The fluid state of the straight conical draft tube is simulated by using Fluent software. The distributing condition of the axial pressure and flow speed inside the straight conical draft tube is analysed and the recovery coefficient of the corresponding running condition is calculated, when the diffused angle is changing.

In this paper, the aerodynamic characteristics of the rocket model that might be used in a cabin air-launched system have been studied through experiments in low speed wind tunnel. The angle of incidence range is 0-80°, and the speed is 17m/s or 25m/s, including typical flight conditions prior to engine ignition. Forces and moments were measured through six-component balance. It is found that vortex asymmetry appears under certain condition with zero side slip. Asymmetrical phenomenon leads to larger side force and yaw moment, which can affect the trajectory of the rocket and put the carrier aircraft at risk. In addition, changes in regulation of the pitching moment with angle of attack are important to longitudinal stability, so the model with convergent-expanded afterbody was designed to improve stability. The effects of nose bluntness and forebody strakes on side force and yaw moment were presented, and the differences of aerodynamic characteristics with pointed and blunt nose, with and without forebody strakes were described. Results show that nose bluntness delays the appearance of asymmetric vortex, and the maximum side force is reduced by at least 50%. The forebody strakes reduce side force and yaw moment by weakening the asymmetric vortical interactions. The results can provide some references for designing the cabin air-launched rocket.