The Evolution of Aircraft Brakes
You’d be hard-pressed to find someone who likes abrupt stops. It’s relatively normal on a bike, worrisome in a car, and just plain old dangerous on a plane. But, surprisingly, airplanes didn’t always have brakes. In the early days of aviation, when the Wright Brothers had just stunned the world with their first sustained flight in a heavier-than-air contraption, there were no brake systems; slower speeds and skidding to a gradual stop were the norm. Fortunately, that’s the no longer the case due to the advancements in aviation made during WWI.
In general aircraft brake systems have mechanical and/or hydraulic linkages connected to the rudder pedals, allowing the pilot to control the brakes. Pushing the right rudder pedal activates the right main wheel brake, while the left rudder pedal activates the left main wheel brake. The entire process converts kinetic energy of motion into heat energy via friction. Common aircraft brakes include the single disc, floating disc, and fixed disc brakes.
- Single disc brakes are typically used on smaller, lighter aircraft. They work via applying friction by pressing wearable brake pads to both sides of the disc from a non-rotating caliper bolted to the landing gear axle flange.
- Floating disc brakes have their brake discs keyed to the wheel but are free to move laterally in the key slots, hence the name “floating”. When the brakes are applied, pistons are forced to move out from the outboard cylinders and their pucks contact the disc. This causes the disc to slide in the key slots, causing the inboard stationary pucks to also contact the disc, resulting in a fairly even distribution of friction on each side.
- Fixed disc brakes work similarly to the floating disc, but instead of being allowed to “float”, the disc is bolted rigidly to the wheel and instead the brake caliper and linings are allowed to “float”.
- Other brakes include dual-disc, multiple disc, segmented rotor, carbon brakes, expander tube brakes, etc.
Most brakes, like the ones described above, use hydraulic power to operate, so they require brake actuating systems to deliver the required hydraulic fluid pressure to the brake assemblies. There are three basic brake actuating systems: an independent system separate from the aircraft’s main hydraulic system; a booster system that uses the aircraft’s main hydraulic system when necessary; and a power brake system that uses only the aircraft’s main hydraulic system. While they vary from model to model, they all operate based on the same principles.
Emergency and anti-skid brakes are another common concept that we can’t imagine living without today but didn’t exist until recently. These are used as added assurance that an aircraft comes to a stop when need be. These generally come with their own backup power supply and actuating system.
And of course, for even more added safety, aircraft brake systems and assemblies are subject to rather frequent and rigorous inspection, maintenance, and repair schedules. Because brake assemblies are typically composed of many different rotables, consumables, and expendables, each with different lifespans, everything needs to be checked properly and on-time.
Share
