What's new

Chengdu J-20 5th Generation Aircraft News & Discussions

You are a real genius. It does not matter if the DSI is sharp or oval, it is still a sphere from certain angles. It's like cutting a sphere in a sharp oval shape such as the J-20's DSI. And the pak-fa's IRST is not translucent it is treated with a gold orange film that you love to rave about. In fact according to you the treated canopies just like the pak-fa's treated IRST are absorbers.

Now this is where you once again get caught in your own web. The IRST on the pak-fa is very small, however, the J-20's pods are large, very large, now according to you those pods on the J-20 are too small to 'compromise stealth' yet you claim an IRST ball is poor for stealth even though it is many times smaller than those under wing pods on the J-20. You have numerous contradictory claims.

J-20's large pods are too small to compromise stealth--but a single and much smaller IRST is poor for stealth.

The J-20's large 4 pods are treated with RAM which you claim make it stealthy but the pak-fa's IRST which is treated in a goldish film is not stealthy?

The J-20's yellowish canopy which you claim is like RAM absorbs EM radiation but the pak-fa's IRST which is also treated does not absorb EM emissions?


Your arguments are con-tra-dic-tory

Contradictory and did I mention contradictory?
 
You are a real genius. It does not matter if the DSI is sharp or oval, it is still a sphere from certain angles. It's like cutting a sphere in a sharp oval shape such as the J-20's DSI. And the pak-fa's IRST is not translucent it is treated with a gold orange film that you love to rave about. In fact according to you the treated canopies just like the pak-fa's treated IRST are absorbers.

Now this is where you once again get caught in your own web. The IRST on the pak-fa is very small, however, the J-20's pods are large, very large, now according to you those pods on the J-20 are too small to 'compromise stealth' yet you claim an IRST ball is poor for stealth even though it is many times smaller than those under wing pods on the J-20. You have numerous contradictory claims.

J-20's large pods are too small to compromise stealth--but a single and much smaller IRST is poor for stealth.

The J-20's large 4 pods are treated with RAM which you claim make it stealthy but the pak-fa's IRST which is treated in a goldish film is not stealthy?

The J-20's yellowish canopy which you claim is like RAM absorbs EM radiation but the pak-fa's IRST which is also treated does not absorb EM emissions?


Your arguments are con-tra-dic-tory

Contradictory and did I mention contradictory?

You are correct that there is an extremely small perpendicular surface from the J-20 DSI intake in relation to a radar emitter. Want me to say RAM-covered surface for the third time (see previous posts #1197 and #1200)?

I will not say RAM-covered surface for the fourth time. If you don't understand it then I can't help you. I'm getting tired of repeating myself over and over again.

----------

Okay, if the IRST probe has an orange RAM-coated surface then there is no penalty in stealth for the transparent surface. However, the IRST probe geometry is a half-sphere of constant radius. The shape is not stealthy. It is basically a small non-stealthy semi-circular beach ball.
 
You guys are blind.

The J-20 DSI intake starts with a somewhat pointy edge and rakes backward into a large radius (e.g. look at the picture below carefully and analytically). That is called continuous curvature, because the radius changes. Also, the radius is different longitudinally from the radius laterally. In contrast, the lump on the F-35 is a long rectangular bump. The radius is constant throughout most of the F-35 lump (e.g. basically a constant-radius cylinder with tapered ends).

The Pak Fa IRST probe is not covered in RAM material. To function, the Pak Fa IRST probe has a non-RAM-covered transparent or translucent surface.

A J-20 RAM-covered aileron pod is stealthy. A Pak Fa non-Ram-covered IRST probe is not stealthy. Where is the difficulty in comprehension?

Can you two understand these critical differences? I hope you can grasp the concepts of continuous curvature and RAM-covered surfaces.

