EVERYTHING YOU NEED TO KNOW ABOUT FLIGHT...
The Four ForcesThere are four basic forces in flight:
Thrust – force produced by powered flight, opposing drag force. Drag – force exerted on an object moving through a fluid, opposing its motion. It is affected by SA, its speed, the momentum of the fluid (e.g. the viscosity) Weight – product of mass and the acceleration due to gravity (mg) Lift – usually directed upwards, opposing weight. It is affected by SA of wing, speed, viscosity. Newton’s second law (F=ma) can be used to calculate the amount of lift needed to overcome weight. If the upward force is greater than the gravitational force imposed on an object, the object will go up. If the gravitational force is greater, then the object will go down or remain on the ground. Watch this video to find out more about flight as a superpower... |
LIFTLift is produced by two main aspects:
1. The Bernoulli Principle The Bernoulli Principle states that an increase of a flow results in a decrease of pressure. Airplanes and birds have an airfoil shape to each of their wings to produce lift. When air hits the top surface which is longer, it is forced to travel faster across the top than the flow below the wing. This is because the air moving over the top surface must travel a longer distance in the same time to prevent creating a vacuum. According to the Bernoulli Principle, the pressure below the wing will be higher than the air pressure above the wing. Due to the difference in pressure, lift is created. 2. Angle of attack The angle of attack is the angle at which the wing hits the air. As it is increased the resultant force from the deflection of the air both above and below the wing acts as a major component to lift. As the speed increases, only a small angle of attack is needed to produce enough lift. As it travels more slowly, the angle must increase to produce enough lift to equal its weight. |
Why can't humans fly?Humans cannot fly in the same way as birds and airplanes do. A bird can fly because its wingspan and the wing muscle strength are in balance with its body size. This would be unsustainable for humans as the wingspan needed would be very large and too heavy to function.
Therefore one way in which ‘flight’ could be achieved is through negative mass – lowering the weight of the human and increasing the weight of air. However, this is impossible on Earth’s atmosphere – the only way superman could fly would be through gliding. Gliders do not generate propulsive thrust through the air. Examples of glider animals include the flying squirrel, flying fish and Draco lizards. Since there is no engine on a glider to produce thrust, the glider has to increase flight time through other means. Gliders optimise flight time through the glide ratio. This ratio tells you how much horizontal distance a glider can travel compared to the altitude it has to drop. Another way to increase flight time is through rising air, the air around it is moving upward faster than the glider is descending, causing it to gain altitude. This can be done through: - Thermals - columns of rising air created by the heating of the Earth's surface. As the air near the ground is heated by the sun, it expands and rises. - Ridge lift - created by winds blowing against mountains, hills or other ridges. As the air reaches the mountain, it is redirected upward and forms a band of lift |