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Welcome everybody to our new series, “Dissecting the X”. In this series, we will take a closer look at different types of airplanes, be it military or civil. We will discuss the characteristics of this type of airplane, what makes it special and different in regards to aerodynamics, mission and equipment. I will try to be thorough but not lost in the detail, so you can get an overview of how each component plays its role as part of the airplane. At the end of each post I’d appreciate it if you could leave a little comment, telling me what you liked or didn’t like, and which airplane you’d like to see next time.

We’ll start this series with the F-15. The McDonell Douglas F-15 Eagle entered service in 1976 and has been in service since. It is expected to stay in service well beyond 2025. This has several reasons. First of all, the F-15 airframe is a true powerhouse. It has been very well designed and several service updates have kept it…well, up to date. It can stil compete with newer generation aircraft, like the Eurofighter (the Eurofighter has the advantage though, as it is a newer design). Another reason is the fact that due to current budget restraints the US government (the main operator of the F-15) cannot afford to field a large number of more modern aircraft (like the F-22) and therefore has to rely on the F-15.
The following video is a pretty impressive proof of the F-15’s capabilities.

Let me recap this: the F-115 in this video flew with only one wing! The other one was missing, it was torn off during a maneuver accident! Now, how could the F-15 do that? Let’s find out!

Fuslage – The F-15 has a very thin fuselage (compared to other aircraft) that also generates lift. See, a special form is not the only way of generating lift for a body. If you stick your hand out of the window of a car in motion and there is an angle between your hand and the wind, you will feel a lifting force on your hand. The same goes with all kinds of bodies. Even a flat board will generate lift if it has been angled relative to the wind. Now, why go through all the trouble of manufacturing and designing wings, if flat boards would do the job, too, you might ask. A relevant question. The reason for the use of special wing “forms” (called wing sections), is the fact that the bigger the angle gets, the harder it is for the air to follow the board. Eventually the flow seperates from the surface of the board, which leads to a dead area downstream of the seperation point and leads to lower lift, and higher drag (the force acting in the opposite direction of motion…which means drag is bad!).
The F-15 has a high wing configuration. One advantage is that a shorter landing gear can be used. But the flow over the wing can also negatively influence the vertical stabilizers, as there is not the fuselage inbetween to prevent this.

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Control Augmentation System (CAS) – When the F-15 was designed, fly-by-wire technology (that is, electronic controls) were not in use. In fact, the F-16 was the first aircraft that relied solely on fly-by-wire. So at first the F-15 had mechanical control systems. Later it was upgraded with a so called Control Augmentation System (CAS). The CAS is an electronic control system that translates and coordinates the inputs of the pilot to achieve superb performance. The mechanical systems were still kept in the F-15, so it could still be flown in case the system went inoperable. How could this have contributed to flying the F-15 with only one wing? Well, the CAS saw that something was wrong with the missing wing (it was missing) and translated all the control inputs of the pilot in such a way that the airplane could still be flown.

Wing Configuration – The F-15 has a swept back wing, that somehow resembles a delta wing. To enable to F-15 to fly several times the speed of sounds without producing exessive drag, the sweep angle of the leading edge is very important. Also notice the big wing area of the F-15. The lift a wing can create is directly related to its’ wing area, the bigger the area, the more lift can be generated at a given speed. A high wing area means the F-15 can fly at lower speeds and have a smaller turn radius when maneuvering, which is very important for fighter planes.

Empennage – The empennage of an airplane is the sum of its vertical and horizontal stabilizers. As a fighter airplane, the F-15’s empennage needs to be as light as possible, but still generate enough force to make the F-15 highly dangerous in aerial combat. A big problem especially fighter planes have is the integration of the empennage and the engines with the fuselage (the body of the airplane) in such a way that the different parts influence each other as minimal as possible. The F-15 is a good example of this integration.
It has two vertical stabilizers as a result of this integration. Two vertical stabilizers mean that the area of each one can be smaller than the area of a single vertical stabilizer. That also means that each one of those two stabilizers doesn’t have to endure as much force as a single one and can therefore be built lighter. Everything has its drawbacks though. Two stabilizers means more interference between the different parts of the empennage and higher drag! An important thing to understand in aerospace engineering is the fact that it basically is a big game of trade-offs. There is nothing one can get without having to give up something else!

