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Why Are The Engines Tilted?  
User currently offlineUal747 From , joined Dec 1969, posts, RR:
Posted (14 years 5 months 3 weeks 5 days 18 hours ago) and read 1361 times:

Why are the engines on these planes tilted back with the front of them higher than the backs? (i.e. #2 on MD-11 and DC-10, #'s 1 and 3 on the 727, and #'s 1 and 2 on the MD-80 and #'s 1, 2, 3, and 4 on the 747) Notice on the 777 and 767 they are parallel with the fuselage.

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5 replies: All unread, jump to last
 
User currently offline747-600X From United States of America, joined Jan 2000, 2789 posts, RR: 15
Reply 1, posted (14 years 5 months 3 weeks 5 days 18 hours ago) and read 1257 times:

A while ago I made a post called 'Engine Angling' asking the same question. The only real answer I got was something along the lines of helping lift the back of the plane in a slightly upward direction. On 747s, it supposedly saves some fuel, I'm not sure how, but probably by helping with the lift as well as forward thrust.


"Mental health is reality at all cost." -- M. Scott Peck, 'The Road Less Traveled'
User currently offlineRonen From , joined Dec 1969, posts, RR:
Reply 2, posted (14 years 5 months 3 weeks 5 days 15 hours ago) and read 1240 times:

when the u.s tried the rescue mission from the american embassy at Teheran they developed a system for their c130 called "snowbird ".it was a group of VERTICAL rockets attached to the plane.the idea was that the c130 could get of a football stadium (120 meters !!!!!!!!!!!!!!!!!!!) .well u all know how it ended but in the test flights the front weel got of the ground after 5 meters and the rear after another 10.
so maybe the tilting of the engines does help to short the t/o run.


User currently offlineBoeing 777 From , joined Dec 1969, posts, RR:
Reply 3, posted (14 years 5 months 3 weeks 5 days 14 hours ago) and read 1230 times:

Ronen's reply makes a lot of sense. I remember seeing on a TV show about future aircraft development and research in which I saw some researchers flying a remote-controlled spy plane with a camera. It's small - not much bigger than 3 ft. in length. The spy a/c was actually built so that its single prop engine could be tilted up while the wings were level as the spy a/c took off! This was so it could take off from very small spaces - about as little as 1/4 to 1/3 the required t/o length of a standard a/c of the same size and power!

So, I think the engine tilt seen on rear-engined a/c like the MD-80 and the DC-10 may actually serve to allow the a/c to take off in hotter weather without using so much runway space! Hot weather does tend to decrease engine efficiency by a good deal. So does altitude. For example, an a/c in DEN(in the Mile High City) will need more power or runway space to take off than in LGA. The same is true for example in Phoenix in July, compared to SFO in July. (Phoenix is one of the hottest major US cities in the summer, while SFO is cooled by the California current during the summer)


User currently offlineBigGiraffe From United States of America, joined Jan 2000, 257 posts, RR: 0
Reply 4, posted (14 years 5 months 3 weeks 5 days 5 hours ago) and read 1199 times:

The engine tilt has to do with airflow at cruise. Air does not flow straight past an airplane; the air near the front of the aircraft would look like a bow wave from a ship except in all directions. If you look at the L-1011 from above you would see that the engines are angled just a little toward the fuselage because of the "bow wave". And the wings stick out and act on air (gaining lift) and so airflow behind them isn't parallel to the ground, either. Engines are positioned for optimum airflow.

User currently offlineUal747 From , joined Dec 1969, posts, RR:
Reply 5, posted (14 years 5 months 3 weeks 5 days 4 hours ago) and read 1196 times:

I agree with Giraffe. I suspected as well that it was only due to airflow. The tilting of the rear engines doesn't make sense if you apply it to making the take off distance shorter and helping the aircraft lift. My reason for saying this is because if the #2 engines like those on the MD-11 and DC-10 were tilted up, then the downward pushing force behind the engine would actually try and push the rear end of the plane higher than the front end thus causing the plane to go nose down. Thanks for all of your replies.

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