Saving climb fuel
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Saving climb fuel
I've found that you can climb at speed faster than max rate climb speed (Vy) and save fuel. When you climb at faster speed, you will get a longer ground distance. So if you climb from the same starting point, to the same target point at higher altitude, a climb at lower speed will need to fly level after reaching target altitude to get to target point. When adding fuel used from both climb leg and cruise leg, the total fuel used can be higher than fuel used from the direct climb to target point at higher speed. Is this a common knowledge? Is it used in some useful applications?
Max rate of climb is min fuel? Since when?
Cost index zero is min fuel (at least at my outfit) and CI 20 is min cost. Neither produces a climb speed at Vy unless it’s a coincidence and both vary dependent on the wind.
Cost index zero is min fuel (at least at my outfit) and CI 20 is min cost. Neither produces a climb speed at Vy unless it’s a coincidence and both vary dependent on the wind.
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Locked door
I remember being told at ground school during my ATPL that climb at full thrust actually saves fuel as you spend less time at climb power and more at cruise power. But you increase maintenance costs.
I remember being told at ground school during my ATPL that climb at full thrust actually saves fuel as you spend less time at climb power and more at cruise power. But you increase maintenance costs.
The difference being, the level segment at TOC is done at a far higher density altitude than your suggested high-speed cruise climb through the lower altitudes. Higher DA = Lower pressure = lower drag.
Lower altitude = higher air pressure = lower TAS for given IAS = more drag = more fuel used in that climb. Best bet as a rule of thumb? Ignoring wind, get as high as you can, as quickly as you can, and stay there as long as you can are the keys to saving fuel. In normal ops? put your desired CI in the box and let it do the thinking for you. It can do it faster and better than I ever could.
Lower altitude = higher air pressure = lower TAS for given IAS = more drag = more fuel used in that climb. Best bet as a rule of thumb? Ignoring wind, get as high as you can, as quickly as you can, and stay there as long as you can are the keys to saving fuel. In normal ops? put your desired CI in the box and let it do the thinking for you. It can do it faster and better than I ever could.
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There is a climb speed, called “Lean and Long Climb (LLC)” speed that maximizes fuel saving from a direct climb to a target point at higher altitude, over an indirect climb with minimum fuel climb plus maximum range cruise to the same target point. I’m preparing an article on LLC to submit to AIAA Journal. I just need to know if I’m repeating a work someone else has done already.
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https://www.aircraftit.com/news/sky-...on-opti-climb/
It's different than what you think.
It's different than what you think.
Last edited by vilas; 6th Sep 2021 at 04:49.
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We don't have CI on our little brain FMSs, but for the Challenger 604/605 series 10 minutes with the Flight Planning manual tells you that according to Bombardier you use less fuel to a point along track by climbing at higher speeds than by climbing at max rate then cruising. But what does the manufacturer know, eh?
It may not be universal, but I saw a study ~20 years ago that for the 757/PW2000, derated climb was a false economy. Derated climb increased fuel burn, and it didn't do anything positive for the engines. In fact, some derated climbs could cause the compressor stators to operate in a range that could cause harmonics that could crack the stators.
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No they don't specifically recommend a profile. They just give fuel/time/distance tables for 2 profiles - 250/.72 (best climb) and 300/.78 (high speed).
When you compare the fuel to climb at 300/.78 with the fuel to climb at 250/.72 then cruise to the same point you get a lower fuel burn. Not by a lot, but it is definitely not more!
When you compare the fuel to climb at 300/.78 with the fuel to climb at 250/.72 then cruise to the same point you get a lower fuel burn. Not by a lot, but it is definitely not more!
There is a climb speed, called “Lean and Long Climb (LLC)” speed
I just follow the company standard procedures which no doubt closely follow the manufacturers procedures.
There is always times when you can save some fuel based on your experience and common sense…. but without rewriting the Performance Manual!
