Are canards bad for stealth? - An Endless Discussion

Just stopping by to salute the thread title. We could probably do with a few more thread marked with '- an endless discussion'... it is a good heads-up about what to expect!
 
WatcherZero said:
From what I heard with Canards it makes a huge difference if they are in line with the wing or not, if you vertically offset them against the wing it massively reduces their return versus if they are mounted at the same level as the wings.
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That seems counter-intuitive to me, but a lot of the Stealth stuff is.
 
My guess is its because if at the same level they add to the wings effective area and the return increases my the radius of the surface area squared.
 
WatcherZero said:
My guess is its because if at the same level they add to the wings effective area and the return increases my the radius of the surface area squared.
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Isn't the point of stealth is to maximize return in specific angle but reducing the amount of angles?
WatcherZero said:
From what I heard with Canards it makes a huge difference if they are in line with the wing or not, if you vertically offset them against the wing it massively reduces their return versus if they are mounted at the same level as the wings.
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So canards as seen on j-20 or natf-23 would be stealthier than x-36 or early lockheed and mcdonnell JAST efforts?
 
donnage99 said:
Isn't the point of stealth is to maximize return in specific angle but reducing the amount of angles?

So canards as seen on j-20 or natf-23 would be stealthier than x-36 or early lockheed and mcdonnell JAST efforts?
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I would have thought it was the reverse since the X-36 canards are on the same level as the wings
note that the X-36 doesn't have vertical tails, so it needs to use a a variety of other means for control
x36_schem_01.jpg

2546583756_1f31d0988f_b.jpg
 
Well, things have to be compared with the requirements of its era. e.g what's the requirement for NATF vs JAST or J-20's. Then things have to be visualized e.g some graphics.

One thing is that the designer if desired may do a tradeoff to ensure the design feature still meet the RFP.. e.g use of exotic Radar absorbent structure for the canard, but this caused some weight penalty. or prohiibit the use of canard for some flight regime and to rely on something else. e.g TVC
 
donnage99 said:
Isn't the point of stealth is to maximize return in specific angle but reducing the amount of angles?
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No, the idea is to make it so that even in the spike angles, you have a lower return than a non-stealth aircraft.
 
Scott Kenny said:
No, the idea is to make it so that even in the spike angles, you have a lower return than a non-stealth aircraft.
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Perhaps I worded badly but yes the point isn't to "maximize" RCS in specific angle but to "concentrate" which should have been the better word choice.
 
Not concentrating but to -Dump- the strong spike to an angle where the enemy is not likely to see. Thus why Leading and trailing edge sweep is important consideration. For example J-20. The LE angle of the Canard is the same as the LE of the wing. Thus the spikes are dumped at same angle. This is example i did in my twitter post depicting RCS changes of J-20 model in varios canard pitch angle.

https://twitter.com/x/status/1728242617039929735
View: https://twitter.com/Flankerchan/status/1728242617039929735


and this is the comparison between J-20 model with and without canard

https://twitter.com/x/status/1683021282986856450
View: https://twitter.com/Flankerchan/status/1683021282986856450


One may notice that the reflection of the canard and the wing are In the same place.


Scott Kenny said:
No, the idea is to make it so that even in the spike angles, you have a lower return than a non-stealth aircraft.
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This is impossible unless you have magical material that can absorb the entirety of the reflected energy, which depending on frequency can reach some 30-40 dB. Fortunately the physics of faceting can actually help here. Just think of the stealth aircraft like a flat plate antenna.

The width of the spikes can then be found by simple equation namely :

Beam = Wavelength/Antenna width or length.

Let's say we have a 5 meter LE and then exposed by X-band with frequency of 10 GHz or exactly 3 cm wavelength. What kind of spike it can produce ?

Beam = 0.03/ 5
Beam = 0.006 Radians or 0.34 Degrees. Notice how Narrow it is. Compare with say typical fighter radar antenna beamwidth which is 2 degrees. The enemy will find it hard to find and pick or even maintain contact with that 0.34 degrees of beamwidth.


How strong the spike ? Since concept of RCS is basically antenna gain, we can crudely estimate the spike's strength by simple antenna gain equation like say K Barton's rule of 30000/beamwidth vertical * Horizontal. If we assume same beamwidth then it would be 30000/ 0.34 ^2 = 259515 Which in log value equal to 54 dB to reduce that to something like 0 dB or 1 sqm, you need 54 dB capable RAM which kinda asking the impossible at the moment. And you still have that 1 sqm which modern fighter could pick some 100 km plus.
 
Could be worse - just imagine the use of FiberGrass (TM).


(From Cheech and Chong)
 
quellish said:
I have not watched the video, but if it is making claims about the magical properties of “FiberMat” I am already laughing.

