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MD-11 Long And Short Exhaust Nacelles  
User currently offlineHkniceguy From Hong Kong, joined Jun 2001, 130 posts, RR: 0
Posted (12 years 3 months 3 weeks 5 days 19 hours ago) and read 2544 times:

What is the different between MD-11 CF6 "long" exhaust nacelles and "short" exhaust nacelles?


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21 replies: All unread, jump to last
 
User currently offlineSteman From Germany, joined Aug 2000, 1381 posts, RR: 7
Reply 1, posted (12 years 3 months 3 weeks 5 days 16 hours ago) and read 2450 times:

The same difference exist between KLM MD-11 (long) and Alitalia's ones (short).
I think it's related to a different subversion of the same engines..

Ciao

Stefano


User currently offlineAirliner rx From United States of America, joined Mar 2002, 19 posts, RR: 0
Reply 2, posted (12 years 3 months 3 weeks 5 days 10 hours ago) and read 2376 times:

If I'm not mistaken the longer Nacelle is a PW-4000 version and the shorter is a GE CF6-50c2

User currently offlineSteman From Germany, joined Aug 2000, 1381 posts, RR: 7
Reply 3, posted (12 years 3 months 3 weeks 5 days 10 hours ago) and read 2361 times:

The PW4000 series doesn't have any cone in the nozzle.


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Ciao

Stefano


User currently offlineJvW From United States of America, joined Nov 2001, 173 posts, RR: 0
Reply 4, posted (12 years 3 months 3 weeks 5 days 10 hours ago) and read 2343 times:

That is a good question; both airlines have the same CF6-80 engines.

JvW


User currently offlineAirliner rx From United States of America, joined Mar 2002, 19 posts, RR: 0
Reply 5, posted (12 years 3 months 3 weeks 5 days 10 hours ago) and read 2334 times:

You are correct STEMAN..... heck I dont know!!!! I'm an old school DC-10 man. I'll stick to the dinosaurs next time!!!

User currently offlineN79969 From , joined Dec 1969, posts, RR:
Reply 6, posted (12 years 3 months 3 weeks 5 days 10 hours ago) and read 2343 times:

I've thought about this question as well. I think it comes down to the final digits/letters on the engine model.

e.g. CF6-80C2B1F or CF6-80C2D2E

(or something like that)

I wonder what a RR powered MD-11 would have looked like.


User currently offlineN79969 From , joined Dec 1969, posts, RR:
Reply 7, posted (12 years 3 months 3 weeks 4 days 11 hours ago) and read 2282 times:

Does anyone know the purpose of the nozzles at the end of CF6 engines on MD-11? They don't appear on PW powered MD-11 nor do they appear on CF6-powered 747 or 767. They reappear on the A300/310/330 that are powered by CF6.

Also they appear on all engines available on the 777. I have wondered what determines when these exhaust nozzles are used or whether they inside the cowling or actually stick out.


User currently offlineHkniceguy From Hong Kong, joined Jun 2001, 130 posts, RR: 0
Reply 8, posted (12 years 3 months 3 weeks 4 days 8 hours ago) and read 2240 times:

As I remember, these two different CF6 (long and short) makes different sounds too, the long nozzles CF6 tend to sounds like the CF6-80E1(CF6 for A330)

User currently offlineN79969 From , joined Dec 1969, posts, RR:
Reply 9, posted (12 years 3 months 3 weeks 4 days 8 hours ago) and read 2239 times:

The old CF6 (CF6-50) on the DC-10 had a distinct "growl" to them. I just put the same question up on the tech/ops page. I am really curious about the answers.

User currently offlineMarcus From Mexico, joined Apr 2001, 1790 posts, RR: 2
Reply 10, posted (12 years 3 months 3 weeks 4 days 8 hours ago) and read 2218 times:

My God I really can't believe this.....a Five star topic filled with questions and no answers.

Don't look at me I have no idea..........but I'm really interested in knowing also.



Kids!....we are going to the happiest place on earth...TIJUANA! signed: Krusty the Clown
User currently offlineDynkrisolo From United States of America, joined Feb 2001, 1863 posts, RR: 7
Reply 11, posted (12 years 3 months 3 weeks 4 days 8 hours ago) and read 2221 times:

I think Hkniceguy has indirectly answered the question. I believe it's of different vintage. Varig's plane was delivered in 1993 while EVA's was delivered in 1997. The older ones must have similar tailcones that can be found on other -80C2 on the B747, B767, A300, and A310. The newer ones must have the -80E-type tailcones. Remember, the A330 came after the MD-11. My guess is GE found some improvement with the -80E-type tailcone . Also, remember, both GE and P&W had problems meeting fuel consumption guarantees on the MD-11. So both of them did a lot of performance improvement packages on the MD-11 engines. So, this might well be one of features introduced in those improvement packages.

User currently offlineN79969 From , joined Dec 1969, posts, RR:
Reply 12, posted (12 years 3 months 3 weeks 4 days 7 hours ago) and read 2193 times:

Dynkrisolo, I think you're correct in pointing out HKniceguy's reply. The length and appearance of the tailcone is tied to vintage. But I also indirectly answered my own question regarding the last digit/letters of the CF6 model number. (See above)

My question remains, what is that tail cone there for exactly? What function does it perform that it is required on some engine/aircraft combinations and not on others?


