MD-11 No.2 Engine

[Mr. Green]

Would anyone care to comment as to why the MD-11 / DC-10 No.2 Centre engine thrust line tends to be tilting up a few degrees?

Thanks for answering!

MG

[Danish Pilot]

Sure....

The number 2 engine is not tilted, but the intake is a bit higher located than the engine itself, which again means the long nacele goes down a bit.

The reason beeing that the closer the designer can bring the engine towards the center of the fuselage, the less pitch down moment is created along the pitch axis when the number 2 engine is produceing thrust. Thats why.

D.P.

[World of Tweed]

Just my 2p's worth here but I understood the larger intake on the No.2 and its positioning above the fuselage was:

a: To allow sufficient air to enter the intake (more powerful engine) but with out ingesting any B.L. (see below)

b: To negate the Boundary Layer on the upper fuselage mixing with the intake airflow.

The B.L. was a significant enough problem on the Tristar that they fitted a smoothing fairing between the fuselage and intake to No.2. Obviously the designs are quite different but a similar issue would have been at play on the MD-11.

[Mr. Green]

Thanks DP and WoT for your posts. I got the answers I needed :D

[Danish Pilot]

Hi W.O.T.

The B.L. problems have nothing to do with this design feature. The number 2 engine on respective DC10/MD11 is the same as number 1 and 3 and can be transfered to pylons number 1 and 3 if needed.

The B.L. problems you refeer to was more of a certification problem regarding x-wind/airflow. The S-duct feature on the Tristar was a bit more complicated from a designers point of view, but on the plus side, engine change/acces was a lot easyer than on the DC10/MD11.

The little tap you refeer to on the Tristar's number 2 intake was fitted on the -500 model series due to shorter fuselage. My gues is (and I am only guessing here:cool: ) that it was neede due to the intake beeing closer to disturbed airflow from wings, and if the aircraft needed to meet requirements in the whole flight envelope (stall, x-wind, highspeed buffet etc...) this little tap was needed.

:rolleyes:

[wileydog3]

Would anyone care to comment as to why the MD-11 / DC-10 No.2 Centre engine thrust line tends to be tilting up a few degrees?
Thanks for answering!
MG


Then too, the DC-10s with the PW engines looked different than the ones with the GEs.

[JW411]

But then the very few airlines that bought the PW-powered "dog" were not being very "wiley" even on "3".

The DC-10 with the Pratts was made available to those airlines who thought that it might be useful to have a common power plant with their 747 fleet.

Northwest Orient ordered them. They were originally designated as DC-10-20s by MDC but Northwest did not want to be behind those operators who had already ordered the GE-powered DC-10-30 and so it was that MDC were quite happy to re-designate the PW-dog as the DC-10-40 just to keep the customer happy.

Only NW and the Japanese bought the Dash 40 and it grossed out way below the Dash 30 and it also suffered from coked-up bleed valves just like its 747 equivalent.

You can always tell a Dash 40 by the fact that it has a "tulip bulge" on the intake to the centre engine.

The other piece of DC-10-40 folklore is that NW had the infinitely-variable flap setting system on the DC-10 removed and only had fixed flap gates.

For those of you who are not familiar with this particular piece of genius let me explain;

For every given runway and every possible meteorological condition there has to be just one exact optimum flap setting. Most aircraft just have some fixed flap settings available so all performance figures are a compromise.

Mr Douglas fitted the DC-10 with a generous amount of fixed flap settings but also had a large wheel (like an elevator trim wheel) which moved a hidden variable detent which was set on a vernier scale to the nearest 1/10th of a degree.

Such witchcraft was too much for NW so they had it removed! In later life they had to eat humble pie when they started to buy DC-10-30s.

They are now about the only major in the world (apart from Biman) still operating this wonderful aeroplane in the passenger role as far as I am aware.

[Danish Pilot]

Hi JW411

You are absolutely right, those old three holers are beautys. About 8 years ago I got close to flying the L1011, but history wanted it different... I still have the books, and I still have to spinn the head a bit if I have the luck to see the L1011 on our regular rutenet.:ugh:

D.P.

[Mr. Green]

Hey guys, does the MD-11 have fowler type or slplit type flaps? Please correct me if I am wrong.

[Loofty]

Hi there.

The MD-11 has 2 fowler-type flaps (inboard and outboard) and 8 slats on each Wing.

I hope this linkage to two of my pictures will work:

http://img72.imageshack.us/img72/6005/xxcl173xt.jpg

http://img63.imageshack.us/img63/3869/xxcl187hf.jpg

These flaps are extended to the max. landing position (50°).

Cheers,
Loofty.:ok:

[CV880]

Going back to the original query, I recall both the L1011 and DC10 No. 2 engines were definitely inclined about 4 degrees tail down. I recall being told it was (on the DC10) to equalise the pitching moments due to thrust changes between the underslung wing engines and the high mounted tail engine however this could have been folklore. It could equally have been to align the nacelles and exhaust flows with local airflows much like the wing engines are toed-in slightly on most or all widebodies so the pylons and nacelles are aligned with the slightly angled airflow in cruise caused by the bow wave off the nose.
L1011 No. 2 fairing
The "Frisbee" fairing (named after its designer) was a redesigned fairing for the splitter area under the lip of the No. 2 intake, principally to reduce drag, but it also reduced airflow noise in the rear cabin. It originally appeared on the L1011-500 but I think it was offered for retrofit to all

[CaptAirProx]

I agree CV880, I have operated on many L1011 series 1's; 50's; 100's and some had the retrofit fairing, some didn't. I noted that all the ex TWA ones had them fitted, so must have been a customer option.

[Basil]

On the L1011s I flew, the Frisbee fairing was fitted to the -200 & -500 but not the -1 (known as the 'minus one' due the less powerful -22B engine variant).
It's a while since I flew them but seem to recollect that the -500 had a two stage Go Around power application for #2 eng out GA. Due to the short moment arm stabiliser control of the pitch-up moment was marginal and one would shortly have the control column fully forward.
Lurvly big flight deck - beats the little B747 doghouse hands down :ok:
Oops! Thread creep :8

[Mr. Green]

Going back to the MD-11, another curiousity coming up is with the winglet. There is a bottom winglet on the MD-11 and can anyone explain the purpose of this second mini-winglet?

Cheers!

[night mission]

...........There is a bottom winglet on the MD-11 and can anyone explain the purpose of this second mini-winglet?
Cheers!

Don't have an answer, but do know the MEL allows it to be missing.

[Danish Pilot]

Hi CV880.

The Tristar #2 engine was tiltet, but I can't recall the Douglas birds had this. But what do I know....

Basil
Lurvly big flight deck - beats the little B747 doghouse hands down

Yep, thats why I just love them. Have e good one out there.

D.P.