Rotaryphile

I built many U/C models with wing and stab in line, and only had problems with pitch stability in a couple of them, and in one R/C pattern model. I think the problem arises when the alignment just happens to be perfect, so the stagnation zone behind the wing hits the stab directly on its leading edge stagnation point, and may thus tend to be develop an unstable attachment to the stab, where random gust effects may attach the flow to either the underside or topside of the stab in a rather indeterminate manner, resulting in peculiar pitch excursions. I think the evidence for this is that a change of wing incidence as small as 1/2 degree corrected the problem completely for me. The fact that no full-scale Edge has reported any problem may be due to renolds number effects. In general, full scale designers tend to avoid having wind and stab directly in line, and I think the fact that such alignments usually work is due to small building errors that inadvertedly place the stab just a little above or below the wing chord line.