Hey IFC, how do you step climb? How much fuel do you have to burn to get to the next altitude? Thanks for your help!😀
Hi there, here is a very useful tutorial on how to step climb:
I just want to know how much percent you need to burn, to get to the next flight level.
Good for long hauls. Let’s say you were flying SYD to AUH. Obviously that’s a loong flight so you would cruise at FL320 initially because of your heavy weight. As you fly, you get lighter and you burn less fuel so you “climb” in altitude to FL 340. The further you go on your journey, you get even lighter so you can climb to FL360 , and so on. This is a great way to save fuel.
This doesn’t matter. The tab with weight tells you all. I like to spread out when I step-climb. Let’s use a 77W for this matter. FL320 is when I am 85-100% in weight. FL340 is when I’m 75-65%. and so on.
One thing you can look at is the N1. If N1 is around 80 you can probably step climb.
However know that step climbing maybe not be as efficient as staying at same level all the time.
Thanks you @xsrvmy
A topic still a bit confusing…
Lets get into detail while keeping it simplified…
So what effects an aircraft altitude…??
Its weight ofcourse… see the wings produces lift. And the higher you go. The air gets thinner. So you need more speed to keep the same maas of air flowing over the wings to generate the same lift. Now the speed of the aircraft is limited by its structural strength. Beyond which it will fall apart.
as you fly higher, the air gets thinner, so less of drag. And subsequently less energy required to push the aircraft to its required speed…
as you fly higher, the air gets colder. Subsequently speed of sound decreases as sound travel slowly in cold air. Which limits the aircraft max speed by its structural strength. This is why you see when you travel at certain mach speed say M0.85 at FL280 you’ll fly faster than same mach speed at FL320.
as you fly higher. The air gets thinner. So your engine has a lot less oxygen to breathe. But thankfully to new technologies. Your engine only consumes that much fuel as much as there is oxygen going into the core to have clean and full fuel burn.
Now computing all those maths (not going into details). It turns out…
As you fly higher you fly a bit slower but consume lot less fuel per nm. But limited by your wieght as how much lift can your wings generate to support your aircraft weight with respect to its structural strenth to certain mach speed and its weight.
So obviously every airliner would want to fly higher. (depending on their cost index. **that is a whole new topic)
But they cannot because of their weight of the aircraft is too high to climb to certain altitude… mostly on long hauls because of extra fuel. And weight of fuel is significantly larger than those of passenger and cargo combined.
So they do step climb…
They start of lower. Burn fuel… get lighter and climb to a higher altitude…
Now back to main question. How to step climb…??
The simple thumb rule. Without going into too much maths…
If you see your engine pushing harder too much to climb or even to maintain certain altitude. You know its his limit. Maintain that altitude for 2-5 hours. Loose weight and start another climb to higher altitude…
What I do…???
Suppose my course is east, and i know i need to cruise at odd multiple of thousand…
I set my Fl290 i initialize. On reaching FL280 I evaluate will my aircraft be able to go another 3000ft…??
If yes i increase my altitude to FL310. And repeat process o reaxhin FL300.
If no. I pause at FL290. Wait few hours that my engine is no longer pushing hard enough and climb…
Wow thank you @niks.goen
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