I am simulating a UAV in simulink with datcom data as input, using light weight aircraft design tutorial in the documentation. I have trimmed and extracted linearized state space model for longitudinal mode. Below is the A matrix of state space form.
Theta U,w(1) U,w(2) q
Theta 0 0 0 1
U,w(1) -9.8 -0.05146 0.503 -0.9097
U,w(2) -0.4377 -0.5939 -6.696 18.57
q -0.2638 -0.03186 -4.762 0.4385
when i compare (q,q) element of above A matrix with theoretically calculated A matrix for longitudinal mode, the element (q,q) should be negative for a stable aircraft. But the simulink model shows the (q,q) element is positive. Is this due to difference in moment notation or is there any explanation for this