Originally Posted by
RetiredF4
Lets start with the 46.5°AOA of the THS (60° Aircraft AOA minus 13.5° NU trim) , which gives us a CL of 1.2 and a CD of 1.2. Lets do some ND input by trimming the THS to 0° and let´s see what it does to our numbers. We end up at 60° AOA at the THS, a CL of 1.0 and a CD of 1.6! Our upforce on the THS needed for lowering the nose has decreased and the drag has increased, our ND trim has caused the opposite of our desired outcome.
First of all: Thanks a lot for the interesting reference.
However there is one thing where I have to admit I disagree a little bit with your conclusion.
The drag along the flightpath would apply a Nose down moment on the Aircraft of (Rho/2 Cd A V^2 * sin (Alpha)* distance from center of rotation (sin Alpha ~0,87 @60°) while lift would act with the cosine, being 0,5 @60°.
Overall moment at 60° would be 0,5 * 1,0 + 0,87 *1,6 = 1,885 times the constant rest.
at 46;5° it would be 0,72 * 1,2 + 0,69 *1,2 = 1,698 times the rest.
Therefore the increase in drag would have more impact than the reduction in Lift in the given example.
The overall ND moment would increase in your given example.
As I already mentioned: at these AoA Drag acting on the tail is a good thing. It supports Nose down moment.