Initial Airspeed Measurements

On 3-3-04 we made some initial airspeed readings using our new KURZ 2444 thermal anemometer, to see what airspeeds we have been flying. I started flying the L-1 at 535 RPM and had guessed this airspeed to be 105 MPH. It was nice to see that I was off by only 1 MPH, or about 1%. For now we simply took some readings at five different settings. Soon we will publish more complete information including airspeed profiles at various heights.
We are doing a careful systematic checkout of our fan system and so hadn't operated above 575 RPM until today when we went to 600 RPM for the first time. Therefore these results are limited to 600 RPM. New measurements will be published later when we turn up the power.
First we measured the airspeed in many places in the jet to within about 2 inches of the edge to see how uniform it is. We found it to be about 98% uniform at 600 RPM. Then we took the following measurements from the center of the jet. The temperature was approximately 70 degrees F. and it was mildly gusty.

    Fan                        Jet                             Motor
RPM    MPH      % Power

 505       100            35.5
 535       106            40.4
 550       110            45.1
 575       115            50.6
 600       120            57.1

Click HERE to see some more recent measurements at higher RPM

This picture shows the Kurz airspeed probe placed in the center of the jet

You should notice that these first measurements are faster than all that follow, that were made before 2008. At first this was a mystery. We use window screen to filter the air, to remove insects and debris, and to prevent birds from being sucked in. We now know the screen becomes clogged after a while due to dust and insect debris adhering to the screen and slowly making the openings smaller. Starting in 2008 we will clean the screens before making measurements. We know the solution for this problem for future L-1 installations..