E6B Flight Computer

Live app: thekayrasari.github.io/e6b · Source on GitHub

Abstract

The E6B is the circular slide rule pilots have used for pre-flight planning since the 1940s. This project is a full-featured digital implementation built in vanilla JavaScript, replicating both sides of the physical device: the wind side for heading and groundspeed calculations, and the calculator side for time/speed/distance, fuel, airspeed, altitude, crosswind, and unit conversions.

The entire application is a single self-contained index.html file — no framework, no build step, no dependencies. A Canvas 2D wind vector diagram renders the triangle of velocities in real time as inputs change.

How It Works

The app is split into two panels mirroring the physical E6B.

Wind Side computes the wind correction angle (WCA), true heading, and groundspeed using vector resolution. Inputs are true course, TAS, wind direction, and wind speed. A live canvas diagram draws the full velocity triangle — true course, TAS vector, wind vector, and groundspeed resultant — updating on every keystroke. Magnetic and compass headings are derived by applying variation and deviation on top of the true heading result.

Calculator Side is a tabbed panel with seven modules:

• TSD — solves for any one of time, speed, or distance given the other two
• Fuel — computes endurance, fuel required, and reserve from flow rate and onboard quantity
• TAS — converts CAS to true airspeed via density altitude, also outputs Mach number and ISA deviation
• Altitude — derives pressure altitude and density altitude from indicated altitude, QNH, and OAT
• Crosswind — resolves headwind and crosswind components for a given runway heading
• TOD — calculates top-of-descent distance for a standard 3° profile
• Units — converts between nm/sm/km, kg/lbs, litres/US gal/Imp gal, °C/°F, hPa/inHg, ft/m

Key Equations

Wind Correction Angle

WCA = arcsin( Vw × sin(θ) / TAS )
GS  = TAS × cos(WCA) − Vw × cos(θ)
TH  = TC ± WCA
MH  = TH ∓ Variation
CH  = MH ∓ Deviation

where θ is the wind angle relative to the true course.

True Airspeed

ISA_dev  = OAT − (15 − 1.98 × PA/1000)
Dens_alt = PA + 120 × ISA_dev
ρ/ρ₀     = (1 − 6.8756×10⁻⁶ × DA)^4.2559
TAS      = CAS / √(ρ/ρ₀)
Mach     = TAS / (661.47 × √((OAT + 273.15) / 288.15))

Top of Descent (3° descent path, geometry only)

TOD_nm = ΔAlt / (tan(3°) × 6076 ft/nm) ≈ ΔAlt / 318.5

GS affects the time to descend, not the distance; the distance is purely geometric.

Implementation

The project is a single index.html file — no npm, no bundler, no runtime dependencies. The wind vector diagram is drawn with the Canvas 2D API. Each calculator module is a self-contained block of DOM update logic with no shared state; modules read directly from input values and write results into output containers via innerHTML.

e6b/
├── index.html   ← all calculation logic, UI, styles, and canvas rendering
└── LICENSE

Calculation functions are pure — they take numbers, return numbers, and have no DOM side effects. The canvas respects dark/light theming by reading CSS custom properties via getComputedStyle on every redraw.

Stack: HTML5 · CSS custom properties · Vanilla JS · Canvas 2D API · GitHub Pages

Parameters & Ranges

Disclaimer

NOT FOR NAVIGATIONAL USE. All outputs must be verified with official charts and certified avionics before flight.

Citation

@software{sari2026e6b,
    author  = {Kayra Sarı},
    year    = {2026},
    title   = {E6B Flight Computer},
    url     = {https://github.com/thekayrasari/e6b},
    license = {MIT}
}