Similar angles = stealth?

Keegan McCarthy
  • Similar angles = stealth? Keegan McCarthy

    Sorry for the awkwardly phrased question, but I learned in my intro to engineering class at my college that 5th gen fighters (which are stealth aircraft) are designed with similar angles to evade radar.

    Why is this true?

    Also, does the angle matter? Many of these modern fighters looks to have very similar angles (no pun intended).

    enter image description here

  • The angle matters because radar works kind of like a mirror. Imagine holding a mirror out in front of you. If you start to twist it in any direction, you reach a certain point where the light coming off of you is no longer bounced back into your eyes, but is reflected off in another direction. Radar however cannot ever be completely reflected away, but this same principle allows a significant portion of the radar's energy to be deflected off in a useless direction, instead of back toward the dish.

    The angles are similar because that angle was determined to have the smallest radar signature. So it makes sense that every other facet on the same (geometric) plane would be at the same angle. This means that the radar's energy is directed away in a very specific direction (away from the source), rather than a bunch of different angles (that would be more likely to return the energy to the source).

  • Define "with similar angles". In itself the phrase means nothing.
    The basic shape of the airframe is of course a function primarilly of its required function to provide lift and enough inner volume for the aircraft's components.
    Stealth depends on several factors:

    • absorption
    • scatter
    • deflection

    These are functions of the shape and materials used. Creating surfaces that cause incoming EM waves to scatter in many directions rather than being reflected directly back causes the return signal received by a RADAR system to be much weaker, reducing the detection range.
    But a big part is also played by placing grids in air intakes, shielding sharp edges with sawtooth overlays (see the canopy and bay doors, for example), and covering different parts of the aircraft in different materials.

  • I assume you're using the term 'similar angles' in a geometric sense, to mean that the angle from a reference like the aircraft centerline to the lines made by two structural features are the same. Your photo shows this well, with the wing leading edge angle the same as the horizontal stabilizer leading edge angle and the same as the inlet (?) angle.

    I believe the reason for this is that the overall likelihood of radar detection is lower because each of these features will reflect radar signal in the same direction as one another. This means that the reflection will be very much stronger in the direction they reflect, but that reflection has a very narrow spread. In contrast, the features will not reflect radar strongly at all other angles. Thus the radar dish has to be "lucky" to be at exactly the right angle from the aircraft to receive the strong signature, and so the overall probability of detection is reduced since at most angles the reflection signature is reduced. This is also the reason that flat surfaces are used in many stealth designs.

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  • Similar angles = stealth? Keegan McCarthy

    Sorry for the awkwardly phrased question, but I learned in my intro to engineering class at my college that 5th gen fighters (which are stealth aircraft) are designed with similar angles to evade radar. Why is this true? Also, does the angle matter? Many of these modern fighters looks to have very similar angles (no pun intended).

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