How does setting flight speed above optimal affect the cost?
Thanks
If you set the speed higher or lower, fuel consumption increases. The higher the deviation, the higher the increase in fuel consumption. To get exact numbers, simply use the aircraft performance tool.
If you set the speed higher or lower, fuel consumption increases.
Hmmm... So even if I make it slower, the fuel consumption increases?
Yes. The reasoning is that the flight needs to take a different (lower) FL in order to travel at the lower speed and therefore the fuel consumption is higher by flying at that lower altitude.
Another way you can look at it is also that the plane gets to the destination at regular speed and then circles above the airport until it’s designates landing time. Circling in the holding pattern also consumes fuel
The current fuel consumption at increased or lowered speed is only temporary until the implementation of the new engine performance system.
i disagree, lower speed doesn't require you to fly at lower flight level. however lower speed takes longer to reach destination, thus increasing the fuel you burn.
i disagree, lower speed doesn't require you to fly at lower flight level. however lower speed takes longer to reach destination, thus increasing the fuel you burn.
Depends how much lower, and how high you fly in the first place... But yes I imagine the biggest factor is that the airplane needs to be kept in the air longer with slower speed. They are closely related with lift though since slower speed = higher angle of attack needed = more fuel burn.
In the end, I now understand why lower speed can make an increased fuel consumption.
But why is it a temporary implementation?
I mean, it does make sense for slower airplane to burn more fuel.
Will this feature be deleted in the new engine?
Or will there be additional penalty for someone whose slowing their planes?
there will be a more accurate calculation of actual fuel burn. this is obviously taking into account the effects pointed out above
Lower speed should indeed burn less fuel than "optimal". This is known in real life as cost index. Cost index reflects fuel cost vs operative costs. A lower cost index (lower speed) will produce less fuel burn but the increased flight time per sector will have increased operative costs (such as maintenance, or crew salaries).
The reasoning above that the aircraft would need a lower altitude in order to fly at that speed is not completely wrong, but would only be true in very extreme situations.
Now back to lower and higher altitude. It was not meant that lower speed requires lower altitude because of construction or technical reasons related to airframe or engines. Rather it was meant that you have different FLs and usually you do not have slow and fast aircraft travelling on the same FL. But I am not an ATC expert and this was my assumption and conclusion after reading an interview on one aviation website.
http://www.ruaviation.com/docs/3/2014/4/14/80/
Interesting thread here and especially post 3 explains why flying at lower than optimum speed increases fuel burn.
http://www.airliners.net/aviation-forums/aviation_hobby/read.main/111703/
Now back to lower and higher altitude. It was not meant that lower speed requires lower altitude because of construction or technical reasons related to airframe or engines. Rather it was meant that you have different FLs and usually you do not have slow and fast aircraft travelling on the same FL. But I am not an ATC expert and this was my assumption and conclusion after reading an interview on one aviation website.
That's where ATC earn their salary ;) They have many means to establish separation and sequencing. Given the case they will ask you to increase/reduce your own speed, and as a last ditch they can instruct a change of level. A typical MD80 will fly ~M.76 while a B777 can be flying ~M.83 at the same level. If that becomes a problem an ATC has many resources, ranging from vectoring, to what they call "Mach number technique" (basically asking one of them to slow down/speed up) and in the worst case a level change.
Interesting thread here and especially post 3 explains why flying at lower than optimum speed increases fuel burn.
That is indeed the "very extreme situation" exception I refereed to in my previous post. Flying way too slow will increase fuel burn (eventually you will also stall if you continue slowing down...)
However that very same post also points out that there is range (rather than a single magic number) of optimum cruise speeds. Within this range total fuel burn increases as speed increases, and decrease as speed decreases. This range goes basically from maximum-range speed (cost index 0) to maximum operating speed (cost index maximum). Within this range total fuel burn for the flight increases as speed increases, and vice-versa. Just to give you more insight about the numbers of the post you refer to, the author quotes .81-.85 as his range of cruise speeds. At 35000ft ISA conditions that equals to 860-910km/h. So, indeed, there is a gap to play with.
The way it works right now in AS is only correct if one assumes that the optimum speed refers to the cost index 0 (maximum range) speed.
Take a look here for more info on cost index: http://www.boeing.com/commercial/aeromagazine/articles/qtr_2_07/AERO_Q207_article5.pdf
Rgrds,