  We continue the study of O-supergiants belonging to the association Cyg OB2
using moderate-resolution spectra. In this paper we present results of the
modeling of the stellar atmosphere of Cyg OB2 #11. This object belongs to the
spectral class Ofc, which was recently introduced and yet small in numbers. Ofc
class consists of stars with normal spectra with CIII
{\lambda}{\lambda}4647,4650,4652 emission lines of comparable intensity to
those of the Of-defining lines NIII {\lambda}{\lambda}4634,4640,4642. We
combined new spectral data obtained by the 1.5-m Russian-Turkish telescope with
spectra from MAST and CASU archives and determined physical parameters of the
wind and chemical composition of the stellar atmosphere using CMFGEN code. The
estimated nitrogen abundance is lower than one in atmospheres of normal
O-supergiants (i.e. O4-6 supergiants without additional spectral index "n" or
"c") and carbon abundance is solar. Also we find an excess in silicon. We
present an illustrative comparison of our modeling results with current Geneva
evolutionary models for rotating massive stars. The position on the
Hertzsprung-Russell diagram corresponds to the star mass of about 50M\sun and
age about 4.5 Myr. Moreover, we carried out the high angular resolution (about
0.02'') observations on the Russian 6-meter telescope aiming to find weaker
companions of this star, which did not reveal any.
