Qatar Airways: Go Slow To Save Fuel?

[enyaw]

Tell me then why is it cheaper flying from Thailand to the UK than it is going the other way? Because the aeroplane's go up and bloody stay there in mid-air and wait for the flippin' earth to spin around don't they, effectively getting more miles per gallon this is why it's cheaper.

A Garnett.

[Spee]

Please, please tell me that you two are not really serious? Let me guess, you think if you jump up in the air that the Earth moves beneath you? And that you land in a different spot? Clearly the educational system you've experienced has failed you.

Whether firmly earth-bound, or floating above the Earth (within the confines of the Earth's gravity), your speed relative to the earth remains constant at ZERO MPH/KPH. If you were floating in space outside the influence of Earth's gravity then yes, the Earth would move beneath you at ~ 700 MPH.

The rotation of the Earth has absolutely no influence on flght times east to west, west to east or north<->south.

I like a lot of your posts, but these comments are a little off base.

The prevailing westerly winds are a direct result of the earth's rotation. Prevailing winds typically result in 150mph tail wind and 150mph head wind on flights from the US east coast to the UK and Europe. A flight from Boston to Heathrow typically takes about 6.5 hours. The return flight usually takes 30-60 minutes longer.

The earth's rotation and latitude position are key reasons for selecting rocket launch sites for non-polar-orbit trajectories. The European Space Agency specifically chose Guyana because it was the closest they could get to the equator. Refer to this link for basic explanation:

http://www.aerospaceweb.org/question/spacecraft/q0080.shtml

WHile no expert, I'm sure the long haul routes are selected on a trade-off between wind gains and least path (aka, great circle routes).

http://en.wikipedia.org/wiki/Great_circle

Here's an interesting tool that I found to look at Great Circle routes:

http://gc.kls2.com/

From my experience, some airline routes follow great circle paths almost exactly (e.g., east coast US to Heathrow) and some deviate significantly for whatever reasons (e.g., LAX-NRT). Interestingly, the tool shows the JFK-BKK route that Thai Airways used to offer, as a polar route, but I'm not sure if that's the route they actually flew.

[Carib]

Warwick is right because the earth rotates west to east alot of airlines when travelling in the other direction will fly the aircraft up and wait there while the earth rotates round till the airport your going to comes around and then slowly descend onto it. It saves a fortune in fuel and is much better for the enviroment, I for one support this and don't mind the extra few hours airtime.

A Garnet.

Earth and it`s rotation has been a part of trip planning since the early days of long distance flights.

I think you are mixing a few things up here.

You don't mind "the extra hours air time". Well, I do because every hour up there costs money, earth rotating or not.

Aircraft will not just go up and wait until the next stop is underneath, and than land there.

The shortest route ( weather and traffic control allowing) will be used to get to a destination, and the earth rotation van be an advantage, just as it can be a disadvantage.

But staying up there longer is not very fuel/cost efficient.

Please, please tell me that you two are not really serious? Let me guess, you think if you jump up in the air that the Earth moves beneath you? And that you land in a different spot? Clearly the educational system you've experienced has failed you.

Whether firmly earth-bound, or floating above the Earth (within the confines of the Earth's gravity), your speed relative to the earth remains constant at ZERO MPH/KPH. If you were floating in space outside the influence of Earth's gravity then yes, the Earth would move beneath you at ~ 700 MPH.

The rotation of the Earth has absolutely no influence on flght times east to west, west to east or north<->south.

Hold the horses, yes you are partly right and some parts absolutely right, but....

I was debunking the rotation theory, in the same way as it was stated. Didn't do a good job because I didn't take the air mass movement in to the whole thing. To me it is a just a fact that doesn't need much thought, and I should have explained better.

You are right to say that if you jump that you will land on the same spot. That is IF the air masses will allow you to do so. That is where the rotation theory comes in and the effect of it on the air masses .

It is a very complex picture. Ones lifting of the earth you are in a different medium , which by the rotation of the earth, and the effect gravity has on it, Will have a different movement than as a stationary mass of air. It will put you down on a different spot that you jumped from, if you went up high enough and stayed up there long enough.

