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Fuel Crossfeed causes unrealistic fuel consumption


kevinh

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I recently flew the A318 from EINN to KJFK. It just about made it despite the high fuel flow. However as usual the left engine used more fuel than the right (the difference was higher than usual on this flight) so I ended up with quite a large fuel imbalance. Using crossfeed to balance things I noticed the FMGS destination fuel decreased rapidly while in that configuration. So I had used extra fuel while crossfeeding.

 

So I tried a test flight to look see exactly what was happening. Having set up total fuel flow at 60 kg/min (using manual thrust), I opened the crossfeed and switched off boost pumps on the left side. After one minute the left tank had decreased by 60 kg and the right tank by 120 kg. Three times more fuel used than the engines were burning. There should be no flow from the left tank and a total of 60 kg/min from the right tank. 

 

I expect Aerosoft may say crossfeed is not normal operation so not to expect it to be correct, but in this case it was necessary due to asymmetric fuel flow which is because of Aerosoft's design. So I respectfully ask that Aerosoft either address this crossfeed issue or make crossfeed unnecessary by limiting the amount fuel flow can be differ between the two engines.

 

I've only tried this in the A318, but there's a good chance all four Airbus versions are similarly affected. There is also another fuel use bug in that if you run the engines with boost pumps off and crossfeed off no fuel is used at all. Perhaps both issues could be looked at?

 

Kevin

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  • Deputy Sheriffs

Hey Kevin. Both issues are known to us. 

 

The X-feed part will not be addressed because of the the non SOP character (like you said) but we have to do something about the fuel imbalance. 

 

It is on the list of things to do for SP4. 

 

 

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  • 10 months later...

I see nothing has still been done about this. It's not just the fuel imbalance (which causes you to need crossfeed). The worst thing is the excessive fuel flow in the A318. It should be able to fly EINN to KJFK with no problems. BA fly the route every day. But the Aerosoft A318 can barely make it unless the prevailing headwind is lower than normal.

 

I can understand Aerosoft saying "SOP only" for complex systems simulation that needs to be added, but even the default aircraft fuel system can manage crossfeed. Surely it should work on the AS Airbus, SOP or non SOP? It isn't as if the crossfeed is merely not working, it's acting like a fuel leak. This is not system modelling that needs to be added, it's a bug in existing Aerosoft code.

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  • Deputy Sheriffs
9 minutes ago, kevinh said:

This is not system modelling that needs to be added, it's a bug in existing Aerosoft code.

 

When saying that only SOP is supported it not only means that only SOP functionality will be implemented. Other functionality is also getting added, but if a bug in such a system shows up it doesn't get a very high priority to get fixed.

 

As Frank told you already last year this is a known but and it's on the list for the next service pack. Plans for a service pack have been changed into a complete new release coming soon. I don't know though, if that fix made it or will make it into that new version.

 

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2 minutes ago, Tom A320 said:

 

When saying that only SOP is supported it not only means that only SOP functionality will be implemented. Other functionality is also getting added, but if a bug in such a system shows up it doesn't get a very high priority to get fixed.

 

As Frank told you already last year this is a known but and it's on the list for the next service pack. Plans for a service pack have been changed into a complete new release coming soon. I don't know though, if that fix made it or will make it into that new version.

 

Thanks for the quick reply, Tom, but this is basic stuff. Fuel transfer. Also Frank's reply is over 10 months old. No sign of any fix since then.

 

Were you aware of the excessive fuel burn in the A318? That's definitely normal operation.

 

I certainly wasn't aware the SP was becoming a new release. I've seen the post you linked to of course, but it says nothing about it being a new release. That's not really fair for loyal customers expecting a long announced SP to find it will now be a paid for upgrade. I understand P3Dv4 is an additional problem but most developers are providing compatibility upgrades at no cost.

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  • Deputy Sheriffs
Quote

[...]  but this is basic stuff. Fuel transfer. Also Frank's reply is over 10 months old. No sign of any fix since then.

 

Please read the first paragraph of my first reply again, where I was talking about priorities.

 

More details on the planned update can be found here:

 

 

1 hour ago, kevinh said:

That's not really fair for loyal customers expecting a long announced SP to find it will now be a paid for upgrade.

 

AS was already last year quite clear on the time frame for the then announced SP4: after the release of the A330. As you can see from the above linked post this has been reverted, meaning the update will be before the A330 release and contains tons of stuff that was newly developed for the A330. 

 

 

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On 09/07/2017 at 9:56 PM, Tom A320 said:

 

Please read the first paragraph of my first reply again, where I was talking about priorities.

 

Oh I read it properly the first time, believe me. Priorites should be that basic functionality works and that bugs in code are corrected. In my opinion fuel crossfeed is basic functionality, you may disagree. However the way crossfeed simulation works in the A320 series is clearly bugged (fuel is being lost at three times the rate the engines are using it) and should be fixed. Either that or disable the crossfeed switch completely because crossfeed isn't simulated properly. Best of luck explaining that move to the community though.

 

Regarding the rest of your reply (I couldn't get the quote feature to separate it): I understand that plans change and I have not been keeping up with day to day developments on the forum, so accept I might have found out sooner. Mathijs' post is detailed, honest and well presented as usual and I can't fault the logic he used. So I accept a price must be charged. But how was I supposed to find info about the A320 series update in a long preview thread of the A330? The news about the update being charged for should also be in the P3Dv4 compatibility announcement.

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