Looks can be deceiving

[Peakster]

This car doesn't look very aerodynamic, but it has a Cd of only 0.212!

So basically I just have to mod my Geo to look like this for low drag?
What exactly makes this car more aerodynamic than say a Prius?

[Silveredwings]

Interesting. For starters, I'd say the well rounded nose, recessed door handles, no mirrors, and wheel pants.

[Peakster]

I would have thought that a vehicle's nose was supposed to angle back sharply for best aerodynamics. That car's windshield isn't angled back much either. What about those huge wheel arches on the front? Are they making the aerodynamics better or worse? Also note that the front wheel doesn't have a wheelcover/hubcap on it.

In comparison, check out this Lamborghini: It has a Cd of 0.42!

[cfg83]

Peakster -

Originally Posted by Peakster

This car doesn't look very aerodynamic, but it has a Cd of only 0.212!

(picture of Tatra T77a)

So basically I just have to mod my Geo to look like this for low drag?
What exactly makes this car more aerodynamic than say a Prius?

I went here :

http://tatraportal.com/tatraklub/

And found the Tatra T77 :

http://tatraportal.com/tatraklub/t77.htm

Here's the magic picture :



Basically, it's an early version of basjoos Honda VX!!! :



PS - Notice how the side view of the Tatra T77 looks like a VW Beetle? Hrmmmmmmm ...

CarloSW2

[onegammyleg]

Originally Posted by Peakster

In comparison, check out this Lamborghini: It has a Cd of 0.42!

It is well known that the Lamborgininihimini has a poor Cd ..as do many other similar shaped supercars..(Many Ferarris suk)

[onegammyleg]

Originally Posted by theclencher

The Countach probably doesn't have any attached airflow!

Maybe not , but the attached chicks make up for it.

[JanGeo]

The Lam has a big wiper that is right in the major windshield air flow and although the cd is poor it also has a very small frontal area which helps a lot more than a low cd. The front lower scoop can't help too much either and the rear wing is a real killer.

[Silveredwings]

Originally Posted by JanGeo

The Lam has a big wiper that is right in the major windshield air flow and although the cd is poor it also has a very small frontal area which helps a lot more than a low cd. The front lower scoop can't help too much either and the rear wing is a real killer.

I think cars like the Lambo are all about the downforce, which of course means a large induced drag.

[Spule 4]

The streamlined Tatras are interesting cars, and with the large rear motors, can be fun to drive, imagine a 1948 Packard - VW bug mix. I drove a friend's 603 once, it had a mix of bias and radial tires at the time, NOT fun.

Hans Ledwinka worked with Ferdinand Porsche briefly during the VW development days, and Hans' son went on to work wtih Steyr Puch to build the infamous Pinzgauer offroad trucks. They are fun too, and better (IMO) than a petrol Unimog (driven both).

[onegammyleg]

Maybe the Tatra wasnt as good as first thought.

http://www.ltv-vwc.org.uk/wheelspin/...amlining02.htm

¨...., culminating in the Type 87. This model was produced from 1936 to 1950, throughout the war, in small numbers. Its Cd was measured in the VW wind tunnel in 1979 and found to be 0.36¨

[MetroMPG]

.36 seems more realistic.

[onegammyleg]

yeah , .36 is still amazingly good for that era..

The model 87 was suposedly a little worse than the 77a , but ime wondering if the wiki figure was in error.
Has anyone found a reliable figure for the 77 apart from wiki ??

[onegammyleg]

This model vw keeps coming into my mind for potential FE mod car....



..but with a modern efi engine.
Best part is that it allows almost any body (aero) modification legally.

[MetroMPG]

Unfortunately, that VW type 3 looks to have about the worst possible rear rake. According to Barnard, the highest drag is associated with rake angles around 30 degrees (from horizontal).

[onegammyleg]

Originally Posted by MetroMPG

Unfortunately, that VW type 3 looks to have about the worst possible rear rake.