To really get into the nitty gritty of it al look at the Coriolis effect, The hadley, Ferris and polar weather cells and if you want to fire a long range missile without it leaving earth`s gravity field also take the Etvos effect into consideration. ( I do this by heart so don't mind the spelling.).

So, yes the earth atmosphere moves together with the earth at the same speed, but the atmosphere has got a mind of its own, with the first push given by earth rotation. Usually very predictable under normal circumstances, hence shorter or longer flights depending on direction. It is an accepted `thing`, nobody really gives it a thought ones you are used to it.

FAA or Jar trained guys/girls don't even really grasp this theory, but just accept it and learn to live with it, and the place where they are confronted with it is usually the met office. Earth rotation all of a sudden doesn't really exist anymore, they are just looking at the result of it. ( of course there is more )

Endless discussions take place about this, especially the ones who are in traing to become pilots or have a job related to aviation or other use of the earth`s airspace. Some will just give up and accept that the earth rotates and that is takes more time to get from A to B than the other way around, depending where you are. I don't discuss this either, I stopped thinking about it and just accepted.

Thanks for the comment Lomatopo, at least someone was really awake.

After all that I can only hope and pray you have nothing to do with the safety of any airline passengers as you appear, from your post(s), to be way too close to "Le Bong".

I admit that I sometimes forget how many truly ignorant ("I stopped thinking...", the definition of ignorance) people there are in our World. Thanks for the reminder. Good luck with that jumping thing!

Jumped lots of times, but out of moving aircraft when I was younger. After your kind words I absolutely donot feel the need to elaborate about my professional career in aviation. But it had everything to do with safety. Bongs are out in that busineness, always have been. That is a safety issue too.

Bye.

[GeorgeW]

Whether firmly earth-bound, or floating above the Earth (within the confines of the Earth's gravity), your speed relative to the earth remains constant at ZERO MPH/KPH. If you were floating in space outside the influence of Earth's gravity then yes, the Earth would move beneath you at ~ 700 MPH.

There is no such thing as being outside the influence of Earth's gravity. No matter where you are in the universe, Earth's gravity will have an effect. It's just that the further away you get, the lesser the effect is, and at some point the gravitational effect of other closer/more massive bodies will have a much greater effect so that the Earth's effect will be negligible in comparison.

Edited August 26, 2008 by GeorgeW

[goonerthegooner]

Hey,

What the hel_l,I am flying Business Class on BKK-DOH-LHR-DOH-BKK,on the 6th,so the longer the flight the better,more Champers too be drunk.

Just love these long flights,trying too beat my record of 3 bottles of Champers on 1 leg.

Will let you know the outcome.

[lomatopo]

Please, please tell me that you two are not really serious? Let me guess, you think if you jump up in the air that the Earth moves beneath you? And that you land in a different spot? Clearly the educational system you've experienced has failed you.

Whether firmly earth-bound, or floating above the Earth (within the confines of the Earth's gravity), your speed relative to the earth remains constant at ZERO MPH/KPH. If you were floating in space outside the influence of Earth's gravity then yes, the Earth would move beneath you at ~ 700 MPH.

The rotation of the Earth has absolutely no influence on flght times east to west, west to east or north<->south.

I like a lot of your posts, but these comments are a little off base.

The prevailing westerly winds are a direct result of the earth's rotation. Prevailing winds typically result in 150mph tail wind and 150mph head wind on flights from the US east coast to the UK and Europe. A flight from Boston to Heathrow typically takes about 6.5 hours. The return flight usually takes 30-60 minutes longer.

OK, now that we've established that an aircraft's relative speed to the Earth is not affected by its rotation we can move on to those things which actually affect an aircraft's relative speed to the earth. Those would be the aircraft's engines and any external effects the aircraft might encounter. External effects are limited to the forces exerted upon it in the form of lift and drag. Drag being the resistance the aircraft encounters as it moves through the air. Drag is affected by the aircraft's speed and profile, along with any directional component the surrounding air might have, i.e. wind. The Jet Stream(s) that circle the Earth can greatly affect an aircraft's relative (to the Earth) speed. Jet Streams take all sorts of paths, and longer-haul flight plans usually try to take as much advantage, as is possible, of that day's forecasted jet-streams, either by flying with the jet-stream, or by avoiding it. The jet streams are not caused by Earth's rotation but rather the coming together of air masses of differing temperatures. Jet streams can certainly affect an aircraft's relative speed to the Earth as they can reach speeds up to 200 mph, and have to be accounted for when planning a flight, and calculating the required fuel. Jet streams vary widely in direction daily and can take some odd, meandering paths. Jet Streams are most pronounced in the northern and southern hemispheres and not prevalent closer to the Equator. Hence I doubt and jet stream would impact a DOH-BKK flight to any significant degree.