K6rKC.jpg

J-20 DSI intake clearly starts off very small and grows larger as it moves backwards. Ergo, the radius of the DSI intake continues to increase as we move rearward. This is the stealth principle of continuous curvature. Get it?
You are wrong. And I dare say that EVERYTHING you learned about 'stealth' you learned it here from me. I corrected you many times long ago about your often physics defying claims. So do not presume to ask me about this made up notion from you called 'continuous curvature'. You got the concept wrong as well as the terminology wrong.

On a curvature, any changes in the electrical path, which is the surface itself, either through enlargement or reduction, affects only the creeping wave mode, not the initial specular reflection. So if the J-20's DSI shaping is not relevant, then neither are the F-35's many protuberances. A structure's RCS contributorship is affected by its aspect to the impinging signal's direction of approach, so for the F-35's assorted protuberances that has curvatures and lengths, if those electrical paths are of the frontal aspect angle, then they are of minimal contributorship.

See if you can figure out what I just said. But the reality is that I doubt it.
 
I don't think DSI has any contribution in stealth. It simply helps with ease of manufacturing and maintenance. Also, it is cheaper compared to non-DSI ones.

The F-22 has no DSI intakes.
 
You are wrong. And I dare say that EVERYTHING you learned about 'stealth' you learned it here from me. I corrected you many times long ago about your often physics defying claims. So do not presume to ask me about this made up notion from you called 'continuous curvature'. You got the concept wrong as well as the terminology wrong.

On a curvature, any changes in the electrical path, which is the surface itself, either through enlargement or reduction, affects only the creeping wave mode, not the initial specular reflection. So if the J-20's DSI shaping is not relevant, then neither are the F-35's many protuberances. A structure's RCS contributorship is affected by its aspect to the impinging signal's direction of approach, so for the F-35's assorted protuberances that has curvatures and lengths, if those electrical paths are of the frontal aspect angle, then they are of minimal contributorship.

See if you can figure out what I just said. But the reality is that I doubt it.

Do you really want me to repost the report from Australia Air Power on the non-stealthiness of the F-35 "lumps, bumps, and warts?" Also, do you want me to post the article from Aviation Week which requested Lockheed Martin to respond to the Australia Air Power report?

Come on, continuous curvature isn't that hard to understand. A sphere or parts-thereof is not stealthy. A constant-radius object like a cylinder is not stealthy. Both surfaces reflect a strong radar signal.

A continuous curvature surface like a duck-bill or the constantly-changing radii of the J-20 DSI intake is stealthy, because it reflects the vast majority of radar waves in different directions away from the emitter. How many times do I have to keep repeating myself?

The reasoning is simple. Let's just say 99% of incoming radar waves are deflected by the J-20 DSI-intake stealth shape. A RAM-covered surface absorbs 99.99% (or so) of an incoming radar wave. When you multiply 0.01 x 0.0001, you get 0.00001. Good luck trying to detect a 0.00001 radar reflection from fifty miles away.

4JVzE.jpg

J-20 continuous-curvature design is readily apparent in the single "smooth broad curve" on the upper-body fuselage. Do you see how the width/radius keeps changing? Just look at the shadows of the upper-body fuselage. The cast-shadow radius constantly varies.

----------

meqfE.jpg

F-35 with "‘hideous lumps, bumps, humps and warts’ [that] have appeared on the JSF to disrupt the shaping imperative." F-35 lumps are basically long tubes (or cylinders of constant radius). Of course, they're not stealthy; the radius is constant. The F-35 lumps exist, because of ad hoc changes to accommodate a bigger payload and side air-to-air missiles. They grafted those lumps onto the F-35 and they couldn't make it stealthy without redesigning the whole plane. If you enlarge the entire airframe, the non-stealthy F-35 lumps along the bottom would all go away. However, there is no money or time for a complete redesign of the F-35. If you change the size and weight of the F-35, you have to change the single engine to ensure sufficient power. It's a nightmare.
 
Do you really want me to repost the report from Australia Air Power on the non-stealthiness of the F-35 "lumps, bumps, and warts?" Also, do you want me to post the article from Aviation Week which requested Lockheed Martin to respond to the Australia Air Power report?
And I got no problems posting Chinese engineers sources that said physical optics ALONE is a totally inadequate tool to guesstimate a complex body's RCS.

