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MAX Update No. 90: Why 'Real Old' Beats 'Old'

3/23/2012 3:48:11 PM

Tags: MAX, 100 mpg, fuel economy, streamlining, downforce, Le Mans, Jack McCornack

The secret to good mileage is streamlining and light weight. Okay, two secrets. Streamlining is essential at highway speeds, light weight is essential in city driving, and the two combined allow one to get satisfactory performance with a small engine. If you cut your car’s drag in half (via streamlining) and cut your car’s mass in half (via weight reduction) you can cut your horsepower in half without losing any performance. At present, MAX’s top speed is 90 mph, which is faster than I have any reason to drive, and that’s on 32 horsepower.

This is why my recent automotive designs look much like 50 year old road racing cars. Race cars have always focused on functionality, but after 1960, the function of race car bodies changed.

Before I leap into sports car racing history, I’d like to point out that streamlining hasn’t changed much in my lifetime.

090aLakestersHere are two “Lakester” class land speed record cars; both were record holders in their day. The rules require exposed wheels but the body shape is up to the builder. Note the visible similarity between these two cars; both have rounded fronts tapering to small sterns, though the upper car body was built in 1952 from a WWII fighter plane fuel tank, and the lower car body was built in 2004 from carbon fiber and polycarbonate. The shapes are slightly compromised by practical needs (the older car has a plexiglass bump on top so the driver can see out, the lower car has a scoop on top to let air in to the radiator) but they’re clearly built for the same purpose—going as fast as possible on a dry lakebed—and form follows function.

Compare those 50 years of lakesters with 10 years of road racers. You can’t tell by looking that a 1970 Le Mans car comes from the same sport as a 1960 Le Mans car—you can barely tell they come from the same planet.

Up to 1960, the limits of horsepower technology forced race car designers to focus on vehicle efficiency, in order to win races. The closest MAX look-alike is the Lola Mk1, a 75 horsepower two-seat sports racer with a great track record from 1958 to the early '60s, including a class win at the 1960 24 Hours of Le Mans.

Because the Lola Mk1 and its peers (such as the Lotus 11, which won the 1957 Le Mans Index of Performance with a 750 cc 59 horsepower engine...sniffing at 125 mph at the end of Le Mans’ 3.7 mile long Mulsanne straight) had so little power, they had to be light weight to accelerate quickly and well streamlined to go fast, and quick and fast won races.

The rules of the day required the Le Mans racers have suitable accommodations for driver and passenger, working headlights and tail lights, a spare tire, doors, space for an overnight case, and generally be practical, roadworthy sports cars. This wasn't hypothetical practicality; it was not terribly uncommon for race cars to drive to the races, even major races, because it saved a lot of gas compared to putting them on a trailer and pulling them with a truck. In 1960, that class-winning Lola Mk1 was driven from the factory in Huntingdon England to the Le Mans race course in...wait for it...Le Mans, France.*

And then horsepower hit the tipping point, with serious V8 power coming out of Detroit, and America discovered sports racing, with Group 7 and the CanAm Series. In 1965, Lola's top model was the T70, which came equipped with 400+ horsepower Chevys or Fords. With horsepower to spare, the corners suddenly mattered more than the straights. The goal of race car aerodynamics switched from streamlining to downforce, and increased drag was the cost of pushing the car firmly onto the track—instead of trying to cut -through- the air, the bodies were designed to wedge themselves -under- the air, and to use air pressure on top of the car to increase cornering and braking force by increasing the effective  "weight" on the tires.

The Lola T70 was known as the  "breadvan" when it was introduced, because its boxy rear end was such a departure from the streamlined racers of the past ("the past" = five years earlier). The T70 was faster on the straightaways that the Mk1, because it had four times the horsepower, and lots faster in the corners thanks to its downforce, but at a huge price in efficiency—the T70 Spyder had twice the aerodynamic drag of the Lola Mk1. With advances in horsepower from Stuttgart, the T70 was obsolete in a few years too, as the twelve cylinder turbocharged Porsche 917 entered the fray, peaking out at over 1500 horsepower in the early '70s. The 917 was the most powerful road racer ever made, and only the 1973 Oil Crisis (and its attendant 3 mpg rule in CanAm racing) ended its dominance.

I got to thinking about this at a recent car show. I was scouting the various solutions that car builders have come up with for getting in and out of covered cars (MAX’s next project is an enclosed cockpit) and came across this Porsche 917 replica.

