CHAPTER 19: SPEED AND ACCELERATION
ACTIVITY 2: COMPREHENSION 1 Read this article and answer the questions that follow.
AVOIDING ‘HOT’ WHEELS
Nervous air travellers concerned about the risks of ageing planes may first worry about how well the wings or engine are holding up. But a plane’s tires suffer a lot of wear and tear too. When aircraft approach their destination, pilots extend the landing gear to prepare for touchdown. Before the plane lands, its tires aren’t spinning, notes Phillipe Lothaller. He’s a 17-year-old engineer at Rondebosch Boys’ High School in Cape Town, South Africa. But the instant a plane’s tires hit the runway, they start spinning at very high speeds. For some aircraft, landing speeds can be as high as 200 kilometres per hour.
That instant high acceleration is very stressful for a tire, says Lothaller. Friction can cause a tire’s rubber to quickly hit 240°C. The stresses of landing also tend to pull the layers of a tire apart, causing them to separate from each other. This separation is known as delamination. Aircraft maintenance crews typically retread a plane’s tires after every 200 landings. And each tire can be retread only five times before it must be replaced. Refitting a plane with new wheels can be quite costly, with each tire running between €1,400 and €9,000.
Now, Lothaller has designed a device to reduce wear and tear on those tires. He attaches a large, circular plate to the wheel rim that holds the tire. As pilots come in for a landing, several metal plates on the device pop out, creating scoops. Each scoop is about 7 cm tall and several times that long. They catch the air, turning the device into a pinwheel. This causes the wheel to start spinning long before it touches the ground. That means the tire won’t have to accelerate nearly as much once the plane touches down. The result: far less stress on each tire.
The teen’s tests suggest that these scoops could reduce tire wear by between 35 and 45 per cent. So instead of retreading a tire every 200 landings, crews could wait to do this after every 250–260 flights. Lothaller points to other benefits from extending the life of airplane tires. For example, airports wouldn’t have to spend as much money removing chunks of damaged tires from runways. Those chunks pose a danger to planes as they land and take off, he notes. An engine might suck them up, causing damage, or parts of the tread shed by a tire could bounce up and pierce the skin of a plane, risking a fuel leak. (Imagine the damage that could be caused by hitting a chunk of tire on the runway at more than 160 km/h!)
Adapted from:
www.sciencenewsforstudents.org a. What speed does the article claim some airplanes land at?
b. What temperature can the tires reach on landing?
c. How often do the maintenance crews retread each tire?
d. What does Phillipe Lothaller’s device do to reduce the stress on the tires?
e. How much could this device reduce the wear and tear on tires?
UNIT 5: MOVEMENT
93
PHYSICAL WORLD
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