Uploaded April 2016 | Updated September 2026, 1 week ago

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This video describes, step-by-step, how to find the inlet diameter of the massive GE90 turbofan engine. After going through a mathematical analysis to find the diameter, we can check it using a picture of the engine (and some known values).

To get the airport planning document, search for 'Boeing 777 airport planning manual' in Google, and it will be the first link (a PDF).

The diffuser stagnation pressure value that I used in this video was taken from Figure 6.6 (pg. 226) in Mechanics and Thermodynamics of Propulsion by Hill and Peterson. This stagnation pressure ratio will decrease as the Mach number increases. Another was to say this is that the efficiency of the inlet/diffuser decreases as the Mach number increases, because there is a larger stagnation pressure loss in the inlet (which is bad). Note that on the plot, r_d is the stagnation pressure ratio as listed on the previous page in Eq. 6.5. The equation relating the diffuser efficiency, eta_d, to the value of r_d is given in Eq. 6.6.

Photo Credits:

1st Picture Shown: Ron Stella
flickr.com/photos/ronstella

2nd Picture Shown: Wikipedia user Kolossos