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Airbus747
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How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 9:45 am

No technical/aeronautical background here, just an aviation enthusiast.

Having seen many articles about records being broken and the debate about the difference between ground and air speed, I would like to ask more about the "mechanics" of what happens when a passenger airliner is "pushed" by such strong tail wind.

How does the plane stay stable with such strong winds? Is it because it aligns itself with the exact bearing of the wind?

Could the wind be so strong to "push" the plane so hard that it can break apart or at least be "derailed" from its air route?

What's the worst that can happen and how are airliners prepared?
 
Birdwatching
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 9:52 am

You have the wrong idea here.
Nothing is "pushed" by the tailwind. It's not like the wind comes from behind and pushes the aircraft or anything like that.
The plane still moves forward at a high speed, relative to the air surrounding it, but this air surrounding it happens to be moving in a certain direction itself.
Think of it like walking from the rear to the front of a bus, while the bus is moving. You're still walking at a normal walking speed and you wouldn't notice the difference. But as the bus itself is moving forward, you're going faster than you normally could (relative to the road).
Hope this explains it.

Soren   
All the things you probably hate about travelling are warm reminders that I'm home
 
sk736
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 9:57 am

Quoting Birdwatching (Reply 1):
Hope this explains it.

That's a really good explanation...thanks!
 
UAEflyer
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 9:57 am

Quoting Birdwatching (Reply 1):

You explained it perfectly, well done
 
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Airbus747
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 10:20 am

Quoting Birdwatching (Reply 1):

Wow, I feel smarter than before. Thanks, I now understand. So basically the whole "huge bubble of air" moves, rather than just some gusts of wind pushing you.

I guess another analogy could be walking on the moving walkway in the airports.

Wait, so now that I think of it, if a 777 reached 1220km/h ground speed, and I ran along the planes at 5km/h, would that mean that I am running at the [ground]speed of sound? 
 
AR385
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 10:31 am

While I really think you will get a much better understanding if you post this in the Tech forum, Soren gave you a pretty good albeit intuitive answer. I´ll give it a try.

Quoting Airbus747 (Thread starter):
How does the plane stay stable with such strong winds? Is it because it aligns itself with the exact bearing of the wind?

What do you mean stable? Do you mean as it doesn´t go crazy and moves all over the place? If so, then, no, it does not align with the wind. It aligns in the best direction that maximizes the benefit of the wind and keeps it going where it wants to go. See "Crabbing" But it will be stable. There might be turbulence for the entire flight, but no dangerous instability.

Quoting Airbus747 (Thread starter):
Could the wind be so strong to "push" the plane so hard that it can break apart or at least be "derailed" from its air route?

No. While 2 or 3 airliners in the modern area have been brought down by weather phenomena, and as such you may include wind, it is very, extemely rare to even worry about such.

Quoting Airbus747 (Thread starter):
What's the worst that can happen and how are airliners prepared?

1) Certain routes in the limit of the plane´s range may not be able to be operated that day.
2) Passengers may have a very uncomfortable ride.
3) The flight can turn out to be extremely long for the usual.
4) A non scheduled stop may be required.
 
rwessel
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 11:08 am

Quoting Airbus747 (Reply 4):
Wait, so now that I think of it, if a 777 reached 1220km/h ground speed, and I ran along the planes at 5km/h, would that mean that I am running at the [ground]speed of sound? 

The speed of sound only applies to the airmass you're moving through. There is no "ground speed of sound" (unless you mean the speed of sound through the ground, which is a different matter altogether). You can, of course, compute your local speed of sound, and then achieve that speed relative to the ground, but at that point it no longer has anything to do with the speed of sound.
 
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Francoflier
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 12:01 pm

Think of it as a giant treadmill....

  
I'll do my own airline. With Blackjack. And hookers. In fact, forget the airline.
 
Mir
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 12:50 pm

Quoting Airbus747 (Reply 4):
Wait, so now that I think of it, if a 777 reached 1220km/h ground speed, and I ran along the planes at 5km/h, would that mean that I am running at the [ground]speed of sound?

You could, but if you claimed that you were running at the speed of sound we'd all know that you were lying.   You're still doing your 5km/h, and you're getting a lot of assistance.

Which is why when you read stories about non-Concorde airliners "going supersonic", don't believe it for a second - the planes themselves are still flying at their normal cruise speeds. They've just got big tailwinds.

-Mir
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Dalmd88
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 1:01 pm

Another way to think about it is a boat on a river. While moving down stream your speed relative to the shore is fast. The speed of the water combined with the speed of your paddling (airspeed) equal your forward speed (groundspeed). While moving upstream is the opposite The speed your paddling (airspeed) minus the speed of the river current (windspeed) equals your speed up the river relative to the shore (groundspeed). In both examples your amount of paddling are the exact same but your progress along the shore is reflected by the speed of the river current and your direction.
 
