View Full Version : DC-9/MD-80 engine angle

26th Jul 2006, 09:03
Hello all, just a quick question. Does anyone know why the engines on the DC-9/MD-80 family are angled upwards (similar to the F-4 Phantom)?

Thanks in advance.

26th Jul 2006, 09:58
Could it be that due to high AOA during some flight phases, the wings deflect the airflow in a direction approximately the same as the engines are set at?
The goal is then to provide full supply of fresh air as perpendicular as possible to the inlet, therefore giving full breathing capabilities to the engines.

Anyone else with a bright explanation of the truth :8

26th Jul 2006, 13:51
From the Douglas DC9 manual:

"The nacelles have been designed to enclose the JT8D engine with a shape that will allow the highest installed performance ( thrust minus drag ) possible at all flight conditions. The nacelle nose cowling is nonsymmetrical to keep the drag to a minimum at the high mach number cruising conditions.

The nonsymmetry is required to maintain an extremely flat nacelle line adjacent to the fuselage, such that the nacelle supervelocity increments, when added to those from the pylon and fuselage, do not lead to super-critical 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 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."

26th Jul 2006, 15:00
Absolutely brilliant. Thanks bafanguy.

All the best.