The mechanical disc brake standard for well over a decade has been Avid’s venerable BB7 caliper. A clear hose is attached to the vent port on the aircraft brake fluid reservoir or on the master cylinder if it incorporates the reservoir. The exposed flat surface of the expander tube is lined with brake blocks similar to brake lining material. It is forced out of the accumulator into the brakes through the system lines under enough stored pressure to slow the aircraft. Many brakes use back-up rings in the seal groove to support the O-ring seals and reduce the tendency of the seal to extrude into the space which it is meant to seal. There are three basic actuating systems: An independent system not part of the aircraft main hydraulic system; A booster system that uses the aircraft hydraulic system intermittently when needed; and. Regular inspection for any damage and for wear on the linings and discs is required. This acts on the end of the slide creating a return force that counters the initial slide movement and gives feel to the brake pedal. The self adjusting feature of the brake maintains the same clearance, regardless of the amount of wear on the brake pucks. The volume and pressure of hydraulic fluid required cannot be produced by a master cylinder. Wheels are often grouped with one relying on the squat switch and the other on wheel speed sensor output to ensure braking when the aircraft is on the ground, but not before then. The compensating poppet reopens. The other end is submersed in clean fluid in a container large enough to capture fluid expelled during the bleeding process. These types of brake are typically found on older transport category aircraft. Instructions for bleeding the brakes are in the manufacturer’s maintenance information. [Figure 39] Regardless of the method particular to each brake, regular monitoring and measurement of brake wear ensures linings are replaced as they become unserviceable. Brake systems must be bled to remove all air from the system. They tend to take a setback when cold. Figure 14 gives an exploded view of an expander tube brake, detailing its components. While two of the big three component manufacturers offer full hydraulic brake systems for road levers, there are those who don’t need or want the added expense of such a system, or prefer the simplicity of a cable-operated mechanical disc brake system. After a thorough inspection, new linings are riveted to the pressure plate and backplate using a rivet clinching tool [Figure 46] Kits are sold that supply everything needed to perform the operation. The steel stators are keyed to the bearing carrier, and the copper or bronze plated rotors are keyed to the rotating wheel. Power brake actuating systems use the aircraft hydraulic system as the source of power to apply the brakes. A test is first done with the aircraft at rest and then in an electrically simulated anti-skid braking condition. [Figure 10], Many modern segmented rotor disc brakes use a housing, machined to fit numerous individual actuating pistons. At the same time, the 11” might fit somewhere that the 9” dual won’t and vice versa. However, a skid can be quickly controlled automatically through pressure control of the hydraulic fluid to the brakes. Disc brake systems for cyclocross and gravel bikes are becoming the norm de rigeur these days. The cylinder is always filled with air-free, contaminant-free hydraulic fluid as is the reservoir and the line that connects the two together. [Figure 9] Rotors are usually steel to which a frictional surface is bonded to both sides. Any evidence of a leak must be investigated for its cause. The fluid expels the fluid contaminated with air out of the bleed hose into the container. It is free to move laterally in the key slots. As the pedal is depressed further, the valve slide moves farther to the left. With the parking brake set, any expansion of hydraulic fluid due to temperature is relieved by a spring in the mechanical linkage. When the brakes are applied, the pressure from the pilot’s foot through the mechanical linkage moves the master cylinder piston in the direction to force fluid to the brakes. The maximum width of the slots is given in the maintenance manual. Over-tightening of fitting can cause damage and make the leak worse. Much of the anti-skid system testing originates from testing circuits in the anti-skid control unit. These prevent circumferential movement of the tube on the flange. It is a lightweight, low pressure brake bolted to the axle flange that fits inside an iron brake drum. he frequency is directly proportional to the speed of rotation of the wheel. TEKTRO BRAKE SYSTEMS - Product, Disc, Brake, Lever, Disc Pads, Brake Pads, Accessories, MTB Road, Cyclocross, TT / Triathlon, Recreation, BMX, E-Bike. In the typical brake system, mechanical and/or hydraulic linkages to the rudder pedals allow the pilot to control the brakes. Multiple disc brakes typically are checked for lining wear by applying the brakes and measuring the distance between the back of the pressure plate and the brake housing. The hose from the pressure tank is attached to the bleed port on the brake assembly. On most designs, brake lining material attached directly to the pressure plate contacts the