FluidForces causes certain assemblies with Seats to get flung when a player enters them

Bug Reports Engine Bugs
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#1

This was encountered in Waste of Space [ALPHA] - Roblox

Reproduction steps:

  • Create a new Baseplate
  • Set the FluidForces option to Experimental
  • Insert the reproduction model: FluidPhysicsBug.rbxm (8.4 KB)
  • Hit play. Entering the seat will cause the entire assembly to be flung at an enormous velocity
  • Disabling FluidForces and trying again does not result in this issue occurring

Sizing the part titled Iron at or below somewhere around 50 studs does not cause the issue. Sizing it to 60 studs instantly causes physics & the camera to break.

I am not sure what specific conditions replicate this problem, but, it only seems to happen with assemblies that are particularly long.

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#2

Hello, thanks for your bug report.! Your reproducer is very helpful.

We have found that aerodynamics can be unstable for some long, narrow, parts. For example, in your repro model you can delete the seat, EnableFluidForces on the long thin part (Iron) and hit run in studio and you’ll see it behave strangely. In your reproducer, sitting in the seat with an aero enabled avatar triggers also this behavior.

We have opened a ticket for this issue and will let you know when we have figured out a mitigation.

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