Aircraft Tires
Friday, September 30, 2011 at 07:55AM Tires are on airplane are one of the more overlooked parts of an aircraft by passengers. However, ask any pilot how important it is to make sure their tires are in proper working order and they will most likely talk your ear off about how their tires need 7 plys. Aircraft tires - here we go:
Aircraft tires are very different from the large treaded tires your have on your car. The first and most visible difference is the lack of treads on aircraft tires. A car enthusiest would call aircraft tires "slicks", meaning there is only two or three small grooves on the surface of the tire. With car tires, treads are used to move water quickly away from underneath the tire, provide traction on a multitude of surfaces (including unpaved roads and very light off-roading) and provide grip during acceleration power from the wheel. Aircraft tires have a different need. The lack of tread is to maximize the amount of vulcanized rubber in direct contact with the tarmac. This is exactly why NASCAR tires have zero tread, because the more rubber touching the road/runway the more traction there is. However, with an airplane, treadless tires are not for traction during turning or acceleration - they are for maximum traction during heavy braking.
Aircraft tires withstand more punishment in a single landing than the tire on a truck does over its entire life. A Boeing 747 may weigh around 500,000 pounds at landing and is traveling well over 100 mph at landing. That means each tire has to not only support around 30,000lbs but has to support that weight slamming into the runway at extremely high rates of speed and go from 0 mph to full speed in a fraction of a second. To help with durability aircraft tires are 7 or 8 ply. A ply is a layer of woven material that reinforces the vulcanized rubber - think of it like steel rebar inside of concrete structure. A pilot can always tell when a tire needs to be replace by noticing a ply becoming visible due to heavy braking or a hard landing.
Aircraft also deal with the dangerous issue of hydroplaning, but because higher rates of velocity are involved there are three types of hydroplaning taught to pilots to increase their awareness of the issue.
The first is dynamic hydroplaning. This is what happens in a car often after driving quickly through a puddle. The water under the tire does not have enough time to move as the tire crosses over it and the wheel actually rides on a sheet of water and loses contact with the pavement. This is a major issue as not only is there a loss of steering but more importantly there is an absolute loss in braking.
The next kind is viscous or contaminate hydroplaning. This is when water on a runway or airport surface mixes with oil, dust, sand, or some other contaminate that creates a dangerous slurry that reduces the effective braking action of the aircraft. This is usually encountered when an aircraft approaches a parking area where resting aircraft may have deposited oil or fluids while on the ground.
The last type of hydroplaning is what is called in the industry as rubber reversion. This is where a stationary tire accelerates so quickly during landing that the rubber actually forms a superheated steam that completely envelopes the tire. It is like dynamic hydroplaning in the way that instead of the aircraft riding on a sheet of water, the tire loses contact with the runway because it is riding on sheets of superheated steam.
In reality, though, these are not issues to be worried about while traveling on today's commercial aircraft. Runways are designed to eliminate standing water and airport personnel check braking effectiveness of every runway multiple times a day. Along with the advances in airport and runway design, aircraft tires have been improved to drastically reduce the potential of hydroplaning occurring. Using vulcanized rubber in tires enables them to withstand extremely intense heat without losing their integrity, and the treads on aircraft tires are used to channel water out from under the aircraft effectively.
So take a look at the tires next time you are waiting to board an aircraft, they really are the shoes of the aircraft.
Reader Comments (2)
A great post and thanks. I agree with your thoughts untl the last. Today's pilots DO have to be concerned with this stuff and the responsible captain do so! Not all runways are up to those ideal standards, even at the largest of airoirts. The smart pilots know the differences and the allow for the imperfect. If the book says 4500 feet (or whaever) the smart driver allows 6000 and then considers how much more is available. One should also note that the odd 'hard' landing is probably not a 'bad' landing or 'bad flying." Most often it is the pilot's intentional plan to contact earl and firmly and then apply near maximum braking as soon as the wheels meet the runway. Some airports, whether short runways or marginal conditions, require the PLANT IT landing. That is not bad flying. In fact, it is exceptionally good flying and demonstrates the pilot's thorough understanding of REAL stopping distances. The book and the computer are only guides. Smart pilots add their own fudge factor and when that is still not good enough, they add more, stay on the ground or divert. Good pilots may slam at times, but they do not run off the end. Nuff said. -C.
You may not realize it, but tires are one of the most important parts of an aircraft. And since an airplane is no ordinary vehicle, it doesn't get equipped with just ordinary tires.