There are quite a few web sites with live jet stream maps (speed, direction, thermal overlays).

http://squall.sfsu.edu/crws/jetstream.html

Prevailing winds vary in direction in direction based on the longitude and are a result of heating and cooling of air-masses which move from high pressure to low pressure. Prevailing winds are also less pronounced near the Equator (i.e the Doldrums).

So yes in an incredibly indirect way the Earth's rotation, because air-masses are exposed to the Sun's thermal radiation, then cool throughout a single day, does have an impact on flight times in any direction.

[Monkeypants]

I think that airlines would not deliberatley be on a go slow, They must get it down refuelled and filled with passengers again ASAP so as to be cost effective. A go slow would lengthen the turnaround time.

But maybe this applies to just short haul flights?

[dekka007]

It is possible. Depending on company policy. There is a cost index (A value) in the flight management computer which directly effects: Climb speeds, cruise speeds, descent speeds.

If you increase the cost index value on the FMC then the aircraft will fly faster in the cruise, descent - resulting in a higher fuel burn - resulting in higher airline costs. Obviously if you reduce the cost index, (Winds playing a role in this also) then aircraft flys slower, longer flight but fuel savings.

I know of several carriers now that are instructing crew to reducing cost index in the cruise to save fuel ONLY if the aircraft is arriving AHEAD of schedule - meaning the aircraft will fly slower saving fuel but still arriving on time to keep the punters the happy they would not do this if it would result in a late arrival in destination.

Edited August 27, 2008 by dekka007

[Naam]

I know of several carriers now that are instructing crew to reducing cost index in the cruise to save fuel ONLY if the aircraft is arriving AHEAD of schedule - meaning the aircraft will fly slower saving fuel but still arriving on time to keep the punters the happy they would not do this if it would result in a late arrival in destination.

arriving too early or too late means missing the allocated slot thus wasting fuel by flying "waiting cycles".

[enyaw]

Some very interesting points have been raised in this thread so far but the question still remains are today's airline pilot's as a result of the increase in fuel prices actually "eco flying" ? As tomolapto pointed out because of the direction in the rotation of the Earth some airlines are choosing to

ascend and then just to stay there in mid-air refusing to accelerate thus alowing the Earth's motion to get them to the destination. Others have suggested flying slowly to gain more miles per gallon, there is a theory of pilot's employing a thrust and glide maneuver to cheat the consumer out of his fuel supplement levy and also the recent events of the BA flight from Hong Kong which when approaching Heathrow to land simply switched off the engines in an attempt to save money.

Tsk!

Edited August 27, 2008 by enyaw

[GeorgeW]

Some very interesting points have been raised in this thread so far but the question still remains are today's airline pilot's as a result of the increase in fuel prices actually "eco flying" ? As tomolapto pointed out because of the direction in the rotation of the Earth some airlines are choosing to

ascend and then just to stay there in mid-air refusing to accelerate thus alowing the Earth's motion to get them to the destination. Others have suggested flying slowly to gain more miles per gallon, there is a theory of pilot's employing a thrust and glide maneuver to cheat the consumer out of his fuel supplement levy and also the recent events of the BA flight from Hong Kong which when approaching Heathrow to land simply switched off the engines in an attempt to save money.

Could someone please delete this totally obvious troll? The trolls posts go way beyond being stupid.

[Naam]

there is a theory of pilot's employing a thrust and glide maneuver to cheat the consumer out of his fuel supplement levy and also the recent events of the BA flight from Hong Kong which when approaching Heathrow to land simply switched off the engines in an attempt to save money.

