Fighters like the F-35, Su-57, and J-20 may be stealthy, but their airborne support platforms (ASPs), like aerial tankers, JSTAR, AW&CS, etc., are not.
US security establishment has been working on heavy platform stealth to evolve low observable (LO) tankers, special operations transports, and large flying sensor and communication platforms, as these will be targeted or kept away from tactical areas.
The US already has the B-2 and B-21 stealth bombers. The Russian Tupolev PAK DA is a next-generation stealth strategic bomber targeted to enter service in 2028. China’s Xi’an H-20 subsonic stealth bomber is expected by 2025.
Most of these aircraft are flying-wing designs. Could the large stealth transport/tanker aircraft evolve from these?
This would allow the ability to fly much closer to borders and insert special operations teams deep behind enemy lines. There are others who feel that stealth is not only expensive but also overrated.
What is Stealth?
Stealth or LO is essentially a combination of many technologies, all of which combine to greatly reduce the distances at which an aircraft can be detected. It involves reducing radar cross section (RCS), acoustic signature, thermal imprint, and many other aspects.
The term ‘Stealth’ became popular during the late eighties when the F-117 stealth fighter was deployed in the Gulf War in 1991.
The aircraft part that contributes significantly to the echo in any aspect is the vertical stabilizer. These were initially tilted to reduce corner reflections. The leading edges of the wing and the tail planes, when set at the same angle in the F-22 Raptor, reduced reflections. Later, the tail was altogether removed in the B-2 Spirit.
All complex bumps or protrusions of any kind on the aircraft were removed. The weapons, fuel tanks, and other stores were placed internally. Stealthy becomes un-stealthy even when a weapons or undercarriage bay door or hatch opens.
The leading edges of the wing were coated with radar-absorbing materials (RAM) to trap the impinging waves. Initially, RAM paints resulted in high weight and drag penalty, but they have improved over time.
Dielectric composite materials are more transparent to radar compared to metals and carbon fibers, reflecting electromagnetic energy incidents on the material’s surface. Coating the cockpit canopy and even the pilot’s helmet with a thin film of transparent conductors helped to reduce the radar reflections from the cockpit.
The aircraft engines were buried within the wing or fuselage so that the compressor blades are not visible to radar. Also, it reduced the infrared (IR) signature. In some aircraft, the jet exhaust is vented above the wing surface to shield it from surface IR missiles.
Aircraft must avoid radiating any detectable energy, such as from onboard radars, communications systems, or RF leakage from electronics enclosures. So, passive infrared and low light TV sensors began to be used to track enemy aircraft and aim weapons. Forward-facing radar had to be used selectively.
Acoustic signature has to be reduced by more efficient low-noise engines. The visual signature is best reduced through camouflage paint or other materials to color and break up the lines of the aircraft. Aircraft must fly at altitudes that don’t leave contrails.
Operational Usage of Stealth – Mostly In Uncontested Environment
The operational use of stealth began with F-117 in Iraq in the 1990 Gulf War. Later, in Yugoslavia in 1999, the F-117 and the B-2 Spirit strategic bomber were used. One F-117 was shot down by a Serbian S-125 ‘Neva-M’ missile.
In the 2003 invasion of Iraq, F-117 Nighthawks and B-2 Spirits were used. The Sikorsky UH-60 Black Hawk helicopter used for the May 2011 operation to kill Osama bin Laden was heavily modified for quieter operations and employing stealth technology to be less visible to radar.
The F-22 made its combat debut over Syria in September 2014, and later, in 2018, Israeli F-35I stealth fighters conducted a number of missions in Syria and even ‘infiltrated’ Iranian airspace without detection. All these have been in uncontested environments.
Stealth Limitations & Countermeasures
Aircraft shaping is of little help against low-frequency radars, which, even with signal wavelength more than twice the size of the aircraft, can still generate a significant return.
Of course, such radars lack accuracy and, because of their large size, are difficult to transport. Multiple emitters are another option. Detection can be better achieved if emitters are separate from receivers. Bistatic or multi-static radars have such separation.
IRST systems may be effective even against stealth aircraft because any aircraft surface heats up due to air friction, and a two-channel IRST can compare the difference between the low and high channels. Many modern fighters have IRST systems that can detect aerial targets at ranges up to 100 Km.
Stealth Cost and Compromises
In December 2022, the cost of a B-21 aircraft was estimated to be $700 million. USAF officials estimated they would spend at least $203 billion over 30 years to develop, purchase, and operate a fleet of 100 B-21s.
Modern platforms are designed by incorporating some level of stealth or LO technology at the initial design stage itself. Even existing aircraft are at times modified to reduce their signature. Creating a stealthy design comes at a price.
It could be in terms of aerodynamic and other design compromises, long periods to perfect the design, or high developmental financial costs. The absence of an external pylon means larger internal bays, and that means additional on-board real estate.
Some stealth features require regular special maintenance. Specific aircraft shapes may also limit weapon and fuel carriage or may not be the best for flight efficiency. Also counters to stealth are all the time evolving.
Operational Constraints
There are some vulnerable phases of flight, even for stealth aircraft. When internal armament bays open for weapon delivery, the plane’s RCS multiplies.
While the aircraft will reacquire its stealth as soon as the bay doors are closed, a fast-response defensive weapons system still gets a short opportunity to engage the aircraft. Also, some weapons require the weapon’s guidance system to acquire the target while the weapon is still attached to the aircraft. This forces relatively extended operations with the bay doors open.
Fully stealth aircraft carry all fuel and armament internally, which limits the payload, while a non-stealth attack aircraft can carry several times more. This would mean the need to deploy more aircraft.
