1.0 Stealth features of the F/A-22
Taking a look at the F/A-22, quickly reveals the fundamental principles of a stealthy design as discussed earlier.
2.0 Continuous curves
The F/A-22 uses a combination of different ways to keep radar waves from bouncing back to their origin. The most sophisticated system is the use of so-called continuous curvature.
Many of of the surface shapes of the F/A-22 are curves with constantly changing radii. These scatter radar beams in all directions instead of back to the radar source. There are no right angles on the exterior of the design.
In order to calculate the curves and the effect they have on radar reflections form any point in 3D space, requires a tremendous computing power.
The first plane using this technology
extensively is the B-2 stealth bomber, also known as the flying wing.
Since computer- and software development has sky-rocketed over the past 20 years, prediction models can now be calculated quite precisely ,taking in account radar reflection versus the shape of the plane, while supporting more naturally aerodynamic shapes.
3.0 Planform alignment
The second way to keep radar waves from returning to the sending antenna, the leading and trailing edges of the wing and tail have identical sweep angles (a design technique called planform alignment).
The fuselage and canopy have sloping sides. The vertical tails are canted. The engine face is deeply hidden by a serpentine inlet duct and weapons are carried internally.
4.0 Saw-toothed edges
The F/A-22 has a low height triangle appearance from the front. This physical cross sectional view ensures a small signature from the front and low observability touches such as paint and materials, as well as little "W" shapes where straight lines might have appeared, all tend to break up the signature by absorption or redirection.
The "W" shapes are found at numerous places on the stealth aircraft. For instance, in the forefront of the cockpit glass, there is a very apparent "W" shape. This reduces the radar energy reflected during a head-on pass to the radar emitter. The "W" shape is also found on landing gear doors, engine inlets and outlets, as well as other openings.
5.0 Engine nozzles
Reduction of radar cross section of nozzles is also very important, and is complicated by high material temperatures.
The approach taken at Lockheed is to use ceramic materials.
The ceramics may be either lightweight, parasitic sheets mounted on conventional nozzle
structures or heavier structural materials forming saw-toothed edges.
6.0 Cockpit
The pilot's head, complete with helmet, is a major source of radar return. This effect is amplified by the returns of internal bulkheads and frame members. The solution is to design the cockpit so that its external shape conforms to good low radar cross section design rules, and then plate the glass with a film similar to that used for temperature control in commercial buildings. Here, the requirements are more stringent: it should pass at least 85% of the visible energy and reflect essentially all of the radar energy. At the same time, one would prefer not to have noticeable instrument-panel reflection during night flying.
7.0 Antennas
On-board antennas and radar systems are a major potential source of high radar visibility for two reasons. One is that it is obviously difficult to hide something that is designed to transmit with very high efficiency, so the so-called in-band radar cross section is liable to be significant. The other is that even if this problem is solved satisfactorily, the energy emitted by these systems can normally be readily detected. The work being done to reduce these signatures is classified.
8.0 Paint scheme
In order to make the F/A-22 disappear for the human eye on the ground, when in flight, special camouflage schemes have been developed. This way the plane will blend with the background sky as much as possible viewed from the bottom and disappear in the ground texture when seen from above.
9.0 Conclusion
The result of all these as well as a number of un-disclosed or non mentioned measures is the F/A-22's BVR capability, meaning that it can detect, engage and kill an opponent fighter, while staying invisible itself.
All from www.f-22raptor.com...
[edit on 11/24/04 by jetsetter]
