At the rear of the wings and stabilizers are small moving sections that are attached to the fixed sections by hinges. In the figure, these moving sections are colored brown. Changing the rear portion of a wing will change the amount of force that the wing produces.
The ability to change forces gives us a means of controlling and maneuvering the airplane. The hinged part of the vertical stabilizer is called the rudder; it is used to deflect the tail to the left and right as viewed from the front of the fuselage. The hinged part of the horizontal stabilizer is called the elevator; it is used to deflect the tail up and down. The outboard hinged part of the wing is called the aileron; it is used to roll the wings from side to side.
Most airliners can also be rolled from side to side by using the spoilers. Spoilers are small plates that are used to disrupt the flow over the wing and to change the amount of force by decreasing the lift when the spoiler is deployed.
The wings have additional hinged, rear sections near the body that are called flaps. Flaps are deployed downward on takeoff and landing to increase the amount of force produced by the wing. On some aircraft, the front part of the wing will also deflect. Slats are used at takeoff and landing to produce additional force.
The spoilers are also used during landing to slow the plane down and to counteract the flaps when the aircraft is on the ground. Aft-mounted engines put a significant amount of weight aft, causing weight and balance considerations.
Under-wing engines are near the center of lift of the wing. Occasionally, the wing distorts the airflow into the aft-mounted engines, causing compressor stalls. This is does not happen on under-mounted engines. One advantage of the aft-mounted engines is that they do not create as much asymmetric thrust as under-mounted engines when one engine fails, because they are much closer to the centerline of the airplane.
Under-wing mounted engines produce a significant yaw when an engine fails, while aft-mounted engines produce less.
Having less yaw after an engine failure makes it easier for the pilot to maintain proper directional control. Q: I sat in the back row on an MD If not for my great headphones, the noise would have been unbearable! The attachment is, in effect, not as strong as it could be.
The bolts that attach to the pylon structure are incredibly strong on the , at least, they are made of a superalloy, nickel alloy , but this is a carefully balanced and calculated construction.
There is a good discussion of these strengths and figures on Stack Exchange. These bolts will support forces significantly in excess of the maximum expected forces, even in the event of very hard landings or extreme turbulence. But they would shear in the event of extreme forces. If the engines come into contact with the ground when landing for example, in a landing without gear or a runway overrun , the forces experienced would break the bolts and cause the engines to break off from the pylons.
This is preferable to them remaining attached a significant fire risk or for the forces transferring to the wing and causing it to break off. This also raises the question of why the engines are not incorporated into the wing.
This was the case with some early aircraft including the first jet aircraft, the de Havilland Comet. Such a design may seem stronger and more streamlined, but it has several problems and has been dropped in commercial jets. Firstly, there is the major issue of safety. An engine fire within the wing would potentially be more devasting than in a distant, podded engine. In a podded engine, the fire can hopefully be extinguished before it causes any wing damage.
Placing the engines in the wing also uses space that is needed for fuel.
0コメント