Are Russia’s Su-57 and China’s J-20 really stealth fighters?

America’s F-35 Joint Strike Fighter and F-22 Raptor, the world’s first two operational stealth fighters, are widely understood to be far less detectable than either China’s J-20 or Russia’s Su-57. But many don’t realize just how much harder to detect America’s fighters really are.

The truth is, Lockheed Martin’s stealth jets aren’t just quite a bit smaller on enemy radar screens, they’re broadly reported to be exponentially smaller… so much so that it’s not uncommon to find people on the internet arguing that neither the Russian nor Chinese 5th generation entries are actually 5th generation fighters at all.

So, if the J-20 and the Su-57 are as visible on radar as some updated 4th generation fighters… does that mean they don’t really belong in the same category as the Raptor and the Joint Strike Fighter?

Well… as strange as this may sound, actually being difficult to detect isn’t necessarily a requirement for a “stealth fighter” or “5th generation” designation. In fact, there isn’t even really an official definition of either of these terms.

The simple truth is, the J-20 and Su-57 may be far easier to detect or target than America’s stealth fighters. Yet, according to the colloquial use of “stealth fighter” and “5th generation fighter” — and even within the more formalized internal definitions used by different organizations — both China’s and Russia’s top-tier fighters do fit the bill.

Because, as weird as it may sound, actually being stealth isn’t really a hard requirement to be considered a stealth fighter.

Related: How do the world’s stealth fighters really stack up?

What exactly is a radar cross-section?

Stealth, for those who aren’t card-carrying aviation nerds, is an often misunderstood capability, in large part because it isn’t a capability at all. Stealth isn’t something you have or don’t have, nor is it something you can just slap onto an aircraft.

What we call stealth is really a combination of technologies, production methodologies, and combat tactics that all overlap to push an aircraft toward the lower end of what you might call an observability spectrum. The further you are on the “low observable” side, the stealthier your aircraft is, while decidedly non-stealth platforms like B-52s and Goodyear Blimps occupy the opposite and highly observable side of that spectrum.

The most common way stealth (as it pertains to radar) is discussed in media and pop culture revolves around an aircraft’s Radar Cross-Section, or RCS — and that creates some issues. We usually use square meters when discussing RCS in media aimed at the general public because square meters are a unit of measurement we can contextualize in our minds. Experts in the field generally use dBsm, or decibels relative to one square meter, which measures the strength of the signal returned to the transmitter. For the sake of simplicity (perhaps even oversimplification) however, we’ll stick to square meters.

Technically speaking, an aircraft’s RCS is the ratio of backscatter power to the power density received by a target, which is sort of a needlessly complex way of saying the amount of energy reflected by an aircraft back toward a receiver. Most nations don’t disclose real RCS figures for their fighters (though some do), so — more often than not — we’re left to rely on third-party analyses. As a result, you should always take online discussions about RCS with a grain of salt.

But even when you have pretty solid figures to work with, RCS is a fickle mistress. An aircraft’s radar return will vary depending on the angle of observation (where the aircraft is in relation to the radar array), and waters can be further muddied by different radar frequencies and the use of Radar Absorbing Materials that absorb electromagnetic energy, rather than reflect it.

As a result, most good-faith discussions about the Radar Cross-Sections of Russia’s Su-57 or China’s J-20 tend to include a range of values, allowing for the idea that there are different variables to account for and potentially even some bias. But, even without exact figures, we can still draw some pretty concrete conclusions.

Related: Fighter Comparison: Russia’s stealth fleet ranks 11th in the world

How do the J-20 and Su-57 compare to the F-35 and F-22 in terms of stealth?

In America, we don’t call anything a stealth fighter unless it’s incredibly difficult to spot on radar… but in Russia, stealth is less about capability and more about perception.

Russia’s premiere stealth fighter, the Su-57 Felon, is said to have a radar cross-section of between 0.1 and one square meters and is broadly considered to be around 0.5. Russia — and most of the world — call this a stealth fighter… despite having a comparable radar return to America’s non-stealth 4th generation F/A-18 Super Hornet when flying without external weapons or fuel tanks.

