b6a322
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DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 2:01 pm

Hi all,

I've noticed over the past few years that most of the DC10s or MD11s I see appear to only have two engines. Although the housing for the third engine remains, It does appears to be vacant. Is this due to re-engining? Or is it just an optical illusion? Is this something, say, DHL could do to their 727s if they wanted to?

Thanks.
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EMBQA
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 2:16 pm

Ah.. no ALL DC-10's and MD-11's are still flying with 3 engines.
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Starlionblue
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 2:16 pm

Optical illusion. They all have three engines.

Do you have any pics that illustrate this phenomenon?
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FX772LRF
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 2:52 pm


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Here's a good example of what B6A322 is talking about.

It's just an optical illusion due to the fact that the engine is really far recessed in the nacelle. If you can compare the size of engines #1 and #3 to the length of the nacelle of #2, you can figure about how much "empty" space there is at the front of the nacelle. In the photo above, you can see the shape change of the nacelle where the engine starts which makes a slight bulge.

-Noah   

Not sure if I'm using the term "nacelle" correctly - I'm referring to the outside engine "cover" that protects the internal parts.
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474218
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 4:41 pm

The picture below illustrates where the engine is (was) located on a DC-10.


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travelavnut
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 4:43 pm

Which leads me to the following question;

If you remove engine No. 2 you would save quite a lot of weight. Although it´s impossible that something like that would offer better economics then 3 engines. I still wonder what kind of economics removing eninge 2 would give. Any experts wanna give this a go? 
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bonusonus
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 5:08 pm

I don't think weight is as much as an issue as drag here. I doubt there would be significant improvements in economics having a hole in the tail instead of a feathering engine, for example. Either way, as you can see in the picture, actually removing that engine likely changes the aerodynamics of the tail quite a bit, and would make the airplane inoperable.
 
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longhauler
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 6:15 pm

Recall though, that McDonnell Douglas did offer a 2 engine version of the DC-10, named the "DC-10 Twin".

Smaller than the DC-10, it was about the size/weight of a domestic B767-200. No airlines however were interested.
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474218
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 7:09 pm

Quoting longhauler (Reply 7):
Recall though, that McDonnell Douglas did offer a 2 engine version of the DC-10, named the "DC-10 Twin".


It was a "paper airplane" just like the L-1011-600 Twin-Star. Neither were ever offered to the airlines just sketches on paper.
 
KELPkid
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 8:22 pm

Quoting travelavnut (Reply 5):
If you remove engine No. 2 you would save quite a lot of weight. Although it´s impossible that something like that would offer better economics then 3 engines. I still wonder what kind of economics removing eninge 2 would give. Any experts wanna give this a go?

Probably not economically feasible. The aircraft has many redundant systems that assume there will be three engines in place at all times, and redesigning the systems for a twin engined role would probably cost about half of what engineering a new aircraft would. Not to mention that the DC-10/MD-11 are designed to be tail heavy (due to not only the engine, but the massive stucture that is needed to support an engine pylon in the tail). Re-engineering the airframe to put the CG/Center of pressure in the proper place, and leaving a substantial payload envelope, without moving the position of the wing on the airframe would be quite the engineering miracle  
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Starlionblue
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RE: DC10 / MD11 Using Only Two Engines?

Mon Aug 16, 2010 11:31 pm

Here's an MD-11 with an afterburner fitted to #2.


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longhauler
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RE: DC10 / MD11 Using Only Two Engines?

Tue Aug 17, 2010 12:32 am

Quoting 474218 (Reply 8):
It was a "paper airplane" just like the L-1011-600 Twin-Star. Neither were ever offered to the airlines just sketches on paper.



I was under the impression that everything starts as a "paper airplane" and when airline interest is garnered, further development is taken.

The McDD internal designation of D-969C was given to the project, although it was always known as the DC-10 Twin. McDD worked on project from before the first DC-10 flight, and continued to refine it until the project was canceled in 1976. It was offered to all airlines, the most interest came from Allegheny, Delta, Swissair, Iberia and Eastern.

However, no airlines were willing to commit, citing the fear the aircraft would still be too large. The DC-X-200 resulted, smaller than the D-969C ... again no interest was shown from airlines and that project was canceled in 1978. That was considered the end of the "DC-10 Twin".
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spacecadet
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RE: DC10 / MD11 Using Only Two Engines?

Tue Aug 17, 2010 3:21 am

Does having that long cowling with all that empty space in front of the engine change anything about the characteristics of the #2 engine vs. the other two? I would think the air rushing in there would get "concentrated" or compressed a bit more than the other two engines before it reaches the engine itself.
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KELPkid
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RE: DC10 / MD11 Using Only Two Engines?

Tue Aug 17, 2010 3:41 am

Quoting spacecadet (Reply 12):
Does having that long cowling with all that empty space in front of the engine change anything about the characteristics of the #2 engine vs. the other two? I would think the air rushing in there would get "concentrated" or compressed a bit more than the other two engines before it reaches the engine itself.

