Why is the B2 bomber called a stealth bomber?

Answer 1

Presuming you are asking about the B-2 Spirit bomber of the US Air Force.

Starting in the early 1960s, the increating power and effectiveness of Surface-to-Air missiles became an considerable concern for air strategists. Existing technologies for defense against these missiles was barely adequate, and the progression of technological advance heavily favored the SAM over the aircraft. There was a great deal of fear that within 20 years, it would be simple and cost-effective to build a SAM defense that was impenetrable by aircraft. In an attempt to change the balance of power in the SAM vs Aircraft contest, designers began to look at passive defenses (making the aircraft harder to detect) rather than active ones (jamming or speed). Thus was born the research programs into Low Observable materials and designs, also known as Stealth.

The original stealth "fighter", the F-117, was really more of a proof-of-concept that stealth technology was now practical. The design of the aircraft was primarily dictated by the current state of the art in stealth materials, which is why it featured so many angular surfaces. While some considerations for performance were included in that design, the major limiting factor was the inflexibility of the stealth materials. The result was a plane which accomplished most (if not all) of the goals of creating a plane which was radically harder to detect than previous aircraft. However, the combat performance of the F-117 was severely lacking, as too many compromises had been made in the name of "invisibility".

The B-2 design built on the experience of the F-117, and was able to take into consideration about a decade's more advances in stealth materials, yielding much more flexibility in design than possible for the F-117. The design criteria for the B-2 were as follows:

1. Intercontinental range, with global range via in-flight refueling
2. Even better low-observable (LO) characteristics than the F-117
3. Strategic-level mission capacity; specifically, the ability to carry virtually any weapon in the US inventory without compromising stealth capability or range

The selection of the "flying wing" design came about for several reasons:

1. The long-range plus required stealth ability dictated a subsonic design, as supersonic engines consumed too much fuel and gave off too much heat, compromising the range and LO goals
2. For a subsonic plane, the flying wing gave considerably more internal usable space than a traditional design
3. The flying wing also made it far simpler to "bury" the engine intakes and exhausts in the airframe, which radically reduced problems associated with LO characteristics of turbine engines. In particular, the large compressor fans of a turbine give a significant radar signature, and the hot exhaust is a massive infrared signature. The extra spaciousness of the flying wing meant that the engines could be buried deep inside, where ducting at both the intake and exhaust could be used to mask the compressor fan and dilute the hot exhaust
4. A flying wing design requires no vertical stabilizers or tail, which eliminates a major radar and visual detection point
5. The design allows for a "wide and shallow" armaments bay, which is more flexible than a "narrow and deep" one commonly required on a traditional airframe
6. The front profile of the flying wing tends to be very narrow with only modest increases where the engines and crew/weapons areas are, rather than a larger round fuselage - this makes for a better radar cross-section, and better LO ability.
7. Advances in electronic flight controls (fly-by-wire) and computer processing overcame many of the issues with stability and maneuvability that plagued earlier flying wing designs. Thus, there was no real difference in aerobatic performance between the flying wing and traditional designs.

Additional features fo the B-2 evolved the way they did for these reasons:

1. The large "bubble" cockpit allows for side-by-side seating of the crew, which is far better for crew performance on long missions. It also provides for space to have a toilet and small galley installed, which are critical for maintaining crew effectiveness for missions which can routinely exceed 12 hours, and often exceed 24 hours.
2. Large amounts of computer automation are included, which reduce the total number of crew to only 2, vs 4 of the B-1B and 5 of the B-52
3. The black color is actually a dark grey, and is special paint impregnated with radar-absorbing materials.
4. The "sawtooth" engine intakes are signficantly less radar reflective than traditional smooth arches.

Answer 2

Stealth bombers can not be detected by radars so they can bomb places secretly.

Answer 3

It's intended to operate with stealth... it's not supposed to be detectable by radar, and intended to operate at altitudes where it won't be seen visually from the ground.