Abstract:To investigate the different engine internal flux effect on spin characteristics for some civil aircraft with high bypass engine, several light weight block which can control the engine internal flux was mounted inside of nacelle of an aircraft freespin model. Based on the spin tunnel test results, these blocks have got less effect on angle of attack, yawing speed and recovery characteristics, but these blocks have got significant effect on rolling speed and sideslip angle, when engine internal flux decreases, blockage effect is increased, the oscillation of recorded data of rolling speed and sideslip angle is dramatically increased. Moreover, asymmetry of left and right engine internal flux has got obviously effect on aircraft model spin characteristics.