More streamlined than a barn door?

LOL, that´s funny right there...

 

In the early 60's there was a fellow named Dr. Kamm who developed aerodynamic theories about the turbulance at the rear of a vehicle. His basic idea was the spinning air could actually push the vehicle IF the rear body had a flat surface. Several sports car racers tried this theory, including Shelby coupes that did pretty well at in the mid 60's beating the Italian prancing horse.

 

If you have ever owned a mini-van or Explorer type vehicle, you know how dirty the rear window gets in bad weather. There is some major turbalance going on back there. But, the rear of a new Corvette is flat as a pancake. Go figure.

 

Rich what about George Fields(cool Guy) Fiat?? Goes plenty fast . Wonder how aerodynamic It is?Your avatar reminds me of his Car.

 

Drive the new Corvette on a clean, dry day and the only dusty place will be the rear of the car--the flat panel in back. Beats me.

 

Real world, reduced drag equals higher speeds and lower fuel consumption.
hence limit to how far most car makers want to go down that road,
over a hundred miles to the gallon has been possible for twenty years plus,
but largely the improvements in fuel ecconamy have stagnated in the USA over this same time, while in Europe the trend has been towards cars that do more than double the mpg in the same twenty year span.
Sure they give you a flat panel back there, it's like giving you a leak in the tank so you will be back to that gas pump as soon as they can get away with.

 

George's Simca is one of my all time favorites. As I recall he started with a steel body, but replaced it with a Ai Fiberglass (later Rod 'n Race) shell somewhere along the line. The design shows how racers have attempted to lower the CD by using as pointy a nose as possible. The long wheelbase adds tremendiously to the overall stability at high speed, but frontal area is still one of the major factors to the potential maximum speed any vehicle can reach.

As air piles up in front of any vehicle, it creates a wall which effectivly stopes the continued acceleration. There are only two basic ways of increasing speed. Lower the CD of the vehicle or add more horsepower to push the mass through the wall of air. George's Simca/Fiat coupe is the perfect example of how he has used both methods to set his world records.

 

You can't get a bag of golf clubs in a corvette without that flat spot. Same with the Beemers and Jaguars of the last few years. Anything nicer than a Ford Focus will not sell if bags don't fit.

 

That "flat spot" is sometimes called a Kammback and is there for a good reason. Properly shaped, with an area of 50 percent or less of the total vehicle flat plate area, it can reduce drag significantly without needing to taper the tail of the vehicle to overly lengthy extremes. Above the 50% mark--Minivans, big trucks, SUVs, etc.--the effect diminished rapidly.

Super streamlined speed record cars have fewer packaging problems, no trunk needed, so tapering the body is more practical. Ironically vehicles of the past were able to be more sharply tapered than they can be today with crash standards becoming ever more severe.

F1 cars are extreme studies in the creative uses of drag to glue the cars to the road. This is a reasonable tradeoff as there are few straights on F1 courses where speeds above 200mph are possible and the ability to corner at more than five gees of side force is much desired. Knocking off a front or back wing or other aero widget may well make the car faster but also may dramatically reduce cornering grip. Their situation is so extreme that F1 cars might not be able to make it through a corner at 70mph but will sail through at 100mph since downforce increases dramatically with relatively small increases in speed.

Not sure if anyone ever answered the original question outright. A stock Model A likely has a coefficient of drag of greater than 1. A Model A should be so lucky as to have only basic flat plate drag. Everything on it catches air big time so whatever can be yanked off and/or chopped in height will pay big drag dividends. Stock it is an aerodynamic disaster area but so what? It wasn't designed or modern freeway travel, to put it as mildly as possible, but rather for slow speeds on the grotty roads of the period. Who cared what the aero efficiency of the car was when it was designed to putter along at 20-40mph on rutted dirt roads?

 

The Kamm tail is greatly misunderstood.

What Wunibald Kamm found is that, no matter how carefully you make your teardrop shape, you're going to get a bit of flow separation around two-thirds of the way back. Losing that would be the Holy Grail, but if you're stuck with it, you won't make things any worse if the shape were just to round off rather abruptly at that point. So it's better to have the front two-thirds of a well proportioned teardrop than the whole of a teardrop that's too short for its girth.

That's the other thing: the Kamm tail isn't square, it's edges are rounded, and not that small a radius. Like this:

 

Back in my teen years my Dad had a '29 model a sedan converted to a pickup. I remember at high speeds the visor would really get to flopping. I know little about areodynnamics, hell I don't even know if I spelled it right... But that visor hanging out over the windsheild looks like a drag.

 

GM's EV1 with it's ultra low 0.19 CD probably shows as near the best shape as one is going to get out of conventional layouts;

Reminds me a bit of the 55 Goddess.

 

I'd rather have the Citroën, though! There's a '70 DS23 in my garage, belongs to a friend of mine.

 

Put enough POWER in it you can make a brick fly! Slam the peddle to the floor and go for it.

 

There are two different (at a minimum) types of forces that the cars have to overcome, first is the frontal area of the car punching a hole through the air and second is the surface friction (drag) of the air passing over and under the car. There is only so much you can do to reduce frontal area, so the bigger goal of aerodynamics is to get the air around the car as smoothly and quickly as possible. If you look at a picture of a car in a wind tunnel you see that the smoke stream starts out close to the surface of the car and then gradually moves further away from the surface towards the middle and back of the body. This is called boundary layer seperation and is the caused by the change from smooth laminar air flow on the front of the car to turbulent air flow created by changes in the body shape, obstructions like visors, exposed wheels and susupensions, mirrors and door handles, and just as a function of the speed of the air and it's own friction against the surface. The goal of "streamlining" is to have the boundary layer stay intact as long as possible and then once it does sperate have it do so in an area that won't upset the stability of the car. The down force adders are neccessary to counter act the instabilities, they do produce more drag but that's the trade off.

 

Interesting info! That 1950 Saab is a bithin lookin beast!! When I worked at NASA we found that a tapered end created a pushing effect as the air flew from the end!! This is calles a BFL, sometimes known as a , big fuckin lie, I didn't work at NASA and don't know squat about this subject, just felt the urge to bullshit. Sorry!! ~Sololobo~