Come on, continuous curvature isn't that hard to understand. A sphere or parts-thereof is not stealthy. A constant-radius object like a cylinder is not stealthy. Both surfaces reflect a strong radar signal.
Apparently, YOU do not understand. Not only did you made up that 'continuous curvature' phrasing, you got whatever few principles involving EM signal behaviors wrong as well as evident in the above post.

A constant-radius object like a cylinder is not stealthy. -- Really? I thought I posted plenty enough about the 10-lambda rule and how it affect a sphere and a cylinder regarding RCS.

A continuous curvature surface like a duck-bill or the constantly-changing radii of the J-20 DSI intake is stealthy, because it reflects the vast majority of radar waves in different directions away from the emitter. How many times do I have to keep repeating myself?
In radar detection and RCS control measures, there is no such thing as 'continuous curvature'. There is consistent or continuous surface integrity, as in no surface gaps that could create edge diffractions. You can repeat the same wrong crap over and over and it still would not change what it is -- crap.
 
I don't think DSI has any contribution in stealth. It simply helps with ease of manufacturing and maintenance. Also, it is cheaper compared to non-DSI ones.

The F-22 has no DSI intakes.
The only advantage a diverterless inlet system (DSI) has over a 'conventional' inlet as far as RCS contributorship goes is that a DSI has a lower contributorship but that is incidental. If a 'conventional' inlet system is used on the F-22, it is because when compared against the other contributors such as wings or cockpit, the 'conventional' inlet system was found to pale in comparison. In other words, it make no sense to work on something when there are greater issues with other things.
 
"Lumps and bumps" seriously degrade F-35 stealthiness

The original X-35 was a stealthy design. The current F-35 SDD AA-1 is a "much inferior contoured design, clearly intended to accommodate the larger weapon bays."

This is a familiar story. The X-35 was well-designed (e.g. "bomb truck") to meet the original military specifications. The military changed its mind and Lockheed had to drastically alter its design to accommodate the new military specifications (of an air superiority fighter) to carry a larger weapons load. This compromised the F-35 stealth design.

Assessing Joint Strike Fighter Defence Penetration Capabilities

"Assessing Joint Strike Fighter Defence Penetration Capabilities
Air Power Australia Analysis 2009-01
7th January 2009

by Dr Carlo Kopp, SMAIAA, MIEEE, PEng
© 2008, 2009 Carlo Kopp

qfj9F.jpg

The evolution of the JSF design from the X-35 demonstrators to the F-35A/B/C SDD configuration has seen significant changes to the aircraft's shaping, critical to its stealth performance. While the design of the inlets was improved, the lower fuselage design is now inferior to the original X-35 configuration. The latter has important implications for the JSF's ability to survive when penetrating modern Integrated Air Defence Systems (Image via Air Force Link).
...
Joint Strike Fighter Stealth Capabilities

The Joint Strike Fighter is an unusual airframe design, since it departs from many of the well established ground rules in stealth shaping, established in other designs such as the F-117A, B-2A, A-12A, YF-23A and F-22A Raptor. Stealth shaping is widely regarded to account for the first hundredfold reduction in aircraft radar signature, compared to non-stealthy designs of similar size, with application of lossy and absorbent materials used to further reduce the signature where feasible.
...
The first major departure from established shaping conventions is the angular or aspect dependency of the Joint Strike Fighter’s radar signature.

mLIvQ.png
Diagram 3.

KJTIF.png
Diagram 4.

Study of the shaping of the aircraft and comparison with other designs shows that the Joint Strike Fighter can provide genuinely good stealth performance only in a fairly narrow ~29° sector about the aircraft’s nose, where the shaping of the nose, engine inlets, panel edge serrations, and alignment of the leading and trailing edges of the wings and stabilators results in the absence of major lobes or “spikes” in the radar signature. The ±14.5° angular limit is constrained by the principal reflecting lobe of the leading and trailing edges of the wings and stabilators. The signature degrades rapidly due to the influence of the lower centre fuselage as the angle swings past ±45° off the nose, refer Diagram 4.

