Airliner Wing Geometry, dihedral Options

[Saltman66]

Hi! My name is Steve. I am new to this site and am overflowing with technical questions. Recently, I have noticed that the 727 has no dihedral in its main wings nor the horizontal stab. All other Boeing airliners have some clearly visible dihedral in their wings. Does this have anything to do with the fact that its power plants are rear-mounted? What are the aerodynamic reasons the 727 does not not require it in order to produce adequate stability in the roll axis?If you've ever noticed, all of the DC-9 series planes (which are rear-engined) have no dihedral either, except the DC-10/ MD-11.

[27driver]

Hi! My name is Steve. I am new to this site and am overflowing with technical questions. Recently, I have noticed that the 727 has no dihedral in its main wings nor the horizontal stab. All other Boeing airliners have some clearly visible dihedral in their wings. Does this have anything to do with the fact that its power plants are rear-mounted? What are the aerodynamic reasons the 727 does not not require it in order to produce adequate stability in the roll axis?If you've ever noticed, all of the DC-9 series planes (which are rear-engined) have no dihedral either, except the DC-10/ MD-11.

Dude...we have enough roll coupling/Dutch Roll tendencies without adding increased dihedral to the mix. Most high-tail, rear-engine, swept-wing sleds are like that. The Yaw-Damper provides all the roll stability that is required, even at high speeds and altitudes. Even if the YD goes totally T/U, the aircraft can be controlled until the speed and altitude can be reduced.

And...uh...the DC-10/MD-11 are not DC-9 series aircraft...they are DC-10 series aircraft...hence the different series number.

[Piltdown Man]

And have you thought about this? Most of the larger Russian stuff has pronounced anhedral - the tail gives enough more than stablity.

PM

[Saltman66]

I never really thought about that but your right - they seem to have adopted an anhedral philosophy.