Flying cars in Heinlein's Gulf

Gulf is a short story by Heinlein in 1949, when helicopters were fairly new and not very common. The ones depicted are a melange of aeronautical parts: the wheels are more like the older tail-dragger airplanes of the past. The helicopters don't have tail rotors; to make them work they would have to have tip jets or forced-air slots along the blades. Heinlein was fairly savvy when it came to flying machines, but this would have been the artist's conception and not necessarily have details grounded in the story.