Question about fuel system.

[Esac_mirmidon]

I´m reading the freaking awesome BS manual in deep and have a question about fuel system.

 

If i have both internal and external fuel tanks and i want to burn first my external tanks, and only when they gets empty, burn the internal fuel tanks what i need to do?

 

Open internal fuel valves and pumps to start the engines and when they are started, open the external fuel pumps and close the internal fuel pumps and valves?

 

How can i know that my external fuel tanks are empty? The audible sound warning about " below 110 kg " are also operative about external fuel quantity?

 

Thanks in advance

[AlphaOneSix]

If i have both internal and external fuel tanks and i want to burn first my external tanks, and only when they gets empty, burn the internal fuel tanks what i need to do?

 

Open internal fuel valves and pumps to start the engines and when they are started, open the external fuel pumps and close the internal fuel pumps and valves?

 

I apologize in advance for giving you more information than you're asking for. ;)

 

There are lots of fuel pumps n the aircraft. Each engine has an engine-driven pump that "sucks" fuel from the fuel tanks. As long as the engines are working, these pumps are working. There is also a fuel boost pump in each fuel tank, rear and forward. Finally, each external tank has it's own fuel pump (turned on in pairs, you can't have one on and not the other in a pair of tanks). The rear and forward fuel tanks deliver fuel directly to the engines, but the external tanks do not. The external tanks feed fuel to the rear and forward tanks. Specifically, external tanks on the left feed into the rear tank, and external tanks on the right feed into the forward tank.

 

To answer your question directly... When using external fuel tanks, you operate as you normally would, but you should also turn on the pumps for the external tanks (meaning, you should ALWAYS have the internal boost pumps on). As your internal tanks lose fuel feeding the engines, they will be continually refilled from the external tanks.

 

How can i know that my external fuel tanks are empty? The audible sound warning about " below 110 kg " are also operative about external fuel quantity?

 

If you start out with full internal fuel, then as long as you have the external tank pumps on, you will not see the fuel gauge move. The external tanks do not have any way of telling you how much fuel they contain. This is where it becomes important to plan ahead with regards to your fuel burn rate so you know when to expect them to be empty. If the external pumps are on, and the tanks become empty, your only indication will be that your fuel gauge for the rear and forward tanks will begin moving, as they are no longer being refilled by the external tanks.

[Esac_mirmidon]

Thanks my master......XD

 

This answer my question in all aspects. Like always reading you is a pleasure.

 

Thanks also for giving me more info than initially asked, very interesting and useful.

 

Another thing, the manual saids that when the engines are running you dont need the internal fuel pumps active, but recomends to do so. This means that if you turn off the internal fuel pumps ( because engines are running ) you cant pump fuel from the external tanks into the internal ones ?

Edited December 6, 2008 by Esac_mirmidon

[AlphaOneSix]

Another thing, the manual saids that when the engines are running you dont need the internal fuel pumps active, but recomends to do so. This means that if you turn off the internal fuel pumps ( because engines are running ) you cant pump fuel from the external tanks into the internal ones ?

 

The fuel pumps that are internal to the forward and rear internal fuel tanks just push fuel from the internal tanks to the engines (and APU). Each external tank will have its own individual pump that pushes fuel from the external tank to one of the internal tanks. If you turn off your forward and rear boost pumps, but leave the external tank pumps on, you will still get fuel from the external tanks into the internal tanks.

 

There are two reasons (well, three I suppose) to have boost pumps pushing fuel (I'm now talking about the boost piumps inside the forward and rear internal tanks): First, during engine start, the engine-driven pumps need help. Since they're barely turning, they don't provide enough fuel pressure for the engines to run. Second, at higher altitudes, the suction effect of the engine-driven fuel pumps can cause fuel to cavitate, resulting in air bubbles in the fuel. Air bubbles are very bad for the engine-driven fuel pump, very bad for the fuel control on the engine, and obviously very bad for keeping the fire lit inside the engines, possibly resulting in a flameout. Third, your engine-driven pump could fail (in theory, anyway).

[Esac_mirmidon]

Thanks again ................... my master....

 

Now i had catched the whole picture about fuel system. Time to master this and the other systems.