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Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

latimes.com

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Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

#21

Post by noir_lord »

AnimalMuppet wrote: post #10
boyter wrote: post #4

Earlier quoted context omitted.

Isn’t that the one that truely matters some you want to go from A to B? Genuinely curious I know nothing about aviation.

I suspect that a 787 traveling at 801 MPH airspeed might suffer some damage to the control surfaces. 787s aren't designed to break the sound barrier. And I would argue that not damaging the plane matters more than how long it takes to get there.

It's travelling at 801mph relative to the ground.

If I'm swimming down stream at 1 mph in water moving at 4mph, relative to the bank I'm doing 5mph relative to the water 1mph.

No sonic booms where involved.

Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

#22

Post by foxyv »

abakker wrote: post #20

This makes me think that some time in the distant future, when we're really great a terraforming, we could influence the weather of the planet specifically to create functional jet streams that we could use to make travel faster, and then plan air routes specifically to use them. A more serious question: I assume this kind of event doesn't actually save fuel because the airplane still has to maintain the same airspee…

Since they arrive faster they will spend less time in the air. Less time in the air means less fuel burnt. They are probably still burning fuel at a similar rate though.

Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

#23

Post by jfk13 »

abakker wrote: post #20

This makes me think that some time in the distant future, when we're really great a terraforming, we could influence the weather of the planet specifically to create functional jet streams that we could use to make travel faster, and then plan air routes specifically to use them. A more serious question: I assume this kind of event doesn't actually save fuel because the airplane still has to maintain the same airspee…

> A more serious question: I assume this kind of event doesn't actually save fuel because the airplane still has to maintain the same airspeed to avoid stalling, right?

If a plane maintains the same airspeed, but gets extra ground speed thanks to a tailwind, it'll complete its journey in less time and therefore should save fuel. (Unless it ends up having to circle the destination airport while it waits for its original landing slot!)

Of course, planes going the other direction will use extra, so overall we don't win.

Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

#24

Post by Xcelerate »

I remember once being on an almost empty flight from SFO to ATL a few years ago. I checked the flight information on the seatback screen in front of me and was startled to see we were going well over 700 mph ground speed. That was pretty much the quickest flight I’ve ever been on; I think the whole trip was well under four hours.

Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

#25

Post by heywire »

Interestingly the National Weather Service in Wilmington, OH posted about the jet stream and its affect on their weather balloon yesterday [0] (please forgive the link to Facebook)

[0] https://www.facebook.com/NWSWilmingtonOH/photos/a.1920894441...

Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

#26

Post by benj111 »

abakker wrote: post #20

This makes me think that some time in the distant future, when we're really great a terraforming, we could influence the weather of the planet specifically to create functional jet streams that we could use to make travel faster, and then plan air routes specifically to use them. A more serious question: I assume this kind of event doesn't actually save fuel because the airplane still has to maintain the same airspee…

If I'm in a tailwind of 100mph and have a cruising speed of 200mph, then I'm essentially travelling at 300mph relative to the ground, but using as much fuel as if I were travelling at 200mph. On the return leg, I would hit a head wind, and be travelling at 100mph while still using as much fuel as if I were travelling at 200mph.

So yes this does save fuel.

Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

#27

Post by btian »

kgermino wrote: post #6

This is probably a stupid question, but how is "ground speed" measured? Is it how quickly the airplane moves past a fixed point at it's altitude, or along the earth's surface? I.e. the plane is effectively moving along the surface of a sphere, but if the plane is 30,000 ft up, then the radius of the plane's sphere is 30,000 ft greater than the radius of the "ground" so traveling at the same angular velocity will requ…

It's measured by repeatedly taking GPS coordinates divided by time.

Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

#29

Post by BonesJustice »

ozzyman700 wrote: post #16
kgermino wrote: post #6

This is probably a stupid question, but how is "ground speed" measured? Is it how quickly the airplane moves past a fixed point at it's altitude, or along the earth's surface? I.e. the plane is effectively moving along the surface of a sphere, but if the plane is 30,000 ft up, then the radius of the plane's sphere is 30,000 ft greater than the radius of the "ground" so traveling at the same angular velocity will requ…

https://www.grc.nasa.gov/www/k-12/airplane/move.html ground speed is the speed of the plane, relative to an observer on the ground, air speed is how fast the people on the plane are going relative to themselves. Airspeed = Ground Speed - Wind Speed (wind blowing towards front of plan is positive, tailwind is negative)

I’m a bit under the weather, so my comprehension may be lacking, but I think you’ve got your signs reversed (or your head/tail terminology flipped).

If tail wind (moving with the plane) were negative, then air speed would exceed ground speed. Intuitively, that doesn’t make sense. Air speed can only exceed ground speed if the wind is blowing in an opposing direction, i.e., the plane must travel faster against the wind to achieve the same speed relative to a ground observer.

Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds

#30

Post by cm2187 »

mertd wrote: post #7
boyter wrote: post #4

Earlier quoted context omitted.

Isn’t that the one that truely matters some you want to go from A to B? Genuinely curious I know nothing about aviation.

Yes but it won't make a sonic boom.

If the wind is unstable, and slows down, can't the plane break it just out of inertia?
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