Drop tank problem

[ff4life4]

Recently back in the P51. 
 

When taking a full fuel load out, I burn left wing tank first. Once airborne, I’ll burn aft tank to 25. Then switch to left drop tank for 5 min and then right drop tank for 10 min. 
 

Now I cannot get the left drop tank to feed again. Every time I switch back engine sputters after a few seconds and fuel pressure drops to zero. All other tanks including right drop tank work fine. But can’t get left drop to feed again. Fuel booster pump is on. 
 

Anyone know what is going on???

 

Thanks

[Art-J]

Maybe you've found a new bug, but more info is needed to investigate. Was it single- or multiplayer? After refueling or straight from mission editor?

I tried to replicate, albeit with much shorter intervals between switching tanks (every few minutes really) and couldn't - all tanks seemed to feed properly.

My replay track is posted below. In either case, please save and attach yours.

 

2.9_P-51D30_tank_test.trk

[=475FG= Dawger]

This shouldn't be causing your issue but sometimes programmers are VERY literal when reading these manuals.

The P-51D manual states that you should takeoff on the fuselage tank if it is serviced, otherwise takeoff on the Main Tank L.H. with boost pump in EMERGENCY.

At a safe altitude, it instructs to switch to drop tanks and alternate between them until empty, and then drop them.

At that point you should switch to the fuselage tank and boost pump NORMAL, and burn it down to 25 gallons. 

 

If the fuel system was programmed in a literal fashion, I can see where your issue might arise. Try taking off on Main LH, switch to drops and see if they burn to empty before ever using the fuselage tank.

[grafspee]

DCS P-51 does not have boost pump switch position EMERGENCY/NORMAL so they should not make any programming based on that particular manual in the first place.

[=475FG= Dawger]

51 minutes ago, grafspee said:

DCS P-51 does not have boost pump switch position EMERGENCY/NORMAL so they should not make any programming based on that particular manual in the first place.

The difference in the fuel system is boost pump in late models is ON/Off only and the vapor return line tank plumbing. Otherwise, the manual will read the same, which is my point.

If taken very literally, a programmer may have introduced the inability to draw from the drop tanks after fuselage is used, which would be in error.

[Art-J]

Nah, I don't think that's the case. In my  track I took off on main LH, then switched to fuselage for a while, then tried drops and they seemed to be feeding allright. Did it all in shorter intervals than OP though, so he must've experienced some more wicked glitch in his mission.

Maybe I'll try to replicate his exact "recipe" for problem later.

[Stackup]

I've definitely had this problem in single player.  Ramp start and takeoff on left main, then fuselage tank until 25-15 gallons(if there's fuel in it), then LH drop tank for 10ish minutes before switching to the RH drop tank for 10, etc.  Two flights ago the RH drop tank failed to feed exactly as OP described.  I then tried an air start and all tanks fed correctly.  Another ramp start and again they all fed correctly.  It's definitely not a consistent problem/bug, but when you're climbing to 20k feet to escort bombers and trying to keep pace with an AI flight, it's a bit of a pain to have the engine randomly cut because one of the tanks decided not to feed.  I've even had this happen to the right main tank a couple patches ago so it's not necessarily a drop tank only issue either.

Edited January 6 by Stackup
misremembered fuselage tank level

[virgo47]

I've experimented with the drop tanks during the last few days and they are definitely a bit peculiar. I've written a script to see the fuel level in messages regularly (only overall, but better than nothing) to see whether the fuel somehow disappears or what. I always burn a bit of left-wing tank to get around 75 mark and it never gets to F, so I hope there is no problem on this front. The mission is my custom free flight and the stories vary:

• I've flown ~angels 20 on the left drop tank, I switched to the right tank drop tank and lost fuel pressure within seconds, although there was no chance I spent the whole fuel. Repeated on at least two flights, no idea what was wrong. (I have no info on the fuel level for these cases, it was before I added the script.)
• I've active-paused the plane after the mission start at angels 6, fuel 157% (100% is for full internal fuel), went over all the tanks, starting with a bit from the wing left, then the combats one after another... fuel pressure dropped when expected based on the fuel %, I switched through all of them and went all the way to 0. The plane "flew" for over 5 hours, no problem. (I used time accel of course.)
• I went over Caucasus again, ~angels 30, used the both left and right drop tank just a bit, then switched to the right drop tank for good when I was ~140% of fuel. The missing 17% went a bit from the left wing and both combat tanks. Neither of the combat tanks could have been empty by this time, it's mathematically impossible. The fuel reported going down all the way to 92%... it worked like there was some kind of interconnect between the drop tanks, because the moment the fuel pressure dropped, I switched to the left combat tank - and it was empty too!

I have no explanation for this behavior, the only normal case seemed the experiment in active pause. I don't know how altitude is involved in all this, reportedly the altitude can make the engine management harder, but I guess you want to use drop tanks first even when you escort bombers in high altitude - and you probably want to fly high to fly further, but I'm not an expert on this.

Edited February 9 by virgo47

[virgo47]

I've made another test, this time at higher altitude, although I'm not sure how important that is.

1. First I went for active-pause test and accelerated time, no problems at all, switching went exactly as expected. Start at 157% of fuel, switch to left combat tank at 152%, then - as calculated and expected - fuel pressure dropped around 123%, so I switched to R combat tank, and then around 95% (first 5% went from the left wing tank) I switched to internal tanks. No problem.
2. Second time I decided to fly actually fly it and also switch more often from tank to tank, but make notes what happens when. To my surprise, things went wrong quickly... again, around 152% I went for L combat tank, then around 143% I switched to R combat tank. I lost a plane for a moment, but I don't believe the maneuvers were that excessive, but... suddenly I lost 50 gals in 10 seconds:

There is nothing in the Score window, I wasn't sure about some malfunction... I made and checked the track again, whether I'd see anything in those moments... nothing obvious in an external view. But 50 gals were lost. Strangely, from the gauges it seemed like some internal fuel was lost as well.

So, naturally, I suspected the maneuvers. I restarted the mission and tried pretty crazy things... but I couldn't replicate it.

Track file is attached.

p51d-lost-fueltrk.trk

[Chipwich]

I just had the issue, single player Reflected's Debden Eagles campaign.  I tookoff on the left main, then switched to fuselage tank at 1000 ft AGL.  I ran this until approximately 25 gallons remaining, then switched to right drop tank.  I ran this for 10 mins, then switched to left drop tank, at which time the engine quit from fuel starvation.  I switched to right main and pickled my drop tanks, thinking that the left was inoperative.  Completed the mission without fuel issues.

[sjebens]

On 2/9/2024 at 9:10 PM, Chipwich said:

I just had the issue, single player Reflected's Debden Eagles campaign.  I tookoff on the left main, then switched to fuselage tank at 1000 ft AGL.  I ran this until approximately 25 gallons remaining, then switched to right drop tank.  I ran this for 10 mins, then switched to left drop tank, at which time the engine quit from fuel starvation.  I switched to right main and pickled my drop tanks, thinking that the left was inoperative.  Completed the mission without fuel issues.

Thank you! I thought I was going crazy - same campaign.