Saturday, August 29, 2015
2009 May 25 - Speed and Cooling Duct Pressure Tests Minimize

NOTE: I do not believe my wing/canard Angle of Incidence is set correctly and that this is the reason for the following results.  I believe that an aircraft with properly set AOI will not see the kind of speed difference (drag) that I am experiencing.

The goal today was to discover how speed and fuselage "angle" at cruise affects the air pressure in the cooling duct inlet and outlet. I ran quite a number of tests but the two of interest follow. The reason for this testing is the high coolant temperature that I have had since reducing the size of the buttom half of my cowling. Current theory is that by doing this, I messed up the flow of air to the P-51 style cooling inlet and duct work thru the radiator in the tailcone. The magnehelic gauge is connected to the cooling ducts in the tailcone - one line to the inlet, the other line to the outlet. This then measures the pressure difference (in inches of water column) between the inlet and outlet. Today I had an outlet duct "extension" attached with the goal of decreasing the outlet duct pressure thus increasing the airflow thru the duct (and radiator).

Note: I took the angle finder photos on 5/27/2009 on a separate flight than the other photos. I attempted to duplicate the configuration of the aircraft and believe the angles are representative of what existed during the first flight.

The first test was ran with the elevators flush with the wheelpant fairing. Note the 128mph IAS (145 mph TAS) at 7608 MSL (9988' density altitude).





This is very hard to see but is showing something around 3-4 degrees.

The second test was ran with the elevators "up" and control surface pressures trimmed with the reflexor. We've known for years that the "up" elevator position yeilds a better cruise speed. These photos show that. Note that at the same RPM as the first test (4000), I am now showing 141 mph IAS (157 mph TAS) at 7318' MSL (9630' density altitude). Additionally, the magnehelic is showing 3.75" WC versus 3.0" WC. So, by flying with the fuselage in a more tail low position, speed increases and, for my cooling system, airflow thru the cooling ducts is encouraged.





Hard to see again, about 1 degree.

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