Overview

Mission analysis refers to the complete set of assumptions regarding the operation of an aircraft and the resulting weight and fuel planning. Several parametric considerations can be added, including mission optimisation, environmental emissions and various commercial ormilitary trade-offs. This chapter illustrates how a detailed mission analysis can be carried out. We start by defining mission scenarios (§ 15.1) and the payload-range charts (§ 15.2). We then make a detailed qualitative and quantitative mission analysis (§ 15.3), including the problems of mission range and mission fuel (§ 15.4), the fuel-reserve policies (§ 15.5) and the short-range performance at MTOW(§ 15.6). In § 15.7 we discuss more advanced problems, such as service with an intermediate stop (§ 15.7.1), tankering (§ 15.7.2) and the point-of-no-return (§ 15.7.3).We proceed with the calculation of the direct operating costs (§ 15.8).We show some case studies: an aircraft selection problem (§ 15.9), a fuel mission planning for a transport aircraft (§ 15.10) and the effect of floats on the payload-range chart of a propeller airplane adapted with floats for water operations (§ 15.11). We close this chapter with an introduction to risk analysis in aircraft performance (§ 15.12).

KEY CONCEPTS: Mission Profiles, Flight Scheduling, Payload-Range Charts, Mission Analysis, Reserve Fuel, Fuel Planning, Tankering, En-Route Stop, Direct Operating Costs, Risk Analysis, Route Selection.

Mission Profiles

A mission profile is a scenario that is required to establish the weight, fuel, payload, range, speed, flight altitude, loiter and any other operations that the aircraft must be able to accomplish. The mission requirements are specific to the type of aircraft.

Overview

In this chapter we present a basic analysis for three key gas-turbine engine architectures: high by-pass turbofan, turboshaft and low by-pass turbojet with thrust augmentation. We consider general gas turbine engine architecture (§ 5.1), the thrust and power ratings (§ 5.2), the turbofan model (§ 5.3), the turboprop engine (§ 5.4) and the low by-pass engine model (§ 5.5).We briefly mention the methods of generalised engine performance (§ 5.6). We finally discuss the role of the auxiliary power unit (§ 5.7). An important aspect of the presentation is the strategy for the determination of the design point of the engine in absence of reliable data. In all cases we discuss the calculation of the engine state as a function of the main operational parameters.

KEY CONCEPTS: Gas Turbine Engines, Thrust/Power Ratings, Engine Derating, Turbofan Engines, Engine Design Point, Engine Simulation, Rubber Engines, Effects of Contamination, Turboprop Engines, Turbojet Engines, Auxiliary Power Units.

Gas Turbine Engines

The term gas turbine is associated with a jet engine consisting of a compressor, a combustion chamber, a turbine and an exhaust nozzle, although the name refers to both jet-thrust engines and shaft-power engines. The main types of gas turbine engines are the turbojet, the turbofan and the turboprop. The gas turbine is the core of the engine. However, there are other parts whose function is essential (inlet, fuel lines, fuel nozzles, sensors, collectors, thrust reverser).

Overview

In this chapter, we present methods for the determination of the geometrical configuration of a modern transport aircraft (§ 2.1). We use the concept of control points and geometric wire-frames (§ 2.2). Thus, we establish a framework for the determination of linear dimensions, position of centroids, reference areas and volumes. The methods shows are valid for any other type of aircraft. We use a stochastic approach for more complex surfaces (§ 2.2.1). Section 2.3 deals with the geometry of the lifting surfaces. We then show a method for the determination of the wetted areas (§ 2.4), aircraft volumes (§ 2.5), including the wing tanks, and the mean aerodynamic chord (§ 2.6). We produce a few examples of verification of aircraft configurations (§ 2.7). Finally, we define some reference systems on the aircraft (§ 2.8).

KEY CONCEPTS: Transport Aircraft, Geometry Definition, Wetted Areas, Aircraft Volumes, Fuel Tanks, Mean Aerodynamic Chord, Reference Systems.

Model for Transport Aircraft

The aircraft geometry represents the basis of all of the aerodynamic calculations, fuel and payload capacity, centre of gravity position, stability and control requirements. The construction of an accurate aircraft model is done in a number of steps that require the choice of reference systems, the determination of the key sub-systems, and an assembly procedure to determine the geometric relationships between parts of the vehicle. Various reference systems are introduced to define geometrical relationships and operational conditions in flight. The procedures shown in this chapter are required to calculate reference areas, reference lengths and reference positions for a wide variety of calculations.

