Author’s note


This book is the outcome of years of frustration trying to make sense of fluid mechanics for the lectures that I was giving to degree students who were studying mechanical engineering. It is always easy for a lecturer to present the current textbook approach to the subject and take refuge in the fact that no-one else was presenting anything else, but the fact remained that, whenever I tried to understand the basic concepts such as viscosity and pressure energy, the textbooks were most unhelpful. When I tried to use textbooks to design laboratory equipment the whole approach in the books seemed to be aimed at creating confusion. When I tried to teach engineering design I had to move right outside the standard texts into engineering handbooks. These handbooks did not even pay lip service to the ordinary texts and I had to evolve my own ways of bridging the gap between them. It was exhilarating to find that I could span that gap and that I could see how to fit it all together but I knew that there was a long way to go.


When I retired after lecturing for 35 years I knew that something was wrong in the heart of my thinking.


I bought a computer and an early word processing package (Chiwriter) and set about trying to understand what I had been teaching. I obtained copies of original papers by Reynolds, Froude, Rayleigh and others just to see where it all began. They proved to be an absolute joy to read after the confused versions that have found favour in the “standard” texts. The early authors were not trying to fit into an inherited mode of thought and so wrote freely and delightfully.


I worked for two years and stopped for two reasons. One was medical and the other was that I found that I could not write a chapter on aerodynamics. Perhaps I knew in my heart that it was not yet right.


The book stayed on the shelf for nearly 10 years but during the latter 5 years I took up model yacht racing. Model yachts are difficult to understand and I could find no coherent text on them. Nor, for that mater, could I find anything convincing about full sized yachts. My experience with teaching design had convinced me that if I plug away at any engineering problem using my knowledge of physics I make progress with it and discover things that I did not know. So I broke the yacht down into its several components and, using a much more modern computer, set about explanations. In the end it became a book on how model racing yachts work. I had 2,000 copies printed and took over 1,800 to the recycling centre. I discovered the hard way that no-one in yachting wanted to think about what they were doing because there was more fun to be had backing hunches. No matter, one lives and learns. However, as the fin and rudder of a yacht is really an aerodynamic contrivance and I had analysed it, I could no longer escape the aerodynamics chapter.


I re-examined my original problem. I had supposed that there would have been fundamental developments in aerodynamics after, say, 1950 yet I could not find them. I supposed that they were in the hands of aircraft makers. Suddenly I realised that there were no fundamental developments in the science of aerodynamics to be found. We know all that we usefully can and nowadays people concentrate on applications.


There was another consequence of writing that book. As far as I can tell my book on sailing mostly cut new ground and I found that it was necessary to use the first person in much of the text because what I was saying was my interpretation of the yacht and how it sailed and not someone else’s. When the sailing book was finished I thought that I would look back at the first book on fluids I was quite appalled by its style. It was just another run-of-the-mill text-book with no spark of life. Something was seriously wrong with it. Gradually it dawned on me that most text-books are a compilation of other people’s work and that authors do not let their own views intrude explicitly. I had long since come to recognise that each of us has some mental model of science that we try to use and all the models are different. I have altered my model several times over the years in large steps and in small steps and, I suppose, others do the same. This means that the model I now use is quite different to the one that I used 10 years or that of 20 years ago. This is a very liberating thought because, once I accepted that I was going to describe my current mental model, the text became much more interesting and much more fun. In addition, as I planned to publish it privately I did not have to persuade someone else of the value of my book.


Then I thought about this aerodynamics business and I realised that what was true for aerodynamics was also true for all the other sections. I concluded that, during my life-time the science of fluid flow has evolved to a level that is adequate for almost all engineering purposes and that most text books contained a good deal of material which only might one day prove to be useful. They also contained material that was included, not for its intrinsic value to the text, but for its mathematical content so that the book would be seen to be mathematically oriented which is seen to good with a capital G. I can now see that much of this material is not going to fit into the coherent body of knowledge that has evolved but it is very difficult to displace and it is singularly difficult to teach for want of a context. I am in a position to examine the material in syllabuses and decide what I think is relevant. This is not a criticism of all existing text-books. How could E. J. Lewitt writing totally honestly in 1923 anticipate the science that evolved in the subsequent 40 years?


The more that I look at technical papers the more it comes home to me that they are not written to be read but to proclaim the erudition of the authors. Only two books seem to me to be totally honest and very competent. They are Lewitt and Prandtl and they are as different as chalk and cheese. In almost every paper the core of the subject is hidden behind a screen of mathematics that has to be penetrated before the core can be found. When the core is reached it is often devoid of any practical value and the whole exercise proves to be pointless.


Over the years I have come to recognise the underlying structure of the science, if that is the word, used by engineers and I can separate it from the bolted-on mathematics. I am going to try to divest the basic things needed for engineering from the over burden that has been acquired over the years. I also want to add some practical content to give a context.


So I pick this project up after 10 more years have elapsed and I want to change nothing in this foreword only to add to it. However I have been learning and the internet has been evolving and now I can put my book into the public domain without having to get it published. This is important because I do not have to consider the views of those who might be needed to recommend it to their students.


As I approach the ripe old age of 81, I am going to try again. I have a web site about all sorts of things that interest me and I have learnt how to get my thoughts into the public domain. I think that I might just write away and post in on the web as I go along. But it not going to be easy!


Ivor Bittle

July 2008