The invention of the electronic pocket calculator brought the slide rule, once an indispensable tool in many professions, to a very quick end. Only in one niche have mechanical computing devices been able to assert themselves to this day, namely in aviation, although this is an area that embodies technical progress like hardly any other. 

In the cockpit of a modern commercial aircraft, however, the old dead reckoning computers no longer have any reason to exist. Even in General Aviation, the mechanical computer has a shadowy existence, which is related to the triumph of satellite navigation.

However, these old parts are still indispensable for the navigation training of pilots and will therefore continue to be produced. This is certainly also due to the fact that the mechanical solutions for the spatial problems occurring here are particularly demonstrative. This is why the electronic navigation computers, which came onto the market very quickly, were not really able to establish themselves.

That the extraordinary variety of the mechanical navigation computers invented in the course of the relatively short history of aviation might not be too well known, led me to the idea of putting these pages on the net. Perhaps in this way I can save some of the knowledge about historical aviation computing technology from being forgotten. Above all, I wanted to pay tribute to the human ingenuity that is particularly evident here.

If you are interested in the topic of navigation in aviation, I would like to encourage you to download the documentation I have compiled on 200 pages. In order to make the explanations accessible to as wide an audience as possible, the paper is written in English.


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Klaus Petzold

26 .10.2021

PDF File

204 Pages


26 MB

About the book

This is not a reading material in the conventional sense, but rather a reference work. It is also not a textbook, but is aimed at readers who already have basic knowledge of flight navigation. In many thousands of flying hours I have gained practical experience, so that I can judge such products regarding their suitability in practice. Regardless of my personal evaluation I wanted to set a monument to the numerous inventors. Unfortunately, I do not know all their names. I am always grateful for hints at necessary additions, errors or mistakes (e-mail: info@flight-computer.de).

It is due to the nature of the task that the calculation methods are sometimes the same or at least similar, which does not necessarily mean that the inventors have been sloppy with intellectual property. With obvious solutions it is not unlikely that they have been found several times and that the creators have worked independently of each other.

To make the descriptions as simple and intelligible as possible, I almost always work with examples. These are chosen arbitrarily, which is not explicitly mentioned in the text. In order to be able to estimate the accuracy of the calculation method, the analytically found exact results are also given. These are indicated by decimal places.

The methods are primarily described without comment and the judgement about their utility value, originality and suitability in practice is left to the reader. Rare exceptions to this rule have been necessary for scientific reasons. The order of the individual chapters is purely arbitrary and in no way an expression of my appreciation.

I am fully aware that many readers who are interested in such a special topic may want to know more about the inventors, how the various inventions are linked to each other and what the influence of technical progress was on the design of these computing devices. Unfortunately, I have to disappoint these readers. Since I am no science historian, it was neither my intention nor am I able to write about it. Therefore, no historical details about individual products and their manufacturers can be found here, nor information about distribution and production figures or biographical information about their creators. For readers who want to learn more about the the very interesting history of navigation computers, I recommend a forthcoming book by Prof. Alexander Piel, whom I would like to thank for his encouragements and valuable hints for this work.