Overview

This chapter deals with flight envelopes in the speed-altitude space. We present various atmospheric models (§ 8.1), standard as well as non-standard. We give several operating air speed definitions (§ 8.2), as well as design speeds (§ 8.3) and the techniques required to measure them. For the steady-state level flight we derive two optimal conditions: minimum drag and minimum power (§ 8.4). We discuss the flight corridors at constant altitude and the ceiling performance airplanes (§ 8.5). We discuss the flight envelopes of subsonic transport aircraft and their limitations (§ 8.6), including the effects of the cabin pressure. We conclude the chapter with flight envelopes at supersonic Mach number (§ 8.7), including dash speed, supersonic accelerations and propulsion limitations.

KEY CONCEPTS: International Standard Atmosphere, Atmosphere Models, Operating Speeds (EAS, CAS, TAS), Transition Altitude, Design Speeds, Optimum Level Speeds, Ceiling Performance, Cabin Pressure, Flight Envelopes, Supersonic Dash, Supersonic Acceleration.

The Atmosphere

Most performance calculations are done with a conventional atmosphere that has been declared standard (§ 8.1.1), although the almost totality of flights take place in far more complex atmospheres, with variation in the thermodynamic properties in both the vertical and horizontal directions. To overcome the limitations of the standard model, alternative atmosphere models are available to take into account extreme temperatures (very hot and very cold), as explained in § 8.1.2. The effect of air humidity is generally neglected in aerodynamics and engine performance, although it is important for other aspects, such as noise propagation.

Overview

The subject of aircraft noise is too vast to be covered in a single chapter; thus, we focus on those issues that are required for a low-order simulation of aircraft noise emission and propagation. The chapter is organised as follows: We first discuss the importance of the subject (§ 16.1) and introduce basic definitions that are used to characterise aircraft noise (§ 16.2). We then establish the framework for the development of an aircraft-noise program that is synchronised with the flight mechanics (§ 16.3). The sources of noise are split into propulsive (§ 16.4) and non-propulsive components (§ 16.6). We include a discussion of the APU noise as a separate item (§ 16.5). The propeller-noise model (§ 16.7) is discussed in isolation from airframe and engines. Chapter 17 deals with propagation effects. Chapter 18 deals with noise trajectories.

KEY CONCEPTS: Sound, Noise Metrics, Engine Noise, Airframe Noise, Propeller Noise, APU Noise, Aircraft-Noise Model.

Introduction

In the beginning there was silence, or so the story goes. Then came human activities and jet engines. This is when the noise started to hurt. Low-flying aircraft cause nasty physiological effects and are bad for your well-being. To be fair, noise pollution is just one of many environmental issues that face the aviation industry; it is part of the larger context of local air quality, combustion emissions, environmental compatibility, policies and regulations and public health.

Overview

The descent deals with that segment of the flight when the airplane decreases its flight altitude in a controlled mode. Landing still requires good pilot skills, which are best appreciated in bad weather conditions. The descent can be a large portion of the stage length, reaching in excess of 100 n-miles. Several distinct phases are identified. We will consider separately the phase of en-route descent down to 1,500 feet altitude above the airfield (§ 11.1) and the final approach down to ˜50 feet above the airfield (§ 11.2).We also discuss two unconventional flight procedures: the continuous descent approach (§ 11.3), which has some advantages in terms of fuel consumption and noise emissions, and the steep-descent approach, which is a more complex manoeuvre (§ 11.4). We analyse the case of airplanes placed on holding stacks (§ 11.6) and optimal performance issues. Landing consists of an airborne phase and a landing run (§ 11.7). Effects of side gusts are considered, including crab landing and wing strike. This chapter ends with considerations of go-around trajectories, which are associated to aborted landing (§ 11.8).

KEY CONCEPTS: En-Route Descent, Continuous Descent Approach, Steep Descent, Unpowered Descent, Holding Procedure, Landing Performance, Crab Landing, Go-Around.

En-Route Descent

The aircraft starts descending from its cruise altitude well ahead of its destination. The flight computer will indicate the distance to the airfield and the estimated en-route descent, that is, the distance and time to landing, based on a number of factors, including speed, altitude and winds.

