vinniewinnie
Posts: 628
Joined: Mon Nov 28, 2005 4:23 am

Influence Of Wind On Cost? How About Africa?

Mon Feb 11, 2013 2:31 pm

Hi Everyone,

I understand that between Europe and the U.S. Winds are very favorable East-bound but that West bounds winds actually work against travel time.

Now is there a similar situation in Africa or are winds more or less even making the journey times similar?

Second question I have is related to costs. What is the influence of winds on cost? Is the extra-cost in one direction (winds unfavorable) compensated in the other directions (very favorable winds)

Should there be no significant winds to/from Africa, does it make it cheaper (excluding all charges related to ATC, landing charges) to fly to Africa due to block time?
 
wilco737
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Joined: Sun Jun 20, 2004 12:21 am

RE: Influence Of Wind On Cost? How About Africa?

Mon Feb 11, 2013 5:07 pm

Quoting Vinniewinnie (Thread starter):
Now is there a similar situation in Africa or are winds more or less even making the journey times similar?

Most north - south flights are constant with the flight time. No huge differences.

Quoting Vinniewinnie (Thread starter):
Should there be no significant winds to/from Africa, does it make it cheaper (excluding all charges related to ATC, landing charges) to fly to Africa due to block time?

Not really. The time you lose on a westbound flight, you gain on the flight back.

wilco737
  
 
Mir
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RE: Influence Of Wind On Cost? How About Africa?

Mon Feb 11, 2013 5:47 pm

Quoting wilco737 (Reply 1):
Not really. The time you lose on a westbound flight, you gain on the flight back.

Actually, any wind will make the total trip at least somewhat longer (assuming it stays constant).

Consider a 3000nm trip, and the airplane has an average airspeed of 500kts. With no wind, it's six hours each way for a total of 12 hours. If you have a 100kt wind, the trip into the headwind will take 7.5 hours and the trip with the tailwind will take 5, for a total of 12.5 hours. So having the wind present costs you a half hour - this is because the fact that the headwind leg is longer means that it's being adversely affected for longer than the tailwind leg is being benefited.

Of course, there is also my strictly anecdotal observation that if you have a 100kt headwind going one way, you will invariably have a 50kt tailwind when it comes time to go home again. But maybe that's just my luck.   

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
rwessel
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RE: Influence Of Wind On Cost? How About Africa?

Mon Feb 11, 2013 6:07 pm

Quoting Mir (Reply 2):
Of course, there is also my strictly anecdotal observation that if you have a 100kt headwind going one way, you will invariably have a 50kt tailwind when it comes time to go home again. But maybe that's just my luck.

Actually headwinds *are* more common. Or perhaps more correctly winds that lengthen your trip are more common than winds that help. A wind doesn't start helping you until it's coming from some angle beyond a right angle to your flight path. The exact angle where a wind becomes profitable depends on the ratio of the wind speed and the speed of your aircraft.
 
wilco737
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RE: Influence Of Wind On Cost? How About Africa?

Mon Feb 11, 2013 6:44 pm

Quoting Mir (Reply 2):
Actually, any wind will make the total trip at least somewhat longer (assuming it stays constant).

Yes, the maths are correct.

Quoting Mir (Reply 2):
Of course, there is also my strictly anecdotal observation that if you have a 100kt headwind going one way, you will invariably have a 50kt tailwind when it comes time to go home again. But maybe that's just my luck.   

Haha, yeah it feels like it. But my groundspeedrecord on the 744 is 693 knots and on the 748i is 646 knots:

http://groundspeedrecords.com/records/record%20B748i%20646kts.html

So we got home pretty fast and a lot faster than the flight westbound as we flew a different route with almost no headwind at all. So you save a lot during the eastbound flight.

Over the North Atlantic that is possible to avoid the wind as good as possible. But flights from PVG to FRA or HKG where you don't have many routes you can fly, you struggle with headwinds a lot.

My last flight to PVG was 9h45 and the flight back was 11h35. So a huge difference.

wilco737
  
 
LH707330
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Joined: Fri Jun 15, 2012 11:27 pm

RE: Influence Of Wind On Cost? How About Africa?

