Hi,
Why an overweight landing may lead to excessive brake temperature? Is it because the speed will be higher? Or is it something to do with the wheels friction?
763 jock
21st Dec 2010, 16:07
Higher speeds/more mass to stop.
SNS3Guppy
21st Dec 2010, 16:07
Wof,
More brake energy is consumed (or created, as you will) stopping a heavy object, than a light one.
Brake energy isn't the issue with an overweight landing, however (though hot brakes can be); there are stresses on landing gear, wing spars, the fuselage, and many other components that are not what the airplane was designed to do. Add to that a hard landing, or a landing in excess of a given rate of descent, and these stresses can be magnified considerably.
Brake temperatures reflect the amount of braking that must be done to slow or stop the airplane.
A lightweight airplane with maximum braking may have hotter brakes than a heavy airplane that uses full reverse and rolls to the end. Where brakes are required, however, for a given stopping distance, the brakes will have to work harder to stop a heavier airplane, and consequently be hotter.
We frequently either land at our maximum landing weight (630,000 lbs), or we're landing nearly empty (on a ferry leg). There's typically a big difference in brake temperatures between a max weight landing and an empty one.
Ever arrive at a stoplight in your car when it's full of friends and heavily loaded, and notice a difference in the amount of braking you have to do to stop the car? It's no different than it is landing an airplane. A heavy airplane moving at a given speed has a lot more energy to stop, which translates to a heat increase in the brakes, than a light one.
rasfcivil
5th Jan 2011, 02:56
Hi there!
That's true what people have wrote. You can simple say:
Ec=(1/2)*m.V^2
more weight (mass) and you have more energy to stop. Just like this. Furthermore, more mass implies more speed during approach and land, Vref (1.3Vs) is higher as stall speed is increased, and remember Kinetic energy varies with the Square of speed.
To worsen the things sometimes, imagine the next scenario:
-You must divert and land and your aicraft is to heavy. The rwy is critical and you have to jettison in order to have the MLW, but you really have no time and need to land. As one problem never comes alone It was rainnig 10m ago and the RWY is wet partially with patches, the wind is calm. Not a good idea at all.
regards!