Overview

Noise propagation involves all of the physical events that take place between the noise source and the receiver. Due to the relatively large distance between source and receiver (from a minimum of ∼100 m to several kilometers), atmospheric absorption is particularly important – no less important than the determination of the noise sources themselves. If propagation takes place over an unbounded medium, the use of the atmospheric absorption model would be sufficient to estimate the effect at the receiver. However, there are cases where the topography of the terrain and the short distance between the airplane and the ground cause effects such as reflection and scattering to become important. We begin by considering briefly the airframe noise shielding (§ 17.1); we continue with the standard absorption model in the atmosphere (§ 17.2). We describe ground-reflection problems in § 17.3. We finally discuss the combination of wind shear and temperature gradients in the propagation of aircraft noise over long distances (§ 17.4).

KEY CONCEPTS: Airframe Noise Shielding, Wing Scattering, Ground Effect, Atmospheric Absorption, Wind Effects, Turbulence Effects.

Airframe Noise Shielding

A number of interference effects take place around the airframe due to the reciprocal position between noise sources and solid surfaces. The effect is frequency-dependent. The investigation of new blended airframes, which actually benefit from the noise shielding, has increased the interest in this acoustic effect.

One method is called the equivalent source method, which uses a finite number of sources to satisfy the boundary condition on the airframe to simulate the acoustic scattering.

Overview

Aircraft propulsion by propeller is still the most widespread method of converting engine power into useful thrust. We seek the propeller parameters required to deliver specified thrust or power to the airplane (§ 6.1), depending on the flight condition. The simplest method for calculating the propulsive performance is the axial momentum theory (§ 6.2.1), which is useful when detailed data of the propeller itself are unknown. When detailed data are available, the combined momentum and blade element theory (§ 6.2.2), along with ancillary models for transonic flow, offers a powerful and accurate method for propeller analysis. The integration of the propeller with the flight mechanics is discussed in § 6.3. We show that when we trim to a specified thrust or power, the propeller generally does not operate at its most efficient point.

KEY CONCEPTS: Propeller Parameters, Propulsion Models, Momentum Theory, Blade Element Method, Flight Mechanics Integration, Propeller Installation.

Propeller Definitions

The basic parameters used in the analysis of the propeller are the forward speed U, the rotational speed rpm and the tip Mach number Mtip. In addition, there are several geometrical quantities: the number of blades, the diameter d, the pitch ϑ, the type of blade section, the chord distribution, the tip geometry and the hub geometry.

The pitch is a measure of the orientation of the propeller on a plane normal to the axis of rotation, as shown in Figure 6.1.

Overview

This chapter deals with basic airplane manoeuvres, including flight in the vertical plane and in the horizontal plane. After an introductory description of these manoeuvres (§ 13.1), we start with powered turns (§ 13.2) and unpowered turns (§ 13.3); the latter turn essentially refers to glider-type vehicles, including soaring flight. Next, we introduce the manoeuvre envelope of the airplane (§ 13.4) and discuss pilot-related issues, such as sustainable g-loads. Roll performance (§ 13.5) is one example of manoeuvre on a straight line by a high-performance aircraft, and pull-up (§ 13.6) is one example of flight path in the vertical plane. Finally, we discuss aircraft flight in a downburst (§ 13.7).

KEY CONCEPTS: Powered Turns, Banked Turns, Minimum-Fuel Turn, Turn Rates, Cornering Speeds, Unpowered Turns, Manoeuvre Envelopes, V-n Diagram, Sustainable g-Loads, Roll Performance, Pull-Up Manoeuvre, Downbursts.

Introduction

The term manoeuvre refers to any change of the flight path. There are at least three basic types of manoeuvres: 1) a turn in the horizontal plane, when the aircraft changes heading and banks on one side (lateral manoeuvre); 2) a turn in a vertical plane, when the aircraft increases or decreases its altitude (pull-up and pull-out); and 3) a roll around the aircraft's longitudinal axis, when the aircraft rotates around itself whilst following a straight flight path (longitudinal manoeuvre).Many complex manoeuvres can be reduced to a combination of these.

During a turn on the horizontal plane, the aircraft gradually changes its banking angle from zero to a maximum and then back to zero.

