Section 4.1 Runway Orientation - Following the Wind

Exam Alert: 🔥🔥🔥 EXTREMELY HIGH - Wind rose numericals are practically guaranteed. This is free marks if you get the concept!

The Core Idea (Visualize This!)¶

Picture yourself trying to throw a paper airplane. Would you throw it:

INTO the wind? (It flies farther, takes off quicker)
WITH the wind? (It crashes faster, needs more space)

Obviously INTO the wind, right? That's literally the ENTIRE concept of runway orientation. You want planes taking off and landing INTO the wind (called headwind - wind hitting the front of the plane).

Why headwind is magic:

Taking off: Wind under wings = more lift = plane goes "wheee!" and lifts off sooner = shorter runway needed
Landing: Wind resistance = natural braking = plane stops faster = shorter runway needed

So the whole game is: Point the runway in the direction the wind usually comes FROM.

The Problem: Wind is Moody¶

Wind doesn't blow from ONE direction all year. Sometimes north, sometimes south, sometimes it takes a vacation (calm period - when wind is basically sleeping, below 6 km/h).

So how do we decide which direction to build the runway?

Enter the Wind Rose Diagram - basically a fancy graph that shows "Hey, wind blows from THIS direction for THIS much time in a year."

Wind Rose Type I: The Simple One (Direction + Duration)¶

What it shows: Just TWO things - which direction wind comes from, and how often (percentage of time).

Think of it like a weird flower where:

The petals point in compass directions (N, NE, E, SE, S, SW, W, NW - 8 main directions covering 360°)
The length of each petal = how much time wind blows from that direction
Each direction covers 22.5 degrees (360° ÷ 16 directions = 22.5°)

How to Make It (Super Easy):¶

Step 1: Get wind data table (they'll give you this - just percentages for each direction)

Step 2: Draw concentric circles (circles inside circles) with compass directions marked

Step 3: Plot the percentage along each direction as a point

Step 4: Connect all the points with straight lines

Step 5: THE LONGEST LINE = BEST RUNWAY DIRECTION!

Memory Trick - "LONGEST LINE WINS" * Function: Wind blows strongest/most often along longest line * Visualization: Imagine wind "pushing" the line outward - bigger push = more wind = that's where you want your runway

The Calculation Game:¶

Once you pick the best direction (say North-South), you add up coverage:

Coverage = All nearby directions + Calm period

For N-S runway: Add up (NNW + N + NNE + SSE + S + SSW) + calm period

The rule: You need minimum 95% coverage to call the runway useful. If you get less, you need a second runway!

Why 95%? Because airports need to work almost all the time. If your runway is useless 10% of the year, airlines will be mad.

Wind Rose Type II: The Fancy One (Direction + Duration + Intensity)¶

What's different: Now we ALSO care about wind SPEED, not just direction and time.

Why it matters: Remember, winds below 6 km/h don't affect anything (calm period - wind too lazy to matter). We only care about winds above 6 km/h.

Type II breaks wind into speed categories: * 6-25 km/h (gentle - plotted inner) * 25-40 km/h (moderate - plotted middle)
40-60 km/h* (strong - plotted outer)

Think of it like: Three flowers nested inside each other, each showing a different wind speed range.

The Critical Concept: Crosswind Component¶

Crosswind = wind blowing ACROSS the runway (perpendicular, hitting the plane from the side)

Imagine landing a plane while wind pushes it sideways - SCARY! Pilots hate this.

The Rule: Crosswind component must stay under 37 km/h (for big planes) or operations become unsafe.

How Type II helps: You can see if stronger winds (outer circles) come from directions that would create bad crosswinds. If yes, maybe rotate runway slightly.

The Template Trick (Exam Hack!)¶

They give you a transparent template - basically a protractor-like thing with: * Two parallel lines (representing runway edges) * Markings showing 22.5° on each side (total 45° coverage zone)

How to use it: 1. Place template center on wind rose center 2. Rotate it until you capture MAXIMUM area of the wind rose between the parallel lines 3. That orientation = best runway direction!