first rotor in the stack to transfer the motion of the piston(s). The other end of the piston is larger and housed in a separate cylinder. [Figure 21] It covers the return port so pressure can build in the brake system. The master cylinders are mechanically linked to the rudder pedals as before. Therefore, bottom up pressure bleeding is not an option for power brakes. A typical brake bleeder pot or tank contains pure brake fluid under pressure. Each cylinder accepts an actuating piston assembly comprised mainly of a piston, a return spring, and an automatic adjusting pin. Caution must be used as different assemblies may vary in how the pin measured. Be sure to bleed auxiliary and emergency brake systems when bleeding the normal brake system to ensure proper operation when needed. As a result, the pressure and return ports are closed and pressure proportional to the foot pressure on the pedal is held on the brakes. A Boeing 737 antiskid control unit internal block diagram. On some brakes, two grooves or cylinders are machined into the carrier to receive the piston cups and pistons. When the rudder/brake pedal is depressed, the slide in the metering valve moves to the left. This provides feel back through the mechanical linkages consistent with the amount of rudder/ brake pedal applied. Discs that have been overheated may have damage to the surface layer of the disc. The aircraft is taxied at a specified speed, and the brakes are smoothly applied. The method used is matched to the type of brake system. Back-up seals are installed on the side of the O-ring away from the fluid pressure. A velocity reference loop output voltage is produced, which represents the instantaneous velocity of the aircraft. The cylinder assembly is bolted to the backplate to secure the assembly around the disc. Magnetic particle inspection is used to check for cracks. With a single piston, only one brake pad moves, pushing the disc rotor against a second, fixed pad. Typically, sintered metal is used in creating the rotor contact surface. Typically, a vented plug is installed in the port to provide positive pressure on the fluid. The hardware should be what is specified in the brake manufacturer’s parts manual. A brake metering valve from a Boeing 737 is illustrated in Figure 21. This can cause excessive lining wear and overheating leading to damage to the disc(s). The trapped air in the brake system would be forced into the main hydraulic system, which is not acceptable. The brake piston(s) push the brake linings against the brake rotor to create the friction that slows the wheel rotation. They may be alternating current (AC) or direct current (DC). Typically, the exposed pin length decreases as the linings wear, and a minimum length is used to indicate the linings must be replaced. This is the design of a common fixed-disc brake used on light aircraft. They also have a tendency to swell with temperature and leak. The fittings threaded into the housing must also be checked for condition. It is possible that the leak is a precursor to more significant damage that can be repaired, thus avoiding an incident or accident. Self-locking nuts should still retain their locking feature. When released, a spring returns the piston to its original position which refills the reservoir as it returns. To ensure that this does not happen, each wheel is monitored for a deceleration rate faster than a preset rate. On these assemblies, the torque plate is bolted to the strut while the remainder of the brake is assembled on the anchor bolts. The output from the velocity comparator is a positive or negative error voltage corresponding to whether the wheel speed is too fast or too slow for optimum braking efficiency for a given aircraft speed. In general, small, light aircraft and aircraft without hydraulic systems use independent braking systems. In most brake actuating systems, the pilot pushes on the tops of the rudder pedals to apply the brakes. The driver prepares the current required to be sent to the control valve to adjust the position of the valve. Most important is that there are no cracks in the housing. Enough hydraulic fluid is contained on the other side of the diaphragm to operate the brakes in case of an emergency. When pressure is applied, the caliper and linings center on the disc via the sliding action of the anchor bolts in the torque plate bushings. The carbon fiber discs are noticeably thicker than sintered steel rotors but are extremely light. On most aircraft, each of the main wheels is equipped with a brake unit. The toggle is withdrawn from the spool via linkages, and fluid pushes the spool back to expose the system return manifold port. If a wheel decelerates too fast, it is an indication that the brakes are about to lock and cause a skid. Lobes on the rotor and stator cause the distance between the two components to constantly change during rotation. [Figure 23]. Remove the brake and perform a complete inspection as discussed in the previous section. The caliper mounting bolts are long and mount through the center carrier, as well as the backplate which bolts to the Large, heavy aircraft require the use of multiple-disc brakes. Single disc and double disc brakes never show their direct impact on the mileage