Which source(s) provides the most authorative and correct flight dynamics theory?

Question

Just like many curious people, the question: " How airplanes actually work?" occupied my mind for a long time.

Different sources gave different answers where most claimed the Bernoulli Principle to be the main reason while many disagreeing with that and so on.

Then I came across this: https://physics.stackexchange.com/q/51503/266050

This has many answers and all in great detail. This gave me a lot of knoweldge and pretty much outlined the many factors that are responsible.

Unfortunately, there is no unanimous consensus even on those answers. The accepted answer (like many others) is detailed and beautiful but there are comments disagreeing with that and people holding different views on which factors actually contribute primarily for the working of airplanes.

Now, usually the answers and discussion given on stackexchange would be more than sufficient but in this case what bugs me is that airplanes are actual things used daily and there are people who design and create them. These people (aircraft engineers, scientists etc) surely must be really certain about how these things work (or so I hope ?) and not be confused with things like whether the upper part of the wing pushes air down or actually pulls it up (not that they would have different outcomes or effects but one ought to know!) or whether the angle of attack really does play a role or not. The reason for my assumption of flight engineers having surity of knowledge to the core is that they need to know with high accuracy and precision the conditions and limits under which airplanes will work and when a certain principle would fail.

Why is it then that not a clear concise unanimous theory is available (or is it?) open-source etc that covers every factor and the extent to which they matter and which is accepted (or rather reffered to) unanimously without confusion?

If, on the other hand, there is a source (or sources) available after reading which I can confidently say that I know with very high certainty and with all technicalities how airplanes work, I hope to know where and how I can find it.

Answer 1

There is unanimous agreement (at least among people who actually understand physics) that

• the Navier-Stokes equations are the best we've got and
• you can't get simpler than that!

By the second point I don't mean it's simple. Not only they are not simple, but they exhibit such complex behavior that it wasn't fully explored even from the pure mathematical standpoint.

What I mean is that all the properties described by the equations (conservation of mass, momentum and energy, viscosity and pressure) are important in creation of lift and you can't skip any of them and still arrive at something at least somewhat approximating reality.

There are some theories with which would can get fairly accurate estimates of lift like the lifting-line theory and the thin airfoil theory with much less calculation, but they all have serious limitations and depend on experimentally-determined factors. They don't really explain lift itself, only some relations around it like what is effect of increasing span or chord.

Answer 2

Your question may not have a certain and definitive answer. Nevertheless, there are two particular areas (and two particular books) that can be discussed in guiding your attempt to find a definitive answer. Indeed, what is an authoritative source for understanding flight-dynamics theory?

The two areas are -

1. The principles of flight
2. The elements of aircraft design

These two areas are an inseparable and expansive body of knowledge. For the engineering practitioner, the common core areas linking these two areas are many, requiring an understanding of a) mathematics at least through differential equations (matrix theory and linear algebra are especially helpful), b) the principles of physics and atmospheric science, and c) engineering and applied science. Within this last area should be knowledge particularly in disciplines of d) fluid mechanics, e) strength of materials and structures, and f) applied mechanical engineering, particularly in g) materials science, h) power and propulsion systems, and i) aircraft systems design. All of these areas are inextricably linked through experimentation and assessment. Properly defining a problem requires a complete understanding of the problem. Things we think of as authoritative and complete are rarely, if ever, totally comprehensive and inclusive or exhaustive. Flight dynamics theory is as much an attempt to understand why things work, as to understand why things don't work.

For a start, the following is suggested -

Gudmundsson, Snorri, 2014, General Aviation Aircraft Design: Applied Methods and Procedures. Butterworth-Heinemann (Elsevier), Oxford. 1034 pp, several appendices.

Upon examination of this book and others, you may be given pause; "but wait... this is just what I did not want to do!" So lets look at another book that is a superbly easy read, absolutely indispensable, and requires only algebra and a little calculus to understand. That book is -

Dommasch, Daniel O., Sherby, Sydney S., and Connolly, Thomas E., 1967, Airplane Aerodynamics, 4th ed. Pitman Publishing Corp., New York. 621 pp.

This book has a clear and authoritative discussion of the principles of flight, and an overview of factors involved in aircraft aerodynamics and flight performance. When you read through this book, you will get a pretty good idea regarding the scope of flight dynamics without frying your brain. This text is particularly helpful regarding propeller driven aircraft. At the heart of the book, which is easily understood, are two central sections, 11:7 and 11:8, regarding the V-g diagram. All of the factors regarding why airplanes break are discussed therein. Gudmundsson's book has an in-depth engineering discussion of the same topic starting in section 16.4; only algebra is needed to work through his examples.

But you may say, I just want to know why airplanes fly. Most books you will read will discuss the part regarding how airplanes fly, leaving the why as seeming conceptually difficult or lacking. When you find references to theory, you should pay close attention (even if your brain gets fried) because that is where the conceptual developments and basic understanding are found; sometimes difficult, as they may be.

A suggestion would be to read, read, read. Take lots of notes, write your own personal text, capture your own ideas, maybe experiment with the math. And look at the cited references in what you read; these may be real gems. See what you think. This can be fun...

Answer 3

A complete theory is taught in universities and takes at least 5 years to master. You would know quite a lot of the science of aerodynamics after obtaining your doctorate, which takes even longer.

Or you could obtain a degree in aeronautical engineering. That is where you learn about the multiple fields of technology that keeps an aircraft in the air and enables passengers to trust them with their lives when flying to Bali. But now there's an issue: there are way more subjects to be taught in 5 years than only fluid dynamics, like thin walled structures, systems technology, safety engineering, human-machine-interaction etc, plus the mathematics and physics that lies at the foundation of all of this. So now we need to start making judgements on where to stop.

What to teach and what not is a function of the end goal and the audience.

• The design engineers of a passenger aeroplane needs to be able to integrate all relevant knowledge to an extent that enables people flying to Bali to trust the machine with their lives.
• Focusing on pilot training: quick decision making and rapid and consistent control is the key element. The airplane is already there, it is tested in the wind tunnel, constructed in the factory, flight tested and calibrated by the test pilots etc. So it is important to provide quick understanding of the principles of flight, only relevant to keeping the plane in the air.

So why do wings provide lift? For a pilot, all knowledge of cruise, max. altitude, static and dynamic stall, anything to do with adverse aircraft state and navigation is the main objective here - we leave out what is not of direct importance, and move on to the science of wind shear at approach. The comments on the physics site comment on what is left out of a relatively simple explanation that is sufficient for 80% of cases.

There is full agreement on what is correct aerodynamics theory. Now with computers, we can finally use the Navier Stokes equations to compute aerodynamics acting on wings. But a very important decision remains: who is the audience, and what would best be left out.