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Trim drag, denoted as Dm in the diagram, is the component of aerodynamic drag on an aircraft created by the flight control surfaces, [1] mainly elevators and trimable horizontal stabilizers, when they are used to offset changes in pitching moment and centre of gravity during flight.
The drag curve or drag polar is the relationship between the drag on an aircraft and other variables, such as lift, the coefficient of lift, angle-of-attack or speed. It may be described by an equation or displayed as a graph (sometimes called a "polar plot"). [1] Drag may be expressed as actual drag or the coefficient of drag.
[1] = where is the aircraft lift coefficient. The lift and drag forces can be applied at a single point, the center of pressure. However, the location of the center of pressure moves significantly with a change in angle of attack and is thus impractical for aerodynamic analysis.
Aircraft flight mechanics are relevant to fixed wing (gliders, aeroplanes) and rotary wing (helicopters) aircraft.An aeroplane (airplane in US usage), is defined in ICAO Document 9110 as, "a power-driven heavier than air aircraft, deriving its lift chiefly from aerodynamic reactions on surface which remain fixed under given conditions of flight".
These vary with speed, so the results are typically plotted on a 2-dimensional graph. In almost all cases the graph forms a U-shape, due to the two main components of drag. The L/D may be calculated using computational fluid dynamics or computer simulation. It is measured empirically by testing in a wind tunnel or in free flight test. [1] [2] [3]
An aircraft is streamlined from nose to tail to reduce drag making it advantageous to keep the sideslip angle near zero, though an aircraft may be deliberately "sideslipped" to increase drag and descent rate during landing, to keep aircraft heading same as runway heading during cross-wind landings and during flight with asymmetric power. [1]
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The maximum endurance condition would be obtained at the point of minimum power required since this would require the lowest fuel flow to keep the airplane in a steady, level flight. Maximum range condition would occur where the ratio of speed to power required is greatest. The maximum range condition is obtained at maximum lift/drag ratio (L/DMAX)