Could someone please delete this totally obvious troll? The trolls posts go way beyond being stupid.

troll perhaps but as amusing as Hägar the Horrible

[GeorgeW]

there is a theory of pilot's employing a thrust and glide maneuver to cheat the consumer out of his fuel supplement levy and also the recent events of the BA flight from Hong Kong which when approaching Heathrow to land simply switched off the engines in an attempt to save money.

Could someone please delete this totally obvious troll? The trolls posts go way beyond being stupid.

troll perhaps but as amusing as Hägar the Horrible

Sorry, I don't see anything the slightest bit amusing in the troll's posts. They're simply stupid and serve no purpose but to clutter up the thread.

[Jai Dee]

Some very interesting points have been raised in this thread so far but the question still remains are today's airline pilot's as a result of the increase in fuel prices actually "eco flying" ? As tomolapto pointed out because of the direction in the rotation of the Earth some airlines are choosing to

ascend and then just to stay there in mid-air refusing to accelerate thus alowing the Earth's motion to get them to the destination. Others have suggested flying slowly to gain more miles per gallon, there is a theory of pilot's employing a thrust and glide maneuver to cheat the consumer out of his fuel supplement levy and also the recent events of the BA flight from Hong Kong which when approaching Heathrow to land simply switched off the engines in an attempt to save money.

Tsk!

I should really just delete it... but it's just tooooo funny!

[GeorgeW]

Maybe funny if it was just one post made in an attempt at humor but the troll keeps posting the same thing. That's at least the third post made in this thread saying the same thing.

[Jimjim]

Also when your flying Easterly you arrive sooner because the earth is rotating towards you, But flying Westerly you are chasing the earth. So LHR-BKK is usually 11.5hrs, BKK-LHR is 12 hrs.

Wrong. Vice versa.

When flying east the Earth is rotating away from you or with you. When flying west the earth is rotating towards you.

Flights from L.A. to Japan, for instance are longer because of prevailing winds (headwind). Flights from Japan to L.A. are shorter because of prevailing winds acting as a tailwind. Therefore, when flying towards the east the plane goes faster not because of rotation of the Earth (which would make the flight longer according to your theory), but because of prevailing winds. Likewise, flights west take longer because of prevailing winds acting as a headwind, but the flights would be shorter according to your reasoning, which is off.

Edit: Yes, also that enyaw's post makes no sense but he must be joking?

Edited August 27, 2008 by Jimjim

[Jai Dee]

Maybe funny if it was just one post made in an attempt at humor but the troll keeps posting the same thing. That's at least the third post made in this thread saying the same thing.

Jai yen yen George... don't bite.

[dekka007]

arriving too early or too late means missing the allocated slot thus wasting fuel by flying "waiting cycles".

no such thing as missing a slot for landing or a "Waiting cycle????" due to arriving early or late. ATC Slots are a departure thing not an arrival restriction. You may arrive at destination and need to hold before commencing an approach but this is not related to arriving too early or late.

Edited August 27, 2008 by dekka007

[Spee]

Flights from L.A. to Japan, for instance are longer because of prevailing winds (headwind). Flights from Japan to L.A. are shorter because of prevailing winds acting as a tailwind.

I've flown this route a few times. Interestly, it appeared that the airpine flew very close the great circle path (fairly close to the edge of Alaska) going "against" the prevailing wind, and a more southerly, slightly longer route coming back. I have to believe this is to minimize and maximize the loss and gain from the prevailing winds.

[Naam]

arriving too early or too late means missing the allocated slot thus wasting fuel by flying "waiting cycles".

no such thing as missing a slot for landing or a "Waiting cycle????" due to arriving early or late. ATC Slots are a departure thing not an arrival restriction. You may arrive at destination and need to hold before commencing an approach but this is not related to arriving too early or late.

no such thing? Frankfurt Airport hands out financial penalties if you arrive too late and the controllers let you fly loops for up to 45 minutes if you are too early. that happened to me at least a dozen times in 25 years and that's how it was explained by most of the pilots.

[dekka007]

Departure slots will be issued before departing if Frankfurt flow control dictates so. Once an aircraft is airborne within its departure slot it continues to destination and arrives when it does.

There are too many variables in flight that could effect the arrival time.

On arrival in frankfurt Terminal maneuvering area - the controllers may reduce your speed / increase your speed put you in the hold to fit in with LOCAL arriving and departing traffic but this happens everywhere.