An important development was that the SDD aircraft saw the original inlet design discarded and replaced with a scaled down inlet arrangement based on the F-22A design. Concurrently the lower fuselage was redesigned.

In the SDD design, the beam/side aspect radar signature is especially problematic, due to the presence of multiple specular reflecting shapes, specifically due to singly and doubly curved lower fuselage surface feature shaping. The Joint Strike Fighter has a complex lower fuselage shape as well as a wing and fuselage lower join shape, unlike any other aircraft designed with stealth in mind, refer preceding images. The result of this design choice is that the beam/side aspect Radar Cross Section will be closer in magnitude to a conventional fighter flown clean than a “classical” stealth aircraft. This is an inevitable result of clustering no less than nine unique convex specular scattering shapes in the lower hemisphere of the aircraft. Diagram 3 illustrates this.

Given that the dimensions of many of these shapes are of the order of metres, the application of absorbent or lossy coatings or laminates will not be sufficient to drive the critical lower hemisphere beam/side aspect signature down to values which qualify as VLO and thus “stealthy”.
Refer Annex C.

The aft sector radar signature is also problematic, as a result of the use of an axisymmetric nozzle design. While the aft fuselage and tailboom shaping qualify as “stealthy” across the upper bands, the nozzle presents as a specular reflector in bands where the wavelength is comparable or exceeds the dimensions of the nozzle segments. This is discussed below.

The second major departure from established stealth conventions is that the Joint Strike Fighter is designed to perform in the X-band, and upper portions of the S-band, with little effort expended in optimizing for the lower L-band, UHF-band and VHF-band. This design strategy is consistent with defeating mobile battlefield short range point defence SAM and AAA systems such as the SA-8 Gecko, SA-9 Gaskin, Chapparel, Crotale, Roland, SA-15 Gauntlet, SA-19 Grison and SA-22 “Greyhound”, where limited radar antenna size forces all acquisition and engagement functions into the X-band and upper S-band. Joint Strike Fighter literature refers to this optimization in terms of “breaking the kill chain”, the intent being to deny the effective use of X-band engagement radars and X/Ku-Band missile seekers, but not acquisition radars in lower bands.

Such SAM systems are the category of “residual” threat which a battlefield interdiction aircraft will encounter once the F-22A force has “sanitized” an area by destroying the long range search/acquisition radars and area defence SAM batteries. With limited range and coverage footprint, but high mobility and autonomous capability, battlefield short range point defence SAM and AAA systems can “pop-up” from hidden locations and ambush interdiction aircraft at medium to low altitudes. Significantly, in a “sanitized” environment such air defence weapons are operating without external support from other sensors or the top cover provided by long range area defence SAMs such as the SA-12/23, SA-20 and SA-21.

The engine nozzle presents a good case study of the band dependency of stealth performance in the Joint Strike Fighter design. In the upper X-band and Ku-band, the individual nozzle segments present as flat panels with a serrated trailing edge. The result will be a circular pattern of narrow reflecting lobes which will produce mostly good effect in these bands. However, in the lower bands this arrangement will rapidly degrade in behaviour to that of a truncated conical shape, which is a strong specular reflector. The resulting external shape related signature will be much the same as a conventional exhaust nozzle on a non-stealthy fighter, with an outer skin contribution and rim contribution. While the interior of the nozzle will be coated with broadband lossy materials and a tailpipe blocker used to obscure the turbine face, the signature of the nozzle exterior below the X-band cannot qualify as “stealthy”. Refer Annex C.

