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I'm looking for a general use-case formula or reference that I can use to calculate the total mass flow rate of bleed air use in the environmental control system of any aircraft. I'm not looking for information on a specific aircraft - simply a general reference that can applies to all civil aircraft.

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    $\begingroup$ For what aircraft? $\endgroup$ – Ron Beyer Sep 24 '16 at 20:12
  • $\begingroup$ Welcome to the site! Your question is a bit broad and "critical condition" is not so clear. You may edit your post to clarify what you want to know. Overall the ECS packs on usual airliners can be shut-off when necessary, so they will not load engines. $\endgroup$ – mins Sep 25 '16 at 0:10
  • $\begingroup$ Tnx Mr Beyer. actually i need any kind of information on this subject. i need to know maximum and minimum mass flow rate . for any civil aircraft. $\endgroup$ – ebrahim hajian Sep 25 '16 at 11:18
  • $\begingroup$ @ebrahimhajian I apologize but that is way too broad for this site. You need to narrow it down to at least a family of aircraft (777, A320, etc). This differs wildly (I'm sure) based on cabin configuration, aircraft size, and engine selection. $\endgroup$ – Ron Beyer Sep 25 '16 at 16:53
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EASA and FAA engine type certificates often identify the total bleed mass flow, as a % of the engine's high pressure compressor exit flow. For example, see section 10, "Maximum permissible air bleed extraction" in this for the CFM56-7B, which shows 7 to 13%. If you assume in a civil aircraft that all the bleed air from the engine if for the ECS, you get an answer. (Or maybe you where actually looking for the total bleed mass flow).

If you can get this data from enough references, you could develop a general guideline.

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  1. Compute aircraft internal volume V [m$^3$]
  2. Refresh this volume every 2 minutes
  3. Take an air density at 2,000 m: $\rho$ = 0.94 kg/m$^3$ (cruise altitude)
  4. Compute the mass flow $\dot{m}$ = V * $\rho$ / 120 [kg/s]
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