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707 Captain >> 707 Captain >> Fuel Boost Pumps
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Message started by wiltzei on Jan 22nd, 2011 at 5:21pm

Title: Fuel Boost Pumps
Post by wiltzei on Jan 22nd, 2011 at 5:21pm
1) Is this a bug?

There´s fuel in L/R main tanks and crossfeed is open. All the other tanks are empty and their corresponding boost pumps are off. Engine runs fine.


After turning empty tank´s boost pumps on, engine dies.


2) Ability to turn heading bug with keyboard commands (or with whatever controller you´ve assigned the bug to with FSUIPC).

3) Pressing autopilot master button after disconnecting the autopilot doesn´t extinguish the AP warning light, but engages the AP again.

Title: Re: Some items I'd like to see in the next SP
Post by Markoz on Jan 23rd, 2011 at 12:32am
Hi wiltzei.

1) The problem with turning the Fuel Boost Pumps for an empty tank seem to prevent/override the fuel flow into the engine from the crossflow feeds of the other tanks. I always leave the Boost Pumps from empty tanks OFF and so the engines remain running. The side effect of that, is that when I'm doing long haul flights, engines will shut down IF I don't turn those Boost Pumps OFF immediately when the tank empties. Is it a bug? I don't know. It doesn't seem like one to me.

2) The 707 doesn't use FSUIPC so I'm not sure if what you are asking for can be done. It would at least be nice if it could be changed in the default keypress of CTRL+SHIFT+H followed by the + and - keys (on the main keyboard, not the keypad). As long as it doesn't change by more than one degree at a time (unlike on others where it moves by ~10 degrees per press of the +/- key).

3) Try pressing the A/P disengaged warning light to extiguish the warning, rather than using turning the A/P Master Switch back ON.

Mark

Title: Re: Some items I'd like to see in the next SP
Post by LOU on Jan 23rd, 2011 at 5:55pm
From Markoz in reply to wiltzei's question about the fuel system....

The problem with turning the Fuel Boost Pumps for an empty tank seem to prevent/override the fuel flow into the engine from the crossflow feeds of the other tanks. I always leave the Boost Pumps from empty tanks OFF and so the engines remain running. The side effect of that, is that when I'm doing long haul flights, engines will shut down IF I don't turn those Boost Pumps OFF immediately when the tank empties. Is it a bug? I don't know. It doesn't seem like one to me.

Hummm,

The engine driven fuel pump - the one mounted on the engine - is a two stage pump.

If both stages were normal the engine would actually suction feed fuel out of its own tank without boost pump pressure. If one of the stages was inop, the engine might quit. The fuel boost pumps for the tank are there to insure positive pressure to the engine at high power settings and to crossfeed fuel from other tanks to other engines. In older Boeing jets there is no fuel transfer, just x-feed.

Turning off the boost pump switch after the low pressure light is on is really just matching the condition of the pump since the pump is already off. That by itself should not make the engine quit. During fuel x-feed in the 707 you would need to turn off the boost pumps in the tank of the engine you were x-feeding to so fuel would move from the supply tank to the engine.

FYI - In the 757 & 767, the center fuel boost pumps are override pumps and would push the fuel from tank 2 to the other tanks even if the other tank boost pumps were left on.

Example: Tank 1 has 10,000 pounds and tank 4 has 9,000 pounds. One way to balance this situation would be ....
1.  Turn on engine ignition.
2.  Turn on both fuel boost pumps in tank 1
3.  Tank 1 x-feed open
4.  Tank 4 x-feed open
5.  Turn off fuel boost pump in tank 4 one at a time while observing engine
6.  Monitor fuel balance
7.  When fuel in tank 1 equals tank 4.... Turn on both fuel boost pumps in tank 4 while observing engine
8.  Close x-feed in tank 4
9.  Engine ignition off

The flight engineer would calculate the x-feed time for the balance procedure and advise the captain before and after this operation.

If the x-feeds were closed and the respective engine tank goes dry, the engine would quit since there is no path to supply fuel to that engine. However, if the x-feed valve for the engine is open and a x-feed valve to a tank with fuel is also open and boost pump pressure from the tank with fuel is available, the engine would keep running.

In playing with the CS-707, the engines will not keep running without boost pump pressure even though there is fuel in the respective tank. I am OK with that since it makes you have to keep an eye on the fuel panel and not run a tank dry, but engines with good engine driven fuel pumps would suction feed if fuel was in its respective tank. If the tank runs dry and you're not on x-feed, it get's quiet.

FWIW - The boost pump in the wing that pushes the fuel to the engine is about the size of a can of Fosters beer.  :o

Lou

Title: Re: Some items I'd like to see in the next SP
Post by Kapitan on Jan 23rd, 2011 at 11:40pm
Wiltzei,
Pitty you didnt open a thread with your problem. Or a KB support.
This thread compiles a list of improvements in future upgrades, and should have been kept clear and ontopic with the excellent suggestions by Rico Van Dijk above :(

Title: Re: Some items I'd like to see in the next SP
Post by Kjetil on Jan 25th, 2011 at 2:28pm
Can't somone with admin rights move the post to a new thread?

Title: Re: Some items I'd like to see in the next SP
Post by Markoz on Jan 26th, 2011 at 2:10am

Kjetil wrote on Jan 25th, 2011 at 2:28pm:
Can't somone with admin rights move the post to a new thread?
I'm sure they can. I guess Alex or Tanya will have come here to see your suggestion and move it into the 707- General forum where it belongs.

Mark

Title: Re: Fuel Boost Pumps
Post by Captain Sim 2 on Jan 26th, 2011 at 1:15pm
Done.

Title: Re: Fuel Boost Pumps
Post by Markoz on Jan 26th, 2011 at 4:19pm
Thank you for doing that Tanya. It's appreciated very much. :)

Mark

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