Load Factor

Load factor is defined as the ration of lift to weight, i. e.,

n = — (A.23)

W

In straight and level flight, since L = W, the load factor n would be unity. For a turning flight, n > 1. The load factor is also referred to in terms of g’s, e. g., during a turn, if the lift is four times that of the aircraft weight, the aircraft is said to be making a 4g turn. The higher the load factor, the smaller will be the radius of turn. The load factor gradient is defined as: na = WL. This quantity is widely used in HQ

specifications.

Stall

As the AOA increases, beyond a certain value, the lift suddenly drops and the aircraft is said to have stalled (Figure A4). This is caused by flow separation on the wing surface. The slowest speed at which the aircraft can fly straight and level is called the stalling speed Vstall and is given by

The aim is always to make Vstan as small as possible. This is achieved by increasing C—m„ with the use of high lift devices, e. g., trailing edge flaps (TEFs).

Drag Polars

The C— vs. CD plot is called drag polar (Figure A5). This is typically plotted for specified Mach and altitude and for a given location of centre of gravity. Systematic evaluation of the drag polars of an aircraft using dynamic maneuvers can be carried out over the full AOA range of the aircraft. Reference [5] describes several para – meter/state estimation methods for determination of drag polars from flight data.