Why does it need one? 'Been watching this thread and wondering all along....where's the warmer, humid air, hitting a cooler "windscreen" supposed to come from in the open cockpit Dallaras? 'Back when the radiators and vents there in open wheelers in front of it, I undersand; that warmer air circulated into the cockpit and could accumulate on the screen as condensation; as in your car when cool/cold out side 'til you turn on the defroster. 'Sports cars (closed cockpit), stock cars, of course. Not the case in open wheelers these days.....the windscreen is the same temp as the humid air on the inside (ambient) adjacent to it, unlike the above.