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Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
- gok 8y agoGround speed
- boyter 8y agoIsn’t that the one that truely matters some you want to go from A to B? Genuinely curious I know nothing about aviation.
- deleted 8y ago[deleted]
- mertd 8y agoYes but it won't make a sonic boom.
- cm2187 8y agoIf the wind is unstable, and slows down, can't the plane break it just out of inertia?
- cyberferret 8y agoNot really - the airplane would still be doing around 500 knots (mph) relative to the air around it. The only way the scenario you mention could happen is if the airplane hit a sudden headwind of around 300 knots in an instant. 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.
- deleted 8y ago[deleted]
- AnimalMuppet 8y agoI 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.
- borkt 8y agoJust an interesting fact that the 787 has been tested to m0.97 in a dive, pretty impressive! But not near 801 MPH airspeed. https://web.archive.org/web/20110408073905/http://www.flightglobal.com/articles/2010/03/10/339258/boeings-albaugh-bullish-on-787-flight-test-admits-eating-schedule.html https://web.archive.org/web/20110408073905/http://www.flight...
- cyberferret 8y agoYes, for those readers who may not be familiar - the speed of sound changes with altitude. At sea level, it is around 750mph but at 40,000 feet it is around 620mph IIRC. It is affected by the density of the air (which is a combination of the air pressure and temperature) - hence why they use Mach numbers to denote airspeed above certain altitudes as that takes into consideration the air density to give you a speed relative to the speed of sound at that altitude.
- theothermkn 8y ago> [The speed of sound] is affected by the density of the air (which is a combination of the air pressure and temperature)... 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.
- cyberferret 8y agoThank you. I stand corrected.
- noir_lord 8y ago
- dlb_ 8y agoYes, correct! 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.
- TheCraiggers 8y agoYes. Ground speed is basically airplane speed + wind speed.
- cyberferret 8y ago<pedant mode>Technically it would be airplane speed + wind speed vector for the same direction the airplane is heading.</pedant mode> :)
- TheCraiggers 8y agoHey, I said 'basically'! :P 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.
- ChuckMcM 8y agoNote 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).
- e40 8y agoDo you know if the rides in higher energy jet streams are less comfortable, or is it undetectable by the passengers?
- ChuckMcM 8y agoAs far as I have been able to tell in flying across the continent is the change in flight time (arriving early or late after departing on time).
- epc 8y agoI was on a flight to London that caught one of these tailwinds last year. I recall a little buffeting mid–Atlantic, don't know if that was in the jet stream or not. Only problem really was that we arrived too early in London and had to circle for half an hour before landing and then wait for immigration & customs to open.
- wefarrell 8y agoIt would be as undetectable as the motion of the earth. It's the change in velocity (not the velocity itself) that causes you to feel something. Moving from one air current to another, with a large change in velocity, would be very noticeable.
- kgermino 8y agoThis 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?
- ozzyman700 8y agohttps://www.grc.nasa.gov/www/k-12/airplane/move.html 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)
- BonesJustice 8y agoI’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.
- deleted 8y ago[deleted]
- FabHK 8y agoWind is "named" after where it comes from. If you fly north, and the wind is a north wind, you fly slower. (This terminology is in line with what GP said.) 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 :-)
- abakker 8y agoThis 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?
- foxyv 8y agoSince 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.
- jfk13 8y ago> 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.
- GaryNumanVevo 8y agoJust make a jet stream going the other way at a different altitude
- jfk13 8y agoOr 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!
- AnimalMuppet 8y agoA 200 MPH tailwind doesn't compensate for a 20,000-mile-longer flight.
- Xcelerate 8y agoI 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.
- chaseha 8y agoWould 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
- brianwawok 8y agoFor me on a trip right now, I have: 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.
- thecopy 8y ago2h airport security? In Zürich im usually done in 10 or 15 minutes...
- aidenn0 8y agoMy experience at ORD is that it's usually done in under 45 minutes, but takes longer often enough for me to budget ~90 minutes for security to be confident of making my flight.
- ashildr 8y agoThen you aren’t properly groped for freedom.
- brianwawok 8y agoWell, parking to at my gate. 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.
- heywire 8y agoInterestingly 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.192089444195219/2552201944850612/?type=3&theater https://www.facebook.com/NWSWilmingtonOH/photos/a.1920894441...
- vanous 8y agoSo 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?
- BonesJustice 8y agoIt 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?
- cm2187 8y agoBut doesn't the plane have any inertia?
