Translating a Fortran F-16 Simulator to Unity3D

Original Article ↗ Hacker News Discussion ↗

Unusual and Legacy Units

  • Many commenters latch onto the article’s “UNITS” section, amused and horrified by slugs, US survey feet, and other obscure imperial units.
  • People share additional odd units (e.g., Sami distance by “reindeer pee interval,” humorous and obsolete units, and informal workplace “ED” units), illustrating how messy non-coherent systems can be.
  • Several aerospace engineers note real confusion between pounds-as-mass vs pounds-as-force, especially in flight dynamics.

Nautical Miles, Knots, and Aviation Units

  • Discussion clarifies that the nautical mile historically tied to Earth geometry (minute of latitude), but is now defined exactly as 1852 m by international agreement.
  • Some participants defend knots and nautical miles as natural for navigation; others argue they’re archaic and should be UI-only while internal calculations stay purely metric.
  • There’s mild frustration at mocking knots without acknowledging their historical and practical rationale.

Array Indexing and Language Design

  • Fortran’s arbitrary array lower bounds (-2..9, etc.) are praised as aligning code with math; other languages with similar features (Pascal, Ada, BASIC, Lua, .NET) are mentioned.
  • There’s debate over 0-based vs 1-based vs arbitrary indexing:
    • Some find 0-based “natural” and less error-prone; others recall it being unintuitive to learn.
    • Arbitrary bounds help when indices are domain values (e.g., temperature bands), but Fortran’s modern interactions with them are described as buggy and non-portable.
    • C tricks with pointer offsetting are discussed, with warnings about undefined behavior and poor ergonomics.

Units in Simulation and Unity Integration

  • One camp says only internal consistency matters; units could be entirely fictional as long as ratios hold.
  • Others counter that real units aid intuition, validation, and reuse of real-world data tables, and become critical when mixing engines (original Fortran integrator vs Unity’s physics).
  • Commenters note numerical considerations (choosing units to avoid bad floating-point ranges) and that engines like Unity have an implicit “comfortable” scale.
  • A side thread covers gravity scaling and how practical VFX and simulations sometimes rescale time or constants to get realistic behavior at non-realistic sizes.

Metric vs Customary in the Port

  • Several people argue the port should have converted all formulas and tables to SI once, for clarity and performance.
  • The author explains they deliberately kept the original tables and units to preserve behavior; converting them without explicit unit metadata would be error-prone.
  • Another commenter suggests using unit tests around the translated model to safely migrate to metric later.

Unit Safety and Static Checking

  • Concern is raised about mixing incompatible units (e.g., slugs vs feet) and ensuring variables like altitude stay sensible.
  • Practitioners report that, in aerospace, unit correctness is handled by manual review, validation organizations, tests, and sims, not automated unit-checking tools.
  • Some link to attempts at compile-time unit checking in Fortran and unit-typed libraries in other languages, but note tradeoffs and limited adoption.

Fortran, Readability, and “Formula Code”

  • One commenter argues that verbose, “developer-style” variable names make numerical/engineering code unreadable; compact symbolic notation better mirrors paper formulas and reduces mistakes.
  • Others echo that Fortran’s terse style lets domain experts quickly recognize algorithms, while heavy abstraction layers in modern code can obscure the actual math.
  • There’s a wistful wish for languages or editors that natively support rich 2D formula/matrix notation.

Flight Sim Nostalgia and Related Work

  • The article sparks memories of classic sims like Falcon 3.0/4.0, early hardware math coprocessors, and timing issues as CPUs got faster.
  • People contrast “study sims” (very high fidelity) with more arcade-like flight games, debating how much realism remains fun.
  • Links are shared to other simulator projects (e.g., a Clojure space sim and a FORTRAN-derived spacecraft simulator in C, a JS port of a similar F-16 model).

Coordinate Systems and Axes

  • The post’s joke image about differing X/Y/Z conventions in 3D tools resonates; commenters argue over Y‑up vs Z‑up world coordinates.
  • Some feel maps make X/Y “ground plane” and Z “up” inevitable; others note that 2D screen heritage makes Y‑up equally defensible, even if disorienting to some.