ORIGINAL: MTK
ORIGINAL: mithrandir
the CFD Simulations I have done so far seem to reveal it is predominantly a Stab height positioning phenomona....
The practical flying experiments we have done with vertical stab positions +/- 1.5'' from the thrust line (all else unchanged) revealed NO difference to pitch coupling on pattern planes (with applied top rudder). But a rudder area distribution change affected pitch (and roll) couple a noticable amount.
Years ago I remember talking wiith Don Lowe about some of his experiments with stab position. Turned out that the stab needed to be placed either right on the bottom of the fuse or on top of the fin to make a significant difference in pitch coupling. So, for those inclined to believe that vertical stab location change of 1/2'' in either direction will fix a particular flight attitude, you may be disappointed after all that work.
Any wing will generate ''downwash'' at its trailing edge. It doesn't matter whether the wing is completely flat like a foamy, flat bottomed or symmetrical. Also doesn't matter if the wing is flying upright or inverted, ''downwash'' of air is a must for lift generation. Ever wonder why a flat bottomed wing can fly inverted? Some fly inverted well, BTW. I am not too sure that wing downwash is even touching the stab on a long tailed pattern plane whose tail moment is 2.5*WingMAC or greater
The stab position thing is SACRED with some enthusiasts.
Do I buy it ?
nope not for a second
Having setup countless pattern /scale models big n little
I never worried about it simply because this issue was put to bed looooong ago - for me (and Lowe and many others ). As for down wash - well mostly hogwash on a lightly loaded model - you need for the wing to really work to produce much "downwash.