[support] delta v calculation wrong with clustered engines

[JeyJeyKing]

KSP Version: v1.7.3 Windows 64-bit

What Happens: The delta v does not seem to work properly when using multiple engines on the engine plates. See the following screenshots.

The first one shows a minimal craft with an engine plate and just one engine. Note from the fuel flow overlay, that the radial decouplers have crossfeed enabled so the second stage has fuel and thus delta v left after the radial tanks are drained and detached. This is reflected in the delta v values.

In the second image we just add a second engine and it breaks.

Mods / Add-Ons: All Stock

Steps to Replicate:

1) Make a hecs probe core, a rockomax 16 tank below it, two radial decouplers with rockomax 16 tanks and crossfeed enabled. Attach an engine plate to the central tank, set the number of attach nodes to two. Add two swivel engines

2) Put the engine plate and engines in the first stage (1) and the radial decouplers in the second stage (0).

Result: Delta v calculation is wrong. Second stage should have delta v but calculator shows none.

Fixes/Workarounds:

- Do the maths myself.  

- Use heavier, more expensive, and less kerbal rockets without radial tanks.  

Other Notes/Pictures/Log Files:

- The engine plates do not seem to be the problem. The same issue occurs with older structural parts or even engines that can be clustered directly on the tank.

- Images Link: https://imgur.com/a/7cpycwv

- Craft file: https://pastebin.com/iXyBVrts

Edited September 23, 2019 by JeyJeyKing

[OHara]

Yes, I see the same problem with a 'bicoupler' engine mount instead of the parts from Making History.

Someone else has reported this as a bug here, https://bugs.kerbalspaceprogram.com/issues/20740, but your example is easier to understand, so I attached it to that bug.

I don't know of any workarounds, either, but the mods that compute delta-V (Basic Delta-V, Kerbal Engineering Redux) get this right.