Mustanf tank switching.

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Ron Attwood
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Mustanf tank switching.

Post by Ron Attwood »

I am at present taking part in a Sim OutHouse event that utilises a neat programme (Duenna) that records everything about your flight. The rules are strict, no GPS, real weather, crash must be on and no inflight refueling. If you do anything against the rules the progamme turns red and your flight is null and void. (Do it again)

To the problem: switching tanks in the Mustang results in a red 'midair refueling' flag. Apparently A2A squirts an amount of fuel into the tank that triggers the fault. To their credit SOH have acknowledged the but and allowed the flight to stand.

The writer of the programme are working on sorting it out but what is the story behind the extra fuel? Is it a bug?

EDIT: After a bottle and a half of a very nice New Zealand Pinot Noir, MustanG does indeed translate into Mustanf :oops:
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Bomber_12th
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Re: Mustanf tank switching.

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It has to do with the way in which the aircraft is coded, in order to mimic/create the effect of a more realistic fuel system. For instance, with the default FSX fuel system, the engine will quit as soon as you move the fuel selector to an empty tank, which of course is not very realistic when you consider that there would still be fuel in the lines, and the engine would only start to sputter and quit after that remaining fuel in the lines has been used up. What the coding does, is mimic how it is when you switch tanks in the real aircraft, as it takes a little bit of time for the fuel to be picked-up from the new tank you have switched to, so in the mean-time the engine is still running on the fuel left in the lines from the previous tank - because of this, you never want to run a tank completely dry before switching to another tank, because of the amount of time it takes before fuel from the next tank gets to the engine. And it is also the reason why if you switch to an empty tank, you won't realize it until the remaining fuel from the previous tank still in the lines has been used up. With the default FSX fuel system, everything happens instantaneously, so the coding works-around this to provide a more real-life/accurate experience.

A good visual of this can be seen in this video (watch it in HD): https://www.facebook.com/video.php?v=10 ... =2&theater. Note just how slow the fuel is picked-up from the drop tank after the fuel selector has been switched to it - until that fuel gets to the engine, the engine is still running on the fuel in the lines from the previously selected tank - and as Mike V. says, never missing a beat.
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Re: Mustanf tank switching.

Post by robert41 »

The extra fuel is the return fuel. Not a bug. Same as real world P51's. Extra fuel not used is returned back to usually the left wing tank or some return to the aft tank. The left wing tank is modeled here. FSDuenna sees this as added fuel and triggers the red.

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Ron Attwood
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Re: Mustanf tank switching.

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You two come riding to the rescue once more. Well done A2A. :D As I said the writer of Duenna is working on a fix.
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Ron Attwood
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Re: Mustanf tank switching.

Post by Ron Attwood »

Further to the red FSDuenna. I (think) I have discovered a workaround. Instead of going by the book and using the left main first and switching to the right main (resulting in error) I used the RIGHT main first and switched to the left main. Result-No error. I'm guessing the the fuel in the lines deal wasn't coded/didn't apply to the right tank.
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CodyValkyrie
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Re: Mustanf tank switching.

Post by CodyValkyrie »

Ron Attwood wrote:Further to the red FSDuenna. I (think) I have discovered a workaround. Instead of going by the book and using the left main first and switching to the right main (resulting in error) I used the RIGHT main first and switched to the left main. Result-No error. I'm guessing the the fuel in the lines deal wasn't coded/didn't apply to the right tank.
I'm pretty sure the vapor coding is there for ALL tanks, but the return line ONLY fills the left tank. So, theoretically if you're running on the right tank first, the vapor return line is filling an already full tank, thus your plane is actually losing fuel because it has nowhere to go. In other words, regardless of which tank you're running, the vapor line will return fuel into the left tank, and if it's full it will be expelled from the plane.

This is why you're expected as a pilot to run off the left tank first, to give enough room in the left wing for return fuel, regardless of which tank you're using. This may mean that even when using drop tanks, I'm pretty sure it's expected to occasionally run the left wing tank to clear room for the vapor return. This ensures maximum range and that you're not incidentally dumping usable fuel.
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Ron Attwood
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Re: Mustanf tank switching.

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CodyValkyrie wrote: I'm pretty sure the vapor coding is there for ALL tanks, but the return line ONLY fills the left tank. So, theoretically if you're running on the right tank first, the vapor return line is filling an already full tank, thus your plane is actually losing fuel because it has nowhere to go. In other words, regardless of which tank you're running, the vapor line will return fuel into the left tank, and if it's full it will be expelled from the plane.

This is why you're expected as a pilot to run off the left tank first, to give enough room in the left wing for return fuel, regardless of which tank you're using. This may mean that even when using drop tanks, I'm pretty sure it's expected to occasionally run the left wing tank to clear room for the vapor return. This ensures maximum range and that you're not incidentally dumping usable fuel.
That makes sense. For the purposes of the race though, I'll see if my 'trick' works again. I'll go back to doing it properly afterwards. I promise. :D
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Re: Mustanf tank switching.

Post by CodyValkyrie »

Honestly, it's likely there's no coding to transfer fuel around if the tank is already full, and that would be excess and unnecessary coding. That being said, the problem won't go away because you'll have a severe imbalance in fuel. At some point you're going to need to use fuel from the left tank, and you'll be back to square one the second you switch tanks. The only way to avoid this would be to somehow keep that left tank full throughout the entire flight, which would absolutely cause an imbalance. Alternatively, the gentleman responsible for coding the rules will need to take this into account.
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Ron Attwood
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Re: Mustanf tank switching.

Post by Ron Attwood »

I think we're at cross purposes here. I'm not transferring fuel I'm simply using fuel from the right tank. When that's all gone I switch tanks over to the left tank and use fuel from that. Yes it certainly does cause an imbalance but it's manageable...just. :D But it does seem to prevent the FSDuenna from handing out a red card.
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Re: Mustanf tank switching.

Post by CodyValkyrie »

Just be aware that you're going to lose fuel from that process. Regained fuel in the vapor line going to the left tank will be lost.
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Ron Attwood
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Re: Mustanf tank switching.

Post by Ron Attwood »

Oh well, at least the cost isn't prohibitive. :D
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Re: Mustanf tank switching.

Post by CodyValkyrie »

Ron Attwood wrote:Oh well, at least the cost isn't prohibitive. :D
Hah! It does make you feel guilty every now and then doesn't it?
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Re: Mustanf tank switching.

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Ron Attwood wrote:I think we're at cross purposes here. I'm not transferring fuel I'm simply using fuel from the right tank. When that's all gone I switch tanks over to the left tank and use fuel from that. Yes it certainly does cause an imbalance but it's manageable...just. :D But it does seem to prevent the FSDuenna from handing out a red card.
I see this now. Because the left tank stays full, there is no added fuel for the duenna to see.
Just dumped fuel. Which is ok with the duenna. And quite a bit if using all of the right tank first.
And further, it must be quite a handful flying this way.

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Re: Mustanf tank switching.

Post by n421nj »

It stinks when other products aren't as advanced as A2A. However I can say over the past few years I've seen other companies trying to copy what they have done.
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Ron Attwood
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Re: Mustanf tank switching.

Post by Ron Attwood »

robert41 wrote:...And further, it must be quite a handful flying this way.
Not if you have the requisite skill level. :mrgreen:
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