Bongodog1964
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 1:02 pm

Quoting Airbus747 (Thread starter):
What's the worst that can happen and how are airliners prepared?

For the average passenger, the worst that can happen is an unscheduled stop at Gander Newfoundland or Bangor Maine.

Once worked with a person who booked a cheapo trip from LTN - the Dominican Republic, they ended up stopping at both Gander and Bangor due to headwinds.
 
N126DL
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 1:20 pm

Those moving walkways at an airport are another example. They get you to the other end faster than if you just walked beside it or if you stood on it without walking.
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b747400erf
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 2:17 pm

you are riding a wave of air moving at a fast speed
 
vv701
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 2:27 pm

Quoting Airbus747 (Reply 4):
Wait, so now that I think of it, if a 777 reached 1220km/h ground speed, and I ran along the planes at 5km/h, would that mean that I am running at the [ground]speed of sound?

Look at it this way.

The world's longest golf putt was achieved by Spain’s Jose Maria Olazabal. His ball was moving for 26.17 seconds before entering the 'hole' He made his putt from the aft end of Concorde's cabin down its 150 foot length. The 'hole' was at the front of the cabin. His ball had actually travelled 9.232 miles before entering the hole as Concorde's ground speed was 1,270 mph.

The putt was made as Concorde was flying the European Ryder Cup Team to the USA. This was not the only record set on that flight. It broke the existing LHR-BOS record setting a new fastest time of 3 hrs 6 mins.
 
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neutrino
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 2:55 pm

Quoting Airbus747 (Reply 4):
would that mean that I am running at the [ground]speed of sound?

But you are already supersonic even when keeping still; on your feet or your bum or lying flat down.
If your location is not far from the equator, you are now hurling at about 1,600 km per hour; a tad slower if closer to the Tropics.      
You see, everything is relative.   
Potestatem obscuri lateris nescitis
 
ThirtyEcho
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 8:42 pm

To confuse the issue further we could throw in the concepts of true airspeed versus indicated airspeed. Look at it this way, at 40,000 feet, your airliner is moving through the air at 500 knots but the airspeed indicator reads 320 knots. Meanwhile, you are clocking a groundspeed of 600 knots due to a jetstream of 100 knots.

If you turned around 180 degrees, you'd still have a true airspeed of 500 knots and an indicated airspeed of 320 knots but your groundspeed would only be 400 knots.

Confused?
 
29erUSA187
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 8:46 pm

Quoting Airbus747 (Reply 4):
I guess another analogy could be walking on the moving walkway in the airports.

You've just reminded me of my favorite pastime during long midnight/overnight layovers. Walking the other way trying to stay in the same spot. I had a 4 hour layover at MDW onetime near midnight, and no one was in the terminal, so I had a very entertaining layover 
 
nicholasjet
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 9:10 pm

Well actually, a quartering tail wind can be the worst conditions for an aircraft, as like any weather vane, a large tail fin will try to turn into wind. So whilst the aircraft is trying to push ahead at a certain track, the wind can try to push against this, and therefore create some lumps and bumps in the flight.

A tailwind will never make an aircraft break the sound barrier, most aircraft are restricted to around 80% of the speed of sound, as their wings aren't made for that type of speed.
 
StTim
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 9:14 pm

Quoting neutrino (Reply 14):
You see, everything is relative.

Well more accurately everything depends on your reference frame.
 
rwessel
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sat Jan 17, 2015 9:55 pm

Quoting nicholasjet (Reply 17):
Well actually, a quartering tail wind can be the worst conditions for an aircraft, as like any weather vane, a large tail fin will try to turn into wind. So whilst the aircraft is trying to push ahead at a certain track, the wind can try to push against this, and therefore create some lumps and bumps in the flight.

Again, an aircraft in (normal) flight will never experience a tailwind, and except for very transient effects, no relative wind except from dead ahead. If the relative wind is not from directly ahead (the occasional deliberate slip excepted), your flight instructor will yell at you and lecture you about coordinated flight. Either that or you need to complain to maintenance that the autopilot is broken.

If by "quartering tailwind", you mean the airmass, within which the aircraft is moving, is itself moving in a particular direction, then sure, but it doesn't impact the aircraft, which is still moving directly into its relative wind. It will alter the aircraft's speed and track over the ground.
 
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Airbus747
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 1:55 am

Thanks for all the replies. Having said all this though...

1. True, the pilots/aviators care about air speed of the plane, but...

2. The passengers/travelers/travel-agents care about how fast they get from place A to place B. For those who travel, what matters more is the old definition of speed, i.e. cover as much [ground] distance as possible in as least time as possible.

