Atlantic jet stream

Suasdaguna1

Haven't seen this type of wind for a while.

bluecode

Any faster and you'll be supersonic.........sorry couldn't resist.

I'll get my coat and go.:o

Ah god love ya!

I noticed today an Open Skies 757 made a stop in Shannon on way from Orly to New York. Wonder could it be refueling due to winds en route?

Shamrock231

bluecode wrote: »

Any faster and you'll be supersonic.........sorry couldn't resist.

I'll get my coat and go.:o

Brings back memories eh? :pac:

emo72

what does all mean. explain it like im a pleb please.

Ah god love ya!

Basically, there's a big jetstream across the Atlantic at the minute (probably responsible for bringing all the sh!t weather at the minute). It makes it harder and easier for aircraft traveling depending on direction. If you have tailwind you're winning.

As you can see in picture above the wind is 275deg 171kt. It's giving that aircraft a groundspeed (GS) of 589 (really high)! The true airspeed (TAS) is 454kt. The GS is what the aircraft is doing over the ground and the TAS is what it's doing through the air (relative motion).

If your TAS goes above speed of sound you are supersonic. Often people get it wrong and think because your GS is over speed of sound you're supersonic. Only if the TAS goes that high are you supersonic (total nerdy in-joke :-) ).

Suasdaguna1

This is tonight's menu on the Atlantic.



I'm glad, we are back to discussing aviation topics as against unhealthy finger pointing as in other threads.

Jet streams to me are a constant source of fascination. They can be vicious when riding outside the core of them and also on the polar side.

bluecode

emo72 wrote: »

what does all mean. explain it like im a pleb please.

Ok, no question is a silly question. Speed of sound varies acccording to temperature.

The joke refers to a previous thread where someone, in my opinion made a joke about being supersonic and got into trouble for it because it made no sense.

Ah God love ya, pretty much explains it.

The mad thing about the whole speed thing, is that there are so many speeds. True airspeed, indicated airspeed, calibrated airspeed, Ground speed, and mach number, oh yeah and rectified airspeed.

It's a bloody nightmare and I'm not going there!

brandon_flowers

bluecode wrote: »

The mad thing about the whole speed thing, is that there are so many speeds. True airspeed, indicated airspeed, calibrated airspeed, Ground speed, and mach number, oh yeah and rectified airspeed.

Fast is another one!

emo72

thats gas lads.....you'd think speed would be an easy thing calculate. point A and point B and the distance between them and how long it took you to get from A to B. easy peasy apparently not!

bluecode

emo72 wrote: »

thats gas lads.....you'd think speed would be an easy thing calculate. point A and point B and the distance between them and how long it took you to get from A to B. easy peasy apparently not!

That's just ground speed, how long it took for A to B. So many variables, too fast you die, too slow you die. Indicated airspeed bearing little connection to true airspeed. Then mach number. They're all important.

Irish Steve

emo72 wrote: »

thats gas lads.....you'd think speed would be an easy thing calculate. point A and point B and the distance between them and how long it took you to get from A to B. easy peasy apparently not!

Not when all the variables are considered. The aircraft moves at a certain speed, which tends to be constant. The speed over the ground then varies depending on the temperature of the air the aircraft it in, another variable is the height of the aircraft, the air pressure in the area, and the wind speed and direction, which in the case being discussed here can make a significant difference.

In order to maintain safe separation from other aircraft over places like the North Atlantic, where radar coverage is not available, ATC may then impose a set air speed to make sure that all aircraft in the same direction at the same level are flying at that set speed to keep them the right distance apart.

Shannon to Newark is 3086 miles (2681 Nautical miles) great circle route. True airspeed on a 757 is about 440 Kts, so still air time is just over 6 hours.

Now introduce the sort of winds we've been seeing this week, which as shown above was 171 Kts, make that 170 for a moment, so 440 Kts now becomes a groundspeed of 270 Westbound, and 610 Eastbound. It's not as simple as that, the winds vary in both speed and direction, but if the wind was constant at 170 Kts, the times now become 9.92 hours westbound, and 4.39 hours eastbound. The westbound flight will most likely have to make a fuel stop en route, as 10 hours at 440 Kts is 4400 Nm, which is slightly above the max range of a 757, when reserves are taken into consideration, the still air range of a 757 is about 4000 Nm.

No airline planner in their right mind is going to plan the entire route in to the teeth of a jetstream of that strength, they will work very hard to find an alternative route or flight level that will keep the aircraft out of that sort of jet, and in the same vein, coming eastbound, they will try and take advantage of it when ever possible, though jets of that speed can be turbulent, which makes for an uncomfortable ride, even if it is shorter than normal.

