Note to readers, land speed not equal to air speed. As the article discusses it doesn't break the sound barrier.
That said, the news here is that the jet stream is carrying more energy than it has in the past (air mass is moving faster, kinetic energy content is 1/2mv^2). I read a paper a long time ago which talked about the impact of thermal 'tubes' where denser cold air travelling at speed would "punch holes" in high pressure systems leading to more complex weather patterns. Sadly I cannot find it! The question I think about when reading this is the impact on the duration and temperature swings of the winter months in the north east of the continent. In particular, atmosphere so cold as to support hurricane formation over land. Most famously exploited in a fairly mundane movie "the day after tomorrow" but the modelling works if the temperatures meet certain conditions.
I don't know if winter "super storms" are possible due to other moderating influences but if they are, having the jet stream behave in a new way is a prerequisite (feeding very cold air into the system).
> Note to readers, land speed not equal to air speed. As the article discusses it doesn't break the sound barrier.
Yes, but the first sentence is not why it did not break the sound barrier. They state it is due to being in swiftly moving air. The speed otherwise, even at airspeed (which is a negligible difference to ground speed) is fast enough to break the sound barrier.
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 require a higher speed the higher you go.
If I'm thinking about this right, across their respective "planes," the airplane will be moving faster than it's shadow. So maybe a better way to ask this is: is ground speed the speed of the plane, or the speed of its shadow?
The Earth has almost a 4000 mile radius; 30,000 feet is less than 6 miles. The difference between movement over ground and movement with respect to the top of a 30,000 foot pole stuck in the ground is pretty negligible.
Private pilot here. As others have pointed out, the difference is mostly negligible, but ground speed is the speed of the vertical projection of the aircraft's location on the earth's surface.
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.
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)
In the old days, you'd take the time between two "fixes". A fix could be a visual reference, or a NAVAID. That'd result in your shadow's speed.
Then came DME, distance measuring equipment. I don't know if DME ever took altitude into account or if the error resulting from altitude was just ignored, but analog DME radios would just tell distance at first and then digital versions had a groundspeed feature. At least instrument rated pilots were aware of the increasing error the closer to the NAVAID.
At some point in the ATC radar system, a controller's screen could show groundspeed. Pilots can ask ARTCC what ground speed is, although I would never ask approach or departure control such a question. This would have the same error as DME.
Today it's a value reported by GPS. I don't know if this is based on the plane's movement, or its shadow, or if there's a regulation that dictates it for aviation certified GPS. From a pilot perspective we don't distinguish between kinds of ground speed, whereas we do distinguish between kinds of airspeed: indicated, calibrated, and true. Mainly groundspeed is important navigationally to know if there's an unexpected headwind that'll lengthen enroute time and thus impact fuel management. And while there can be big enough error between estimated winds aloft and actual that this computation will affect enroute planning, I tend to only care about tens of minutes or hours, not seconds.
30k ft is nothing compared to the radius of the Earth which is 21M ft. The measurement instrument has larger error sources, so the answer is it doesn't actually matter.
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.)
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 airspeed to avoid stalling, right?
> 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.
1. The plane has to fly sufficiently fast (to avoid stall), and sufficiently slow (to avoid "Mach tug"). As one flies higher (air density sinks), these two speeds converge, forming the dangerous "coffin corner". Now, in general, planes don't fly as high as possible, I'd say, so that there is some leeway in terms of chosen airspeed.
2. For given airspeed, the plane flies less time with a tailwind than a headwind.
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.
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.
Where air masses, that are travelling at different velocities, meet you get shearing. Shearing causes turbulence. So even if we could create two jet streams moving in two different directions the turbulence in the zone where you transfer between the two would probably be too severe to actually fly through it.
This makes me think that some time in the distant future, when we're really great a terraforming
We're great at accidental terraforming now, we're actually warming the temperature of the planet.
But based on global reaction to the current terraforming I'm skeptical that we'll ever reach the point to where we can intentionally terraform the planet.
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)
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?
>The ordinary cruising speed of a Dreamliner is 561 mph, with a maximum propulsion of 587 mph. Any speed gained on top of that is thanks to Mother Nature's helpful boost.
Wow, cruise speed is that close to 'max' speed? Or maybe that's just a max suggested cruise speed.
An incredible visualization of winds aloft (and several other parameters can be seen at https://earth.nullschool.net/. Currently the jetstream (i.e. winds at 250 hPa altitude) are hitting around 230mph (360km/h).
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
Last time I flew from SFO to MUC, we had almost 100mph tail winds, that was already very impressive and shortened the flight time considerably, but nothing compared to this.
That is 1289.085 kilometres per hour! The title should be updated on to include a measurement used by the rest of the world including the scientific community.
If you're being pedantic about science-related matters, it's 1290 km/h. Don't give false precision with your conversion; there's no way the original measurement has >3 significant figures.
Even better yet, 361 m/s. km/h is a derived unit. ;)
If you want to get pedantic then you and the article are both wrong! Navigation, marine and aeronautical, is done in Nautical Miles, called Knots when used to measure speed. 1NM used to be exactly 1 minute of latitude but is now defined as very closely approximate to this as earth is now understood to be not a perfect geoid. There are 60 Nautical Miles to a degree of latitude. This allows distances and courses to be measured and plotted easily on charts which are Mercator projections.
The aircraft is rated in knots equivalent air speed. Everywhere but China and Russia tend to call out speeds in knots. If anything, it should be in knots. So, about 696 knots.
