flyrotary@lancaironline.net Mailing List Archive

Hi Al,

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.

Ed;

Perhaps you could enlighten me on this. Where does the .84 come from? Is this static pressure? I thought that as the air was expanded and slowed, dynamic pressure was converted to static pressure and the value increased. You’ve obviously studied this more than I.

Regarding your second sketch, since you do have slower moving boundary layer air moving next to the skin of the fuselage (and duct), the vane would probably help it turn around the corner. However, you are still ingesting slower moving air with less dynamic pressure to recover from it. It is my opinion (no experience or hard data) that moving your inlet fuselage side of your inlet opening approx 1 1/2 - 2"away from the fuselage would make an improvement.

You are very right about that. Actually in the location that it is, even an inch or less away from the surface would make a big difference. Keep in mind that the scoop is about 23” wide with about 1 ¼” opening. How do you get BL diversion with that configuration? Of course this configuration began the way it did because another Velocity builder had put his standard aircraft oil cooler (for a Lyc) in the same location, and said it worked great without a scoop – just the differential pressure above and below the wing was enough. Go figure.

As I as looking over this diagram more carefully (Winginstallation.jpg), it became apparent that it main point was to show one duct installation with the inlet stand off (bottom one) and the other without inlet stand off using a vane to assist the airflow. So, one could draw the conclusion that you have a choice? either use inlet stand-off OR using a vane.

FWIW

Where did that diagram come from? Very interesting. I think that my scoop opening is large enough, and the BL thin enough, that if I can get effective diffusion in the duct it should work just fine.

Thanks for your input on this.

Thanks,