Landing
From Wikipedia, the free encyclopedia
- For other uses, see Landing (disambiguation).
Landing is the last part of a flight, where a flying animal or aircraft returns to the ground. When the flying object returns to water, the process is called alighting, although it is commonly called "landing" as well. Hitting the ground too hard is prevented by wings (including rotor wings), a parachute or rockets or a vertically directed jet engine; in the case of a balloon the buoyancy is slightly decreased for a soft landing. Aircraft usually land at an airport on a runway or helicopter landing pad.
For aircraft or birds, landing is generally accomplished by gradually tapering down airspeed and lift. The first phase is the flare, where the rate of descent will be reduced by transitioning to a stall attitude. After slowing down, the plane changes pitch into the landing attitude shortly before touching down.
In a perfect touchdown, assuming there is no crosswind, contact with the ground is made just as the forward speed is reduced to the point where there is no longer sufficient lift to remain aloft. If there is a crosswind, techniques such as a crab landing or a slip landing are used to land the plane safely.
During landing, the ground effect becomes significant for aircraft. This tends to make the aircraft "keep flying" when it ordinarily would not (at higher altitudes) and therefore to extend the distance required to land.
Large transport category (airliner) aircraft land differently than described above. If the pilot waited for the aircraft to stall too much runway length would be used so the flare just reduces the rate of descent at touchdown and the aircraft is flown onto the runway. Usually spoilers (Sometimes called "Lift Dumpers") are immediately deployed to dramatically reduce the lift and transfer the aircraft's weight to its wheels, where mechanical braking can take effect.
Reverse thrust is used by many jet aircraft to help slow down just after touch-down.
To land on an aircraft carrier, a conventional aircraft (moving at, perhaps, 150 mph (240 km/h)) is equipped with tailhooks to engage one of up to four arresting cables stretched across the deck, stopping the aircraft within 320 feet (100 m) after engaging one of the cables. To assist safe landings, the carrier will usually steam directly into wind at full speed, thus reducing aircraft's speed relative to the carrier deck, and eliminating any crosswind.
[edit] Landing Technique
The techniques described below apply to single-engine aircraft such as the Cessna 172.
- While it is dangerous to fly a low final, flying a high approach will force the pilot to lose a significant amount of altitude in a short amount of time. It will become more difficult to hold the aircraft off the ground during the flare and a hard landing is more likely. Also, the aircraft could enter what is called a dynamic stall.
- Approach at the correct airspeed. Approaching too fast can result in a ballooned landing, while approaching too slow can result in a stall.
- Do not wait too long to begin holding back pressure on the yoke. Doing so will result in a hard or bounced landing. A good rule of thumb is when the aircraft reaches the runway threshold, power should be set to idle and the pilot should begin holding slight back pressure. The amount of back pressure held should increase as the aircraft loses altitude. At the same time, holding too much back pressure could result in a balloon or early stall.
- When approximately the distance of the wingspan from the ground, ground effect will cause induced drag on the aircraft to decrease, possibly increasing flare distance. If the aircraft balloons in this situation, the pilot should continue holding back pressure and should not allow the aircraft to quickly settle back to the ground.
- At the beginning of the flare, the pilot should look approximately half way down the runway. This is important because a repetitive "landing sight" will help develop continuity.
- Once the main gear touches down, do not push the yoke forward. This could cause the nose wheel to bounce, cause damage to the nose gear, or induce a nose wheel shimmy, in which case the pilot should hold slight back pressure to divert weight from the nose wheel.
- Do not forget to account for wind. A crosswind will require the pilot to crab into the wind. In this instance, one main wheel, the wheel which is into the wind, should touch the ground before the other; this is correct. If the aircraft is crabbed but touches down on both main gear at the same time, skipping may occur. The direction of motion of the aircraft should be parallel to the aircraft's longitudinal axis (the imaginary line running from front to back).
[edit] See also
es:Aterrizaje fa:فرود fr:Atterrissage it:Atterraggio pl:Lądowanie pt:Aterragem
