Stability/Control Augmentation System (S/CAS) is widely recognized as a basic framework of flight controllers, and its usefulness has been well established. In general, SAS is composed of a proportional controller using attitude rate signals, and CAS is composed of a proportional-integral controller using the errors between attitude/attitude rate/acceleration commands and their current values; that is, S/CAS is a kind of a PID controller with the input signal to the derivative controller being set as the attitude rate signals. The interpretation of PID gains, i.e. appropriateness of PID gains, is very easy since PID gains are directly related to their control actions. On the other hand, due to this too much simplified structure, it is hard to implement another function to PID controllers. In this paper, we propose a novel S/CAS which has the ability to estimate some of plant states in addition to the original control function of improving the stability and the controllability, and we also propose its design method in terms of tractable LMI conditions.

This paper investigates the flight performance of a compound helicopter with varying gross weight and advance ratio through high-fidelity CFD simulations. The compound helicopter configuration studied here consists of a single main rotor used on UH-60A helicopter and a wing-body designed by JAXA (Japan Aerospace Exploration Agency) as the conceptual model of a compound helicopter. The empennage, anti-torque rotor and other details are omitted for simplicity. The gross weight changes from 60% to 110% of the maximum gross weight of UH-60A. The advance ratio varies from 0.1 to 0.8. As the results, the net effective lift to drag ratio of the aircraft decreases rapidly at high advance ratios and overweight (110%) because of increasing magnitude of aerodynamic interaction between the main rotor and the wing-body. The collective pitch and longitudinal cyclic pitch angles are also influenced significantly as the gross weight increases. When the gross weight is 1.1 times of that of the UH-60A, the net required power increases to 1.3 times compared to the net required power when the rotor/wing-body aerodynamic interaction is not considered.

This paper proposes a methodology to autonomously design wiring and piping routes for aircraft systems within a given airframe, by the use of a Physarum-inspired algorithm. The methodology is expected to enable an efficient estimation of characteristics dependent on the actual wiring and piping routes, such as system weight and pressure loss, at early stages of aircraft design. An experiment was conducted to validate the methodology against a design problem to route hydraulic pipes for a triple-redundant hydraulic system within an airframe model based on an actual aircraft. Results of the experiment display the capability of the methodology to produce short routing patterns with reduced overlap between redundant systems, and increased survivability against particular events such as rotor burst. Possible applications and limitations are further discussed.

For Electric Vertical Take-Off and Landing (eVTOL) aircraft, aerodynamic efficiency and noise are two of the most important performance indices. A single coaxial rotor and quad coaxial rotors are studied from these two viewpoints. A coaxial rotor has larger efficiency such as Figure of Merit at hover and equivalent lift-to-drag ratio in forward flight than a single rotor. However, the noise generated from the coaxial rotor is higher than that from the single rotor mainly due to the interaction between the upper and lower rotors. Quad coaxial rotors have smaller efficiency than an isolated coaxial rotor because of the interaction between the rotors. However, the noise generated from the quad coaxial rotors is lower than the simple sum-up of four single units of coaxial rotors with no interference between them.

Advancements in uncrewed aircraft technologies, in particular small drones, are soon going to enable simultaneous operations of crewed and uncrewed vehicles in disaster response missions. Such operations are envisioned to be segregated spatially to achieve both safety and efficiency. The feasibility of such segregation relies, however, on accurate pre-flight modeling of reference trajectories for all airspace users. This study focuses on manned helicopter visual flight rules operations, in particular reconnaissance missions, and uses recorded flight experimental data to develop a reference trajectory model. The model development is divided into two stages-- first, the landmark geometry and typical flight characteristics are used to obtain the initial trajectory. Second, the initial trajectory is tuned based on recorded flight data analysis to obtain more accurate reference trajectories, focusing on the average lateral deviation. The method proposed in this paper enables the modeling of a reference trajectory with consistently high accuracy by primarily excluding the impact of uncertainty stemming from pilot subjectivity.