![drag coefficient with aspect ratio calculator drag coefficient with aspect ratio calculator](https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/Images/dragco.gif)
Instead, it occurs at a slightly greater speed. The lift/drag ratio is given by the slope from the origin to some point on the curve and so the maximum L/D ratio does not occur at the point of least drag coefficient, the leftmost point. Speed is shown increasing from left to right. The varying ratio of lift to drag with AoA is often plotted in terms of these coefficients.įor any given value of lift, the AoA varies with speed. The rates of change of lift and drag with angle of attack (AoA) are called respectively the lift and drag coefficients C L and C D. The total drag on any aerodynamic body thus has two components, induced drag and form drag. Profile drag is lowered primarily by streamlining and reducing cross section. For this reason profile drag is more pronounced at greater speeds, forming the right side of the lift/velocity graph's U shape. This type of drag, known also as air resistance or profile drag varies with the square of speed (see drag equation). The tangent gives the maximum L/D point.įorm drag is caused by movement of the body through air. This term dominates the low-speed side of the graph of lift versus velocity.ĭrag curve for light aircraft. At low speeds an aircraft has to generate lift with a higher angle of attack, which results in a greater induced drag. Whenever an aerodynamic body generates lift, this also creates lift-induced drag or induced drag. The lift then increases as the square of the airspeed. The aerofoil is often cambered and/or set at an angle of attack to the airflow. Lift can be created when an aerofoil-shaped body travels through a viscous fluid such as air. A glider flying faster or slower than this airspeed will cover less distance before landing. This airspeed (vertical line) corresponds to the tangent point of a line starting from the origin of the graph. It is the flattest possible glide angle through calm air, which will maximize the distance flown. Polar curve showing glide angle for the best glide speed (best L/D). Parasite plus Induced) Coefficients of drag C D and lift C L vs angle of attack. L/DMAX occurs at minimum Total Drag (e.g. The L/D ratios for hydrofoil boats and displacement craft are determined similarly to aircraft. The L/D ratio can also be used for water craft and land vehicles. This results directly in better fuel economy. The L/D ratio is inversely proportional to the energy required for a given flightpath, so that doubling the L/D ratio will require only half of the energy for the same distance travelled. It depends principally on the lift and drag coefficients, angle of attack to the airflow and the wing aspect ratio. The L/D ratio is affected by both the form drag of the body and by the induced drag associated with creating a lifting force. It is measured empirically by testing in a wind tunnel or in free flight test. The L/D may be calculated using computational fluid dynamics or computer simulation. In almost all cases the graph forms a U-shape, due to the two main components of drag. These vary with speed, so the results are typically plotted on a 2-dimensional graph. The term is calculated for any particular airspeed by measuring the lift generated, then dividing by the drag at that speed. For a glider it determines the glide ratio, of distance travelled against loss of height. The L/D ratio for any given body will vary according to these flight conditions.įor an aerofoil wing or powered aircraft, the L/D is specified when in straight and level flight. It describes the aerodynamic efficiency under given flight conditions. In aerodynamics, the lift-to-drag ratio (or L/D ratio) is the lift generated by an aerodynamic body such as an aerofoil or aircraft, divided by the aerodynamic drag caused by moving through air. Measure of aerodynamic efficiency Lift and drag are the two components of the total aerodynamic force acting on an aerofoil or aircraft.