Data reduction and correction checks for Walter H. Beech Wind Tunnel internal balance tests demonstrate an offset in observed pitching moment for model upright and inverted test runs. Root-cause analysis determines longitudinal variation in flow angularity is the primary cause, which is quantified via direct probe measurements. A horizontal tail effectiveness correction is developed to apply the flow angularity variation to a model's longitudinal lifting surfaces, with good resulting upright-to-inverted pitching moment correlation.