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The F-15’s horizontal stabilizers are all-moving. This gives the pilot more control over the aircraft, but it also means heavier and more complicated controls. An interesting thing to remark about the F-15’s horizontal stabilizer is the distinct sawtooth on the leading edge. This sawtooth is supposed to generate extra lift via vortices. It is usually used when late in the design phase experiments and calculations show that the body is not generating enough force, but a total redesign would be too expensive. It is sort of a quick and dirty fix.

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Variable geometry intake – The F-15 is supposed to fly at a speed higher than twice the speed of sound, which makes every aspect of its design more complicated. Everything has to be custom tailored for these special situations. For that reason the air intakes for the two turbines have variable geometry, to adapt to the changing conditions of supersonic flight. (In the following picture you can see the intake of the F-14, but the F-15’s intakes look pretty similar.)

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The intakes are positioned on the shoulders of the airplane. This is kind of unfortunate, because positioning the intakes under the center of the airplane leads to a better airflow into the intake at all angles of attack, in contrast to the position chosen for the F-15. Wind tunnel experiments and CFD calculations have shown that the two intakes, if centered side by side under the center of the fuselage would influence each other in an unacceptable way.

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Mission – The F-15 is a tactical fighter and was mainly designed to gain and mantain air superiority. Air superiority basically means controlling ones own aerial territory and having a distincting advantage over the opposing air force. So the F-15 was basically designed for air-to-air combat (also called dogfight). How do all the different components fit into this? Well, the powerful engines allow a very high thrust-to-weight ratio, that allows the F-15 to have a very high acceleration. Combined with the variable geometry air intakes, this allows the F-15 to reach supersonic speed. The big wing area and low wing loading (the ratio of the wing area to the weight of the aircraft) give it superb maneuverability and a small turn radius, which allows the F-15 to easily turn into an enemy airplanes turn.

Little Copyright Info:
Some of the pictures were taken by members of the US Armed Forces while on duty, so they are in the public domain. One schematic was taken from wwwf-15e.info, they have all the rights to that schematic. All other schematics were taken from Klaus Hünecke’s book “Modern Combat Aircraft Design”. I do not own those copyrights!

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When you are new to programming and want to start learning, it is very hard to find a good introductory book. Most books are either too simple, just teaching a few routines, and not the underlying way of how to think as a programmer. Others are way too complicated and abstract, bombarding the reader with hard-to-grasp concepts. Common Lisp: A Gentle Introduction to Symbolic Programming by David S. Touretzky is a nice little exception to that rule. Mr. Touretzky is a researcher at Carnegie Mellon University and a champion of free speech, and it is reflected in his book: even though it was published in the 90s it is available for free and legally on the internet.

Lisp is an old programming language, that has some unique characteristics and will be very different at first look. It has a unique style, that will make you fall in love with it. You can read more about Lisp

Common Lisp begins with a gentle introduction into programming in general and Lisp in particular. The difference between functions and data, number types and some basic programming concepts are explained. He then moves on to explain lists, the basic building blocks of Lisp. The relationship between lists and  elements of lists is explained in a very clear and concise manner. Some basic list operations are introduced. After explaining the eval notation, a special type of notation to describe Lisp functions, Touretzky then moves on to explain conditionals, like the if- and when- functions. Before you know it, you can do some pretty crazy things with Lisp, and this is just the beginning! Chapter 5 is all about variables, their scopes and their effects.

All in all, there are 14 chapters, totaling more than 500 pages. Every chapter is divided into an introductory section, which explains new functions and gives examples, exercises which really enforce what has just been learnt, and an advanced topics section. Solutions for the exercises are not given, which some might see as a drawback, but I think it is really well thought out like that! Because when you are working on real world problems you don’t have the solutions at the end of the book. You have to find your own ways to make things work, and this book does a great job in forcing you to think hard!

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Computers are taking over the world. What was once a nice to have has become crucial. The good aerospace engineer should know at least a little bit of programming in order to be able to write programs for automation, for control and to understand how computers work and interact, so he can design his airplanes in a way that makes it more suitable for computerized or remote control.

