and GE does not know this when the say the 777X engines will have PR of 60, this is for the max performance part like ToC, this means the important cruise phase will land at around 40-50 and 1700-1800K where the max efficiency will reside with real world components and fuels, at least according to Kurzke.

[Edited 2013-02-11 10:54:02]
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 12, 2013 2:20 am

Quoting ferpe (Reply 41):
As can be seen beyond 40 and especially 1800K at cruise there is not much more to gain by higher temperatures. For pressure ratio you do gain a bit up to 60 but then no more. This is not the same as RR and GE does not know this when the say the 777X engines will have PR of 60, this is for the max performance part like ToC, this means the important cruise phase will land at around 40-50 and 1700-1800K where the max efficiency will reside with real world components and fuels, at least according to Kurzke.

Very interesting paper...I'm fuzzy on the maths but the concepts and graphs are pretty clear. It does seem that the engine makers are running out of headroom. That being said, the new engines will be crazy efficient...which is quite a feat considering the current generation of engines already have amazing efficiencies, and to top it off, those efficiencies are coupled with anvil like reliability.

What happens if the TF42 engine fan is geared?
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 12, 2013 3:09 am

Quoting ferpe (Reply 41):
As can be seen beyond 40 and especially 1800K at cruise there is not much more to gain by higher temperatures.

This should be modified to PR 45 and 1500K, here the conclusive diagram from the Kurzke paper. This is an aircraft turbofan cruising at FL360 with typical components, only the core (thermal) efficiency is evaluated. What is drawn is the thermal efficiency mountain with the thermal efficiency as TSFC in SI units as height rings and with PR and T4 ie burner temperature on the axis. As can be seen reaching the absolute optimum would need PR 60 and 1650K ( 2 ) but we would only loose 0,5% TSFC by staying at 45 and 1500K (TSFC in SI units means 13.6 represents 0.480 and 13.4 is 0.473 in lbm/hr/lbf ) :

http://i298.photobucket.com/albums/mm262/ferpe_bucket/ThermalefficiencyatFL360_zpsff6f3139.jpg

So down to TSFC 0.5 is doable, then it gets hard with the classical core technology used today. Further if one asks an engine guy, does he prefer cruise values of PR 45 and T4 1500K over 55 and 1650K you know the answer , it is the law of diminishing return, better go and search in some other corner for those last drops of fuel.

Quoting JoeCanuck (Reply 42):
What happens if the TF42 engine fan is geared?

This corner we will explore now  Wow! .

[Edited 2013-02-11 19:11:49]
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 12, 2013 3:28 am

Quoting ferpe (Reply 43):
it is the law of diminishing return, better go and search in some other corner for those last drops of fuel.

...and something sometimes forgotten in the quest for those last drops, reliability. Airlines have become pretty spoiled with those bullet proof CFM 56's and the like hanging from their wings. They are not likely to accept marginal gains in fuel efficiency at the expense of that reliability.

Quoting ferpe (Reply 43):
This corner we will explore now

My gut feeling is CFM will pretty much match the first gen GTF's with their Leap engine...but where the Leap seems to be pretty much maxing out the current technology, (pun intended), Pratt's GTF seems to have more room to grow. It looks like it can achieve at least the same efficiencies as the Leap but without having to be quite so bleeding edge with the materials.

Methinks everybody is going to have a GTF in the next generation or two. Since Pratt seems so reluctant to supply an engine for the TF42, our engine maker might be well served by hunting down a likely gearbox maker.

[Edited 2013-02-11 19:30:22]
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 12, 2013 4:23 am

First, Ferpe has been inviting me to this thread for a bit. I must apologize for not being proactive, but I had a reunion last weekend.   

Second, the numbers do come out very analogous to the LEAP-X optimization.

Quoting JoeCanuck (Reply 42):
What happens if the TF42 engine fan is geared?

Now as to how a GTF helps. The GTF decouples the fan from the low turbine. So both improve in efficiency as does the low compressor. Does the TF42 have a variable fan nozzle? This allows for there to be multiple 'fan lines.'

Quoting JoeCanuck (Reply 38):
I assume Specific Thrust can never be zero

There can be negative thrust. For example, during flight idle.

Quoting ferpe (Reply 43):
This is an aircraft turbofan cruising at FL360 with typical components, only the core (thermal) efficiency is evaluated.

Just to be clear, by GE raising their metal temperatures, they improve efficiency at higher temperature by requiring less cooling.

Quoting ferpe (Reply 35):
Boosters are tricky as they sit on the same shaft as the Fan but at a fraction of the optimum radius. The Fans tips are placed at optimum speed of around M1.1, it then follows that the boosters blades are far of their optimum speed.

Not in a GTF or triple spool.   

Quoting ferpe (Reply 35):
The Fans tips are placed at optimum speed of around M1.1

New blade profiles reduce the shock losses and thus move the optimum up to M1.2 or so. (LEAP-X), not applicable to the GTF.   (Its not worth putting in the high cost fan blades when there is a gearbox.)

Quoting ferpe (Reply 37):
BPR 11 raises the propulsive efficiency but might lower the thermal efficiency unless one reoptimizes the core for this higher load on the low pressure turbine.

