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.
 
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.
 
You are going to have trade-off some reduction in LO capability with canards, even the the NATF-23 traded-off LO in order to meet carrier take-off and landing requirements. The SU-57 I would assume for the BVR condition, would have to lock it's LEX surfaces in order to minimize any returns, plus these surfaces are definitely for the close-in engagement scenario.
 
Just need to look at the J-20, that has really huge canards and I always thought that they looked really bad for stealth reasons. If you are going to design a VLO fighter it is best to do away with canards especially for land based aircraft.
 
I forget who at Skunks Works coined the term; "Canards belong on someone else's aircraft". In regards to the J-20, China created a hybrid of the MiG 1.44, F-22 (weapons bay config) and F-35 (inlets). Curious regarding how effective Chinese LO is? You can copy, copy, copy but in the end, it has to work.
 
Was it at the time of JAST, ASTOVL? I seem to remember several of Lockheed's designs featuring canards for some time but then they disappeared at about the time of the amalgamation to the JSF program.
 
FighterJock said:
Was it at the time of JAST, ASTOVL? I seem to remember several of Lockheed's designs featuring canards for some time but then they disappeared at about the time of the amalgamation to the JSF program.
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I think you are correct, around the time of JAST.
 
I've heard a few engineers and pilots over the years opine that that canards are for "European" fighters and have no place on American designs even when not talking about VLO stealth considerations. Clearly there have been designs and prototypes that are exceptions to this rule. Convair favored the delta wing layout on their fighters, their advanced F-106 concepts as well as their Model 200 and 201 featured large canards.

The delta wing on the F-102 and F-106 was definitely selected because it was suitable for the high speeds demanded of an interceptor, but on the Model 200/201 I have to assume a delta wing + canard was found preferable for their STOVL design. Perhaps the center of gravity and lift is more ideal for a design that features lift-jets or a lift-fan. As FighterJock and Hydroman mentioned Lockheed's CALF/JAST used a delta wing with canards prior to a redesign to a more conventional layout when the program turned into JSF.

Lockheed Martin also had a requirement that the fighter's overall length had to be short enough to fit within the aircraft elevators on USN LHA and LHD amphibious assault ships which influenced those earlier ASTOVL/CALF/JAST configurations. The main driver of switching to a conventional wing + tail is said to have been the Navy's standards for CATOBAR operations at sea, but I'm also starting to wonder if a desire for a greater level of VLO stealth also factored into it.

In a way it seems odd that Northrop switched to a delta wing + canard layout to meet NATF requirements, yet Lockheed had to do the reverse with the JSF. So maybe there was more to the decision than just carrier suitability. What exactly about the early Lockheed layout was so troublesome for CATOBAR operation anyway? The French routinely operate the Rafale from carriers. There was also the change to a conventional wing + tail that occurred late with Boeing's JSF design, of course that didn't have canards, so I don't think stealth concerns factored into that case.
 
In a way it seems odd that Northrop switched to a delta wing + canard layout to meet NATF requirements, yet Lockheed had to do the reverse with the JSF.
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Not very odd. There were really only two options available to make NATF requirements - canards or VG wings. Northrop chose canards, Lockheed chose VG wings.
 
FighterJock said:
Just need to look at the J-20, that has really huge canards and I always thought that they looked really bad for stealth reasons. If you are going to design a VLO fighter it is best to do away with canards especially for land based aircraft.
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As I understand it, you need really big canards to let them be stealthy. So big it's almost a tandem wing.

Small control surface movements, plus enough distance to allow dissipation of the appropriate wavelengths.

The dinky canards on the Typhoon are excellent reflectors.
 
