Your points are noted mate. However, what is your evidence that the adoption of a canards on the airframe compromise its low RCS profile in such a disastrous way?
When the jet first flew, Dr Michael J Pelosi and
Dr Carlo Kopp did an assesment of the 1st prototype's performance as a VLO platform
https://www.ausairpower.net/APA-2011-03.html
When airframe shaping is subjected to physical optics simulation algorithms at various frequencies, it delivers "robust VLO performance in the nose aspect angular sector". In their neutral position, the canards do not contribute in any significant way to backscatter.
As mentioned in my earlier post, large deflections during BFM would definetly increase RCS, however thats true for ALL control surfaces on a stealth fighter, including LEVCONs, horizontal and vertical stabilizers. Even leading and trailing edge surfaces on the wings. Which is why all stealth platforms manage control surface deflection during BVR engagements.
The number 1 issue this peer reviewed paper had with the J20's shaping was the use of axisymmetric engine nozzles. That's an issue for all stealth fighters in production bar the F22.
Canards? no.
1. J20's rear aspect VLO shaping is not as optimal as the front or lateral aspects. That's a given. The only operational stealth fighter today that does not use axisymmetric engine nozzles is the F22. Are you saying the F35 and SU57 are not VLO too? They all incorporate some RCS reduction measures in this aspect, but its not as optimal as the solution adopted by the F22. That's obviously a decision made to minimize weight and cost.
Even the models displayed for the Korean KFX and your own AMCA show the same nozzle arrangement on the J20... Are they not VLO designs either? Even worse for the KFX, it uses semi recessed spaces for its armament instead of weapons bays
2. RCS reduction = stealth shaping, RAM application plus control surface management. It has nothing to do with overall size. If that were so then Mig 21's would be stealthier than F22's and F35's due to their size alone.
3. The JXX programme as detailed by Dr. Song's paper was to develop a heavy weight air superiority fighter. Even US pentagon reports from the 90's to date refer to the programme as an air superiority platform. Its long voluminous airframe translates to more fuel than either the F22 or the F35.
And the development of the 4 large EFT's and noticeably shallow weapons bay only adds further credence to the obvious fact that the PLA envision the platform as a very long range air superiority asset. Its not a bomber.
If you've read aussipower blog post on J20 structural and stealth analysis, let me stop you there.
Observations:
The model uses PO method.
The model has limitations. (see my third point to why optical methods does not give the complete picture)
The model doesn't consider
Surface traveling EM wave (most realistically aspect of target RCS). (I suggest instead of seeing a static diagram like of the PCPR, try seeing an actual EM wave polarization incident to a planform with different incident angle.
(
Source: MIT Radar technology playlist Lecture on "Target RCS")
Canard increases RCS, as its a control surface, and that two misaligned one. (explained later)
Limitations of the model:
- The simulator at this time does not model backscatter from edge diffraction effects although the resulting error will be mitigated by the reality that in a mature production design these RCS contributions are reduced by edge treatments (not done yet, I can pull images to point out where the edge treatment isn't still done);
- The simulator at this time does not model backscatter from surface travelling wave effects (biggest motherload of all),. In the forward and aft hemispheres these can be dominant scattering sources where specular contributions are low. The magnitude of these RCS contributions is reduced by edge treatments, lossy surface coatings, gap treatments, and panel serrations; (Now mitigates in the FOC variant)
- The simulator at this time does not model backscatter from the AESA bay in the passband of a bandpass radome, due to the absence of any data on the intended design of same, the resulting error will be mitigated by the reality that in a mature production design much effort will be expended in suppressing passband RCS contributions;
- The simulator at this time does not model backscatter from the engine inlet tunnels (because its solution is serpentine intakes which is applied in J20) or engine exhaust tailpipes,
- The simulator at this time does not model structural mode RCS contributions from antenna and EO apertures, panel joins, panel and door gaps, fasteners and other minor contributors; although the resulting error will be mitigated by the reality that in a mature production design these RCS contributions are reduced by RCS reduction treatments. (Now mitigates in the FOC variants)
- The PO computational algorithm performs most accurately at broadside or near normal angles of incidence, with decreasing accuracy at increasingly shallow angles of incidence, reflecting the limitations of PO modelling. The simulator does not implement the Mitzner/Ufimtsev corrections for edge currents (See MIT lecture, for the edge currents on a planform). While a number of test runs with basic shapes showed good agreement between the PO simulation and backscatter peaks in third party test sample measurements, even at incidence angles below 10°, characteristically PO will underestimate backscatter in nulls. This limitation must be considered when assessing results for the nose and tail aspects, where most specular RCS contributions arise at very shallow angles39.
Coming to the point to your questions
1. I never said RCS spike due to canards would be "disastrously drastic". I said, it going to spike RCS time to time especially during STR performance which will contribute to different AoA as
trailing edge electric diffractions. (In MIT lecture).
Why do you assume the canards would be always in neutral position? (Read #1 again)
2. I am not talking about frontal aspect stealth here, J20 achieves that thus making it LO. Refrain yourself from pulling this discussion to a different angle such as "frontal aspect stealth characteristics".
"Please understand that LO doesn't mean VLO."
Here's what an expert has to say. (Watch from 2:18) and here's the drawdown:
LO at frontal aspect, but not all aspect (here the benchmark is F22, not F35 nor SU57)
Airspace denial, putting high value assets such as tankers, awacs, bombers or gunships at bay.
High endurance, interceptor.
3. Its a
bomber too, considering missions where stealth isn't required, with its long endurance, high service ceiling and upcoming better engines, why wouldn't PLAF would consider it as nuclear delivery platform? Cruise missiles can be fitted on its pylons considering its a Delta Canard?
3. Finally, I'll ask a single question to end this debate once and for all. Why is your next
J31 fighter drops the idea of canards all together than? Why go to a conventional stealth jet airframe design much like F35?
Because J20 was never considered all aspect stealth (True VLO stealth), J31 can be thought as VLO at frontal aspect.
And to your question that F35 and SU57 is VLO? Yes and No. Yes because at frontal aspect, F35 show radar returns much lower than even F22. No because not all aspect stealth.
The case of red flag exercises:
1. Most F22 interception had the aggressors clearly mentioning that F22 or F35 approach angles are chosen by the pilots at the very start, meaning that battle to approach an adversary is already decided.
2. This means that F22 or F35 come close in at classified altitude, AoA, speed and direction.
Here the end cookie
Figure1: Proposed advanced design to J20.
Observations:
- Complete elimination of tail section, essentially a tailless configuration. (looks like someone is cutting down on RCS at tail section and Canards desperately)
- Canards size reduced.
- Improved LO.
