How to Throw a Subaru Impreza WRX STI into the Atmosphere!!

How to Throw a Subaru Impreza WRX STI into the Atmosphere -

The physics behind rally driver Ken Block’s jumps.

Rally driving is Ken Block’s passion, but what’s earned him YouTube immortality are his gymkhana videos and those jumps where he throws his Subaru Impreza WRX STI into the atmosphere with apparent recklessness. Of course, once Block is up in the air, he puts Sir Isaac Newton in the driver’s seat. “You have to be very calculating,” says the 41-year-old co-founder of DC Shoes.

Currently, the essential element to Block’s calculations is a Microsoft Excel spreadsheet developed by mathematically minded snowboarder Aaron Dettling. Relying on the fact that physics is scalable, Dettling’s program (originally developed for constructing snowboard jumps) uses the same basic formulas that determine the parabolic trajectory of an arrow shot from a bow or a shell shot from a cannon. “I start by converting the velocity of the projectile leaving the ramp in miles per hour to feet per second [Vt],” Dettling says. “Then I convert the velocity of the projectile into vertical velocity [Vv], horizontal velocity [Vh], and angle of the jump [A].”

That works out to this:

Vv = sin A (Vt)
Vh = cos A (Vt)

Next, those numbers can be used to calculate horizontal distance (X) or vertical distance (Y), in feet, at any point in the trajectory, using the gravitational constant (G) of 32.17 feet per second²:

“These equations don’t look like what you find in college physics books—but they work,” says Dettling. “I replaced a lot of the symbols with conventional numbers and letters in an attempt to make it easier to grasp. It’s real easy to build a jump. To make it work and function correctly, is actually pretty difficult to do.”

Block jumps his race cars, with the addition of about 150 pounds thrown into the trunk to offset the engine’s mass up front. But the launch angle for Block’s jumps is constantly evolving. While his launches used to be set at 18 degrees, he and Dett­ling now find he’s most comfortable at an angle between 10 and 15 degrees. Dettling has also found that, at the relatively low speeds of the short-duration jumps, the aerodynamic drag’s effects are within the tolerances of the landing zones. But since drag increases exponentially with speed, those forces will become critical at more radical velocities.

Landing ramps have changed with a move from “step-down” ramps, set below the launch altitude, to “step-up” ramps, where the landing zone is higher than the liftoff point. When executed with the precision of an Olympic ski jumper, the impact on landing is minimized because the car’s trajectory matches the angle of the ramp. Assuming, of course, Block gets the velocity perfect at launch.