090b917Stern 

The gullwing doors are slick, but the stern is definitely not slick. It’s a big blunt slab and there’s more than 15 square feet of it, and it’s the biggest reason this VW-bug-powered 917 gets 1/3 of MAX’s fuel economy.

090cVetteStern 

Despite the inefficiency of the breadvan rear end, it looks really racy and it’s been a styling inspiration for sports cars ever since. Here’s the 2013 Corvette Convertible for example—fast, powerful, 24 highway mpg.

 

 

 

090dMAXSternMAX (like pretty much all the road racing cars up to 1960) is rounded in front and tapers down in back, which reduces drag but does cause some lift. By the late ‘60s, all the serious Le Mans cars had doorstop noses and breadvan sterns, and generated negative lift (downforce) at the cost of drag. It is telling that the Lotus 11 that won the 1957 Index of Performance got 30 mpg and surpassed the 2011 CAFE standard for passenger cars—while racing at Le Mans for 24 hours at speeds up to 120 mph—and 15 years later, the fastest race cars in the world were going twice as fast at roughly 2 mpg.

Lift is not much of an issue at highway speeds, but drag sure is, and the energy issues of today beat 1973’s Fuel Crisis Lite by scads. And so MAX, and the rest of the cars on my drawing board, get their styling cues from racers of yesteryear. Extreme yesteryear.

*They didn't have the chunnel yet so there was a ferry involved.


Photos by Jack McCornack and GM Media 

Browse previous MAX Updates 

Check out the 100-mpg Car page  for all things MAX.  



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Carlos Monteiro-Bonifacio
4/15/2012 8:49:36 PM
In South Africa 150 mph will get you locked up and you loose your license for one year and as this is a criminal offence you automatically get a criminal record. In real life 80 mph is more than enough and it is at this speed that I intend to get 33.33 kms per litre. At lower speeds 40 kms per litre could well be achieved, but I would like to keep up with the traffic flow.

Carlos Monteiro-Bonifacio
4/15/2012 8:33:01 PM
Everyone is a critic. John - your minimalistic Locost, heck 32hp is minimalistic but your fuel consumption is awesome. I particularly liked your Lotus 11 comment; Frank Costin was truly a great aerodynamicist and his work whilst not very well known, outstanding. like you I intend, in the near future, to produce a Max like vehicle. The car will be as a close a replica as possible of the original Marcos GT and like the original will be a wooden monocoque and the powerplant will a Citroen 1.4 turbo Hdi Diesel motor using a six speed box geared to give 60 k.p.h.per 1000rpm in top. I am still doing research and will build a 1/4 model first to refine the building process and do basic aerodynamic testing. My aim is to achieve 94 miles per Imperial gallon which equates to 33.33 kms per litre. The original C3 in which the motor was fitted manages 25 kms per litre = 70 miles per imperila gallon with little effort. With a mass goal slightly higher than yours at 1 210 lbs and a frontal area much smaller than the C3, a 33.3% improvement should be achievable. I have already scratch (plan) built a 3 wheeler, the Tri-Magnum, so this should be emminently doable.

JACK MCCORNACK
4/8/2012 9:13:19 PM
> Mileage is like horsepower, you can get what you are willing to pay for! True enough, Abbey, though as MAX demonstrates, you don't have to pay for it with money. I'm willing to pay with comfort and acceleration and a whole lot of design and construction work. But I think I've overdone the comfort sacrifice, and since there's still a little money in the budget, I'm going to invest in an enclosed cabin. If weatherproofing drops MAX's mileage to, say, 90 mpg, but lets me drive it in comfort when it's raining, I'll use MAX more and other cars less, which will improve my personal fuel consumption. Of course, I'll make the enclosure (roof, windows, different doors) removable -- it doesn't rain in Oregon -all- the time and MAX is such a treat on sunny days.

JACK MCCORNACK
4/4/2012 12:36:52 AM
Good points, Abbey and T. The airbag thing is a particular peeve with me because air bags are a substitute for serious safety harnesses (as found in every race car, and oh yes in MAX too). People don't like buckling up, the seat belt and chest strap is about the most hassle that most folks will put up with. BTW, MAX has rear drum brakes, but then again, MAX weighs about 1200 pounds and I never pull a trailer, so they work just fine. > Do not get me wrong the Max is cute, and your project is fun, but Y'know, I think a MAX-like vehicle pass safety regs, with perhaps a 100 pound and a $2000 penalty, in lots of 1000. The engine could pass emissions regs about as easily as VW and Mercedes did (urea injection, particle filters) but again it would call for a lot of sales. > It does illustrate what is easily doable Yep, that was the idea.

