Hi,I think so too.Bottle half full or half empty..."It's a draw".Remember first flight lessons.Jan

In an aircraft, the center of gravity can move. Weight distribution, fuel burn are factors that change the location of the center of gravity.The center of lift is a non-moving point. It's a point somewhere in the chord of the wing. I say 'somewhere' because the only time it changes is if you have wings that can change their shape (F14 as example). However, because the center of lift is actually defined by the physical wing... it's not a moving point.

I originally said "For a trimmed aircraft the centre of lift is at the cg by definition." Re-read it and understand it before saying it's wrong - because it isn't. You are confusing the centre of lift of the aircraft with the centre of lift of the wing. They atre not the same.What's artificial about the lift on the tail? It's real and has to be taken accountf in trimming an aircraft. Also, what other centre of gravity is there other than that of the "actual weight"? The centre of gravity doesn't have to be ahead of the centre of lift of the wing. See the picture showing a trimmed aircraft. As long as the wing and tail pitching moments are equal and opposite the aircraft is trimmed.Of course lift and weight are vector quantities - they have position, magnitude, and direction as shown in my pictures.

Hi,I think so too.Bottle half full or half empty..."It's a draw".Remember first flight lessons.Jan

Yeah that is the basic four forces of flight

I originally said "For a trimmed aircraft the centre of lift is at the cg by definition." Re-read it and understand it before saying it's wrong - because it isn't. You are confusing the centre of lift of the aircraft with the centre of lift of the wing. They atre not the same.What's artificial about the lift on the tail? It's real and has to be taken accountf in trimming an aircraft. Also, what other centre of gravity is there other than that of the "actual weight"? The centre of gravity doesn't have to be ahead of the centre of lift of the wing. See the picture showing a trimmed aircraft. As long as the wing and tail pitching moments are equal and opposite the aircraft is trimmed.Of course lift and weight are vector quantities - they have position, magnitude, and direction as shown in my pictures.

I think this is where are misunderstanding is from. There is a Center of Pressure for the wing and Center of Lift that acts on a location on the aircraft. I was using CoL for CoP so maybe this is where the misunderstanding came from. Here is the center of pressure and showing it move back and forth with the pitch of the aircraft:

The centre of pressure (lift) of a wing doesn't necessariy change with incidence. There is little change with a symmetric wing (upto the stall) - see the left-hand figure below. With a positively cambered wing the centre of pressure is an infinite distance aft of the wing at zero lift - see the right-hand figure, where it can be seen heading off to infinity. To complicate matters further, it then moves instananeously to an infinite disance ahead of the wing as the lift becomes negative.

The centre of pressure (lift) of a wing doesn't necessariy change with incidence. There is little change with a symmetric wing (upto the stall) - see the left-hand figure below. With a positively cambered wing the centre of pressure is an infinite distance aft of the wing at zero lift - see the right-hand figure, where it can be seen heading off to infinity. To complicate matters further, it then moves instananeously to an infinite disance ahead of the wing as the lift becomes negative.

Yes what you said is what wikipedia said almost exactly... There is a change in location of lift which is important to make sure you have the center of gravity far enough in front of this force to aid the tail in lowering the nose and angle of attack to regain flight from stall.

Yes what you said is what wikipedia said almost exactly... There is a change in location of lift which is important to make sure you have the center of gravity far enough in front of this force to aid the tail in lowering the nose and angle of attack to regain flight from stall.

Wikipedia is sometimes correct.. If the centre of wing lift is ahead of the centre of gravity that will give a nose up pitching moment. Reducing the wing lift as the wng stalls reduces that, causing the aircraft to tend to pitch down. On the other hand, if the centre of lift is aft of the centre of gravity that will give a nose down pitching moment. Reducing the wing lift as the wing stalls reduces that, causing the aircraft to tend to pitch up.

Hi,Another, probably known, source:http://www.grc.nasa.gov/WWW/K-12/airplane/short.htmlJan