Hummm, I'm not sure what you are doing, but the 727 fuel system should not act like that.

This is the way the RW plane is designed to work...

The 727 has 3 tanks. The wing tanks are smaller than the center tank. The center tank has 4 boost pumps, the wing tanks have 2 pumps.

If the tanks are equal with fuel, the set up should be tank-to-engine.
All boost pumps ON, x-feed on 1 & 3 closed, x-feed on tank 2 open to keep the manifold under pressure.

Because tank 2 has four pumps the pressure is a bit higher and if you leave all the x-feed valves open the fuel could flow from tank 2 to all engines.

You cannot transfer fuel, only cross feed the fuel.

Example: If tank 1 has 7,000 pounds and tank 3 has 6,700 pounds you would do the following...

1. Engine continuous ignition on..................................ON
2. Boost pumps tank one on.......................................ON
3. X-feed valve tank one open....................................OPEN
4. X-feed valve tank three open..................................OPEN
5. X-feed valve tank two closed..................................CLOSED
6. Boost pumps in tank 3 off, one at a time - observe engine.
7. When tank 1 & 3 equal, all boost pumps on...............ON
8. X-feeds 1&3 closed, X-feed 2 open..........................CHECK
9. Ignition off.............................................................OFF

This is in checklist format because anytime the F/E does something with the fuel panel the crew must be involved to prevent engine failure.
In real life at low altitude and good engine fuel pumps, the engine will most likely suction feed from its tank, but you never know!  
At higher altitudes it may or may not, but are you feeling lucky?

I think there are some issues with the fuel system in the CS model along with a few other problems that CoolP (one of the forum members) is compiling a list so the next version can address these problems.

Lou

CXA546 asked: What is the reason for shutting off the pumps on 1 & 3? I don't have an engineer, or a co-pilot, so if I forget to check my fuel config, by leaving the pumps on, if the center tank is depleted, the 1 & 3 should feed all engines because the cross-feeds are open? I seems safer to just leave the pumps on and use the valves to direct the fuel.

The lack of a "good" flight engineer on the 727 is a problem, but you do have to keep an eye on the fuel & keep it in balance both in pitch and roll. If you kept all the cross feed valves opened and left all boost pumps on you would only use the fuel from the center tank and would exceed the operating limits of the 727 in having wing fuel and no center fuel. CG & Structural limits.

If you don't care about operating the fuel panel in the correct manner, sure you could let the tank run dry and have the wing tanks try to feed all engines. You might just find that one of the boost pumps in tanks one or three is putting out a bit more pressure than the others and soon you will have a roll balance problem.

It would have been nice if CS had given us a "good" F/E (auto oilier) who would watch the systems...  

Lou

LOU wrote on Jan 27^th, 2013 at 10:01pm:


Let me see if I understand this, as I'm still a bit confused   If you open the crossfeeds, the center tank goes first until its empty regardless of the pump status on 1&3? Once the fuel in the center matches the wings, you reconfigure the configuration, and each tank serves its respective engine. So some monitoring and pump juggling would be required to ensure the tanks remain even?

Is it possible that some of the wing fuel will still be used with the pumps on,  and crossfeeds all open, and that could cause an imbalance as well?

Sorry for being a pain!