Experiencing Technical Difficulties (resonant) wrote,
Experiencing Technical Difficulties

IDEA: Airplane wheel hubcap turbines

I flew back from Nova Scotia Saturday night on a Q-400. My seat was right under the wing, so I could watch the landing gear. The wheels on the landing gear weren't rotating until the instant they touched the runway - then they accelerated instantly in a puff of black smoke.

This seems like it would be rather hard on the tires. Googling showed that the tires need to be replaced every 125 landings, at $1000 per tire. That would add $32 to the cost of each flight.

If we could get the tires spinning before the aircraft touched the ground, we could probably make the tires last longer. We could also reduce the risk of a tire blowing out upon landing.

We could spin up the wheels using a hydraulic actuator or an electric motor. However, either option would add weight (increasing fuel costs), and add complexity (increasing maintenance costs).

When the landing gear descends, the aircraft is moving through the air at up to 215 knots. What if we used the air blasting past the tires to start them rotating? What if we made hubcaps for the tires with wind vanes to catch the breeze?

It turns out other people have already thought of that. There are dozens of patents for hubcaps for aircraft tires that will catch the wind and start the wheels spinning. There was even a proposal to include wind scoops in the treads of the tires on the Space Shuttle. These solutions are lightweight and nearly zero-maintenance.


So, if this idea has been thought of before, why are airlines still burning rubber every time they land a plane?

It turns out that aircraft tires can exert impressive gyroscopic forces once you get them spinning. Maneuverability is critical when an aircraft is taking off or landing. When pilots need to suddenly turn their aircraft, they don't want to have their tires fighting their every move. On some aircraft, brakes automatically engage when the landing gear retracts, to kill the angular momentum of the tires. On other aircraft, pilots will tap the brakes once the wheels lift off. So, any attempt to spin up the tires before landing would infuriate pilots.

So it wasn't a good idea after all. But I had fun learning about things while I looked intoit.
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