Digital Theory Confronts Modern Computer; Traditional Stance Remains Intact
In a groundbreaking study published 45 years ago, B.H. Carson, a renowned aeronautical engineer, calculated the optimal cruising speed for small aircraft that minimises fuel consumption while maximising speed. This speed, now known as the "Carson Speed," offers a significant improvement in efficiency for single-engine propeller planes.
The Carson Speed is calculated as the fourth root of 3, which equates to 1.31607. This optimal speed was determined through simulations run for various types of single-engine aircraft, including the Cessna 172, Mooney M20J, Bonanza, and Cirrus SR22. The highest products of true airspeed and miles per gallon (mpg) were achieved at indicated airspeeds of 106 knots for the C172, 134 knots for the M20J, 151 knots for both the V35 and SR22.
Carson's argument focuses on the lift-drag ratio (L/D) as a metric of efficiency. The L/D ratio is a measure of the lift generated by the wings of an aircraft compared to the drag it experiences while moving through the air. The higher the L/D ratio, the more efficient the aircraft.
Interestingly, the Carson Speed is a very blunt instrument, and the penalty for using more power is not as significant as it might seem. Propellers, including variable-pitch propellers, have a design speed for greatest efficiency, and manufacturers place it above the Carson Speed. However, the calculated best L/D speeds for the planes were lower than their published gliding speeds, with the difference being approximately 10 knots.
The AIAA paper titled "Fuel Efficiency of Small Aircraft" discusses the efficiency of airplanes, using specific range (miles per gallon) as a yardstick. Carson's essay introduced the terms "Carson Speed" and "the least wasteful way of wasting." The paper also delves into the efficiencies of vehicles in general, including battleships, race horses, and trolley cars.
When it comes to practical applications, the optimal cruising speed for small aircraft is generally near the aircraft's Long Range Cruise (LRC) speed. This speed provides about 99% of the maximum specific range—the greatest fuel efficiency per nautical mile while allowing a small margin in speed. Flying higher generally improves true airspeed for a given fuel flow, meaning the aircraft covers more distance for each gallon burned, often encouraging cruise at or near the service ceiling for small aircraft when feasible.
In conclusion, the Carson Speed offers a valuable insight into the optimal cruising speed for small aircraft. By balancing fuel burn and forward velocity, this speed maximises efficiency and provides a significant improvement in range for these aircraft. Pilots planning flights should consider the Carson Speed to minimise fuel consumption and optimise their journey.
The Carson Speed, calculated as the fourth root of 3, offers optimized cruising speeds for various single-engine aircraft, such as the Cessna 172, Mooney M20J, Bonanza, and Cirrus SR22, resulting in increased fuel efficiency and speed without significant power penalties. Interestingly, the Carson Speed is a rather blunt instrument, as propellers have a design speed for greatest efficiency, often placing it above the Carson Speed. The AIAA paper titled "Fuel Efficiency of Small Aircraft" further delves into the efficiency of vehicles, including airplanes, battleships, race horses, and trolley cars. When planning flights, considering the Carson Speed can help pilots minimize fuel consumption, optimize their journey, and achieve the least wasteful way of wasting fuel. Flying higher generally improves true airspeed for a given fuel flow, making it practical to cruise at or near the service ceiling for small aircraft when feasible. Connecting the Carson Speed to health-and-wellness and fitness-and-exercise, pilots can build a more efficient and eco-friendly lifestyle through sport-flying practices. Adhering to the Carson Speed principles can indeed be a significant improvement in science, aviation, sports, and one's health and wellness.
