[en] The determination of the top loss coefficient of a flat plate collector critically depends on convective heat losses due to wind (hsub(WC)). This paper critically analyzes the commonly used McAdams' relation for hsub(WC), which yields significantly higher values of hsub(WC), and does not take into account the nature of the air flow (laminar or turbulent) and the temperature dependence of physical properties of air. It is further discussed that in practical situations one should consider a transition from laminar to turbulent flow at a critical distance from the leading edge of the collector in order to calculate hsub(WC). A qualitative comparison of data is given using McAdams' relation and other relations governing purely laminar, purely turbulent or mixed flow conditions. The best fit equations for calculating the needed physical properties of air at different temperatures are also given. (author)