Monday, February 18, 2008

The "putt putt car" misconception

If you talk to people about imposing a physical top speed on motor vehicles, and thus reducing the engine size to something on the order of five horsepower, right away people have the vision of a noisy "ridable lawnmower" as the ill-received "trade" they will receive for their current automobile. Cars such as the S.M.A.R.T. and other "mini-boxes" are often hailed as "solutions" to urban driving, even though the aesthetics of such vehicles are viewed by 95% of the population as "ugly" and "undesirable". Visions of tiny Messerschmidts, Isettas, F.I.A.T.s, Renault Dauphines, and VW Beetles fill the mind!

There is simply no reason in the world that lightweight vehicles have to be small, or that small engines have to be noisy and simplistic.

A car that only travels a maximum of 35 mph can get away with a lot more aerodynamic "problems" or compromises than one that needs to go over 55mph. Remember that as speed increases, the effects of drag and the power to overcome aerodynamic drag increase substantially. The cube of the speed!

We live in a non-linear world, best explained by calculus, but only a vanishingly small number of society is aware of this. And pushing a vehicle through the atmosphere, and the relative efficiency of how we do this is unknown to most people. In the 19th century, steam trains operated widely and successfully, and everywhere with a thermal efficiency of only three percent!

Cars do not have to be small if they have a small engine, so long as that engine doesn't have to propel the car at a high speed. Typical bicyclists, bad aerodynamics and all, can go all day at 15 mph using about 1/7th horsepower. One-seventh! Contests where human-powered vehicles, utilizing maximum aerodynamic shape and top-conditioned atheletes, have on surpassed 50 mph for over an hour, on a test track.

Take a large "van" type vehicle used for carpooling and large families. If its maximum speed were only 35 mph, you could have lighter tires, lighter wheels, plastic glazing, lighter doors, lighter seats, a smaller engine with a variable speed transmission (these work best when not attempting to transmit more than twenty horsepower) and would still get from "A" to "B" in an urban setting, with only (guessing) about 10% more time required, and, no question, 100% better gas mileage.

Unknown to most people, the automotive industry spends a lot of money quieting "noise", and cylinder head noise emission has been the subject of vast spending. Only because people tolerate gas mowers, gas weed wackers, and don't make purchases based on quiet operation, do these IC engines emit so much noise. Honda has a "quiet generator", and if buried within an engine compartment, could probably be even quieter.

So, in sum, not going so fast does not mean reverting to small, tiny vehicles. It was the necessity of the ability to travel at sustained highway speeds of 55-70 mph, with European-legislated tiny gasoline engines, that forced the overall size and weight of the 1950s vehicles like the Messerschmidt and the Isetta BMW, to be small. But, if you only need to travel 34 mph top speed, your vehicle can be sizeable and keep up with traffic, even with a very modest engine.