(v1.0.3+)
The fuel system of the SR-71 is highly complex. Here, I will try to explain the 'what' and the 'how' in general.
For complete understanding of the fuel system refer to the SR-71A-1 Manual.
Development note:
Although most of the components are now being simulated, there are still various differences between the simulated and the real SR-71 fuel system. The differences 'gap' will get smaller with each future update of this system!
The VSKYLABS SR-71-TB fuel system architecture in v1.0.3+ mimics the authentic SR-71A fuel system, including the general function of all related system-switches. Due to the complexity of the actual SR-71A fuel system, some of the internal-components have been simplified, while still demonstrating the general behavior of the real system.
1st example, manual transfer rates between the tanks are higher than the actual one, and the transfer 'resolution' conditional wide, is lower. In current version v1.0.3+ it serves an educational/experimental purpose during flight, allowing to 'play' with the modes of the system more efficiently.
2nd example is the nitrogen inertic tank pressurization which is not yet being calculated for the entire phases of flight (for example variable consumption which is dependent on the actual climbs and descends).
3rd example, the automatic transfer scheduling overrides some of the nuances in the system. There are more examples...
As the project evolves, more and more components and internal conditions (including the examples above) will be implemented.
Fuel System Main Components (main):
- There are 5 individual fuselage tanks (1A,1,2,4,5) and two wing-fuselage tank groups (3,6).
- Interconnecting plumbing and electrically-driven boost pumps are utilized for fuel feed, transfer and dumping.
- Other components of the fuel system include pump-control, nitrogen inerting, pressurization and venting, single-point refueling receptacles and a fuel-quantity indicating system.
Main effect of the fuel system on the center of gravity:
- Automatic tank sequencing to the engine feed manifolds to control the fuel level in the various tanks (simulated).
- Manual tank transfer (aft and forward, simulated).
- For the automatic cg scheduling to be effective, the directed fuel loading distribution must be followed (simulated - this happens in every flight initiation or reloading of the aircraft).
Fuel feeding fast-guide:
- The left engine is supplied from the left fuel manifold which is normally fed from tanks 1,2,3 and 4.
- The right engine is supplied from the right fuel manifold which is normally fed from tanks 1,4,5 and 6.
- Cross-feed can be used to feed either engine from any tank.
Fuel tank pressurization system:
- Includes nitrogen inerting gas to allow fuel tanks safe pressurization above Mach 2.6.
- In general, the real SR-71 aircraft consumes nitrogen for various 'tasks' throughout taxi, run-up and takeoff. It takes part in keeping positive pressure in the tanks during descends.
- In the VSL SR-71-TB the nitrogen plays part after full air-refueling session, where the tanks are draining all air in favor of nitrogen while filled up to maximum.
Fuel boost pumps switches and indicator lights:
- Six square plastic fuel boost-pump push-button switches are installed in a vertical line on the RH side of the panel (front cockpit).
- The switches control the manual operation of the fuel boost pumps.
- The switches have an electrical hold and bail mechanism that allows manual selection of only one tank of tang group 1,2,3 and one tank of tank group 4,5,6 at the same time.
- Manual operation supplements, but does not terminate the automatic fuel sequencing.
- Pump release switch - a push button 'PUMP REL' is located below the fuel boost pump switches.
Fuel quantity selector switch
- Installed on the pilot's RH instrument side panel.
- It has 7 positions: TOTAL and 6 individual tank positions.
GOLDEN TIPS FOR NORMAL OPERATION OF THE AIRCRAFT:
- The aircraft is being initiated with fuel load within the cg limitations.
- The automatic transfer scheduling system works in the background (like in the real aircraft) and will maintain the CG within the limitations throughout the flight, from takeoff, to fully loaded after the air-refueling sequence, to landing on minimum fuel. You will notice the CG indicator moves along within the scheduled operation.
- Under normal conditions, in version v1.0.3+ you can fly the aircraft without 'interfering' the system with manual operations and fur transfers.
- You are welcome to experiment with these, and see the resulted effect on the fuel-tanks, CG, aircraft performance (for example, CG in supersonic cruise has impact on fuel consumption due to changes in trim).