Some assessments of China’s Chengdu J-20 Mighty Dragon are similarly critical (or even worse) of the Chinese design. A few assessments place the J-20’s RCS at somewhere between one and three square meters, while one assessment out of Taiwan, measuring the J-20’s RCS from the side, concluded it’s as big as 20 square meters (even larger than the famously detectable F-15) from that angle. However, from head-on (as many fighters would be approaching the J-20 in combat) most expert assessments place the J-20’s RCS at somewhere between 0.08 and 0.3 square meters — quite a bit better than Russia’s Su-57, but still significantly larger than either the F-22 or F-35 on their worst days.

The F-35 Joint Strike Fighter is said to have a radar cross-section of somewhere between 0.0015 and 0.005 square meters. The F-22 Raptor is reportedly to be even harder to detect, with an RCS ranging from 0.0001 to 0.0005 square meters.

That means that if we were to give both the J-20 and Su-57 the benefit of the doubt and assign them the lowest reported RCS figures, the F-22 still remains hundreds of times harder to detect than the J-20 and thousands of times harder than the Su-57.

The F-22’s RCS is reported to be anywhere from 1,000 to 5,000 times smaller than the Su-57, whereas it’s only between 160 and 800 times smaller than the J-20.

So what gives? How can we possibly call the Russian and Chinese entries “stealth” fighters if they’re so much easier to detect than the world’s first stealth fighter, the F-22? Well, for a few reasons.

The fact of the matter is, the J-20 and Su-57 may be much larger on radar than America’s stealth fighters, but all four of the world’s operational 5th generation jets fall within this area of the observability spectrum we looked at earlier:

Despite being far more detectable than either of America’s stealth fighters, both the Russian and Chinese entries are significantly smaller on radar than many (if not most) previous-generation fighter aircraft.

Related: Is Russia’s Su-57 the worst stealth fighter on the planet?

What makes them “5th-generation” fighters?

Generational designations often come (or at least used to) from within the aviation community itself. Each generation comes with a somewhat subjective list of capabilities that may have existed in some particular aircraft before, but became requirements across the board for fighters of the next generation.

Fighter generations are subjective — with different definitions used by different organizations — so here’s how the U.S. Air Force breaks down what new capabilities prompted a new generational designation:

• 1st Generation: Jet propulsion
• 2nd Generation: Swept wings, range-finding radar, and infrared-guided missiles
• 3rd Generation: Supersonic flight, pulse radar, and missiles that can engage opponents from beyond visual range
• 4th Generation and beyond: High levels of agility, some degree of sensor fusion, pulse-doppler radar, reduced radar signature, fly-by-wire, look down/shoot down missiles, and more.

Because new 4th generation fighters are still being produced, it is perhaps the muddiest of all fighter generations. As a result, 4th generation fighters are often further broken down into sub-generations such as 4, 4+, and 4++. These more advanced 4th-generation platforms often boast some 5th-generation capabilities, but not all.

Today, there are four operational 5th-generation fighter platforms in the world: America’s F-22 and F-35, China’s J-20, and Russia’s Su-57, flying alongside more than 25 different 4th-generation platforms. Here’s a rundown of the commonly accepted attributes that go into a 5th-generation fighter:

• A design that prioritizes stealth from the onset
• A high degree of maneuverability
• Advanced avionics systems including AESA radar
• Multi-role capabilities
• Network or data fusion capabilities

There is no established requirement for where an aircraft must fall on the aforementioned observability spectrum in order to be considered “5th-generation.” Instead, the categorization simply requires a design that incorporates stealth right from the onset — criteria both the Su-57 and J-20 do indeed meet.

So while these fighters may not be nearly as stealthy as America’s top-tier fighters, calling them stealth — or 5th-generation — is still appropriate.

Read more from Sandboxx News

• How much stealth can you add to a 4th generation fighter?
• Why is it so hard to develop stealth aircraft?
• America’s enemies can track stealth fighters on radar (and it isn’t a problem)
• Russia doesn’t seem sure the Su-75 Checkmate will be stealth
• Fighter Comparison: Russia’s stealth fleet ranks 11th in the world