Thats Ok , cut and paste.

with larger front window layed back and modified roof section

with 2 inch sectioning and lowering.

Almost looks like a sports car now.

[MetroMPG]

If the wacky Cd figure came from wikipedia, I wouldn't be surprised.

I corrected a wrong entry there for the Cd of the Audi A2, which someone had listed as .24. (Its lowest model was .25 - info I got from Audi's corporate site. Same Cd as the Insight).

[red91sit]

I still like the idea of turning a Plymouth Breeze, Dodge Stratus, Chysler Cirrus, into a more economical car. They start off with real good c/d .31. I'm thinking a little work woudl drop the cd nicely

.01 Lowered 1-2 inches
.005 Front Dam smoothened and smaller grilll opening
.01 Smooth Underbody
.005 Partailly covered rear wheels and smooth hubcaps
.01 Mirror removal

Capow! if you could get these good of numbers, It'd drop to around .27! Now you just have to deal with the poopy motor.


My parents own one of these cars which i "MIGHT" get for graduation, otherwise they're very cheap, cuz well they're really nothing special.

[Peakster]

Check out this vehicle:
vestatwo.jpg

VESTA%202%20RENAULT.jpg

It's a Renault Vesta 2 research vehicle and it has a Cd of only 0.186! Note how the back end is totally sliced off. Sources say that it used 1.94 litres/100km (121 US miles per gallon) for 500km trip with an average speed of 100km/h!

[onegammyleg]

Originally Posted by theclencher

Am I going to have to go verify the Cd on this???

I found this on a french page..
¨A prototype named Renault Vesta II is with 3.5 l/100 km expenditure-comes.¨

from what I read that 1 point whatever per hundred was a one off freak figure., and 3.5 was its long term figure. -- which is nothing truly amazing.

[onegammyleg]

3.5 = 67mpg , so 1.9 = 110mpg (roughly)

[Peakster]

Originally Posted by theclencher

Am I going to have to go verify the Cd on this???

I remember seeing this car in a book called "Cataway Cars" I got when I was 9 years old. The 1994-published book rates it at 0.19.

Only after finding the book, I looked it up on the internet.

[MetroMPG]

Looks a lot like the Daimler Bionic car (claimed .19 Cd), doesn't it?

[The Toecutter]

If anyone is wondering, I added many of those aerodynamic cars to wikipedia months ago. That is why they are now there.

I have two sources claiming the Tatra's low drag coefficient of .212 that are not wikipedia:

http://www.tatra.demon.nl/cars_history_T77_T77A.htm

The smooth body of the T77a gave a coefficient of aerodynamic drag of 0.212. An incredibly low value even for today's cars as only a few modern prototypes are able to achieve this figure.

http://www.ltv-vwc.org.uk/wheelspin/...istory-pt1.htm

In 1935 followed the improved Tatra 77a. An extra central headlight was added and could optionally be made to turn with the steering wheel (more precisely, three different directions of the headlight were possible), that must have been quite the experience for night drivers! Increasing the capacity of the V8 to 3.4-litres raised output to 75 bhp and maximum speed to 150 km/h. Driving characteristics were also improved and the styling (aesthetically speaking) was cleaned-up slightly. Aerodynamics were still awesome with the drag coefficient of 0.21 (the cd of the original 77 is not exactly known but presumably is very similar).

Here's more pics of her in all her beauty to jerk off to, if you feel so inclined :






Looks can indeed be very deceiving. I know of many old cars that achieved extraordinarily low drag coefficients relative to the production cars of their time. Here's pics of them and references to back up the numbers:

1921 Rumpler Tropfenwagen, .27 drag coefficient



www.gi.alaska.edu/ScienceForum/ASF7/702.html

As an example, in 1921 Germany's Dr. Edmund Rumpler used experience that he had gained from the aircraft industry during World War I to design a car. The Rumpler Wagon, as it was called, was a peculiar-looking affair, teardrop-shaped when viewed from above, and looking somewhat like a boat mounted on wheels from the side. Recently, curious engineers trundled one of the fragile relics into Lockheed's wind tunnel in Georgia and turned on the fan, probably just for a laugh.

