London based Visual Effects house, Double Negative, has simulated thrilling aerobatic visual effects sequences for Dean Devlin’s new movie Flyboys.

Due out in Australian cinemas on February 15, Flyboys is one of the first feature films to be shot on Panavision’s new Genesis camera. The film is the story of the men of the Lafayette Escadrille, the first American fighter-pilot squadron to see action in World War I.
Double Negative, led by Visual Effects Supervisor Peter Chiang, began their work by creating the pre-visualisations that were used to shoot the live action and then later focused on digitally creating and enhancing the aerial battle sequences. Visual effects shots make up approximately 50 minutes of Flyboys and Double Negative’s work covers 740+ shots, including CG models of the period aircraft, animation, CG environments and matte paintings.
There were six battle sequences in the film and the ethos was to try to capture as much as possible in-camera as live action and then let the VFX take over when they could go no further. Knowing that the CG animated aeroplanes would have to blend seamlessly into the film with live action stunt flying, Double Negative, led by Peter Chiang, came up with the idea of capturing real flight movement.
An IMU (Inertial Measurement Unit) was attached to a Jungman’s stunt plane and sent up to fly in similar types of flight styles as would be seen in the film. The IMU records the exact movements of the plane 128 times a second. Once back on the ground, this data was extracted and analysed by Double Negative with their IMU importer, created by R&D Supervisor, Oliver James. This allowed them to apply real flight characteristics to a CG plane. Indeed, when a CG plane using this data for its movement was placed over the original plane in a shot, the movement matched perfectly. Using this technology, Double Negative had successfully “motion-captured” the plane’s flight.
The Double Negative artists were then able to apply real flight characteristics directly to the CG planes without having to become experts in aero-dynamics first. Some of the action captured was amazing, including a death spin, but due to the speed and aerodynamics of the planes the live action did eventually have its limitations. Then the animators could embellish the motion, adding touches of drama as required and all the IMU movements could be distilled by lowering or raising the noise frequency, so the animation could have more bob and weave where needed.
Another piece of software, dnG-Force was written to alert the animators when they were exceeding the aircrafts limits. Wider shots of the flying were executed through an animation process while the animation for the 3D pilots was motion captured and that action was applied and manipulated via a slider.

In order to introduce a real sense of speed and danger to the dogfights in Flyboys, the decision was made to use clouds as geographical waypoints, helping to introduce a sense of scale to the proceedings and anchoring the battles into a real world continuity. This was important, as most of the time, the choreography of the battles dictated that the camera become unchained from its usual constraints and swung around the scene tracking the action as it unfurled across all three dimensions. To help the audience in maintaining a sense of up and down, clouds would be used as static anchors in the shots. This meant that the clouds would have to be full volumetric entities. Double Negative developed a tool called dnCloud to model 3D clouds in Maya's viewport, which employed implicit spheres and noise functions to generate exactly the types of clouds that were needed. R&D also created custom volumetric shaders to make the clouds react to lighting in a believable way, incorporating such effects as multiple forward scattering and
self-shadowing.

Many of the close-ups of the pilots in their planes were shot on set. A practical plane section was built and placed on a gimble rig for movement. Double Negative’s pre-visualisations were used for the gimble shots to maintain the continuity of flight pattern on the greenscreen set. The pre-vis team knew the constraints of the set and where the
plane should be and were able to use all this information to give the cameramen a start, middle and end frame, allowing them to replicate the camera move. In some cases the gimble’s centre of gravity proved to be too low and in those shots the entire gimble had to be replaced with a CG version. In order to do this, the pilots were rotoscoped out of the
shot and placed back in with the CG gimble before being composited with the backgrounds. The planes were also augmented with CG extensions for the wider shots and IMU noise was used to add realistic plane movement to the gimble. The animation rig included a slider with a huge queue of IMU data, allowing the animator to slide it up and down depending on how much frequency was wanted, from turbulent to quite calm.