Why 22.5° each side? Because planes can handle wind coming at an angle UP TO 22.5° from runway direction without excessive crosswind. Beyond that = dangerous.

The Second Runway Decision¶

When do you need it? When first runway gives less than 95% coverage.

How to pick direction? Find the SECOND longest line on wind rose (the runner-up direction).

Important: Don't double-count! If first runway was N-S and covered N, NNE, NNW, S, SSE, SSW... the second runway (say E-W) can ONLY add E, ENE, ESE, W, WNW, WSW to total coverage.

Memory trick - "NO DOUBLE DIPPING" * Like getting ice cream: You already counted vanilla (N-S directions), now you can only add chocolate (E-W directions) to your total.

Changes to "Perfect" Orientation¶

Sometimes you pick the best direction from wind rose, but then reality hits:

1. Noise Nuisance¶

If your perfect runway aims straight at a residential area (places where people live and sleep): * Rotate slightly to avoid it * Why? Planes are LOUD, especially during takeoff. People will protest, sue, or worse - airport gets banned from night operations.

2. Excessive Grading¶

Grading = cutting and filling earth to make the runway surface level.

If your perfect direction goes up/down a mountain: * Costs go CRAZY (moving millions of tons of soil) * Rotate to flatter area even if wind coverage drops slightly * Rule: If slope exceeds 1%, you'll need insane earthwork (soil moving operations)

3. Obstruction¶

If your perfect direction has: * Tall buildings in approach zone (the area where planes descend) * Mountains * Transmission towers (tall metal structures carrying electricity)

Then orientation MUST change. Safety beats wind coverage every time.

Priority: Obstruction-free > Noise-free > Cheap grading > Perfect wind

Exam Strategy (Free Marks Blueprint):¶

For Theory Questions:¶

Just remember the FUNCTION: "We want headwind because it helps planes take off shorter and land safer. Wind rose shows us which direction wind blows most often. Longest line = best runway direction. Need 95% coverage or add second runway."

Then elaborate with: * Headwind benefits (2-3 sentences) * How wind rose is plotted (3-4 steps) * Coverage calculation (add nearby directions + calm) * Second runway logic (if first < 95%)

For Numerical Problems:¶

They're giving you FREE MARKS. Seriously, these problems are just:

Type 1: Add numbers from table → Plot on circles → Find longest line → Add percentages

Type 2: Same but also calculate calm period (100% - total of all winds above 6 km/h)

The formula that always works:

Total Coverage = (Sum of directions along chosen runway) + Calm Period
If Total Coverage < 95% → Design second runway
Second runway coverage = New directions only (don't double count)

Common Trap: Forgetting to add calm period! It's free percentage points.

Memory Anchor - "PILOT WANTS HEADWIND" (Function-based)¶

Visualize: A pilot in cockpit, wind hitting face, smiling because: * Plane lifts off Perfectly (shorter takeoff) * Increased lift on wings * Landing becomes Lighter (natural braking) * Orientation follows wind * Takes Wind rose's Longest line

Everything flows from function: Headwind good → Point runway toward wind source → Need wind data → Wind rose shows it → Pick longest line → Calculate coverage → If low, add second runway → Reality checks (noise, grading, obstacles) may adjust

Quick Reference (Screenshot This):¶

Concept	Simple Truth
Runway Orientation	Point where wind comes FROM most often
Headwind	Wind hitting plane's front = GOOD
Crosswind	Wind hitting plane's side = BAD (max 37 km/h)
Wind Rose Type I	Direction + Duration only
Wind Rose Type II	Direction + Duration + Intensity
Calm Period	Wind < 6 km/h (doesn't matter)
Coverage Needed	95% minimum
Best Direction	Longest line on wind rose
Second Runway	Second longest line, only if first < 95%
Template Use	Capture max area within 45° (22.5° each side)

Bottom Line: This topic LOOKS scary with all the circles and percentages, but it's literally just "find which direction has the longest line, add up the numbers, check if ≥95%." That's it. The rest is just explanation of WHY (headwind good) and WHEN to adjust (noise, obstacles, cost).

Master this, and you're looking at easy 13 marks! 🎯