Why do airplanes have to fly at 30,000+ft.

I know…hey its my first question so gime a break, yeah as you can tell im really terrified of traveling by air but ONLY because its usually at 33,000ft and 600mhp hahaha…yeah.

It’s mostly for economy. At that height the air is nice and thin and easy for the plane to push out of its way, so drag is reduced big time, leading to much better fuel economy. This is really necessary given that big jets burn lots of fuel on a long-haul flight as it is.

As for safety, 50 feet and 100mph can kill you quite thoroughly. :smiley:

They are flying above the weather (on most days) and can get an extra push from the jet stream if it’s in the right direction.

Does it require more fuel to fly in the opposite direction of Earth’s rotation? What I mean is, would that be like flying into a constant headwind?

To give an example. The turbo-prop I fly has a long range (best economy) cruise of about 185 knots and uses 1250 pounds of fuel per hour at 2000 feet. At its max altitude of 25000 feet it cruises at 240 knots and burns 1000 pounds of fuel per hour. So it’s using 60% less fuel for distance traveled at high altitude compared to low altitude. If you can get higher the savings are greater.

ivan, no, the Earth and everything in it including the atmosphere is rotating at the same rate, so the Earth is stationary from the aircraft’s perspective.

Missed the edit.

There is generally a westerly wind at high altitudes, it is caused by a temperature gradient at the tropopause combined with the coriolis effect. The temperature gradient causes a wind from the equator to the poles, and the Earth’s rotation causes that wind to veer to the east (coriolis effect.) This results in the jet streams and can make a big difference in flying time between travelling east and west.

You could say that the earth’s rotation makes flights in one direction longer than the other but it is not in the treadmill fashion you were thinking of, and it is actually slower travelling with the Earth’s rotation, not against it.

I’ve got this part wrong, disregard.

And it’s safer to be higher. Altitude above you does no good, altitude below you gives you time and distance. Would you rather have an engine go dead at 1000 feet or 30,000 feet?

Well at 30000 feet you might have a chance of the engine recovering. At a 1000 feet you’ve hit the ground before you knew what the problem was.

A plane that goes hundreds of miles per hour is going be a real mess regardless of the altitude before it had before a crash. I feel a bit safer being above the thunderstorms rather then in them.

Hijack, whats the max height for most commercial jets, both 2 and 4 engined.

Note that the higher a plane goes, the margin of safety if something goes wrong goes up in many cases. E.g., the engines lose power. More glide time to restart them. (There was this famous case of a jetliner making an unpowered landing. It would have been toast if the problem had happened at a much lower altitude.)

That varies, and it isn’t necessarily directly related to the number of engines. Somewhere between 40,000 and 45,000 feet might be typical. You can google “<your chosen plane> service ceiling” to get more specifics.

I live on the flight path for Teterboro Airport, and sometimes in bad weather I see planes coming in very low. After 9/11, it took about a year before I stopped freaking out about it.

Depends on the specific model, but 41,000 or 43,000 are common maximum legal (“certificated” in the jargon) altitudes.

If lightly loaded the aircraft might be able to get a couple thousand feet higher, but just barely. If fully loaded, most commercial jets cannot reach their max certifacted altitude.

The numbers tend to be odd round thousands of feet because prior to just a few years ago, odd round thousands were the only altitudes used at very high altitude. Recently the industry has begun using even round thouands as well, so you may find an even max altitude ona newer design.

Bizjets often can go a little higher, up to 49,000 or even 51,000.

Well, for that matter, 0 feet and 70 mph kills far more people than commercial air travel.

And the other posters have summed it up pretty nicely, by explaining how range goes up and fuel consumption goes down as you go up in altitude. Less air to plow through is generally a good thing.

So you may ask yourself, “Why not go even higher?” Surely if higher is better, than flying at 70,000 ft must be better than 35,000 ft. While thinner air is a benefit for flying more efficiently, there is such a thing as too thin. Wings need a certain amount of air mass to generate lift. Engines need enough air to push out the back and create thrust. And that’s why all air-breathing aircraft have a “service ceiling”. It’s the height above which one of those two things (the wings or the engines) just won’t work any more. Even getting right up to the service ceiling becomes harder and harder the closer you get to it. So most aircraft are going to stay well below it. For a given airplane, there’s a particular altitude with an optimum balance of air that’s thin enough to cause low drag, but not too thin to fly in. And somewhere near there is where you’ll find your typical passenger jet.

If your craft is not air-breathing, and doesn’t use air to generate lift, you can go as high as you want. We usually call these things satellites. They get up to high altitudes above the earth’s atmosphere using rockets, which don’t breathe air. They stay in motion by pure inertia, so they don’t need to power themselves once they’re up there. And in fact, the only reason they go as high as they do is to escape the drag of the earth’s atmosphere. If there were no atmosphere, there’s no reason you couldn’t have a satellite orbiting 50 ft off the ground. (Okay, let’s also ignore the presence of tall things like buildings and mountains.)

Altitude above you is one of the three most useless thing a pilot can have the other two being
[li]Runway behind you[/li][li]Fuel still in the tanks back at the airport.[/li][/ul]

I remember reading about someone in the early 1920s who claimed that fast transcontinental and transoceanic passenger flight was a pipe dream. He pointed out that increased speed means increased drag and so denied that any airplane could ever fly at hundreds of miles per hour. Apparently his calculations were based on constant altitude, completely ignoring increased lift at higher speeds and less drag at higher altitudes.

In my skydiving days, it was commonly understood that seasonal changes in temperature effected the ceiling and climb rate of our aircraft. Slower and lower in the summer because hot air is less dense. This is in the 10-15k foot range. Is this effect noted at commercial altitudes, or is it minimal/non-existent?

For the reasons stated in this thread I am always amused when Westworld pops up on cable somewhere and we get to see the supersonic passenger aircraft which travels at 50 feet above the ground…

Incidentally, this is why helicopters fly slower the higher they go.