XtTMH.jpg

X-35 Dev/Val prototype (above) vs F-35 SDD AA-1 (below). The clean wing fuselage join and flat low curvature lower fuselage of the X-35 had the potential to yield quite good beam/side aspect radar signature, but the revised SDD design discarded this arrangement in favour of a much inferior contoured design, clearly intended to accommodate the larger weapon bays. While the F-35 SDD engine inlet arrangement is superior to the X-35 Dev/Val prototype inlet design, the gains in the forward sector cannot overcome the performance losses incurred in the beam/side aspect sectors (Images via Air Force Link).

IsKEh.jpg


vmXl5.png
Diagram 5: Very Low Observable airframe shaping should be optimised to produce best effect, i.e. lowest radar cross section, from those angles from which the aircraft is most likely to be illuminated by a threat system such as an engagement or acquisition radar in a Surface to Air Missile battery. This diagram shows the cardinal depression angles for an aircraft at the tropopause, accounting for the curvature of the earth and atmospheric refractive effects which 'bend' the ray path between the aircraft and threat radar. The specific angles in this diagram are determined using Russian specifications for missile range, the SBF refractive model for short ranges, and an exponential CRPL refractive model for ranges in excess of 100 nautical miles. It is important to observe that in straight and level flight all surface based threats are firmly in the lower hemisphere, putting a premium on low Radar Cross Section in the angular range between 3.7 and 36.5 , as area defence missile systems will illuminate the aircraft within this angular range. Point defence missiles systems and 'trash fire' such as AAA and MANPADS are generally altitude limited to 10 - 15 kft and are a much less critical threat. A smart IADS operator will not radiate until a potential target is close enough to get a steep elevation angle for a shot, a tactic commonly associated with 'shoot and scoot' operations - the cardinal example being Serbian ZRK Kvadrat / SA-6 operations in 1999 (Author).

semMn.jpg

The shaping changes to the inlet area and lower fuselage are prominent on these images of F-35A SDD prototype AA-1 (Images via Air Force Link).

hpH24.jpg

Diagram 4 summarises the qualitative comparisons of Joint Strike Fighter shaping aspect and band dependency, with green denoting performance which qualifies as Very Low Observable, yellow as Low Observable, and red as order of magnitude closest to conventional reduced signature aircraft designs. The aircraft performs best in the X-band, and Ku-band, with performance declining through the S-band with increasing wavelength. In the L-band the axisymmetric nozzle design no longer produces useful effect, and the length of the inlet edges sits in resonant mode scattering rather than clean optical scattering, degrading performance. In the VHF band (~2 metres) Joint Strike Fighter airframe shaping has become largely ineffective.

The aircraft will have a credible ability to defeat S-band search/acquisition radars, X-band engagement radars and X/Ku/K/Ka-band missile seekers only in the narrow ±14.5° angular sector under the nose. As the angle relative to the threat radars increases, the unfortunate lower fuselage shaping features will produce an increasingly strong effect with a cluster of “flare spot” peaks around 90° where the longitudinal panel and door edge joins produce effect.

In the narrow ±14.5° angular sector under the tail, the design will produce best effect against X/Ku/K/Ka-band missile seekers, but less useful effect against X-band engagement radars due to their higher power-aperture performance. At S-band the nozzle exterior signature will become increasingly prominent, leading to loss of effect in the vicinity of the L-band.

It is clear that these design choices were intentional and no accident. By confining proper stealth shaping technique only to the forward fuselage and inlet geometry, the designers avoided incurring the development, and to a lesser extent, the associated manufacturing costs of a fully stealthy design, with the YF-23A and F-22A presenting good comparisons.

This is an acceptable optimization if the intent is only to defeat an isolated individual low power aperture pop-up short/medium range mobile battlefield air defence system
in the category of the SA-6 Gainful, SA-8 Gecko, SA-9 Gaskin, Chapparel, Crotale, Roland, SA-11 Gadfly, SA-15 Gauntlet, SA-19 Grison or SA-22 “Greyhound”. It is a completely unsuitable optimization for a wide range of other threat types which are in service, and the associated characteristic engagement geometries. It is also a problematic optimisation where short/medium range battlefield air defence systems are deployed in a coordinated manner.

