IV.

Other Braking Systems

Bicycles have one of three types of brakes. Coaster brakes are used on the rear wheel of single-speed bikes, which do not have shiftable gears. A mechanism inside the rear wheel hub creates a binding action that slows or locks the rear wheel when the pedals are operated in the backward direction. On bicycles with multiple gears, caliper and cantilever brakes (also called side-pull and center-pull brakes, respectively) are used on the wheels. Both of these types of brakes use hand levers and cables to operate the brake mechanism, which consists of two levers that squeeze a pair of rubber pads against both sides of the wheel rim. Both types are spring-loaded to retract the pads when the pull cable is released. Cantilever brakes are considered better for mountain bikes and for bicycle racing, because these brakes provide more leverage for increased braking force.

Aircraft have hydraulic brakes on their landing gear for stopping after they have landed. The antilock brake system was first developed in 1947 for use on the B-47 bomber. Many aircraft also have special flaps or spoilers called air brakes that can be extended from the wings to increase aerodynamic drag. These flaps may be used to slow the aircraft when it is diving or maneuvering in flight and to help slow it after it has landed. Other means of braking aircraft include propeller blades that can change pitch (operating angle) and thrust reversers that redirect the jet blast sideways or forward in jet engines. Many high-performance military aircraft also have special parachutes called drogue chutes that deploy upon landing to assist braking. The space shuttle uses several drogue chutes for braking, because it lands at speeds in excess of 480 km/h (300 mph). Some types of racing cars also use drogue chutes to assist braking (see Automobile Racing).

Electric cars and other electric vehicles use drum and disc brakes to stop, but some vehicles also make use of magnetic brakes, which create opposing magnetic fields to resist motion. Called regenerative braking, this technique recaptures some of the vehicle’s momentum as electrical energy. Regenerative braking uses the magnets within the electric motor itself to slow the vehicle. When the driver releases the accelerator pedal, the electric motor changes into a generator, recapturing the energy from the moving car and transforming it back into electricity. The extra electricity is then used to recharge and extend the driving range of the batteries. See also Electric Motors and Generators.