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Fuel System Issues


Grach

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I've noticed some issues with the interactions between the main, alternate and auxiliary tanks. Firstly, the center wing tank doesn't seem to feed into the mains properly; you have to open the alt 2 and 3 fill valves (and only alts 2 and 3; neither alts nor mains 1 and 4 will take center fuel as far as I can tell) and then follow the procedure to pump fuel from them into mains 2 and 3. Secondly, I talked with Richboy and we both had an issue with the outboard alts where it'd feed all four engines from them, regardless of the tank selector position. Essentially, it's as if the crossflows are open all the time. That said, when I happened to me I tried to cycle the tank selector and as the alt tank for that engine was empty it correctly shut down, so there might be some issue with the logic there. Finally, this is more of a request, but modelling the crossflow levers and the main-to-alt fill valve would be nice, because then in the event of haphazard fuel management the user can get themselves out of it instead of their recourse being "reload the sim".

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4 minutes ago, Grach said:

Finally, this is more of a request, but modelling the crossflow levers and the main-to-alt fill valve would be nice, because then in the event of haphazard fuel management the user can get themselves out of it instead of their recourse being "reload the sim".

+1 for modelling of fuel crossfeed levers. I'm enjoying this bird and would love some more control  over the fuel management, even if only as an option you have to turn on through a config menu.

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I am looking for some explanation for the problems some of you have reported with the fuel system, but can't see anything so far.  It works for me and worked for all the beta testers, one of whom spent five years as a DC-8 flight engineer.  If you have a problem I need a detailed description of it and ideally a screenshot of the fuel panel taken at the time of the problem.  Tanks selection is delayed on loading the aircraft a little to ensure it happens after P3D sets the tanks itself. If the delay is not enough on some systems it would result in fuel being fed from the wrong tanks, but it would not affect fuel transfer.  I just tested again every step from transferring from the centre tank onward and couldn't see any problem with how it functions. 

 

With fuel transfer and fuel management generally, I would like to be sure everyone fully understands the system.  Only then can a bug be recognised as a bug. 

 

If there is enough fuel loaded the some of it is in the centre aux tank, you start fuel management by transferring it into the four main tanks.  You must pull down the centre wing aux lever and turn on the pump for that tank as well, then turn on all four main tank fill valves.  Fuel will only transfer when there is room in the main tanks. If the rate of transfer is faster than you are burning fuel, the mains may fill to capacity and then the transfer will turn on and off. 

 

You can monitor the transfer by putting the automatic shutoff switch to VALVE CLOSED.  This doesn't shut any valves; it just energises the blue lights that turn off when valves open to allow fuel to be transferred into the indicated tanks.  Blue light off, means fuel is being transferred to that tank.

 

You shouldn't attempt any other transfer until the centre tank is down to 3,000 lbs. Then you shut the transfer valves to nos. 1 & 4 main tanks, but keep transferring to nos. 2 & 3. 

 

When the centre tank is empty, then start transferring from the nos. 2 & 3 alts to mains.  You do not use the levers to do this.  All you do is turn on the alt pumps and keep open the main fill valves. If you mess with the selector levers you will either start feeding engines from alt tanks, or shut down the fuel supply completely, neither of which is desired.  

 

When the nos. 1 & 4 main tanks get below 7,500 lbs you can start transferring from their alt tanks.  Again, no levers are used.  Just put the alt pumps on and open the main fill valves.  Note that although you have set everything up for transfer, it won't start to happen until the level of the main tanks gets a little below 7,000 lbs.  The automatic shutoff valves for these tanks will prevent transfer from their alt tanks to more than 7,000 lbs in order to preserve a desired weight distribution.  These valves may stop and start the transfer intermittently as the level of the main tanks reach and then dip below 7,000 lbs.  Again, you can monitor this with the valve closed lights if you put the switch to the valve closed position. 

 

 

 

 

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Same here. Currently on the first mid-range flight.

 

Start config: Fuel 80000lb, automatic distribution

 

No 1&4 Alt: around 10000lb

No 1&4 Main: around 11000lb

No 2&3 Alt: around 2000lb

No 2&3 Main: 17600lb

Both Center: 0

 

About 1,5 hours into the flight, it looks like this:

 

Please login to display this image.

 

No 2&3 Alt depleted, but Mains not used at all.

 

Using P3D4.1.

