Galaxy is correct. When considering a Thrust Required curve, the lowest point is L/D max, whether piston or jet airplane. However, when determining Max Range and Max endurance, a piston airplane uses the Power Required curve, not Thrust required.

For a reciprocating engine, specific fuel consumption (commonly abbreviated SFC) is defined as the weight of fuel consumed per unit power per unit time. Anderson, John. Introduction to Flight (p. 501). McGraw-Hill Higher Education. Kindle Edition.


Thus Breguet Endurance and Range equations are determined from using Power Available versus Power Required curve. See attached. For a propeller airplane, maximum range is CL / CD max. Max endurance occurs at a CL^3/2 / CD max.


To maximize range for a reciprocating-engine, propeller-driven airplane, we want the following:

1. The largest possible propeller efficiency η.

2. The lowest possible specific fuel consumption c .

3. The highest ratio of W0 / W1 , which is obtained with the largest fuel weight WF .

4. Most importantly, flight at maximum L / D .


Anderson, John. Introduction to Flight (p. 505). McGraw-Hill Higher Education. Kindle Edition.


For a jet airplane, the Breguet Equations are derived from Thrust Required. As such, for jet airplanes CL / CD max corresponds to Max Endurance. Max range occurs at CL^1/2 / CD max.


to obtain maximum range for a jet airplane, we want the following:

1. Minimum thrust-specific fuel consumption ct .

2. Maximum fuel weight Wf .

3. Flight at maximum CL^1/2 / CD

4. Flight at high altitudes


Anderson, John. Introduction to Flight (p. 512). McGraw-Hill Higher Education. Kindle Edition.