# How much air, by mass, enters an average CFM56 turbofan engine cruising per minute?

How many kg of air enters an average CFM56 turbofan engine cruising per minute?

I have looked everywhere and cannot find it or figure out how to find it, if you could either tell me or give advice on where or how to find it I would appreciate it. Thanks

• A reasonable first approximation would be the mass of air that the engine flies through in a minute - i.e. frontal area of the fan blades $\times$ aircraft velocity $\times$ air density. As a sanity check on your estimate, though at different conditions where the inlet velocity is not equal to the aircraft speed, at takeoff each engine on a B747 generates about 200kN of thrust, with an air mass flow of about 1 tonne (1000kg) per second. – alephzero Jan 10 '17 at 23:34
• Aviation.SE is the right place to ask this. – Mostafa Jan 10 '17 at 23:44
• When you say "how much" do you mean by mass or by volume? – TomMcW Jan 11 '17 at 1:47
• @SRawes Put that back in :) – TomMcW Jan 11 '17 at 16:04

The CFM56-5C, the largest CFM56, powers A340. Its thrust is about 145 kN at takeoff. It has an air mass flow of 485 kg/s (source).

The Trent XWB (A350 XWB), a larger engine developing 430 kN at takeoff, has an air mass flow of 1,440 kg/s (source).

T/O vs cruise power and fuel consumption

According to this document, the CFM56-5C T/O thrust is 150 kN and the cruise thrust is 40 kN (other sources states 30 kN), 27% of the T/O thrust. Related fuel consumption are 2.3 and 0.5 kg/s, meaning cruise fuel consumption is 22% of the T/O fuel consumption.

Air mass vs fuel mass

For a fuel consumption of 22% of the T/O consumption, it can be assumed relatively safely that the air flow is in proportion, so we can roughly estimate air mass flow in cruise to be about 485 * 0.22 = 107 kg/s. This is supported by figures found online in non authoritative sources, like page 245 of this book:

• will that not be different at a cruising altitude @mins – SRawes Jan 11 '17 at 16:00
• Is this figure the amount passing through the intake, or the amount passing through the combustion chamber? Can you break down the two for a feel for how much air is bypassed? – PJNoes Jan 11 '17 at 16:54
• @PJNoes: This is the total air mass thru the fan. After the fan, air is separated in two flows: core (hot/primary) and bypass (cold/secondary) according to the bypass ratio, here 6.4:1. So the part used in the core for combustion, bleed air and core cooling is 485/7.4 = 66 kg/s and 419 kg/s are bypassing the core. – mins Jan 11 '17 at 18:49
• @SRawes: Yes, this is the maximum thrust/airflow. I have updated the answer. – mins Jan 11 '17 at 19:33