B-2 “Stealth”: A Flying Wing
Предпереводческий анализ:
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An ordinary airplane consists of a fuselage (the main body), two wings and three rear stabilizers attached to the tail. The wings generate lift, hoisting the fuselage into the air. The pilot steers the plane by adjusting movable components of the wings and the stabilizers. Adjusting these components changes how the air flows around the plane, causing the plane to ascend, descend and turn. The stabilizers also keep the plane level.
The B-2 bomber has a completely different design: It's one big wing, like a boomerang. This flying wing design is much more efficient than a conventional plane. Instead of separate wings supporting all the weight of the fuselage, the entire craft works to generate lift. Eliminating the tail and fuselage also reduces drag – the total force of air resistance acting on the plane.
Greater efficiency helps the B-2 travel long distances in a short period of time. It's not the fastest craft around -- the military says it's high subsonic, meaning its top speed is just under the speed of sound (around 1,000 ft/sec or 305 m/s) -- but it can go 6,900 miles (11,000 km) without refueling and 11,500 miles (18,500 km) with one in-flight refueling. It can get anywhere on Earth on short notice.
THE CREW AND SUPPORT
The B-2 bomber needs only a two-person crew – a pilot and a mission commander who sit in a cockpit at the front of the plane. By comparison, the B-52 bomber has a five-person crew, and the B-1B has a four-person crew.
The original idea of the B-2 was that because of its stealth capabilities, it should be able to penetrate enemy airspace without fire support, doing the work of dozens of planes. In practice, the B-2 usually flies with some fighter jet protection. The risk of losing such an expensive aircraft is too great to send it into battle solo.
DRIVING THE WING
The B-2 has four General Electric F-118-GE-100 jet engines, each of which generates 17,300 pounds of thrust. Just as in an ordinary plane, the pilot steers the B-2 by moving various parts of the wings. Flying wings have been around for a long time, but in the past, they suffered from major stability problems. Without the rear stabilizers, the plane tends to rotate around its yaw axis unexpectedly. The U.S. military didn't go for Northrop Grumman's earlier flying wing designs from the 1940s mainly because of these concerns.
By the 1980s, advancements in computer technology made the flying wing a more viable option. Northrup Grumman built the B-2 with a sophisticated fly-by-wire system. Instead of adjusting the flaps through mechanical means, the pilot passes commands on to a computer, which adjusts the flaps. In other words, the pilot controls the computer and the computer controls the steering system.
The computer also does a lot of work independent of the pilot's input. It constantly monitors gyroscopic sensors to keep track of the plane's attitude – its position relative to the airflow. If the plane starts to turn unexpectedly, the computer automatically moves the rudders to counteract the turning force. The corrections are so precise that the pilot usually won't feel any shift at all. The B-2 also has a small wedge-shaped flap in the middle of the trailing edge. The computer adjusts this flap, called the gust load alleviation system (GLAS), to counteract air turbulence forces.
OUT OF SIGHT
Northrop Grumman's primary goal for the B-2 was stealth, or low observability. Simply put, stealth is the ability to fly undetected through enemy airspace. Ideally, a stealth aircraft will be able to reach and destroy desired targets without ever engaging the enemy in combat.
To do this, the aircraft needs to be nearly invisible in a number of different ways. Obviously, it needs to blend in with the background visually, and it needs to be very quiet. More importantly, it needs to hide from enemy radar as well as infraredsensors. It also needs to conceal its own electromagnetic energy.
The B-2's flat, narrow shape and black coloration help it fade into the night. Even in the daytime, when the B-2 stands out against blue sky, it can be hard to figure out which way the plane is going. The B-2 emits minimal exhaust, so it doesn't leave a visible trail behind it.
As with most planes, the B-2's noisiest component is its engine system. But unlike a passenger jet or B-52, the B-2's engines are buried inside the plane. This helps muffle the noise. The efficient aerodynamic design helps keep the B-2 quiet as well, because the engines can operate at lower power settings.
The engine system also works to minimize the plane's infrared (heat) signature. Infrared sensors, including those on heat-seeking missiles, typically pick up on hot engine exhaust. In the B-2, all of the exhaust passes through cooling vents before flowing out of the rear ports. Putting the exhaust ports on the top of the plane further reduces the infrared signature, since enemy sensors would most likely scan below the plane.