B707-700 fuel feed logic observation

[jardx]

I posted in the Douglas forum about a similar fuel feed logic error that I saw while attempting to conduct realistic operations of the fuel system in the DC-9.

1. I did match model version to panel version

2. No, I did not mess with the aircraft cfg or air file

3. Yes, I am using the most current core gauge/panel/model files

4. Yes, I read Mark's Handling Notes

I saw something in the same neighborhood with the B707-700 with the CFM engines with a fuel load that required fuel in the center tank, not sure about the other B707 models.

If you use one boost pump per main tank (for at the bare min engine start) then turn the second boost pump on with at least one main crossfeed valve open to assure positive fuel feed in the event of engine or boost pump failures, you get tank to engine feed.

When you attempt to burn out of the center only, open the 1 through 4 crossfeeds turn on the center tank boost pumps turn off mains 1 and 4 I saw the feed come from number 2 and 3 main tanks only. 

In the fuel management document it was stated that this config of the fuel system should yield a feed from the center tank only as the pressure output from the center pumps is greater then the main pumps there for overriding the feed from mains 2 and 3.

"3. Main tanks boost pumps 1 and 4: off; Main tanks boost pumps 2 and 3:on; central tank boost
pump: on; 1, 2, 3 and 4 crossfeed selectors: open.
This is the setup for using the central tank fuel. Notice the main boost pumps 1 and 4 are turned
off and the central tank boost pumps are on. This way fuel will be supplied from the central
tank to engines 1 and 4. A smaller quantity will also go to engines 2 and 3. This mode is used
after takeoff, when a certain amount of fuel from the main tanks has already been used
(14,000lb recommended)"

I did not get this result.

As a test I turned all main pumps off to see if the feed logic would shift to the center tank, it did not instead it started feeding from number 2 main tank only.

With all this in mind I wanted to test/check the crossfeed and boost pump operation by purposely starving an engine, in this case number 3, of fuel by keeping the boost pumps off in tank 3 and closing the number 3 crossfeed valve. As expected after closing the number 3 crossfeed valve engine 3 shutdown.

I re configed for a tank to engine feed for number 3 restarted number 3 then recycled all main boost pumps and finally got a center tank only feed with no main boost pumps on, center tank pumps on, and all main crossfeed valves open. 

So my conclusions from this experience are either there is a coding error in the fuel system, the fuel tutorial document needs to be reworded as the present text is misleading or in the case of the DC-9 you simply can not use only one boost pump in the tanks even though the panel manual states that you can. 

As with the DC-9 fuel system post/thread I am simply throwing this observation out there. I know that more then likely nobody has the time to fix it if there is indeed a bug in the coding of the fuel feed logic and I know that these models and panels have been published for 10+ years with no one else seeing this behavior.

So maybe this post was made in case anyone saw this behavior and was wondering if they were crazy.

Jared                 

[walterleo]

Hi Jared:

Your post is quite old and not answered yet. I take the liberty to refer to some problems with the fuel system.

Main problem is the wording of the tanks names in FS9 and in the fuel manual:

So I tried to bring that in order:

FS9 .............Fuel System Tutorial / Boeing real

LEFT MAIN........R 1 Reserve

LEFT AUX........ T 1 (main)

CENTER 2.........T 2 (main)

CENTER 1.........CTR Tank

CENTER 3.........T 3 (main)

RIGHT AUX........T 4 (main)

RIGHT MAIN.......R 4 Reserve

Disconcerting a little. But other high-quality simulations like the PT Tu-154`s have the same problem. So: FLYING and flight simulation is not for everybody!

Did not check if your problem comes from my problem, but as I have done similar checks like you using both fuel-pumps together I did not notice it.
Besides trying to rename the tanks according to the real names in the aircraft.cfg does not work, as the fuel pumps cannot be activated then.
But I am using only the updated versions of the HJG 707.

Kind regards

Walter

P.S.: The 707s are nice simulations all together! And thanks for the updated FDE!

[aerofoto - HJG Admin]

This thread was posted way back in 2019

the wording of the tanks names in FS9 and in the fuel manual ....
.... other high-quality simulations like the PT Tu-154`s have the same problem ....
.... trying to rename the tanks according to the real names in the aircraft.cfg does not work, as the fuel pumps cannot be activated then.

Walter's analysis is "almost" right on the money .... and right down to his comparisons with other simulations

In "some" of our simulations/panels the fuel tanking is "renamed" due to the dictates of FS versus what we want to be able to achieve.

