Published by The Independent
Divine Eagle: How much of a threat is China’s new high-flying drone to US air superiority?
Fly bye: the F-117 Nighthawk stealth fighter could become an outdated weapon Rex Features
In May, grainy pictures emerged of a huge new twin-fuselage, high-altitude Chinese drone called the Divine Eagle. Those in the know instantly labelled it the “stealth-hunting drone”. Stealth technology is the equivalent of electronic camouflage for planes, making them hard for enemy radar to spot – but the Chinese drone is certainly big enough to carry the special radars developed to detect stealth aircraft. It’s able to fly high enough to detect them long before they can reach their targets. Its radar is rumoured to have been able to pick out an American stealth F-22 Raptor off the coast of South Korea almost 500km away.
To some analysts, the Chinese drone represents the death of stealth – for others, merely a serious threat to the future of the technology on which America has based its air superiority.
Stealth, or “low observable technology”, is a combination of aircraft design, tactics and electronic countermeasures designed to make planes less visible to radar and other systems, which the US has pioneered. As well as trying to create the lowest possible radar signature by getting rid of the tail, it also tries to reduce things such as infrared emissions from the engine exhaust and electromagnetic emissions from the computers on board. Stealth tactics involve looking for gaps in air-defence systems.
When people think of stealth aircraft, they tend to picture the triangular black F-117 stealth fighter and B-2 bombers that penetrated Saddam Hussein’s much-vaunted air defences at the start of both Gulf wars – or perhaps the troubled Lockheed F-35 Lightning stealth fighter programme on which the UK has gambled the future of its aircraft carriers. However, the Horten Ho 229 flying wing developed by the Nazis during the Second World War was probably the first. While the Lockheed SR-71 Blackbird spy plane used some basic stealth technology, the great leap forward in stealth really occurred in the 1970s with the Lockheed Have Blue project to develop a stealth fighter. This programme led directly to the F-117 and B-2.
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A CLOSER LOOK AT CHINA’S DIVINE EAGLE DRONE
THE WORLD’S BIGGEST UAV
weibo.com, tiexue.net, cdjby.net – Divine Eagle -The Divine Eagle is a low observable, high altitude UAV meant detect stealth aircraft at long ranges, using special purpose radars. This low resolution photo shows that similar to the port (left) side seen in the next photo below, the starboard (right) side of the fuselage is also colored grey.
Since photos in May 2015 emerged of the Divine Eagle, China’s giant UAV has been getting a lots of international attention. With its giant, double bodied design, carrying high performance anti-stealth radars, the drones are a potential key part of China’s offensive and defensive military strategy in the coming years. Formations of Divine Eagle UAVs are expected to provide an early warning line to detect threats to China’s airspace, like cruise missiles and stealth bombers, as well as be able to take on such missions as hunting for aircraft carriers in the open waters of the Pacific.
Blitzo at China Defense Forum – Divine Eagle – By using the single deck bus in the background (probably 3.2 meters tall, like most buses of its type) as a very crude visual yardstick, a very rough comparison suggests that the Divine Eagle is about 6 meters tall, and 15 meters long (since most high altitude large UAVs have a wingspan to body length ratio of 2.5:1 to 3:1, the wingspan of the Divine Eagle is likely its be 35 to 45 meters across). With a maximum take off weight of at least 15 tons, the Divine Eagle is the world’s largest UAV, edging out the RQ-4 Global Hawk.
In late June 2015, new photos emerged of the Divine Eagle prototype, allowing a clearer look at its details. The Divine Eagle has a single engine nestled between its tailfins, with a diameter of over 1 meter. This makes the engine likely to be a medium non-afterburning turbofan producing 3 to 5 tons of thrust, which in turn is usually enough to power a UAV of 12-18 tons in maximum takeoff weight. In comparison, the largest American UAV in open service, the RQ-4 Global Hawk, uses a F-137-RR-100 turbofan engine with 3.4 tons of thrust. The Divine Eagle has a five wheel landing gear layout. The double bodied layout was chosen in order to provide the surface area for carrying large radars, while minimizing internal volume and weight.
Iron Eagle via Weibo – Color in the Eagle – This CGI offers a view of the differing yellow, green and grey blue primer coatings on the Divine Eagle suggest the usage of different materials like composite and aluminum alloys for different sections of the UAV. For example, the grey blue forward dome on the port (left) body is likely to contain a satellite dish for long distance communications, while the grey blue sections on the twin bodied fuselage likely house radar arrays.
