These stunts often require the demonstration of large props, such as cars, SUV's, other vehicles, or other large scale props, traveling at high speeds, traveling through the air and flipping over.
Techniques for achieving cinematic special effects such as overturning a vehicle have been limited over the years. For instance, the most widely used method for inverting a vehicle, known as the black powder method, dates back to the early days of movie making. Its primitive technique can achieve positive results, however, it also carries several variables relating to both safety and effectiveness.
The black powder method involves attaching a cannon to the object or vehicle being overturned, placing a certain amount of black powder inside the cannon, and finally inserting a wooden or metal rod into the cannon. Once ignited, the powder emits a small explosion inside the cannon. The force created by this explosion expels the rod out of the cannon into the ground, and the resulting push force from the rod flips or overturns the vehicle.
Depending on the desired course of the vehicle and height of the flip, the amount of powder needed to accomplish the effect fluctuates; however, there is no definitive equation in which to determine the exact amount of force that will be generated from the amount of black powder used. Methods are indecisive at best, as it has remained over the years mostly a guessing game. These variables pose several threats to the overall success of the effect, including a significant safety risk to the crew, but especially to the stunt driver.
Another significant component in the black powder method is the use of wooden posts as the rod. Once detonated, the rod is expelled from the cannon shaft with unpredictable force. This is generally known as “the spit wad effect”. It is this force that ultimately launches the vehicle, however its unpredictable nature imposes a real safety threat for both crew and drivers. It is impossible to predict the course of the rod once it is ejected from the cannon shaft, and its resulting impact with the ground will often times cause a wooden rod to shatter, creating dangerous splinters which can injure those nearby.
Furthermore, the explosion itself causes an excessive amount of smoke and other fumes which manifest into a large cloud that trails the vehicle. It is then necessary to remove this cloud of smoke in post-production with the use of a computer, leaving a costly burden for the production.
No system currently exists which creates the desired effect of overturning a vehicle, or similarly large object, while not only maintaining a safe environment on set, but also with foreseeable accuracy.