[+] [-] ChuckMcM|7 years ago|reply
That said, the news here is that the jet stream is carrying more energy than it has in the past (air mass is moving faster, kinetic energy content is 1/2mv^2). I read a paper a long time ago which talked about the impact of thermal 'tubes' where denser cold air travelling at speed would "punch holes" in high pressure systems leading to more complex weather patterns. Sadly I cannot find it! The question I think about when reading this is the impact on the duration and temperature swings of the winter months in the north east of the continent. In particular, atmosphere so cold as to support hurricane formation over land. Most famously exploited in a fairly mundane movie "the day after tomorrow" but the modelling works if the temperatures meet certain conditions.
I don't know if winter "super storms" are possible due to other moderating influences but if they are, having the jet stream behave in a new way is a prerequisite (feeding very cold air into the system).
[+] [-] e40|7 years ago|reply
[+] [-] samdoidge|7 years ago|reply
Yes, but the first sentence is not why it did not break the sound barrier. They state it is due to being in swiftly moving air. The speed otherwise, even at airspeed (which is a negligible difference to ground speed) is fast enough to break the sound barrier.
[+] [-] unknown|7 years ago|reply
[deleted]
[+] [-] kgermino|7 years ago|reply
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 require a higher speed the higher you go.
If I'm thinking about this right, across their respective "planes," the airplane will be moving faster than it's shadow. So maybe a better way to ask this is: is ground speed the speed of the plane, or the speed of its shadow?
[+] [-] dragonwriter|7 years ago|reply
[+] [-] lisper|7 years ago|reply
[+] [-] TheLoneAdmin|7 years ago|reply
[+] [-] ozzyman700|7 years ago|reply
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)
[+] [-] cmurf|7 years ago|reply
Then came DME, distance measuring equipment. I don't know if DME ever took altitude into account or if the error resulting from altitude was just ignored, but analog DME radios would just tell distance at first and then digital versions had a groundspeed feature. At least instrument rated pilots were aware of the increasing error the closer to the NAVAID.
At some point in the ATC radar system, a controller's screen could show groundspeed. Pilots can ask ARTCC what ground speed is, although I would never ask approach or departure control such a question. This would have the same error as DME.
Today it's a value reported by GPS. I don't know if this is based on the plane's movement, or its shadow, or if there's a regulation that dictates it for aviation certified GPS. From a pilot perspective we don't distinguish between kinds of ground speed, whereas we do distinguish between kinds of airspeed: indicated, calibrated, and true. Mainly groundspeed is important navigationally to know if there's an unexpected headwind that'll lengthen enroute time and thus impact fuel management. And while there can be big enough error between estimated winds aloft and actual that this computation will affect enroute planning, I tend to only care about tens of minutes or hours, not seconds.
[+] [-] frankchn|7 years ago|reply
[+] [-] kevmo314|7 years ago|reply
[+] [-] foota|7 years ago|reply
[+] [-] unknown|7 years ago|reply
[deleted]
[+] [-] glitchc|7 years ago|reply
[+] [-] unknown|7 years ago|reply
[deleted]
[+] [-] btian|7 years ago|reply
[+] [-] JoblessWonder|7 years ago|reply
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/...
[+] [-] abakker|7 years ago|reply
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?
[+] [-] jfk13|7 years ago|reply
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.
[+] [-] FabHK|7 years ago|reply
2. For given airspeed, the plane flies less time with a tailwind than a headwind.
So, this does save fuel, I'd think.
[+] [-] rconti|7 years ago|reply
[+] [-] foxyv|7 years ago|reply
[+] [-] benj111|7 years ago|reply
So yes this does save fuel.
[+] [-] bronco21016|7 years ago|reply
[+] [-] Johnny555|7 years ago|reply
We're great at accidental terraforming now, we're actually warming the temperature of the planet.
But based on global reaction to the current terraforming I'm skeptical that we'll ever reach the point to where we can intentionally terraform the planet.
[+] [-] United857|7 years ago|reply
801 MPH is not even close to the record, even for a 787.
[+] [-] selectodude|7 years ago|reply
[+] [-] heywire|7 years ago|reply
[0] https://www.facebook.com/NWSWilmingtonOH/photos/a.1920894441...
[+] [-] vanous|7 years ago|reply
[+] [-] rconti|7 years ago|reply
Wow, cruise speed is that close to 'max' speed? Or maybe that's just a max suggested cruise speed.
[+] [-] kawfey|7 years ago|reply
[+] [-] ilovecaching|7 years ago|reply
[+] [-] Xcelerate|7 years ago|reply
[+] [-] brianwawok|7 years ago|reply
2h drive to ORD 2h airport security Theater 4h Flight to SFO 1h to deplane get an Uber to someplace
So 9 hour total journey on a direct flight. A 50% faster flight would make it be 8 hours instead of 9? I don't think I would pay anything for that.
[+] [-] chaseha|7 years ago|reply
[+] [-] pdx_flyer|7 years ago|reply
[+] [-] _ph_|7 years ago|reply
[+] [-] graycat|7 years ago|reply
[+] [-] bamboozled|7 years ago|reply
[+] [-] photojosh|7 years ago|reply
Even better yet, 361 m/s. km/h is a derived unit. ;)
[+] [-] willyt|7 years ago|reply
[+] [-] kevin_b_er|7 years ago|reply
[+] [-] Kye|7 years ago|reply
[+] [-] speeq|7 years ago|reply
[+] [-] gok|7 years ago|reply
[+] [-] boyter|7 years ago|reply
Genuinely curious I know nothing about aviation.
[+] [-] mrfusion|7 years ago|reply
[+] [-] nonickfx|7 years ago|reply
[+] [-] jsjohnst|7 years ago|reply
Essentially zero.