rigo
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Aircraft With Multiple Powerplant Choices

Wed Jun 11, 2008 4:34 am

Hi all,

Here is a probably trivial question I have been wondering about lately. It is quite common for aircraft to be offered with various powerplants (for example, the A380 can use RR Trent 900 or GP7200), but what are the practical implications? Is this mainly an opportunity for airlines to leverage the competition between engine suppliers to obtain better deals, or are there some noticeable differences in performance? Can pilots fly either model indifferently or are type ratings specific to a given engine configuration?

Regards,
Rigo
 
Zuluaviator994
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RE: Aircraft With Multiple Powerplant Choices

Wed Jun 11, 2008 2:29 pm

And just to add to the questions, I read in a book that the 787 can use both types of engines (Trent and GE) at once because of the new software. How would this affect Performance/Operations? Are there any other planes that can do this?
Cheers
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CJAContinental
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RE: Aircraft With Multiple Powerplant Choices

Wed Jun 11, 2008 2:59 pm

I suppose one factor could be existing engine types within the rest of the airline's fleet. For instance, the 767-3ER shares the same GE engine as the 747-4. So, maintentance could be taken into account economically in this respect; training up engineers for new engine types would be more costly.

Also, like you say, it may be a choice of performance. There's not really any such thing as one's better than the other; its more of a case as to which one fits this airline, this route and this range more effectively (specific requirements). So, its optimum choice based on the airlines specific needs, and this results in different engine choices. (airlines have different, although common needs, and so require different engines).
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Jetlagged
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RE: Aircraft With Multiple Powerplant Choices

Wed Jun 11, 2008 8:58 pm

Quoting Rigo (Thread starter):
Can pilots fly either model indifferently or are type ratings specific to a given engine configuration?

I'm sure some pilots can fly any aircraft indifferently.  

Type ratings are not dependent on engine type, but differences in engine handling and control can be noticeable. The biggest obvious difference is that some engines set power with N1 rpm, others with EPR. Different numbers which behave in different ways.

Performance will not vary much between the different engine combinations. Engine choice may be down to fleet compatibility. It might just be that the finance deal through one engine manufacturer is more favourable than another.

Quoting ZuluAviator994 (Reply 1):
I read in a book that the 787 can use both types of engines (Trent and GE) at once because of the new software.

Both at once? Not GE on one wing and RR on the other, that's for sure. The engines have a common interface, but aren't exactly interchangeable.

[Edited 2008-06-11 13:59:32]
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Zuluaviator994
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RE: Aircraft With Multiple Powerplant Choices

Wed Jun 11, 2008 11:50 pm



Quoting Jetlagged (Reply 3):
Both at once? Not GE on one wing and RR on the other, that's for sure. The engines have a common interface, but aren't exactly interchangeable.

That's what I meant, not on the same wing  Wink
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tdscanuck
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RE: Aircraft With Multiple Powerplant Choices

Thu Jun 12, 2008 5:03 am



Quoting Rigo (Thread starter):
Is this mainly an opportunity for airlines to leverage the competition between engine suppliers to obtain better deals, or are there some noticeable differences in performance? Can pilots fly either model indifferently or are type ratings specific to a given engine configuration?

Generally, GE's are designed towards minimum fuel burn, P&W are designed towards minimum weight, and RR's are designed towards maximum durability. This is only a rough comparison, but each of the major engine OEM's does their trades slightly differently. Depending on your route structure and how you feel about fuel cost vs. engine maintenance cost vs. engine capital cost, a different engine may represent a better value proposition.

Quoting ZuluAviator994 (Reply 1):
And just to add to the questions, I read in a book that the 787 can use both types of engines (Trent and GE) at once because of the new software.

You need to swap struts too but yes, you can change a 787 from RR to GE and back.

Tom.
 
roseflyer
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RE: Aircraft With Multiple Powerplant Choices

Thu Jun 12, 2008 2:17 pm

Providing dual sources on key components is important to an aircraft manufacturer. Going with a single source engine supplier can put a program at risk if that supplier has problems. Lockheed learned this the hard way when Rolls Royce's failures seriously cut into the number of L1011s produced.

The biggest counter example of this though is the 737. The most popular aircraft in the world has a single source for engines since they all have similar CFM engines. However that does not mean that the engines are the same. I believe there are 4 choices on power ratings available. It depends on which minor model is chosen and what performance characteristics an airline needs.
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Starlionblue
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RE: Aircraft With Multiple Powerplant Choices

Thu Jun 12, 2008 2:29 pm

Here's an example. On the 773 (apart from the 772LR and the 773ER) you can get RR or GE or PW. (I know just saying "GE90" will turn most a.nutters into drooling blobs of gelatin but bear with me here). The GE90 is certainly the most powerful choice. But IIRC it is also the heaviest. So unless you really need the extra power you can save lots and lots of weight by choosing, say, RR instead.
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tdscanuck
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RE: Aircraft With Multiple Powerplant Choices

Fri Jun 13, 2008 1:02 am



Quoting RoseFlyer (Reply 6):
The most popular aircraft in the world has a single source for engines since they all have similar CFM engines. However that does not mean that the engines are the same.

Actually, it does, almost.

Virtually all 737NG's up until very recently had CFM56-7B engines. They come in multiple thrust ratings but the *only* difference between the ratings is the programming plug that tells the engine what thrust rating it is. The engines are identical in all other meaningful respects.

There are a couple of minor wrinkles; you used to be able to get dual-annular combustor versions (I think they're coded CFM56-7B/2 but I'm not positive) that burn a little more fuel but have better NOx/HC/CO emissions. And, recently, they switched over to the "Tech Insertion" engine (CFM56-7B/3), which has a better combustor and HP spools. But, again, all /3 engines are functionally identical except for the thrust programming plug.

Tom.

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