By using the single deck bus in the background (probably 3.2 meters tall, like most buses of its type) as a very crude visual yardstick, a very rough comparison suggests that the Divine Eagle is 6 meters tall, and 15 meters long (since most high altitude large UAVs have a wingspan to body length ratio of 2.5:1 to 3:1, the wingspan of the Divine Eagle is likely its be 35 to 45 meters across). The differing yellow, green and grey blue primer coatings on the Divine Eagle suggest the usage of different materials like composite and aluminum alloys for different sections of the UAV. For example, the grey blue forward dome on the port (left) body is likely to contain a satellite dish for long distance communications, suggesting that the material used in the grey blue sections are likely to be highly permeable to electromagnetic waves. The grey blue is also to be found on the starboard side of the right body (facing outside), and if the airframe composition is symmetrical, likely to be found on the portside of the left body (also facing out). Such electromagnetic permeables are likely to house the Divine Eagle’s long range anti-stealth radars (radomes are made of radar transparent materials), indicating that its radar arrays are 10 meters long, which suggests transmitting lower frequency (L and S Band) radar waves (most stealth aircraft are optimized to evade higher frequency, such as X band, radar). The green primer likely covers lightweight materials such as composite, while the yellow primer near the engine suggests some stronger metal alloy, probably to support the engine weight and height.
Hongjian via China Defense Forum – Divine Eagle Hunts – The offensive applications of the Divine Eagle are demonstrated here, as two Divine Eagles mark out not just the enemy aircraft carrier, but also its escorting warships and aviation wing, while vectoring friendly aircraft and ships into combat. One presumes that the Divine Eagle would also be able to find targets for the infamous DF-21D anti-ship ballistic missile.
There is much to learn about the system, but its significance is great. Given the long endurance of the huge Divine Eagle, it could in the future take on tasks that range from watching over China’s manmade South China Sea islands to tailing foreign warships in waters near and far.
Copyright © 2016 Popular Science. A Bonnier Corporation Company. All rights reserved.
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China’s Divine Eagle anti-stealth UAV is probably an interferometer
Why would China build a complex double-body aircraft instead of a single large fuselage (like the Global Hawk)?
The only scientific explanation is an interferometer.
Satellites in space (where there is no air) can fly in fix formations and perform as a single larger interferometer. An example is China’s NOSS (ie. Naval Ocean Surveillance Satellite) triple satellite formation.
The problem with aircraft is air turbulence. It’s difficult to maintain a fixed distance between two radar receivers.
Thus, China’s Divine Eagle UAV has two long connected fuselages to serve as an interferometer that detects longer-wavelength L-band electromagnetic waves.
As a reminder, an interferometer dramatically increases the resolution (or clarity) of a returned radar signal. However, it does not affect the range of the radar. Also, an interferometer requires an atomic clock to time-stamp the two sets of images (or data) and allow post-processing algorithms to refine the picture.
Question: If NASA can create an L-band interferometer on a single fuselage airplane, why did China use a double-body design?
Answer: China needs longer range. Thus, the emitters (e.g. two L-band radars in the radomes) have to be much larger to allow for more power. This would explain the two large radomes on China’s Divine Eagle anti-stealth UAV.Also, China could be using a VHF interferometer. The two long fixed-distance fuselages would allow for the transmission and reception of long-wavelength VHF signals.
More T/R modules in bulbous radomes result in a more powerful L-band AESA radar
An L-band AESA radar is based on individual transmit/receive (T/R) modules. By increasing the number of modules in the bulbous radomes, the number of constructive interference waves has been increased. This results in increased range. Another way of expressing the increased range is to say there has been an increase in the power of the radar.
The L-band radar is more powerful, because more T/R modules have been placed in the radomes of the Divine Eagle anti-stealth UAV.
VHF wavelength starts at 1 meter and requires the length of the Divine Eagle anti-stealth UAVSince VHF wavelength is one meter and higher, very few VHF T/R modules can be placed in the radomes. Thus, due to the constraints imposed by physics, the only place to locate a VHF AESA radar with reasonable resolution is along the length of the fuselage.To achieve interferometry, it would require two fuselages at a fixed distance from each other. The Chinese Divine Eagle anti-stealth UAV fulfills both requirements.
———-By the way, an atomic clock is a small box and could easily be carried on-board the Divine Eagle UAV.
“Rubidium clocks are the most compact method of atomic time keeping. These are commonly used on satellites.”
- Divine Eagle UAV is most likely an interferometer based on China’s fourth-generation airborne L-band AESA radar
China’s Divine Eagle anti-stealth UAV is probably the world’s first military airborne L-band radar interferometer.
China is an expert at L-band phased array radars. An example is the Chinese ground-based YLC-2 L-band phased array radar.
The Chinese Divine Eagle UAV should be a continuation of China’s miniaturization in airborne L-band phased array anti-stealth technology.
