I was curious about the relative efficiency of front flush versus rear a rear block. In aviation, we use cowl flaps located at the air outlet to control cooling air through an engine compartment and at high speed, reduce drag. But most of those air inlets were fairly normal or flat relative to the incoming air. Our Prius has a 'bend' and I wondered if excess air might dip-in and bleed out the lower edges and take away energy. However, the measured difference 0.3 MPG versus 2.0 MPG is pretty much 'in the noise.'
From a design standpoint, this means a set of sliding, black, rear panels will work. Right now, I'm thinking of these control laws:
- ICE < 85C - drives to closed position
- ICE > 95C - drives toward open position
- PID control - to smooth operation and partial opening
- curved and feathered lip - to reduce noise at high speed
In the summer, I'll have low drag in the morning commute. In the late afternoon commute home, the vent opens to avoid overheating the ICE. I'm not too worried about ice freezing the slide as it is difficult to overheat even with a full block at 32F/0C.
Bob Wilson