Or go to a GTF with a tubrine at a far more optimal mach #. Most of the GTF's efficiency improvement is the low turbine.   

Quoting ferpe (Reply 37):
As the frame does not always flies for 11 hours but often shorter trips of perhaps half max duration the gain in fuel burn is halved but the weight and drag increase remains and we are better off with a BPR 9 engine.

There you sound like a RR engineer.   However, there are two ways out of this 'pickle.' #1, work on a lighter engine as GE did with the LEAP (how they brought down the weight of the low pressure turbine, I would love to know...). The other is the GTF where by having the low turbine spin at a more optimal Mach #, far fewer blades are required keeping the weight down allowing for the optimization at higher bypass ratios.

Quoting ferpe (Reply 41):
Kurzke, the ex MTU chief performance guy and the maker of the Gasturb program has made a paper about it:

That paper is interesting, but the author is a bit too fixated on a maximum pressure ratio of 40. That is a limit for a plane doing short hops, but not a limit if cycle life is cut for long haul. New generation coatings are becoming available to raise the temperatures and that will raise the practical pressure-ratio limit. While the progress has been slowed waiting for an effective ceramic.


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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 12, 2013 4:54 am

A post that helps this thread on the GTF (warning, pdf):

See slide 16 as the GTF allows lower fan pressure ratios and thus less noise and higher fan efficiency.

Slide 18 represents engine efficiency a bit more simplified (not good enough for this engine design, but for those trying to wrap their mind around the concept).

http://events.aviationweek.com/html/...ngine%20Concept.SABNIS%20(P&W).pdf


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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 12, 2013 5:33 am

Quoting lightsaber (Reply 45):
Does the TF42 have a variable fan nozzle? This allows for there to be multiple 'fan lines.'

Not up to now, but we could introduce it, we could have a tigther bypass nozzle for cruise that we open up for low RPM operation. What would it bring us?


Quoting lightsaber (Reply 45):
Just to be clear, by GE raising their metal temperatures, they improve efficiency at higher temperature by requiring less cooling.

And by raising T4 they improve the ability of a core to drive a bigger fan at the same core mass flow. The Kurzke diagram ONLY talked about the thermal efficiency, the engine efficiency is about thermal and propulsive efficiency. So by raising T4 even beyond the 1500-1600K discussed a DDTF would be able to run a higher BPR for the same size fan and fan case, ie same weight and drag. It would make for a more efficient engine.

The difference is that while raising PR and T4 used to deliver a double whammy (thermal and propulsive gains), now it is gradually going to a single whammy (smaller core gives a better BPR for same size engine).

But let's now see what a GTF brings.

[Edited 2013-02-11 21:52:32]
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JoeCanuck
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 12, 2013 5:36 am

Quoting lightsaber (Reply 46):

To me, the true beauty of the GTF is the simplicity...it's dead simple to visualise how the gearbox improves efficiency. If one has a grasp of multiple shaft jet engines, then the huge difference in diameter between the fan and the lpt shows a mismatch...in some way or another...without having to know much about engines at all.

Gears are easy...everybody whose ever driven a car or a multi speed bike knows about the effects of gearing. Add to that, knowing that turbines like to spin really fast, (the whistles coming from the turbo in my Dodge diesel attest to that), and fans would rather spin more slowly, then...bang...the pieces just fall into place.

Even the RR triple spools make sense, having another shaft and turbine powering an intermediate compressor, without having all low pressure compression tied to the fan.

I have no doubt the Leap will do what GE says it can, but by essentially decoupling the lpt and the low compressor from the fan, it just seems the GTF has not only taken the simpler, (relatively), route, but has more room to improve in the future...especially on the really big engines...and it has the advantages of a triple spool, without nearly the level of complexity a third shaft brings, compared to a gearbox.

The idea of a GTF on an engine the size of a GE-90, is really quite interesting to my inner geek.

I stick with my assertions that the GTF makes so much sense, that I have no doubts at all that the boffins at GE are throwing a lot of R&D at a gearbox. I bet Pratt is doing a lot of chatting with Boeing about the 77X...and if they can prove they have a reliable gearbox that can handle an engine putting out 100,000 lbs of thrust, GE will have a real run for its money.

[Edited 2013-02-11 21:41:47]
What the...?
 
ferpe
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RE: TF42, Our Engine Project For The Airliners-200

Tue Feb 12, 2013 5:48 am

Quoting lightsaber (Reply 45):
However, there are two ways out of this 'pickle.' #1, work on a lighter engine as GE did with the LEAP (how they brought down the weight of the low pressure turbine, I would love to know...). The other is the GTF where by having the low turbine spin at a more optimal Mach #, far fewer blades are required keeping the weight down allowing for the optimization at higher bypass ratios.

Just as a reference, here the LPT tab from the engine dimensions of the BPR9 TF42, total weight was 10.000 lbm, thereof:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/T42LPturbineandshaft_zps9d6e0432.jpg

the LPT is 45% !!! and it is just the rotating part! And this is a 4 stage LPT, now take that to 6 or 7 stages of a high BPR DDTF of today (even if they use smarter design and lighter materials).
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