The most generous description of the stealth design used in the Joint Strike Fighter is that it is 25% VLO, in the nose sector, 25% LO in the tail sector, and 50% “reduced observable” in the beam sectors, with a strong threat operating frequency and angular aspect dependency in stealth performance. It is clearly not a stealth design in the same sense as the F-117A Nighthawk, B-2A Spirit, YF-23A and F-22A Raptor, and to label it a “VLO design” is at best a “quarter-truth”, quite indifferent to the physical realities of the design and the threat systems it will need to defeat in future conflicts."
 
A constant-radius object like a cylinder is not stealthy. -- Really? I thought I posted plenty enough about the 10-lambda rule and how it affect a sphere and a cylinder regarding RCS.

It's simple physics to understand the reason that a cylinder is not stealthy. An incoming radar beam impacts the side of a cylinder. The entire length of the cylinder reflects the radar signal. This is obvious and Gambit has lost his mind in claiming otherwise.

In the citation below, do you see the spikes to 5 dbsm on the graph when the cylinder is perpendicular to the radar emitter? You can ignore the -30 to -40 dbsm when a cylinder is turned on its edge. Obviously, when you look down the tube of a straw, it has a very low dbsm. However, when you are looking at a straw from the side, you can see the entire length. So can a radar. Don't listen to Gambit, he doesn't know what he's talking about.

http://www.ausairpower.net/APA-NOTAM-070109-1.html

"Air Power Australia NOTAM
7th January, 2009
WgCdr Chris Mills, RAAF (Retd)

You have all seen the movie. Our top-gun heroes fly their F-35 Lightning II’s on an Offensive Counter-Air mission. They have four AIM-120Ds aboard and the mission is Air Dominance.

Today, the enemy is being cooperative, and they have old Su-27s on combat air patrol. The F-35’s sensors detect the Su-27’s radar, and to clear the air, the Lightning IIs head towards these targets. The 100% reliable, 100% kill probability AIM-120Ds quickly down each Sukhoi with a single shot, so each F-35 kills up to four Su-27s until all are gone from the sky. Our heroes fly back to base, where they enjoy the adoring applause from the troops in the same way as Top Gun’s Maverick and Iceman returning from their air combat defence of their Aircraft Carrier.

This scenario draws on the thesis that the F-35 Joint Strike Fighter’s ‘invisibility equals invincibility’, such that the invisible Lightning II always wins, no matter what the odds. While stealth comes at a high cost, it's value is eminently ‘marketable’. The recent fighter competition in Norway has produced a rubbery, but pre-world economic crisis price-point for the F-35 Joint Strike Fighter somewhere between $US160-230M per copy. That price is substantially more that the price of aircraft that provide the same, or superior fighter characteristics like greater speed, range, payload, flexibility and agility, but without ‘stealthiness’.

Every thesis has its antithesis. Stealth technology has played an important part of modern battles, and complicates an enemy’s air control strategies and tactics, but the advantages of partial or ‘CAIV-driven’ low observability are fading as ‘counter-stealth’ systems and tactics penetrate its cover. So this is a reasonable question: ‘would a rational Nation purchase the F-35 Joint Strike Fighter at an inflated price if it were not stealthy, when lower cost, more effective air combat aircraft are available?’ The answer is self-evident.

There is a deadly corollary to this antithesis. If a Nation purchases the F-35 Joint Strike Fighter without testing its actual stealthiness, it runs the risk of buying an aircraft that is stealthy from some aspects, but observable and hence vulnerable from others. Any competent enemy would know these weaknesses, and exploit them on the first day of battle in a way that a substantial portion of the air combat fleet would be lost. The consequences are dire: probable defeat in battle and loss of sovereignty. It is this ‘sovereign risk’ that makes it imperative to know the real limitations of the Joint Strike Fighter’s stealthiness.

The signature of stealth aircraft is a closely guarded State secret, and for most people is ‘unknowable’. Until now that is. A State can classify its secrets like radar signatures, but it cannot classify the Laws of Physics.

