Why are the engines angled up on the MD-80, 90?

[mirrodie]

I just spent that last few beers at LGA and have always wondered why the engines on the MD-80 and like aircraft angle upwards.


well, why is that? Any thoughts?

considering I gave the 411 on optics, maybe an engine guru can advise?

[Midnight Mike]

I just spent that last few beers at LGA and have always wondered why the engines on the MD-80 and like aircraft angle upwards.


well, why is that? Any thoughts?

considering I gave the 411 on optics, maybe an engine guru can advise?

How many beers did you have, the engines are perfectly straight!

Just kidding, I will ask some of the Douglas/Boeing people.....

[USAF Pilot 07]

Maybe something to do with weight distrubution, especially since the engines are at the rear of the airplane. For example, when descending, in order to have the engines "level" the nose of the a/c would be pushed down, giving the pilots a much better view and sense of what's going on around them, where they are etc... (especially for visual approaches).
Plus, on takeoff, with the engines pointed downward a little bit, perhaps it gives the planes a little better "push-off" or something....

[KLM777]

For the same reasons the A310 and A300 have their engines pointed inward!

[T-Bird76]

For the same reasons the A310 and A300 have their engines pointed inward!

And that is?????? Care to tell us?

[Alex T]

I have heard weight distribuation, also it provides a certain lift, as when the plane is taking off, it provides a high angle to lift easier. Also makes it harder for things to get into the engine such as dirt and gravel.

If you look at the 737-300 engine you will see a slight rise as well.

[Futterman]

For the same reasons the A310 and A300 have their engines pointed inward!

And that is?????? Care to tell us?

One of the books I have says that the engines are pointed, or 'toed' inward to balance the force of thrust on the airframe.

Personally, I'm not quite sure as to what this means...wouldn't the force of thrust be balanced regardless of the angle as long as it was the same angle? It seems reasonable to say that angling the input in towards the fuselage (and exhaust away) protects the airframe from unnecessary heat and force, whereas angling the input away and exhast in - or simply putting it straight - would be placing the thrust right on the hull.

Pretty interesting, I'd like to know more. Thoughts?

Brian

[mirrodie]

Maybe something to do with weight distribution, especially since the engines are at the rear of the airplane. ....

I used to think the same, but it that were indeed true, wouldnt the other similar aircraft, such as the ERJs, CRJs, DC-9, and other rear mounts also appear the same way?

And again, just ot reinterate, I am referring to the fact that when you view an MD-80 from the side, the fuselage is horizontal but the engines are slightly at an angle UPwards.

For the same reasons the A310 and A300 have their engines pointed inward!

Well, as Tommy noted, that was useless ;) Tommy, what he meant and what Brian refers to as Towing in, means that if you view the aircraft from directly above or below, the engines are pointed-in, toward the midline, and are NOT 100% parallel to hte fuselage. its very subtle.

And as many of you might know, this same concept refers to a TRUE wheel alignment. The two front wheels on your car, even when driving perfectly straight, are slightly "towed" in or angled in towards the cars' midline.

I am not 100% sure why but Ithnk it also has to do with forces on the wheel. But if you think of what toeing in does to a wheel, that is one reason why wheels needs to be rotated from time to time.

Flying Colors might be able to give the low down on toeing in, and might also give us hte best spelling!


As for the MD-80 engine pointing slightly up relative to the fuselage, toeing in, if I understand the concept, doesnt apply here. Maybe MIdnightMike can enlighten us??

[Midnight Mike]

I just spent that last few beers at LGA and have always wondered why the engines on the MD-80 and like aircraft angle upwards.

well, why is that? Any thoughts?

So the mechanics don't overfill the oil tanks! :lol: :shock:

[Derf]

Actually it is for the best airflow. Engineers design these aircraft for best fuel econmy in cruise and that will always be the reason the engines are on any angle. the DC-9 had the engine and wings so close that it did not matter much. I will ask an industry Jet engine expert in the am an post an answer that you can take to the bank.

[mirrodie]

thanks, let us know whn you hear from them.

as for the toe-in, here is a link the the auto example.

http://www.familycar.com/alignment.htm

jus a tad different from the upward angle I mentioned.

[Midnight Mike]

Mario


The inlets are slanted upwards in order to align the intakes with the airflow, as it is disturbed by the wings & fuselage, so, "airflow reasons"

[mirrodie]

Is that only on the md-8o series b/c of the distance of engine to wing?

in order words, if the same thing is on the dc-9, Tu-154, and other similar rear mounts, the effect is much less pronounced, isnt it?

[FlyingColors]

Well, for cars, especially more performance orientated ones, the front wheels are "toed in" a few extra degrees. That way, when the car is traveling fast the load on the front suspension will torque up and "un-toe it" a bit giving the car the best handling characteristics while at speeds, abate at slightly higher increase tire wear.

And yes, all cars should have the tires rotated as outlined in your owners manual, will greatly affect/increase tire life.

[mirrodie]

dude, thanks for explaining. I love the torque :)