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DC-10 And L-1011 Tail Engine Designs And Mounts  
User currently offlineThrust From United States of America, joined Sep 2003, 2691 posts, RR: 10
Posted (9 years 11 months 2 weeks 6 days 4 hours ago) and read 11145 times:

Hi. I wanted to ask several questions regarding the differences in performance of the DC-10 tail mounted engine on a strut vs. the L-1011's S-duct design for its no. 2 tail engine. What are the advantages and disadvantages of each design? What, in your opinion, is the better design, the DC-10's no. 2 engine design, or the L-1011's?


Fly one thing; Fly it well
29 replies: All unread, showing first 25:
 
User currently offlineAUAE From United States of America, joined Apr 2004, 296 posts, RR: 3
Reply 1, posted (9 years 11 months 2 weeks 6 days 4 hours ago) and read 11117 times:

I am not sure of the total length of the ducts, but by intuition, the s-duct is a bit longer and probably has a slightly bigger negative effect on engine efficiency. The plus side to the s-duct however, is that it puts the engine closer to the ground making it slightly easier to service and it also puts the thrust line closer to the c.g. of the aircraft. Since the thrust line is closer to the c.g. in an s-duct configuration, I would also think the overall structure would be lighter. But that might not necessarily be true. Personally, I think the Lockheed design is better, just because it looks better.  Smile

Shawn



Air transport is just a glorified bus operation. -Michael O'Leary, Ryanair's chief executive
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17172 posts, RR: 66
Reply 2, posted (9 years 11 months 2 weeks 6 days 2 hours ago) and read 11094 times:

Apart from the servicing improvements with the engine closer to the ground, the S-duct allows for a smaller fin/rudder. This decreases drag and also decreases the tendency for Dutch roll. However the aerodynamic design of an S-duct is more complex. The 727 had surge problems on the center engine early in it's design due to turbulence in the duct, and still suffers from occasional surges on rotation today.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAaron747 From Japan, joined Aug 2003, 8289 posts, RR: 26
Reply 3, posted (9 years 11 months 2 weeks 5 days 20 hours ago) and read 11020 times:

^
didn't boeing attempt to resolve those issues by installing vortex generators in the s-duct?



If you need someone to blame / throw a rock in the air / you'll hit someone guilty
User currently offlineA350 From Germany, joined Nov 2004, 1101 posts, RR: 22
Reply 4, posted (9 years 11 months 2 weeks 5 days 19 hours ago) and read 10996 times:

A bit OT:
What was the reason why the L-1011 had such little success compared to the DC-10, although many people claim it to be the more innovative a/c? Was it simply the range of the DC 10-30?

Thanks in advance for answers

A350



Photography - the art of observing, not the art of arranging
User currently offlineBroke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 5, posted (9 years 11 months 2 weeks 5 days 19 hours ago) and read 10988 times:

Early in the development of the L-1011, Rolls-Royce has significant problems with the RB211-22C engine resulting in several design changes that delayed the introduction of the L-1011.
This led to the bankruptcy of Rolls-Royce and the near bankruptcy of Lockheed.
Delta hedged their bets by ordering 5 DC-10-10 airplanes and stayed with the L-1011. Eastern tried to start wide body service by leasing 3 747-100's from Pan Am, but their reliability (or lack of) did not help Eastern at all.
Then further major reliability problems with the RB211-22C, including a fan disc burst in December, 1972 and Eastern losing the first wide body ever in the Everglades west of Miami at the end of December did nothing to help L-1011 sales.
The changes to the RB211-22C became so significant that the engine was redesignated the RB211-22B. I don't know why the "B" succeeded the "C", but it did.
Until the RB211-524 engine came out, the RB211 was not considered a very good engine.
P&WA had the same problem with the JT9D-3, but for other technical reasons, and the JT9D-7 series were much better engines.


User currently offlineA350 From Germany, joined Nov 2004, 1101 posts, RR: 22
Reply 6, posted (9 years 11 months 2 weeks 5 days 19 hours ago) and read 10984 times:

@Broke: thanks a lot.

So, after all, the fate of the L-1011 had nothing to do with her technology?



Photography - the art of observing, not the art of arranging
User currently offlineGigneil From United States of America, joined Nov 2002, 16347 posts, RR: 85
Reply 7, posted (9 years 11 months 2 weeks 5 days 17 hours ago) and read 10962 times:

This led to the bankruptcy of Rolls-Royce and the near bankruptcy of Lockheed.

