In the present paper we present results of calculations obtained with the use of the theoretical method describedin our preceding paper [Eur. Phys. J. D, DOI 10.1140/epjd/e2007-00328-9] and perform detail analysis of -helix random coil transition in alanine polypeptides of different length. We have calculated the potential energy surfaces of polypeptides with respect to their twisting degrees of freedom and construct a parameter-free partition function of the polypeptide using the suggested method [Eur. Phys. J. D, DOI 10.1140/epjd/e2007-00328-9]. From the build up partition function we derive various thermodynamical characteristics for alanine polypeptides of different length as a function of temperature. Thus, we analyze the temperature dependence of the heat capacity, latent heat and helicity for alanine polypeptides consisting of 21, 30, 40, 50 and 100 amino acids. Alternatively, we have obtained same thermodynamical characteristics from the use of molecular dynamics simulations and compared them with the results of the new statistical mechanics approach. The comparison proves the validity of the statistical mechanic approach and establishes its accuracy.