Ed wrote:

 

If a "full-strength" Streamline duct were tested under the conditions of

9.5"H20 at the entranced to the inlet then at the widest part of the duct

you should theoretically measure 9.5*.84 = 7.98".  I recall Tracy Crook

getting 5.6" at 120 MPH in front of his core - certainly he had a different

configuration, but just a data point.  So your 3+" H20 is certainly a bit on

the low side.  So what could cause that?  I see three possible causes:

 

1.  Duct not properly shaped (but, based on your sketch it looks fine to me)

 

It is attempt to follow the K&W diffuser shape; but is truncated to fit the short distance available.  Perhaps that plus the turn . . .

 

2.  Exit area insufficient (you don't mention the ratio of inlet to exit

area) –

The ratio is about 1.6 : 1. 

 

3.  Boundary layer ingestion.  With no standoff from fuselage for you inlet,

it is possible (likely?) that a percentage of your air into the duct could

be composed of the boundary layer. 

 

The BL is being ingested; no doubt about that.  The ram pressure I measured at ½” from the under-wing surface suggests to me that there is not much of a boundary layer effect; IOW the 9 ½” H2O represents roughly the average velocity into the scoop – which extends to 1 ¼” below the surface.  It could well be that the BL along the surface exacerbates the flow separation/turbulence in the duct.

 

I’m wondering about a vane in the scoop – roughly as show in the attached drawing.

 

The experts on the other list are suggesting the second sketch (attached).

 

Al