Originally Posted by
mithrandir
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...
I've never seen wing incidence affect roll couple. Dihedral, yes, a second smaller wing surface with anhedral or dihedral, yes; For these 2M models, building the top wing surface flat and placing the wing's CL at 12mm below the thrust line, will produce ZERO roll couple. Proven over several designs with differing wing planforms / areas /sweeps, and different thicknesses.
Plus wing inc also means minus engine thrust, exactly right. Down thrust on engine will typically cure uplines pulling to canopy with practically no effect on downlines. The thrust vector is always THE dominant vector on uplines
I've observed also on one of my models so equipped, that small cannards just behind the prop will practically eliminate the effect of SAFS ( spiral air flow stream, it isn't a slip stream per se'). For a typical 20" prop, 1100 square inch wing, 2% of the wing area is all it took (20 squares or 10 on each side) POOR MAN'S CONTRA.... I should complete this experiment but my health may give out before I complete it so I am giving it out here for anyone else to follow up.
If anyone does this and it works for you as I say, pay me poor royalty of 5% or make a donation to our World team in my name c/o NSRCA (TIC)