On my first Model IV, I put radiator shutters on it. They worked pretty well. There was an interesting result when closing the shutters, though. On the IV with the belly mounted radiator when the shutters were closed, there was a minor, but difinite nose down pitching moment. I could control pitch by a degree or so by opening and closing the shutters.

Something that might also be of interest to some, I used NACA vents on the side of the cowl for ventalation and made what I called doors that were controllable to close them off in cool weather - I also have them on my current IV. The reason I mention it is that when helping a friend finish his V with 7 FWF, we pretty much did the same with the NACA vent on the bottom of the cowl that feeds air to the radiator and oil cooler. It is cable controlled with a mechanism we designed. Unfortunately the owner has had work challenges that have precluded him from flying so can't report on the function, but it is soon, I understand. When we cut the cowl to the NACA shape, we left the forward edge uncut to act as a fiberglass hinge and added joggles on the sides and aft edge of the door to snug against the cowl when the door is closed. We also put springs on the mechanism so open would be the natural position in the case of a cable failure. I should mention that the mechanism reversed the cable motion so that when the knob is pulled to close the door, it pushed the mechanism that closed the cowl. The push allowed for a ball and socket joint so no tools would be needed when removing the bottom cowl.

This shows the door with joggles and the foam stiffeners on the aft edge.
Cowl Flap Glass.jpg
This shows the arms that run through the duct housing.
Cowl Flap 1.jpg
This shows the control rod and the adjustable housing through arms for the door control.
Cowl Flap 2.jpg
This shows the mechanism that reversed the cable pull and the socket for the control rod.
Cowl Flap 3.jpg