Module 1. Overview of Aircraft Structural Design and Manufacturing (Part 2).pdf

AE641: Aircraft Structures 1 Module 1:Overview of Aircraft Structural Design and Manufacturing (Part 2) Presented by: John Gabriel G. Decena M.Eng Department of Aeronautical Engineering, FEATI University AE641: Aircraft Stru...

AE641: Aircraft Structures 1 Module 1:Overview of Aircraft Structural Design and Manufacturing (Part 2) Presented by: John Gabriel G. Decena M.Eng Department of Aeronautical Engineering, FEATI University AE641: Aircraft Structures 1 1–1  Outline The module is divided into the following topics:  1.1 Major & Minor Structural members  1.2 Design Process  1.3 Planning & structural Weights  1.4 Engineers Responsibility  1.5 Production/Manufacturing AE641: Aircraft Structures 1 1–2  Module Outcomes At the end of the module the students should be able to:  Identify the different structural members and explain their functions.  Narrate the design process for aircraft in general.  Explain how are structural weight derived.  Discuss the responsibility of an engineer.  Narrate the production process for aircraft structures. AE641: Aircraft Structures 1 1–3  Overview Creating an external layout and design not only of an aircraft but other vehicles must satisfy certain requirements set by the customer. However after the design is done, it is now the task mostly of an structural engineer to ensure that the structures could adapt the shape and configuration while ensuring integrity of the structure. It is not uncommon that during this process some requirements may not be met and thus compromise is needed. In this part we will look onto the processes involved and decision making needed by an Engineer. AE641: Aircraft Structures 1 1–4  Overview Aircraft Structural Breakdown of an F16 Fighter Jet (Photo taken from Niu MCY. Airframe Structural Design) AE641: Aircraft Structures 1 1–5  Design Process Aircraft Structural Design and Testing Process (Photo taken from Aircraft Structural Considerations PPT of Vought Aircraft Industries) AE641: Aircraft Structures 1 1–6  Design Process Development Progress 1. 1900 to 1915 – Wright Flyer (relies on ultimate strength of critical parts) 2. 1915 to 1930 – Engine reliability was improved by ground qualification (fatigue testing) 3. 1930 to 1940 – design and analysis focused static ultimate strength with little regard to airframe fatigue. 4. 1940 to 1955 – increase in material static strength but little increase in fatigue strength. Fatigue design is now included 5. 1955 to present – fatigue design was joined by fail safe damage tolerance design. Periodic inspections included. AE641: Aircraft Structures 1 1–7  Design Process Currently we design for: 1. Static Ultimate and Yield Strength 2. Fatigue life of airframe (crack propagation) 3. Static residual strength of damaged structures (damage tolerance) 4. Fatigue life of damage structure thru regular inspections 5. Thermal stress of supersonic aircraft AE641: Aircraft Structures 1 1–8  Design Process All airframe structural design goes through these phases: 1. Specification of function and design criteria 2. Determination of basic external applied loads 3. Calculation of internal element loads 4. Determination of allowable element strengths and margins 5. Experimental demonstrations or substantiation test program AE641: Aircraft Structures 1 1–9  Design Process Airplane design, development and certification (Photo taken from Niu MCY. Airframe Structural Design) AE641: Aircraft Structures 1 1 – 10  Planning and Structural Weights L-1011 complete structural test program (Photo taken from Niu MCY. Airframe Structural Design) AE641: Aircraft Structures 1 1 – 11  Planning and Structural Weights During structural weight planning one should consider that: 1. The structural engineer determine structural sizes while being sensitive to weight. 2. In some instances, there is a separate weight engineer. 3. The structural weight ranges around 20-40% of the gross take off weight. 4. Just a small increase in structural weight (5%) can have big impact in the aircraft performance. 5. However one should also consider other factors such as lifespan and fuel efficiency. AE641: Aircraft Structures 1 1 – 12  Planning and Structural Weights During structural weight planning one should consider that: 1. The structural engineer determine structural sizes while being sensitive to weight. 2. In some instances, there is a separate weight engineer. 3. The structural weight ranges around 20-40% of the gross take off weight. 4. Just a small increase in structural weight (5%) can have big impact in the aircraft performance. 5. However one should also consider other factors such as lifespan and fuel efficiency. AE641: Aircraft Structures 1 1 – 13  Engineer’s Responsibility As a design engineer during the process must: 1. Coordinate thoroughly and integrate the design package into the overall structure. 2. Establish basics as early as possible: – Functional requirements – Loads and materials – Aerodynamic requirements – Geometry and jig information, interchangeability, producibility, repairability, replaceability, maintainability, etc. 3. Spend adequate time to plan the job AE641: Aircraft Structures 1 1 – 14  Engineer’s Responsibility As a design engineer during the process must: 4. If you encounter interface problems, make adequate sections to show: – Where clearances are required and the requirements for such clearances – The interface to which the detail attaches 5. Review processes, finishes, assembly procedures, etc: 6. Subcontractor-built production joints for assemblies that must conform to shipping limitations 7. Check production of joints resulting from raw materials size restrictions or size of fabrication tools, etc. AE641: Aircraft Structures 1 1 – 15  Engineer’s Responsibility As a design engineer during the process must: 8. Create subassembly plans and how these subassemblies are loaded into the final assembly fixtures. 