RussianJet
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TU-154 Engine Intake Shape

Mon Jan 07, 2008 9:49 pm

Couldn't find anything on this, sorry if it's been up before.

On the TU-154, why is the middle engine intake a sort of oval shape, taller than that on the other engines, whereas the outer two engines are round as normal? I haven't seen the same thing on other tri-jets such as the 727. What is the reason for this?
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KELPkid
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RE: TU-154 Engine Intake Shape

Mon Jan 07, 2008 9:55 pm

The Boeing 727 had occasional problems with the center (#2) engine surging, and, IIRC, a captain or first officer who rotated the plane a little too overzealously (which disrupted the clean airflow into the #2 engine's S-duct) could cause this problem. I'm wondering if Tupolev encountered the same problem during testing, and provided this as their solution?
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2H4
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RE: TU-154 Engine Intake Shape

Mon Jan 07, 2008 10:34 pm



Quoting KELPkid (Reply 1):
The Boeing 727 had occasional problems with the center (#2) engine surging

I wonder if the switch from the -100s oval duct to the -200s circular duct had anything to do with this:

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-100 duct on left, -200 duct on right


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RussianJet
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RE: TU-154 Engine Intake Shape

Mon Jan 07, 2008 11:04 pm



Quoting 2H4 (Reply 2):
I wonder if the switch from the -100s oval duct to the -200s circular duct had anything to do with this:

I never even noticed that shape on the 727-200, probably because the engine intakes are smaller overall than on the TU-154 it seems less pronounced.
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prebennorholm
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RE: TU-154 Engine Intake Shape

Tue Jan 08, 2008 12:08 am



Quoting 2H4 (Reply 2):
I wonder if the switch from the -100s oval duct to the -200s circular duct had anything to do with this

Sure that change has something to do with the surge tendency at high pitch angle.

Anyway, I would assume that the most important change is that the bottom of the -200 intake is lifted quite a few inches higher above the fuselage - more out of the turbulent boundary layer.

Since the intake was changed from oval to circular, then there are probably much more important changes in the internal shape of the S-duct. To produce an efficient S-duct and make it work well at high subsonic speed is a very difficult task. It is far from just a bent tube. That's the reason why Douglas "gave up" on that and accepted the weight penalty of placing their #2 engine high on the DC-10.

Never mind how well an S-duct is designed, it will always mean a slight efficiency penalty compared to a straight intake. So maybe Douglas was right assuming that the weight penalty of the extra structure for the high engine was minor compared to the S-duct engine efficiency penalty.

Anyway there were people 35 years ago who insisted that Douglas with the high engine made a shortcut in order not to be too late on the market compared to the head on competitor Lockheed L-1011 Tristar. Saving the time and engineering resources to design and test a good S-duct. Time would show that it was hardly needed since the Tristar suffered massive EIS delays caused by the RB-211 engine development troubles and the RR bankruptcy.
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KELPkid
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RE: TU-154 Engine Intake Shape

Tue Jan 08, 2008 6:29 am



Quoting 2H4 (Reply 2):
2H4

2H4, you never cease to amaze me! I never knew that the -100 series 727's had an ovuloid-shaped S-duct intake for #2...
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RussianJet
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RE: TU-154 Engine Intake Shape

Tue Jan 08, 2008 10:21 am

http://www.airliners.net/open.file/1314642/L/

No ovular intake on the L1011 - is the fact that the intake is wider enough to counteract the airflow issues described with the 727-100?
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Jetlagged
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RE: TU-154 Engine Intake Shape

Tue Jan 08, 2008 4:55 pm



Quoting KELPkid (Reply 5):
2H4, you never cease to amaze me! I never knew that the -100 series 727's had an ovuloid-shaped S-duct intake for #2...



Quoting RussianJet (Reply 6):
No ovular intake on the L1011

At the risk of being pedantic, ovuloid is not a word and ovular is something to do with ovules (small eggs or seeds). The word you are both striving for is oval, or if you want something more technical sounding, elliptical or ellipsoidal.
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RussianJet
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RE: TU-154 Engine Intake Shape

Tue Jan 08, 2008 9:35 pm



Quoting Jetlagged (Reply 7):
At the risk of being pedantic, ovuloid is not a word and ovular is something to do with ovules (small eggs or seeds). The word you are both striving for is oval, or if you want something more technical sounding, elliptical or ellipsoidal.

No problem. You are, of course, perfectly correct, and it's the kind of thing I myself would point out!  Smile
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N231YE
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RE: TU-154 Engine Intake Shape

Wed Jan 09, 2008 11:28 am

Just to clarify, Boeing did fix the problem on the 727-100 somewhat, by placing vortex generators along the duct of the #2 engine.

As for the original question, I am not sure about the TU-154.

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