Flying Machines Today — Key Ideas to Explore

Theory vs. Practice in the Excerpts

The catalog subjects “Aeronautics; Flying-machines” suggest a broad survey, but the excerpts reveal a strong bias toward quantifiable engineering. Ennis repeatedly reframes practical problems as mathematical ones. For instance, he calculates that at the most effective condition, “the resistance to propulsion is only about one-tenth the weight supported,” concluding that “the air is helping the motor.” He also derives optimal angles and speeds by balancing direct pressure resistance against skin friction, noting that the latter “does not depend on the angle of inclination.” These passages show a writer more interested in deriving principles from numbers than in describing machines.

Yet the excerpts also contain practical warnings: if a dirigible’s steering gear breaks and the wind strikes the side, “the pressure of the wind against this greatly increased area would absolutely deprive it of dirigibility.” Ennis thus moves fluidly between abstract formulas and real-world failure modes, a duality that the catalog subjects alone do not capture.

The Dirigible as a Case Study in Trade-offs

Ennis devotes considerable attention to dirigible balloons, analyzing how shape, size, and structure interact. He notes that a hemispherical bow reduces head-end resistance by about one-third, while a sharp cone can reduce it by four-fifths. However, he warns that “unless the stern is also tapered, there will be a considerable eddy resistance.” Longer balloons reduce head-end resistance but become structurally weak: “more is lost by the extra bracing necessary than is gained.” He cites the Zeppelin as “the limit of progress in this direction,” implying that further lengthening would be counterproductive.

This section is notable for its frank admission of trade-offs. Ennis does not simply catalog types; he evaluates why certain designs succeed or fail. The excerpts also mention the smallest dirigible ever built—Santos-Dumont’s 5,000-cubic-foot craft—as a point of comparison. The overall tone is one of cautious engineering judgment rather than promotional enthusiasm.

The Role of the Lay Reader in a Technical Subject

Ennis states in his preface that the book aims to be “comprehensible to the lay reader” and to convey “even a small proportion of the writer’s conviction that flying machines are to profoundly influence our living.” Yet the excerpts are dense with formulas, references to “the square of the velocity,” and discussions of “frictional resistance” and “direct pressure resistance.” The tension between accessibility and rigor is palpable. Ennis occasionally simplifies—for example, by assuming “square flat planes” while acknowledging that real sails are “arched and of rectangular form”—but he does not shy away from presenting the underlying mathematics.

This approach suggests that the intended lay reader is not a casual enthusiast but someone willing to engage with technical reasoning. The book’s structure, with chapters on “The Question of Power” and “Resistance of Dirigibles,” reinforces this impression. The catalog subjects do not convey this pedagogical stance, which is central to understanding the work’s character.

Readers should approach Flying Machines Today as a period document that reveals how an engineer in 1911 thought about flight: through equations, trade-offs, and a conviction that theory must guide practice. The excerpts offer only a partial view—the full text likely includes more illustrations and descriptions of specific aeroplanes—but they are enough to show that Ennis’s book is far more than a catalog of machines. It is an argument for a particular way of knowing, one that values calculation over anecdote.

That rainy afternoon, the professor’s maths for lift and drag kept me company, yet my mind wandered to the ground beneath—its unseen layers, its stubborn geology. Odd, how one technical passion drifts into another. I found myself reaching for Water Supply: the Present Practice of Sinking and Boring Wells With Geological Considerations and Examples of Wells Executed — Inside the Classic, and the rain seemed to listen.