When I bought my Milan, I was surprised at how much air flowed through its tiny NACA duct. That duct was much smaller than the duct on my DF but seemed more than adequate. It was located quite a bit further back, towards the visor than the DF’s duct. My guess was that there was more turbulence in that area, causing higher pressures closer to the visor. That thought went on the back burner for a few years. Recently, I was looking for a project and remembered that old observation.

Perhaps it’s not this simple, but it seemed to me that a smaller duct should cause less drag. Location of the duct could also contribute to its drag. In order to play with these ideas, I made a new panel with a smaller duct, located as far aft as possible.In order to compare the duct’s ability to move air into the cockpit, I taped a small anemometer (wind speed meter) in the duct outlet in the DF’s dash. I did some back to back rides, noting the wind speed while traveling at 20 mph. With the ducts configured as shown above. At 20mph velomobile speed, the wind speed for the larger duct read 6-2 to 6.5 mph. The wind speed for the smaller duct read 8.1-8.3 mph. The small duct passed the first test – keeping me as cool as possible.

Now on to the next test. Does the smaller duct reduce the drag or at least not increase overall drag of the DF? To test this, I’ll do some back to back coasting / maximum speed tests in the 30mph range. TBD.