All the answers so far are correct, but don't directly address the reason for the
confusion between you, your sister, and your sister's teacher.
- In a
steady climb, lift will be less than weight. The vertical component of lift, plus the vertical component of thrust, minus the vertical component of drag will be equal to weight.
But this only applies in a
steady climb.
could someone please confirm, (if indeed this statement is correct) that in a climb, as of the moment an aircraft lifts off the ground and starts a climb, WEIGHT will theoretically be GREATER than LIFT?
This is not true, because it is not a
steady climb. At the moment of rotation, lift will indeed be greater than weight, as your sister's teacher says.
What is actually happening is that, as the aircraft is rotated, the angle of attack is increased, and this gives a corresponding increase of lift, until eventually lift is greater than weight and the aircraft becomes airborne. At this point, the aircraft's path through the air changes - it is no longer just horizontal, but it has some vertical element, too, because it is going up. This changes the direction of the relative airflow the wings experience, reducing the angle of attack, so that once a steady climb has been achieved, lift is back to being less than weight.
FFF
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