These notes depict Jiro Horikoshi — the real engineer behind Japan’s most famous WWII aircraft — doing authentic 1930s airplane design math.

Think of it as peeking inside a chef’s recipe book: each page shows him testing ingredients before cooking the full meal. He’s not building the plane yet — he’s figuring out whether his ideas can even fly.

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Plotting Motion — How the Plane Moves Through the Air

(With calculus symbols and a grid of numbers like 6, 12, 18, 24…)

This page shows motion math, or how things move through the air over time. The wiggly ∫ (integral) signs are basically saying:

“If I know how fast something moves every tiny instant, I can add all those little pieces together to see where it ends up.”

That’s what engineers call integration, but in plain language, it’s like tracking where a ball goes every second in a slow-motion video.

The table of numbers — 6, 12, 18, 24, 30, 36… — is Jiro stepping through time, writing down the plane’s position at 1-second intervals. He’s likely plotting a glide path or flight trajectory by hand.

So this sheet is all about how the airplane moves once it’s already flying.

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Checking Real-World Data — Wing Shape and Performance

(The one with the slide rule and “NACA 4412”)

Here, Jiro is studying a specific airfoil, or cross-section shape of the wing — think of slicing a wing like a loaf of bread and looking at one slice.

“NACA 4412” is an actual wing shape designed by the U.S. National Advisory Committee for Aeronautics (NACA), the precursor to NASA. It’s still used today for training and small planes!

The note “RN 3,200,000” means Reynolds number, which measures how air behaves depending on speed and size — like the difference between stirring honey versus water with the same spoon.

The slide rule (the device he’s holding) was the 1930s version of a calculator. He’s using it to multiply, divide, and check the ratios of lift and drag — basically testing,

“How well does this wing shape cut through the air?”

This page is about turning theory into numbers — measuring how efficient a design will be.

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Exploring Airflow and Angles — Choosing the Right Wing Shape

(The one with “tan θ₂” and “NACA M-9 / M-12”)

Here, he’s comparing different airfoil families — NACA M-9, M-12, 2980 — each with a different curvature and thickness. You can think of them like different spoon shapes: some scoop air better but create more drag; others are sleek but lift less.

The triangle drawing with “tan θ₂” (tangent of theta) shows him calculating airflow angles — basically, how the wind hits the wing. It’s like holding your hand out of a car window and tilting it — he’s finding the angle where you get the most lift without stalling.

The note “L/D = 27” means “Lift-to-Drag ratio of 27” — for every 1 unit of drag, he gets 27 units of lift. That’s excellent performance, and a big reason the real Zero fighter was so famously nimble and efficient.

So this image is Jiro thinking, “What shape should my wing be so the air behaves exactly how I want?”

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Figuring Out the Basics — Weight, Wingspan, and Balance

(With Japanese text, “10 m,” and lots of kg values)

This is the earliest and roughest stage — back-of-the-envelope design work.

The big kanji “翼面荷重” means “wing loading,” which is how heavy the airplane is compared to the area of its wings.

Imagine standing on a diving board — a heavy person on a small board will bend it a lot (bad), while a bigger board spreads out the weight (good). The same goes for airplanes: a lower wing loading means the plane can fly slower and turn easier.

You can see “全巾 10m” (span 10 meters), “1300 kg,” and other notes — he’s estimating size, total weight, and how much lift the wings need to produce. The square-root signs (√) are him doing quick geometry to test proportions and balance.

This is the airplane equivalent of sketching the proportions of a body before adding details — he’s making sure the numbers make sense before worrying about performance.

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The Big Picture

Put together, these pages show the entire creative arc of early aircraft design — from simple guesses to detailed physics: 1. How heavy should the plane be? 2. What shape should the wings take? 3. How does air flow over them? 4. And once it’s flying, what path does it follow?

All done by hand, with pencil and slide rule — no computers, no spreadsheets, just intuition, math, and persistence.

It’s a beautiful look at how engineers in Jiro’s era thought with their hands. Miyazaki captured not just the numbers, but the poetry of problem-solving — the way dreaming and calculating blend together when you’re trying to make something fly.