Instead, they rely on slow speeds, soft airfield surfaces, and the friction developed by the tail skid to reduce speed during ground operation.
By Rick Durden Aircraft Brakes: Brakes Stopping general aviation airplanes has come a long way from the days when a pilot simply closed the throttle, pulled back hard on the stick to drive the tail skid into the turf and hoped.
Main gear wheel brakes went through numerous iterations including drums, expander tubes and, best of all, hydraulic disks. The Cleveland line of wheels and brakes became the gold standard for general aviation several decades ago.
It was bought out by Parker Aerospace, which kept the Cleveland name alive, and now accounts for about 80 percent of the wheels and brakes installed on general aviation airplanes. The fluid pressure increase is transmitted through lines to the brake assembly on the landing gear wheel.
When the pilot removes pressure from the toe brake, a spring pushes the piston back to the full off position, which allows the fluid that was pushed into the brake assembly to be pulled back toward the master cylinder. In a single-disk system, the brake works by applying friction to both sides of a rotating disk that is attached to the main landing gear wheel.
The idea is to convert kinetic energy to heat. Steel has proven to be the best all-around metal for absorbing heat for maximum braking. The caliper also contains a piston or pistons in cylinders, which are used to move the outboard brake linings.
Hydraulic pressure from the brake master cylinder enters the brake cylinder and forces the piston toward the disk, pushing the brake lining on that side of the caliper against the disk. The disk is free to move laterally, so it is pressed against the inboard brake lining by the outboard brake lining, creating the friction required for braking.
Self Adjusting There is a self-adjusting mechanism and pin in the brake cylinder, so that as the brake linings wear, the piston travel is adjusted so that the same travel of the piston is always required to apply the brake. A bleeder valve is installed on the brake housing so that air can be bled from the system.
Organic linings are used for lighter weight airplanes. Courtesy of Grove Aircraft Exploded drawing of a typical general aviation disk brake assembly. Stainless steel is used as well, but it has only half the ability to absorb heat as steel.
At least one supplier offers a nickel-plating of the disk, but it degrades brake effectiveness, so it is removed from the portion of the disk swiped by the brake linings after the plating process.
Certification Certification of braking systems involves a calculation as to the heat energy that has to be created to stop the airplane in slightly over 10 seconds.
Testing then involves putting the system designed from those calculations on a dynamometer test stand and demonstrating that the system can make the required to second stop times the brakes are allowed to cool after each stopwhile changing brake pads no more than once.
As the lining heats up, it loses its effectiveness. Courtesy of Grove Aircraft Typical general aviation brake system drawing. Care and Feeding The brake system can correct for small fluid leaks through a compensating port in the master cylinder. Two are needed per brake and replacement takes about 30 minutes a side, according to Scott Utz.
No Wear Indicators There are no wear indicators for brake pads. Minimum thickness for brake pads is generally 0. Once the linings are worn below limits, there will be metal-to-metal contact between either the steel rivets of organic linings or the metal backing plate and pins of metallic lines and the brake disk.
Grove Aircraft brakes use brass rivets that will not damage steel brake disks. The steel-to-steel contact will rapidly start to erode the disk. In addition, the brake piston is designed for used with a brake pad that is within tolerances.
Once the pad is worn below tolerances, the piston will extend too far, potentially leading to a brake fluid leak. Worse, its O-ring may come out of the caliper, which will result in a massive brake fluid leak and early brake failure.Modern aircraft brakes are reliable, effective and inexpensive to keep up, if common sense preventive maintenance is performed.
We stand on them, we ride them, we ignore them—and yet, fortunately, they rarely let us down. Aircraft disc brakes in the landing gear, used to brake the wheels while touching the ground. These brakes are operated hydraulically or pneumatically.
In most modern aircraft they are activated by the top section of the rudder pedals ("toe brakes"). In some older .
Generally in older aircraft as well as some light modern aircraft the brakes where more or less the same as modern day disk brakes on cars. Most were manufactured from gray iron or high carbon steel, with a copper core. In fact, unlike the thrust reversers on most airliners, including the Boeing jumbo, they do not stop the aircraft in a shorter distance than brakes and spoilers alone.
They do, however, take some of the strain off the brakes and are . Modern aircraft typically use disc brakes. The disc rotates with the turning wheel assembly while a stationary caliper resists the rotation by causing friction against the disc when the brakes are applied.
Aircraft Hydraulic Systems The Average modern aircraft utilizes hydraulic systems to operate several systems. • • Pascal’s Law Pressure exerted on a fluid in an enclosed container is transmitted equally and undiminished to all parts of the container and acts as right angles to the enclosing walls.