The first system is the series of flaps and configerations in which these can be arranged.
These flaps on this Boeing 747-400 are set for landing. Notice how they are extended. This allows the aircraft to decelerate and fly at a lower speed, thus reducing the speed on touchdown. The flaps can be extended to any configuration in order to meet the demands of the pilots. Normally the lowers the percentage of flaps, the better lift ratio, but once you cross a certain percentage of flaps, normally 30 percent the drag starts to overcome lift, causing the aircraft to slow. These flaps can be used for take off configurations, during flight, and on landing.
The picture on the right shows a configuration of flaps during landing. A speed brake is another part of the flap system that can help slow the aircraft. It does exact what it's name implies. It is a braking system that is applied "to the wings" to help slow the aircraft. You can tell when the aircraft is nearing landing or needs to slow to enter the pattern before landing. You can hear the flaps extending from the wing. Usually followed by a "THUD." This is the flaps locking into place.
This video here from Flight Level 350 is an excellent example of the flaps being extended. Normally they are not this loud.
The second component of stopping an aircraft is right after the rear wheels touch down and the front set is coming to a rest on the ground. This is the reverse thrusters. Because aircraft are getting heavier, bigger, and just need more room to stop, all of the newer planes have them. This video also from Flight Level 350 shows this MD-82 deploying the reverse thrusters twice.
As you can see the flaps are fully extended. The speed brake is pointing up on the wings. And the cowling that surrounds the engine looks as if it has fallen apart or away from the engine. This forces the air that is being pulled through the aircraft engine to be pushed down and up, instead of back, altering the thrust. This inturn slows the aircraft significantly.
You might remember that Southwest 737 that slid off the runway in Midway Airport in Chicago. A pin that is suppose to activate the reverse thrust failed to operate in a timely manner. This reduced the slowing and stopping capacity of the aircraft. Since the runway at Midway is fairly short this lead to the aircraft sliding off the runway and into a car, resulting in the death of a passenger in the car.
You can tell when the reverse thrusters are working, the noise is fairly intense for a few seconds. You can also see the dust or water droplets kicking up if they are present on the ground. This is an amazing sight. The sheer power of the engines is easily seen and heard. The thrusters will normally operate for a short period of time until the aircraft can be slowed to a manageable speed in which the next system can be used.
The brakes on the wheels are the third system in the process of slowing and stopping aircraft. If the brakes were just used to stop the aircraft it would take a great deal of runway length and the replacement intervals would be greater.
All three of these are important in slowing and stopping aircraft, especially heavy ones.
Great post, Rob. That's excellent information. It's fascinating to me. I love the videos. Thanks! Dan.
Posted by: Dan Smith | January 26, 2006 4:08 PM | Permalink to Comment