1st generation: KJ-200 “balance beam” AEW&C with L-band phased array radar (first flight November 2001)
2nd generation: KJ-2000 Mainring AWACS with L-band phased array radar (first flight 2003)
3rd generation: ZDK-03 AEW&C with L-band phased array radar (first flight November 2010)*
4th generation: Divine Eagle anti-stealth UAV L-band interferometer (2015)
China has 15 years of experience with airborne phased array L-band radars. We expect China’s software algorithms and filters to be optimized for L-band radar interferometry.
China’s KJ-2000 AWACS and passive detector Divine Eagle L-band UAV would be a devastating anti-stealth combination
KJ2000 AWACS: Details
According to Australia Air Power, China’s KJ-2000 AWACS uses L-band radar to search for stealth aircraft.
The distance from the KJ-2000 AWACS L-band radar emitter to the target is 470km. The distance from the target to the radar receiver on the KJ-2000 AWACS is another 470km. Thus, the total distance from the KJ-2000 AWACS L-band radar emitter to the receiver is 940km.
By using the KJ-2000 AWACS with a silent listening partner in the Divine Eagle (which has an extremely sensitive L-band interferometer), the KJ-2000 AWACS can illuminate a stealth aircraft at 840km and have the Divine Eagle pick up the signal at 100km away from the target.
By figuratively separating the receiver from the KJ-2000 AWACS and moving it much further down the field, a stealth aircraft can be detected at an extreme range of 840km by the Divine Eagle anti-stealth UAV.
Divine Eagle UAV is a 10,000 T/R module L-band Interferometer
Whether you use the bus or the UAV itself as a benchmark, the height of the Divine Eagle UAV is about 1.5 meter in height.
“By using the single deck bus in the background (probably 3.2 meters tall, like most buses of its type) as a very crude visual yardstick, a very rough comparison suggests that the Divine Eagle is about 6 meters tall….”
The radome is usually equidistant in the vertical and horizontal directions. This means the horizontal width of the Divine Eagle UAV radome is about 1.5 meters. The Divine Eagle interferometer has a diameter of 5 radomes or 7.5 meters.
The diameter of the Divine Eagle L-band interferometer is 7.5 meters. L-band is 0.15m. However, the transmit/receive (T/R) module of an AESA radar is built with a half-wave dipole antenna design. In the case of L-band, the half-wave of 0.15m is 0.075m.
7.5 meters / 0.075 meter per T/R module = 100 T/R modules horizontally
An AESA radar is mostly circular in shape. The horizontal and vertical lengths are approximately equal.
The calculation of a square 100 T/R module (horizontally) x 100 T/R module (vertically) AESA radar is a close approximation of an actual circular AESA radar.
100 T/R modules horizontally x 100 T/R modules vertically = 10,000 T/R modules in total
Divine Eagle L-band interferometer is eight times more sensitive than F-35 X-band AESA radar.
10,000 Divine Eagle L-band T/R module interferometer / 1,200 F-35 X-band T/R module AESA radar = Eight times greater sensitivity based on module count
Why does China’s Divine Eagle UAV have a maximum altitude of 79,000 feet?
According to Popular Science, China’s Divine Eagle UAV has a maximum altitude of 25km (or 79,000 feet).
In contrast, the US Global Hawk has a maximum altitude of only 18km (or 57,000 feet).
Why is there a huge difference of 22,000 feet between China’s Divine Eagle and the US Global Hawk?
The most likely explanation is the two UAVs are designed for different roles.
The US Global Hawk was designed for reconnaissance. It is looking for ground targets.
The Chinese Divine Eagle UAV was designed to detect stealth fighters and bombers.
The total path length from a KJ-2000 AWACS transmitter-(to target)-(to receiver) is about 900km. By using a passive Divine Eagle UAV L-band receiver, it permits a much earlier detection of a stealth aircraft by about 200 to 300km (or 120 to 180 miles). By flying at nearly 80,000 feet, the Divine Eagle passive receiver can avoid being illuminated by the KJ-2000 AWACS L-band radar.
Alternatively, a high-flying Divine Eagle UAV can use its UHF/VHF dual-fuselage interferometer to detect a stealth aircraft. If the Divine Eagle was flying at the same altitude as an F-22, the other fuselage would block the transmission/reception of the UHF/VHF array. By flying at nearly 80,000 feet, the Divine Eagle dual-fuselage interferometer would have an unobstructed view of a stealth aircraft.
The Chinese KJ-2000 AWACS has a service ceiling of 42,651 feet.
The American F-22 has a service ceiling of 60,000 feet.
Martin Su asiawind.com