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:

B.H. Carson's 45-year-old paper introduced "Carson Speed," defined as 1.32 times an aircraft's best lift-to-drag (L/D) speed, designed to yield the greatest saving in time for the least excess fuel.
Carson's original model neglected practical variations in engine and propeller efficiency, which are typically optimized for higher power settings and speeds than the theoretical Carson Speed.
Accounting for these efficiencies, a "Real Carson Speed" (maximizing the product of speed and miles per gallon) is generally higher than the theoretical Carson Speed based solely on L/D.
Simulations show that the efficiency curve around the "Real Carson Speed" is relatively flat, meaning operating at higher power settings (e.g., 75% power) results in only minor percentage losses in the speed-mileage product.

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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.”