Classic Theory Meets Digital Computer; Status Quo Emerges Unscathed

A 45-year-old essay about 'Carson Speed' became a point of reference for the wonkier class of pilot.

Peter Garrison

Wednesday, May 07, 2025 at 08:30 AM ET

Verified

Edited By:

Travis Tingle

It turns out that the 'Carson Speed' is a very blunt instrument. [Adobe Stock]

Key Takeaways:

Carson Speed, from B.H. Carson's seminal paper, identifies a cruise speed (approximately 1.32 times the best lift-to-drag (L/D) speed) that optimizes speed gained for the least excess fuel consumption.
The article refines this concept to "Real Carson Speed" by integrating real-world factors like engine specific fuel consumption and propeller efficiency, which tend to push the most efficient speed higher than the theoretical Carson Speed.
Simulations show that "Real Carson Speed" for various aircraft types occurs at typical cruise power settings (e.g., 60-70 percent power) and is higher than the theoretical Carson Speed derived purely from L/D.
Crucially, the efficiency curve around the "Real Carson Speed" is quite blunt, meaning pilots flying slightly faster or at higher power settings experience only minor losses in the speed-mileage product, suggesting common cruising practices are practically efficient.

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The late B.H. Carson’s AIAA paper on “Fuel Efficiency of Small Aircraft” emerged unsought, like a dinosaur bone poking out of eroded Wyoming topsoil, from the scree of papers on my desk.

First published 45 years ago, Carson’s essay became a point of reference for the wonkier class of pilot, to whose vocabulary it contributed a couple of novel phrases: “Carson Speed” and “the least wasteful way of wasting.”