Talk:Center of lift

Verifiability of center of lift

This article began in September 2006 when Ericg inserted the first text. He summarised his work by writing center of lift is absolutely not the same as center of pressure. He left no reference or citation to show that his text was verifiable.

The present text states An aircraft's center of lift is the location at which the net lift produced by all airfoils is located. I am not aware of any author who has used the term center of lift, either for this purpose or any other purpose. (However, there may be one or two authors who make use of the term. If so, they should be cited.)

Perhaps the reason mainstream authors don’t define a point called center of lift is because the net lift produced by all the airfoils on an aircraft must act through (or extremely close to) the point called center of gravity! It is the function of the horizontal stabilizer to generate just enough lift, usually in the downwards direction, to keep the aircraft balanced in pitch. In steady flight the vector sum of the lift on the horizontal stabiliser and the lift on the wing and fuselage passes through the center of gravity. If the center of lift and the center of gravity were not aligned vertically the aircraft would begin to tumble nose to tail.

In unsteady flight, such as pitching nose up or down in a maneuver, the net lift does not act through the center of gravity in order for the lift vector and the weight vector to generate the necessary pitching moment. However, any mismatch of lift and center of gravity for the purpose of conducting a maneuver is a very small distance and a brief period of time.

Similarly, if the thrust vector and drag vector are not aligned they will generate a small pitching moment. This pitching moment must be counteracted by an equal and opposite pitching moment generated by the net lift not passing exactly through the center of gravity.

The present text also states the center of lift is an important factor in the performance and stability of an aircraft. I disagree. The important parameters in assessing the stability of an aircraft are aerodynamic center and neutral point. The center of pressure on an airfoil is also useful for a preliminary understanding of aerodynamic center and longitudinal stability, but the usefulness of center of pressure is limited because it moves fore and aft, depending on angle of attack (or lift coefficient). See movement of center of pressure.

Many authors in the field of aircraft stability use the terms center of pressure and aerodynamic center, but I am not aware of any author who has used the term center of lift. The center of pressure and aerodynamic center are defined for an airfoil and are arbitrarily located on the chord line at the point where the lift vector intersects the chord line. A complete aircraft does not have a chord line so if there is a formal definition of center of lift I am puzzled as to where it is located vertically.

WP:Verifiability contains the policy statement that the threshold for inclusion in Wikipedia is verifiability, not truth. Unless someone can provide a citation to support the verifiablity of this article, I propose that it be deleted or again redirected to center of pressure. Dolphin51 (talk) 03:40, 26 June 2008 (UTC)

I kind of forgot about this project when I purged my watchlist. Just a quick google search shows that fiu.edu (an educational site connected to NASA) and How It Flies (which is an extensive print/online textbook about flying) both refer to the 'center of lift', and are both well-regarded. My college aerodynamics courses used the term CL, and I will hit my library the next time I'm at work to get citations from a couple of aerodynamics texts. ericg ✈ 00:58, 28 June 2008 (UTC)

Ok, quick update. Aerodynamics for Naval Aviators (NAVWEPS 00-80T-80, p 47-49) uses aerodynamic center to refer to the same concept. I'll save everybody the trouble and replace this page's contents with a redirect. ericg ✈ 01:03, 28 June 2008 (UTC)