I read a lot about 5th-generation aircraft, and one thing I noticed they do to induce stealth is through the usage of Radar-Absorment Material (RAM) coating & certain geometry. And I’m focusing on the latter.
What I know about these are…
* The geometry of these aircraft makes sure that as many surfaces of the aircraft reflect radar waves AWAY from the source. Via flat surfaces. Enemy radar waves of course.
* Engine blades & vanes give out a lot of RCS. (Which is what the Su-57 suffers from)
What I’m still confused is that…
* Flying wing stealth bombers (B-2, B-21) have curved shapes under them where radar waves are most probably going to be blasted to.
* Do radar waves need to have the least amount of times they bounce from each surfaces, that if, for instance, radar waves pointed towards the aircraft in such a way that it bounces 3 times on the aircraft before being reflected away from the aircraft at an angle of 70 degrees away from the incidence ‘ray’, it will increase the RCS of the aircraft?
* Does Point no. 2 the reason why canards are not preferred on stealth aircraft?
* Why is the vanes on the the YF-23 [not properly hidden from the front](https://data3.primeportal.net/hangar/howard_mason4/yf-23/images/yf-23_06_of_51.jpg), despite being deemed “stealthier than the F-22”? Or does it depend on the distance of the aircraft from radars to hide the vanes from radars via perspective?
In: Physics
RCS is calculated using standard radio frequency simulation techniques. You can load up your model into a sim and hit it with a bunch of frequencies at different aspects.
Curved surfaces also work for reflecting the RF away from the source. Doesn’t have to be a flat surface *per se*.
Reflections at joins can indeed be problematic for RCS reduction. In fact, this effect is used in certain decoys (called “corner reflectors”) and can be a cause of “glint” (where the reflected power spikes for a short period of time). If you ever go down to a marina and look at smaller seagoing boats (perhaps small fishing vessels) you’ll often see them with metal diamond-looking things high up; these are corner reflectors, to increase their signature on other ships’ radar.
Aspect does indeed matter. The production version of the YF-23 would likely have S-ducted those fan blades away, though. Remember that what you’re looking at there is a testbed, not a production platform.
In the broader sense, RCS depends on 5 things
– Materials from which the target is constructed
– Shape of the target
– Frequency of the radar
– Aspect angle
– Elevation
Which is why in real use-cases we don’t use a single number to describe an RCS. Instead, we plot diagrams (one for each frequency that we care about) which show the variation of RCS with aspect and elevation.
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