- FabHK 8y agoYeah. Good question. It would really seem to depend on how fast the air speed changes. 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.
- cyberferret 8y agoFluid dynamics would spread that deceleration over a short period of time, so it wouldn't be like 'hitting the brakes in a car' type sensation. Passengers may feel a slight shift, but overall, as you explained to the previous poster, the speed is all relative to the air around the airplane. 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!
- rconti 8y ago>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.
- danepowell 8y agoI'm not an expert. But my understanding is that the "maximum propulsion" speed (587 mph) is limited by the "critical mach number" of the airframe, which for jetliners is something like 0.85. 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.
- markab21 8y agoWhen I was getting my pilots license I stumbled into a really cool video NASA did showing exactly what happens when you reach a fluttering condition like what you described. This is a link to the NASA recording if anyone is interested. https://www.youtube.com/watch?v=pEOmCkZyXzk https://www.youtube.com/watch?v=pEOmCkZyXzk https://www.youtube.com/watch?v=OhwLojNerMU https://www.youtube.com/watch?v=OhwLojNerMU (Older with music, kinda funny old-school science video from NASA) Edit: formatting.
- rochaporto_ 8y agoSimilar video with a dg300 17m glider (modified by the akaflieg). https://www.youtube.com/watch?v=qhJ1tVTtfPw https://www.youtube.com/watch?v=qhJ1tVTtfPw
- theothermkn 8y agoIn practical terms, flutter due to approaching transonic conditions is probably pretty rare. That kind of flutter is (mostly or most often) due to the interaction of normal shocks with the control surfaces, or coupling with an elastic mode of the wing or tail surface. 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.
- ilovecaching 8y agoIs this dangerous for the plane if the wind hits it sideways or something? Does this mean the flights will be extremely bumpy?
- subhro 8y agoNo it's not. The airplane just has to do wind correction by either crabbing into or away from the wind depending on the wind direction.
- cyberferret 8y agoIf you stay within the jetstream, it is a surprisingly smooth ride - a bit like being in a canoe in a middle of a fast flowing current in a river. Jetstreams tend to be fairly long and continuous. 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.
- _ph_ 8y agoLast 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.
- kawfey 8y agoAn incredible visualization of winds aloft (and several other parameters can be seen at https://earth.nullschool.net/ https://earth.nullschool.net/. Currently the jetstream (i.e. winds at 250 hPa altitude) are hitting around 230mph (360km/h).
- gHosts 8y agoWhen I first heard about global warming, the physicist in me said, hmm, the major effect of this will be energetic weather systems will become more energetic. 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 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.
- yread 8y agoApparently, climate change brings more irregularities to the jet stream https://insideclimatenews.org/news/31102018/jet-stream-climate-change-study-extreme-weather-arctic-amplification-temperature https://insideclimatenews.org/news/31102018/jet-stream-clima...
- bamboozled 8y agoThat 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.
- Kye 8y agoThat would be editorializing.
- dingaling 8y agoThey have already editorialised by converting the speed from knots Anyway, still doesn't set an unofficial record by variant or type: https://groundspeedrecords.com/wof-top-3/?aircraft-manufacturer=Boeing&wpvaircraftmodel=b787-9 https://groundspeedrecords.com/wof-top-3/?aircraft-manufactu... 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.
- deleted 8y ago[deleted]
- deleted 8y ago[deleted]
- jsjohnst 8y agoThat site only includes submissions where the pilot took a photo of the instrument panel, so yeah, definitely not the true top speed record as I’m sure that not every pilot takes a photo, let alone knows of the site.
- photojosh 8y agoIf 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. ;)
- United857 8y agoFor those of you who find this interesting, there's a whole site dedicated to this: https://groundspeedrecords.com/ https://groundspeedrecords.com/ 801 MPH is not even close to the record, even for a 787.
- selectodude 8y ago865mph in a 744 is something.
- pdx_flyer 8y agoThe tweet from Peter James: https://twitter.com/jetpeter1/status/1097682898013044736 https://twitter.com/jetpeter1/status/1097682898013044736
- speeq 8y agoDoes the Supermoon affect the Jet Stream?
- graycat 8y agoGee, maybe in an extreme case, to fly from NYC to Tokyo, fly east out of NYC and take the jet stream and save time and fuel!
- mrfusion 8y agoSo why do planes get slowed down by a jet stream? Can’t they simply stay out of it?
- nonickfx 8y agocan any pilot here please comment on the danger of this?
- jsjohnst 8y ago> danger of this Essentially zero.