For a similar payload, the stealthy aircrfa6t has to be larger in size. This apparent disadvantage, however, is offset by the reduction in fewer supporting aircraft that are required to provide air cover, air-defense suppression, and electronic countermeasures.
A non-stealthy aircraft can delay detection by exploiting ground radar’s Doppler slot. With knowledge of enemy radar locations and the RCS pattern of own aircraft, a flight route can be flown that minimizes radial speed while presenting the lowest-RCS aspects of the aircraft to the threat radar. There are other flight tactics, such as maneuvers combined with chaff dispensation, to confuse enemy radars.
Future Stealth Initiatives
With the invention of meta-surfaces, means of reducing RCS have been improved significantly. Thin two-dimensional meta-material layers allow or inhibit the propagation of electromagnetic waves in desired directions.
Plasma stealth is proposed to use ionized gas (plasma) to reduce RCS. Interactions between electromagnetic radiation and ionized gas might create a layer or cloud of plasma around the platform to deflect or absorb radar.
The concept of flexible or adaptive aero-elastic wings and fluidic controls using air jets could replace control surfaces. All these are still evolving and costly.
Large Stealth Platform Projects
USAF’s demand for more survivable tankers and transport aircraft has been driving new designs. Evolving threats require mobility. Adversaries are reaching out to increasingly long ranges to engage aircraft.
The flight refueling aircraft (FRA) cannot remain too far deep. The transport aircraft must penetrate enemy lines for para-drop and special operations. The next-generation stealthy tanker is being dubbed KC-Z.
They are separately seeking a successor to the C-17 Globemaster III cargo aircraft, which has been out of production since 2015. USAF has sought a large-transport flying demonstrator ready by 2026. This could be critical to supporting forward hub-and-spoke logistics and refueling operations in a higher-end conflict, as well as penetrating missions.
As of now, the flying wing, or blended wing body (BWB), also known as hybrid wing body (HWB) with lifting aerofoil fuselage, is a possible contender for transport applications.
The revolutionary bi-directional flying wing is also evolving. The first scaled model of KLM Royal Dutch Airlines’ futuristic Flying-V aircraft designed by Delft University of Technology first flew in 2020. Both Airbus and Boeing are working on flying-wing airliners.
Boeing has unveiled a BWB-scaled model of its ‘Revolutionary’ Stealthy Tactical Cargo Aircraft Concept, which is designed around a payload capacity roughly equivalent to that of a C-130 Hercules, the aircraft it is meant to replace. The concept was displayed at the American Institute of Aeronautics and Astronautics (AIAA) SciTech in January 2023.
The design incorporates partly serpentine ducting into its engine inlets. This aids in hiding the turbine fan blades and reducing the RCS. It is claimed to have at least 30% more aerodynamic efficiency than the Boeing 767 and Airbus A330 families of commercial and military aircraft, thus increased range, loiter time, and offload capabilities.
Even Lockheed Martin has also showcased its tanker based on a hybrid wing-body HWB concept designed for enhanced stealth and features an embedded engine.
Kendall, the secretary of the US Air Force, had said that having more airlifters and FRA that can survive will be important in future high-end conflicts against near-peer adversaries, especially China. Clearly, the existing stealth bomber’s design can make a great starting point for such roles.
Is Stealth Overrated
Radar-evading warplanes require careful design work, extensive testing, and exotic materials for their construction, all features that can double or triple their cost compared to conventional, non-stealthy planes, say experts. They argue that stealth is overrated and that buying cheaper, non-stealthy planes is better.
The high expense of developing, buying, and maintaining stealth jets means they may be used sparingly. Many stealth aircraft still have questionable abilities. Many long-range AAMs are difficult to carry internally in fighters.
Canard controls and aircraft external hard points are ‘stealth killers.’ Also, the cost-to-benefit ratio of stealth is still in question. If a modern air force wants to attack an adversary with significant anti-aircraft defenses, it needs an effective Suppression of Enemy Air Defences (SEAD) to avoid unacceptable losses.
A fast jet that is well armed and highly maneuverable, ‘electronic attack’ aircraft of the class of Boeing EA-18G Growler have the ability to jam across the entire spectrum. SEAD may be much cheaper than stealth. The requirement for stealth is reduced with more unmanned platforms and very long stand-off weapons. Technologies are already fast evolving to counter stealth.
At US $100 million, even a small aircraft like F-35 is not cheap. The F-22 Raptor costs nearly US $150 million. US Air Force had to shut down the F-22 assembly line after just 187 aircraft due to affordability.
All countries are developing advanced radar systems that will be able to detect these aircraft in the near future. The Russian Su-57 is known to be less stealthy and has faced technology and cost issues.
The Chinese J-20 and J-31 parallel stealth programs are shrouded in secrecy, and China was forced to purchase the expensive Russian Su-35 jet fighter. The quality of stealth on the J-20 with canard controls is being questioned.
Stealth aircraft also require high maintenance costs and time. Most stealth fleets are known to have high downtime.
Choices India
Undoubtedly, India must master stealth technology, even if it means through collaborations and joint ventures.
Accelerate the work on the Advanced Medium Combat Aircraft (AMCA). Currently, it would have to remain in two phases, a non-stealthy Mk1 and a stealthy Mk2. India must first get its numbers right with 4.5-generation fighter aircraft, LCA Mk2, and maybe additional Rafale or equivalents.
Build counter-stealth capabilities in parallel. Many game-changing technologies often get overtaken by disruptive technologies. India must concentrate first on must-do lists. Large stealth platforms would remain a watch moment for India.
- Air Marshal Anil Chopra (Retired) is an Indian Air Force veteran fighter test pilot and is currently the Director-General of the Center for Air Power Studies in New Delhi. He has been decorated with gallantry and distinguished service medals while serving in the IAF for 40 years. He tweets @Chopsyturvey
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