9. Most importantly dedicate his/herself to the job. AE641: Aircraft Structures 1 1 – 16  Manufacturing Finally the engineer must check on the following before giving a go to the design: 1. Producibility 2. Maintainability 3. Tooling AE641: Aircraft Structures 1 1 – 17  Manufacturing How an airplane is built (Photo taken from Niu MCY. Airframe Structural Design) AE641: Aircraft Structures 1 1 – 18  Producibility Principles of producibility design: 1. General configuration Rectangular vs tapered wings Minimum number of major structures Cylindrical, straight or conical surfaces vs compound curvature Extend of fairing and filleting required AE641: Aircraft Structures 1 1 – 19  Producibility Principles of producibility design: 2. Major Breakdowns Adequate access for assembly Ease of handling and transportation Assembly Joints AE641: Aircraft Structures 1 1 – 20  Producibility Where A320 parts are manufactured? (Photo from Airbus) AE641: Aircraft Structures 1 1 – 21  Producibility Principles of producibility design: 3. Structure and Equipment Simplicity (avoid complex shapes, minimum fabrication) Parts (multiple use and minimum number) Detail design (interchangeability or use of readily available parts, tolerances, machining economy) AE641: Aircraft Structures 1 1 – 22  Maintainability Aside from producibility the engineer must also: 1. Must undergo 2-3 maintainability training 2. Be in close touch with engineering and maintenance department. Noting that: Typical aircraft structure last from 15-20 years Civilian aircraft fly continuously while military aircraft spends most of its time on the ground AE641: Aircraft Structures 1 1 – 23  Tooling Tooling is the process of acquiring, obtaining, or even manufacturing the manufacturing components, machines, and equipment needed for production. However, the tooling process varies from type to type, and no one size fits all when it comes to tooling. Some tooling includes: 1. Numerical Control 2. Robots 3. Shot-peening 4. Assembly Fixture AE641: Aircraft Structures 1 1 – 24  Assembly Introduction In the last part we discussed the production, in this part we will discuss some ways to assemble or join the parts that were manufactured. Levels of detail (by courtesy of H. Assler, Airbus Deutschland GmbH) AE641: Aircraft Structures 1 1 – 25  Assembly Introduction Two load transfer modes to classify the three major joining techniques in aerospace; shear (a-c) and tension (d-f). (TU Delft, n.d., 11-1.jpg.) The figure above not only shows the different loads but also the joining techniques. Mainly; (1) Mechanical fasteners, (2) Welding (3) Adhesives AE641: Aircraft Structures 1 1 – 26  Mechanically fastened joints On the left side we can see the different types of mechanical fasteners. Some are permanent, some are temporary. In the aerospace industry, nuts and bolts together with rivets are the most Figure 7.3. Illustration of the four major commonly used. fastener types (TU Delft) AE641: Aircraft Structures 1 1 – 27  Mechanically fastened Mechanically fastened joints joints We can see one of the most common applications of mechanically fastened joints are on skin to stringer interface. However this only applicable to aircrafts made of metal skins. Same fasteners may apply Typical fuselage longitudinal riveted lap to other parts of the splice joint. (A.Skorupa et al) aircraft such as the wing. AE641: Aircraft Structures 1 1 – 28  Mechanically fastened Mechanically fastened joints joints From left to right are rivets used on wing skin, spar and ribs. (google images) AE641: Aircraft Structures 1 1 – 29  Mechanically fastened Mechanically fastened joints joints In addition to rivets, the other most commonly used faster are threaded fasteners in a form of bolts and nuts. The most common applications are those Definition of the bolt dimensions. (TU Delft, n.d.,.) parts that are needed to be removed for inspection. AE641: Aircraft Structures 1 1 – 30  Mechanically fastened Mechanically fastened joints joints A sample bolt that joins the engine to the. (Airbus SRM) AE641: Aircraft Structures 1 1 – 31  Mechanically Mechanically fastened fastening joints in composites Although mechanical fasteners can also be used on composites, care should be taken in using them. The direction of the fiber should be considered as this is where the strength Relation between fibre orientation and failure mode; longitudinal plies are weak against shear-out, while of the composite material transverse plies are weak against net-section failure and bearing. (Alderliesten, 2011, 11-15.jpg.) is. AE641: Aircraft Structures 1 1 – 32  Mechanically Mechanically fastening fastened joints in sandwich composites For composite laminates and sandwich structures, Hi Lok, Cherry’s E-Z Buck and Eddie Bolt are the most commonly used. Titanium alloy Ti-6Al-4V is the most common alloy for fasteners used with carbon fiber reinforced composite structures. (aircraftsystemstech.com) AE641: Aircraft Structures 1 1 – 33 AE641: Aircraft Structures 1 1 – 34 AE641: Aircraft Structures 1 1 – 35  Welding Welded joints Unlike mechanical fasteners, welding is a permanent joining process that joins the material together as one. Contrary to belief, welding is not only for metals but can also be used in Aircraft Engine mounts are the most common part that uses welded joints. (Kitplanes Magazine.) plastics and composites. AE641: Aircraft Structures 1 1 – 36  Welding Welded joints Figure 7.9. Comparison between mechanically fastened, bonded and integral structures; integral structures do not provide barriers against cracking. (Alderliesten, 2011, 11-19.jpg.) AE641: Aircraft Structures 1 1 – 37  Welding Welded joints There are two major welding techniques applied in aerospace structures: Laser beam welding – heat directly from the laser Friction stir welding – parts are not directly subjected to heat but uses friction (rotation) that will melt and join the part together AE641: Aircraft Structures 1 1 – 38  Welding Composite structures In composite structures welding can only be performed with thermoplastic composites. The principle of welding is that the matrix material locally is heated above the glass transition temperature to bond parts together. The following welding techniques are currently available: Resistance welding Induction welding Ultrasonic welding AE641: Aircraft Structures 1 1 – 39 AE641: Aircraft Structures 1 1 – 40