How is d(Cl)/d(alpha)@stall and Cl increment to stall defined in Xrotor?

Question

I hope there are some people around here with some experience in Xrotor than me. (Xrotor is:"XROTOR is an interactive program for the design and analysis of ducted and free-tip propellers and windmills." Found: here documentation is at the end of the site) For the Blade Section Properties, I need following:

========================================================================
1) Zero-lift alpha (deg):   0.00       7) Minimum Cd           : 0.0070
2) d(Cl)/d(alpha)       :  6.280       8) Cl at minimum Cd     : 0.150
3) d(Cl)/d(alpha)@stall :  0.100       9) d(Cd)/d(Cl**2)       : 0.0040
4) Maximum Cl           :  2.00       10) Reference Re number  : 2000000.
5) Minimum Cl           : -1.50       11) Re scaling exponent  : -0.2000
6) Cl increment to stall:  0.200      12) Cm                   : -0.100
                                      13) Mcrit                :  0.620
========================================================================

Now does anyone know how 3) d(Cl)/d(alpha)@stall and 6) Cl increment to stall is defined?

If I had to guess 3) is just the slop after Maximum Cl. But 6) which is also mentioned in the doc as "delta CL for the stall transition region" gives me some headache.

Any help is appreciated.

Cheers

Answer 1

I interpreted the values as follows:

1. The angle of attack at which the specified propeller airfoil generates zero lift
2. The change in lift coefficient per change in $\alpha$ in radians
3. The same as 2, except that it is this value around the stall angle (it is mostly a safety factor for numerical calculations I think, small but non-zero)
4. Maximum $C_l$, which is achieved at the theoretical stall angle
5. Minimum $C_l$, which occurs on the backwards sweep of the propeller
6. The $C_l$ increment from the last linear part of the $C_l$ polar to the stall point
7. The $C_d$ at $\alpha=0$
8. The $C_l$ at $\alpha=0$
9. Quadratic drag dependence on $C_l$, slope of the $C_d,C_l^2$ curve
10. The Reynolds number at which these values are obtained
11. Re scaling exponent as explained in the XRotor documentation
12. Moment coefficient $C_m$
13. The critical Mach number.