Center engines on jetliners are notorious for having various assorted air flow problems, mostly in the takeoff or landing regimes. Even with all the aerodynamic tweaks and tricks, overzealous use of the elevator can disturb the smooth airflow into the intake. Look at Starlionblue's picture in post #10 above. If that wasn't a bird strike, the other distinct probable cause of the flame coming out of the back of #2 is most likely a compressor stall   I have been on a 727 when the pilot flying caused a compressor stall in #2 on takeoff...scares the bejezzus out of everyone on board.
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Starlionblue
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RE: DC10 / MD11 Using Only Two Engines?

Tue Aug 17, 2010 7:14 am

727 was/is notorious for compressor stalls on rotation. It happened on the maiden flight. The subsequent optimization of the s-duct cost Boeing quite a bit of money.

As for the VASP pic, I think that may have been an oil leak, but not sure.
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daviation
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RE: DC10 / MD11 Using Only Two Engines?

Tue Aug 17, 2010 4:21 pm

Yes, I was a passenger in an Eastern 727-200 when we had a compressor stall on takeoff from LGA. It was quite a bang. But we continued the climbout, and the cockpit crew made up for it with the smoothest landing (in RIC) that I have ever experienced.
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citationjet
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RE: DC10 / MD11 Using Only Two Engines?

Tue Aug 17, 2010 5:35 pm

I am surprised that no one has mentioned the two engine 727 or the three engine 747.


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tb727
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RE: DC10 / MD11 Using Only Two Engines?

Tue Aug 17, 2010 8:03 pm

Quoting CitationJet (Reply 16):
I am surprised that no one has mentioned the two engine 727

Check Essential!!! (Just seeing who the real 727 guys are )
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Starlionblue
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RE: DC10 / MD11 Using Only Two Engines?

Wed Aug 18, 2010 9:54 am

Quoting daviation (Reply 15):
the cockpit crew made up for it with the smoothest landing (in RIC) that I have ever experienced.

Going to nitpick here and say that very smooth is not a requirement for a good landing. It is just a bonus, and really only for the pax.
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FlyHossD
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RE: DC10 / MD11 Using Only Two Engines?

Thu Aug 19, 2010 3:07 am

Yes. I'll never forget that one, though I usually said it as "Check Essential, cover the bus."

The 727 was (is) a fine, fine machine.
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KELPkid
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RE: DC10 / MD11 Using Only Two Engines?

Thu Aug 19, 2010 4:56 am

Quoting Starlionblue (Reply 18):
Going to nitpick here and say that very smooth is not a requirement for a good landing. It is just a bonus, and really only for the pax.

In the 727, it is a double bonus, as a smooth arrival in a 727 is something of a miracle (one more thing the 727 was notorious at-making an aircraft carrier arrival rather than a smooth landing)  
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tb727
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RE: DC10 / MD11 Using Only Two Engines?

Thu Aug 19, 2010 2:17 pm

Quoting FlyHossD (Reply 19):
Yes. I'll never forget that one, though I usually said it as "Check Essential, cover the bus."

The 727 was (is) a fine, fine machine.

Sure is! Thankfully the only times so far that I have called Check Essential, outside of the sim of course, is when the FE forgets to switch Essential to APU when we shut down! Of course when the APU shut itself down and we were sitting in there in the pitch black it got a good chuckle from the crew. Never heard anyone say the "cover the bus" part but it makes sense.
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bri2k1
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RE: DC10 / MD11 Using Only Two Engines?

Thu Aug 19, 2010 3:49 pm

Quoting Starlionblue (Reply 18):
only for the pax

Operationally speaking and for safety, smoothness is a secondary factor, I agree. But to the pilot's ego (which fuels the pilot, who flies the plane) it's rather important.
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kimberlyRJ
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RE: DC10 / MD11 Using Only Two Engines?

Thu Aug 19, 2010 8:58 pm

Hey hey

While the MD11 is taxing on the ground am I correct in saying that the number 2 engines is started at the same time as 1 and 3?

Is the number 2 engine used as the others on the ground? I mean the same amount of thrust? Or is it used less or more? I was just thinking that the height of the number 2 engine could cause problems at certain airports to terminals and buildings?

Also, after landing is the number 2 engine kept running or is it shut down before the other engines? Thinking logically I guess the number 2 engine would be kept running when the MD11 aircraft arrives at the stand? I mean there is less risk of ingestion due to its position?

Thanks

Kimberly
 
CosmicCruiser
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RE: DC10 / MD11 Using Only Two Engines?

Fri Aug 20, 2010 1:02 am

Actually, you're thinking right but don't have the facts.

Quoting kimberlyrj (Reply 23):
Is the number 2 engine used as the others on the ground? I mean the same amount of thrust? Or is it used less or more? I was just thinking that the height of the number 2 engine could cause problems at certain airports to terminals and buildings?