Hope that clarifies why things can and do go pearshaped sometimes and end up with a stop often in places like Gander, Goose or Halifax, or Bangor, and in a case mentioned above this week, Shannon.

Not that many years ago, the aircraft of the day left Shannon with tanks full to the top, and for a considerable number of hours, they didn't know if they were going to be able to make it to the Easr coast or not, and on occasions, they would get to the famous "point of no return", and decide that they could not make it to the East coast, and have to return to Shannon, and then effectively refuel and try again the following DAY!. Now, more times than not, within a few minutes of departure, the in flight tracking map on the aircraft will be showing an arrival time that is often accurate to less than 10 minutes in a flight that may last 10 or 11 hours, or longer, depending on the aircraft type, and fuel stops en route are a rare event.

If any of the figures above are not exactly accurate, it's because I've not gone and read up all the relevant manuals, and not done all the conversions that would normally be needed to get really accurate figures, all I'm interested in doing here is making the reasons for the significant differences in time and fuel requirement clearer.

Ah god love ya!

emo72 wrote: »

thats gas lads.....you'd think speed would be an easy thing calculate. point A and point B and the distance between them and how long it took you to get from A to B. easy peasy apparently not!

You are right. At its most basic it is just the basic speed, distance, time formula. The problem with flying is that you need to fly through the air at such a rate that a certain mass of air passes over the wing. To do this you need a measure of the velocity of the air (also called dynamic pressure). For this pilots use Indicated (or more correctly calibrated) airspeed indicators. It is rarely correct for the actual speed of the aircraft over the ground, it's mainly for determining the speed of air over a wing. That's why theoretically you could fly with a massive headwind, a very low stall aircraft and do zero knots over the ground.

When you have your calibrated airspeed you then need to correct for density changes as you climb. The air gets thinner but you still need that mass of airflow over the wing. Therefore the aircraft moves quicker through the air but still indicates the same speed indicated. This 'hidden' or 'quicker' speed is called True Airspeed and allows you calculate your ground speed using the wind vector which leads back to the basic formula you use for determining how long it will take you to get from A to B.

It really takes some working out in your head when you start pilot training!

LeftBase

bluecode wrote: »

Any faster and you'll be supersonic.........sorry couldn't resist.

I'll get my coat and go.:o

If you had a TAS of 460 and a tailwind in a jetstream of 201kts your ground speed would be 661kts which is close to the standard speed of sound at sea level of 661kts.

Ah god love ya!

LeftBase wrote: »

If you had a TAS of 460 and a tailwind in a jetstream of 201kts your ground speed would be 661kts which is close to the standard speed of sound at sea level of 661kts.

You still ain't supersonic. If it were you would need to radically change the design of pax aircraft. It is all relative to the air, not the ground, as that's the medium sound travels in and that's what would give adverse effects should you exceed that speed.

Generally pax aircraft do about 0.84 the speed of sound.

LeftBase

Ah god love ya! wrote: »

You still ain't supersonic. If it were you would need to radically change the design of pax aircraft. It is all relative to the air, not the ground, as that's the medium sound travels in and that's what would give adverse effects should you exceed that speed.

Generally pax aircraft do about 0.84 the speed of sound.

I'm aware of that. However your speed over the ground is faster than sound is at sea level in the above conditions even if you are sub Mach 1 at FL380.

You may not have supersonic airflow, but your GS is fast enough to be supersonic at MSL.

I'm being perhaps a little bit tongue in cheek here about this!:cool:

It's the black and white literal thinking of a lot of people added to some people's desire to show off at the time that lead to this whole supersonic issue in the 1st place!

Ah god love ya!

LeftBase wrote: »

I'm aware of that. However your speed over the ground is faster than sound is at sea level in the above conditions even if you are sub Mach 1 at FL380.

Speed of sound at FL370 (the flight level of the aircraft shown) is around 574kt. Its GS is 589kt so you want to say the aircraft is going faster over the ground than sound is traveling through the air there? You can say that and you are right but it's of little practical relevance other than trying to imagine what the speed of sound looks like.

LeftBase

Ah god love ya! wrote: »

Speed of sound at FL370 (the flight level of the aircraft shown) is around 574kt. Its GS is 589kt so you want to say the aircraft is going faster over the ground than sound is traveling through the air there? You can say that and you are right but it's of little practical relevance other than trying to imagine what the speed of sound looks like.

