Non-zero drag forces on vessels with no aerodynamic drag elements specified

[ThChicken]

When enabling atmospheric wind effects under Physics settings in Orbiter 2024, simple vessels with no drag elements defined (no airfoils, no set_cw, no variable drag elements etc.) still experience a significant drag force when not landed.

This was observed in the following context:

https://www.orbiter-forum.com/threads/the-battle-for-a-flag.42168/#post-627612

This was observed with a Lua script vessel. I cannot replicate this with an API vessel as I do not have a means to compile a module, and to my knowledge there are no default Orbiter vessels that do not have drag elements applied. I do not know if it is an Orbiter 2024 issue globally or with Lua only.

EDIT: The observed drag can apparently be removed by explicitly setting the wind coefficients to 0:

vi:set_cw({x=0,y=0,z=0,zn=0})

But there is nothing in the documentation for set_cw() indicating that there is some non-zero default setting.

[GLS-SSV]

I'm not sure this is described somewhere, but I'm pretty sure Orbiter gives some default aero values to the vessels, based on their Size parameter. Otherwise the vessels would be "imune" to an atmosphere.

IMO, vessels should not be imune to the atmosphere, as it is not realistic.

[ThChicken]

I'm not sure this is described somewhere, but I'm pretty sure Orbiter gives some default aero values to the vessels, based on their Size parameter. Otherwise the vessels would be "imune" to an atmosphere.

IMO, vessels should not be imune to the atmosphere, as it is not realistic.

I disagree with this. If I make an add on with no drag elements, I expect no drag, realistic or not. The add on I was making where I discovered this really needed to have no drag. Having a mystery default behavior coding for you is maddening.

At very, very least, this default behavior should be documented (if it is in fact the default behavior) and it should also be made clear that it needs to be explicitly shut off with set_cw() all set to 0.

These sorts of things are aggravations to folks who may be new at add on making and who are actually doing their due diligence and read the documentation to make an add-on.

[ThChicken]

I re-titled this issue as it is not an issue with the atmospheric wind effect model.

After further digging (documented in the Orbiter thread linked in my original issue post) it seems that if you do not use SetCW() to zero out the wind coefficients and do not specify cross sectional areas with SetCrossSections(), Orbiter will assume that the vessel is an object with projected cross sectional areas of 10 m2 in the x,y, and z directions, and wind coefficients {x=0.3, y=0.3, z=0.1, zn=0.3} and calculate drag forces based on these values.

At a minimum I would suggest putting words to this effect in the documentation for SetCW() and set_cw() for Lua, and perhaps crosslink it with the documentation for SetCrosssections() / set_crosssections().