Do the wheels and tires spin before touchdown” ?
On big airplanes do the wheels and tires spin before touching down on a runway for landing ?
Question asked by Glenn
Wheels and tires do not spin before touching down on a runway. They start turning upon contacting the runway, as the weight of the airplane is transferred from wings to the wheels and tires. That is why when you watch airplanes landing, when the tires touch the runway there is a puff of smoke. The smoke is generated as the tires sliding on the runway pavement, before they spin up to the airplane speed. So the tires and wheels spin up from zero speed to about 240 kilometers per hour, which is about an average touchdown speed of large airplanes, within approximately 3 seconds. It is during this time when the tire slippage occurs and the puff of smoke is generated.
There have been several technologies tested to spin up the wheels in flight before touchdown. However, none of them have proven to be cost effective, thus none have been installed on airplanes. Ideas such as fins on wheels, so the air flow could spin the wheels have been tried, but they do not spin the wheels fast enough. Electric and hydraulic motors have been tried to spin the wheels. However those mechanisms are heavy and it costs fuel to carry them for an entire flight, yet they would work for a few seconds before touchdown only. The cost of fuel needed is much greater than the cost of tire wear due to the slippage when the airplane touches down on a runway. Despite of the wear during this slippage, tires on large airplanes can still absorb approximately 200 to 300 landings.
A bit more about Captain Dan:
Captain Dan Baz enrolled in Flight School at the age of 16.
He has completed studies in Aircraft Engineering and Master of Business Administration. He has been at the controls of many different types of aircraft, from single engine Cessnas to large intercontinental jets on global routes.
Over the last four decades he has flown thousands of hours up in the blue sky.
Have a question for the Captain ? Send it to Captain Dan Baz firstname.lastname@example.org Every week a question from the readers will be selected and answer posted in this column.