BAE selected by U.S. DARPA for ‘revolutionary aircraft design’

The goal is always to reduce signature, you can never eliminate it, most low observability aircraft are designed to minimise their frontal aspect return as your more likely to need it when heading towards your enemy than away. The Chinese and Russian aircraft in particular have quite poor side on concealment but their primary concern is flying as fast as they can directly towards an enemy fleet, launching then running away.

Do they still turn on its lights at night?

Reminded me of Buccs too. Lovely aircraft.

It is not new. Russians have anti stealth radars. Data fusion of low frequency radars – so less precise – can be enough for tracking. Or going millimetre wave and imagery radar for final interception.

Both Russia and China have claimed that their HF/VHF/UHF radars can detect stealth aircraft. But you have to take their statement with a pinch of salt, as what was the target aircraft they were using and thereby what was its radar cross section?

Aircraft like the F22 and F35 will be susceptible to resonant affects due to the following phenonium: “There is a ‘step change’ in an aircraft’s signature once the wavelength exceeds a certain threshold and causes a resonant effect. Typically, such resonance occurs when any feature on the aircraft is less than eight times the size of a particular wavelength, as happens with the tail-fin of a fighter.”

However, radars using wavelength of 1m or greater can generate these resonant effects. Higher frequency radars with shorter wavelengths can also generate resonant effects, but it helps if the aircraft has a 90 degree angled cavity, such a the joint between a flying control and the wing.

But this effect by longer wavelength radars also relies on the aircraft having straight edge that meets the criteria. A curve may resonate under some conditions, but the signals direction will be dispersed over a greater width of angles and thereby reduce what is reflected back to the receiver. Low frequency radars operating with 1m or longer wavelengths are much more susceptible to picking up background noise that can be misinterpreted as a legitimate target. Furthermore, older style radar absorbent materials (RAM) such as the ferrite coatings, had little if any effect on these wavelengths. But today RAM has moved on and incorporates both signal capturing as well as attenuation. Yes, there is a physical threshold, whereby the radars signal strength will overcome the ability of the RAM to counter it. But the manufacturer will know this limitation and it will be passed on to aircrew. Who will use radar warning receivers to detect the radar’s signal strength and thereby be able to plot a no-go radius from the radar.

This is where I have my doubts on their statement of being able to detect a stealth aircraft, as its based on what evidence? It certainly won’t be based on actual live radar scanning of a B2, F22 or F35, so it will be based on a theoretical model, which does not take into account the actual performance of the RAM.

To have a guaranteed chance of detecting a stealthy aircraft you need to use multiple active or bi-static radars that build up a picture of the target through additive triangulation. So far all the Chinese have stated is that they have designed a HF radar that operates much in the same way as an AESA radar, where individual elements are tied together in an array and when used form a coalesced picture of an object. Hmm, nothing new there, synthetic aperture radar has been doing it for decades! A single array operating on its own will struggle to detect a stealthy aircraft, however, using a number of them networked together, you may get a hit, tracking it may be a problem though, as it will depend up the relative return angle from the aircraft, which wont be flying straight and level on a mission.

Radars that transmit using wavelengths greater than 1m, have real target resolution issues, as the article describes. But its also due to the larger beam width. A lot of the beam will miss the target, as there will be less energy hitting the target, there will be less returned to the receiver, which is further compounded by the background noise it receives. You can improve the situation by multiplexing a lot of individual signals/transmissions together. But that means you also have to have a similar number of receivers to detect the individual transmissions. By interleaving the signals you can then work out the approximate range, velocity of target, the relative bearing and to some degree the height. Even by using this method, you will not get a pinpoint fix on the target again due to the beam widths used. However, if you then network together lots of these radars, you can reduce the error quite significantly through signal processing.

The B2 was the first production stealth aircraft to use a form of embedded RAM. The F22 used the same techniques, but the F35 took this to a new level. The B21 Raider builds on the F35’s technique. Due to its size and wingtip chord lengths, it will be less susceptible if at all to the resonant affects attributed to HF radar. It will probably generate resonance at longer wavelength which match the criteria for the wing tip chord length. But as the wavelength gets longer so does the beam width and therefore the error will be compounded. Which means even ,more signal processing. So good luck trying to detect that!

Until these countries produce documented evidence of not only the specifications of the radar used but also the target, I will only see the statement as Nationalistic spin. I have no doubt that you can detect a stealth aircraft through a combined radar network. But for it to have the ability to generate a missile tracking solution, I have my doubts, especially as the missile will have to be command guided to the target., whereby the target has a large enough IR signature or the missile’s radar can get a decent hit.

If you keep conventional moving flying controls, you will still need a gap, where the edges meet the wing/fin/fuselage to allow for material expansion through either high g manoeuvres or heat. These gaps will allow certain radar frequencies to either directly reflect or resonate. So that will have to be taken into account during the design.

BLC will take a lot of energy from the engine. But it is highly dependent on how much BLC is used. If it used just to clean up the boundary airflow over the wing to reduce drag, then this will be fairly minimal. If it used instead of flaps, then this will take up a large portion of the energy available, as you will want the BLC to be used for the entirety of the flap deployment, i.e. during take-off and landings, but also high alpha angles manoeuvring. If you require it to replace an aileron, elevator or rudder. Then this gets a bit more complicated.

If an aircraft has relaxed stability. The flight control computer during flight will be constantly making aileron, elevator and rudder adjustments just to maintain the aircraft in a straight and level condition. Now, for example you want to roll the aircraft to the right. Traditionally you’d increase the lift on the left wing, whilst decreasing it on the right wing. So left aileron down and right aileron up. The airspeed over the wings, along with aileron area, deflection angle and distance from the CoG will dictate how fast the aircraft rolls. For a controlled turn you will also use a bit of rudder and elevator to make sure you don’t slip or loose height during the turn.

If we are using BLC to control the roll. We have the advantage of using the whole of the wing tip area for the BLC jets. This will have a larger leverage. It can also be made more responsive in that you can use the jets to force the wing down, if they are blown perpendicular to the wing or used to disrupt the airflow and therefore lift. Correspondingly, on the opposite wing you could have the jets blowing perpendicularly below the wing to force it up. However, if it was practical, you would include the jets over the majority of the wings surface. As this would allow a better proportional control of the airflow over the wing and how lift is controlled.

For a controlled turn you will also need to include the moments generated by the elevator and rudder to add the pitch and yaw to the turn. This would need something along the lines of the Harrier’s/F35’s reaction jets placed at the extremities of the aircraft’s fuselage. So by using them behind the CoG they cause a lever action to point the aircraft in the desired direction.

The proposed delta and canard aircraft shape that has been shown above, does not have any fin/fins, so no rudders! The Magma drone used a pair of canted out fins which moved for yaw control. The majority of tailless aircraft either use pop-up slats or wing tip split elevators for primary yaw control (B2 also uses differential thrust). Will it therefore be using blown reaction jets for yaw control? It’s certainly possible and would get rid of a major radar reflector and drag generator. You could even use wingtip perpendicular air jets to disrupt the airflow above and below the wing that kills lift generating lots of drag as airbrakes. But I don’t believe the Magma program has investigated that, yet!

For this to happen, it would be desirable for the engine, if its a turbofan to have a higher bypass ratio, where some of the bypass air can then be used for the blc. You could also run a number of dedicated air pumps along with air pressure accumulators for the blc, so that the engine thrust is not affected.