Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.
Issue link: http://experimenter.epubxp.com/i/307497
EAA Experimenter 31 BR A K E S: F I X ED OR F L OAT ING DISC, C A L IP ER Either the disc or the caliper needs to "float" to make up for wear, disc warp, and inevitable tiny misalignments. Most automobiles use a fixed disc/floating caliper design, where the rotor is mounted directly and rigidly to the wheel, and the caliper is on a pivot. Costs are low; the necessary offset disc and caliper placement pose no great space penalty in a car; and maintenance requires a bit more disassembly than with a floating disc. The floating-disc design, where the caliper is mounted rigidly to the airframe, tolerates greater misalignment, and the disc is less likely to get stuck while parked for months than in a floating caliper system. The fixed caliper system is often considerably less bulky and lighter than the au- tomotive approach, important in retractable or low-drag designs. But a floating disc is generally more expensive and has a higher parts count, as the relatively soft wheel must be protected from the hard disc, usually by replaceable steel shields. Also, a floating disc's diameter is limited by wheel size. Though in practice it is rarely seen, a fixed disc mount- ed alongside the wheel can be of larger diameter. Disc material: The disc absorbs and then radiates the heat generated in braking. Though some have tried stain- less-steel and carbon discs, the most common material is still iron. Iron can absorb a lot of heat, so it's almost univer- sal, even though it does rust overnight. That light surface rust disappears quickly with brake application and does not affect operation. Brake pads: There are two families of pad materials: organic and metallic. Organic pads grip well when cold, offering good braking immediately and good control when taxiing, but they wear relatively fast and fade as they get hot. Metallics have the inverse characteristics. Consider when you first touch down, your airplane is light and can't use a lot of braking power, but as it settles onto its wheels, more braking is desirable. A brake material that grips better when hot best exploits available traction during landing. However, metallic pads require considerably higher pedal pressure when taxiing and are not effective when cold. Calipers: The caliper works like a C-clamp on the rotat- ing disc. There is a brake pad on each side of the disc. In one side of the caliper is one or more pistons, driven from the master cylinders by the pilot's feet. That pressure moves the pistons, which push the pads against one side of the disc, tightening the "clamp" against the disc on both sides. More pistons (typically two) allow more even pressure to T e basics matter when choosing the right wheels and brakes for your aircraf . What is the airplane's gross weight, landing weight, and speed? The Cleveland setup on F1 racer Endeavor. Very light, very small aircraft don't need a lot of braking power. This Infi nity powered parachute carries only one tiny, cable-operated brake on the front wheel. E A A E X P _ M a y 1 4 . i n d d 3 1 EAAEXP_May14.indd 31 5 / 5 / 1 4 3 : 1 9 P M 5/5/14 3:19 PM