Aircraft Fuel Supply System with Three Tanks
The fuel supply system represented in the example consists of three tanks and an engine. The tanks are connected by the fuel lines and the pressure drop in the fuel lines depends on the bank angle of the aircraft or the relative elevation of the ends of the fuel lines. The central tank bottom is elevated by 36 in with respect to the reference plane, which is drawn horizontally through the entry point of the engine. The side tank bottoms are elevated by 4.2 in each at zero bank angle.
The engine is fed from the central tank, while fuel from the left wing tank and the right wing tank is pumped to the central tank with respective pumping stations. Each pumping station consists of two centrifugal pumps, connected in parallel, with check valves installed in the pump outlets to prevent back flow. The pumps are driven by prime movers at angular velocity of 120 rev/s. The movers are simulated with the ideal torque source. The fuel lines with varying elevation are represented by the Pipe Variable Elevation (TL) block.
In the left wing, right wing, and central tanks, the controllers cut the outlet off if fluid volume in the tank becomes less than preset volume. In the central tank, the controllers also prevent the tank from overflowing. In all tanks, the cutoff is performed with the 2-way valves. The model can be simulated under different flight scenarios including different pump failure.
Tank System Center Subsystem
Tank System Left Wing Subsystem
Simulation Results from Scopes
The plots below show the amount of fuel remaining in the tanks. The rate of fuel consumption from each tank is affected by the pressure drop across the fuel lines due to the elevation change relative to the center tank. Since the pump flow rate controllers keep flow rates independent of the aircraft bank angle, the effects of elevation on the tank flow rate will be small.
Simulation Results from Simscape Logging
The plots below show the speed for all four pumps in the fuel supply system. For Flight Scenarios 2 and 3, pump speeds drop below the maximum speed to observe the effect on the fuel levels in the tanks.
The plot below shows the CG offset due to fuel distribution as a percentage of the half distance between left and right fuel tanks. The plots show the results for three tests where different combinations of pump failures are triggered.
The plots below show the characteristic curves of centrifugal pumps at reference condition in the fuel supply and engine systems.