Thursday, September 10, 2009

Mig-21 - wheel and brakes

The Cold War Air Museum, Mig21 wheels and brakes are massive, as you might expect.

The size of the wheel allows a larger brake assembly to be housed inside, provides more area for heat dissapation from the brakes and allows for a larger dianeter tire to provide more tread area to absorb high landing wear. The Mig lands at about 200 mph (330 kph) and a set of tires may typically last for only ten landings.

In earlier and smaller aircraft,drum brakes were used. Disk brakes were developed when military and commercial aircraft got larger and faster and needed more efficient breaks to stop on reasonable length runways. This brake stack has four rotor plates that rotate with the wheel and five stator plates that remain stationary with the wheel hub.

The tabs on the rotor plates must be lined up and slid into the grooves on the inside of the wheel rim shown above. That is what causes them to rotate with the wheel between the stationary plates. When pressure is applied to the stators, the moving and stationary plates are squeezed together eventually bringing the wheel to a stop. All of the excess energy from the speed of the aircraft is turned into heat. Brakes get very hot after a landing and must be allowed to cool before another landing cycle.

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