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?
Google for Clear Air Turbulence.
Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
121–130 of 191 posts
Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
#122Earlier 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…
> 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 - Vol…
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.
Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
#123Earlier quoted context omitted.
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. So,…
Reading your comment, I thought "how bad is a high-altitude stall anyway? it's obviously undesirable, but what makes it dangerous? possibly entering a flat spin?" 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.
Air France 447.
Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
#124An 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).
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
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.
Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
#125Does the Supermoon affect the Jet Stream?
Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
#126Note 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 hi…
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Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
#127Earlier quoted context omitted.
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 su…
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…
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.
Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
#128So 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?
I would expect the jet stream not to end abruptly, but there is likely a gradient you have to cross before reaching "still" air. When leaving the stream, airspeed will increase, because of inertia, and so will drag. This will quickly bring the plane back to its cruising speed. 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, w…
After some clarifications from replies to my sibling post, the answer is "definitely more than 50%" because the lift-induced versus parasitic drag curve is at its minimum when the two are equal, but the efficiency curve is a relatively flat-bottomed bathtub shape, so the cruising speed is selected to be faster than where this point is as you get significant reductions in travel time for relatively small reductions in total efficiency when you are near the 50% point and increase airspeed.
Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
#129That 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.
That would be editorializing.
They 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-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.
Re: Boeing 787 Reaches 801 MPH as a Jet Stream Packs Record-Breaking Speeds
#130This 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
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 = sqrt(V), the headwind is so high that you can't make any progress toward the destination).