Lift Coefficients

Summary

• Airfoils CLmax
• Aircraft CLmax and Control Systems
• Powered Lift Systems

Table 1 reports some typical coefficients for airfoils in a wide range of Reynolds numbers.

The maximum lift coefficients of complex wing systems (wings with leading edge slats and one or more flaps), is strongly dependent on the configuration and the design. Reference values can be CLmax between 3 and 5 (for 2-D data).

These figures may shift toward higher values with the up-to-date design methods. Three-dimensional data are more difficult to find in the technical literature. They must be considered lower than the corresponding 2-D data.

Some data gathered from Boeing (Brune and McMasters, 1991) are as reported on Table 2. Data from Fokker show a CLmax=3.25 for the Fokker 50 (1982), and CLmax=3.45 for the Fokker 100 (1984). Note that the CLmax may not be the same as the one certified by the aviation authorities.

Table 3 is a summary of CL ranges for some powered high lift systems, designed for V/STOL aircraft. The data have been elaborated from Boeing Aircraft (1973), as reported by Kuethe-Chow (1998). Flap angles are in the range 30-60 degs. The data are somewhat approximate.

Table 1: Maximum Lift Coefficients

Configuration	Re
single element airfoil (E387)		1.2
single element airfoil		–
single element airfoil (0012)	3 .	1.55

Table 2: for some Aircraft Wings

Wing	Configuration
Boeing B52 (1947)	Slat + Fowler flap	1.80
Boeing 727 (1963)	Slat + single flap	2.45
Boeing 767 (1981)	Slat + triple flap	2.79

Table 3: for Powered Systems

System	CL
Internally Blown Flap	4 ÷ 9	9
Upper Surface Blowing	4 ÷ 8	8
Externally Blown Flap	5 ÷ 7	7
Augmentor Flap	4 ÷ 7	7
Vectored Thrust	1 ÷ 3	3