In the engine wind tunnels, the test cell pressure does not coincide with the nozzle static pressure and the forces (thrust, lift and pitching moment) are influenced by change of the nozzle pressure ratio. In order to separate effects by the external flow from the force measurement, experiments were conducted by using M3.4 and M5.4 subscale wind tunnels. The three component force was measured by a force balance and the effects of the external flow were investigated by controlling of the nozzle pressure ratio. Measurements of the engine wall pressure enabled to itemize the force distribution delivered by the engine internal flow. The results showed that the external drag of engine occupied from 36% to 70% of the total drag. The nozzle pressure ratio varied the drag coefficient by more than 20% in the M3.4 wind tunnel and greatly influenced the lift and the pitching moment. The boundary layer ingestion promoted the engine unstart especially in higher Mach number testing. The inlet wall pressure was lowered and the pressure distribution was smeared by the ingestion of boundary layer. However, it was found that the engine drag was not affected by it under the operation condition far from the engine unstart.