A colleague, Dr Carlo Kopp, has used open-source radar signature analysis software verified against known shapes and empirical results, to generate radar signature estimations for two key components of the F-35 Joint Strike Fighter: the section of the lower fuselage around the weapons bays, and the axi-symmetric nozzle of the F135 engine. This ‘radar cross section simulator’ can cope with a range of radar operating frequencies used in modern air combat, and plot reflections from complex shapes from any angle.

Many people will find it incredible that a private individual can generate radar signatures of a supposedly stealth aircraft, notwithstanding that Dr Kopp is an internationally recognised expert in the field, and an experienced design engineer and university research scientist. I am as sceptical as the next scientist, and demand proof that an open-source academic radar signature tool can produce reliable results. What convinced me was the calibration of the software output. In this case, the radar signature of a cylinder of known size was used, with the simulation output being compared with actual measurements of a physical object. The results can be seen in these images:

4siYs.jpg


MsTYA.jpg

Simulator calibration plots for a cylindrical shape at 5.8 GHz V-pol (Knott et al and Kopp).

Even a non-expert eye can see the high degree of similarity between the actual and simulated measurements. Experts in the field advise that the correlation is remarkable and highly significant. This result is an important part of the validation and verification of the radar signature simulator. (article continues)"
 
It's simple physics to understand the reason that a cylinder is not stealthy. An incoming radar beam impacts the side of a cylinder. The entire length of the cylinder reflects the radar signal. This is obvious and Gambit has lost his mind in claiming otherwise.

In the citation below, do you see the spikes to 5 dbsm when the cylinder is perpendicular to the radar emitter? You can ignore the -30 to -40 dbsm when a cylinder is turned on its edge. Obviously, when you look down the tube of a straw, it has a very low dbsm. However, when you are looking at a straw from the side, you can see the entire length. So can a radar. Don't listen to Gambit, he doesn't know what he's talking about.

Coffin Corners for the Joint Strike Fighter

"Air Power Australia NOTAM
7th January, 2009
WgCdr Chris Mills, RAAF (Retd)

You have all seen the movie. Our top-gun heroes fly their F-35 Lightning II’s on an Offensive Counter-Air mission. They have four AIM-120Ds aboard and the mission is Air Dominance.

Today, the enemy is being cooperative, and they have old Su-27s on combat air patrol. The F-35’s sensors detect the Su-27’s radar, and to clear the air, the Lightning IIs head towards these targets. The 100% reliable, 100% kill probability AIM-120Ds quickly down each Sukhoi with a single shot, so each F-35 kills up to four Su-27s until all are gone from the sky. Our heroes fly back to base, where they enjoy the adoring applause from the troops in the same way as Top Gun’s Maverick and Iceman returning from their air combat defence of their Aircraft Carrier.

This scenario draws on the thesis that the F-35 Joint Strike Fighter’s ‘invisibility equals invincibility’, such that the invisible Lightning II always wins, no matter what the odds. While stealth comes at a high cost, it's value is eminently ‘marketable’. The recent fighter competition in Norway has produced a rubbery, but pre-world economic crisis price-point for the F-35 Joint Strike Fighter somewhere between $US160-230M per copy. That price is substantially more that the price of aircraft that provide the same, or superior fighter characteristics like greater speed, range, payload, flexibility and agility, but without ‘stealthiness’.

Every thesis has its antithesis. Stealth technology has played an important part of modern battles, and complicates an enemy’s air control strategies and tactics, but the advantages of partial or ‘CAIV-driven’ low observability are fading as ‘counter-stealth’ systems and tactics penetrate its cover. So this is a reasonable question: ‘would a rational Nation purchase the F-35 Joint Strike Fighter at an inflated price if it were not stealthy, when lower cost, more effective air combat aircraft are available?’ The answer is self-evident.

