Hi there, either this is a bug or I'm stupiud, or both....but the fuel system of the 727 seems completely illogical to me.

By default, all 3 tanks are used and the CF valves are like this: - | -

on a long flight, I'm required to switch to center tank only, for this, I turn off the boost pumps of Tank 1 and 3, and need to turn on CF für 1 and 3. (I think to tell the system to accept the CF fuel from tank 2)

When I change back this state, and try to leave ALL CF switches on, fuel is only drained from tank 1 and 2, not tank 3.....why?
So to use all 3 tanks, I have to turn CF of 1 and 3 off.

Then I tried to make my engines use wing tanks only: So I switch all boot pumps of tank 2 OFF, the No. 2 CF ON, and CF of 1 and 2 OFF, then it drains fuel from all tanks. this changes, when I Turn No. 1 or No. 3 CF ON, then it only uses wing tanks.  But if I switich ALL CF on, then No. 1 and 2 tanks are used regardless of the pump state.

:D

anyone has an idea how to get the hang of this?

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!  :o
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

Sorry, I know this is an old topic, but I just wanted to ask:

Since the center tank has 4 pumps, and there for higher pressure,  by opening the cross-feeds of 1 & 3, would that not drain the center first? Once the tanks are equal, then you can close the cross-feeds. 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.

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

When you have fuel in all the tanks and you open the crossfeed valves, the fuel is feed alternatively by the left wing tank, then the center tank and then the right wing tank (not necessarily that order). This also causes the 727 to have a roll balance problem if you want fly it manually.

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

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. Lou

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!

This is how my settings look when the fuel in all three tanks is about equal:
http://i669.photobucket.com/albums/vv58/Markoz958/example1.jpg

This is how my settings look when the amount of fuel in the Center Tank is greater than the amount of fuel in each of the Wing Tanks:
http://i669.photobucket.com/albums/vv58/Markoz958/727fuel.jpg

Hope this helps.