Further Reading

DF-100 Long Sword-100 - cruise missile

China on 01 October 2019 presented to the public its new DF-100 (Dongfeng-100) cruise missile among other advanced military equipment at a parade marking celebrations for the 70th anniversary of the founding of the People's Republic of China. The "Long Sword" 100 cruise missile team in the military parade, the launch vehicle uses two joint launch boxes. Little is known about the weapon that is speculated to be a replacement for the PLA's current CJ-10 cruise missile which has an estimated range of about 1,500 kilometers (930 miles). The CJ-100s are "characterized by a long range, high precision and quick responsiveness and are the latest addition to the CJ missile series," Xinhua reported.

It was displayed in the launching box, and the model had been rarely heard of. The military parade said that the supersonic cruise missile debuted with high precision, long range and fast response speed. It is the latest model of the "Long Sword" series, and it is also the first time in the world. As we all know, long-range cruise missiles generally use high subsonic speeds in order to balance the range, such as the famous US "Tomahawk" cruise missiles, as well as China's previous "long sword"10.

The news about the development of supersonic cruise missiles in China has been circulating for a long time, basically staying in the foreign trade products of the industrial sector. For example, the CX-1 foreign trade supersonic cruise missile. However, there was no news that the military was equipped with such weapons. Until September 25, 2019, a few days before the military parade, the Rocket Army’s Weibo issued a video clip to confirm that the military had already equipped the supersonic cruise missile. This short video shows the slender dorsal fins, propellant and collapsible tail fins, which have traditionally helped missiles fly at speeds above sonic speeds and achieve long range operations. The video shows a missile like a supersonic aerodynamic shape in a series of known rockets including the "Sword" 10, using a multi-package launcher like the "Long Sword" 10 cruise missile. And the use of near-vertical launch, if not the rocket army's promotional video, it is easy to think of it as an air defense missile weapon. The video shows the slender back fins of the missile, the propeller and the collapsible tail, and even the rectangular abdomen inlet.

It is estimated that the missile may adopt a cruise flight mode, so it is speculated that its range is more than 1 000 kilometers, which is consistent with the fact that it is arranged in the strategic strike module. This approach to supersonic flight in the adjacent space at an altitude of 20 to 100 kilometers can enhance the missile's penetration capability and avoid interception of the missile defense system. Although the target of the cruise missile is small, it can easily be intercepted by subsonic flight. Ground-based anti-aircraft guns and shoulder-mounted anti-aircraft missiles can be aimed at, so in the Syrian battlefield, government forces often intercept cruise missiles launched by the United States or Israel. This is the case with small countries, and it is even more difficult for big powers to intercept cruise missiles. Therefore, major powers are developing supersonic cruise missiles.

Inlet integration in supersonic cruise missile propulsion systems using gas-turbine engines is a significant challenge due to the broad operating speed range from subsonic to Mach 4. The additional requirements for light-weight, low-cost, and compactness due to launcher-imposed size constraints conflict with the need for high efficiency and low-drag which further exacerbates the difficulty in system design. Lower drag and higher efficiency benefits mission effectiveness through greater payload weight, longer range or higher speed.

An inlet needs to supply an airflow rate equal to or greater than that required by the engine. The excess flow must be either bypassed via a duct leading to the engine exhaust nozzle or through overboard exits, or spilled around the inlet cowl. Drag forces arise from the failure to employ the potentially captured flow to produce thrust from the engine. The state-of-the-art approach to supersonic missile inlet design usually involves a fixed-geometry design sized for the maximum capture area requirement set by the engine, and efficiency (total pressure recovery) optimized for the most critical thrust operating point. Certain variable geometry axisymmetric inlet concepts use either a translating or expanding centerbody. Alternative concepts include opening annular slots or other air inlet apertures to change the internal area contraction ratio for inlet "start" conditions.

Significant drag and efficiency penalties result at off-design flight conditions with fixed geometry inlets compared to what may be obtained with a variable geometry inlet. Excess air flow is usually bypassed around the engine with a drag penalty due to air flow energy loss associated with the inlet terminal normal shock and duct friction. Inlet internal contraction ratio, defined as the open area of the inlet divided by the area of the inlet throat, is limited by the ability to "start" at a certain Mach number. "Starting" can be defined as a stable condition in which the flow is supersonic at the cowl inlet lip and the terminal normal shock wave is located downstream of the inlet throat (i.e., the minimum cross-sectional area of the inlet duct).

An inlet has a limited internal contraction ratio at a given flight Mach number to allow self-start. Once started, the internal contraction ratio can be increased to a higher value. Increased internal contraction ratio results in a lower cowl angle (the angle of the interior and exterior surfaces of the inlet cowl relative to the horizontal) which decreases drag or increases efficiency for a given cowl angle.

Variable geometry inlet concepts use a mechanism that is relatively heavy, costly, complex and occupies significant volume. Such variable geometry inlets have high actuation forces which require bulky and expensive actuators. Such inlets also typically have trailing surfaces aft of the point of maximum diameter to provide a continuous surface with added associated weight and volume.

Two-dimensional inlet configurations have been provided for achieving the desired design efficiencies. However, some air vehicle concepts may require semi-cylindrical "chin" or "eyebrow" or full cylindrical axisymmetric inlets due to launcher interface dimensional constraints, or requirements for lower weight or drag.