Conceptual Aircraft Design: An Industrial Approach

Conceptual Aircraft Design: An Industrial Approach Kundu, Price & Riordan January 2019 Helicopter Flight Dynamics: Including a Treatment of the Tiltrotor. Title: Conceptual aircraft design: an industrial approach / Professor Ajoy Kumar Kundu, Queen's University Belfast, UK, Professor Mark A.

FAR25 74

Series Preface

Preface

Furthermore, such advanced aircraft cannot be well understood without first mastering the basic principles of this book. We extend our sincere thanks to Ms Anne Hunt, Associate Commissioning Editor, Mechanical Engineering at John Wiley & Sons, Ltd, the publisher of this book.

Individual Acknowledgements By Ajoy Kumar Kundu

Teachers/Academic Supervisor/Instructors

Heads of Establishments/Supervisors

My Ex-Students and Most of My Ex-Colleagues (Both Shop-Floor and Oﬃce)

Personal Observation

I'm sure a second edition will follow in the capable hands of my fellow writers, but I don't think I'll be doing anything more than remaining in a supporting role. In today's world of cooperative ventures between countries, especially in the defense sector, the methodologies adopted in this book should be applicable.

By Mark A. Price

I can't thank my family enough, my wife, Denise, and my daughter, Rachel, who have been patient beyond their calling, giving me space and time to pursue my dreams. My mother, Ann, who gave me the gift of words, and my late father, Matt, who instilled in me the virtue of giving the customer what they really need, and hence my enthusiasm for this book; to meet an industry need and the graduates they require.

By David Riordan

List of Symbols and Abbreviations

S area, usually with a subscript that projects the part SB's side area of the fuselage. PHA Positive high angle of attack PIA Positive medium angle of attack PLA Positive low angle of attack.

Road Map of the Book

1 Objectives and Aims

2 The Arrangement

Prerequisites (Chapters 1–7)
Introduction
Design Process
Aerodynamics
Statistics

It presents aircraft statistics to observe a strong statistical correlation within different designs of the aircraft classes. Military aircraft designs must necessarily be bolder and take bigger leaps to be decisive ahead of potential adversaries, regardless of cost.

Aircraft Design (Chapters 8–16)

Conﬁguring Aircraft – Concept Deﬁnition)
Undercarriage
Weights and CG
Drag
and 13 – Powerplant
Sizing and Engine Matching – Concept Finalisation)
Performance Analyses
Cost Analyses

Variant family review should start at the initial stage to get the products right the first time (ie the Six-Sigma approach). This will require re-configuring the aircraft by making slight changes to the component geometries.

Further Design Considerations (Chapters 17–24)

Loads
Materials and Structures
Manufacturing Considerations
Miscellaneous Design Considerations
Aircraft Systems
Electric Aircraft

Discussion
Note

This chapter provides an overview of the role of CFD in the conceptual design study phase. Full assessment of the aircraft performance of the worked examples (Bizjet, AJT and TPT) is carried out in [8].

3 Suggested Route for Coursework

Only then will the project move towards concept completion through a formal method of aircraft dimensions with matching engines. There is then a linear progression from concept definition to concept completion in the steps described above.

4 Project Assignment

5 Suggestions for the Class

Prerequisites

Introduction

Overview

Brief Historical Background

Flight in Mythology
Fifteenth to Nineteenth Centuries
From 1900 to World War I (1914)
World War I (1914–1918)
Period between World War I and World War II – Inter War Period, the Golden Age (1918–1939)
World War II (1939–1945)
Post-World War II

Exactly a century later, a flying replica of the Wright Flyer failed to take off on its first flight (more details online). Some of the other famous Italian aircraft of the time bore the names of Società Italiana Aviazione, Ansaldo and so on.

Aircraft Evolution

Aircraft Classiﬁcations and their Operational Environments

I encourage readers to examine the design of the nearly half-century-old SR71 aircraft, which still holds the speed-altitude record for aircraft powered by air-breathing engines. The next level of speed and altitude is with turboprop engines which operate at shorter distances (ie civil aircraft use) and are not time critical due to lower speed (ie propeller limitations).

