This chapter is dedicated to present the principles that constitute the fundamentals of helicopter flight physics, starting from the basics of the main rotor aerodynamics and of the component parts related to flight control. The chapter opens with a short history of helicopter development, taking the date of 13th November 1907 for a reference point; this is the date when the first helicopter flight occurred, having the French man, Paul Cornu, for a pilot. The main constructive solutions for helicopters are presented and the basic equations of fluid mechanics are applied on a helicopter model with one main rotor and tail rotor. Helicopter hovering, vertical flight, and forward flight are approached, too, one by one. Furthermore, the ground effect, autorotation, stability, and helicopter control are focused on. At the end of the chapter, the main factors that determine the helicopter performances are mentioned.

This paper presents the results from an experimental study of the aerodynamic performance and efficiency of a model helicopter rotor in steady hover at Reynolds numbers below 70000. Results are shown for a two-, three- and four-bladed rotor configuration for various pitch angles and speeds of rotation. The influence of the rotor solidity on the aerodynamic efficiency in terms of the Figure of Merit is highlighted. The profile drag component is evaluated as a function of the Reynolds number. The internal friction losses of the test stand are estimated and taken into account in all measurements. A brief description of the designed test stand is provided. The experimental setup allows for the measurement of thrust and torque of helicopter rotors with diameters of up to 1 meter, for pitch angles varying from -12° to +24° and for rotational speeds of up to 3000 RPM. Conclusions are drawn about the aerodynamic performance and efficiency of the studied rotor configurations. This experimental study provided a significant database, which will serve for validation purposes.

Experimental studies of a helicopter rotor in ground effect aim to quantify the effect of the ground proximity on their performance. As a result of the performed experimental work, dependencies between the produced thrust (T) and torque (Q), varying the rotor’s distance to the ground (H) and blade pitching angle (8) are drawn from one perspective, and the correlations between the generated thrust (T) and torque (Q), and their corresponding coefficients C_T and C_Q, varying the distance to the ground (H) and blade pitching angle (8) at several fixed rotational frequencies (n). Additionally, a dependency between the generated relative thrust coefficients (C_TIGE/C_TOGE) against the relative distance to the ground (H/D) at a fixed rotational frequency of 750 RPM, varying the blade inclination angle (8) is also derived and presented in this study. In summary, the research successfully quantified the effect of the rotor’s static characteristics in the ground effect zone and posed topics for further research.

This article presents a comparative study of three numerical algorithms for computation of the flow-field of a rotor in hover and the net static thrust that is produced. The flow-field is induced by a series of vortex rings, modelling the near wake of the hovering rotor and a single semi-infinite vortex cylinder, accounting for the velocity deficit in the far wake. All three models are based on the vortex theory and differ in the choice of the numerical scheme for the estimation of the exact position of the vortex rings, emitted at the tips of the blades of the rotor. Thus, the numerical models perform a real-time simulation of the propagation of the vortex rings in the downwash. The first model uses an Euler-predictor scheme, while the second and third models use respectively first and second order predictor-corrector schemes. The aim of the study is to assess the rapidity and accuracy of each algorithm. For that purpose, the numerical results are compared with the experimental data, obtained from a wind tunnel test of the model rotor. The best results in terms of computational speed and accuracy are obtained with the use of Adams-Bashforth predictor-corrector scheme of second order.

Satellite swarm operations require robust methodologies to distinguish between leader-induced reference frame biases (global errors) and individual follower anomalies (local deviations). This is the challenge of distributed fault diagnosis. In leader–follower topologies, distinguishing between a global reference error (leader satellite broadcasting incorrect navigation data) and a local node error (follower satellite drifting) is mathematically ambiguous when we use standard methods. Even recent unsupervised frameworks, such as Model-Guided Online Transfer Learning (MGOTL), that excel at single-satellite component diagnosis, suffer from adaptation and signal bleed when they are applied directly to distributed topologies. Therefore, we propose the Isolation-First Consensus Anomaly Detection (IF-CAD) framework for Decoupling Global and Local Faults in Satellite Swarms. We introduce a Smart Freeze mechanism to prevent the learning of persistent faults and a hierarchical logic that prioritizes local isolation over global agreement. The IF-CAD framework successfully decouples global leader faults from local follower faults. Fault detection remains stable even during long-duration anomalies.