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Old 20-10-2008, 13:43   #1
karlosg
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how fast does a 747 have to go to stay up in the air

Just wondered how fast does a 747 or a plane of a similar size have to travel to stay up in the air , in other words whats the slowest it can go and still stay up ??
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Old 20-10-2008, 14:08   #2
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Would depend on altitude
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Old 20-10-2008, 14:10   #3
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Less than 200 mph for take off
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Old 20-10-2008, 14:20   #4
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Yes, but if it kept going at 200mph it would fall back down to Earth.

To stay in the air and at a constant altitude, it would probably be nearly double that.

They cruise at over 500 mph, but again, the speed would vary depending on the altitude.
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Old 20-10-2008, 14:22   #5
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The take-off or "rotate" speed for airplanes differ depending on size, type, etc...

On average lets say most of your small single engine airplanes rotate at about 55 knots which equals about 60-65 mph. They then speed up during climb to about 80-90 knots (about 90-110mph). Cruise speed is anywhere from 100-140 knots (115-150 mph).

Now obviously as the airplane gets bigger it tends to get faster.

Your jet aircraft usually stay around the same speeds though. Rotate speed is about 130-150 knots (150-170 mph). They then cruise anywhere from 250-400 knots (290-460 mph). Such a big possibility for the speeds because it all depends on the airplane and the altitude.
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Old 20-10-2008, 14:24   #6
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I never mentioned what speed it would have to maintain But its not as much as you'd think
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Old 20-10-2008, 14:25   #7
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Take off speed for a 747 is between 178-184 mph, that is the minimum speed the aircraft needs to obtain to become airbourne.

It's stall speed will be very similar.
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Old 20-10-2008, 15:22   #8
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A 747 will "take off" at around 180mph, this will depend on conditions such as weight, air temperature etc.

As altitude increases, density decreases so lift reduces; so

a 747 will stay in the air at 50ft at 180mph give or take, but as altitude increases the speed for lift to overcome gravity will increase.

For more information on this google Density Altitude.
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Old 20-10-2008, 15:27   #9
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Quote:
Originally Posted by corky_79 View Post
The take-off or "rotate" speed for airplanes differ depending on size, type, etc...

On average lets say most of your small single engine airplanes rotate at about 55 knots which equals about 60-65 mph. They then speed up during climb to about 80-90 knots (about 90-110mph). Cruise speed is anywhere from 100-140 knots (115-150 mph).

Now obviously as the airplane gets bigger it tends to get faster.

Your jet aircraft usually stay around the same speeds though. Rotate speed is about 130-150 knots (150-170 mph). They then cruise anywhere from 250-400 knots (290-460 mph). Such a big possibility for the speeds because it all depends on the airplane and the altitude.
Nicely ripped from Yahoo Answers brainiac

http://answers.yahoo.com/question/in...0174213AAd0rqd
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Old 20-10-2008, 15:30   #10
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Quote:
Originally Posted by Ben_S View Post
A 747 will "take off" at around 180mph, this will depend on conditions such as weight, air temperature etc.

As altitude increases, density decreases so lift reduces; so

a 747 will stay in the air at 50ft at 180mph give or take, but as altitude increases the speed for lift to overcome gravity will increase.

For more information on this google Density Altitude.
Technically the plane will only stop becoming airbourne once it reaches 0 ft, so it's stall speed at 30,000 ft is pretty much irrelevant.
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Old 20-10-2008, 15:32   #11
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Originally Posted by youngsyr View Post
Technically the plane will only stop becoming airbourne once it reaches 0 ft, so it's stall speed at 30,000 ft is pretty much irrelevant.
Sorry, I really don't understand what point you're trying to make?

Edit: I now get what you're trying to say. What about at elevation say, 8000ft in the US (as some airfields are). Your speed required to "rotate" or take-off will be greater due to lower air density. Hence my reference to Density Altitude.

Last edited by Ben_S; 20-10-2008 at 15:39..
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Old 20-10-2008, 15:34   #12
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Originally Posted by Blair View Post
Nicely ripped from Yahoo Answers brainiac

http://answers.yahoo.com/question/in...0174213AAd0rqd

I added the last 2 words, and took the first paragraph out

But I knew the answer anyway, see post earlier
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Old 20-10-2008, 15:39   #13
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Quote:
Originally Posted by Ben_S View Post
Sorry, I really don't understand what point you're trying to make?
Just an observation on a boring Monday afternoon, but the OP asked "whats the slowest it can go and still stay up".

The lowest speed the plane will need to travel will normally be at very close to ground level, therefore you complicating the issue by posting that the plane needs to maintain a higher speed the higher it flies is not really relevant.
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Old 20-10-2008, 15:42   #14
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Quote:
Originally Posted by Ben_S View Post
Sorry, I really don't understand what point you're trying to make?

Edit: I now get what you're trying to say. What about at elevation say, 8000ft in the US (as some airfields are). Your speed required to "rotate" or take-off will be greater due to lower air density. Hence my reference to Density Altitude.
Given that the vast majority of the Earth's surface has an altitude of sea level (or very close to), talking about the very small percentage of places that are significantly above that seems to unnecessarily complicate matters.
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Old 20-10-2008, 15:46   #15
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Originally Posted by youngsyr View Post
Given that the vast majority of the Earth's surface has an altitude of sea level (or very close to), talking about the very small percentage of places that are significantly above that seems to unnecessarily complicate matters.
I'm just giving a complete answer - I was about to add wind into the equation! ;-)

Are you a pilot btw?
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