Static longitudinal stability - converting airspeed to lift coefficient
Hello,
as some of you probably remember from my previous threads, I am currently working on my thesis related to flight testing. While describing steps for creating stick-fixed static longitudinal stability characteristics, I have encountered one little issue which I do not understand. Maybe you will be able to help me..
According to Kimberlin's "Flight Testing of Fixed Wing Aircraft", first step is to plot elevator position vs calibrated airspeed for each flight at different CG position. Based on the points you create the curves. Until now all clear. After that there is another step in which you plot elevator position vs lift coefficient CL (which is supposed to be obtained from airspeed).
I know that CL can be calculated from the lift formula (L = (1/2) d v2 s CL). Lift itself must equal the airplane's weight.. but that is true only for straight and level flight. In case of climb or descent, to know the lift we must know the angle of attack. If that is true, I do not know why Kimberlin does not mention it while describing parameters which must be recorded during actual flight test. And apparently flights are conducted in climb, cruise and approach condition. Am I missing something?
Enclosed you can see a pdf containing two screenshots - first one show the first and second step (converting airspeed to CL), the other one describes flight test method.
Thank you!
P.