1. Title of the invention

Passive fuel flow proportioner in aircraft fuel transfer system.

2. Field of invention

It is a mechanical engineering design used in aircraft fuel transfer system.

3. Use of invention

This invented passive fuel flow proportioner can be used in the aircraft fuel transfer system consisting of multiple tanks disposed at different locations at an appreciable distance from the aircraft center of gravity for continual fuel transfer in a pre-determined transfer ratio between the transferring tanks.

4. Prior art

Aircraft fuel system generally consists of multiple fuel tanks of different capacities disposed at various locations in the aircraft structure.

Figs. 1 and 2 show a typical arrangement of fuel tanks in an aircraft. Tank 1 is located in the front fuselage, Tanks 2 and 3 are in the wings. Tank 4 is in the center fuselage and is called the supply tank. Fuel transfer takes place from Tanks 1, 2 and 3 to Tank 4 with the aid of air pressurization. The withdrawal sequence is controlled by the float valve / transfer valve arrangement (based on the fuel content in the supply tank) installed in the supply tank.

Since a large quantity of fuel is stowed and transferred from the transferring tanks (Tanks 1, 2 and 3) to supply tank (Tank 4) and sequence of fuel transfer will have a profound impact on aircraft center of gravity, stability and controllability.

Fig. 3 is the plot of CG location versus the aircraft mass - the CG envelope. With the current fuel transfer sequence, the longitudinal CG travel is not within the maximum permissible limit of control band of Mean Aerodynamic Chord (MAC).

5. Draw backs of prior art

The following are the drawbacks:

• The longitudinal CG travel is beyond the limit specified by the control law and will impact on the aircraft performance. Refer Fig. 3

• Control logic for initiating the fuel transfer from the front fuselage tank (Tank 1) when the wing tanks (Tanks 2 and 3) are empty.

6. Comparison between prior art and present invention
A passive fuel flow proportioner is integrated in the fuel transfer system. This will ensure simultaneous fuel transfer from transferring tanks (Tanks 1, 2 and 3) to supply tank (Tank 4) in a pre determined transfer ratio derived based on the location and capacities of the tanks.

The continual and automatic fuel transfer in the predetermined ratio maintains the center of gravity of the aircraft within the control band as specified by the flight control law.

7. Aim of the invention

The aim of the invention is to design a simple and reliable device to maintain the continuous, automatic and simultaneous fuel transfer from transferring tanks to the supply tank in a pre determined ratio, thus ensuring aircraft center of gravity well within the prescribed limit of control band of MAC.

8. Summary of the present invention

A passive fuel flow proportioner is designed and integrated in the fuel transfer system which ensures simultaneous fuel transfer from the transferring tanks to the supply tank in the pre determined ratio, thus maintaining the aircraft center of gravity close to the aft CG limit, well within the prescribed limit of control band of MAC.

9. Brief description of drawings

Figs, land 2: arrangement of aircraft fuel tanks

Fig. 3: Center of gravity versus aircraft mass plot for the current fuel transfer configuration (without proportioner)

Fig. 4: Schematic representation of the fuel transfer system with proportioner integrated in the transfer circuit.

Fig. 5: Passive fuel flow proportioner manifold

10. Statement of invention

This invented passive fuel flow proportioner in the fuel transfer system ensures the continual, simultaneous fuel transfer from the transferring with the predetermined transfer ratio, thus maintaining the aircraft center of gravity well within the control band of MAC.

11. Detailed description of invention

Refer Figs. 1 and 2. Fuel system of an aircraft typically consists of multiple fuel tanks housed in wings and/or fuselage, known as integral tanks. The arrangement of fuel tanks is shown in Figs, land 2. Tank 1 is located in the front fuselage section, Tanks 2 and 3 are located in the wings. Tank 4 (supply tank) is in the center fuselage section which is the feeder tank. It can be noticed that fuel is stowed at an appreciable distance from the aircraft center of gravity and as a result the sequence of fuel transfer from the transferring tanks will impact the stability and controllability of the aircraft.

Tanks 1, 2 and 3 are transferring tanks. Fuel from Tanks 1, 2 and 3 are transferred to Tank 4 with the help of air pressurization. Fuel is supplied to the engine from the supply tank at the required flow and pressure with the help of a booster pump located in the supply tank.

The fuel transfer system is designed such that the fuel transfer rate from the transferring tanks is commensurate with the fuel burn rate.

Tanks 1, 2 and 3 are pressurized by the engine bleed air. Tank 4 is vented to the atmosphere. Fuel transfer from transferring tanks to the supply tank is affected by the pressure difference between the tanks.

The fuel transfer from the transferring tanks is controlled by the float valve/transfer valve arrangement in the supply tank. When fuel level in the supply tank is below the float level, the float valve/transfer valve combination initiates the fuel transfer. The fuel transfer stops when the fuel level in the supply tank is above the float level.

Since large quantity of fuel is transferred from Tanks 1, 2 and 3 to Tank 4 (the combined capacity of transferring tanks is approx. 2 times the capacity of the supply tank) and based on the location of the tanks, the transference of fuel from transferring tanks to supply tank and the fuel transfer ratio greatly affects the aircraft center of gravity during the flight.

The transfer system is characterized and optimized to meet the CG requirement with respect to the CG envelope control band defined by the flight control law .

This is achieved by simultaneous fuel transfer from all the transferring tanks (Tank 1, 2 and 3) in the pre determined transfer ratio derived based on location and capacities of the tanks. Refer Figs. 1 and 2.

Fig. 4 indicates the schematic representation of transfer system with a passive fuel flow proportioner integrated. Fig. 5 is the actual installation configuration of the proportioner.
Fig. 6 is the aircraft CG versus mass plot with the proportioner. It is evident form the plot that maximum CG travel due to the fuel transfer is brought well within the maximum permissible limit of the MAC.

Claims

A passive fuel flow proportioner integrated in the fuel transfer system of a supersonic combat aircraft with multiple fuel tanks of different capacities, disposed at different locations away from aircraft center of gravity, which ensures:

1. Continual and automatic fuel transfer from transferring tanks, the transfer rate commensurate with the fuel burn rate.

2. Fuel transfer is optimized and characterized to maintain the predetermined transfer ratio between wing tanks and front fuselage tanks, thus maintaining the aircraft center of gravity close to the aft limit, within the control band as defined by the aircraft flight control law and center of gravity envelope.

3. Simple design and highly reliable - no moving parts like valves, diaphragms, flow control devices etc.