# How to Calculate The Top Of Climb/Cruise Altitude?

I see a lot of top of descent calculators,Formulas, and such. But they all ask for your cruise altitude! I have seen a way to calculate that,but it appears I have lost it. Anybody know how?

Here is the one I have. I myself am a math freak, and like to calculate these numbers,compare them,and see which formula has the most accurate outcome.

Calculating top cruise altitude:
Formula: Total Route Distance / 2
Subtract 10 from Ans
Divide by 3
Multiply by 1000
Example: TRD: 200nm/2 = 100nm
100nm - 10 = 90nm
90nm / 3 = 30
30 x 1000 = 30,000ft
So cruise at any altitude at or lower than FL300.

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What are you asking here? How to calculate TOC, or how to calculate cruise altitude?

Well I have mistake for them to be the same,but currently I am asking for cruise altitude.

Is ToC how much time it takes for you to get that high?

TOC is the distance it takes to reach your cruising altitude. If you want that, I can try to explain. If you are wondering how to determine cruise altitude, I can explain that. :)

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Actuly(sorry spelling) I would like both! As I said,I’m a math freak.

I made an equation out of it, since you like math ;) GS is Ground Speed
CRZ is Cruise altitude
VS is Vertical Speed

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And for cruise altitude?(I’ll give ya time;)

Are you asking how to work out what cruise altitude you should use for a route?

not for a certain route.

Roughly speaking:

Cruise FL = Trip distance (nm) e.g. for 60 nm flight optimum is FL060

Once you go above distances of 250 nm you can just head up to somewhere in the region of FL300-400.

This will also help.

https://community.infiniteflight.com/t/cruising-altitudes/60607

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And for cruise altitude, it’s basically as high as you can, below service ceiling. This is to ensure the highest fuel efficiency possible. IRL it would be given to you by either your FMC/MCDU, by ATC, or by your airline.

I didn’t know exactly how to calculate it, but I found this. Enjoy.

The higher you fly (in the troposphere) the colder the air is, which makes the thermodynamic cycle of all air-breathing engines more efficient. Also, the air gets thinner, so your friction drag is reduced at the same TAS. The specifics depend on the thrust over airspeed, and generally you want to fly at a lift coefficient between and where cD0 is the zero-lift drag and AR the wing’s aspect ratio.

The higher value is perfect for piston engines and props, and the lower one for turbojets (think fighter aircraft engine). With a turbofan you will be between both values. To yield more precise results, both formulas will be longer, but these are the major factors for optimum lift coefficient.

Since there is an optimum cl for maximum range, you might want to climb continuously during the flight to compensate for the lower mass (due to fuel burn) with lower air density, so in reality you adjust altitude in steps, in accordance with traffic control.

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So I calculated a ToC of GS as 220 CRZas 12000 and VS as 1800. I got 23.9. Is this correct?

Also, 125 x fpl distance gives a reasonable cruise altitude.

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Oh,thank you man,but I am the age of 12, So my math-Knowledge goes as far as 7th grade. Like I said I love math,but im not that far into it yet. Could you simpliify?[quote=“Mats_Edvin_Aaro, post:13, topic:73128, full:true”]
And for cruise altitude, it’s basically as high as you can, below service ceiling. This is to ensure the highest fuel efficiency possible. IRL it would be given to you by either your FMC/MCDU, by ATC, or by your airline.

I didn’t know exactly how to calculate it, but I found this. Enjoy.

The higher you fly (in the troposphere) the colder the air is, which makes the thermodynamic cycle of all air-breathing engines more efficient. Also, the air gets thinner, so your friction drag is reduced at the same TAS. The specifics depend on the thrust over airspeed, and generally you want to fly at a lift coefficient between

and

where cD0 is the zero-lift drag and AR the wing’s aspect ratio.

The higher value is perfect for piston engines and props, and the lower one for turbojets (think fighter aircraft engine). With a turbofan you will be between both values. To yield more precise results, both formulas will be longer, but these are the major factors for optimum lift coefficient.

Since there is an optimum cl for maximum range, you might want to climb continuously during the flight to compensate for the lower mass (due to fuel burn) with lower air density, so in reality you adjust altitude in steps, in accordance with traffic control.
[/quote]

Is this a efficent(sorry spelling) calculation? I will bbl.

THAT, is a good thumb rule.

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Climb until ya’ stall:)

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Your “divide by 3” rule should be replaced by this for the most accurate calculation:
Divide by pi, raise to exponent e and take the square root.

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