Overview

The aircraft climb includes a variety of flight problems in which the airplane usually (not always) gains altitude. We define the general governing equations for flight in the vertical plane and thence some closed-form solutions for the propeller and jet airplane (§ 10.2). We then present the general problem of climb by a transport aircraft and show numerical solutions for both types of airplanes (§ 10.3), including the case of one engine inoperative (§ 10.3.6). The case of the turboprop aircraft is discussed in § 10.4. A powerful method for dealing with aircraft climb, particularly at transonic and supersonic Mach numbers, is the total energy approach (§ 10.5). There is a wide range of climb problems addressed with the energy methods. We report a few of these cases in § 10.6.

Accelerated climb problems are exclusively the domain of numerical solutions. Some of these methods are mathematically involved and will not be discussed in sufficient detail. The assumption of quasi steady flight is valid for many conventional aircraft.

KEY CONCEPTS: Closed-Form Solutions, Climb to Initial Altitude, Energy Method, Specific Excess Power, Optimal Climb, Climb Trajectories.

Introduction

There are two methods for solving climb problems: by solution of the differential equations that govern the motion of the centre of gravity and by the use of energy methods. There is a difference in the climb characteristics of propeller- and jet driven aircraft.

Overview

In Chapter 16 we discussed various methods that can be used for the rapid prediction of aircraft-noise sources. In Chapter 17 we described the effects of atmospheric propagation, interference and scattering. In this chapter we deal with aircraft-noise trajectories. In particular, we discuss noise certification (§ 18.1) and noise-abatement procedures (§ 18.2). The implementation of the various sub-models requires a flight mechanics integration (§ 18.3) and a data-handling structure, to process the large matrices produced by several noise sources. A noise sensitivity analysis is presented (§ 18.4) to show the relative importance of the various noise sources to explain the most useful strategies for noise reduction. We discuss two case studies: the ICAO/FAR noise trajectories of a jet-powered aircraft (§ 18.5) and the ICAO/FAR noise trajectories of a turboprop aircraft (§ 18.6). We also present a number of noise applications, such as steep descent and wind effects (§ 18.7). To complete our discussion of the noise modelling, we provide an example of verification with flight data (§ 18.8). The last item of investigation is the noise footprint around the airfield (§ 18.9).

KEY CONCEPTS: Aircraft Noise Certification, Noise-Abatement Procedures, Flight- Mechanics Integration, Noise Sensitivity, Noise Trajectories, Wind Effects, Footprints, Sonic Boom.

Aircraft Noise Certification

Unlike a Beethoven symphony, aircraft noise is not welcome music to the ear. The second movement of the Ninth Symphony does not start with a landing-gear deployment. Communities that live near large airports know this fact rather well. In fact, they have been making noise on their own by voicing their concern.

Overview

This chapter deals with a realistic model of the aircraft at take-off conditions. After an introduction to general take-off procedures, we deal with transport-type airplanes (§ 9.1) and write the general take-off equations (§ 9.2).We carry out numerical solutions with all-engines operating §9.3 and consider the case of one-engine inoperative, both accelerate-and-go and abort-and-stop (§ 9.4). The takeoff of a turboprop aircraft is solved in §9.5. Lateral control issues in both cases are dealt with in the analysis of the minimum control speed (§ 9.6). We discuss the important cases of aircraft braking (§ 9.7) and performance on contaminated runways (§ 9.8), including extreme cases such as hydroplaning and other forms of contamination. For the sake of completeness, we present more rapid closed-form solutions (§ 9.9). The chapter ends with considerations on field performance, including taxiing and turning (§ 9.10) and the effects of bird strike (§ 9.10.2).

KEY CONCEPTS: Take-Off Equations, Normal Take-Off, OEI Take-Off, Balanced Field Length, Decelerate-Stop, Accelerate-Go, Minimum Control Speed, Contaminated Runways, Ground Manoeuvring, Bird Strike.

Take-Off of Transport-Type Airplane

The take-off phase is dependent on a vast array of aircraft parameters and external circumstances – including the pilot's skills. Take-off lasts little time and burns a considerable amount of fuel.

There are several different types of aircraft take-off and landing. We will refer exclusively to Conventional Take-Off and Landing (CTOL). This class includes most civil, commercial and military vehicles, that is, subsonic jet transport, turboprop airplanes, and cargo airplanes that take off and land horizontally.

