The airbus a380 has a cruise mach number m = 0.85 with a lift to drag ratio l/d = 20. for simplicity, assume it cruises at a constant altitude of 35, 000 feet with a constant total weight of 450 metric tons (of course, in practice both of them change. the plane is going to get lighter because of fuel burn and will be scheduled to fly at a higher altitude before descending to the destination airport). it uses 4 turbo-fan engines.

(a) what is the thrust needed from each of the 4 engines at the cruise?

(b) as a very rough estimate, assume the average exhaust velocity of the jet from the engine is 400 m/s. estimate the total mass flow rate of the propellant (air breathed-in by the engines plus a small amount fuel).

(c) calculate the flight time from la to beijing. if the overall efficiency of the engines is 35%, estimate the total fuel that the plane has to carry onboard.

(d) now assume we use rockets with the same jet velocity, calculate the total rocket propellant (fuel and oxidizer) one would have to carry with the airplane if we were to use rocket engines with the same jet velocity. (note the thrust equation for rockets is different from that for the air-breathing engine). compare the propulsion efficiencies of the two options.

(e) we can reduce the amount of needed propellant for the rocket option by increasing the rocket exhaust velocity to 2000 m/s/. redo the calculations for the total amount of propellant needed and the resultant propulsion efficiency.