Thank you so very much for scanning through my upload. I am trying to follow the SDK as closely as possible, without creating another GaugeAircraft, or Cabri G2. I think it is probably ok that a node is named "ELEVATOR," because the term "node" corresponds to the invisible helper, which is the part we animate, so the model part becomes animated by linking it to the invisible helper. In the image below, you can see the node name "Elevator," is used to create the "elevator_percent_key" animation.
I've composed a screen capture of my test project loaded alongside the GaugeAircraft sample and I've noticed two discrepancies.
The first is that the default layer is not set "visible" in the GaugeAircraft Layer Hierarchy, as opposed to the test model, which probably doesn't matter, however, in the Babylon Animation Groups flyout (the white and blue pane), the Babylon animation hierarchy for GaugeAircraft, starts and ends at "skel_Elevator," while my test model Babylon animation hierarchy includes the base helper "HIPS," as well as the model part. I'm pretty sure "skel_Elevator," is the invisible node helper, I think it's probably ok my invisible helper is named "Elevator," so long as the animation that is derived from it, is "elevator_percent_key," as you suggest.
I'll make some changes and report back, I'm highly suspecting the botched hierarchy in the animation groups window, because my propeller animations are also frozen, there is no "propeller_percent" variable, but the hierarchy discrepancies are likely shared by the propeller animations. I likely would not have noticed this, if not for your reply, so thank you again, Federico.