Overview

The previous chapters have shown several aspects of environmental performance, including aircraft noise and carbon emissions. This chapter elaborates further on the impact of aviation. We discuss the effects of commercial aviation on the formation of condensation trails (§ 19.1) and possible methods for mitigation, including altitude flexibility. We discuss briefly the controversial issue of radiative forcing of various forms of pollution (§ 19.2) and a method for calculating the landing and takeoff emissions (§ 19.3). We show a case study for a transport aircraft to illustrate key parametric effects on carbon-dioxide emissions (§ 19.4). We then propose an example of “perfect flight” (§ 19.5), that is, a flight that is not constrained by air traffic regulations. One of the key aspects that is due to dominate emissions (the trading scheme) is briefly reviewed in § 19.6.

This chapter does not attempt to enter the debate of environmental performance and its relationship with the climate change, as many stakeholders and interdependencies are involved. Furthermore, these deeper issues now overlap those of atmospheric physics, biochemistry and policy-making, which are beyond our context.

KEY CONCEPTS: Aircraft Contrails, Contrail Factor, Radiative Forcing, Altitude Flexibility, Carbon Emissions, LTO Emissions, Emissions Trading, Perfect Flight.

Aircraft Contrails

The blue skies! – What a rare pleasure at our latitudes. One cold afternoon, a clearing in the clouds brings crispy skies. The air traffic, which is normally invisible above the clouds, reveals the full scale of its impact, as shown in Figure 19.1.

Overview

This chapter deals with thermodynamic and structural models of various aircraft sub-systems. Two main aero-thermodynamic problems are discussed: cold-weather operation (§ 14.1), including aircraft icing (§ 14.1.1), and fuel temperature in the aircraft tanks (§ 14.3 and § 14.4). Basic characteristics of aircraft fuels are discussed in § 14.2. A lumped-mass model for thermo-structural performance of aircraft tyres is presented in § 14.5 and aims at the rapid prediction of tyre temperatures. This is useful at high speeds, heavy aircraft and rejected take-off. The final problem is that of jet blast (§ 14.6), which is of relevance during ground operations, for safety of infrastructure and ground personnel.

KEY CONCEPTS: Cold-Weather Operations, Aircraft Icing, Aviation Fuels, Fuel Temperature, Tyre Heating, Jet Blast.

Cold-Weather Operations

Cold-weather operations cause a number of problems on the ground, at take-off, at landing and in flight. There are a variety of issues of relevance, including icing, in flight ice protection, de-icing on the ground, fuel characteristics at low temperatures and aircraft performance on contaminated runways (including breaking performance, precipitation drag, aquaplaning).We will not deal with ice protection, de-icing and the atmospheric causes of icing because they are beyond the scope of flight performance. Our presentation will focus on icing effects on performance characteristics.

The problem of aircraft icing is exemplified by a number of fatal crashes that over the years have plagued commercial aviation. Aircraft icing has its beginning in World War II, with bombers flying at high altitudes and at all-weather conditions.

The Gulfstream G-550 is a long-range business/executive jet powered by two Rolls-Royce BR710 turbofan engines. It has advanced cockpit avionics (see Figure 1.1) and a variety of seating configurations. The G-550 is a transport-type airplane, certified for day and night, extended over-water and polar navigation. A few examples of calculations are shown throughout the book (see, for example, the SAR analysis in §12.3.1 and the payload-range in § 15.2).

A summary of weights, capacity and limitations is given in TableA.1.Asummary of geometrical dimensions is given in TableA.2. The wing is swept back 27 degrees at the quarter-chord location, with a 3-degree dihedral, and with a tip-mounted upper winglet. The wing does not have a leading-edge slat. The main flight controls are a single Fowler-type flap, ailerons and trim tabs. There are three spoilers per side. There are some drag-reduction devices, such as vortex generators that wrap around the winglet junction, vortex generators on the upper side of the wing and blunt trailing edges. Furthermore, there are seals installed around rudder, elevator, and thrust reverser and fairings around antennas. A summary of operational limitation is given in Table A.3.

Power Plant

The engine is a two-shaft high-by-pass ratio Rolls-Royce BR710 C4–11 turbofan engine with a single-stage low-pressure compressor, a ten-stage high-pressure compressor, a two-stage high-pressure turbine and a two-stage low-pressure turbine. The engine is equipped with FADEC. Basic data are shown in Table A.4. The engines are mounted high in the aft fuselage through horizontal pylons.