A sad, sick laugh that descends into tears.
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just material technique that reduces the returns of the the intentional rcs spikes. don't know how reliable it is.

don't have to watch whole video. I timestamped the relevant part in the link.
 
donnage99 said:
just material technique that reduces the returns of the the intentional rcs spikes. don't know how reliable it is.

don't have to watch whole video. I timestamped the relevant part in the link.
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Yeah no.

Materials that defy the laws of physics are science fiction.

Intentional RCS spikes are… intentional! Because they are unavoidable. The energy has to go somewhere. Aircraft need leading and trailing edges, etc. At best, you can get this down to 4 spikes and make them very narrow, at which point it doesn’t matter if the spikes are very strong.

BTW still crying.

Anyway, back to canards!
 
quellish said:
Yeah no.

Materials that defy the laws of physics are science fiction.

Intentional RCS spikes are… intentional! Because they are unavoidable. The energy has to go somewhere. Aircraft need leading and trailing edges, etc. At best, you can get this down to 4 spikes and make them very narrow, at which point it doesn’t matter if the spikes are very strong.

BTW still crying.

Anyway, back to canards!
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Just to understand you clearly - are you saying that there's no need to reduce these RCS spikes or that the spikes still gonna be there? The video doesn't refute that the spikes will be there.

The video talks about technique to taper the releases of rcs as radio waves travel toward the edge of the aircraft not so much of any particular material that completely takes away the spikes. Are you saying the technique is BS or you're just talking about that magical fiber mat that made the round of news in 2010s
 
donnage99 said:
Just to understand you clearly - are you saying that there's no need to reduce these RCS spikes or that the spikes still gonna be there? The video doesn't refute that the spikes will be there.
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They will still be there. You can make an effort to reduce the "width" of the spike, i.e. the number of aspects where the spike returns energy to the transmitter. You can't eliminate the spike. If you succeed in making the spike very narrow, the spike can be very energetic and it won't be much of a problem.

This would be difficult to explain well without creating illustrations, and this is off topic.

donnage99 said:
The video talks about technique to taper the releases of rcs as radio waves travel toward the edge of the aircraft not so much of any particular material that completely takes away the spikes. Are you saying the technique is BS or you're just talking about that magical fiber mat that made the round of news in 2010s
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That sounds more like creeping waves and diffraction, which rarely create spikes. Diffraction certainly contributes to RCS, but rarely creates an individual "spike" visible on a polar plot. Again, this is difficult to express without creating illustrations.
 
quellish said:
They will still be there.
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Agreed. I don't think the video claims otherwise.

quellish said:
That sounds more like creeping waves and diffraction, which rarely create spikes. Diffraction certainly contributes to RCS, but rarely creates an individual "spike" visible on a polar plot. Again, this is difficult to express without creating illustrations.
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no the video only claims the technique tapers the release of rcs as radio waves travels toward leading edge where the spike occurs leading to a weaker rcs spike at the leading edge.

Are you saying that reducing rcs of the spike is less important (or not important at all) than trying to make the "width" of the spikes narrower?
 
donnage99 said:
Agreed. I don't think the video claims otherwise.


no the video only claims the technique tapers the release of rcs as radio waves travels toward leading edge where the spike occurs leading to a weaker rcs spike at the leading edge.

Are you saying that reducing rcs of the spike is less important (or not important at all) than trying to make the "width" of the spikes narrower?
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if the spike is narrower than likely to hit a receiver that is in the rough direction of the spike, then yes, a narrower more intense spike is better than a wider spike that is at lower intensity.
 
Forest Green said:
What about canards that can deploy or swing back to be flush with the wing?
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I can't think of too many examples of that.
there were the older F-14s, where the "canards" came out of the Lerx.
But they don't function like your modern day canards and later models seemed to have ditched them.
 
WatcherZero said:
From what I heard with Canards it makes a huge difference if they are in line with the wing or not, if you vertically offset them against the wing it massively reduces their return versus if they are mounted at the same level as the wings.
Click to expand...

Scott Kenny said:
That seems counter-intuitive to me, but a lot of the Stealth stuff is.
Click to expand...
Right if they're inline with the wing should reduce as opposed to not at least in the frontal aspect
 
helmutkohl said:
I can't think of too many examples of that.
there were the older F-14s, where the "canards" came out of the Lerx.
But they don't function like your modern day canards and later models seemed to have ditched them.
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The Soviet supersonic “Concordski” airliner had retractable canard “whiskers” that were only extended during low-speed flight. They helped compensate for delta wings notoriously draggy performance at slow airspeeds and high angles of attack.
More recently, the Indian TEJAS light fighter uses double delta leading edges and leading edge flaps that can droop to improve lift during landings.
 

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