There is a deadly corollary to this antithesis. If a Nation purchases the F-35 Joint Strike Fighter without testing its actual stealthiness, it runs the risk of buying an aircraft that is stealthy from some aspects, but observable and hence vulnerable from others. Any competent enemy would know these weaknesses, and exploit them on the first day of battle in a way that a substantial portion of the air combat fleet would be lost. The consequences are dire: probable defeat in battle and loss of sovereignty. It is this ‘sovereign risk’ that makes it imperative to know the real limitations of the Joint Strike Fighter’s stealthiness.

The signature of stealth aircraft is a closely guarded State secret, and for most people is ‘unknowable’. Until now that is. A State can classify its secrets like radar signatures, but it cannot classify the Laws of Physics.

A colleague, Dr Carlo Kopp, has used open-source radar signature analysis software verified against known shapes and empirical results, to generate radar signature estimations for two key components of the F-35 Joint Strike Fighter: the section of the lower fuselage around the weapons bays, and the axi-symmetric nozzle of the F135 engine. This ‘radar cross section simulator’ can cope with a range of radar operating frequencies used in modern air combat, and plot reflections from complex shapes from any angle.

Many people will find it incredible that a private individual can generate radar signatures of a supposedly stealth aircraft, notwithstanding that Dr Kopp is an internationally recognised expert in the field, and an experienced design engineer and university research scientist. I am as sceptical as the next scientist, and demand proof that an open-source academic radar signature tool can produce reliable results. What convinced me was the calibration of the software output. In this case, the radar signature of a cylinder of known size was used, with the simulation output being compared with actual measurements of a physical object. The results can be seen in these images:

Here's a question though: you're using the ray model (with the implicit assumption that the cylinder is very large compared to wavelengths; good in optics, bad in radar). what about diffraction effects of the cylinder? what if the cylinder is conducting?

however, I do remember a physical optics model that takes into account diffraction and interference in Air Power Australia that gave J-20 all directional stealth in 9 wavebands.
 
Here's a question though: you're using the ray model (with the implicit assumption that the cylinder is very large compared to wavelengths; good in optics, bad in radar). what about diffraction effects of the cylinder? what if the cylinder is conducting?

however, I do remember a physical optics model that takes into account diffraction and interference in Air Power Australia that gave J-20 all directional stealth in 9 wavebands.

I've been typing for hours in having to deal with those two guys, who were clearly wrong. I'm sorry, but I'm done for tonight. My eyes hurt.

However, let me say that I've never heard of a cylinder conducting all of the incoming radar energy in the real world. You might be able to build a small laboratory prototype under specialized conditions. However, I'll like to see them build a fully-conducting flying airframe. It's b.s.

Also, why bother stopping at a cylinder? Why not make the whole plane conducting and not worry about stealth shaping at all?

I would put an entirely radar-conducting surface/airframe into the same b.s. heap as plasma stealth and Russian radar blockers. What a bunch of hooey. They never have a reputable citation and keep throwing crazy ideas out there.
 
If F-35 is a cost-effective stealthy platform as Gambit said,why Japanese at the begining want to buy F-22 even not considering F-35 a bit. who tell me the reason?

---------- Post added at 12:55 PM ---------- Previous post was at 12:53 PM ----------

Every one in the world could understand except for Gambit.
 
If F-35 is a cost-effective stealthy platform as Gambit said,why Japanese at the begining want to buy F-22 even not considering F-35 a bit. who tell me the reason?

The Japanese did ask for the F-22. The Americans refused. The F-22 is strictly not for export after Congress voted for a ban on exports.
 
If F-35 is a cost-effective stealthy platform as Gambit said,why Japanese at the begining want to buy F-22 even not considering F-35 a bit. who tell me the reason?

---------- Post added at 12:55 PM ---------- Previous post was at 12:53 PM ----------

Every one in the world could understand except for Gambit.

Thats because F-22 is not available for export, so Japan went for second best. Besides Japan can use F-35's on its helicopter carriers(with some modifications).
 

Latest posts

Back
Top Bottom