# Henk Tennekes

The MIT Press 1997
A book review by Danny Yee © 1997 http://dannyreviews.com/
Unlike most works of popular science, The Simple Science of Flight doesn't shy from equations and simple algebra. It also uses units such as newtons and joules and assumes a basic understanding of vectors (for simple force triangles). Anyone with high school physics should be able to follow it without problems, however, and it wouldn't be a bad choice for someone wanting to learn some simple physics. Tennekes uses examples from everyday life to help illustrate physical concepts and units, and he writes about flight quite generally, treating insects, birds, and aircraft (powered and unpowered) together. Simple but attractive ink drawings complement the text.

The Simple Science of Flight begins with the relationship between wing size, weight, and speed. This is embodied in a "Great Flight Diagram", which plots weight against cruising speed. It goes on to look at the power requirements of flight and the "nutritional" requirements of birds and aircraft. The energy values of different fuels and the efficiencies of various forms of transport are compared — have you ever wondered how a budgie stacks up against a Porsche or a 747 when it comes to energy per unit weight per metre travelled?

Wind and weather affect everything that flies. Slope soaring and the use of thermals are important for both soaring birds and hang-gliders; strong winds can play havoc with the migrations of birds and the scheduling of airline flights; and wind direction is a major issue at take-off and landing. The critical ratio between lift and drag (the glide ratio or "finesse") is illustrated in the "Great Gliding Diagram", plotting rate of descent against airspeed. The aerodynamics behind this explain why the slenderness (aspect ratio) of wings matters, and why hovering (in the fashion of hummingbirds) is so inefficient.

A chapter on "flying playthings" covers ultralights and sailplanes, the design of paper airplanes, and the history of human-powered aircraft. And the final chapter is a hymn of praise to the Boeing 747, which Tennekes considers one of the great engineering wonders of the world. He argues that it fits perfectly into a niche created by the constraints of physics and engineering (and of air temperature and density) on the one hand and the practical realities of commercial aviation on the other.

Reading the The Simple Science of Flight was pure pleasure. It is clear and readable without being at all patronising, and should be enjoyed by everyone from school students and bird-watchers to physics and engineering graduates.

September 1997

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