Current Aircraft Design Trends for both Civil and Military Aircraft (the 1980s Onwards)

Current Civil Aircraft Trends
Current Military Aircraft Trends

Unmanned aerial vehicle (UAV) technology is on the horizon – the conflict in the Middle East has seen the successful use of UAVs for surveillance and military operations. Spanning almost four decades of production to date, the Boeing737 series has become the best-selling aircraft in the history of the commercial aircraft market with more than 10,000 aircraft delivered and ordered.

Future Trends

Civil Aircraft Design
Military Aircraft Design
UAVs/UASs
Military Applications
Civil and Commercial Applications
Recreational Applications
Research and Development Applications
Rocket Applications in Future Aircraft Design Trends

The GEV is not really new: the Russians built a similar vehicle (Figure 1.12) called the "Ekranoplan", but it did not appear in the free market economy.). Interest in this aircraft continues to grow - the $10 million prize offered could be compared to a transatlantic prize followed by commercial success.

Forces and Drivers

Airworthiness Requirements

It is concerned with the technical operating rules to be observed by operators and is set out in extensive detail in a formal manner in FAR 121/JAR-OPS-1, revised when necessary. The contents of the AFM are repackaged into the Flight Crew Operating Manual (FCOM) which outlines the aircraft's limitations and procedures, along with the full envelope of aircraft performance data.

Current Aircraft Performance Analyses Levels

By the Designers

Aeronautical engineering does not progress without these documents to guarantee a minimum safety in design and operation. The FAR 23 (general aviation aircraft – currently under revision) and the FAR Part 103 (ultra-light aircraft) have significantly lower level requirements and use the same performance equations for performance analyses.

Aircraft Classiﬁcation

Comparison between Civil and Military Design Requirements Design lessons learned so far on the current trend are summarised as follows

Topics of Current Research Interest Related to Aircraft Design (Supersonic/Subsonic)

Laminar flow requires surfaces that are smoother, with fewer steps, gaps, or contamination than the surfaces that can typically be fabricated today. Aerodynamic analyzes of unsteady flow and aeroacoustic prediction capabilities for airframe and propulsion noise sources associated with future concepts.

Cost Implications

The Classroom Learning Process

Classroom Learning Process versus Industrial Practices
Use of Computer-Assisted Engineering (CAE)
What is Not Dealt With in Depth in this Book?

The purpose of the book is to provide close to industry standard calculations in the coursework and engineering approach sciences needed for analysis. The old method of cage on large drawing boards is completely eliminated - the CAD algorithm takes it with precision manually, impossible.

Units and Dimensions

Use of Semi-Empirical Relations and Datasheets

Semi-Empirical Relations Compared to Statistical Graphs
Use of Semi-Empirical Weights Relations versus use of Weight Fractions
Aircraft Sizing

The user of semi-empirical relations and graphs must be aware of the extent of error that can occur. The following subsection discusses an example of using semi-empirical formulas for an aircraft and estimating its component weight.

The Atmosphere

Hydrostatic Equations and Standard Atmosphere
Non-Standard Atmosphere/Oﬀ-Standard Atmosphere
Altitude Deﬁnitions – Density Altitude (Oﬀ Standard)
Humidity Eﬀects
Greenhouse Eﬀect

Appendix B gives the ISA table up to an altitude of 25 km, which is sufficient for this book, as all aircraft described (except rocket-powered special purpose aircraft - eg space plane) fly below 25 km. Challenges in a better, faster and cheaper era of aircraft design, engineering and manufacturing. The Aeronautical Journal.

Aircraft Familiarity, Aircraft Design Process, Market Study

Overview
Introduction
Aircraft Familiarisation

Civil Aircraft and Its Component Conﬁgurations
Turboprop Aircraft
Military Aircraft and Its Component Conﬁgurations

Typical Aircraft Design Process

Input

Market Survey – Project Identiﬁcation

Civil Aircraft Market – Product Identiﬁcation

Four Phases of Aircraft Design

Understanding Optimisation
Typical Resources Deployment
Typical Cost Frame
Typical Time Frame

Typical Task Breakdown in Each Phase

In this book, finishing surfaces are treated schematically – the main task is to finalize the size of the aircraft and the conﬁguration in Phase I. Due to design differences due to the mission role (Table 1.3), the structural sub-component groups of the fighter aircraft differ. of the civil aircraft structural subgroups as described earlier.

