Middle Engine on DC10/MD11

[WindSheer]

Could somebody kindly explain why the engine has a slight upward angle??
I would guess this would give a slight nose down force, the more power that is applied?

Cheers.:ok:

[MD80rookie]

From what I've been learned, the position of the engines (above or below wings) is what causes a pitch up or a pitch down tendency when thrust is applied. Something with stability?

The MD80 has a nose up tendency, engines mounted over the wings. DC10/MD11 has wing mounted engines which would cause a nose down tendency with thrust.

I stand to be corrected :O

[rigpiggy]

look at lake amphibian accidents, as far as thrustlines are concerned nuff said.
Actually has to do with the flow coming off the wing, and angle of attack in cruise. look at the engines on a 727, lear or just about any other tail mounted engine.

[bfisk]

MD80: to clarify; what is the main point is if the thrust lies above or below, and in front of or behind, the centre of gravity. You know that objects tend to rotate around their centre of gravity. A line of thrust directed through (or equally around, for aircraft, probably) will not tend to influence pitch, while a thrust line below (say for underslung engines) will tend to make the aircraft pitch up when power is applied. Conversely an engine mounted above and behind the CG, directed straight backwards, will tend to pitch the aircraft nose down, with increasing power.

This is of course not taking aerodynamics into effect, such as an increased airflow over the horizontal stabilizer or trim speed stability.

[orion1210]

Thats how I understand it bfisk.

So on the dc10/md11 the center engine mounting angle will increase its nose down inducing tendency.

This might be to increase pitch stability at high power settings, a kind of dihedral between the wing engines and tail engine. Either way I wonder if there are any significant changes in pitch trim or response in different engine out scernarios?

[Halfbaked_Boy]

It's to do with wing upwash/downwash.

If you think about it, the engine wants a good parallel flow of air into the intake - generally the air in the proximity of the tail will have a small downward vertical component due to the downwash as it leaves the wing. This explains the 'upward' part of your question.

As for the 'slight' upward part, well, the engine is mounted some distance above the wings vertically, so although the air in this region will be affected, it will only be, as you put it, 'slight'.

I also understand the other posters to be correct too, regarding a pitching moment, but I know nothing more about this.

:)

[rudderrudderrat]

Hi orion1210,

I wonder if there are any significant changes in pitch trim or response in different engine out scernarios?

Oh yes!

I never flew the DC10 - but the L1011 has a similar thrust line on the tail engine (above the c of g). When flying with No 2 engine shut down on the -500 variant (shorter fuselage and hence smaller tail moment), the GA EPR on 1 & 3 had to be limited to a pre-calculated value - else the crew could end up with a high pitch attitude & falling airspeed with full forward control column - when full GA power was set.

[WindSheer]

Oh yes!

I never flew the DC10 - but the L1011 has a similar thrust line on the tail engine (above the c of g). When flying with No 2 engine shut down on the -500 variant (shorter fuselage and hence smaller tail moment), the GA EPR on 1 & 3 had to be limited to a pre-calculated value - else the crew could end up with a high pitch attitude & falling airspeed with full forward control column - when full GA power was set.

Think that answers it, well and truly!!