Stance and mast track

Foot position and mast track set where the center of gravity sits relative to front and rear wings — and therefore trim and balance.

Two coordinate systems

flowchart LR
  Board["Board fixed"]
  Straps["Straps on board"]
  Track["Twin-US tracks"]
  Mast["Mast slides"]
  Physics["Physics mast-centred"]
  Board --> Straps
  Board --> Track
  Track --> Mast
  Straps --> Physics
  Mast --> Physics

• Board-fixed: straps and track sit on the board
• Physics: computed in mast coordinates (levers, moments, trim)

Mast track

Shifts the mast axis on the board’s twin US tracks:

Value	Meaning
0 mm	Center of the track box
+ toward tail	nose lighter, feet move forward relative to mast
− toward nose	opposite

Limits come from the board catalog (track_travel_mm).

Independent of advance

Fuselage advance shifts the mast on the rig. Mast track shifts the board relative to the mast axis — two orthogonal degrees of freedom.

Foot position — board mode

With straps from tail (default for catalog pump boards):

• Front foot from tail — smaller value = closer to mast
• Rear foot from tail — must be farther from the tail edge than the front foot

When switching boards, the app applies strap defaults from the catalog when available.

Foot position — mast mode

Alternative input: distances to the mast axis along the board:

• Front foot (+ = toward nose)
• Rear foot (+ = toward nose, − = toward tail)

Switch mode via the advanced controls in the stance group.

What you should see

Shift mast track toward tail (+50 mm):

• Trim and balance may change
• Trim not solvable badge if no equilibrium exists
• Panel A shows shifted foot positions relative to the rig

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