bafanguy
Well-known member
- Joined
- Apr 4, 2004
- Posts
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The only factual info I have re the original question comes from the Douglas DC9 manual, but the principle is probably close enough to the -80. I can't scan the whole page devoted to this so I'll put in the pertinent stuff the hard way:
"...The nose cowl is nonsymmetrical to keep drag to a minimum at high mach number cruising conditions.
The nonsymmetry is required to maintain an extremely flat nacelle line adjacent to the fuselage, such that nacelle supervelocity increments, when added to those from the pylon and fuselage, do not lead to supercritical velocities with resultant shockwave losses.
The nacelle axis and pylon have been set at 3 degrees angle of attack relative to the fuselage to align them with 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 emiminating the pitching effects due to thrust." [ Performance Section 5, 1-0-0, Code 30, Page 11]
Hope this is what you wanted. As I said, I'm guessing the MD80 is canted for much the same reasons.
As for the earlier reference to the DC9/MD80 being "centerline thrust". Many years ago, a Douglas production test pilot explained to me that Vmca is below the stall speed, and this the reason it's considered "centerline thrust". Don't know where one can see this in an official document...Part 25, maybe ?
The reason I asked the question originally was that when I got my initial ATP with a DC9 rating, the MEL rating they threw in with it was "...limited to centerline thrust." Useless. I called my contact in LGB and was given the above answer.
I think the 727 was the same thing, but don't know for sure as I added a 737 rating after the DC9 and that wiped out the centerline thrust thing.
"...The nose cowl is nonsymmetrical to keep drag to a minimum at high mach number cruising conditions.
The nonsymmetry is required to maintain an extremely flat nacelle line adjacent to the fuselage, such that nacelle supervelocity increments, when added to those from the pylon and fuselage, do not lead to supercritical velocities with resultant shockwave losses.
The nacelle axis and pylon have been set at 3 degrees angle of attack relative to the fuselage to align them with 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 emiminating the pitching effects due to thrust." [ Performance Section 5, 1-0-0, Code 30, Page 11]
Hope this is what you wanted. As I said, I'm guessing the MD80 is canted for much the same reasons.
As for the earlier reference to the DC9/MD80 being "centerline thrust". Many years ago, a Douglas production test pilot explained to me that Vmca is below the stall speed, and this the reason it's considered "centerline thrust". Don't know where one can see this in an official document...Part 25, maybe ?
The reason I asked the question originally was that when I got my initial ATP with a DC9 rating, the MEL rating they threw in with it was "...limited to centerline thrust." Useless. I called my contact in LGB and was given the above answer.
I think the 727 was the same thing, but don't know for sure as I added a 737 rating after the DC9 and that wiped out the centerline thrust thing.
