Post
by CodyValkyrie »
SD hit the nail on the head.... however would like to add a little as I created the guide regarding the fuel system in the manual. As SD described, it is not exact. Therefore, we created the most accurate emulation of how the system works. This required me to spend many hours looking at the fuel knobs and fuel gauges to ensure proper movement/flow on the gauges to write correctly in the manual how the system operates.
As suggested, the fuel will drain from the center tank first. In fuel balancing, it is not a transfer act as some might suspect. The tanks do not physically transfer fuel from one tank to another, and in fact the 377 inhibits this operation in the real world for safety reasons. There is no in flight fuel transfer.
There is however, a fuel balancing act that can be performed to ensure proper balance in the fuel tanks. It takes time. The diagrams provided work perfectly, but a few things must be kept in mind.
1) When fuel balancing, the center pump and valve should be closed.
2) The tank that needs balanced (the one with the most fuel) must have the fuel pump on and the selector set to TANK TO ENG.
3) The remaining fuel boost switches should be off and the selectors set to MAN TO ENG.
Fuel will continue to be consumed at a slow rate from the center tank (if there is fuel in it), however... fuel will also be consumed from the tank to be balanced.
In the example provided at the beginning of this thread, I replicated the results exactly. Please note that I am running with the latest updates on the 377 (for testing), however the fuel system has not had a change made to it at this point.
I set number one fuel selector to TANK TO ENG with boost pump on. All other boost pumps are off and the selectors are set to MAN TO ENG as described in the manual. After a minute or so running with cowl flaps open at 30 inches manifold pressure, I checked the fuel in the tanks.
NO1 Tank - 10,570 lbs
NO2 Tank - 9,120 lbs
Center Tank - 7,113 lbs
NO3 Tank - 9,120 lbs
NO4 Tank - 10,620 lbs
As you can see, the NO1 tank (tank to be balanced) has consumed 50 pounds of fuel.
Therefore, if I found while in flight one tank had more fuel than other tanks, I could fuel balance and consume from a specifc tank(s) to ensure I had a proper lateral balance.
The test was repeated for all other tanks (minus center tank) and produced similar results.
With that said, as described previously, when a selector is set to MAN TO ENG, then the order will be as described. If you need your inner tanks to drain in preference to your outer tanks, then you simply have your MAN TO ENG selected on all tanks (if the center is empty) or your inner tanks set to TANK TO ENG with fuel pumps on. Both have the same effect but however unnecessarily hard on your fuel pumps in the latter form.
If you were to plan a flight, you would consider how much fuel would be required for the flight (including secondary airport and emergency fuel) and equalize the fuel between all four tanks until they are full, then fill the center tank to the desired amount. (Keep in mind as described, the outer wing tanks should be equal or have more than the inner wing tanks. This is normal.
A schematic was not provided in our manual (by my decision) for several reasons. First of all, in both the American Overseas Airlines and the United Airlines flight manuals which I used as reference, had very different schematics (likely due to the many variations of 377 available). One of my manuals had none at all! Another reason was that the schematics were not pertinent to our model due to the nature of which our designers modelled it. Our 377 is not a specific model, but is reminiscent of the early models. Boeing even made it more complicated by the fact that these different variations of the plane were not given any special numerical sequencing to differentiate the various versions, and the airlines who had the different versions made no attempt to do so either. At best, one could only say that this plane could be a AOA 377, a PanAm 377, etc.... This is not the case with our model however. The inconsistency with the real planes, and the absolute complexity of the fuel system lead me to mimic to the best that I could the AOA version, which schematic also unfortunately isn't necessarily perfect either.
The AOA model had 10 fuel pump switches, a center body valve switch and 5 rotary positions on the selectors. Each fuel pump switch had multiple positions. Unfortunately however, the diagrams on these schematics are far from perfect, and as so are barely readable, which makes modeling them even harder.
We had to make the best of all worlds based upon our hands on experience with the KC-97, pilots accounts and multiple differing schematics.
Simply put, I put in the manual how to physically operate them and a basic understanding of how they work rather then get into the overly complex explanation of them. As in multiple manuals I was provided and purchased myself, this is however not necessarily unrealistic. One may find that when comparing the AOA 377 manual to say, the official Air Force T.O. for the C-97, there is a difference of 300+ pages! To say that the original 377 manuals of which the pilots used to operate the airplanes in the various versions the airlines used was skimpy is saying a lot.
It also goes to show have times have changed. No rivet goes unnoticed in aircraft manuals for the newer birds produced by giants like Boeing. The manual provided to you for the 377 is in many cases, including 90% of the fuel section, is taken verbatim directly from the original manuals.
The last thing I would like to address is the error you encountered in the very first post. After ensuring that the starting selector switch is set to off, I would be interested to see the experiment reproduced. As is, my current updated model is working correctly, therefore if there is an issue, it will soon be resolved nonetheless... IF there is an issue at all.
I hope our explanations help clear up some of your questions and testing.
. The fuel system does not behave at all as expected. Unfortunately there's no schematics to depict the whole system.
but I can't come to the same conclusions that you gave in your reply. According to your answer I tried to depict the fuel systematics and I'm quite sure that I got it more or less right. At least it would reflect exactly the behaviour that you described.
