Best method for determining control surface effectiveness

[Dave@JTEC]

We're trying to determine elevator, aileron, and rudder effectiveness for our aircraft (Arcturus T-16).

I'm posting a few questions asked by my aero engineer:

"I have been trying to determine the best method to find rudder effectiveness for our aircraft.    I found no instruction for doing this.
Rudder effectiveness is defined in the Piccolo User's Guide (v. 2.1.1d) as:

20    Rudder effectiveness    Change in sideslip per change in rudder position [rad/rad]...

For aileron and elevator effectiveness the control law tuning document says to run a doublet.  The dimensionless roll rate and Cl values reach a constant value for a given deflection, the differences can be measured for two deflections and  used to calculate the effectiveness.   

When I run a rudder doublet (in the software simulator)the sideslip value changes constantly and never settles to a single value.  How can we use this data to calculate the rudder effectiveness?

Am I correct in interpreting sideslip as yaw angle measured from initial flight direction?

Is the definition of rudder effectiveness correct in the documentation or should I be looking at Yaw rate rather than sideslip angle?
(This would be closer to the definition of aileron effectiveness)

On a related note, is there a recommended method to determine the Elevator Power, Rudder Power, and Sideslip effect? 
I found no suggested method in the documentation. 


Note:  I am not using the matlab tools, I have created a spreadsheet in excel with the same functionality."

Thanks for any help.

Dave

[Bill Vaglienti]

The rudder effectiveness is a steady condition.  You simply need to offset the rudder (using the trim) and observe the steady sideslip that results.  Note the simulator should do this for you when you run the FWG2 option from the menu.

-Bill

[astro]

Hi, I'm Dave's aero engineer.  Thanks for  your quick response.  I was able to determine the rudder effectiveness.

Is there a suggested method for determining Elevator Power, Rudder Power, and Sideslip effect?

[Bill Vaglienti]

The best method is to use the simulator, which has a function for measuring all these terms and outputting them to an xml file.

-Bill

[astro]

Yes, but we would like to validate the simulator values by performing flight tests.
We ran aileron and elevator doublets for the effectiveness terms, but we want to experimentally verify the other vehicle parameters.
Your response to my question about Rudder Effectiveness makes me to want to validate my test methodologies.

[Bill Vaglienti]

Not all of the variables are going to be observable from a flight test.  For example the autopilot does not have a sideslip estimate, and so rudder effectiveness is not going to be observable.  Aileron effectiveness is pretty easy by plotting dimensionless roll rate against aileron.  Elevator effectiveness is similar by plotting body lift coefficient against elevator deflection.  The powers (i.e. moment due to deflection) are much harder since you have to take the derivative of the rate gyros, which are noisy to start with.  The best thing I've been able to come up with is to curve fit the gyro versus time, and take the derivative from the curve fit, then compute the moment (knowing the inertia) from the acceleration, non-dimensionalize and plot against control deflection.

-Bill