User currently offlineJvW From United States of America, joined Nov 2001, 173 posts, RR: 0
Reply 13, posted (12 years 3 months 3 weeks 4 days 7 hours ago) and read 2190 times:

Then why have the oldest models from KLM (1993) have the long cone?


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Have they upgraded the older models? Doesn't sound right....

Can anybody answer this question for crying out loud???


JvW


User currently offlineN79969 From , joined Dec 1969, posts, RR:
Reply 14, posted (12 years 3 months 3 weeks 4 days 7 hours ago) and read 2185 times:

Is that KLM one of the newer MD-11s? KLM had them rolling in as late as 1997 or 1998.

User currently offlineDynkrisolo From United States of America, joined Feb 2001, 1863 posts, RR: 7
Reply 15, posted (12 years 3 months 3 weeks 4 days 7 hours ago) and read 2176 times:

N79969:

Not quite. On the CF6, the B designation is for Boeing applications, and the D designation is for Douglas/MDC applications.

All turbofan engines have tailcones or mixer devices. They "regulate" the flow coming out from the engine core. The flow will expand to the ambient in a controled manner. If you don't have one, the engine core flow might "violently" mix with the ambient flow. Then it means a potential loss in efficiency and increase in noise. That's why Hkniceguy observed different noise patterns with different tailcones on the CF6.

JvW:

Engine companies often provide optional retorfit kits for a charge. It's up to the airlines whether they want the kits or not. Some airlines are willing to pay an upfront charge and expecting to recover the cost over the life of the equipment. Some airlines are willing to live with a higher operating cost and save the upfront charge. So, I am not surprised that KLM has retrofited their CF6 engines on the MD-11.


User currently offlineN79969 From , joined Dec 1969, posts, RR:
Reply 16, posted (12 years 3 months 3 weeks 4 days 6 hours ago) and read 2165 times:

Thanks, Dynkrisolo. That was the answer I for which I was looking. Given what you said, the PW has its mixer device on the inside of the tailpipe. Do you know the advantage/disadvantage of that design feature?


User currently offlineDynkrisolo From United States of America, joined Feb 2001, 1863 posts, RR: 7
Reply 17, posted (12 years 3 months 3 weeks 4 days 6 hours ago) and read 2161 times:

Look carefully at the Delta picture in this thread. The PW engine does have a tailcone, too. It just does not protrude behind the exhaust. A mixer device is usually used when you mix the engine core and fan bypass flow. Some examples are the newer RB211s on the B767 and B747-400, Trent 700 on the A330, V2500, and the CFM56-5C on the A340.

User currently offlineJkelley480 From United States of America, joined Feb 2000, 127 posts, RR: 0
Reply 18, posted (12 years 3 months 3 weeks 4 days 6 hours ago) and read 2137 times:

I always assumed it was due to wear, i.e. the tailcones start out sharp and "dull" over time. But after reading this thread that assumption now seems ridiculous!

User currently offlineCX773 From Hong Kong, joined Sep 2001, 365 posts, RR: 6
Reply 19, posted (12 years 3 months 3 weeks 3 days 10 hours ago) and read 2093 times:

I hope this can answer your question.

for example, A330 (Trent 700) is a mixed engine (hot and cold nozzles are merged inside the integrated exhaust nozzle) which has convergent jet nozzles and is used for examining the effect of the component performance ( efficiency for the compressors and turbines, pressure loss for the combustor) on the engine performance. once the fan pressure ratio is selected, the bypass ratio is determined for a given turbine inlet tempreture and overall pressure ratio.

With the mixed engines, the choice of fan pressure ratio fixes the pressure downstream of the LP turbine and hence the power output from the turbine. For a given choice of turbine entry temp. and overall pressure ratio, the fan pressure ratio therefore fixes the bypass ratio. ( this is in contrast with the unmixed engine eg."PW 4000" for which the bypass ratio and fan pressure ratio can be selected independently, at least over some range.)

The benefit conferred by the working line being further to the right for the mixed engine augments the small increase in thrust arising directly from the mixing of core and bypass flow. it means the pressure ratio falls more rapidly as turbine inlet tempreture decreases, but the mass flow thru the fan decreases proportionally less. this steeper working line of the fan is a primary reason for the use of the mixer ( sorry can't show graph here). This maximum fan pressure ratio occurs during climb, but of far greater concern to the overall fuel consumption are conditions when the engine is throttled back somewhat, such as cruise, because the engine operates for much longer at this condition. A further benefit is that there is a smaller drop in rotational speed required to reduce thethrust with the steeper working line; this higher rotational speed, relative to that for the unmixed engine, means that at the reduced thrust condition for cruise the LP turbine will operate at lower value of change in stagnation enthalpt/blade speed(square) which is likely to give a further increase in efficiency.


User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 20, posted (12 years 3 months 3 weeks 3 days 9 hours ago) and read 2084 times:

As was mentioned, the Pratt incorporates a tailcone which is inside thus obscured by the tailpipe.

The GE tailcone protrudes aft of the tailpipe and a section forward of that which is not visible unless you were looking into the tailpipe.



You're only as good as your last departure.
User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 21, posted (12 years 3 months 3 weeks 3 days 4 hours ago) and read 2050 times:

The shape of the exhaust cone transforms the turbine exhaust gas stream to thrust.


You're only as good as your last departure.
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