Aircraft Design Notes PDF

UNIT-1 NOTES FACULTY NAME: CLASS: B.Tech AERONAUTICAL SUBJECT CODE: SEMESTER: VI SUBJECT NAME: AIRCRAFT DESIGN Preliminaries: Aircraft Design Requirements, specifications, role of users. Aerodynamic and Structura...

UNIT-1 NOTES FACULTY NAME: CLASS: B.Tech AERONAUTICAL SUBJECT CODE: SEMESTER: VI SUBJECT NAME: AIRCRAFT DESIGN Preliminaries: Aircraft Design Requirements, specifications, role of users. Aerodynamic and Structural Consideration, Importance of weight. Airworthiness requirements and standards. Classifications of airplanes. Special features of modern airplane. Air Loads in Flight: Symmetrical measuring loads in flight, Basic flight loading conditions, Load factor, Velocity - Load factor diagram, gust load and its estimation, Structural limits. INTRODUCTION: The process of design of a device or a vehicle, in general involves the use of knowledge in diverse fields to arrive at a product that will satisfy requirements regarding functional aspects, operational safety and cost. The design of an airplane, which is being dealt in this course, involves synthesizing knowledge in areas like aerodynamics, structures, propulsion, systems and manufacturing techniques. The aim is to arrive at the configuration of an airplane, which will satisfy aforesaid requirements. The design of an airplane is a complex engineering task. It generally involves the following. a) Obtaining the specifications of the airplane, selecting the type and determining the geometric parameters. b) Selection of the power plant. c) Structural design and working out details of construction. d) Fabrication of prototype. e) Determination of airplane performance, stability, and structural integrity from flight tests. STAGES IN AIRPLANE DESIGN: The design process can be divided into the following three stages. a) Project feasibility study. b) Preliminary design. c) Design project Project Feasibility Studies: The aim of this study is to evolve a complete set of specifications for the airplane. It involves the following steps. 1) Comprehensive market survey to assess the number of airplanes needed. Page 1 Currently this stage is avoided by the use of CAD(Computer Aided Design) packages which provide detailed drawings of various components and subassemblies. 3) Complete wind tunnel testing of the approved configuration. Currently CFD (Computational Fluid Dynamics) plays an important role in reducing the number of tests to be carried-out. In CFD, the equations governing the fluid flow are solved numerically. The results provide flow patterns, drag coefficient, lift coefficient, moment coefficient, pressure distribution etc. Through the results may not be very accurate at high angles of attack, they are generally accurate near the design point. Further, they provide information on the effects of small changes in the geometric parameters, on the flow field and permit parametric studies. 4) Preparation of detailed drawings. 5) Final selection of power plant. 6) Calculations of (a) c.g. shift (b) performance and (c) stability. 7) Fabrication of prototypes. These are the first batch of full scale airplane. Generally six prototypes are constructed. Some of them are used for verifying structural integrity and functioning of various systems. Others are used for flight testing to evaluate performance and stability. Classification of airplanes At this stage, it is helpful, to know about the different types of airplanes. The classification is generally based on (a) The purpose of the airplane, (b) The configuration and (c) Design Mach number (e.g. subsonic, supersonic and hypersonic). Classification of airplanes according to function There are two main types of airplanes viz. i) Civil aircraft and ii) Military aircraft. The civil airplanes are categorised as a) Passenger, b) Cargo, c) Agricultural, d) Sports and e) Ambulance. The military airplanes are categorised as a) Fighter, b) Bomber, c) Interceptor, d) Reconnaissance, and e) Airplanes for logistic support like troop-carriers and rescue airplane. Page 3 The military aircraft are often designed to cater to more than one role e.g. fighter-bomber or interceptor-fighter. Influence of the function of airplane on specifications/design requirements The specifications or design requirements of an airplane are decided by its function. It can be mentioned that a passenger airplane should have: (a) High level of safety in operation, (b) Adequate payload carrying capacity, (c) Economy in operation, (d) Comfort level depending on range and cruising altitude, (e) Ability to fly in weather conditions normally encountered on chosen routes and (f) Ability to use airfields of intended destinations. A bomber airplane should have: (a) Range corresponding to the mission, (b) Capacity to carry and deploy intended bomb load, (c) High values of speed, endurance, and ceiling (d) Adequate protection against accidental fire. An interceptor airplane should have: (a) Adequate thrust to give high (i) Rate of climb, (ii) Maximum flight speed and (iii) Maneuverability (b) Ceiling 3 to 4 km above that of contemporary bombers (c) Ability to fly in adverse weather conditions and (d) Appropriate armament. Civil & Fighter Aircraft Page 4 Classification by Configuration Airplanes can be classified in accordance with their shape and structural layout, which in turn will contribute to their aerodynamic, tactical and operational characteristics. It can be done by classification of the following: (a) Shape and position of the wing (b) Type of fuselage (c) Location of horizontal tail surfaces (d) Type of landing gear (e) Location and number of engines. Classification of airplanes based on wing configuration Early airplanes had two or more wings e.g. the Wright airplane had two wings braced with wires. Presently only single wing is used. These airplanes are called monoplanes. When the wing is supported by struts the airplane is called semi cantilever monoplane. Depending on the location of the wing on the fuselage, the airplane is called high wing, mid-wing and low wing configuration. Further, if the wing has no sweep the configuration is called straight wing monoplane. The swept wing and delta wing configurations are shown in Figs. (a) Shape and Position of the Wing (1) Braced airplane – D.H. Tigermoth (2) Braced sesquiplane – An- 2 (3)Semi-Cantilever monoplane, Pushpak, Piper Cub, (4)Semi-cantilever parasol monoplanes…Baby Ace (5) Cantilever low-wing monoplaneDC-3, HJT-16, IL-18, DH Comet (6) Cantilever mid-wing monoplane …Hawker Hunter, Canberra (7)Cantilever high-wing monoplane…An-22, Breguet 941, Fokker friendship (8)Straight wing monoplane… F-104 A…. (9)Swept-wing monoplane… F-24, MIG-21, Lightning …… (10)Delta-monoplane with small ARAvro-707, B-58 Hustler, Avro Vulcan. Page 5  Types of Wings Straight Wing Swept Wing Forward Swept Wing Oblique Wing Page 6  Types of Wings Variable Sweep Wing Delta Wing Biplane Triplane Classification of airplanes based on fuselage Generally airplanes have a single fuselage with wing and tail surfaces mounted on the fuselage. In some cases the fuselage is in the form of a pod. In such a case, the horizontal tail is placed between two booms emanating from the wings. These airplanes generally have two vertical tails located on the booms. The booms provide required tail arm for the tail surfaces. Some airplanes with twin fuselage had been designed in the past. However, these configurations are not currently favoured. (b) Type of fuselage (1) Conventional single-fuselageHT-2, Boeing 707, (2) Twin-fuselage design (3) Pod and Boom construction. Fairchild Packet, Vampire Page 7 Classification of airplanes based on horizontal stabilizer In a conventional configuration, the horizontal stabilizer is located behind the wing. In some airplanes there is no horizontal stabilizer and the configuration is called tailless design. In these airplanes, the functions of elevator and aileron are performed by ailevons located near the wing tips. When both ailerons (on left and right wings) move in the same direction, they function as elevators and when the two ailerons move in opposite direction, they function as ailerons. In some airplanes, the control in pitch is obtained by a surface located ahead of the wing. This configuration is called canard configuration Types of Tails T Tail Twin Fin Horizontal Tailless Vertical Tailless Page 8 (c) Location of horizontal tail surface (1)Conventional design with horizontal tail located behind the wing Krishak, Avro-748, (2) Tail-less design with no horizontal tail …Mirage IV, B-58 Hustier, Concorde (3)Canard design with horizontal tail located ahead of the wing… (XB-70-A …) (d) Type of landing gear (1)Retractable landing gear… DC-9, TU-114, SAAB-35 (2)Non-retractable landing gear…Pushpak, An-14, Fuji KM-2 Fixed type of landing gear Retractable type of landing gear Classification of airplanes based on number of engines and their location Airplanes with one, two, three or four engines have been designed. In rare cases, higher number of engines are also used. The engine, when located in the fuselage, could be in the nose or in the rear portion of the fuselage. When located outside the fuselage the engines are enclosed in nacelles, which could be located on the wings or on the rear fuselage. In case of airplanes with engine-propeller combination, there are two configurations – tractor propeller and pusher propeller. In pusher configuration the propeller is behind the engine. In tractor configuration the propeller is ahead of the engine. (e)Classification by Power Plants a. Types of engines Piston engines – Krishak, Dakota, Super Constellation, etc. Turboprop engines – Viscount, Fokker Friendship, An-12, etc. Turbo-jet engines – Turbo-fan, By-pass engines –HJT-16 (Kiran), Boeing 707 MIG-21, etc. Ram-jet engines Rocket engines – Liquid propellant – Solid propellant – X-15A b.Number of engines Single-engine – HJT-16, DH Chipmunk, Hawker Hunter, etc. Twin-engine – HF-24, DC-3, Canberra, etc. Multi-engine – An-22, Boeing 707, Belfastetc. c.Engine Located Propeller single engine located in fuselage nose (HT-2, YAK-9, BEAGLE A-109). Page 9 “Pusher”-engine located in the rear fuselage (Bede x BD-2) Engines (jet) submerged in the wing (a) At the root – DH-Comet, TU-104, Tu-16 (b) Along the span – Canberra, U-2, YF-12A Jet engines in nacelles suspended under the wing by “POD” mountings - Boeing 747, Airbus, Boeing 707, DC-8, Convair 880, Boom and Pod construction - Fairchild Packet, Vampire Engines (jet) located on the rear fuselage – Trident, VC-10, IL-62, Caravelle Jet engines located within the rear fuselage – HF-24 (Marut), Lightning, MIG-19,… Engine Arrangement Factors affecting the configuration The configuration of an airplane is finalized after giving consideration to the following factors. (I) Aerodynamics (II) Low structural weight (III) Lay-out peculiarities (IV) Manufacturing procedures (V) Cost and operational economics (VI) Interaction between various features (I) Aerodynamic considerations – drag, lift and interference effects The aerodynamic considerations in the design process involve the following. Page 10