When rearranging the lift force equation to solve for lift coefficient instead of lift force, why is the numerator often given as F not 2F? the standard description of the Lift force affecting the lift surface is:

$$
F={\dfrac{1}{2}}\rho v^{2} SC_{L}
$$
the basic rearrangement gives the following definition of the lift coefficient:
$$
C_{L}={\dfrac{2F}{\rho v^{2}S}}
$$

why is the above expression met so rarely? with the standard skipping the 2 multiplier?
$$
C_{L}={\dfrac{F}{\rho v^{2}S}}
$$

I've checked 30 scientific papers, those measuring the lift\drag coefficients. 


28 papers have had F 
2 papers have had 2F
The definition of the coefficients differs between countries/regions. The factor ½ is used in most of Europe and in Russia, because it is part of the dynamic pressure equation. In the USA the 2 is incorporated in the coefficient.