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).
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.
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?
"Assume the Earth is a perfect sphere, and its circumference is 25,000 miles. You have a 25,000 mile long rope looped all the way around the Equator, so it is tight against the surface. Now you want to raise the rope one foot in the air, all the way around. How much more rope do you need?"
I thought about this and said, "You need a lot more rope! I don't know how much, but it will be a lot. It has to reach all the way around the Earth, only higher!"
Of course the real answer is "You only need about three more feet. To be specific, you need another 3.14159... feet."
That's all you need to raise a rope a foot in the air, all the way around the Earth.
I'd better buy an extra 3-4 feet of rope before I try this experiment.
For someone who doesn’t know, or hasn’t calculated/thought about it that is pretty astounding.
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)
That makes no sense.
How can people be moving relative to themselves?
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.
Then, ground speed = air speed - wind speed.
Thus, GP seems to have either the sign wrong, or ground and air speed mixed up (but not both :-)
This is absolutely true, but has always infuriated me because it seems needlessly contrary as compared to the way we speak about anything else travelling in a direction as read from a compass. Does anybody know why it's the case?
I can understand that it might be just an ancient tradition originating from a particular part of the world, that we've turned into a convention, but it loses meaning when you go elsewhere.
If you go to Cape Town, a "north wind" presumably doesn't mean cold, because the area north of the city isn't colder than the city itself. This didn't matter to the people who first said "north wind" and I don't think it means much nowadays either. Just another little thing to watch out for in intercultural communication.
KIAS: Knots Indicated Airspeed (i.e. the speed at which air is hitting the pitot tube)
WS: Wind speed
To calculate ground speed (as required for navigation and fuel planning) you need true airspeed (not indicated) as well as wind direction and speed.
See some discussion here: https://www.quora.com/In-aviation-what-is-the-difference-bet...
IAS is what the pilots care about while flying because it’s what matters for aerodynamics (ie stall speed)
You mean relative to the air outside the window. Relative your yourself you're always standing still.
I'll show myself out.
Ground speed = true airspeed + wind component (where you're computing a vector based on wind direction to determine what amount of it is either tail wind (+) or headwind (-).
If acceleration is zero.
(Internet, therefore pedantry).
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.
It's colloquially called "slant range" for this reason, and if you care about actual ground distance you have to use trigonometry.
EDIT: assuming a constant altitude flight
If you fly from point A to point B in one hour at 10,000 feet, and then fly from point A to point B in one hour at 30,000 feet, GPS will report the same speed for both flights. It does not bother to correct for the slightly longer path at 30,000 feet because that level of precision is simply not needed for commercial aviation.
GPS is inherently 3 dimensional.
The solution is a datum, a model of the Earth's surface that is used for the conversion. WGS84 is the datum used by GPS, and approximates the Earth as a specified ellipsoid. However, maps can use use different datums (data?), so there can be a discrepancy of many meters between what GPS says the location is, and what the map says the location is, and they can both be right relative to their datum.
GPS allows you to directly measure displacement of any 2 points in 3 dimensions.
You're speaking of the altitude + lat/lon instead, which is in polar coordinates.
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/...
You are explaining the difference between airspeed and ground speed, which can be much more substantial (e.g., ~10%, or ~%100 in extraordinary situations).
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.
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. 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
 flightradar24.com or similar
It's even worse than not winning. You actually lose if you have to fly in the same wind both ways, once as a headwind and once as a tailwind. The extra time in the into the headwind direction is more than the time saved in the with a tailwind direction.
If the ground distance each way is D, airspeed is V, and wind speed relative to the ground is w, total time is D/(V-w) + D(V+w) = 2DV/(V^2-w^2) = 2D/(V-w^2/V).
For 0 < w < sqrt(V), this is more than the 0 wind case. (For w >= sqrt(V), the headwind is so high that you can't make any progress toward the destination).
If the ground distance each way is D, airspeed is V, and wind speed relative to the ground is w, total time is D/(V-w) + D/(V+w) = 2DV/(V^2-w^2) = 2D/((V^2-w^2)/V).
For 0 < w < V: this is more than the 0 wind case.
For w >= V: the headwind is so high that you can't make any progress toward the destination).
The last result being somehow obvious ;)
The jetstream is small. You can avoid it and not have to pay extra. So yes, it can be an absolute win.
So yes it's a win, but a little more subtly.
2. For given airspeed, the plane flies less time with a tailwind than a headwind.
So, this does save fuel, I'd think.
Doing a little digging, it seems that there's also a significant risk of entering an overspeed condition during recovery, and inducing a structural failure! Makes sense considering that we're talking about speeds near Mach 1 to begin with.
It was in and out of the coffin corner before the pilots realized what was happening.
I watched a TV programme a couple of years ago talking about this on the U2 as the speeds were only a few knots apart and also varied with altitude and other factors.
The image at https://i.stack.imgur.com/Lu2Xt.jpg shows the airspeed corridor the pilots have to fly through. It's constantly flying on a knife edge.
So yes this does save fuel.
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.)
Conclusion: increased wind increases the round trip time.
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.
801 MPH is not even close to the record, even for a 787.
I had a debate with a friend on this one the other day, but I am pretty sure something like 80% of the engine power is there to combat drag, which increases with v² (if you discount lift from that, otherwise it' obviously 100%).
That is if the thrust vector of the engine is 100% level and the airspeed is constant, then 100% of the engine power applied is offset by drag.
The distinction is that, that that part of the drag is impossible to reduce, while friction you can work to reduce.
That's what the GP meant by "discounting lift".
The energy requirements are split between those two.
If the plane is not generating lift then it's on the ground or about to end up in the ground.
