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.

Legal tender science

I.
Money comes in a wide variety of forms nowadays, ranging from bits in a bank's computer to paper bills to coins. Historically it came in other forms from wampum to cowrie shells. But it all has one thing in common, or it isn't money: it is a widely trusted medium of exchange. When you take money in trade for a good or service you provide, you do so in the belief that the next person from whom you want a good or service will accept it just as readily.
Originally, money grew out of trade goods of one kind or another, and tended to evolve to they types that were compact and non-perishable. In western Civilization, this evolved into gold and silver being the standard forms.
In time, bankers and governments realized that they could issue promises printed on paper if they had, or enough people believed they had, sufficient gold in stock they they could redeem the promises in actual gold to anyone who wanted it. That is the way money worked in the US up to the 1930s or so. Then, and the reasons are not important to the discussion, the US quit promising to redeem bills for actual metal, and began to print something about "legal tender" on them instead.
Legal tender is another way to have faith that you can believe that the next person in the chain of trade will accept your money. It doesn't mean that the government has promised the money can be traded for gold or silver at the treasury window; what it means is that the government has promised instead that they will force, at gunpoint if necessary, the next person in the chain to accept it.

II.
Science is a way of persuading someone that an idea you have is true. It works like this: I claim that objects without support will tend to accelerate toward the center of the Earth at 9.8 meters per second squared. If you doubt my assertion, I reply "Just try it!" I describe the experiment carefully and completely, and you can do it yourself and get the same results. This is scientific gold: the bottom-line truth cannot be disputed because you did the experiment yourself.
Much of what we call science nowadays is a bit more like paper money: someone states that they have done the experiment, and everybody trusts them and believes the result, since of course nobody has the time and resources to do all the experiments personally.
Then there is what we might call "legal tender science;" in some fields we do not expect people to believe what we say because they could do the experiment, but because we will use force against them if they don't. It is tempting to call this form of persuasion religious, because religions have used it throughout history, but that is probably too broad a brush.
It is all too easy for people to revert to legal tender science in the face of skepticism, because that's the way people think and act. When a group gets power, even just the power of the purse, the ever-present temptation is to use it to enforce shared beliefs and short-circuit the hard work of real experiment: but real experiment is the real value of science.
The bottom line is simple: if everybody believes something, it might be because it is true, but if they are forced to believe it by the means of social or fiscal power, its truth is suspect.