
Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds - ilamont
https://www.latimes.com/science/la-sci-sn-jet-stream-flight-20190219-story.html
======
ChuckMcM
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).

~~~
e40
Do you know if the rides in higher energy jet streams are less comfortable, or
is it undetectable by the passengers?

~~~
jsjohnst
I’ve had a SFO -> London flight once where the pilot intentionally flew into a
very strong jet stream current (saved us a lot of flight time, think it was
close to an hour). Experienced a short burst of mildly rough turbulence
entering and exiting, but otherwise smooth sailing.

~~~
henvic
Just curious... How do you know that? I wonder how some nervous passengers
might react if they learned the pilot decided to enter a turbulence area on
purpose.

~~~
jsjohnst
The pilot got on the intercom and specifically stated he was doing it. He
assured everyone there was zero risk outside the brief bumpiness and it would
get us there much faster. He got loud cheers of support from the cabin, so I
guess those nervous just kept to themselves.

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kgermino
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?

~~~
ozzyman700
[https://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
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.

~~~
FabHK
Wind 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 :-)

~~~
bartread
> Wind is "named" after where it comes from.

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?

~~~
yesenadam
Can you name anything else named after where it's going, not where it comes
from? I can't think of anything named like that, but I guess there must be
some.

~~~
cr1895
Within a marine context, current is typically given as direction to while wind
and waves are direction from.

------
abakker
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?

~~~
jfk13
> 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.

~~~
logifail
> 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

~~~
pdx_flyer
Typically yes. Right now there is a general avoidance of Ukrainian (Crimean
and nearby) and Syrian airspace so the flight plans will take that into
account, the winds aloft, and the airways available.

------
United857
For 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
865mph in a 744 is something.

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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...](https://www.facebook.com/NWSWilmingtonOH/photos/a.192089444195219/2552201944850612/?type=3&theater)

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vanous
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?

~~~
BonesJustice
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?

~~~
cm2187
But doesn't the plane have any inertia?

~~~
FabHK
Yeah. 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.

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rconti
>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
I'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
When 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.

~~~
theothermkn
In 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.

~~~
markab21
Interesting.

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.

~~~
theothermkn
Only in the most general terms, and from first principles: Composite
structures will have a higher stiffness per unit mass, which will cause the
fundamental frequencies to be higher both for the pure structural modes and
the control surface interaction modes. It's therefore likely that you'd only
begin to encounter these aeroelastic modes at higher speeds. In other words,
if you take the driving frequency as something like the inverse of the time it
takes for air to pass over the wing, that may match the metal wing more
closely than the composite wing. Modeling that stuff in a wind tunnel is very
tricky, and you used to end up with these not-at-all-realistic-looking models
that, nonetheless, captured some aspect of the full-scale aircraft being
modeled.

Don't die. Stay in the envelope. Flutter is only the quickest way to ruin your
airframe and day, not the only one.

------
kawfey
An 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
When 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
Apparently, climate change brings more irregularities to the jet stream

[https://insideclimatenews.org/news/31102018/jet-stream-
clima...](https://insideclimatenews.org/news/31102018/jet-stream-climate-
change-study-extreme-weather-arctic-amplification-temperature)

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ilovecaching
Is this dangerous for the plane if the wind hits it sideways or something?
Does this mean the flights will be extremely bumpy?

~~~
cyberferret
If 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.

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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.

~~~
brianwawok
For 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
2h airport security? In Zürich im usually done in 10 or 15 minutes...

~~~
brianwawok
Well, 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.

------
pdx_flyer
The tweet from Peter James:
[https://twitter.com/jetpeter1/status/1097682898013044736](https://twitter.com/jetpeter1/status/1097682898013044736)

------
_ph_
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.

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graycat
Gee, 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!

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bamboozled
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.

~~~
photojosh
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. ;)

~~~
bamboozled
You’re right I did just paste that figure from Google conversions.

Using the metric system over the imperial system isn’t being pedantic, it’s
just courtesy in 2019

~~~
photojosh
It's from a USA-based newspaper. I hate imperial with a passion, but it is
still their backarsed standard. Surely anyone with a scientific bent can do a
rough calculation in their head. For me, it was "oh, around 1300 km/h, cool"
and moved on...

~~~
Symbiote
In many countries, miles are as obscure to people as leagues, perches and
gills probably are to you.

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](https://en.wikipedia.org/wiki/Mile)

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speeq
Does the Supermoon affect the Jet Stream?

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gok
Ground speed

~~~
boyter
Isn’t that the one that truely matters some you want to go from A to B?

Genuinely curious I know nothing about aviation.

~~~
AnimalMuppet
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.

~~~
noir_lord
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.

~~~
AnimalMuppet
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.

------
mrfusion
So why do planes get slowed down by a jet stream? Can’t they simply stay out
of it?

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nonickfx
can any pilot here please comment on the danger of this?

~~~
jsjohnst
> danger of this

Essentially zero.

