Using ss2tf to obtain two transfer functions

I have the following system associated with the short period response of a plane to wind:

My task is to Write a Matlab program that uses the command ‘ss2tf’ to obtain the two transfer functions associated with the input w_g(t).

Here is what I have so far:

    clear, clc

    % Create first matrix A

    % Create second matrix B

    [s1, s2] = ss2tf(A,B,[],[],1)

This causes s1 to be an empty matrix, so I know it isn't quite this simple. I don't have a particularly good feel for transfer functions, and I'm not sure how to get them associated with B as an input. Any push in the right direction by someone with experience with 'ss2tf' would be really appreciated!

Chris

Answer 1

[Azzi Abdelmalek]

You need A,B and the two matrices C and D, and use

[a,b]=ss2tf(A,B,C,D,ni)

look at http://it.mathworks.com/help/matlab/ref/ss2tf.html

[Chris]

Thanks for the help. I guess my confusion is what A, B, C, and D should be for my case. The system I gave you is all the information I have.

Looking at the equation I believe it is a 4 input - 2 output system, but I only have the 2 matrices, so i have no idea what should be in the other two spots. It's possible this is more of a math question than a Matlab one, but I figured this might be a good place to start.

[Azzi Abdelmalek]

What are the outputs in your case?

[Chris]

(Not sure if you mean for the matrices or for my code so I'll give both)

The outputs of the system are A_dot and q_dot, the matrix on the left side.

My code as-is outputs s1 = Empty matrix: 0-by-3 s2 = 1.0000 0.6359 0.8240

[Azzi Abdelmalek]

The outputs are maybe alpha and q, in this case:

C=eye(2); 
D=zeros(2)

then use

[a1,b1]=ss2tf(A,B,C,D,1)
[a2,b2]=ss2tf(A,B,C,D,2)

[Chris]

Cool! Thanks a lot for the help.