Stealthy compressor face and inlet guide vanes - is it possible?

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I generally don't like to reference Key Pubs forums due to the amount of noise there, but occasionally there are interesting finds and discussions. In particular, regarding the PAK FA, a certain user believes that advances in composite materials can make the engine's compressor face or the inlet guide vanes stealthy, rendering S-ducts unnecessary and therefore obsolete. He did link several studies in the public domain, like this one. I'm wondering if members of this forum can pitch in on this concept: can this concept be implemented right now? Because if this really is possible, then more efficient straight inlets may return for 5.5 or 6th generation aircraft.
 

totoro

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even that paper you linked says they only used x band frequencies. problems will arise when using c band, s band and longer wavelengths. As far as i can understand it -it's a quick and fast solution, saving quite a bit of weight and volume inside the plane, but only against certain radars. so as far as radar stealth goes, it's really a half-solution, more of a deliberate design compromise.
 

Trident

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totoro said:
even that paper you linked says they only used x band frequencies. problems will arise when using c band, s band and longer wavelengths. As far as i can understand it -it's a quick and fast solution, saving quite a bit of weight and volume inside the plane, but only against certain radars. so as far as radar stealth goes, it's really a half-solution, more of a deliberate design compromise.

Wouldn't at some point longer wavelengths work in your favour, as they will exceed the size of the inlet opening (which will then cease to act as a cavity). Think mesh screen! So if you can successfully deal with higher bands by this method you may well be a quite a ways along the path to a broadband solution.
 

totoro

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But most intakes are pretty big across, and even a half wavelength still gives off quite a bit of radar return. Half a meter (across) sized intakes could still be quite visible for a VHF radar. Larger ones, like on big, modern fighters with 150 kn+ of thrust per engine/intake could possibly be visible even with HF radars. I'm sure someone with more knowledge of RCS calculations will step in, this is an interesting topic. :)
 

saintkatanalegacy

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But think about it, as a frontline fighter, what threats would it realistically deal with?
 

totoro

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exactly.

one would deal with sub x band radars from missiles. those could come from any direction, but a good deal would come from frontal hemishpere.

one would deal with x band radars from fighter's own radars and from fire control radars on sam batteries. threat direction more or less the same as above, very roughly speaking, except for sam battery control radars, of course, which would always come a bit from below.

then from C and S band dual fire control/early warning radars, awacs. mostly from below, with the exception of awacs based threats.

then with L, UHF and possibly VHF from ground based early warning radars (with further awacs threats using L or UHF bands). even more so from below than the previous category. still some awacs do operate up to UHF though.

And possibly HF (and lower) threats coming from above, in the manner of ionospheric OTH radars.

It is just very, very hard to cover all of that. especially in a tactical sized plane. Next to impossible really. Which is why picking your fight to win and making compromise on other areas does seem like a prudent way to go, unless one wants to spend billions and decades.
 

AeroFranz

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I'm a bit skeptical because historically it's been simpler to make fixed RAM IGVs than fan blades subject to spinning and having to contend with birdstrike.
Still, interesting discussion, material science might make this possible.
 
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