HoldDown

[jonsberndt]

Some years ago I believe there was a HoldDown parameter in FGAircraft.cpp - at least there was in my local source tree. Anyone know if this was removed at some point? There was an associated property, "hold-down". I might not have actually ever submitted that change.

[seanmcleod]

It's in the current source, e.g.

jsbsim/src/FGFDMExec.cpp

Line 166 in 5530ed2

instance->Tie("forces/hold-down", this, &FGFDMExec::GetHoldDown, &FGFDMExec::SetHoldDown);

[jonsberndt]

Interesting. The implementation is different. In 2007 it was in FGAircraft. I can't remember if I changed that myself or someone else. LoL. Oh well, that it is still there is the important thing. I need it. :-)

[seanmcleod]

There are a couple of scripts in the current repo that make use of it and @bcoconni also developed a test for it.

https://github.com/JSBSim-Team/jsbsim/search?q=hold-down

[bcoconni]

@jonsberndt

Some years ago I believe there was a HoldDown parameter in FGAircraft.cpp - at least there was in my local source tree. Anyone know if this was removed at some point? There was an associated property, "hold-down". I might not have actually ever submitted that change.

You did 😄. It is just that I moved the feature first to FGAccelerations (commit 6ce8a7e) and then to FGFDMExec (commit 2bf0140). If my memory serves me well, I have moved the HoldDown feature first to FGAccelerations because the purpose of the feature is really to nullify accelerations, not filtering out some forces. This first change gave more stable results which allowed the vehicle to remain motionless for a longer time when forces/hold-down was set to true. The second change has been implemented because you can still have non zero velocities even when accelerations are zero. Obviously the point of holding down a vehicle is to force both velocities and accelerations to be zero which implies some coordination between FGAccelerationsand FGPropagate. As a result FGFDMExec seemed a better place to manage the feature.

[jonsberndt]

That sounds good. When I saw the change I understood why it was made. :-) A lot of my ideas over the years have been "half baked". Glad there are people on the team that can finish the "baking". :-D

[bcoconni]

As sir Isaac Newton (sort of) said : "If we have hacked further it is by standing on the shoulders of Giants."

[bcoconni]

I have migrated this topic to "Discussions" just to try the feature 😄
Let me know what you think.