ORIGINAL: rmh
ORIGINAL: mithrandir
I did some CFD simulations on a 2 meter Yak 55 and found a relationship between tucking and pulling verses tail height...
there was definitely a ''sweet spot''....
Honestly -I don't believe there is a relationship as such
In real life the craft does not have a variable tail height .
HOWEVER
The placement of the center of drag -vertically- does affect trim.
I have proven this using split rudder which was controlled by two servos
as the rudder opened -the model climbed
The center of the rudder was higher than the thrustline by a fair amount (std setup.)
Tho some tend to doubt it - -you can steer a craft by simply shifting drag at the tail left-right-up or down.
it is easily proven.-by actual demonstration.
It was evident from the CFD, that a high stab had a higher pressure on the lower surface, and a lower stab had a higher pressure on the top surface... it appeared that there is a sort of "Stagnation" line along the side of the fuselage that marks the location that seperates the flow that goes over the fuse from the air that goes under the fuse... if the stab is on that line, there is no yaw coupled pitching...
Curiously, I ran a case of
Zero Beta with 45 degrees of rudder... and regardless of the tail location, there was a nose up response... the coupling does not occur until there is some degree of sideslip...
I will see if I can find the simulation and post some pictures.....
As far as an offcenter drag... I remember back in 1993, with my Jekyl Pattern plane, lowering the gear had a definite pitching consequence...even with the long tail....