How to use this site

Two ways in

• Learning a topic? Start at the top of a page and read down. Every topic is written in the same order, so once you have read one you know where everything is in the rest.
• Need a number or a tool? Press / or Ctrl+K to search, or jump straight to the calculator from the page’s table of contents.

Finding your way

• The mission rail (left; the ☰ menu on a phone) lists every one of the 64 zones in workflow order, grouped into eight phases, each with its own colour. Bright entries are rebuilt v2 pages. Entries tagged v1 open the original reference directly at that zone, so nothing is ever missing.
• The orbit map at the top of the rail shows the eight phases as planets, with the zone you are on in the sun. Select a planet to jump to that phase in the list.
• The zone banner at the top of each page tells you where you are — PHASE 3 OF 8 · SIZE · STEP 5 OF 10 · Z25 — with a dot for every zone in the phase (filled = v2, dashed = v1) and PREV / NEXT through the rebuilt pages. The same route continues at the foot of every page.
• Zone numbers match REF·DB v1 exactly, so a number on an old note still points at the same topic. Primer pages such as How a solid motor works are marked P and don’t take a number.
• MODE switches between the dark mission view (default) and a light drawing-office view. PAUSE MOTION stops the background and every animation; it remembers your choice, and your system’s reduced-motion setting is always obeyed.

How every topic page is laid out

1. At a glance — the idea in one line and what to read first.
2. Why it matters — what goes wrong on real hardware if you get this wrong.
3. Intuition — an everyday analogy (the blue Think of it like… boxes) and a diagram.
4. The physics — the equations, each one explained in words.
5. The tool — an interactive calculator built on the same equations. Copy link shares your exact inputs.
6. Worked example — the tool’s answer done by hand, step by step, so you can check both.
7. Where this stops — the limits of the method and the traps experienced engineers watch for.
8. On the drawing — how the result is specified and verified.
9. References — open literature and the standards that govern the real design.

Reading the numbers

• Units. SI throughout: MPa, mm, kg, °C. Pressures can be shown in bar or psi where it helps.
• Margin of safety. $MS = \dfrac{\text{allowable}}{\text{applied}} - 1$. Zero means exactly at the limit; negative means it fails the requirement.
• Material data is typical or minimum published data for early design, shared with REF·DB v1. Fracture toughness ($K_{IC}$) varies strongly with heat treatment, orientation, thickness and temperature, and is always flagged as indicative.

Screening values, not design allowables

Everything here is for learning and early sizing. Before anything is built, verify against the current issue of the governing standard, your organisation’s design rules, and approved allowables, and get the analysis signed off by the responsible authority.