The engineers were stunned when the puttery little car, which Rumpler had designed without ever having heard of a computer or a wind tunnel, turned in a Cd value of barely 0.27--better than any car on the market in 1984.

1940 Kamm K-Wagen, .23 drag coefficient



www.lotus-europa.com/setright.html

Earlier still, Professor Kamm’s K-Wagen (a specially modified bodied 3.5litre BMW) registered 0.23.

1950 Panhard Dyna 54, .28 drag coefficient



www.factbites.com/topics/Panhard-Dyna-Z

The Dyna-Panhard was a dream car for its time, 1950-1953: excellent aerodynamics (an estimated drag coefficient of 0.28), 2-cyl boxer, 850-cc engine delivering 42 hp (twice the power of the 600-cc Fiat Seicento), top speed of 130 kph (81 mph), only 550 kg (1,210 lbs) of weight, low fuel consumption.

1951 Hotchkiss Gregoire, .26 drag coefficient



www.voitures-d-ingenieurs.com/biography.htm

The 50-year-old Gregoire, with a CX of only .26 (today's cars are not so aerodynamic), had exceptional handling, a high level-of silence and comfort and, to this day, does not show its age. Jean Albert Gregoire was not alone when he proclaimed that the French industry lost a great opportunity.

1953 Alfa Romeo B.A.T. 7, .19 drag coefficient



velocetoday.com/cars/cars_76.php

Scaglione’s BATs certainly pushed the envelope in terms of the Cd factor—the B.A.T. 7, (the one with the wild fins), registered about .019 on the drag coefficient scale.

1957 Lotus Elite, .29 drag coefficient



www.sandsmuseum.com/cars/elise/information/press/press/press2004/company.html

Lotus's first closed passenger vehicle, the 1957 Elite, was the first production car to feature a glass-fiber monocoque chassis. The stylish Elite had a drag coefficient of 0.29, which is better than most of today's aerodynamic cars.

1967 Panhard CD Peugeot 66C, .13 drag coefficient



www.ultimatecarpage.com/frame.php?file=car.php&carnum=1337

The CD 66 C was powered by a Peugeot 204 engine modified by Moteur Moderne. The bodywork was extremely efficient (a drag coefficient of only 0.13 cd) allowing for top speeds of 250 km/h with only 108 bhp on tap. Unfortunately neither of the two cars made it past the twelve hour mark in the 1967 LeMans race. It was the last LeMans entry for Panhard.

1969 Dodge Charger Daytona, .28 drag coefficient



http://www.allpar.com/model/superbird.html

One of the more interesting chapters in technological history was the 1969 Dodge Daytona. This vehicle had a drag coefficient (cd) of just 0.28, better than most cars made today. It would have produced even less drag, if it weren't for the tall spoiler (added to keep the rear wheels on the ground at high speeds).

1966 Lotus Europa, .29 drag coefficient



www.lotus-europa.com/setright.html

According to Motorcar, the drag coefficient (Cd) of the Europa is 0.29.










The automakers commonly claim they are doing everything possible to maximize fuel economy. They commonly claim that today's cars are as aerodynamic as possible, and that going to low drag designs would cause uniform body styles. Those claims are a bunch of bullshit!

I dream of one day having a carbon-fibre replica of that Panhard CD, and shoving a 300+ horsepower V8 diesel in it,. Imagine the fuel efficiency AND performance possible in the same car. I don't believe it really is as low as a .13 though, I'm thinking it may be a typo and is really .23. But who knows, that number may be right.

[Spule 4]

The Panhards were well ahead of their time. These early Dynas were aluminum, and their small and VERY stressed flat twin motors made them quite fast for the day. They were also a true six-seater body, with column shift four speeds.