JACK MCCORNACK
4/4/2012 12:07:56 AM
> Interesting article as far as it goes, but several overlooked items. The most blaring is... Crimeny, Abbey Bend, cut me some slack! This was a blog entry, not a textbook, and the subject is why for extreme fuel economy cars such as MAX, 50+ year old racers are better examples than are younger race cars. > ...what happens to a vehicle once it starts going, fast, fast is around the 150 MPH mark, lots of things really change then. Roger that. For example, the aerodynamic forces at 150 are more than five times the forces at 65. If MAX has 20 pounds of lift at the rear axle at 65, it'll have 100 pounds of lift at 150, which would cause significant stability issues in fast corners. I car reduce that risk by keeping MAX's speed down under 150 MPH in the corners. > ...design flaws, yes they are flaws... I contend that what would be a flaw in a modern road racer (for the reasons you explained) is a feature in a low power high mileage car such as MAX. > The cars driven to and from the tracks, has little going for them, most were a mild class, with small money behind it. MAX has little going for it (32 horsepower) is a mild class (street legal high mileage sports car) and has small money behind it (you can duplicate MAX for $10k). Aerodynamically, MAX is much closer to an old Le Mans car (or a modern Bonneville car) than to a modern Le Mans car, and that's on purpose. What's worse is, you're luring me to the Dark Side. If I make a high performance MAX for some reason (ooh the temptation), I will change the rear spoiler to make the stern lift-neutral at 150 miles per hour.

JACK MCCORNACK
4/3/2012 5:07:51 PM
> 2) Have you considered the effectiveness of the 'Kamm' tail? Heck yeah, I read my Hucho. Unfortunately "Kamm" got to be a marketing phrase, and many people think you can get Kamm effect by chopping the back off a car. Kamm effect requires the vehicle begin tapering before the cutoff; by putting sharp edges at the back, the air separates cleanly and continues its travels in whatever direction it was headed already. So if you have a teardrop shape and cut off the last quarter of it, the airflow is much the same as if the last quarter were still there. If you have a wedge shape, the air continues to split apart if you cut the end off. > Testing often shows the flaws in assumptions. :) Indeed it does. Herr Kamm discovered the value of the sharp edged stern for drag reduction long ago, and in his testing he determined that the body had to taper down to less than half the area of the widest point forward of the stern, for the sharp edged stern to have any drag reduction at all. MAX has a Kamm tail, that 'vette does not.

ABBEY BEND
3/31/2012 4:50:04 PM
I would say much of the fuel economy jumps in just the last year show this is exactly what is going on. It is easy to purchase an inexpensive car from most of the auto builders that give a smooth, quiet ride, carry four or five people, groceries, meet safety standards, can be driven in all weather, and last 300,000 miles, for under $15,000.00 and produce 40 miles per gallon on the highway. If one wants to spend more money, the mileage goes up towards 100 miles per gallon. Mileage is like horsepower, you can get what you are willing to pay for!

ABBEY BEND
3/31/2012 4:44:31 PM
Very good point David about the Kamm design. Testing often shows the flaws in assumptions. :) The Kammback design shows how the mind and testing is where it is at!!!!

ABBEY BEND
3/31/2012 4:38:41 PM
Actually, the road death rates started to fall with the introduction of padded dash and seatbelts. While some parts of the modern car are "softer", some parts of the modern car are stiffer! The front and rear is designed to crumple at a controlled rate, and manner, while the driver's compartment is designed to move as little as possible, without having to crawl through a maze of re-enforcing like in a NASCAR vehicle. As for disc brakes, much nicer than the drums. Although properly designed drums will stop a car faster than disc brakes, and give better mileage, just not after the first stop, and definitely not at the bottom of a grade, towing a trailer!!! :)

T BRANDT
3/31/2012 1:29:21 AM
I agree with you about govt & regulations. It's the govt that prevents someone from building a modern day VolksWagen (Peoples' Car)- a simple vehicle without all the gadgets & perks that run up expenses...Paradoxically, modern cars are safer because they aren't built as solidly as old cars. In a crash, modern cars crumple &/or fly apart, scrubbing off kinetic energy, softening the blow to the occupants....speaking of cornering: do you remember drum brakes? Talk about scary! How did we ever survive? Road death rates didn't start to fall until disc brakes became the standard.