It actually caused the bankruptcy of both. The State of California paid to keep Lockheed alive.

The major problem with sales was the continuous slippage of the delivery date. The RR and Lockheed problems kept causing the plane to miss deadlines, and potential purchasers fled.

N


User currently offlineMoose135 From United States of America, joined Oct 2004, 2401 posts, RR: 10
Reply 8, posted (9 years 11 months 2 weeks 5 days 17 hours ago) and read 10943 times:

the S-duct allows for a smaller fin/rudder

Actually, it allows for a larger rudder. By having more rudder surface, it allowed for greater control in an asymmetrical (wing-engine out) situation. That allowed the 1011 wing engines to be mounted further outboard on the wing, improving wing loading, making it more efficient that the DC-10.

Moose



KC-135 - Passing gas and taking names!
User currently offlineThrust From United States of America, joined Sep 2003, 2691 posts, RR: 10
Reply 9, posted (9 years 11 months 2 weeks 5 days 16 hours ago) and read 10927 times:

What was the purpose of the frisbee fairing on the DL L1011-500? I just noticed that no other L-1011 models except the -500 have the frisbee fairing.


Fly one thing; Fly it well
User currently offlineThrust From United States of America, joined Sep 2003, 2691 posts, RR: 10
Reply 10, posted (9 years 11 months 2 weeks 5 days 15 hours ago) and read 10922 times:

Excuse me, I meant all L1011-500s in general, not just DL's  Big grin


Fly one thing; Fly it well
User currently offlineTimz From United States of America, joined Sep 1999, 6902 posts, RR: 7
Reply 11, posted (9 years 11 months 2 weeks 5 days 15 hours ago) and read 10922 times:

Only the -500 had it as built, but didn't some earlier L1011s get retrofitted?

User currently offlineDoug_Or From United States of America, joined Mar 2000, 3441 posts, RR: 3
Reply 12, posted (9 years 11 months 2 weeks 5 days 15 hours ago) and read 10914 times:

yep

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Photo © Michael Carter



FWIW, I've heard the DC-10 almost wasn't made becuase of the lack of customers, until United decided to purchase it instead of the L-1011 (they wanted to make sure both were built to keep prices lower). Don't know if this is true, or just a tristar fans view of the facts.



When in doubt, one B pump off
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 13, posted (9 years 11 months 2 weeks 5 days 13 hours ago) and read 10881 times:

The frisbie fairing was fitted to reduce aft cabin engine/airflow noise, on the long body aircraft.

On the -500, it helped (but did not totally eliminate) engine surging, at lower speeds with high power settings.


User currently offlineDeskPilot From Australia, joined Apr 2004, 767 posts, RR: 0
Reply 14, posted (9 years 11 months 2 weeks 5 days 13 hours ago) and read 10866 times:

"..The frisbie fairing was fitted to reduce aft cabin engine/airflow noise, on the long body aircraft..."

Does anyone have a picture of this ? Where's it located ?



By the way, is there anyone on board who knows how to fly a plane?
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 15, posted (9 years 11 months 2 weeks 5 days 9 hours ago) and read 10801 times:

Clearly visible on the photo above (TWA TriStar) just below the number two engine intake (the curved bit)...

Worked very well indeed...much quieter in the aft cabin.


User currently offlineSATL382G From , joined Dec 1969, posts, RR:
Reply 16, posted (9 years 11 months 2 weeks 5 days 1 hour ago) and read 10725 times:

IMHO..

That little fairing also did a lot for the asthetic qualities of an already good looking airplane. Gives the leading edge of the vert stab a nice long "sweep".

regards


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17172 posts, RR: 66
Reply 17, posted (9 years 11 months 2 weeks 4 days 22 hours ago) and read 10691 times:

the S-duct allows for a smaller fin/rudder

Actually, it allows for a larger rudder. By having more rudder surface, it allowed for greater control in an asymmetrical (wing-engine out) situation. That allowed the 1011 wing engines to be mounted further outboard on the wing, improving wing loading, making it more efficient that the DC-10.


Sorry I was unclear. The S-duct allowed for a smaller fin/rudder in total including the engine. That is, the part that sticks upward  Big grin over the fuse is smaller in total.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offline2H4 From United States of America, joined Oct 2004, 8956 posts, RR: 60
Reply 18, posted (9 years 11 months 2 weeks 4 days 17 hours ago) and read 10646 times:
AIRLINERS.NET CREW
DATABASE EDITOR

Every other three-engined jet I can think of uses the S-duct layout, as opposed to the DC-10/MD-11 design. For example, the Falcon 50 and 900, the Yak-42, the Trident, the Tu-154, etc, etc.

