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Why MD-80's Engines Are Facing Upwards?  
User currently offlineJgore From Argentina, joined Feb 2002, 550 posts, RR: 2
Posted (12 years 2 months 6 days 23 hours ago) and read 7770 times:


Could anyone explain the reason MD-80's engines are facing a bit upwards ?
Is that related to its design and/or dynamics ?

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Thanks in advance

Jgore  Smile

6 replies: All unread, jump to last
User currently offlineQantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 22
Reply 1, posted (12 years 2 months 6 days 22 hours ago) and read 7739 times:

This should answer your question. As explained there, MD-80 engines are angled in such a way to align them better with "clean" airstream -- in short, for airflow reasons.


User currently offlineDeltaGuy From , joined Dec 1969, posts, RR:
Reply 2, posted (12 years 2 months 6 days 20 hours ago) and read 7587 times:

So I also hear, it's a good thing to help prevent FOD (foreign object damage)...not sure where it came from, so don't quote me  Big grin But the aero charactersitics are more important there...


User currently offlineQantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 22
Reply 3, posted (12 years 2 months 6 days 19 hours ago) and read 7490 times:

I'm sure the "engine tilt" helps to reduce FOD to a very -- I repeat, very --limited extent, but, as you said, airflow orientation is the major consideration involved.


User currently offlineCFIcraigAPA From United States of America, joined Jan 2004, 223 posts, RR: 4
Reply 4, posted (12 years 2 months 6 days 15 hours ago) and read 7419 times:

This should help too. It's not just for airflow reasons, look for my reply about four or five down.

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User currently offlineVikkyvik From United States of America, joined Jul 2003, 12142 posts, RR: 24
Reply 5, posted (12 years 2 months 6 days 14 hours ago) and read 7390 times:

The inlets are slanted upwards in order to alighn the intakes with the local airflow, as it has been disturbed by the wings and fuselage.

In the reply in the linked thread, you stated that the horiz. stab. gives a nose-down moment, which is not correct. The H-stab gives a nose-up moment; it's an inverted airfoil, meaning it's generating lift downwards, which would obviously cause the tail end to lower and the nose to raise.
Also, adding power will cause a nose-up moment as well. The whole reason the H-stab is in existence is because the center of lift is ahead of the CG, therefore, causing a nose-up moment. Adding power will increase the aircraft speed, therefore increasing the lift. As far as as I know, this will counteract the very slight nose-down moment created by the engines increasing their thrust.
Someone correct me if I'm wrong.

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User currently offlineDarkblue From United States of America, joined Sep 2003, 233 posts, RR: 9
Reply 6, posted (12 years 2 months 6 days 10 hours ago) and read 7354 times:

This topic has been discussed before, you may want to do a search.

Note that it is the inlets of the engines that are facing up, not the actual engine. Aft-mounted engines are in the downwash of the wing so the inlets usually face upward to be aligned with the flow. Wing mounted engines are in the upwash of the wing and the inlets usually face downward to be aligned with the flow.


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