X-Mozilla-Keys:                                                                                 
Fred wrote:

By the way, on the diffuser chart you sent out, it is interesting to note
that the "good" diffuser was able to get about 45% of the total available ram
pressure, while the theoretical maximum for the area ratio is 84% meaning
that the good diffuser is only about 45/84= 54% effective.  This shows the
need to do some diffusion in front of the inlet.  If one slows the flow to
50% of the free stream velocity in front of the inlet, you get about 75% of
the ram pressure because deceleration in front of the airplane is
frictionless (but requires some bluntness in the airframe and inlet to
distort the streamlines to get the deceleration).  The diffuser then collects
54% of the balance (about 13%) giving a total overall diffusion effectiveness
of 75+13 = 88% which is a very good value.  I typically use 75% overall for
first estimates.

Fred

 
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