Wind-adjusted fuel burn ±20% + refuel-for-flight buys 150% margin (ISS-070, ISS-071, v0.36.0)

lib/sim/movement.test.ts

@@ -10,6 +10,7 @@ import {
   progressAt,
   requiredFuelFor,
   travelDurationMs,
+  windBurnFactor,
 } from './movement';
 
 // Synthetic in-flight fixtures — no DB needed: everything is a pure function of
@@ -166,6 +167,53 @@ describe('weighted burn model (v0.16.0)', () => {
   });
 });
 
+describe('windBurnFactor (v0.36.0, ISS-070)', () => {
+  it('full headwind at max wind is exactly +20%', () => {
+    // bearing == windDirDeg: the wind blows straight from ahead.
+    expect(windBurnFactor(30, 90, 90)).toBe(1.2);
+  });
+
+  it('full tailwind at max wind is exactly −20%', () => {
+    // windDirDeg = bearing + 180 (mod 360): the wind blows from behind.
+    expect(windBurnFactor(30, 270, 90)).toBe(0.8);
+  });
+
+  it('a pure crosswind (90° off) leaves burn unchanged', () => {
+    expect(windBurnFactor(30, 0, 90)).toBeCloseTo(1, 9);
+    expect(windBurnFactor(30, 180, 90)).toBeCloseTo(1, 9);
+  });
+
+  it('small wind stays near 1', () => {
+    const f = windBurnFactor(2, 45, 45); // worst case: full headwind at min wind
+    expect(f).toBeGreaterThan(1.01);
+    expect(f).toBeLessThan(1.02);
+  });
+
+  it('stays within [0.8, 1.2] for the whole weather range', () => {
+    for (const kt of [2, 15, 30]) {
+      for (const off of [0, 45, 90, 135, 180, 270, 315]) {
+        const f = windBurnFactor(kt, 100, (100 + off) % 360);
+        expect(f).toBeGreaterThanOrEqual(0.8 - 1e-12);
+        expect(f).toBeLessThanOrEqual(1.2 + 1e-12);
+      }
+    }
+  });
+
+  it('applied as burnPerKm × f, requiredFuelFor and fuelAtWeighted scale accordingly (pinned)', () => {
+    // Fixed inputs: ATR numbers, 1000 km leg / half of the FRA→MAD leg.
+    expect(requiredFuelFor(BURN * 1.2, WE, TANK, 1_000)).toBeCloseTo(1444.911589, 6);
+    expect(requiredFuelFor(BURN * 0.8, WE, TANK, 1_000)).toBeCloseTo(944.348095, 6);
+    expect(fuelAtWeighted(TANK, BURN * 1.2, WE, TANK, KM, 0.5)).toBeCloseTo(4867.313136, 6);
+    expect(fuelAtWeighted(TANK, BURN * 0.8, WE, TANK, KM, 0.5)).toBeCloseTo(5331.677856, 6);
+
+    // Headwind always costs more than tailwind over the same leg…
+    expect(requiredFuelFor(BURN * 1.2, WE, TANK, KM)).toBeGreaterThan(requiredFuelFor(BURN * 0.8, WE, TANK, KM));
+    expect(fuelAtWeighted(TANK, BURN * 1.2, WE, TANK, KM, 1)).toBeLessThan(fuelAtWeighted(TANK, BURN * 0.8, WE, TANK, KM, 1));
+    // …and a neutral factor (f = 1) reproduces the unadjusted model exactly.
+    expect(requiredFuelFor(BURN * windBurnFactor(30, 0, 90), WE, TANK, KM)).toBeCloseTo(requiredFuelFor(BURN, WE, TANK, KM), 9);
+  });
+});
+
 describe('maxRangeKm (v0.28.0)', () => {
   it('ATR 72-600 full tank ≈ 4439 km (±5%)', () => {
     const r = maxRangeKm(BURN, WE, TANK);