ABBEY BEND
3/30/2012 8:54:18 PM
On a different note, modern cars are keeping the weight down as much as possible, but all of the airbags, side impact barriers, front crumple zones, etc... add a great deal of weight. Look at the crash worthiness of a modern car. Something that would have killed a person 30 years ago, you can walk away from today! Do not get me wrong the Max is cute, and your project is fun, but would never be able to come close to passing any of the federal mandates for safety or emmissions forced on today's automobiles. One of the leading reasons most foreign vehicles never see the light of day here. It is not because manufacturers do not want to bring them in, it is because of the regulations involved, (also lack of market), which keeps most of them out of the country. Tata's Nano has MPG of 59.6, and safely hauls four people with a few groceries. Never see one here though, the Feds would never allow it into the country. It does illustrate what is easily doable, without some stupid battery looking to start a fire. :) If we could get the government out of the car business, we could have some of these available, and affordably!

ABBEY BEND
3/30/2012 8:31:54 PM
Interesting article as far as it goes, but several overlooked items. The most blaring is what happens to a vehicle once it starts going, fast, fast is around the 150 MPH mark, lots of things really change then. Once you get past 130 life starts becoming interesting, design flaws, yes they are flaws in road or cicle track racing, like a very smooth backend, tend to try to kill you at high speeds! Fine if you are going straight, but truly miserable and dangerous if going around a corner. One needs a great deal of down force, instead of the neutral to negative force developed by a streamliner, which quickly becomes deadly at speed. Also at higher speeds C (http://www.lmnoeng.com/Drag/index.shtml) becomes increasing interesting about what has a higher C and what does not. Going around a corner is not really about C, nor any other one item. The cars driven to and from the tracks, has little going for them, most were a mild class, with small money behind it. Look to the Pre-WWII teams, lots of horsepower, lots of money, lots of streamlining and time in wind tunnels. Europe was broke, after the war, but people wanted to have fun, just needed to be cheaper fun.Much of the Pre-War streamling was banned, because noone knew how to make tires for the speeds. Also the money being spent was huge! Much the same thing happened to the 917, went faster in races than the brakes and tires of the day could handle. Also the money being spent was huge!

DAVID ROOTS
3/30/2012 7:57:42 PM
Hi Jack I understand your arguements re streamlining but with two caveats. 1) Cross sectional area - given the need for two seats a tandem arrangement is more efficient than a side by side configuration. I live in the UK and we had a sports car called the Light Car Company 'Rocket' which used this configuration (designed by F1 designer Gordon Murray and racer Chris Craft).. So for true aerodynamic efficiency a narrow profile is the way to go. 2) Have you considered the effectiveness of the 'Kamm' tail? see http://en.wikipedia.org/wiki/Kammback . The basic premise being that a sharp cut off to the tail (rather than streamlining) loses less in aerodynamic efficiency than it gains in the reduction in the weight (of a streamlined rear end).

JACK MCCORNACK
3/27/2012 12:16:14 AM
Thanks for the thanks, T BRANDT. The '60s was a time of interesting change, and one of the changes was a redefinition of automotive performance--the heyday of the muscle cars and all that. The '70s and early '80s had another big change (high quality small cars from Japan, which raised the bar for everybody) and fuel economy improved considerably. Since then, fuel economy (from the mainstream manufacturers) has pretty well held its own, despite cars getting larger and more powerful again. I think the engine engineers deserve considerable credit for maintaining fuel efficiency these last 30 years, despite the cars getting bigger and heavier, and of course, more expensive. But it's time for another jump. If we could be satisfied at the current level of performance and luxury for the next 30 years, fuel economy would take care of itself. I'd love to see the major manufacturers give fuel economy the same attention today that they gave to the horsepower wars of the '60s.

T BRANDT
3/24/2012 2:26:10 PM
??got cut off)...The old Ford Pinto, top speed

T BRANDT
3/24/2012 2:18:36 PM
Thanks for a concise synopsis of the history racing design... Almost all of the improvements in gas mileage over the past 30 yrs have been accomplished by building lighter, more streamlined vehicles, not the marginally improved engine performance from expensive computerized control systems. Fish & birds figured this out eons ago.....The old Ford Pinto, top speed







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