"6th generation" fighters
The Brits and the French have shown their mockups for 6th gen fighters.
I never understood why the Americans didn't use a delta wing without any separate tail fins (fully tailless). It's the bare bones configuration, without any stabilisers that function as reflectors.
Nor did I understand why the F-35 was built as a single engine aircraft (though is suspect it's one of the drawbacks caused by the STOVL version). Two engine aircraft have multiple advantages, including the ability to control roll with thrust vectoring. The F-35 was never realistically going into the low (cost) end, a niche that's now reserved for the Gripen (NG) in the West.
I myself think a completely tailless design is the obvious choice from an aerodynamic and radar stealth point of view. Two engines and a limitation to an exportable size and price (rather a F/A-18E/F equivalent than a F-22 equivalent) seem obvious things to go for as well.
The really important things that I expect in "6th gen" combat aircraft are different, though:
(1) DIRCM, likely in dorsal and ventral position and likely retractable.
Directional infrared countermeasures (lasers) that dazzle the IR sensors of incoming short and medium range missiles are very effective given enough output power and accuracy and could ruin IR-guided missiles' probability of hit. Radar-guided missiles can be messed with by many means, but smart IR-guided missiles are very difficult to defeat, as they reject decoys quite well and can even re-engage after missing.
The upper (dorsal) DIRCM 'turret' may also serve as satellite communication emitter, and both DIRCM turrets may serve as laser communication emitters for datalinks between friendly aircraft. The DIRCM may even be used as first choice IFF (identification friend or foe) interrogator (with normal radio interrogation as backup if there's no positive reply).
The lower (ventral) DIRCM 'turret' might be used to sweep the ground in search of skyward-looking optics (detecting them by characteristic reflections), which might make sense if the approximate origin of hostile surface-to-air missiles is known. The ventral DIRCM might also double as laser target designator. Overall, compact DIRCM in (strike) fighters may be one of the two new big things in air warfare.
(2) Rear-looking smartly devised AESA radar
'Stealth' aircraft, ground-based standoff jammers, long range SAMs and long-range air-to-air missiles make the life of AEW&C aircraft such as the famous AWACS miserable and short in wartime. Our combat aircraft would not be able to lean much on AEW support, and certainly not when over hostile ground.
Fighters should thus better have a good all-round situational awareness without AEW support. Passive sensors such as DAS are limited in effective range due to their resolution, and datalinking to enable multiple aircraft to join their radar data is very imperfect. You'd still need to have some allied fighter to look to the rear, and that quite impractical much of the time, particularly on strike missions over hostile ground.
The simple technical answer is to have 360° radar field of view with onboard radars. This sounds extremely expensive because high performance AESA radars such as APG-77 have only a field of view of about 110...120° because the antenna is fixed. That's too primitive. An angled AESA antenna (say, angled by 40°) that can be rotated 360° can turn a 100° field of view AESA antenna into a 40°+100°+40°=180° field of view AESA antenna (just not all 180° in a fraction of a second).* It's also possible to combine typical 1980's mechanical antenna steering with active electronic steering as for the European CAPTOR-E radar antenna. The latter approach fits better to non-rotation-symmetric radomes and antennas (those with far from circular shape)
Such a hemispherical field of view is half of a spherical field of view, so you can achieve the latter by adding a second (tail) radar. That's why having two engines (thus having space for an antenna radome behind and in between the nozzles) makes even more sense than we're used to.
Such a pair of radars with lots of quite automated modes (including jamming in their frequency ranges) would address many tactical challenges. The rear radar wouldn't even need to be as big as the front antenna; a quarter of the antenna modules (and thus sectional area) yields about a third of the range. That should be enough for most purposes.
Such 360° RF coverage could double as quite directional RF datalink emitters and receivers. It could also detect incoming low signature missiles in time for ECM or DIRCM efforts.
An important purpose of a rear radar would be the tracking of already detected aircraft (which requires somewhat less power than detecting). The rear radar could on its own track a target that a missile has been launched at, upload target info updates to the missile - all while the fighter itself is running away at supersonic speed.
The disconcerting thing is that the Russians thought of ventral and dorsal DIRCM in their Su-57, and were pioneers regarding modern (strike) fighters with tail radar in the Su-34/-35 series. The Su-57 features a tail radar as well.
Another disconcerting thing is that the Franco-German concept for a new fighter shows off neither DIRCM nor a tail radar in its admittedly very basic published model:
Avionics have been huge drivers of combat capabilities in modern combat aircraft, and also huge drivers of their price.** I suppose it's important to reserve the volume, power supply capacity, cooling (or heat sink) capacity and surfaces for key avionics in future combat aircraft. An aircraft without such reserves could be uncompetitive by the time it becomes operational, quite as non-'stealth' aircraft cannot really be upgraded into 'stealth' aircraft.
Though there is one thing to remember; no matter how sophisticated fighter avionics become, such fighters will be irrelevant against small near-ground drones. A post-2025 high end "air war" might be de facto split into a mixed on-ground and near-ground drone war, conventional air war, ballistic missiles (defence) and and space war. We shouldn't focus resources on the conventional air war domain that we got used to.
(...)
*: This is an analogy to the smart use of rotating AESA antennas on modern warships. Some warships use a single AESA antenna or a two-sided rotating AESA antenna high up instead of using much bigger, heavier, larger and more expensive fixed AESA antennas. That's more economical and due to the higher vantage point it even pushes the radio horizon farther out despite lesser power.
**: Turbofans are obscenely expensive as well.
