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Gr@y

Multiple engines + decoupler = incorrect DeltaV

Question

Using multiple engines on the stage and a decoupler with fuel transfer on the upper stage breaks DV calculations.

Here is normal DV:

AqOdAHt.png

But everything breaks if we add some engines:

gtrTzGi.png

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Are the drop tanks set to feed fuel into the core tank or is it drawing from all tanks at once? It tends to get confused when it has no way of knowing when drop tanks are supposed to be staged. It's possible that both of those readings are wrong, regardless of engine count. The DV calculator requires very clear staging/fuel drain order to give accurate results.

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Yeah, its really easy to confuse the stock DV calculator.Also Fuel Priorities can mess it up :( .

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12 hours ago, Loskene said:

Are the drop tanks set to feed fuel into the core tank or is it drawing from all tanks at once? It tends to get confused when it has no way of knowing when drop tanks are supposed to be staged. It's possible that both of those readings are wrong, regardless of engine count. The DV calculator requires very clear staging/fuel drain order to give accurate results.

THe difference between two screenshots it just engines number. All other conditions are the same.

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3 minutes ago, Gr@y said:

THe difference between two screenshots it just engines number. All other conditions are the same.

I'm asking what those conditions are because the DV calculator is affected by a large number of inputs. Bring up the fuel priority display so we can see when (the game thinks) the drop tanks are supposed to stage. The only difference I can think of is the number of engines changing the rate of fuel consumption, which might in turn affect when the calc thinks the tanks are supposed to drop and the resultant dry mass values. There's not a lot to go on here and we don't really know what the DV calc's exact order of operations is when figuring this out. Drop tanks always give it problems.

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2 minutes ago, Loskene said:

I'm asking what those conditions are because the DV calculator is affected by a large number of inputs. Bring up the fuel priority display so we can see when (the game thinks) the drop tanks are supposed to stage. The only difference I can think of is the number of engines changing the rate of fuel consumption, which might in turn affect when the calc thinks the tanks are supposed to drop and the resultant dry mass values. There's not a lot to go on here and we don't really know what the DV calc's exact order of operations is when figuring this out. Drop tanks always give it problems.

Nope. Adding an negine just exclude droptank from DV calculations entirely. It's just considered as a ballast.

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2 minutes ago, Gr@y said:

Nope. Adding an negine just exclude droptank from DV calculations entirely. It's just considered as a ballast.

Strange. Crossfeed enabled on the decouplers, yeah? And fuel from all tanks is feeding to all engines in the fuel flow display? If the centre engine is node-attached and the others are surface attached there may be flow problems idk.

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There are multiple posts about this problem its not a fuel flow problem...i think its just a bug...cant calculate all the crossfeeds correctly.

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