Conceptual Study Phase (Feasibility Study)

Generally, at the end of this phase, a management decision is expected to go ahead with the final configuration selected from the candidate configurations offered. Management may request a level of detail (eg, risk analysis) that could extend the study phase or move to the next phase, thereby delaying an approval decision until early in Phase II.

Project Deﬁnition Phase (Preliminary Design)

Planning portfolios with budgetary provisions, manpower requirements, progress milestones, potential subcontractor/risk sharing partner input, and so on are included as the starting point for the design process. Continuous interaction with potential customers (ie operators and subcontractors) takes place in this phase with the aim of arriving at a family of aircraft as the most 'satisfactory' design with compromises rather than an 'optimal' solution.

Detailed Design Phase (Full-Scale Product Development)

Final Phase (Certiﬁcation)

Functional Tasks During Conceptual Study (Phase I)

The design approach of military aircraft is not significantly different, except that the payload is the armament, which is generally submerged under the fuselage or carried within the fuselage bay. The mission profile is the flight profile for the military role that meets the target range with return-to-base capabilities.

Project Activities for Small Aircraft Design

Payload determines the fuselage size and shape and leads to undercarriage design depending on wing and engine positioning. Select the airfoil profile, its thickness to chord ratio, wing reference and planform areas, aspect ratio, wing sweep, taper ratio, wing twist, spar location, flap area, flight control and wing location relative to the fuselage.

Project Deﬁnition – 9 months 1. Integrated and component drawings in CAD

Configurations of candidate aircraft for placement with fuselage, then wing, fins (considering the canard), landing gear, power plant and so on.

Detailed Design (Product Development) Phase – 12 months 1. Completion of detailed component design in CAD

Testing and Certiﬁcation Phase) – 9 months 1. Final assembly and prototype equipping

Aircraft Speciﬁcations for Three Civil Aircraft Case Studies
Military Market – Some Typical Military Aircraft Design Speciﬁcations

Aircraft Speciﬁcations/Requirements for Military Aircraft Case Studies

Airworthiness Requirements

Code of Federal Regulations (CFR) – Title 14

Coursework Procedures – Market Survey

Extended Derivative Version: 12–14 Passengers In the Baseline Aircraft Family (Far 25). (The extended derivative works similarly by inserting fuselage plugs with continuous sections on both sides of the wing.). Derivative version in the aircraft family (typically the Airbus 319 and Airbus 321class on both sides of the baseline Airbus 320 aircraft).

Aerodynamic Fundamentals, Deﬁnitions and Aerofoils

Overview

Introduction

The behavior in a supersonic flow is different, but it is still preferable that the tail closes gradually. Streamlining is synonymous with speed and its aerodynamic influence on design is reflected in any object in a relatively moving airstream (e.g. boats and cars).

Airﬂow Behaviour – Laminar and Turbulent

Aerofoils

At the surface, whereu=0,du/dy is the velocity gradient of the flow at that point. Airflow over curved surfaces accelerates or decelerates depending on which side of the curve the ﬂow negotiates (dp/dx≠0).

Flow Past an Aerofoil

Under Recrit, laminar flow has a lower skin friction coefficient, Cf., and therefore a lower friction (i.e. lower resistance). Aerofoil designers must shape the aerofoil LE to maintain laminar flow as much as possible.

Generation of Lift

This section points out that designers should maintain laminar flow as much as possible over the wetted surface, especially at the airfoil LE. The flow over an airfoil develops a lift per unit span ofl=𝜌U𝛤 (see other textbooks [2–7] for the derivation).

Aircraft Motion, Forces and Moments

Motion
Forces
Moments
Basic Control Deﬂections – Sign Convention
Aircraft Loads

If there was any force/moment imbalance, it would show up in the aircraft's flight profile. Note that Lis is used to indicate lift and V is used to indicate the aircraft's true airspeed.

