FEAT/Rail Button Bending Moments

[Monta120]

Pull request type

• Code changes (bugfix, features)

Checklist

• Tests for the changes have been added (if needed)
• Docs have been reviewed and added / updated
• Lint (black rocketpy/ tests/) has passed locally
• All tests (pytest tests -m slow --runslow) have passed locally
• CHANGELOG.md has been updated (if relevant)

Current behavior

Flight class calculates rail button normal and shear forces during launch phase but does not compute bending moments at attachment points. This data is needed for structural analysis of airframe and fasteners. See #893.

New behavior

Adds bending moment calculation using beam theory:

New Flight attributes:

• rail_button1_bending_moment (Function): Upper button bending moment (N⋅m)
• max_rail_button1_bending_moment (float): Max absolute upper moment
• rail_button2_bending_moment (Function): Lower button bending moment (N⋅m)
• max_rail_button2_bending_moment (float): Max absolute lower moment

Formula: M = N × d_CM + S × h_button where:

• N: Normal reaction force, d_CM: distance to center of dry mass
• S: Shear force, h_button: button height (cantilever moment)

Unit tests verify non-zero moments with off-axis forces and zero otherwise. Updated Flight.rst docs and CHANGELOG.md.

Breaking change

• No

Additional information

• Resolves ENH: Calculate Bending Moments on Rail Buttons #893
• Added button_height attribute to RailButtons class (default: None) for cantilever moment calculation (S × h)
• Unit tests cover zero/non-zero moments and serialization roundtrip

[Monta120]

@Gui-FernandesBR Apologies for PR #900. It accidentally included unrelated commits. I have since closed it.

Regarding your rail button height concern: I've added a button_height attribute to the RailButtons class (default 0.015m) to account for the cantilever moment from shear forces. The bending moment calculation now uses M = N × d_CM + S × h_button. The implementation assumes simple supports (no moment reaction at rail contact) and uses beam theory with the already-calculated normal/shear forces.

[Gui-FernandesBR]

Would you mind updataing flight_plots and/or flight_prints too? including these values to the .info() or .all_info() outputs would be key here.

[Gui-FernandesBR]

The implementation assumes simple supports (no moment reaction at rail contact) and uses beam theory with the already-calculated normal/shear forces.

@Monta120 did you left any comment about this in the code? Ensure users can read about your assumptions or any simplification.

[Monta120]

The implementation assumes simple supports (no moment reaction at rail contact) and uses beam theory with the already-calculated normal/shear forces.

@Monta120 did you left any comment about this in the code? Ensure users can read about your assumptions or any simplification.

Just added detailed comments in the docstring explaining the simple support assumption (no moment reaction at rail contact), beam theory approach, and both moment contributions (normal force × distance + shear force × height). Also documented and explained in Flight.rst.

[codecov]

Codecov Report

❌ Patch coverage is 98.63014% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.77%. Comparing base (9cf3dd4) to head (679b63b).
⚠️ Report is 15 commits behind head on develop.

Files with missing lines	Patch %	Lines
rocketpy/simulation/flight.py	97.50%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #901      +/-   ##
===========================================
+ Coverage    80.27%   80.77%   +0.50%     
===========================================
  Files          104      107       +3     
  Lines        12769    13374     +605     
===========================================
+ Hits         10250    10803     +553     
- Misses        2519     2571      +52     

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[Monta120]

Would you mind updataing flight_plots and/or flight_prints too? including these values to the .info() or .all_info() outputs would be key here.

This is also taken care of as of the last commit.