Question for those who know about MD's

[.LSinLV.]

of all the AC I see on a daily basis, only one has the engines tilted down, the MD series. If anyone knows as to why, I'd like to know as this is a curious design. I'll have to check on the 95's and the 717's as I don't think these AC with the larger BR700 engines have this like the older AC with the JTD's.

in fact, if the AC is horizontal in flight, the nacel's AOA seems like it might mitigate smooth flow into the engine, let alone vectored thrust out the back (which is down).

anyway....just curious.

TIA

[joness0154]

of all the AC I see on a daily basis, only one has the engines tilted down, the MD series. If anyone knows as to why, I'd like to know as this is a curious design. I'll have to check on the 95's and the 717's as I don't think these AC with the larger BR700 engines have this like the older AC with the JTD's.

in fact, if the AC is horizontal in flight, the nacel's AOA seems like it might mitigate smooth flow into the engine, let alone vectored thrust out the back (which is down).

anyway....just curious.

TIA

I'm no engineer, but it would seem to me that it might have something to do with the way the air flows over the tops of the wings in a curved fashion (assuming you're just talking about aircraft with tail mounted engines).

[.LSinLV.]

maybe...but look at these images to better see what I am talking about:

MD-80 Series


MD-90 Series


Boeing 717


Here is the Boeing 727 Series, note the engines and their AOA, no noticable angle difference from fusalage.


Llyshin II-62

[Jettavr666]

I'm no engineer, but it would seem to me that it might have something to do with the way the air flows over the tops of the wings in a curved fashion (assuming you're just talking about aircraft with tail mounted engines).

this or better takeoff performance?

[B3sat16v]

It is PBFM! Most likely due to airflow, CG (Vectoring the thrust slightly downward keeping the nose down with low loads up front), to get the best answer you would have to ask an Engineer that designed these aircrafts. Any of our answers are going to be pure speculation.

And the IL-62 has a downward tilt as well as the VC-10, and so does the 727. Your picture does not show it too well.



And as we know the 727 has a nose low attitude with WOW.

[Gern_Blanston]

Here's what the original DC-9 manual says:
"The nacelle axis and pylon have been set at 3 degrees angle of attack relative to the fuselage to align them with the local flow conditions prevalent at cruising conditions. This is necessary to eliminate the interference and high induced drag that they would otherwise be subjected to. The nozzle is then canted upward relative to the engine axis, thus eliminating the pitching effects due to thrust.
The air coming of the back of the wing is headed down just a bit after following the camber of the top surface.

[Zombiee313]

A-10's are like that also

[B3sat16v]

Here's what the original DC-9 manual says:
"The nacelle axis and pylon have been set at 3 degrees angle of attack relative to the fuselage to align them with the local flow conditions prevalent at cruising conditions. This is necessary to eliminate the interference and high induced drag that they would otherwise be subjected to. The nozzle is then canted upward relative to the engine axis, thus eliminating the pitching effects due to thrust.
The air coming of the back of the wing is headed down just a bit after following the camber of the top surface.

After reading that, I went and looked and some pics and damn the nozzle is canted quite a bit upwards in the DC/MD aircrafts, but the above one from the 727 it is not canted at much upwards.

[dubraycer36]

After reading that, I went and looked and some pics and damn the nozzle is canted quite a bit upwards in the DC/MD aircrafts, but the above one from the 727 it is not canted at much upwards.

The quiet kits that are installed make it look like they are at a less severe angle than 3 degrees.
Plus the angle of the picture makes it seem weird too.
But the pitch of the engine in relation to the rest of the fuse can be noticed.

[B3sat16v]

The quiet kits that are installed make it look like they are at a less severe angle than 3 degrees.
Plus the angle of the picture makes it seem weird too.
But the pitch of the engine in relation to the rest of the fuse can be noticed.

We are talking about the Nozzles right? Because the engines are tilted, and what Gern posted talks about the Nozzle being canted upward to maintain the thrust at linear as possible to avoid a moment causing a nose down attitude.

Let me maker sure I explain. The Inlet (Diffuser) is canted upwards to take advantage of a more straight flow due to the downward flow coming from the top of the wing. The nozzle is also canted upwards to cancel any angle with relation to the longitudinal axis of the aircraft, thus providing a thrust vector that wont cause any moments. This can be seen very well on the DC/MD pictures, but I know for a fact that the IL-62 does not do this (Also seen in photos), as well as the VC-10 and if you look at the 727, the upward canted nozzles still have to angled thrust (Downward).

[.LSinLV.]

thanks guys! I appreciate all of the help/input.

[gr8shandini]

Here's what the original DC-9 manual says:
"The nacelle axis and pylon have been set at 3 degrees angle of attack relative to the fuselage to align them with the local flow conditions prevalent at cruising conditions. This is necessary to eliminate the interference and high induced drag that they would otherwise be subjected to. The nozzle is then canted upward relative to the engine axis, thus eliminating the pitching effects due to thrust.
The air coming of the back of the wing is headed down just a bit after following the camber of the top surface.

This image is somewhat exaggerated, but gives a good idea of the effect they're talking about:

[ATL_Av8r]

Come on Larry, you've been in the MKIV forum. it's all about the reverse rake

[.LSinLV.]

Come on Larry, you've been in the MKIV forum. it's all about the reverse rake

so is that why 757's have such a sharply angled cockpit/front of the fusealge??