TOM MOORE'S H6 COWL VENTS

Cowl Inlet/Outlet Area Calculation:
 
Inlet Area = 2 X (7.5" X 3.375") = 50.625 square inches
Oil Cooler Inlet Area = 5" X 6.375" = 31.875 square inches
Total Inlet Area 50.625 + 31.875 = 82.5 square inches
 
Outlet Area = 4" X 14" = 56 square inches
Less exhaust pipe area = 2 X 3.315 = 6.63 square inches
Total Outlet Area = 56 - 6.63 = 49.37 square inches
 
Inlet to Outlet Area Ratio = 1.22. Outlet area should be 100.65.
Outlet Area is under sized by 51.28 square inches
 
Need 2 Outlets, which should be at least 25.64 square inches each, or 5" X 5.128"
 
The opening is designed with a 2"curved radius to smoothly exhaust the cowl air. The deflector has a 20 deg angle down from the bottom of the cowl to help evacuate the air. This angle could be adjustable as a cowl flap arrangement if needed.
 

Cowl Vent Construction:

click on any pic for a larger detail view

  The vents are made by cutting two holes in lower cowl just outside of the center lower drop down area.  These holes are approximately 5” X 5”.  Cut the sides and across the front.  Don’t cut the rear.  The cutout area is scored so that the cutout area can be bent upward to form a curved ramp.  Add side support areas, and fiberglass in place.

  The deflector helps pull the air out through the vents.  Make a pattern and then cut out of .025 aluminum sheet to form these deflectors.

  From the inside of the cowl, the vents will look like the picture on the left, after glassing the sides of the vents and the deflectors in place.

  This picture shows the right cowl vent and the deflector.  The deflector was made longer so it could be bent to shape, or cut off, as needed.

  This view shows the lower cowl area from the front.  The deflectors extend below the cowl.

These vents reduce the temperature on all the liquids (Oil, Coolant, and Gearbox) in both climb and during cruise. (See Table below). The initial cruise numbers indicate there does not appear to be any decrease in cruising speed with the vents in place. Further testing is required. The deflectors could be made adjustable but that doesn’t appear to be necessary.

The results are a decrease in all temperatures. There doesn’t appear to be negatively affected on speeds and maybe a little gain.

Another builder made his cowl vents by cutting "H" patterns in the lower cowl.   Then strip the inside fiberglass leaving the honeycomb.  Curve the rear portion of the "H" up and the front portion downward.  When the proper curve is set, fiberglass both surfaces in place.  Install fiberglass side supports to hold everything rigid.  The side supports are made by laying up fiberglass on both side of a core and letting it cure.  Then cut it to shape and fiberglass in place on both side of the curved portions of the vents.  The core can be of 1/8" to 1/4" hard foam, balsa wood or even heavy cardboard.  The end result is easy to build and ends up with a nice clean look.  The front deflector can be extended farther forward for a more gentle slope, or you may be able to eliminate the front deflector entirely and just leave the openings approximately 5" square.
 

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