As I said above. My tongue in cheek point is that with enough tailwind you can cover more ground in your aircraft at FL370 than a supersonic car at SL while not achieving supersonic airflow over the wings.

Ah god love ya!

LeftBase wrote: »

As I said above. My tongue in cheek point is that with enough tailwind you can cover more ground in your aircraft at FL370 than a supersonic car at SL while not achieving supersonic airflow over the wings.

Sorry to be pedantic. In fact, I think, most modern airliners do achieve supersonic flow over the wings. This being due to the fact they have super critical wings where there is less adverse effects from drag wave.

islanderre

Think I'm going to have the read the posts in this thrread a few times to attempt to comprehend the different 'types' of speed!!!!!!

Thanks all; great info

amen

In fact, I think, most modern airliners do achieve supersonic flow over the wing

was that not partially why they introduced the winglets? Supersonic airflow at the wing tips caused dragged and thus a decrease in wing efficiency ?

Ah god love ya!

amen wrote: »

was that not partially why they introduced the winglets? Supersonic airflow at the wing tips caused dragged and thus a decrease in wing efficiency ?

As far as I know the winglets are mainly for the vortexes that are created when lift is produced. They impede relatively high pressure underneath the wing mixing with the low pressure above and hence reduce induced drag. You can also have fuel tanks positioned there and wing tips that point downwards for the same effect.

To counter drag as a result of flying a speed that gives supersonic speeds to air flowing over the wing they have sweepback (directing the wing backwards) and the super critical wing which is flatter on top I think.


That's my basic understanding of it. Maybe others might have more info. Hope that helps!

Preset No.3

I did IAD-DUB on Thursday night. There was a 45 minute delay at the tailwinds were about 90mph so they couldnt take off due to there not being ready in DUB when we arrived.

LeftBase

Preset No.3 wrote: »

I did IAD-DUB on Thursday night. There was a 45 minute delay at the tailwinds were about 90mph so they couldnt take off due to there not being ready in DUB when we arrived.

A lot of the time aircraft must depart on time for slots. A few years ago I was flying LAX-LHR-DUB and we had to slow to a crawl on the LHR-LAX according to the pilot as we were too early but had to meet our take off slot at LAX.

Tenger

Preset No.3 wrote: »

I did IAD-DUB on Thursday night. There was a 45 minute delay at the tailwinds were about 90mph so they couldnt take off due to there not being ready in DUB when we arrived.

Nice winds for those heading Eastwards at the moment.
Looking at arrivals this morning. The 2 early EI arrivals (JFK and BOS) both arrived in an hour early......

Best username ever

Tenger wrote: »

Looking at arrivals this morning. the 2 early EI arrivals (JFK and BOS) both arrived in an hour early......

As did I on the JFK-DUB route some time back.

Veloce

Always wondered how does the wind speed indicator work on the instrument display? Is it actual wind speed measured using an aircraft system or a feed from a local weather information to where the aircraft currently positioned?

Suasdaguna1

Directly from the airbus manual

"Wind direction and speed ADIRS provides the wind direction and speed. The digital direction reflects the true north reference, and the analog direction (indicated by the green arrow) reflects the north reference that is in use. The green arrow only appears, if the wind speed is above two knots and the true airspeed is above 100 kt. If the display does not receive either wind speed or direction, dashes replace the numbers on the display."

Ah god love ya!

Veloce wrote: »

Always wondered how does the wind speed indicator work on the instrument display? Is it actual wind speed measured using an aircraft system or a feed from a local weather information to where the aircraft currently positioned?

It's calculated by the Air Data Computer using True Air Speed (indicated airspeed corrected for density - uses the pitot, static and air data computer to calculate), ground speed (distance taken from Inertial reference system and divided by time) and drift (again taken from inertial reference system by comparing your heading vs. your track made good). Two vectors are made and where they are joined is the magnitude and direction of your wind. No connection needs to be made with the ground although pilots do do that to know what weather they're headed for e.g. destination airport.

Veloce

Ah god love ya! wrote: »

It's calculated by the Air Data Computer using True Air Speed (indicated airspeed corrected for density - uses the pitot, static and air data computer to calculate), ground speed (distance taken from Inertial reference system and divided by time) and drift (again taken from inertial reference system by comparing your heading vs. your track made good). Two vectors are made and where they are joined is the magnitude and direction of your wind. No connection needs to be made with the ground although pilots do do that to know what weather they're headed for e.g. destination airport.

Makes sense. Thanks for the explanation.