Lecture Notes in Rotorcraft Engineering

This chapter introduces the reader to the aerodynamic aspects of rotary wings. It is written as an introduction for aspiring students, not as a replacement of well-known texts used for rotorcraft classes at University level. It should be used as a first read what is a very complex but fascinating topic in rotorcraft. This chapter illustrates the aerodynamic environment of the rotor, the rotorcraft blade sections and their features, modern aerofoil developments, advanced blade tip designs and advanced rotor design methods. While studying this chapter, one should keep in mind that aerodynamics means different things to different people. When looking at pilot training, the lines between aerodynamics, performance, and aircraft handling are blurred. The technical literature on rotorcraft aerodynamics is dominated by the rotor, but there is a volume of work on fuselage drag as well.

Experimental techniques for aerodynamics have been essential tools for the development of rotorcraft. This includes wind tunnel, water tank testing, and flight testing. Rotor flows are rich in their physical complexity, and consequently an awareness of range of experimental methods is required. The chapter contains an introduction to wind tunnels, followed by a description of important experimental techniques, such as flow visualisation, pressure measurements, force and moment measurements, thermal anemometry and instrument calibration. Their performance and relative merits are discussed. Results are presented include forces and moments on a rotor, dynamic stall, particle-image velocimetry of a vortex ring state, and more.

This chapter introduces rotorcraft engines. the discussion is largely limited to gas turbine engines that dominate the field of modern helicopters. The Chapter is split into four main parts: (1) rotorcraft power plants and power trains; (2) engine ratings (with certification requirements); (3) performance envelopes; (4) intake protection systems. Rotorcraft engines are seldom treated as part of core rotorcraft engineering, since they are considered an element of propulsion; thus, they are associated to a different discipline. In this Chapter we demonstrate that there are peculiarities in this type of engines. Their integration into the airframe via transmission systems, rotor head, intake separators is unlike any fixed-wing vehicle.

This chapter introduces rotorcraft steady-state flight performance and stability, and we explain key concepts of the conventional helicopter as well as other rotorcraft types (tandem helicopter and compounds). Numerical models of performance estimations are provided for level flight, climb-out, and descent. Stability issues presented include longitudinal/lateral trim and speed stability. Different take-off procedures are illustrated, alongside the certification requirements (Category A and B rotorcraft). There is further discussion of ground effects, such as lift augmentation and ground resonance. We provide examples of methods used to estimate the direct operating costs, which are one of the major limiters to the use of rotorcraft. We complete the performance analysis with fuel planning methods, payload-range assessment, and speed augmentation concepts (compound helicopters).

This chapter explores several aspects of the tiltrotor configuration and covers challenges in their design, modelling and simulation. An overview of the aircraft is first given that details the operational role this configuration aims to fulfil and summaries the amalgamation of a rotary-wing and fixed-wing aircraft into a single flight vehicle. Two important challenges of the tiltrotor configuration are then examined: the interactional effects of the aircraft through different phases of flight; and the undetermined control problem arising from the existence of both rotary-wing and fixed-wing controls. The tiltrotor aeromechanics are then introduced to give an outline of the required modelling and simulation elements of the different aircraft components through their extensive flight envelope. Finally, a numerical example is presented to better understand the transitional regime of flight in terms of aircraft performance and trim behaviour.

This chapter explores selected aspects of rotor acoustics. With increasingly stringent certification requirements, this field is becoming steadily more important in the design of rotorcraft. In this chapter, we discuss the importance of studying rotorcraft acoustics and the process used by regulators to evaluate their noise emissions. We then introduce the various noise sources and their importance in relation to the vehicle’s total noise emissions. We proceed by introducing Lighthill’s acoustic analogy and subsequently the Ffowcs Williams and Hawkings equation. Based on these, we describe a number of approaches to estimate the contributions of the various noise sources. We describe the implementation of an acoustic code and accompany with sample MATLAB scripts to evaluate the thickness and loading sources of an arbitrary rotor. We conclude the chapter by looking at a range of methods to reduce rotorcraft noise sources and discuss the future outlook for rotorcraft acoustics.

This chapter provides an overview of flight control systems for rotorcraft at an introductory level. There exist many rotorcraft configurations, however, we will focus our attention on conventional helicopters to provide a fundamental understanding. We will cover standard and advanced control design methods to design and validate flight control algorithms for both stability augmentation and autopilot systems. We will touch on some essential elements of feedback control theory before showing how the design methods are implemented. A key characteristic of the discussed design methods is that they are suitable for multivariable systems, which offer advantages for minimising key helicopter dynamic couplings. The control design methods also offer improved robustness properties leading to flight envelope protection characteristics. We will cover key metrics to assess the robustness and performance properties of the flight control laws from a control theory approach. These control laws form the basis for the assessment of the flight control laws in terms of handling qualities.

This chapter introduces conceptual and preliminary design concepts for a conventional helicopter. The subject of rotorcraft design is too vast to the presented in a single book chapter, and thus we limit the presentation to a few key design aspects, as discussed in our lecture series. We provide a top level discussion of the multi-disciplinary team-work required, including analysis of design requirements, costs, risks and compliance. The design consists of a main rotor system and the associated tail rotor, both of which require sizing, with determination of the number of blades, rotor solidity and angular speeds. We discuss concepts for rotor blade design, which is essential in reducing shaft power, improving overall rotor performance, limit vibrations and noise. Concepts are shown for fuselage sizing, including assessment of aerodynamic drag We discuss items such as the empennage (horizontal and vertical stabilisers) and the landing gear.