Not really to buildings because the engine points downward therefore creating a hazard for ground things far behind the jet. In tight ramps we use 1 & 3 first then bring up #2. We limit all engs to 40% N1 in tight ramps.

Quoting kimberlyrj (Reply 23):
Also, after landing is the number 2 engine kept running or is it shut down before the other engines? Thinking logically I guess the number 2 engine would be kept running when the MD11 aircraft arrives at the stand? I mean there is less risk of ingestion due to its position?

We usually shutdown #2 on the taxi in because 1 & 3 have the hydraulics on them for brakes.
 
KELPkid
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RE: DC10 / MD11 Using Only Two Engines?

Fri Aug 20, 2010 5:34 pm

Quoting CosmicCruiser (Reply 24):
We usually shutdown #2 on the taxi in because 1 & 3 have the hydraulics on them for brakes.

Any sort of cool down period that has to be observed before shutting it down? Seems like the MD-11 carries a bit of thrust on a typical stabilized approach  
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Fly2HMO
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RE: DC10 / MD11 Using Only Two Engines?

Fri Aug 20, 2010 6:28 pm

Quoting Starlionblue (Reply 10):
Here's an MD-11 with an afterburner fitted to #2.

Ahh so that was the long forgotten MD-11 Sport version that MD offered for hot and high airports wasn't it   

(This would have been the perfect troll thread but no ya'll had to be too honest  Silly )

[Edited 2010-08-20 11:30:39]
 
KELPkid
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RE: DC10 / MD11 Using Only Two Engines?

Fri Aug 20, 2010 6:31 pm

Quoting Fly2HMO (Reply 26):
Ahh so that was the long forgotten MD-11 Sport version that MD offered for hot and high airports wasn't it

(This would have been the perfect troll thread

Close to this topic: Didn't McDD create a special DC-10 version for either AeroMexico or Mexicana that had Pratt & Whitney JT9D's so that they could get decent takeoff performance at MEX?
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MrFord
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RE: DC10 / MD11 Using Only Two Engines?

Fri Aug 20, 2010 8:38 pm

Quoting KELPkid (Reply 27):
Close to this topic: Didn't McDD create a special DC-10 version for either AeroMexico or Mexicana that had Pratt & Whitney JT9D's so that they could get decent takeoff performance at MEX?

The DC-10-15, with CF6-50C2Fs tho, derated Series 30 engines.


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Series 40 were equipped with JT9D, main customer was NW, but as fas as I know, they were at a slight/certain disadvantage range wise vs Series 30 models.
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CosmicCruiser
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RE: DC10 / MD11 Using Only Two Engines?

Fri Aug 20, 2010 9:11 pm

Quoting KELPkid (Reply 25):
Any sort of cool down period that has to be observed before shutting it down? Seems like the MD-11 carries a bit of thrust on a typical stabilized approach

It's not the thrust used for the approach which isn't really that high but the temp achieved during reverse thrust. The GE has a different cooldown time than the Pratt. GE is shortest.
 
Viscount724
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RE: DC10 / MD11 Using Only Two Engines?

Fri Aug 20, 2010 10:01 pm

Quoting MrFord (Reply 28):
Quoting KELPkid (Reply 27):
Close to this topic: Didn't McDD create a special DC-10 version for either AeroMexico or Mexicana that had Pratt & Whitney JT9D's so that they could get decent takeoff performance at MEX?

The DC-10-15, with CF6-50C2Fs tho, derated Series 30 engines.

Seven DC-10-15s were built -- 5 for MX and 2 for AM.
 
Fly2HMO
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RE: DC10 / MD11 Using Only Two Engines?

Sat Aug 21, 2010 3:19 pm

Quoting KELPkid (Reply 27):
Didn't McDD create a special DC-10 version for either AeroMexico or Mexicana that had Pratt & Whitney JT9D's so that they could get decent takeoff performance at MEX?

Indeed. I've heard more than a few older captains call them the "sport", that's what I based my lame joke on 
 
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DocLightning
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RE: DC10 / MD11 Using Only Two Engines?

Sun Aug 22, 2010 6:51 am

Quoting travelavnut (Reply 5):


If you remove engine No. 2 you would save quite a lot of weight. Although it´s impossible that something like that would offer better economics then 3 engines. I still wonder what kind of economics removing eninge 2 would give. Any experts wanna give this a go?

In fact, your idea was considered by McDD and Lockheed (for the Tristar...er "Bistar"). But it was Boeing who actually pulled it off. See, the problem is that you can't just take out the #2 engine and leave the remaining two because in an engine-out situation, you would only have one of those engines lifting the airplane. So each engine has to be able to lift the aircraft after V1. That requires bigger engines.

And so Boeing got to work on it. A few other things were changed. The fuselage was made a bit wider, the nose was recontoured, the wings needed to be relofted, and a few other minor changes were made.

The resulting "Twin-Engine DC-10/MD-11" has been wildly successful:


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