Lift, Drag, L/D Ratio, Thrust, Pitch Angle of Attack, Sink Rate, CofG. The list of technical terms are many, but what do they mean?
Lift: Lift can be produced by the profile of the wing (see your physics books) or by deflecting the air with the wing (stick your hand out of an open car window). Any surface tilted in an air flow to deflect the air will produce a resultant force against the surface pushing in the other direction. This force is called LIFT.
Drag: A wing moving through the air feels resistance and is 'dragged' backwards. This force is called Drag.
L/D Ratio: This is the amount of Drag a wing produces compared to the amount of Lift it produces when flying.
Profile Drag: This is the drag produced by a "body" moving through the air (wind resistance). Aerodynamic tests at Oxford University Wind tunnel showed that a pilot in a semi reclined RAD harness is more streamline, and produced about 5Kg of Drag, whilst pilots sitting upright with 'Bulky' motors produced 12Kg of Drag.
Total Drag: The sum of the drag and profile drag. A wing carrying an 80Kg pilot and 20Kg of equipment will need to produce 100Kg of lift to maintain level flight. Carrying 30Kg increases Lift needed to 110Kg. So If the L/D ratio of the wing is 5:1. The 100Kg of Lift results in 20Kg of Drag, while 110Kg Lift results in 22Kg Drag. To get the total drag we have to add the profile drag to the answer. Total drag is therefore 25Kg (20+5) of drag for the pilot using lighter equipment, or 34Kg (22+12) of drag for a heavier unit. However, drag is not a fixed quantity. The figures given are for illustrative purposes only and any reducion in drag will imporve the lift to drag ratio. A reduction in drag of 1Kg will reduce the amount of thrust required by the same amount. "More drag means burning more fuel for the same flight!"