Register

The Very Best Speed to Fly

Gemini Sparkle

Key Takeaways:

  • The article explores optimal aircraft cruising speeds, balancing fuel economy with the inherent value of speed itself, proposing a "figure of merit" like speed squared divided by fuel flow.
  • This leads to the concept of "Carson speed," which identifies the most efficient speed when considering both distance and time saved, often higher than the best range speed due to practical aerodynamic factors.
  • Building on Gabrielli and von Kármán's work, Carson devised a normalized efficiency metric to compare any type of conveyance against a theoretical performance limit, which also serves as a preliminary design tool for aircraft.
See a mistake? Contact us.

I’ve noticed lately that I fly more and more slowly and pay more and more attention to fuel flow. Clearly this behavior is related to the rising cost of fuel; as it goes up, the best speed to fly goes down. But that relationship – speed divided by fuel flow – must be corrected by a scaling effect related to one’s impatience, anxiety regarding disposable income, age, number of children in college and so on. No doubt one could construct a long equation, loaded with fractional exponents whose values would vary from day to day, and whose solution is the reading on my airspeed indicator.

At a first glance you might suppose that by slowing down I was doing nothing more complicated than trying to maximize my airplane’s specific range, or what in common parlance is called its gas mileage. If that is the case I’m not doing a very good job of it, because that number, which is about 25 nautical miles per gallon for Melmoth 2 at 12,000 feet – I usually cruise as high as I can without needing oxygen – is achieved at an indicated airspeed of 100 knots. I’m going slower, but I’m not going that slow.

Peter Garrison

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, ""Technicalities"" and ""Aftermath,"" with FLYING readers.

Ready to Sell Your Aircraft?

List your airplane on AircraftForSale.com and reach qualified buyers.

List Your Aircraft
AircraftForSale Logo | FLYING Logo
Pilot in aircraft
Sign-up for newsletters & special offers!

Get the latest stories & special offers delivered directly to your inbox.

SUBSCRIBE