Anhedral Tail Planes
 

Just a quick one...

Why would you have an anhedral tail plane as can be seen on the Falcon 900 for example?

For stability reasons possibly?

Your thoughts please....

different reasons for different aircraft.


Concerning the F-4...

The original design was unstable at high Mach numbers and did not have acceptable low speed flying characteristics for carrier operations. McDonnell overcame the high Mach number problem by incorporating 23 degrees of anhedral for the horizontal tail and 12 degrees of dihedral in the outer wing panels, yielding greater stability at high mach numbers

Concerning the Harrier...

The anhedral angles of the wing and horizontal tail are intended to minimize the aircraft rolling moments due to sideslip. Even so, at certain combinations of low speed and high angle of attack, aerodynamic rolling moments greater than the combined aerodynamic and reaction control power may occur if the angle of sideslip is allowed to exceed a prescribed value. To assist the pilot in maintaining the angle of sideslip within acceptable limits, a small yaw vane that provides a visual indication of sideslip angle is mounted on the fuselage just ahead of the windshield.

Concerning the Mitsubishi T-2 jet trainer...

The tail assembly is conventional, featuring slab all-moving tailplanes with an anhedral of 15 degrees. The steep anhedral kept the tailplanes out of the engine exhaust while allowing them to remain effective through the wing wash.

Also it can be used to affect the loads on the fin for aircraft with fin-mounted or T- tails.

If the tail is level, then in sideslips you get a pronounced rolling moment imposed onto the fin by the tail, which has to be borne in addition to the direct fin sidesload due to sideslip. By finessing the tail dihedral/anhedral you can alleviate it a little.

While on the subject of anhedral, can anyone put me out of my misery regarding why all of the Russian rear engined airliners have a pronounced anhedral on the wings.
Their western clones(727,VC10 etc) certainly didnt have this feature.
The only reason I can come up with is that the fin is larger creating a tendency to overwhelm the rolling element of the flight controls, so anhedral instability was the quick fix??