Before Mig-29 derailed the thread with irrelevant economics arguments, I was making the point that the latest "Physical Optics simulation across nine radio-frequency bands" from Australia Air Power shows the pecking order for the world's stealth fighters are:
1. F-22
2. J-20
3. F-35
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In January 2011, I ranked the stealthiness of the world's premier fighters as F-22, J-20, and F-35 (see post replicated below). Six months have passed. How does my assessment hold up in comparison to professional analysis by "Peter Goon, BEng (Mech), FTE (USNTPS), Head of Test and Evaluation, Air Power Australia" (see
)?
Not surprisingly, the thorough analysis by Mr. Goon is in perfect agreement with my initial assessment from six months ago. Here is a key excerpt from Australia Air Power's analysis by Mr. Goon:
"Engineers and Scientists who work in ‘stealth’ (AKA ‘Low Observable’) designs have a way for explaining it to lay people:
‘Stealth’ is achieved by Shaping, Shaping, Shaping and Materials (Denys Overholser).
The F-22A is clearly well shaped for low observability above about 500 MHz, and from all important aspects.
The J-20 has observed the ‘Shaping, Shaping, Shaping’ imperative, except for the axisymmetric nozzles, and some curvature of the sides that smears a strong, but very narrow specular return into something of a more observable fan.
The X-35 mostly observed the ‘Shaping, Shaping, Shaping’ rule, but since then, to quote a colleague, ‘hideous lumps, bumps, humps and warts’ have appeared on the JSF to disrupt the shaping imperative, forcing excessive reliance on materials, which are at the rear-end of the path to ‘Low Observability’.
While discussing ‘rear-ends’, both the F-35 and the J-20 have large signature contributions from their jet nozzles. However, the difference is much like the proverbial ‘Ham Omelette’: the F-35 Pig is committed, but the J-20 Chicken is a participant.
If the Chinese decide that rear sector Low Observability is tactically and strategically important, they are at the design stage where they can copy the F-22A nozzle design for the production configuration of the J-20.
In a market now dominated by “a total indifference to what is real”, no such option is now or ever was possible for the JSF, as its design is based upon meeting the bare minimum (a.k.a. “Threshold”) requirements of the JORD wherein “excellence is the enemy of good enough”; as has the STOVL F-35B as the baseline design; and, thus, is heavily constrained by the specified roles for this aircraft as well as the risks to reputations based political imperatives of accelerating a much-delayed and grossly over-budget program.
The issue of the use of materials to suppress radar signature is interesting. Publications show that the Chinese are making a substantial investment in use of materials to reduce radar signature and have produced large volumes of research results. So far, there have been no Chinese public disclosures on materials that make a substantial reduction of signatures across a broad range of air combat radar frequencies. Come to think of it, there are no United States research papers on the subject. Why is that, one wonders?"
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Let me translate Mr. Goon's insights into plain English.
1. F-22 is fully optimized for stealth. Its clean lines and flattened engine nozzles are obvious to even a casual observer.
2. The J-20 is very close to the F-22 in stealth shaping. The two notable flaws from the
"Physical Optics simulation across nine radio-frequency bands" are "some curvature of the sides" that need to be re-worked and glaring round engine nozzles.
3. To save money, the F-35 has a compromised design of "‘hideous lumps, bumps, humps and warts’ [that] have appeared on the JSF to disrupt the shaping imperative." Also, the F-35 and the J-20 both share the round engine nozzles, which do not measure up to F-22 stealth standards.
Why are "hideous lumps, bumps, humps and warts" a problem? Recall your experience of driving on a rain-slicked road at night with your headlights turned on. Very difficult to see the road, right? The rain-slicked road is almost a perfect mirror. The beams (which are electromagnetic radiation like radar waves) from the car headlights bounce away from you.
However, if there are lots of "hideous lumps, bumps, humps and warts" in the road then you can see much better (like a radar receiver), because the car's lights are being bounced back into your eyes. For the same reason that you can easily see a bumpy rain-slicked road, it is much easier for a radar to detect a F-35 with bumpy surfaces.
Finally, the F-35 was always intended to be an economy-model stealth fighter. The U.S. military will not redesign the F-35's round engine nozzles. The U.S. already has the F-22. There is no point in redesigning the F-35 until it looks like a F-22. There wouldn't be any cost savings.
China's J-20 Mighty Dragon is a very different story. It is China's premier stealth fighter and its design won't be finalized until about 2018. It is likely the Chinese will alter the J-20 Mighty Dragon design in the next seven years to eliminate its partial weakness from "some curvature of the sides" and round engine nozzles. In 2018, do not be surprised to see a finalized J-20 Mighty Dragon that matches the F-22 in all-aspect stealth and with flattened engine nozzles.
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My January 22, 2011 post:
My estimate of J-20's RCS is 0.005-0.0001 m2 (or -30 to -40 db)
From the front, the J-20 matches the F-22's stealth profile. While the J-20 is flying at you, the incremental increase in area from its canards is minimal (e.g. look at a piece of paper edge-wise; you only see a line). Also, the J-20's canards are probably made of composite material, coated with RAM, and curve-shaped to deflect radar waves. For all intents and purposes, the J-20 has a F-22 RCS frontal profile of 0.0001 m2.
From the rear, with its circular saw-toothed engine nozzles, the J-20 looks like the F-35 and it should have a similar rear RCS of 0.005 m2.
In conclusion, depending on your point of view, the J-20's RCS ranges from 0.005 to 0.0001 m2 (or -30 to -40 db).
From Global Security:
Radar Cross Section (RCS) / RCS (m2) / RCS (dB)
- automobile 100 20
- B-52 100
- B-1(A/B) 10
- F-15 25
- Su-27 15
- cabin cruiser 10 10
- Su-MKI 4
- Mig-21 3
- F-16 5
- F-16C 1.2
- man 1 0
- F-18 1
- Rafale 1
- B-2 0.75 ?
- Typhoon 0.5
- Tomahawk SLCM 0.5
- B-2 0.1 ?
- A-12/SR-71 0.01 (22 in2)
- bird 0.01 -20
- F-35 / JSF 0.005 -30
- F-117 0.003
- insect 0.001 -30
- F-22 0.0001 -40
- B-2 0.0001 -40
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I said the J-20 canards were irrelevant for four reasons:
1. Composite material composition
2. RAM coating
3. Curved surface to deflect radar waves
4. Small incremental increase in surface area
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Ranking of world stealth fighters:
1. F-22 0.0001 m2
2. J-20 0.005-0.0001 m2
3. F-35 0.005 m2
4. French Rafale 1 m2
5. Russian Pak-Fa (or T-50) 3 m2
6. F-16 5 m2