What I’m not clear on is, would the passengers feel like they just decelerated by 200+ mph in an instant?
More likely the turbulence and vortices in the demarcation zone between the jetstream and the different air current the plane enters would jostle and toss the passengers around more than the deceleration would.
From the article, it said the 787 was cruising at 35,000 feet. Seeing as the 787 was built to cruise close to 40,000 feet (above most traffic and weather) I daresay the pilot or company flight planners deliberately asked for a lower altitude based on expected wind conditions. I bet many other airlines were doing the same, leading to a very busy jetstream highway that day!
I mean, the opposite effect is well attested to - you fly along with a headwind (and sufficient airspeed), then comes along a sudden tailwind, and your airspeed drops sufficiently that you stall, or at any rate descent. Wind shears, often associated with cold fronts or thunderstorms.
Maybe a) mach 1 is further from cruise speed than cruise speed from stall speed, and b) drag slows down the plane more effectively and quickly than the engines can accelerate it.
That could explain why wind shear has and does lead to stalls, but not to sonic booms/structural disintegration.
As other people mention, it doesn't happen immediately - it's like merging onto a very bumpy freeway.
Wow, cruise speed is that close to 'max' speed? Or maybe that's just a max suggested cruise speed.
Faster than that, air around portions of the plane may start moving faster than the speed of sound (even though the airframe as a whole is going slower than the speed of sound), and this wreaks havoc in terms of lift, drag, controllability, and structural integrity ("mach buffet").
I think cruise N1 is something like 80% (that is, of full power). If you pushed the engines to 100% power at cruise altitude, they could probably get you past 587 mph / mach 0.85, but you'd be having a really bad day.
https://www.youtube.com/watch?v=OhwLojNerMU (Older with music, kinda funny old-school science video from NASA)
The flutter in the first video is occurring at very much subsonic speeds, and looks to be either the result of flying a purposely underdesigned tail surface, or flying a properly built one beyond its rated flight envelope. The second video contains a wide variety of flutter instances, some of them aeroelastic, some of them transonic, and so on.
One way to get into a transonic flutter, however, is to be a hotshot business jet pilot who flies higher and higher and faster and faster. The higher you go, the lower the density, so your minimum speed increases. Also, the temperature goes down, so the speed of sound decreases. Where these two meet is called "coffin corner," and you don't always have to fly yourself into it by increasing your speed and altitude; you can fly close to coffin corner, and then fly into colder air or less dense air. No matter how you get there, you're stuck. Slow down, and the wings stall, the nose drops, you pick up speed, and hit transonic flutter. Speed up to stay in the air, by dropping the nose, and you hit transonic flutter directly.
Do you have any thoughts on composite-based aircraft like a Cirrus and flutter? A few times I've had a Cirrus SR22 into a pretty steep descent with poor controller sequencing for an approach into busy terminal space and had to push it down, but the plane felt solid even at 180-190kts TAS. I backed it off only because I get nervous with any unexpected turbulence which is not uncommon in Florida.
The Piper Saratoga I flew for a bit didn't seem to like the speed as much, that or the toga was a bit more vocal than the Cirrus in what it was feeling with regards to airspeed.
Don't die. Stay in the envelope. Flutter is only the quickest way to ruin your airframe and day, not the only one.
Now put that together with my personal experience of extreme weather events both in NZ and ZA, the jet streams has _always_ been involved.http://squall.sfsu.edu/scripts/shemjetstream_model.html
ie. If I see a major stream coming near me... Big Stuff happens with the weather. If something extreme is happening with the weather, I check and a big stream is going very near by.
ie. I expect we will see more interesting stuff happening with the jet stream as the climate cooks.
Where it gets bumpy is if you are transitioning in or out of the jetstream zone - a bit like the abovementioned canoe hitting some rapids in a shallow part of the river.
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.
If you park at the airport - It's about a 20-30 minute journey from parking lot to the front door of the airport. If parking offsite it can even be longer.
Then going through TSA, even with pre-check, can be from 20-60 minutes. 20 minutes is about the minimum time, just due to how BIG the airport is. You can end up having to walk a mile door to gate. I can run a mile pretty fast, but that is generally frowned upon.
And if you need to somehow deal with an agent for checking bags or anything else? That can easily be another 30 minutes down the crapper.
Even better yet, 361 m/s. km/h is a derived unit. ;)
Using the metric system over the imperial system isn’t being pedantic, it’s just courtesy in 2019
In others, the word refers to a significantly different measure. For example, Norwegian and Swedish people often use the word to mean 10km, and can misunderstand a phrase like "it's just five miles outside London".
There's a list of possibilities here: https://en.wikipedia.org/wiki/Mile
Anyway, still doesn't set an unofficial record by variant or type:
Absolute fastest I can find on that site is a 747-400 at 752 knots / 866 mph but I do have a memory of one of that type breaking 800 knots over the Pacific within the last few years.
Genuinely curious I know nothing about aviation.
And because the wind is not constant, airline dispatchers will generally try to pick the route and altitude with the most favorable wind direction and speed.
But yes, you are correct. However, the person I was replying to already said they were ignorant of this stuff, so I didn't want to get too crazy.
Fluid dynamics basically means that it is impossible for any parcel of air to have an instant demarcation from nil wind to 300 knot wind without going through a (very very turbulent) transition layer. And 300 knot winds?? Maybe routine on Venus or Jupiter, but very very rare if not nonexistent on Earth.
And I would argue that not damaging the plane matters more than how long it takes to get there.
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.
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.
This is incorrect. The speed of sound in an ideal gas is a function of temperature only, and not its density. Namely, it is sqrt(gamma x R x T), where R and gamma are unchanging properties of the gas.