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Aircraft
Published in Suzanne K. Kearns, Fundamentals of International Aviation, 2021
Drag is the force that works against an aircraft moving through the air. Drag occurs when the surfaces of an aircraft come into contact with the air, resulting in friction. Smooth aircraft surfaces produce less friction and therefore result in less drag. Thrust is the force that causes an aircraft to move through the air. Thrust is produced by an aircraft’s engine(s), and when thrust is stronger than drag, the aircraft accelerates in the direction of the net force.
Aerodynamic Forces – Subsonic Flight
Published in Rose G. Davies, Aerodynamics Principles for Air Transport Pilots, 2020
Drag is another major component of the aerodynamic forces exerted on an aircraft when it is in flight. Drag is a force, so it is a vector. Its direction is the same as the relative air velocity of the aircraft. There are two types of the total drag the aircraft experiences in flight: induced drag, which is related to lift produced by the aerofoils, and parasite drag, which exists over the aircraft body due to the airflow around the aircraft. Understand the origin, or the cause of different parts of the drag can lead pilots controlling the aircraft more effectively.
Flow over Immersed Bodies
Published in William S. Janna, Introduction to Fluid Mechanics, Sixth Edition, 2020
First, it is necessary to define the concept of streamlining. A ground vehicle requires power to move it over land. A portion of this power goes to overcoming the rolling resistance offered by friction between the tires (or wheels) and the road, and by friction in bearings or other surfaces moving with respect to each other. Another portion of the power required goes to overcoming the drag encountered by the vehicle as it moves through air. With ground vehicles, it will in general not be possible to significantly reduce the skin friction drag. We can, however, modify the shape of the vehicle so that the form or pressure drag is reduced. When the shape is modified and the pressure drag is reduced, the object is said to be streamlined.
How do freezing to scorching environmental temperatures influence the aerodynamic performance in race cycling: a quasi-steady numerical analysis.
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
F. Beaumont, F. Bogard, S. Murer, G. Polidori
The main goal of this study was to assess the influence of ambient air temperature on the aerodynamic passive drag of the cyclist and bicycle setup. The results showed that the thermophysical properties of air, intrinsic to temperature, had a significant impact on the aerodynamic performance of the cyclist and bicycle setup. It has been shown that the total drag value decreases by approximately 2.8% in 10 °C steps, which is the first analytical proof that aerodynamic drag decreases with increasing temperature. In addition, we found that the pressure drag is greater than the viscous drag, the latter accounting for about 92% of the total drag. The main finding of this study suggests that riding in a warmer environment reduces aerodynamic drag forces, which could improve performance by increasing the cyclist’s speed.
Aerodynamic investigation of the inrun position in Ski jumping
Published in Sports Biomechanics, 2021
A large group difference in inrun position between the WC and COC athletes was also observed. The average difference in CDA between the groups in the preferred position was 0.016 m2 (~15.5%), which would give a speed difference of 0.6–1.3 kmh−1, and almost 0.01 m2 (~10.8%) for the best tested position, which corresponds to a speed difference of around 0.4–0.8 kmh−1. The only significant difference in body position between the groups was the trunk angle. For the preferred position, variations in thigh and leg angle were observed but there were no significant differences between the groups due to a large variation within the COC group. The difference in trunk angle between the groups was ~3° both for the preferred and best tested position. A ~3° larger trunk angle would increase the frontal area, thus increase the CDA. In other sports where aerodynamic forces play a big role like cycling, alpine skiing and speed skating, the athletes try to maintain a streamlined shape, like a water drop or airfoil, to reduce the drag. A streamlined shape will cause a later flow separation, which will reduce drag coefficient. This will also apply for a ski jumper in an inrun position, and a 0° will give a more streamlined positioning of the torso. Hence, a higher trunk angle will increase both the drag coefficient (CD) and the frontal area (A). From a biomechanical point of view, a 0° could also move the centre of mass closer to the centre of application of the drag force, which again could make it easier to maintain balance.
Effect of square dimples on the temperature distribution and heat transfer coefficient of an NACA0012 airfoil
Published in International Journal of Ambient Energy, 2019
Although the drag coefficient increases with the temperature the rate of increase is smaller compared to the rate of increase of lift coefficient as shown in Figures 5–7. Furthermore, the drag coefficient variation is not smooth. The lift/drag coefficient ratio increases with Re and temperature difference. This shows the favourable lift enhancement flow situation due to temperature difference as shown in Figures 8–10.