ORIGINAL: gkaraolides
Greetings all,
Apropos of the above, I've always wondered why in all designs I've seen, tailplanes use thinner sections than wings. Does anyone have an explanation for this?
My guess is that, since the airflow is already deflected by the wing, the effective angle of attack on the tailplane remains within a narrower range than that on the wing. So a thicker section would only add drag, and offer nothing in return. But this is only my own guess. I have never read about this or seen it discussed anywhere. I'd be glad to hear from anyone who knows for sure.
Best regards,
George
George,
not being an aerodynamicist, I'm going to venture some ideas.
At least in single engine nose mounted model airplanes, I think the concept is that the propwash airstream flowing over the stab is more turbulent than that flowing over the wing due to the increased distance of the tailplane compared to the wing. A thinner airfoil aids in keeping air speed up thereby retaining stab and elevator effectiveness.
Changing airspeed flowing over a wing causes the center of lift (CL) to move back and forth with respect to the CG of the airplane. I believe in general, as airspeed (i.e., increased power) is increased, the CL moves aft and vice versa. This CL movement over the wing causes the model to pitch up and down and is what necessitates the stabilizer which is aptly named and counteracts the pitching movement
I always found it interesting how Bridi went from rather thin airfoils on the Dirty Birdy (particularly on the stab) to much thicker airfoils on the UFO. I can only venture that these changes were made in an effort to obtain a model which had a lower critical stall speed and was able to be flown at a slower speed. Although I haven't flown either of them, I wouldn't be surprised if the DB needs to be flown faster than the UFO in order for the two airplanes to exhibit similar behavior.
My thinking (and I think some others too) was that Joe increased the stab airfoil thickness to cause it to stall
after the wing in slow speed pattern maneuvers. Presumably the model didn't need that high an airspeed over the stab in order for it to remain effective.
It seems that in full scale aircraft, stabilizer theory with respect to stalling conditions and recovery means is not quite fully understood. I find this amazing considering the airplanes that we have built and fly and the fact that it has been over 100 years since we first took to the airs. Stabilators which are often thought of as a more modern device compared to fixed stab with movable elevator (we see stabilators in modern jet aircraft) are actually older. The wright brothers initially used a canard stabilator in their experiments before finally changing that to the more conventional fixed stab/movable elevator.
I guess not much of this relates directly to dihedral though.
David.