Unfortunately, they switched to steel and the pounds poured on by the later Dyna/PL-17 days. They were not cheap either, the 1960s sporty BT and CTs cost as much as a contemporary Jaguar. But, they are fun to drive, the last one I drove was a PL-17 cabrio, one of maybe 12 in the US.

The aluminum was continued for a lot of trim parts, motors, etc and the bumpers. A friend had a bumper on the floor of his shop, he asked me to go over and pick it up....I figured I would give it a try....to my surprise, one hand can lift one very easily.

If someone wanted a classic car of interesting technical merit and good FE, the postwar Panhard should be on the list. There is an active club in France and in the US (I was a member several years ago) and a lot of parts support in France and the Netherlands.

On a side note, my wife did manage to find my Tatra T600 blown glass christmas ornament that came from Czechoslovakia. (it hangs nose down, the hole with the hook is at the tail). I picked it up many many years ago in a giftshop. I have never seen another one like it in the States.

Edit-Here is one identical to mine:

[The Toecutter]

How low-volume were the Panhards? That might explain their high price.

I'm amazed someone else here even heard of a Panhard.

That Tatra ornament is pretty nice too. A shame we can't buy the real cars though.


I always wonder how a modernized version of the Tatra T77a or alfa romeo BAT7 would perform in regard to fuel efficiency. Imagine an updated version of either of them with their streamlined bodies, and a 1.9L VW TDi chipped to 130 horsepower. That would be a true 80+ mpg family car that had acceleration to match or beat the cars typically sold in the U.S.(0-60 mph < 11 seconds).

[Spule 4]

Originally Posted by The Toecutter

How low-volume were the Panhards? That might explain their high price.

I'm amazed someone else here even heard of a Panhard.

That Tatra ornament is pretty nice too. A shame we can't buy the real cars though.


I always wonder how a modernized version of the Tatra T77a or alfa romeo BAT7 would perform in regard to fuel efficiency. Imagine an updated version of either of them with their streamlined bodies, and a 1.9L VW TDi chipped to 130 horsepower. That would be a true 80+ mpg family car that had acceleration to match or beat the cars typically sold in the U.S.(0-60 mph < 11 seconds).

Why on Panhard? Builder of many famous racing and luxury cars before WWII. They were the oldest car maker in the world, and they are still in the armored vehicle and military vehicle business after the purchase by Citroen and the conversion of their plant to 2CV trucks in '67. While not one of "the big three" (Peugeot, Citroen and Renault) of France, they were just as important, and many of their basic designs (cab forward) are still in use today.

Panhard production numbers...yes, the BT/CTs were limited. The book with those figures would be under my bed somewhere, and if I go back there, I will stay and not post, but some like the PL-17 were 166,000. Now, only about 400 were cabrios, and of that, only 47 were made for the US (production code L2) The early Dynas were similar numbers. US importation numbers were low, not much call for a car that got 40 MPG that was expensive.

I was hoping for a nicer engine photo, but Google turned this up, the motors are beautiful affairs, with torsion bar valve springs:

[Spule 4]

There was another page, full restoration of a car back in Holland, but the owner did not keep the site up. The Interet Archive does have it, not sure if all the chapters work:

http://web.archive.org/web/200509051...d.250free.com/

[Spule 4]

Originally Posted by The Toecutter

That Tatra ornament is pretty nice too. A shame we can't buy the real cars though.

We can, a friend here in Nashville has about 12 or so, including the oldest extant 603 based on production number. He has a couple other 603s, 600s, a 700, T87, a 613 and ambulance, and a huge flatbed six wheel drive truck that looks like it came from the movie Brazil.

[The Toecutter]

I bet those would fetch a pretty high price too.


But I did mean as in buy them new. They are no longer being made, sadly. The T77a is really the one I'd like. Out of all the Tatras I know of, it had the best drag coefficient.