Tue Feb 12, 2013 7:11 am

Winds, on net, are bad in terms of en-route fuel burn and distance flown. All winds can be broken down into headwind/tailwind and crosswind vectors to determine their net effect, which is bad in both cases. We already know headwind/tailwind combos are bad, per Mir's comment:

Quoting Mir (Reply 2):

Consider a 3000nm trip, and the airplane has an average airspeed of 500kts. With no wind, it's six hours each way for a total of 12 hours. If you have a 100kt wind, the trip into the headwind will take 7.5 hours and the trip with the tailwind will take 5, for a total of 12.5 hours. So having the wind present costs you a half hour - this is because the fact that the headwind leg is longer means that it's being adversely affected for longer than the tailwind leg is being benefited.

In addition, crosswinds are bad too: Assume you want to fly 4 miles forward, but there is a strong crosswind that pushes you 3 miles off course to the left in the time it takes you to get there. To correct, you need to point into the wind a bit to track a straight line. In this case, if you know you'll get pushed 3 miles left, you aim three miles to the right. What happens is you fly the hypotenuse of a right triangle, in this case 5 miles, to go 4 miles forward with a square crosswind. More generally, if you need to crab X degrees into a crosswind to fly distance A, then you end up flying A/cos(X).

Between overcoming the crosswind component (flying the hypotenuse) and the headwind/tailwind problem that Mir mentioned, there are few ways to game the system. Most flights are short haul and one thus can't generally fly around the wind, and on long hauls, per Wilco's point, there are few use cases where one can fly around the headwinds. If there's a well-defined jetstream, as over the North Atlantic, there may be times you can game it, but once you add in Europe-Asia, you're still losing.
 
vinniewinnie
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Joined: Mon Nov 28, 2005 4:23 am

RE: Influence Of Wind On Cost? How About Africa?

Tue Feb 12, 2013 1:32 pm

So moral of the story you never win with winds correct? U may win in one direction, but lose on the other...

Thank you for all your replies.

So can one say with relative precision that it is cheaper to operate to/from Africa than the US from Europe for the same distance (excluding landing fees...) due to block times being lower?

Reason I'm asking this actually is that I was wondering of African flights worked. From my little research, other than the lack of competition, flights to africa appear to have high Y and low J configurations, Higher rock bottom Y fares, but also higher costs (Landing charges...)

So wind was one of the factors I thought might explain how they might be working better from a cost perspective.
 
roseflyer
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RE: Influence Of Wind On Cost? How About Africa?

Wed Feb 13, 2013 12:19 am

I believe the worst routes in the world for winds are HNL-ICN. Hawaiian averages 11 hours eastbound and only 7.5 hours westbound. HNL-NRT is similar. 6 hours eastbound, but 9 hours westbound. The route is not fun as a passenger since eastbound is the redeye so you don't get much time to sleep, yet westbound you are flying on the never ending day.

Overall if the winds follow the normal pattern, there isn't a whole lot of added cost. However when the jetstream moves, there can be a lot of added cost.

For example, North Atlantic winds can cause more of an impact in the winter. High tailwinds make for a short eastbound flight, which results in an early arrival. Sometimes that can cause a problem with arriving before landing slots are available or before the airport opens. Airlines can avoid this with delays.

However westbound it can be a big problem. On 95% of the days a 757 can easily operate most transatlantic routes between western europe and new york. However with heavy winds, it cannot which results in fuel stops. Not only is the flight time longer, but there is an additional fuel stop which results in the plane arriving 2 hours late. Passengers miss connections and the airplane is not ready for its next flight. It causes quite a bit of havoc with the schedule. Even planes that have adequate range can be delayed 1 hour due to unseasonably high winds. If airlines proactively try to manage with a big buffer, they end up with many early arrivals and worse fleet utilization since they have excessive ground time.
If you have never designed an airplane part before, let the real designers do the work!
 
LH707330
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Joined: Fri Jun 15, 2012 11:27 pm

RE: Influence Of Wind On Cost? How About Africa?

Wed Feb 13, 2013 3:43 am

Quoting Vinniewinnie (Reply 6):
So moral of the story you never win with winds correct? U may win in one direction, but lose on the other...

Basically, yes. You lose more going against the wind than you gain back with the tailwind, and a crosswind always costs you.

Quoting Vinniewinnie (Reply 6):
Reason I'm asking this actually is that I was wondering of African flights worked. From my little research, other than the lack of competition, flights to africa appear to have high Y and low J configurations, Higher rock bottom Y fares, but also higher costs (Landing charges...)

There are other drivers of that that are more important than wind. If fuel is ~40% of the cost, and 10% (generous estimate) of that is lost to wind round trip, that still leaves you with a variance of

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