Pilots are not told you must arrive at FRA at a specific time and dont be late or early. On the rare occassion you will be told to cross a enroute airway point at a specific time, not before a specific time or later than a specific time. But this usually to do with conflicting traffic in your current airspace not destination restrictions.

Fines for arriving late never heard of that in 15 years of flying commercially. If an aircraft departs in its allocated atc departure slot at origin....Frankfurt control has no right to fine the airline. I could imagine FRA getting upset with an airline who consistently misses its departure slots but once airborne its airborne.

Some pilots over simplify explanations to passengers because not all pax are as intelligent or as knowledgeable as your average Thaivisa member about every subject in the world.... .. .....

Edited August 27, 2008 by dekka007

[zorro1]

Simple. Jets fly at the optimum lift/drag ratio. If its at MTW then more power is required to fly at the best lift to drag ratio. slowing the plane down does NOT WORK as it is followed by higher drag = higher fuel usage. If the plane is empty it will need less power to fly at optimum lift/drag ratio. The profit from a flight comes from fuel saves so its never ending quest to find/avoid jet streams and also why the jets are nearly always on auto pilot. By the way they slow them down during turbulence but ere xtremely loathed to do so. Slowing down a plane to save fuel does not work. Hope this helps

[dekka007]

Slowing down a plane to save fuel does not work. Hope this helps

Sorry mate, that post was simply wrong....

Lets for example take a look at the performance manuals for a boeing or airbus (Keeping it simplified). Lets say M0.80 is the cruise speed for the majority of commercial aircraft.

Now we are low on fuel what do we do?

We set a power setting/fuel flow that equates to what is called Long Range Cruise. (The figure is obtainable for aircraft performance tables / graphs)

Which as an example would be a cruise speed of around M0.74 in this scenario which results in a lower Fuel Flow per engine perhaps 2400kgs per engine per hour instead of 3000kgs therefore saving fuel, reducing speed and increasing flight time. Long Range Cruise is the optimum speed to fly at a certain weight at a certain level at a certain temperature that will result in max air/nm per kgs of fuel.

Flying slower DOES NOT increase the overall drag for high altitude, high speed wing aircraft.

By the way they slow them down during turbulence but ere xtremely loathed to do so

In no way are we loathed to reduce speed in turbulence it is a necessity for the safety of the airplane we dont think twice about doing it.

The profit from a flight comes from fuel saves so its never ending quest to find/avoid jet streams and also why the jets are nearly always on auto pilot

The autopilot is not aware of the jetstreams / able to avoid jetstreams. Pilots make the decisions on where to fly, how high to fly, what speed to fly. Once we have decided we tell the autopilot to do it.

Edited August 27, 2008 by dekka007

[zorro1]

Agree with you it was just a generalisation as in slow her down must save on fuel (very laymen). You have gone into specifics very detailed that from a senior commercial pilots rating. By Auto pilot I meant hand flying is less efficient in maintaining a direct course again relating to fuel savings. I know auto pilot doesn't search for jets streams and is a useless machine without human input. Obvioulsly safety come first but most people here who fly regular have been in some pretty bad turbulence(perceived of course) before the A/C is slowed down

Edited August 27, 2008 by zorro1

[dekka007]

Obvioulsly safety come first but most people here who fly regular have been in some pretty bad turbulence(perceived of course) before the A/C is slowed down

Passengers would not be aware of the speed reduction taking place apart from engine noise reduction.

The speed reduction in the cruise for a modern day aircraft entering turbulence is not really much.

Cruise M0.80 Turbulence Speed Penetration M0.78 for example. The reduction in speed will not make a significant noticeable difference to passenger comfort during the period of turbulence. It is there rather to prevent exceeding aircraft limitations and stresses to the airframe.

[enyaw]

Some very interesting points have been raised in this thread so far but the question still remains are today's airline pilot's as a result of the increase in fuel prices actually "eco flying" ? As tomolapto pointed out because of the direction in the rotation of the Earth some airlines are choosing to

ascend and then just to stay there in mid-air refusing to accelerate thus alowing the Earth's motion to get them to the destination. Others have suggested flying slowly to gain more miles per gallon, there is a theory of pilot's employing a thrust and glide maneuver to cheat the consumer out of his fuel supplement levy and also the recent events of the BA flight from Hong Kong which when approaching Heathrow to land simply switched off the engines in an attempt to save money.