Given point 2, would it be possible for airlines to plan and schedule flights based on predictions of tailwind?
 
maxpower1954
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 2:28 am

Quoting nicholasjet (Reply 17):
Well actually, a quartering tail wind can be the worst conditions for an aircraft, as like any weather vane, a large tail fin will try to turn into wind. So whilst the aircraft is trying to push ahead at a certain track, the wind can try to push against this, and therefore create some lumps and bumps in the flight.

It's a common misconception, even among less experienced pilots, but airplanes don't "weathervane" in flight. rwessel explains it well.
 
prebennorholm
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 3:35 am

Maybe is becomes easier thinking this way:

Wind is when the rocky part of planet Earth and the atmosphere do not rotate around the Polar Axis at exactly the same speed.

Aircrafts fly in the atmosphere. They don't feel any movements of the rocky part of the planet.

The only force by the rocky planet on the aircraft is gravity, a 1G gravity in direction of the center of the Earth. The rocky planet can spin at any speed underneath, it still provides the same 1G and nothing else.

The only effect of tailwind is that a fixed point on the rocky planet (for instance your destination) is moving closer to you while you a flying. Therefore you reach it earlier.
Always keep your number of landings equal to your number of take-offs
 
bourbon
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 4:55 am

Think of the tailwind from the Jetstream as a moving walk way assisting you through an airport terminal and the headwind as if you were walking against the moving walk way.
 
simpilot459
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 5:16 am

Quoting nicholasjet (Reply 17):
Well actually, a quartering tail wind can be the worst conditions for an aircraft, as like any weather vane, a large tail fin will try to turn into wind. So whilst the aircraft is trying to push ahead at a certain track, the wind can try to push against this, and therefore create some lumps and bumps in the flight.

A common misconception. As soon as the airplane wheels leave the ground, the airplane has no idea (and doesn't care) what it is doing relative to the ground. It only cares what it is doing in the "bubble" of air it is flying in. It the bubble is going forward, back, up, down, or sideways, the airplane doesn't care, the "bubble" could be traveling at 1000mph (and depending on your frame of reference it may be due to earth's rotation, or even it's orbit around the sun) it just knows it's flying in that bubble. It is true that the airplane may have a wind correction angle. but this is merely the geometric difference between the path the airplane it flying in the air (heading), and the path the airplane is flying over the ground (course). This is due only to the direction the "bubble" is moving, and nothing the airplane itself is doing (remember, the airplane doesn't care what it is doing relative to the ground). This is the basics of reference frames and relative motion. Common examples are the moving walkway and taking a boat across a flowing river.
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luganopirate
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 5:46 am

But why a higher speed at 40,000' or at the Equator?
 
ThirtyEcho
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 5:49 am

My Treadmill Proximity Warning System just gave an alert.
 
WingedMigrator
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 6:26 am

Quoting Airbus747 (Reply 20):

Given point 2, would it be possible for airlines to plan and schedule flights based on predictions of tailwind?

Yes of course, they already do this. For example, compare the scheduled time for a direct flight LHR - JFK to the time for JFK - LHR. Because of prevailing winds, eastbound is faster.
 
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antoniemey
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 7:59 am

Quoting Airbus747 (Reply 4):
So basically the whole "huge bubble of air" moves, rather than just some gusts of wind pushing you.

You can (sometimes) get a similar effect in a car on a day with high, straight winds., except that in the car the difference isn't really an impact on your speed, because that's determined by how many times the wheels rotate on the ground per second, but in how much fuel you burn to keep that speed. If you're driving with the wind it's a heck of a lot easier for your car to get to (and past) the speed limit so you can go faster on less fuel. Driving back into that wind on your return trip your car will have to work harder to maintain speed, and so burn more fuel. In either case, you're already going faster than any wind short of a hurricane would blow, but it affects how hard your engine has to work to get you where you want to go.
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Airbus747
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 9:15 am

Quoting simpilot459 (Reply 24):

How big is this [imaginary?/real?] bubble?
 
StTim
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 11:00 am

 
Rara
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RE: How Are Airliners "pushed" By Jetstream Tailwind?

Sun Jan 18, 2015 3:13 pm

Quoting maxpower1954 (Reply 21):
It's a common misconception, even among less experienced pilots

Indeed.. I've been on the jumpseat during a holding, and the co-pilot said something to the extent of "now as she's turning into the wind, the airspeed goes down" or some such. Sounded almost nautic, was complete bollocks of course. I didn't say anything.

Quoting Airbus747 (Reply 20):
2. The passengers/travelers/travel-agents care about how fast they get from place A to place B. For those who travel, what matters more is the old definition of speed, i.e. cover as much [ground] distance as possible in as least time as possible.

Given point 2, would it be possible for airlines to plan and schedule flights based on predictions of tailwind?

That's not really practical because passengers need to get to their destination, and planes follow fixed schedules, but in fact routes are planned based on wind predictions every day. In fact, the standard routes over the North Atlantic are revised everyday to maximize wind on the eastbound sector, and minimize wind over the westbound sector.
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