Programming

The Python Tutorial – Python is a nice little programming language and one of the best languages to get started in programming. The great thing about Python is the fact that it is easy and powerful. It is an object-oriented programming language, but fairly high level, which means the programmer doesn’t have to worry about every tidbid in order to get working code. Great for beginners! The Python Tutorial is a pretty good introduction to programming with Python for the beginner.

Google’s Python Class – Google has a lean and mean introduction to Python. It is more of a weekend Python crash course. The cool thing about this class is the fact that there is text, exercises and video lectures! One should have a little experience with another programming language though.

Rapid GUI Programming with Python and Qt (Summerfield) – After learning the basics of Python programming, it’s time to get serious. Nobody wants to program command-line programs all their life, most people want a nice and crisp user interface every now and then. There are several ways to do that, one of them is with PyQt. Qt is a cross-platform toolkit for user interface design, and a very powerful one. Summerfield does a great job of teaching how to use PyQt.

Beginning C (Horton) – C is a good language to use if time-critical execution is important. An experienced programmer can write highly efficient code with C. It is also very low level and therefore used  to program microcontrollers and has all kinds of applications in engineering. Plus it is a nice basis for C++. In his book Horton takes you from beginner to intermediate user, and that in a very easy going and comfortable way.

Common Lisp: A Gentle Introduction to Symbolic Programming (Touretzky) – I love Lisp, it’s so different than any other programming language! It is what you can call an old language and has been around for a long time. The structure is very different from other programming languages and will be confusing at first. But once you get used to it, you will love it! Touretzky’s book is an eye opener. Programming concepts are introduced and explained in a clear and concise manner. It really is the total beginners guide to learning Lisp and programming and as an added bonus is freely and legally available on the internet.

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The last post was about general engineering books. They are important, but aerospace engineers need specialized knowledge about fluid dynamics, thermodynamics, and airplanes (duh). Let’s check out some of the cooler books for aerospace engineering students.

Aerospace Engineering

Introduction to Flight (Anderson) – This is THE introduction to aerospace engineering. Anderson covers all necessary basics to understand airplanes and flight. He starts by explaining basic fluid dynamics and thermodynamics. But he doesn’t stick with just the basics. Chapters about flight mechanics, performance and stability, propulsion and aircraft structures make up the bulk of the book. Another chapter about Astronautics completes the coherent presentation. If you are unsure which book to get, get this one! Actually, you should get this book as soon as you have decided on studying aerospace engineering, as it is the most essential introduction to the field!

Modern Combat Aircraft Design (Huenecke) – Modern Combat Aircraft Design is almost as well suited as an introduction as Introduction to Flight. Whereas Anderson’s book takes a more scientific approach, Huenecke’s book is more about the practical aspects of aircraft design in general and combat aircraft design in particular. You might have asked yourself “Why does the F-16/-15/-14… look the way it does?” Well, after reading this book you will understand. You will be able to look at any airplane and identify it’s unique characteristics and the reason why it looks the way it looks. I knew a little bit about airplanes, engineering and flight (just a little bit) and I read this book before I read Introduction to Flight. It was an eye opener for me and helped me understand the different aspects of an airplane a lot better.

Aerodynamics (Anderson) – This is another one of Anderson’s many masterpieces. Rather advanced topics of aerodynamics are discussed. Anderson lays out the scientific basics of aerospace engineering. It is another must read if one wants a good grounding in Aerodynamics, and who wouldn’t want that? At first, basic concepts of fluid dynamics are explained. Then Anderson proceeds with incompressible flow. He explains the basics of potential theory and modern methods of aerodynamic analysis. The book finishes with explaining the basic concepts of compressible flow, as they appear in flight faster than Mach 0.3 . Again, this is a must read for any aerospace major, as it is a very gently introduction into the rather complicated field of aerodynamics!

Aircraft Design: A Conceptual Approach (Raymer) – This book is the bible of aircraft design. Raymer takes a practical approach and explains how every little part of an airplane is designed in the conceptual design phase. The first part of Aircraft Design is about getting the plane on the paper and the conceptual workflow. The second part is about analyzing designs. Suited for both the student and the practicing engineer, Aircraft Design does a very well job introducing basic and more advanced topics of aircraft design.