Although what we represent is usually "reasonably authentic" it might not strictly conform to the actual R/W specifications of the featured aircraft type.

The "FUEL TUTORIAL PDF" for these simulations is a separate document based on R/W manual extracts (for just one only B707 configuration .... others will differ) and its stated tanking references may not correspond with what's actually represented within our simulations.

This PDF document should be interpreted as "a guide only" in respect of basic fuel management .... it's not actually part of our endorsed manual.

Our "forum based manual/s for both the B707's/C-135's" state our "recommended" use of the fuel system featured within these simulations as follows .....

B707 FUEL SYSTEM & PROCEDURE/S

HJG offer a basic "FUEL MANAGEMENT TUTORIAL" (compiled by Harerton DOURADO) .... and which may be downloaded from the "B707" section of the HJG "BOEING PANELS" downloads page. The Fuel System featured within each HJG B707 panel is very "functional", however, unlike is the case with some other panels offered by HJG, "no specific fuel procedure is recommended for any of these B707 simulations .... beyond what is advised". Normally either tank to engine, or cross-feed configurations, are more than sufficient for the needs of most virtual flights .... without imposing unnecessary complexity. If one configures the fuel system as discussed within the HJG B707 Engine Startup tutorial (see Section 7 on this manual) .... and leaves it as such .... THEN .... one should not, ever, encounter any fuel related issues at all .... provided one loads sufficient fuel for the duration of any intended virtual flight. Whilst HJG, to a certain extent, encourages End User experimentation .... "using what's provided and as-is" .... in the absence of any other prescribed fuel system related procedure (specifically recommended by HJG), and solely in the interests of promoting enjoyment of one's flights using these B707 panels/simulations without imposing too much complexity, HJG, for the moment, "DOES NOT" recommend trying to invent fuel procedures as such may result in systems related difficulties. Therefore .... set up/configure each simulation "only in accordance with what HJG recommends/advises" .... and which is based on what is "KNOWN", from experience, works best using any of these B707 simulations

PLEASE NOTE: Using any these B707 simulations fuel loading and distribution "WILL" tend influence both static ground pitch .... as well as inflight pitch attitude and stability too .... so loading with caution is advised.

Whilst a number of the panels we offer feature systems fidelity some people like/expect not all of them do (it depends on their origin .... whether or not the basic panel was designed by us from the very start or designed by an external/non-HJG author and imported by us) therefore the long and short of all this (in regard to the fuel system represented among our B707/C-135 simulations at least) is as follows ....

1. Using the fuel system "as advised per our forum based manual" shouldn't result in any major difficulties at all

2. Despite certain functionalities represented in each of these B707/C-135 panels don't invent procedures in cases where none are specified .... as such will likely result in issues arising

Mark C
AKL/NZ

[walterleo]

Hi friends:

Wanted to add, that I came to a good relation with the 707-fuel system, works really fine.
I used always both fuel pumps even down low below 15.000 feet and everything works as described in the tutorial.
In some circumstances the sequence of turning off/on the cross feeds and off/on the fuel pumps is important: Never switch off pumps before opening the correct cross feeds. And never switch off a cross feed before putting on the correct fuel pumps. This could be misunderstood in the tutorial.
Altogether I feel, the programming of the fuel system is quite good and quite near to the real thing. AND the tutorial is a great help, as long as you respect the correct sequences. Seems the noncompliance with the correct sequences brought down some real airplanes seems no 707s were among them.
For those of us, who don't like to play FE instead of PIC, the advice "all pumps on and all cross feeds (and the reserve tanks) on" is a good advice.

I even tried today feeding all engines from centertank alone and it works fine. But if one experiments with manual tank selection one has to be prepared to know how to restart a fuel starved engine again. So, it has an additional learning effect! LOL!
And also in that case: Have a good altitude below you before switching around on the fuel panel.

Kind regards

Walter

P.S.: Remember the three most unnecessary quantities in aviation: Runway behind, altitude above and air in the tanks.

[aerofoto - HJG Admin]

For those of us, who don't like to play FE instead of PIC, the advice "all pumps on and all cross feeds (and the reserve tanks) on" is a good advice.

That's the simplest method .... and is "precisely" what I recommend within the B707 and C-135 manuals since both use the same very panel assignments.

Using this Fuel System configuration one simply can't starve the engines unless .... (a) one hasn't calculated/loaded enough fuel to start with .... or (b) one forgets to engage the Fuel Boost pumps "above 10,000 FT .... either of these 2 scenarios will then result in unwanted engine shutdowns.

Mark C
aKL/NZ