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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

#31

Post by GaryNumanVevo »

jfk13 wrote: post #23
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 origin…

Just make a jet stream going the other way at a different altitude

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

#32

Post by ummonk »

TheLoneAdmin wrote: post #18
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…

The radius of the earth + 30,000 ft is about 0.14% more than just the radius of the earth. Basically ignore it, unless you are programming guidance control systems.

0.14% is enough to throw the number off by 1mph so it isn’t irrelevant.

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

#33

Post by [deleted] »

BonesJustice wrote: post #29
ozzyman700 wrote: post #16

Earlier quoted context omitted.

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…

[deleted]

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

#34

Post by jfk13 »

benj111 wrote: post #26
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.

It saves fuel for the downwind leg of the trip.

However, it's worth noting that if the outward (downwind) and return (upwind) legs are affected by the same wind, the outward savings are more than offset by the extra fuel needed for the return. Suppose the journey in your example is 200 miles. With no wind, that's an hour each way, so 2 hours total cruising time.

With the 100mph wind, the outward journey only takes 40 minutes (200 miles at 300mph), but the return takes 2 hours (200 miles at 100mph) for a total cruising time of 2:40, and a significantly greater total fuel burn.

(In practice, airlines may route the two legs quite differently to optimize better, taking advantage of the tailwind in one direction while avoiding it as much as possible when going the other way.)

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

#35

Post by BonesJustice »

vanous wrote: post #28

So what if they suddenly left the jet stream, for example flew a bit below or besides... If that's possible... and happened to be in normal wind speed, the plane would disintegrate due to sonic boom?

It wouldn’t disintegrate due to a sonic boom, because this extraordinary speed is due to the plane being helped along by tailwinds. If the tailwinds disappear, the plane slows down; it doesn’t speed up.

What I’m not clear on is, would the passengers feel like they just decelerated by 200+ mph in an instant?

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

#36

Post by JoblessWonder »

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…

Ground speed is what most people would think of when they think of a speed. How fast is it moving from Point A to Point B.

Airspeed takes into account how fast you are going you are going AS WELL as how fast and in what direction the air around you is going.

Another example would be a person walking on a motorized walkway (like at an airport.) Person A is going WITH the direction of the walkway like someone normally would. Person B is going AGAINST the direction of the walkway but still making progress forward. How fast the person is going when observed from off the walkway is ground speed. To maintain the same ground speed, Person A needs to only walk slowly (less effort/lower airspeed) while Person B needs to be sprinting all out (more effort/high airspeed.)

* Here is an interactive example from NASA: https://www.grc.nasa.gov/www/k-12/airplane/Animation/airrel/...

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

#37

Post by chaseha »

Xcelerate wrote: post #24

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.

Would it be nice? Flying is already a tremendous environmental burden with the focus on fuel economy. I'm happy to sit in my seat a few minutes longer if it means taking away some of that emissions impact

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

#38

Post by jfk13 »

GaryNumanVevo wrote: post #31
jfk13 wrote: post #23

Earlier quoted context omitted.

> 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 origin…

Just make a jet stream going the other way at a different altitude

Or just fly with the jetstream in all cases, all the way around the earth if necessary. Some trips would be quite long, but think how much fuel they'd be saving!

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

#39

Post by logifail »

jfk13 wrote: post #23
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 origin…

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

Aren't some(all?) long-haul routes chosen on a flight by flight basis to take advantage of favourable winds where possible?

Compare yesterday's eastbound BA11 (LHR-Singapore) vs the westbound BA12 (Singapore-LHR) flights.[0] Neither route looks like a great circle.

Eastbound routing: London - north of Berlin - Minsk - Voronezh - Volgograd - cross Caspian sea - Turkmenistan - Lahore - New Delhi - KL - Singapore.

Westbound: Singapore - KL - south of Jaipur - Iran - just touched Turkmenistan - south of Baku - Tbilsi - Turkey (just) - south of Prague - south of Dortmund - LHR

[0] flightradar24.com or similar

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

#40

Post by AnimalMuppet »

noir_lord wrote: post #21
AnimalMuppet wrote: post #10

Earlier quoted context omitted.

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.

I'm quite well aware of that. I'm not sure how you read my post as saying anything different.

boyter asked how anything but time from A to B could be relevant. Well, not damaging the plane is relevant. And therefore the airspeed not being 801 MPH matters.

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