Theory of Wing Sections (Abbott, von Doenhoff) – Wings generate the necessary force to lift an airplane off the ground. They do this by changing the flow field around an airplane. They key parameter for creating a flow suitable for flight is the profile, or section, of the airplane. For this reason the NACA (National Advisory Comittee on Aeronautics, later to become NASA) conducted a lot of research into this particular area. The results of that research are compiled in this book. Theory of Wing Sections has the necessary data for the design of wings in a thorough and handy form.

Stay tuned for the next part in The Aerospace Engineer’s Library, where we will discover a few books for the digital world of the aerospace engineer!

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As a first year aerospace (or mechanical) engineering student it is really hard to find out which books are really worth the money and which are not. Being almost done with my bachelor’s degree in aerospace engineering, I have gone through a lot of books, some rather disappointing, others eye opening. I found out that it is hard to find god reviews and recommendations for books that could help one along the journey. Textbooks unfortunately are shamelessly overprized, reviews usually go to both extremes (ranging from “Oh my God this is the bible!!!” to “Worst book ever printed in human history”, I read it all). Most students have had bad experiences with textbooks early on, since scientists sometimes tend to boast and cherish a complex and hard to understand style of writing. Money beeing scarce, students oftentimes don’t want to take the risk. So here is my very special selection of books that will help anybody who is, or wants to, study aerospace (or mechanical) engineering. Beware, as some of the books I recommend will be in German.

In this first instalment of The Aerospace Engineer’s Library we will discuss books for mechanical engineering (of which aerospace engineering is a sub-field) in general.

General Mechanical Engineering

Technische Mechanik (Heinz Ulbrich) – Every mechanical engineer (and related) needs a thorough grounding in engineering mechanics. Paradoxically, this is one of the courses that students are most afraid of! The reason for this paradox is fairly easy; most mechanics professors (especially in Germany) suck at teaching and are proud if more than 40% of the students fail their class. How crazy is that! Heinz Ulbrich did a pretty good job with his book. There are no explanations, as this is left to other books, but instead worked problems. There are plenty of solved problems for all important fields of mechanics (statics, dynamics and mechanics of materials). This book is a real gem, because the solutions are very thorough. One can basically reach a working knowledge of engineering mechanics by knowing the basics and working through this little book.

Control Systems Engineering (Norman S. Nise) – Wow, this one is a real beauty. Partly in color, very complete. In this book one can find everything that is needed as an undergraduate mechanical engineer and more (I’d even theorize that it’s all you need to have as a graduate and doctoral student, depending on where you want to go)! The writing style is great, concepts and theories are very well explained and the text is enhanced with many diagrams, pictures, real world examples and sample problems. Problems can be found at the end of each chapter and solutions at the end of the book.

Maschinenelemente (Roloff/Matek) – Knowledge is nice to have. But if that knowledge cannot be transformed into practical value, it is worthless. This book helps to transform the theoretical knowledge one has learned in college into real-world problem solving. See, the theory you learn in college will not help you at all in dealing with the real world problems of a mechanical engineer. You need to know how things are done in the real world, and this book will show you. The Roloff/Matek, as it is affectionately called, is a textbook that shows how classic mechanical engineering tasks are solved. Almost everything you need to know is in here, from the design of specific mashines to the preliminary calculations. Emphasis is on how things are done, not so much the theory.

CATIA V5, Grundkurs für Maschinenbauer (Ronald List) – Back in the day mechanical engineers had to do everything by hand. There was no cool computer program that could help them. Now things have changed (though it is still not certain if the computerization of engineering has made the task easier or harder). CATIA is one of these programs, helping to shape an engineers ideas in a 3D instead of a 2D environment (pen&paper). Unfortunately somebody has done a very bad job writing a documentation and tutorial for CATIA. This book fills the niche. It is a coherent collection of more or less step by step tutorials that give you hands on practice. This makes it fantastic for learning the basics of CATIA. Of course there will be much more to learn but this book will teach you more than your college classes!

Stay tuned for Part 2 of this series, where we will discover a few books specifically for aerospace engineering.

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