Episode 154: Reverse Engineering
Air Date: November 17, 2010
Some 1970s sportscars were so badly designed that they would be more aerodynamic if the body were turned backward on the frame.
busted
Adam and Jamie first placed a small-scale car model in a water chamber to visualize the airflow around it. Whether it faced forward or reverse, they saw a large area of turbulence above the trailing end. Next, they measured the amount of drag force on the model when placed in a wind tunnel to gauge its aerodynamic character. The results were 0.34 pounds of drag forward and 0.37 pounds of drag in reverse.
In full-scale testing, Adam drove a typical 1970s sportscar through three tests: a timed quarter-mile, time to accelerate from 0 to 60 mph (0 to 97 km/h), and fuel efficiency for a 1 mi (1.6 km) course at 50 mph (80 km/h). The car’s body was then removed, turned around, and reattached to the chassis, and Adam performed the same three tests. The forward car yielded averages of 14.0 seconds in the quarter-mile, 8.0 seconds in acceleration, and 0.87 lb (394.63 g) of fuel used. In reverse, the corresponding results were 16.6 seconds, 8.66 seconds, and 1.25 lb (566.99 g) of fuel. Finally, they brought the cars up to full speed – Adam in the reversed one, Jamie in an unmodified one – then put them into neutral and let them coast to the finish line. Jamie finished the race first, leading him and Adam to conclude that the cars were more aerodynamic as designed.
If a car with a surfboard on its roof gets into a 40 mph (64 km/h) collision and stops dead, the board will be thrown ahead with enough force to punch through another car’s windshield and kill the driver.
busted
The Build Team set up a full-scale test, towing a car with a board (“board car”) into a parked vehicle (“crash car”) set in front of a crash barricade to stop it dead on impact. A third vehicle (“target car”) was placed 40 ft (12.2 m) behind the crash car. Three attempts to replicate the movie crash failed, with the board pivoting sharply down and/or getting caught in the target car’s wreckage after flying off the roof.
Small-scale tests in the water chamber revealed that the board would not generate enough lift force to keep itself on a level path, leading the team to focus simply on the impact of the board against the windshield. Tory built a rig to launch it straight ahead, using bungee cords to provide the needed force; once it was properly calibrated, the team set a target vehicle directly in front and put Buster (outfitted with a human-analog neck) in the driver’s seat. The board only glanced off at 40 mph (64 km/h), while at 85 mph (137 km/h) it penetrated partway but was stopped by the safety glass in the windshield. Having failed to replicate either the movie crash or its results, the team declared the myth busted.
(This myth is based on a scene in the film Lethal Weapon 2.)
gmc suburban 4×4 6600lb broken in half from jumping four ft jumps is it possible for that to happen I have suburban just wondering if you be interested in experimenting with the idea of breaking it in half this is probably not the right place to ask but are you interested
I’d be interested in the myth of whether or not punctuation exists.
Reverse Engineering comments:
The testing as performed is biased against the ‘reversed’ car, because all of the aerodynamic smoothing material under the chassis and around the wheels of the original car was removed in switching the body.
As noted on the show, water tank flows forward and reversed were fairly similar over the top and around a model car that essentially had no flow-trapping difference to the under chassis area.
In the show, the air dams and wheel well liners were stripped out in removing the car body. Their weight was restored in the modified car, but it does not appear that any attempt was made to ‘restreamline’ the underbody area.
I’m not saying the reverse car would end up smoother, but I don’t think it would be as bad as your testing indicated.
Since replacing air dams, wheel wells, etc. is impractical, I would strip out those components from the original car before establishing baseline conditions, so that the airflow under the car’s chassis is essentially the same in both forward and reversed body configurations.
Love the show.
I agree with Stanley but think the major difference in the results was due to less traction on the reversed car due to the weight being over the wrong wheels.
Why was the test not done by removing the car differential and turning it over which would make all the forward gears work as reverse gears. It would take a good driver but then there is no difference in the car. Also love the show
Hi Team,
I am just curious to know about the see through x-ray glasses. Is there any such thing like one we have seen in james bond movies :-). Please help me understand
Hi Mythbusters. Just had a thought about the “Lethal Weapon” myth. In the clip you show, the car that is hit by the surfboard is a what appears to be a Ford Bronco and more importantly the glass breaks with the telltale shards and pieces of tempered glass. In all the tests, modern glass was used, as is pointed out by Grant. The glass did it’s job by not breaking and flexing. However, would the results be any different if tempered glass, like in the movie was used.
Likely the glass in the movie was ‘sugar glass’ – as having real shards of glass flying about film sets ain’t so safe! It also smashes particularly easily, as you’ll know from all the bottling and window diving moments from countless movies..
I noticed that the tires were spun longer on the start in the reversed position, this coupled with what Stanley said will affect the result.
Ijust wanted to tell you guys that Ireally love your show.keep up the good work guys.
If you look closely at the slow mo replay the motion of the surfboard through the windshield in the final test was not halted by the windshield itself but by part of the trigger mechanism on the surfboard hitting the front edge of the roof of the car.
Did anyone else notice it was a windsurfer board on the car in the movie (there was a sail one the roofrack also) not a surfboard at all. It did not have a turned down nose and would have been a lot heavier that a surfboard.
Mythbusters,
I love your show. Honestly you would produce a few shows a year if you we’re required to do a FEMA
failur modes and affects audit on every myth. Basically I am saying it is not realistic to think tank every myth.
The whole crew does a great job of getting most of the
Issues addressed. The 9## sport car episode disappointed me a bit. The removal of specific under penting components and inner fenders was necessary and reviewed. I honestly think the addition of free weights to compensate for lost weight was a feeble attempt for a group as technically minded as yours.
The loss in aerodynamics from removing these items has a huge affect on wind drag. Specific German auto companies have ha extensive experience with air cooled mid-mounted engines which require an undercarriage specific to direct cooling air to the correct areas. They have I figured out.
A chin spoiler on some sports models mounted at the from most lower edge of the front bumper cover at 90 degrees to the road surface will reduce the coefficient of drag .01.