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Stealth technology uses angles in the aircraft shape, and homogeneous orientation of the surfaces. In the F-22A Raptor wing leading edges, tail surfaces, air intake bypass doors, refueling aperture, etc have the same orientation.

This is a example of planform alignment

Incoming radar waves are deflected in a different direction, giving the enemy the impression that there is nothing there.

This is a example of planform alignment

However, as mentionned in Wikipedia: "Shaping requirements detract greatly from an aircraft's aerodynamic properties. The F-117 has poor aerodynamics, is inherently unstable, and cannot be flown without a fly-by-wire control system."

I'd like to know what are the impacts of such planform alignment on planes capabilities, and how does a passive stealth shaping, using a small number of surface angles, compare to a "5th generation fighter"

This is a different question than Do similar angles on a plane make it more stealthy?" I'm looking for the advantages and disadvantages of using planform alignment.

fooot
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  • could you add some pictures/drawings? I seriously have an hard time trying to understand what you are asking. – Federico Jun 02 '15 at 22:08
  • I think you've already answered your own question (or maybe I'm not getting what exactly you want to ask). Though, according to Lockheed Martin : Fifth Generation Airplanes are having all-aspect stealth even when armed, low probability of intercept radar (LPIR), high-performance airframes, advanced avionics features, and highly integrated computer systems capable of networking with other elements within the battlespace for situation awareness. – Victor Juliet Jun 03 '15 at 05:08
  • possible duplicate of Do similar angles on a plane make it more stealthy? – Peter Kämpf Jun 03 '15 at 09:53
  • I've simplified the question to emphasize that the subject is not about getting or improving the stealth characteristics, but about comparing capabilities of a stealth aircraft with those of a "5th generation fighter". I feel the currently selected answer doesn't address this latter aspect. – mins Jun 09 '15 at 05:52

1 Answers1

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To understand the functioning of planform alignment in befitting the fifth generation air-crafts in increasing their stealth, one first need to understand how Radars work:

  1. Radar transmits a radio wave signal.
  2. This signal when comes in contact with a surface (of an aircraft), it is reflected back. This reflection is a mixture of Specular and Diffused reflection.
  3. The radar then after receiving the reflected signal, measures the speed (by computing the shift in the time period taken by the wave to be received over a period of time), and size (by computing the intensity of the reflected wave) of the air-craft.

But there is a problem, since the radar needs to get back its own transmitted wave back, if it is reflected off the surface of the plane only at a specific angle (specular reflection), then the receiver of the radar needs to be at specific places to receive the reflected wave.

Modern planes utilize this shortcoming of the radar by letting the incoming radar signal pass through them (using plan-form alignment), which then greatly reduces the reflected signal. The reduced reflected signal would be seen as an incoming signal of very low strength (intensity) by the radar, which then reads the size of the incoming air-craft as a very small object. This is called Stealth. The air-crafts also use special paints and composite coverings on the surface to again reduce the intensity of the reflected wave, to reduce the percieved size of the air-craft by the radar.

The shortcomings of such radars are removed by using radars such as AWACS, which is moving radar and can receive too directional signals (Specular reflection). Or, using radars such as AESA, which scans a large portion of area around it without having any moving parts.

Victor Juliet
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    How would AWACS have better detection of stealth aircraft? The fact it is moving is irrelevant; it still needs to be in the place to which the signal gets reflected and since the radar is not larger, the chance it will be in the right place where the reflected signal is not higher. – Jan Hudec Jun 03 '15 at 08:48
  • That was based on the following logic:

    In so-called "moving radar", a gun receives reflected signals from both the target vehicle and stationary background objects such as the road surface, nearby road signs, guard rails and streetlight poles. Instead of comparing the frequency of the signal reflected from the target with the transmitted signal, it compares the target signal with this background signal. The frequency difference between these two signals gives the true speed of the target vehicle.

     – Victor Juliet Jun 03 '15 at 08:52
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    How would AESA have better detection of stealth aircraft? It has many advantages, like being more resistant to jamming, having shorter scan period, being able to also act as passive detector, being more difficult to detect by passive detector. But it still can't do anything about where the target reflects the incoming radio wave and thus probability it will get reflected back to the detector. – Jan Hudec Jun 03 '15 at 08:52
  • You yourself pointed out : Shorter scanning period. – Victor Juliet Jun 03 '15 at 08:53
  • Also, it has no moving parts (which means it can be scanning all around itself, at all points of time). This though can be somewhat included in the shorter scanning period – Victor Juliet Jun 03 '15 at 08:55
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    No magic with doppler shifts is going to help you get a signal that is not reflected towards you in the first place. And if you meant secondary reflections, they are too weak and you can't really calculate the target position from them anyway. – Jan Hudec Jun 03 '15 at 08:58
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    Shorter scanning period improves the chance that you get the occasional flash when the constellation is momentarily such that the signal is reflected back. It still won't allow tracking the target though. – Jan Hudec Jun 03 '15 at 09:00
  • Not the Doppler shifts, but the Background object (if the are there) – Victor Juliet Jun 03 '15 at 09:00
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    Let us continue this discussion in chat. – Victor Juliet Jun 03 '15 at 09:01