MY friend, you don't seem to understand the relationship between, speed, and angle of attack over an airfoil. Given that the weight of the aircraft is generally the same no matter what the altitude, then yes, during lift off the lift is the greatest. But not because of engine thrust: BECAUSE THE ANGLE OF ATTACK OF THE WING IS AT ITS HIGHEST during Take Off. During cruise weight=lift, therefore no change, angle of attack is at around 2-3 degrees. During descent the weight overcomes lift, but some lift is still required to stop the aircraft just plummeting out of the sky.
The main part that the engines play is to create thrust which creates airflow over the wings, this creates enough of a pressure difference over the top and bottom of the wing to allow for lift. The two main factors in a wing producing lift is speed and angle of attack (up to alpha max) Increase either one and you get more lift.
The thrust of the engines produces very little lift force. In fact props have more of a lift advantage because the airflow from the prop flows over the wing.
What is your level of education vis a vis theory of flight, you are asking some pretty strange questions and based upon your comments you sound pretty confused. The question you are asking is quite straight forward. Like I said I don't think you understand the basic principles of flight.
Last edited by Airmann; 29th October 2012 at 12:32.