Search Results (6)

To enhance the survivability of armed helicopters in high-threat environments, integrated infrared (IR) suppressors are increasingly adopted to reduce thermal signatures. However, such integration significantly alters the exhaust flow field, which may in turn affect both the infrared and acoustic characteristics of the helicopter. This study investigates the aerodynamic, infrared, and acoustic impacts of an integrated IR suppressor through the comparative analysis of two helicopter configurations: a conventional design and a design equipped with an integrated IR suppressor. Full-scale models are used to analyze flow field and IR radiation characteristics, while scaled models are employed for aeroacoustic simulations. The results show that although the integrated IR suppressor increases flow resistance and reduces entrainment performance within the exhaust mixing duct, it significantly improves the thermal dissipation efficiency of the exhaust plume. The infrared radiation analysis reveals that the integrated suppressor effectively reduces radiation intensity in both the 3~5 μm and 8~14 μm bands, especially under cruise conditions where the exhaust is more efficiently cooled by ambient airflow. Equivalent radiation temperatures calculated along principal axes confirm lower IR signatures for the integrated configuration. Preliminary acoustic analyses suggest that the slit-type nozzle and integrated suppressor layout may also offer potential benefits in jet noise reduction. Overall, the integrated IR suppressor provides a clear advantage in lowering the infrared observability of armed helicopters, with acceptable aerodynamic and acoustic trade-offs. These findings offer valuable guidance for the future development of low-observable helicopter platforms. Full article

To study the electromagnetic scattering of tilt-rotor aircraft during multi-mode continuous flight, a dynamic simulation approach is presented. A time-varying mesh method is established to characterize the dynamic rotation and tilting of tilt-rotor aircraft. Shooting and bouncing rays and the uniform theory of diffraction are used to calculate the multi-mode radar cross-section (RCS). And the scattering mechanisms of tilt-rotor aircraft are investigated by extracting the micro-Doppler and inverse synthetic aperture radar images. The results show that the dynamic RCS of tilt-rotor aircraft in helicopter and airplane mode exhibits obvious periodicity, and the transition mode leads to a strong specular reflection on the rotor’s upper surface, which increases the RCS with a maximum increase of about 36 dB. The maximum micro-Doppler shift has functional relationships with flight time, tilt speed, and wave incident direction. By analyzing the change patterns of maximum shift, the real-time flight state and mode can be identified. There are some significant scattering sources on the body of tilt-rotor aircraft that are distributed in a planar or point-like manner, and the importance of different scattering sources varies in different flight modes. The pre-studies on the key scattering areas can provide effective help for the stealth design of the target. Full article

Unmanned aerial helicopters (UAHs) have been widely used recently for reconnaissance operations and other risky missions. Meanwhile, the threats to UAHs have been becoming more and more serious, mainly from radar and flights. It is essential for a UAH to select a safe flight path, as well as proper flying attitudes, to evade detection operations, and the stealth abilities of the UAH can be helpful for this. In this paper, a stealth–distance dynamic weight Deep Q-Network (SDDW-DQN) algorithm is proposed for path planning in a UAH. Additionally, the dynamic weight is applied in the reward function, which can reflect the priorities of target distance and stealth in different flight states. For the path-planning simulation, the dynamic model of UAHs and the guidance model of flight are put forward, and the stealth model of UAHs, including the radar cross-section (RCS) and the infrared radiation (IR) intensity of UAHs, is established. The simulation results show that the SDDW-DQN algorithm can be helpful in the evasion by UAHs of radar detection and flight operations, and the dynamic weight can contribute to better path-planning results. Full article

The integrated infrared suppressor can reduce the infrared radiation signal of a helicopter and is compatible with radar-acoustic stealth. However, the issues that are caused by the integrated infrared suppressor, such as temperature increases on the rear fuselage surface and a lack of shielding at the exhaust port, need to be addressed, in order to further improve the infrared stealth capability of the helicopter. Aiming at this, the effects of the ambient temperature, fuselage surface emissivity, mixing duct shielding, and exhaust port shielding on the infrared radiation characteristics of the helicopter are studied with numerical simulation. The results show that the infrared radiation intensity of the helicopter, in 3–5 μm band and 8–14 μm band, decreases by about 20% and 10%, respectively, for every 6 K reduction in the ambient temperature. As the emissivity of the rear fuselage surface reduces from 0.8 to 0.5, the helicopter’s infrared radiation intensity, in a 3–5 μm band and a 8–14 μm band, decreases by about 6% and by about 4% and 1.3%, respectively, after the mixing duct is equipped with a shielding sheath. Installing deflectors at the exhaust port of the fuselage can prevent the detection rays from detecting the high-temperature components inside the fuselage, and when the emissivity of the deflectors is reduced from 0.8 to less than 0.5, or the deflectors are cooled by more than 80 K, they begin to play a role in suppressing the infrared radiation at the bottom of the helicopter. Full article

In order to study the radar signature of a tandem helicopter in the X-band, a dynamic analysis approach (DAA) is presented to determine its radar cross-section (RCS) under different influence factors. The basic passage time, rotation speed, observation angle, rotor disk inclination, fuselage attitude angle and Doppler feature are studied and discussed in detail. The results show that the dynamic characteristics of the rotor RCS will bring significant changes to the peak and average values of the helicopter RCS. Within a given observation angle range, a larger elevation angle is undesirable for helicopter stealth. The inclination of the rotor disc will affect the many small peaks and local fluctuations of the helicopter RCS. The positively increased attitude angle will have an undesirable effect on the average RCS and dynamic characteristics of the helicopter. The DAA is feasible and effective for studying the radar cross-section of a tandem helicopter. Full article

With the continuous improvement and development of armed helicopters, the research on their stealth characteristics has become more and more in depth. In order to obtain the complex effect of stealth characteristics caused by the high-speed rotation of rotor-like components, a dynamic scattering method (DSM) is presented. Rotation speed, azimuth, elevation angle, pitching angle, and rolling angle are studied and discussed in detail. The results show that the electromagnetic scattering characteristics of the main rotor and tail rotor are dynamic and periodic. This period characteristic is related to the rotation speed and attitude angle of the rotor. The radar cross-section (RCS) of the helicopter varies greatly at different observation angles and attitude angles, but the dynamic electromagnetic scattering effect caused by the main rotor and tail rotor cannot be ignored. The presented DSM is effective and efficient for studying the dynamic RCS of the rotor-type parts of a helicopter or the whole machine. Full article