Saturday, June 4, 2011

Airport Runways, direction of flight, direction of wind

Pattern traffic: treat it as a rectangle
A -------------------------------B

C -----------Runway-------------D

E -------------------------------F

C, and D are named with 2 digit numbers. In fact, they are directional number: 30 for 300 degrees; 15 for 150.

The difference between C and D is 18, since they are opposite, 180 degrees apart.

In major airports, you see parallel runaways--one for landing, one for takeoff. For instance, SFO got 28L and 28R (opposite ends being 10R and 10L). You also happen to see another perpendicular runway-At SFO, you see two perpendicular runways 19L and 19R (opposite ends being 1R and 1L).

When the airplane is in the air, it’s relatively simple to calculate the effects of it. But what if the aircraft is near the ground? We first consider the take-off and then look at the landing.

During take-off the aircraft needs to reach the lift-off speed Vlof to be able to lift off from the ground. This speed is measured with respect to the wind. The speed of the aircraft is, however, measured with respect to the ground. So there is a difference. Let’s suppose Vlof = 100kts. If there is a headwind of 20kts, then the aircraft only needs to have a velocity of V = 80kts with respect to the ground to take off. If, however, the wind comes from the back of the aircraft, it needs a velocity of V = 120kts. So if you take off with headwind, you need a much lower velocity, and thus a much shorter runway. Therefore its preferable to take off with headwinds.

The situation is virtually the same for landings. If you land with headwinds, you have a much lower velocity with respect to the ground, and therefore it’s much easier to come to a full stop. If you land with the wind blowing in your back, then you need a much greater distance to come to a complete stop.


The other intuitive way: the more headwind there is, the easy it is take off. Propeller blades, for instance, can make use of more wind coming towards it.

Names for runway pattern:

LP: left pattern; RP: right pattern

Upwind (Take off)
Left or Right Crosswind
Left or Right Downwind
Left or Right Base
Final (Landing)


Left quartering headwind
right quartering headwind
cross wind (3 o' clock) btw o' = contraction of 'of the'
right quartering tailwind
left quartering tailwind
cross wind 9 o' clock
Headwind, tailwind

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