# Longitudinal Stability Anlaysis Beginner Help

1. Jun 15, 2012

### meganlove19

I am currently working on a project where I am trying to find the A matrix for longitudinal stability analysis, ultimately to get my short period and phugoid modes to determine my level of handling (for any of you familiar with Etkin and Reid chapters 4-6 specifically). I think I've got the math worked out but I'm struggling with some of theory or algorithm to getting what I want.

I've modeled my aircraft in Digital Datcom (I will also probably start and AVL model to compare the two) and have a nice little table of values which I have attached. I also have formulas for getting the dimensional derivatives making up the A matrix that break down essentially to Lift-Curve Slope, C$_{D}$$_{0}$, C$_{L}$$_{0}$ (where the '0' signifies the reference condition) and a few other basic values I'm confident I can get. My question lies with the reference condition values.

My understanding is that the reference conditions are the deflections on the control surfaces to maintain steady level flight and the corresponding values for coefficient of lift and drag. First is this correct? Second how can I get this information from the data I have?

Thanks again!!

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