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# Lift coefficient

Lift Coefficient
MACH - Various MACH Related Definitions
Magnus effect ...

Lift Coefficient
An indication of the relative lift of an aerofoil.
Lift-Drag Ratio ...

LIFT COEFFICIENT - A number that aerodynamicists use to model all of the complex dependencies of shape, inclination, and some flow conditions on lift. CL is the non-dimensional coefficient of lift. If the subscript used is a lowercase l, then the section or airfoil (2D) lift coefficient is meant.

The Lift Coefficient and the Drag Coefficient represent the changes in lift and drag as the angle of attack changes. CL and CD are not expressed by any physical unit, they are rather absolute numbers obtained from either wind tunnel tests or derived mathematically.

The lift coefficient can thus be effectively doubled with relatively simple devices (flaps and slats) if used on the full span of the wing.

If the Stall Model is used and the wing stalls, these plots are not available.
The remaining plot choices show Lift or ~ -Cl versus each of the input variables. For these plots, the current value of the flow conditions is shown as a red dot on the plot.

The wing section (tested as the Gottingen 289 section after the war) had a maximum ~ of about 1.4. Making estimates for each of the triplane wings (working as independent surfaces), the planes would require 19.2, 20 and 21 degrees respectively to reach the maximum ~.

When the wing is stalled and the angle of attack is greater than the stalling angle, any increase in angle of attack causes a decrease in ~ that causes the wing to descend.

Since the AOA is fixed at best glide, so, also, is the ~. There is only one factor that we can vary to adjust the lift to match any change in effective weight, the speed. Moving the CG aft, you reduce the second contribution, but leave the first unchanged.

With classic airfoils, those used over the last 30 to 50 years, we have accustomed to a maximum ~ of 1.4 to 1.5 with a 12 to 15% thick (d/e) airfoil and a drag coefficient of .01 in cruise configuration (ie. NACA 4412, NACA 22012 and NACA 23012 or 23015).

Non-symmetrical cambered airfoils have a higher ~, but they also
have a negative pitching moment (Cm) tending to pitch nose-down, and thus
being statically unstable, which requires the counter moment produced by the
horizontal stabiliser to get adequate longitudinal stability.

LIFT-DRAG RATIO - The ~ of a wing divided by the drag coefficient, as the primary measure of the efficiency of an aircraft; aka L/D Ratio.

L is the lift
k is the Smeaton coefficient- 0.005 (the drag of a 1-square-foot (0.093 m2) plate at 1 mph)
Cl is the ~ (the lift relative to the, or L/D)
A is the area in square feet ...

See also: What is the meaning of Lift, Aircraft, Wing, Speed, Drag?

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