of the bike. An inoperative anti-skid system can be shut off without affecting normal brake operation. An exploded view of one type of segmented rotor brake assembly is shown in Figure 9. All cards are housed in a single control unit that Boeing calls a control shield. A compensating port is included in most master cylinders to facilitate this. The pressure plate slides off the anchor bolts and linings can be replaced by riveting on the pressure plate and back plate. With the brakes applied, the ratchet is engaged by pulling the parking brake handle. All modern aircraft are equipped with brakes. A coil around it is connected to a controlled DC source so that when energized, the stator becomes an electromagnet. Each main wheel assembly has two wheels. On many other brake assemblies, lining wear is not measured via a wear pin. By unbolting the cylinder housing from the backplate, the backplate is freed to drop away from the torque plate. An expander tube brake is a different approach to braking that is used on aircraft of all sizes produced in the 1930s–1950s. It is not possible to immediately ascertain in the flight deck when a wheel stops rotating and begins to skid, especially in aircraft with multiple-wheel main landing gear assemblies. Tech 3 E4 The ultimate enduro brake. This is known as brake “fade”. A bleed port can also be found. A warped disc(s) in a multiple brake disc stack produces a condition wherein the brake is actually applied and removed many times per minute. They provide effective braking through a power brake system but require less than maximum hydraulic system pressure. A skid not corrected can quickly lead to a tire blowout, possible damage to the aircraft, and control of the aircraft may be lost. Until the aircraft has weight on wheels, the detector circuitry signals the anti-skid control valve to open the passage between the brakes and the hydraulic system return, thus preventing pressure build-up and application of the brakes. A wide variety of single disc brake options are available to you, such as braking system, use, and material. [Figure 28] Ground safety switches are wired into the circuitry for anti-skid and auto brake systems. By moving the flapper closer to one nozzle or the other, pressures are developed in the second stage of the valve. Leaks may also result. The return pin must be straight with no surface damage so it can pass through the grip without binding. Troubleshooting anti-skid system faults is either performed via test circuitry or can be accomplished through isolation of the fault to one of the three main operating components of the system. Master cylinders are used to develop the necessary hydraulic pressure to operate the brakes. This accomplishes the same operational verification, but allows an additional degree of troubleshooting. Most feature numerous elements that aid in the control and dissipation of heat. The tube expands outward, and the brake blocks make contact with the wheel drum causing friction that slows the wheel. A file can be used to smooth out minor irregularities. Aircraft hydraulic system pressure flows through the valve to the back side of the piston. To supply the lower pressure, a brake debooster cylinder is installed downstream of the control valve and anti-skid valve. The volume of output fluid increases since a larger piston and cylinder are used. The manufacturer’s data also provides a burn in procedure. The rotors and stators are relatively thin, only about 1/8-inch thick. Most contain three main types of components: wheel speed sensors, anti-skid control valves, and a control unit. Lower pressure is then maintained to the brake at a level that slows the wheel without causing it to skid. When the brakes are applied, the pistons move out from the outboard cylinders and their pucks contact the disc. Fluid quantity may need to be adjusted to assure the reservoir is not over filled. A passage in the slide directs brake pressure fluid into a compensating chamber at the end of the slide. independent braking system with a remote reservoir. The majority of the rudder/brake pedal feel is supplied by the brake control or brake metering valve in a power brake system. More fluid and air is expelled through the hose into the container. Maintenance requirements on all single disc brake systems are similar to those on brake systems of any type. The fixed-disk, floating-caliper design allows the brake caliper and linings to adjust position in relationship to the disc. It is essential that the brakes are not applied when the aircraft contacts the runway upon landing. They should be in good condition without signs of wear. Thus, regardless of the amount of wear, the same travel of the piston is required to apply the brake. Braking is accomplished by applying friction to both sides of the disc from a non-rotating caliper bolted to the landing gear axle flange. The brake is ready to be applied again. Once the squat switch is open, the anti-skid control unit sends a signal to the control valve to close and permit brake pressure build-up. What you are asking is the difference between apple and orange my friend. [Figure 30]. This is similar to the brake system of an automobile. 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