I regards NATF-23, I am not aero or LO guy but with just enough learned knowledge to be dangerous based upon the programs I have worked on, I am a vehicle systems/flight actuation guy. I could see the large canards would not need to deflect as much in order to gain a pitching or rolling moment when coupled with the wing trailing edge surfaces, thus keeping the RCS lower. Also, the flight control laws play a big part involving this and we had an excellent aero sciences/flight controls group. The YF-23 flight controls architecture was very refined (similar level of refinement as the with Tacit Blue/B-2) for maneuvering optimization in all flight regimes along with unique flight actuator design configurations, much different than the YF/F-22. I'm sure the NATF-23 not only took advantage of this but also refined this even further. Plus we did not like lumps and blisters anywhere on our aircraft for covering the actuators thus very clean aircraft for aero and LO.

I think the NATF-23 LO performance probably would have been better than expected and I also think the USN would have had an excellent F-14 replacement. The USN made a big mistake in not selecting our ATA design, LO does not work well when flying on the deck, especially when they can eventually visually see you.
 
overscan (PaulMM) said:
Not very odd. There were really only two options available to make NATF requirements - canards or VG wings. Northrop chose canards, Lockheed chose VG wings.
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Those were indeed the solutions Northrop and Lockheed selected, but why do you think those were the only options?

I believe the F-22A has a rather high approach speed on landing despite having generally excellent flight qualities, and obviously the NATF would need to be heavier, so a VG wing was probably the best option to reuse any of the basic airframe layout.

But did the YF-23 or estimates for the F-23A also suggest that the approach speed would be too high to use the same layout of wing and tail? Or were there other considerations? I'd be interested in knowing what other options were looked at or rejected for the NATF by both teams, but as far as I know that information has never made it into the public record.
 
Colonial-Marine said:
Those were indeed the solutions Northrop and Lockheed selected, but why do you think those were the only options?
...
But did the YF-23 or estimates for the F-23A also suggest that the approach speed would be too high to use the same layout of wing and tail? Or were there other considerations? I'd be interested in knowing what other options were looked at or rejected for the NATF by both teams, but as far as I know that information has never made it into the public record.
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Considerations and decision made by Northrop are outlined in the book YF-23 ATF by Paul Metz*... One of the major requirements for the Navy was that the aircraft could not be longer than the F-14... Northrop investigated a conventional tail (DP533) and a canard version (DP527). DP527 "...proved to be the best overall solution..."

*the book includes some very nice pictures and illustrations btw.
 
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VTOLicious said:
Considerations and decision made by Northrop are outlined in the book YF-23 ATF by Paul Metz*... One of the major requirements for the Navy was that the aircraft could not be longer than the F-14... Northrop investigated a conventional tail (DP533) and a canard version (DP527). DP527 "...proved to be the best overall solution..."

*the book includes some very nice pictures and illustrations btw.
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I need to pick that book up for sure. Do you know if photos of those configurations are included?

I knew YF-23 was big, but I didn't realize it was quite that big till I just compared the length of the two. Technically the CVNs must be able to handle aircraft the size and length of the old A-5 Vigilante, which was roughly 76½ ft, but I'm sure a few of those would rapidly take up a lot of deck and hangar space.
 
Finding a printed copy seems to be a pretty difficult. You'd think in this day and age it would be easier to get your hands on a book even for admittedly a rather niche subject. I noticed just now that their NATF design had 2D thrust vectoring. That is quite a change. Though I'll take that subject to the NATF thread.
 
overscan (PaulMM) said:
Drawings and models, yes.


DP-527 windtunnel model with canards removed is on public display

zmg_8858-jpg.574287


Desk model

navy-yf23-jpg.176704


Original Drawings

natf-jpg.176760


DP-533 is illustrated in the book by Paul Metz.
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If you look at the top image, that is the Northrop ATF before the v-tails and dem-val. So you see that the basic YF-23, F-23, NATF-23 design changed very little but evolved from the basic configuration. Unfortunately for the NATF requirement, the top configuration would not meet what was required for takeoff and landing, hence adding another 100 sqft of wing area, the canards and thrust vectoring but you did not have deal with added weight and complexity of a variable sweep wing. The USN will probably never get an aircraft with the level of LO the USAF land-based aircraft have but it will still be very good and will do the job, plus the USN flies their jets more aggressively than the USAF and with greater mission freedom, a proven fact.
 

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