Flight and movement (making rockets)

Dealing with gravity From stored to kinetic energy Bernoulli’s Conservation of Energy Law In order to move by flying we need to utilise one force to overcome another as stated in Newton’s third law of motion. The force we need to overcome to remain elevated is gravity, then we need to change a stored form of energy into kinetic energy in order to move along. With conventional aircraft stored energy (fuel) is converted to kinetic energy (movement along the runway) until a sufficient quantity of a force called lift is generated that can overcome the force of gravity. The principle of lift can be described by Bernoulli’s Conservation of Energy Law.

Lift Lift is generated on conventional aircraft using an aerofoil. Examples of aerofoils are the wings on a plane, the blades of a propeller or turbine or rotors on a helicopter. Let’s look at the example of a plane’s wing to see how lift is generated by forward motion.

Aerodynamic lift As we can see in cross section a plane’s wing is a streamlined shape but thicker at the front (leading edge) than the back (trailing edge). The underside of the wing is also ‘flatter’ than the curved upper surface. This means as the plane moves through the air the wing splits the flow of air above and below it. Air moving over the top of the wing has to travel further due to the shape and as a result the air travels faster than air moving on the underside. This creates higher air pressure under the wing than on top and ‘lifts’ the plane up. Of course a conventional plane has to be moving quickly enough to generate enough lift to get airborne and that’s why planes accelerate to take off.

Propellers and lift Helicopter rotors are really ‘rotary wings’ and are forced through the air on the end of a propeller shaft in a rotary motion instead of by movement along the ground. Once the rotational speed of the rotor reaches a critical point then enough lift will be generated for the helicopter to rise from the ground. Because the ‘airframe’ of the helicopter doesn’t need to move along a runway in order to take off we say that it has vertical take-off and landing capability. We can build a simple propeller and look at how energy changes and related forces work together to overcome or work with gravity. The rear rotor on a helicopter is required to counteract another law of motion (the third law of motion i.e. for every action there is an equal and opposite reaction. Without the trail rotor counteracting the torque or twisting forces between the helicopter airframe and rotors the airframe would spin in a counter rotational direction to the rotors.

Build a simple propeller https://www.youtube.com/watch?v=BNNPehhcrjU Follow guidance and instructions in the short video to build (in small groups of 3-4) a propeller. What happens when a helicopter loses power in mid-air – can it glide like a plane? Use you simple propeller to test your hypothesis. What happens in real life – ask the RAF about auto-rotation.

Rockets and missiles A missile is something that fly through the air – rockets are cylindrical missiles that are traditionally propelled by burning gases. The engines that power this type of vehicle are called rocket motors and the typical gases that are burned together are hydrogen and oxygen. In space vehicles used to launch satellites and astronauts into orbit two types of rocket fuel are used 1. Liquid propellant 2. Solid propellant All rocket propellants use a fuel (hydrogen) and an oxidiser (oxygen) to enable them to react and burn. Liquid propellants hold the fuel and oxidiser separately; solid fuel rockets combine the two. Question: where can you commonly find hydrogen and oxygen combined together? Answer: In H2O or water!   The hydroxyl combination released from water through electrolysis is perfect for making fuel to power bottle rockets. However this combination is proper rocket fuel and can be dangerous. Instead you can power your bottle rocket using baking soda and vinegar. Exercise: Make a bottle rocket

Let’s build a rocket! https://www.youtube.com/watch?v=tGp7jn6iDMg Follow guidance and instruction on youtube video to build your own rocket. Work in teams (3-4 pupils per team) to build the rocket that can travel the furthest!

RAF examples: flight and movement in action Look at the wing shape on these two aircraft. One of them is quite old – the Spitfire (first image). One of them is much more modern (the Typhoon). From the shape of the wing – can you see how the typhoon is much more aerodynamically shaped and therefore will (given sufficient thrust) find it easier to get into the air and manoeuvre.