F-35 is the newest Western flying piano. Apparently US have already forgotten all the lessons of World War II and Vietnam war, where such impressive-on-paper-but-sluggish fighters ended up on mercy of far more nimble fighters and were thus relegated to ground attack roles. In fact, F-35 was designed as a ground attack aircraft, only to be pressed into service as “multirole” fighter after F-22 killed itself with cost overruns (how decision-makers figured that three-service aircraft would be better than a single-role single-service aircraft in that respect is beyond me, especialy after Aardvark disaster; only thing F-35 has for it is that it is lighter than the F-22, allowing for limited cost savings for some variants when compared to the F-22). And despite what some might think, F-16 was the first – and last – US fighter designed with maneuverability in mind; both P-51 and F-86 ended up maneuverable by pure luck, as they had to have low wing loading to function as high altitude bomber interceptors, and P-51 also got equipped with excellent British Merlin engine. F-22 is similarly a high-altitude bomber interceptor, and while it does have good maneuverability, it is not designed for it, as evidenced by the fact that it needs thrust vectoring to achieve angle of attack required for maximum lift; comparably low wing loading (about same as F-15C) and high thrust-to-weight ratios are features required by its role as a high-altitude fighter.
Due to this maneuverability shortcoming, F-35 has to rely on surprise attacks against the enemy: detect before being detected. That is, after all, entire purpose of stealth. But how stealthy is the F-35? Is it stealthy at all? What must be kept in mind is that stealth is not limited to just radar. For this reason, I will take a look at F-35s stealth in multiple areas.
F-35 was designed from the outset to be less stealthy against X-band radar than the F-22. But it has characteristics which will reduce stealth level even further. Both F-35 and F-22 are only stealthy against enemy radars that are horizontal or few degrees from horizontal. Due to lower inclination of surfaces from the horizontal, this “stealth area” for the F-35 is far less than F-22s; and as soon as F-35 maneuvers, it becomes instantly unstealthy unless maneuvers are done only by vertical tail surfaces, keeping aircraft completely level. F-35 also has many irregularities in its surface – there is bulge above left wing, presumably where the gun is located on the A version, as well as bulges below wing root, on weapons bays doors, below the engine and below the nose where IRST is located. These all help increase F-35s RCS when it maneuvers away from horizontal plane.
VHF radars are radars with wavelengths in 1-3 meter range. For this, it is important to understand two terms: Rayleigh scattering region is region where wavelength is larger than shaping features of target or target itself. In that region, only thing that matters for RCS is actual physical size of target itself. Resonance occurs where shaping features are comparable in wavelength to radar, resulting in induced electrical charges over the skin of target, vastly increasing RCS.
As it can be seen, many F-35s shaping features are in either Rayleigh or resonance scattering region of VHF radars. Situation with early warning HF radars is even worse, as they not only have very long wavelengths, but also come from above after reflecting from the atmosphere. Situation is somewhat better with S and L band radars, but F-35s RCS against these is still far higher than against X band radars. Even against X-band radars, it is only stealthy (LO) from front and rear; against S-band radar, it is stealthy from narrow front aspect, while only limited reduction is achieved from direct front against L-band radar; this is in part thanks to nozzle design, whose segments act as Rayleigh or resonance reflectors in all bands with lower frequency than X band. Against ground-based X-band radars, its side RCS will likely be similar to that of conventional fighter.
When combined with lack of kinematic performance, it means that F-35 will be held back until F-22s and Growlers – or in European ventures, Rafales and Typhoons – have neutralized enemy air defenses. This removes only justification for all-aspect stealth.
There is an ongoing shift from radar to IRST as a primary sensor for air-to-air combat, and pilots fighting a competent opponent quickly learned to shut down radar. When it comes to ground threats, radar SAMs have had a disastrous performance, worse than IR SAMs. Consequently, IR stealth is far more important than radar stealth – even if it is not as flashy – and if somebody designs for radar stealth and not for IR stealth, he’s an idiot. Yet IR stealth is one of many areas where F-35 is sorely lacking.
In fact, F-35s IR stealth can be summed up in one word: nonexistant. It is the heaviest single-engined fighter in the world, and its single engine produces amount of thrust that equals that of many twin-engined fighters while having no IR signature reduction whatsoever (IR signature reduction measures were deleted to save weight). Its shape means large amount of drag, which also increases IR signature, as well as providing larger target for an IRST. Drag means that F-35 has to use afterburner to fly supersonically, increasing IR signature even further due to the large exhaust plume. Powerful radar also helps increase IR signature due to the cooling requirements.
F-35 is comparably large aircraft. From top, its visual signature is comparable to that of F-2A, Dassault Rafale or Eurofighter Typhoon. However, its signature from side and especially front is larger than signatures of aircraft mentioned. As modern IR sensors are basically visual sensors, and are capable of detecting differences in temperature on order of few degrees Celzius, its visual signature will also have a role to play in IR detection.
Acoustically, F-35 is far louder than the F-16 or Gripen, and in fact one of problems with basing is that it is so much noisier than the F-16 that air bases which were able to accomodate F-16s without causing undue discomfort to people living nearby cannot accomodate F-35 without displacing lare numbers of inhabitants nearby. There are two basic reasons for this.
First reason is that F-35 is a far heavier aircraft and thus needs far stronger engine. Stronger engine means more noise, and F-35s engine (F-135) is the most powerful engine in the world – it has to be as it pushes around weight more suitable for two engines. Second reason is that F-35 has aerodynamic performance of a brick. Its basic shape does not offer good aerodynamic performance, and it has many irregularities in surface, just like conventional fighters.
All stealth features are irrelevant if aircraft has to use its radar to detect the enemy. This is one of few areas where F-35 fares well, as it has very good coverage with numerous IIR sensors. As a result, F-35 will not have to use its radar to detect the opponent, relying instead on detecting opponent’s IR signature. However, this situation is still a loss-loss for the F-35: if it uses IR sensors, it will be at disadvantage against most other fighters equipped with IR sensors due to its IR signature, and if it uses radar, its emissions will be detected far sooner than it will detect the enemy by using the radar.
In real terms, F-35 is as stealthy as a pink elephant in the porculan store, far less stealthy than Saab Gripen, Dassault Rafale, F-16 or Eurofighter Typhoon. While it does have comparably low radar signature from some angles and to some frequencies, as well as good passive sensor suite, it is severely lacking in two most important measures of visibility – visual and infrared. But US military is disconnected from reality, as are most Western policymakers, who either can’t or don’t want to understand limitations and compromises of designing fighters for radar stealth.
Problem when facing enemy radar-guided SAMs is that F-35 can only jam radars that are in front of it (+-60 degrees off nose), and are within frequency coverage of its own radar. This frequency coverage excludes anything except X-band radars. Its reliance on – rather lacking – stealth characteristics of airframe itself has left it without robust countermeasure suite likes of DASS or SPECTRA, including lack of DRFM jammers.