10
$\begingroup$

Stealth shaping like on the B-2 relies on making sure the radar beam is not returned to its source by minimizing the number of directions it scatters.

But this is known to fail when wavelengths become comparable to or longer than aircraft dimensions due to diffraction widening the scattered beams. For normal stealth aircraft, this begins in the 1-10m range.

But suppose we took a B-2 and shrank it to the size of a throw-drone. Than the diffraction-limited range would go into centimeters - the domain of fire control radars.

Improve this question
$\endgroup$
0

1 Answer 1

Reset to default
11
$\begingroup$

There are multiple radar bands in active use. Both NATO and whatever replaced the WP use at least VHF, L, S, C, X, K, and EHF bands.

Your guess is correct: smaller aircraft and drones benefit a lot less from stealth shaping, and generally have a higher RCS in some bands. This compounds with RAM coatings being less effective when they're much shorter than the wavelength.

It works both ways, as large aircraft are more vulnerable to VHF radars. Detection uses all bands, so generally large stealth planes are easier to detect. Fire control is generally shorter wavelengths, so small stealth targets can be easier to track and engage.

This is part of why there's less stealth-shaping effort for smaller drones and munitions: it won't work.

Improve this answer
$\endgroup$
5
  • 1
    $\begingroup$ On the other hand, small and relatively slow unmanned aircraft can use radar-transparent materials like plastic. $\endgroup$ Commented Apr 13 at 5:03
  • $\begingroup$ @jpa throw an empty water bottle or tumbler, made of "transparent" material in the air, it's still pretty viewable because 4 interfaces between air and n=1.4 material builds up a lot of Fresnel reflection. Aren't radar-absorbing materials (e.g. impedance-matching graphene composites) lower reflectivity than non-absorbing "transparent" dielectrics? $\endgroup$ Commented Apr 13 at 13:40
  • 1
    $\begingroup$ @uhoh Yeah, I was thinking about "normal metal / heavy composite aircraft" vs. "lightweight plastic aircraft". I agree that radar-absorbing material is probably even better than average plastic. $\endgroup$ Commented Apr 13 at 14:53
  • 1
    $\begingroup$ @uhoh Radome fiberglass, for example, has an εr of 1.1-1.2 at 1 GHz which means an index of 1.04, far lower mismatch than a bottle. $\endgroup$ Commented Apr 13 at 20:29
  • 1
    $\begingroup$ @user71659 can you support that number with a link? I'm getting εr values of 3 to 5 at 1 GHz for any kind of material in the glass, plastic, or epoxy world. I think the only way you can get to 1.2 is to make it mostly air (foam, honeycombs, etc) which would not be my first choice for airframe structural materials. $\endgroup$ Commented Apr 14 at 1:24

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.