I may be forgetting an exception, but the popularity of the S-duct design certainly lends some credibility to it.


2H4



Intentionally Left Blank
User currently offlineMlsrar From United States of America, joined Mar 2000, 1417 posts, RR: 8
Reply 19, posted (9 years 11 months 2 weeks 4 days 14 hours ago) and read 10599 times:


I may be forgetting an exception, but the popularity of the S-duct design certainly lends some credibility to it.



The DC-10 was originally designed to be a twinjet that, if produced, would have borne a significant similarity to a shorter 777. The lack of a suitable powerplant was the genesis of the mounting scenario of engine 2.



I mean, for the right price I’ll fight a lion. - Mike Tyson
User currently offlineBuzz From United States of America, joined Nov 1999, 697 posts, RR: 21
Reply 20, posted (9 years 11 months 2 weeks 4 days 11 hours ago) and read 10569 times:

Hi Thrust, Buzz here. I've worked DC-10's a lot, and L-1011-500's a little. My opinion is that the Lockheed was more expensive over the long run, it wasn't really a tail engine issue. Lockheed does tend to make innovative airplanes (Model 18 Electra, P-38, Constallation, C-130, U-2, C-141, A-12) where as Douglas uses proven technology.
I'm no fan of the "patio party" under a #2 engine of a DC-10, in that regard i think the L-1011 has an advantage... not as cold / windy / oily.
And i think the extra metal required to reinforce the vertical fin to carry the load of the #2 engine is a drawback. I don't know how much weight penalty that carries... not a factor anymore.
g'nite
Buzz Fuselsausage: Line Mechanic by night, DC-3 Crew Chief by choice, taildragger pilot for fun


User currently offlineScbriml From United Kingdom, joined Jul 2003, 12877 posts, RR: 46
Reply 21, posted (9 years 11 months 2 weeks 4 days 10 hours ago) and read 10559 times:
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Does anyone have a picture of this ? Where's it located ?

Ahem, as seen on the original L1011 testbed about the time of the rollout of the first -500:


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Photo © Steve Brimley
View Large View Medium
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Photo © Steve Brimley





Time flies like an arrow, but fruit flies like a banana! #44cHAMpion
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1610 posts, RR: 52
Reply 22, posted (9 years 11 months 2 weeks 3 days 11 hours ago) and read 10484 times:
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A couple of points:

1) RR went bankrupt and was rescued by the UK government. Lockheed did not go bankrupt. They only got loan guarentees from the US government that were never exercised. The loans being guarenteed were paid off ahead of schedule.

2) An S duct suffers higher total pressure losses than a straight duct, plus it creates flow distortion, both being bad things. The 727-100 prototype suffered a surge of the #2 engine on its maiden takeoff due to flow distortion. This was solved by a series of rather large vortex generators in the #2 inlet. I am not aware of the L-1011 having such a problem.

3) The "frisbee" fairing should be "Frisbee" fairing, as it is named after Lloyd Frisbee, an aerodynamicist at Lockheed.


User currently offline2H4 From United States of America, joined Oct 2004, 8956 posts, RR: 60
Reply 23, posted (9 years 11 months 2 weeks 3 days 10 hours ago) and read 10479 times:
AIRLINERS.NET CREW
DATABASE EDITOR

AeroWeanie,

Did the large vortex generators in the #2 inlet have (or need) any kind if ice protection?


2H4



Intentionally Left Blank
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1610 posts, RR: 52
Reply 24, posted (9 years 11 months 2 weeks 3 days 9 hours ago) and read 10476 times:
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I seem to recall they do have anti-ice protection. The AIAA design case study on the 727 says for certain, but I don't have it available to me right now. I'll check...

25 AeroWeanie : I just checked the AIAA case study - they are anti-iced. The case study also indicates that the 727-100 (with JT8Ds) has one row of 11 VGs and the 727
26 Max Q : Having the engines further out on the wing also allowed for a quieter cabin, quite noticable compared to the DC10.
27 A350 : My opinion is that the Lockheed was more expensive over the long run, it wasn't really a tail engine issue This is something you can read quite often.
28 Thrust : Question: did the 727 also receive the frisbee fairings at some point? Remember that the 727 also had the S-duct.
29 AeroWeanie : The 727 never received Frisbee fairings. I proposed them to Valsan at one point...
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