Perry Mick wrote:

Flew this morning with the cowl piece removed, so I had a big
hole in the cowl.  That is the configuration that allowed me to
fly to KS.  Took pressure data from inside cowl.  Then put the
cowl piece back in to close off the hole, so only the 16 slots
1/4" x 5" for oil cooler exit.  Flew again.  Here is the data:

Open + slots:
-80mph at 80 knot climb = 0.114 psi = 3.15 in. H2O
-75mph at 130 knot cruise = 0.100 psi = 2.77 in. H2O

Slots only:
-55mph at 80 knot climb = 0.054 psi = 1.59 in. H2O
-50mph at 130 knot cruise = 0.044 psi = 1.25 in. H2O

So now I'm going to mod the cowl to put a circular hole
around the fan hub, and hopefully maintain the lower pressures.

--
Perry J. Mick
Duckt N7XR
http://www.ductedfan.com

Am I reading this right? Large hole open.... pressure in the cowl
was + 3.15 in H2O?  Large hole closed..... pressure in the cowl
+ 1.59 inches of H2O?


Dynamic pressure at 80 Kts:

80 kts is 1.151 X Kts = MPH = 92 mph.
130 kts is 150 MPH.

Dynamic pressure at 92 mph is .0026 X MPH^2 or 22 #/sq ft
or .15 psi or 4.14 in of H2O 
One inch of water is .037 psi.

Dynamic pressure at 150 mph is .0026 X MPH^2 or 58.5 #/sq ft
or .41 psi or 11 in of H2O 


Looks like the pressure is lower with slots only. What am I missing? 
Is the pressure in the cowl above or below dynamic pressure? Does your 
airspeed meter read negative mph or are you using the static port
on the airspeed meter? 

I am totally confused.

I wish you used just one U tube water manometer instead. A lot less confusing.
It is then easy to tell if you are above or below dynamic pressure
by using dynamic pressure in one side of the tube.

What is the spacing on those slots?

Where under the cowl was the pressure tap? Did it have porous foam
on the end?

Paul Lamar
 
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