Deﬁnitions of Aerodynamic Parameters

The load factor, n=2, indicates a two-fold increase in weight; that is, a 90-kg person would experience a 180-kg weight.

Aerofoils

Subsonic Aerofoils
Aerofoil Lift Characteristics
Groupings of Subsonic Aerofoils – NACA/NASA

NACA Five-Digit Aerofoil
NACA Six-Digit Aerofoil
NACA Seven-Digit Aerofoil
NACA Eight-Digit Aerofoil
Peaky-Section Aerofoil
NASA Supercritical Aerofoil
Natural Laminar Flow (NLF) Aerofoil
NACA GAW Aerofoil
Supersonic Aerofoils
Other Types of Subsonic Aerofoil

Coordinates of the upper and lower surfaces are given by yUandxL for the distance measured from the chord line. The aerofoil designation is divided into two segments – the first three-character segment starts with SC, indicating that it is a supercritical aerofoil, and the number in parentheses shows the stage of development – in this case stage II of three stages of development as described Next.

Reynolds Number and Surface Condition Eﬀects on Aerofoils – Using NACA Aerofoil Test Data

Camber and Thickness Eﬀects
Comparison of Three NACA Aerofoils

For low speed aircraft below Mach 0.3 the airfoil thickness is on the higher side; many successful aircraft have 15-18% t/c. The camber effect of the NACA series two confirms similar characteristics to the NACA six series.

Centre of Pressure and Aerodynamic Centre

Relation Between Centre of Pressure and Aerodynamic Centre

Estimating the Position of the Aerodynamic Centre, a.c

However, it is observed that the moment around the quarter chord of the airfoil is invariant with respect to the angle of attack (dCm/d𝛼=0) until stall occurs. The CG can be forward or aft of the wing MAC quarter chord point.

Types of Stall

Gradual Stall
Abrupt Stall

The center of pressure and aerodynamic center can be determined analytically if the airfoil characteristics can be expressed analytically. Inside the operating region the airfoil lift characteristics can be expressed as a straight line and the moment characteristic is not exactly a straight line but can be tolerated as a straight line;.

High-Lift Devices

There are several types of high-lift devices as shown in Figure 3.35, the choice depends on the category of aircraft as listed in Section 4.15. When high-lift devices are installed on a wing, their 3D effects reduce the Clmax to a lower value of CLmax, as shown in Figure 4.31.

Flow Regimes

Compressibility Correction
Transonic Eﬀects
Supersonic Eﬀects

Critical Mach (Mcrit) is the beginning of the transonic flow field and is lower than the MDD. The airfoil thickness distribution along the chord length is the parameter that affects the induction of transonic flow.

Summary

Simpliﬁed Aerofoil Selection Methodology

The four-digit NACA cam is given by the first number (only camber stretches 2 and 4% of chord length are considered). Select the highest t/cratio allowed by the wing sweep for the aircraft category as given previously.

Aerofoil Design and Manufacture

Direct Aerofoil Design Method
Inverse Aerofoil Design Method

Current Practice
Manufacture

With more refinement in the numerical algorithm and with advances in computer processing power, the airfoil design process has changed. The manual rivet had dimples, there were mismatches at the joints, waves in the wing skin and so on.

Aircraft Centre of Gravity, Centre of Pressure and Neutral Point

Aircraft Centre of Gravity (CG)
Aircraft Neutral Point
Summary

It is strongly recommended that readers can compare the finished surfaces of some older aircraft models, say the Mustang P class, Douglas DC3 and so on, with some newer aircraft models, say the F35 class, Airbus 320 and so on, to get a feel for the difference.

4 Wings

Overview

Introduction

Generic Wing Planform Shapes

Unswept Wing Planform
Swept Wing Planform
Civil Aircraft
Military Aircraft (Supersonic Wings)

The rectangular wing shape (Figure 4.2a) is used for low speed (i.e. incompressible flow) aircraft below Mach 0.3. A tapered wing can be adjusted with a built-in crank (kinked) (i.e. two tapered wings joined into one – Figure 4.2c).