 

Edit: A bit later, and No 1 Alt is depleted, No 1 Main is at 6800, No 4 Alt is a at 2200 and No 4 Main at 7460. No 2&3 mains still at 17600. It seems No 2 &3 draw their fuel from the #1 tank system.

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Ok, one hour later.

 

Please login to display this image.

 

No 1 Main is depleted, and No 1 engine has quit (as we have no working crossfeed *poke*). Now that there is no fuel left in the No 1 system, Engine No 2 starts using fuel from its own tank, No 2 Main. I planned for a diversion, downloaded a freeware scenery for the diversion airport and put it in the library on the fly, however P3D crashed afterwards. So I cannot tell exactly, but I guess once No 4 fuel is depleted, No 3 engine would then start using its own tank.

Well, I started preparation for this flight this morning and now spent 5 hours for nothing.. the aircraft is grounded for now. Back to the Maddog.

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A working crossfeed would not be any solution at all to the fuel system not working correctly on your system, yes?  You need it it work correctly.

 

Thanks for the screenshots and descriptions -- it makes it a lot easier to understand the likely cause.

 

I have a new file for you to try out which may fix the problem; the link to download is at the end of this post. 

 

When the aircraft loads, tank selection for each engine is initiated.  I found that I had to delay the initiation for about 1.5 seconds to prevent the sim from overriding the selection with some default one.  Maybe the delay is not enough time for some systems, so with this file, it will be five times longer.  Try it out and let me know if it corrects the problem as I would like to put the new file in the next update. 

 

The file goes in DC-8_50/Panel/DC8_Fuel.  Overwrite the existing file. 

 

It should only take a couple of minutes to test.  Load the aircraft on the ground.  You can set the fuel level or leave the tanks full -- it doesn't matter. Make sure the parking brake is on and advance the throttles a little to increase the fuel flow. Also turn time acceleration to 4x to further increase the rate of flow. Now see if the fuel quantity is going down evenly in the four main tanks. 

 

https://drive.google.com/open?id=1MgjcgtEdmY0SREEtyCWBVHgi1y5kxjuP

 

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8 hours ago, MatzeH84 said:

Same here. Currently on the first mid-range flight.

 

Start config: Fuel 80000lb, automatic distribution

 

No 1&4 Alt: around 10000lb

No 1&4 Main: around 11000lb

No 2&3 Alt: around 2000lb

No 2&3 Main: 17600lb

Both Center: 0

 

About 1,5 hours into the flight, it looks like this:

 

 

No 2&3 Alt depleted, but Mains not used at all.

 

Using P3D4.1.

 

Edit: A bit later, and No 1 Alt is depleted, No 1 Main is at 6800, No 4 Alt is a at 2200 and No 4 Main at 7460. No 2&3 mains still at 17600. It seems No 2 &3 draw their fuel from the #1 tank system.

 

 

In your pic, above, you need to have your #1 pump set to "Feed Only", and your (A)lternate fuel would begin flowing into the #1 Main tank.

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vor 17 Stunden , Michael2 sagte:

A working crossfeed would not be any solution at all to the fuel system not working correctly on your system, yes?  You need it it work correctly.

 

Thanks for the screenshots and descriptions -- it makes it a lot easier to understand the likely cause.

 

I have a new file for you to try out which may fix the problem; the link to download is at the end of this post. 

 

When the aircraft loads, tank selection for each engine is initiated.  I found that I had to delay the initiation for about 1.5 seconds to prevent the sim from overriding the selection with some default one.  Maybe the delay is not enough time for some systems, so with this file, it will be five times longer.  Try it out and let me know if it corrects the problem as I would like to put the new file in the next update. 

 

The file goes in DC-8_50/Panel/DC8_Fuel.  Overwrite the existing file. 

 

It should only take a couple of minutes to test.  Load the aircraft on the ground.  You can set the fuel level or leave the tanks full -- it doesn't matter. Make sure the parking brake is on and advance the throttles a little to increase the fuel flow. Also turn time acceleration to 4x to further increase the rate of flow. Now see if the fuel quantity is going down evenly in the four main tanks. 

 

https://drive.google.com/open?id=1MgjcgtEdmY0SREEtyCWBVHgi1y5kxjuP

 

 

What I meant was, I had no chance to feed the #1 engine from any other tank, so it just shut down. Admitted, if everything works correctly, this wouldn't be necessary.

 

I tested the updated file, and everything seems to work properly now. Many thanks for your quick action!

 

@Mace: I know the theory, however it didn't work. That's why I posted ;)

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