Thrust and Drag

The air-intake used to induce air from the flight-altitude atmosphere plays an important role in determining the overall efficiency of ducted rockets. The air pressure built up by the shock wave determines the pressure in the ramburner. The temperature of the compressed air is also increased by the heating effect of the shock wave. The fuel-rich gaseous products formed in the gas generator burn with the pressurized and shock-wave heated air in the ramburner. The nozzle attached to the rear-end of the ramburner increases the flow velocity of the combustion products through an adiabatic expansion process. This adiabatic expansion process is equivalent to the expansion process of a rocket nozzle described in Section 1.2. 

Referring to Fig. 1.3, the momentum entering the air-intake is given by rhj and that exiting from the nozzle is given by (m -i- m v. The thmst created by the momentum change is fundamentally represented by Eq. (1.62). When the air-intake and the nozzle attached to the ducted rocket are designed to obtain maximum thrust efficiency, the pressures at the front end of the air-intake and at the aft end of the nozzle become Pa = Pi = Pr and then Eq. (1.62) is represented by 

When a projectile assisted by a ducted rocket flies at velocity V along a trajectory with an angle 0 with respect to the ground, the thrust F is represented by 

The parameters shown in Table 15.1 are used to determine the thrust and aerodynamic drag in a computational process as outlined in Table 15.2. 

---