Originally Posted by
Alex Voicu
Hi Torben,
I don't think that changing the stab position affected the roll coupling, but it allowed me to use lower wing incidence.
I tried +0.7 deg. incidence on the wing before, but with the stab in the initial position the plane pulled to the canopy on the vertical uplines, so i had to use more wing incidence (+1.1 deg.) to counter this tendency.
Moving the stab lower eliminated the pull to canopy on the uplines, so i was able to follow Bryan's advice and reduce the wing incidence to +0.7 deg. I think it's the change in wing incidence that fixed the roll coupling, moving the stab probably had very little to do with it and only affected the vertical uplines.
I am confused.... having a high stab.. above the "Drag" center will result in pulling the nose up no? so how does increasing the wing incidence help?
I typically trim my 40% planes to be as close to neutral as possible.. and then just a little RCH fwd CG of that... and very little (non really) pull to canopy in vertical up or down...
think about this.. the stab is producing in level unaccelerated flight mere ounces of lift... and likely a tenth of that in drag.... (I assume the drag from the tail, above the aircraft center is creating a moment and that is what you think is causeing the pull to canopy?)... this can't be a dominant force...
Pattern planes are assymetrical... and that causes a lot of s'prising flow phenomonon... but it seems that moving the CG aft thusly reducing the decalage between the wing and tail would go a long way....(Or rather reducing the incidence and putting the CG where it will trim out)
**********On second thought, if you increase the incidence on the wing and retrim the elevator, now the thrust line with respect to the wing is negative.....
can you comment on downline pull/push compares between now and before?
IMHO, stab height effect on pitch is not a big driver.... If I can find some old CFD studies I did.. I will interrogate them for pitch effects in level flight vs tail location...
I was also able to measure yaw coupled pitch vs tail location in the CFD study
To Flyincajun... I don't understand how wing incidence affects Proverse/Adverse roll... I can see how dihedral or wing height/location on fuselage would affect this... but not
incidence...