Could someone please delete this totally obvious troll? The trolls posts go way beyond being stupid.

Lighten up, only having a laugh with earth rotation theory - I guess you've never heard of Alf Garnett?

Anyway joking aside the OP's concerns are on the button and to coin a newly invented phrase pilot's are indeed "eco-flying" in an effort to save on fuel cost.

Take a look at this artical.

http://www.dailymail.co.uk/news/article-10...ord-levels.html

[Spee]

Take a look at this artical.

http://www.dailymail.co.uk/news/article-10...ord-levels.html

Classic "Peter Principle" thinking.

3mph?

On an aircraft that cruises at >500mph?

That's probably within the error margins of the ambient wind estimates.

ROTFLMAO!

[enyaw]

Take a look at this artical.

http://www.dailymail.co.uk/news/article-10...ord-levels.html

Classic "Peter Principle" thinking.

3mph?

On an aircraft that cruises at >500mph?

That's probably within the error margins of the ambient wind estimates.

ROTFLMAO!

This was just one example, I'm sure there are many more where the airlines are admitting a reduction in speed more than 3mph. In the OP's case arriving over an hour later on a mid-haul flight this is obviously not the answer but he asked the question "Are airlines flying slower to save fuel" and the answer is yes so it seems.

[Carib]

Thread is still alive I noticed.

It has been stated by Lamatopo that earth rotation got nothing to, do with the yet streams

But ends saying that in an incredible way earth rotation way does have an effect on flight times. True, it does and our weather and heating of the earth and the larger water bodies would be very very different without earth rotation. Coriolis effect would not exist, winds would travel in different ways, you could go from A to B in a straight line ( up down equator to the pole v.v. ) tidal movements would be totally different . Any way, in whatever way you look at it, earth rotation is a major factor for the weather as we know it, and all that comes with it, including faster/slower times of transit west east v.v. To me it is the base and all other effects are a result off . Not an easy subject I agree, and not really in the back of the mind when discussing weather.

Of topic; Seen some effects of rotation, and now talking depression/hurricane. Been hopping through the Caribbean last two days and it is just going through curtains of showers/ turbulence and misery right now.

Developing hurricane Gustav is having a go at some islands and up till now over 20 dead already been reported and it is not even a real grown hurricane yet. Not real pleasant Caribbean trips, did not look like just sun and blue waters. The whole area is upside down as far as the weather is concerned.

Seen the projected path of mentioned hurricane/storm and it looks like it is now heading to Jamaica upper side >>> and clipping Cuba >>> gulf of Mexico and will hit land in one of the US gulf states ( Will take a few days, IF it happens !). Several other major weather swirls around, maybe they will rip it apart before it generates real power.

There has been some talk about saving fuel ( Spee. Enjaw) and that it is too insignificant compared to the total, burned up. True, saving $ 500- 800 looks like nothing, but fleet wide it does make sense. That is what it is about. When a taxi company tells it’s drivers to lose the “ heavy foot” nobody blinks an eye. Or even when we do it ourselves as private drivers. But with aircraft it seems to be different?

Sorry for not quoting but something went wrong posting what I had written already, it got lost in space, so just did this version. I don’t feel like starting all over again.

[Ping]

Some very interesting points have been raised in this thread so far but the question still remains are today's airline pilot's as a result of the increase in fuel prices actually "eco flying" ? As tomolapto pointed out because of the direction in the rotation of the Earth some airlines are choosing to

ascend and then just to stay there in mid-air refusing to accelerate thus alowing the Earth's motion to get them to the destination. Others have suggested flying slowly to gain more miles per gallon, there is a theory of pilot's employing a thrust and glide maneuver to cheat the consumer out of his fuel supplement levy and also the recent events of the BA flight from Hong Kong which when approaching Heathrow to land simply switched off the engines in an attempt to save money.

Tsk!

Good idea! Next time I need to travel, I'll simply strap on a couple of balloons and just dangle about until my destination arrives beneath me...