  CONTEXT. Because of the presence of rotation and accretion disks, classical T
Tauri stars have symmetry planes that are normally inclined relative to the
plane of the sky. The inclination angles affect the observed spectral
properties of these objects. AIMS. We study the influence of the inclination
angles on classical T Tauri star spectra in an empirical manner. METHODS.
Published inclination angles, derived from the stellar photospheric rotation or
from spatially resolved circumstellar disk observations, are compared with
various observed spectral properties, and correlations are established and
investigated. RESULTS. Inclinations derived from the stellar rotation are found
to be much less accurate than the published disk inclinations, and no
significant correlations between spectral properties and inclinations based on
rotation data could be detected. In contrast, significant correlations are
found between the disk inclination angles and the apparent velocities observed
for the forbidden emission lines and the wind absorption features of permitted
lines. These data support the assumption of cone-like polar winds with opening
angles smaller than $\approx 45^\circ$. Other spectral features show weaker or
no inclination dependence. Using these results, the true (deprojected) flow
velocities of the polar winds are derived for the investigated sample of T
Tauri stars. Deprojected wind-ejection velocities appear to differ by a factor
of two among the stars in our sample, which spans a range of mass-loss rates
from $10^{-10} $M$_\odot$/yr to $3 \times 10^{-7} $M$_\odot$/yr.
