Thrust
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DC-10 And L-1011 Tail Engine Designs And Mounts

Wed Jan 05, 2005 9:21 pm

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?
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AUAE
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Wed Jan 05, 2005 9:29 pm

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
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Starlionblue
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Wed Jan 05, 2005 10:53 pm

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.
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Aaron747
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Thu Jan 06, 2005 4:57 am

^
didn't boeing attempt to resolve those issues by installing vortex generators in the s-duct?
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A350
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Thu Jan 06, 2005 6:02 am

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
 
broke
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Thu Jan 06, 2005 6:32 am

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.
 
A350
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Thu Jan 06, 2005 6:36 am

@Broke: thanks a lot.

So, after all, the fate of the L-1011 had nothing to do with her technology?
 
gigneil
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Thu Jan 06, 2005 7:56 am

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
 
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Moose135
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Thu Jan 06, 2005 8:19 am

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.

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Thrust
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Thu Jan 06, 2005 9:41 am

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.
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Thrust
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Thu Jan 06, 2005 9:43 am

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

Thu Jan 06, 2005 9:44 am

Only the -500 had it as built, but didn't some earlier L1011s get retrofitted?
 
doug_or
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Thu Jan 06, 2005 10:07 am

yep

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Click here for bigger photo!

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.
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411A
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Thu Jan 06, 2005 12:18 pm

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.
 
DeskPilot
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Thu Jan 06, 2005 12:31 pm

"..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?
 
411A
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Thu Jan 06, 2005 4:25 pm

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.
 
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Fri Jan 07, 2005 12:14 am

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
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Fri Jan 07, 2005 3:36 am

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.
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2H4
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Fri Jan 07, 2005 7:52 am

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.


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mlsrar
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Fri Jan 07, 2005 10:59 am


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.
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Buzz
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Fri Jan 07, 2005 1:52 pm

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
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Fri Jan 07, 2005 3:07 pm

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


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aeroweanie
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Sat Jan 08, 2005 2:36 pm

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.
 
2H4
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Sat Jan 08, 2005 2:44 pm

AeroWeanie,

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


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aeroweanie
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Sat Jan 08, 2005 4:01 pm

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...
 
aeroweanie
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Wed Jan 12, 2005 4:53 am

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 727-200 has an additional row of 9 VGs.
 
Max Q
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Wed Jan 12, 2005 1:42 pm

Having the engines further out on the wing also allowed for a quieter cabin, quite noticable compared to the DC10.

The best contribution to safety is a competent Pilot.
 
A350
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Mon Jan 17, 2005 8:47 pm

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.

Does anybody know the reason? Thanks in advance

A350
 
Thrust
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RE: DC-10 And L-1011 Tail Engine Designs And Mounts

Sun Jan 23, 2005 4:40 am

Question: did the 727 also receive the frisbee fairings at some point? Remember that the 727 also had the S-duct.
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aeroweanie
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RE: DC-10 And L-1011 Tail Engine Designs And Mount

Sun Jan 23, 2005 6:09 am

The 727 never received Frisbee fairings. I proposed them to Valsan at one point...

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