I am trying to obtain the mass flow rate of the Allison T56-A-15 used on the C130H at cruising altitude (so as to solve the Joule-Brayton cycle at cruising altitude). I know from "Turboshaft, Turboprop and Propfan: database Handbook" that the mass flow rate is 14.7 kg/s at static sea level (not sure about the meaning of this). In order to compute the mass flow rate at cruising altitude, what should I do? I've tried writing $\dot{m} = \rho A_{in} v_{TAS}$ but in this way I obtain a value of mass flow rate that I consider excessive. Any suggestions?

  • $\begingroup$ Hi and welcome to the site. I have changed the title to match the problem you're solving. Please check the edit and see if other improvements can be made. $\endgroup$
    – user14897
    May 13 at 13:42
  • $\begingroup$ Mass flow is determined by the thrust. $\endgroup$
    – Koyovis
    May 17 at 22:08

1 Answer 1


What you are attempting to calculate is an off-design operating condition based on a known reference point (Sea Level Static performance, which is usually off-take performance).

You cannot simply do this by hand, this requires a model for the engine and knowledge of the off-design characteristics of the engine (map characteristics, e.g. compressor map), furthermore you need the cruise power specification.


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