Hacker News Reader

Comment by carapace | Hacker News Reader

Kind of a non sequitur, but I once found a flyer on the sidewalk in Boulder CO that advocated for inclining airplane runways by, I forget, 5% or so.

The idea was that departing flights would take off in the downward-sloping direction, gaining boost to momentum from gravity, while incoming flights would land uphill making it easier to brake.

I have no idea if this would actually work, but the idea has stuck with me.

View on HN

Some runways in mountainous areas are built this way out of necessity. The best known is this one:

https://en.wikipedia.org/wiki/Courchevel_Altiport

https://www.youtube.com/results?search_query=Courchevel+Alti...

It makes for some really dramatic landings. Upon touchdown you have to apply full power, or you might not make it to the top of the runway. Also, there is no go-around. You either land successfully, or you crash. There is no third option.

The take-off is quite a ride too.

https://www.youtube.com/watch?v=c6Wr3ilAWpo

Ditto for Lukla Airport: https://en.wikipedia.org/wiki/Tenzing%E2%80%93Hillary_Airpor...

Just to add to the fun it's at 2,845m too. Take off seems to be not some much about lift, but rather not falling too much when you drop off the end of the runway. It's an experience.

It's not mentioned in the Wikipedia article, but the opening scene of Goldeneye was filmed there.

Most people fly into Chambery airport and get a coach. Mainly just the oligarchs that use the altiport. :)

Runways are aligned with the prevailing winds in the area, such that aircraft can land along either direction depending on the wind. The uphill/downhill slope thing would require twice as many runways per airport lest pilots be stuck trying to take off uphill into the wind.

It might be a disadvantage to take off uphill, but I believe that it's desirable to take off into a head wind.

The wind generates some of the lift required for take off, and by taking off sooner there is more runway available in case you need to make an emergency landing.

> It might be a disadvantage to take off uphill, but I believe that it's desirable to take off into a head wind.

Both takeoff and landing are safer and more efficient in headwind, since lift is a function of airspeed an increase in airspeed (from headwinds) a larger margin or security or lower groundspeed in both situations.

GP's point is if your runways are slanted (rather than flat), instead of having both takeoff and landing use the same runway in the same direction (headwinds) you now need a runway slanting into the headwind (for takeoffs) and one slanting away from it (for landings).

Ah, I misunderstood. Thanks for explaining.

But what about a runway where the wind almost never changes direction? I imagine LAX is like that, being perpendicular to the coast.

I don't know about other coastal areas, but the winds in SoCal will frequently blow either from the water or to the water due to other meteorological factors: https://en.wikipedia.org/wiki/Santa_Ana_winds

At hundreds of miles an hour, isn't wind resistance orders of magnitude stronger than rolling friction? If you live somewhere with even moderate wind, and that wind doesn't always blow in the same direction, you'd want to take off with the wind and land against it, which would cause problems when that meant landing on the downslope or taking off on the upslope. I suppose you could mitigate that by having runways that slope up and to the east, down and to the east, etc.

You always want to take off and land into the wind -- it increases your effective airspeed.

Reply on news.ycombinator.com