[aerohead]

A few thoughts: the prop on the RC car is in relatively "clean" air,whereas behind the van/suv,it would be in the lee of the vehicle,with only the turbulent wake as a source of air.That means the prop would have to induce air from behind itself,forward around the outside of the disc area.Then the air would be blasted rearward through the prop,setting up a circulation of sorts(like a helicopter in ground-effect,only sideways)making it difficult to induce the air forward again,to re-circulate through the prop.Unlike a suction slot,the prop would have no boundary layer effect,and a dubious amount of thrust if any,only stalled,in a region of recirculating air within the wake.--------------------------------- Also,to get 10-hp of thrust would require about 12.5-Bhp at the shaft (very inefficient).-------------------------------- Finally,as others have touched on,the safety ramifications,should some unfortunate motorist or cyclist rearend the prop,is too grim to even contemplate.