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Knowledge of the radiative heat transfer from flame to flame tube is an important factor when designing combustion chambers. When examining different design solutions information of wall temperatures and cooling air requirements are needed. This means in practice that the design engineer wants a method for predicting the heat flux to the combustor walls with reasonable accuracy, where the determining variables such as fuel quality, inlet air temperature and pressure, air-fuel ratio and combustor size are allowed to vary over a wide range. A number of methods have been suggested the volume within the flame tube is divided into fractions and the radiation exchange between the surrounding walls and each of the volume fractions is computed. These methods require knowledge of the axial and radial distribution of velocities, burning rate, temperature and absorption properties within the gas body. These distributions are unknown at the moment of designing and are difficult to determine even for an operating combustion chamber. Simplified procedures, more suitable for design work enable the gas volume within the flame tube to be regarded as a single zone. Flame temperature and emittance are evenly distributed in this zone. The surrounding combustor wall is isothermal. This procedure results in simple equations, where flame temperature and emittance need only be calibrated with a few measurements in the actual combustion chamber. This paper discusses the simplified method. There are no new analytical approaches introduced here. Equations for heat flux and emissivity are taken, with minor modifications. The advantage of this paper is the large number of tests carried out at different conditions. The test results permit a general use of the analysis for widely varying conditions.