Bosch All Around You Roadshow How to make your own hovercraft supported by
Curriculum links SCIENCE FORCES - Balanced and unbalanced forces, forces measured in newtons PRESSURE IN FLUIDS - Atmospheric pressure, upthrust effects, floating and sinking, pressure measured by ratio of force over area acting normal to any surface FORCES AND MOTION - Forces being needed to cause objects to stop or start moving MATHEMATICS ALGEBRA - Substitute numerical values into formulae and expressions, including scientific formulae GEOMETRY AND MEASURES - Areas of circles The Bosch All Around You Roadshow visits schools to enthuse young people about engineering and technology. During the show students find out that many things in our daily lives are impacted by engineering. Engineers get to be involved in making and designing things which are critical to our society. From the technology powering our cars and heating our homes to systems that lift huge weights, the opportunities and industries covered by an engineering career are vast. During the show, one demonstration showed how by using problem-solving skills and two cordless leaf blowers, you can successfully lift a person off the ground. 02 I Royal Academy of Engineering
How to make your own hovercraft How it works The hovercraft that features in the Bosch All Around You Roadshow is made using two standard Bosch cordless leaf blowers powered by rechargeable lithium-ion batteries. It works by blowing air into the space underneath the hovercraft on which the operator kneels (see Figure 1). FIGURE 1 The leaf blower s impeller rotates at high speed, sucking in air and forcing it downwards into the space underneath the board Impeller FIGURE 2 Some of the air escapes through six circular holes cut into the sheet material, which causes the craft to hover above the floor. Underneath the hovercraft, the air fills a space that is made using a sheet material. Once it is full the air in this space has enough pressure to escape downwards, creating an air cushion underneath the board that can lift both the vehicle and its pilot. This cushion of air also reduces the friction between the hovercraft and the floor, which makes it easy to move. The Bosch All Around You Roadshow hovercraft works like a real hovercraft. 03
Hovercrafts help to save lives FIGURE 3 The photograph in Figure 3 shows the Royal National Lifeboat Institution s (RNLI) hovercraft, which operates on the coast around Morecambe, Lancashire. The hovercraft can travel on shallow water and over difficult types of terrain such as the mud at Morecambe Bay. Commercial hovercrafts, such as the one used by the RNLI at Morecambe, work like the Bosch All Around You Roadshow hovercraft. Powerful blowers are used to force air into the volume underneath the craft. The hovercraft s skirt, which is labelled in Figure 3, traps much of the air being forced under the craft and creates a cushion of air pressure. The skirt also helps to force air against the surface directly below the hovercraft. When this force equals the weight of the hovercraft, it hovers. Engine Figure 4: The propellers draw air into the space underneath the hovercraft 04 I Royal Academy of Engineering Propeller Image: RNLI/Chris Jameson Hovercraft Skirt
How to make your own hovercraft Under pressure: a scientific guide to making a craft hover Pressure is the key scientific concept that helps engineers to create machines that can hover. As we learned above, when the force created by the air pressure below a craft equals the weight of the craft, it will start to hover. Pressure can be described as the ratio of force to area and it can be calculated using the following formula. P Pressure = F Force A Area The unit of measurement for pressure can be newtons per square metre (N/m 2 ) or the pascal (Pa). 1 N/m 2 is the same as 1 Pa. Time to think: 1 How much pressure do the Bosch leaf blowers need to create in order to lift the Bosch All Around You Roadshow hovercraft? Try to solve this problem yourself. If you get stuck, there are some steps below to help you. 1 Calculate the force exerted by the Bosch All Around You Roadshow hovercraft, and its pilot, on the area directly below it using the formula: F Force = M Mass x G Gravity (which is 9.81 m/s 2 ) 2 In order to complete step 1, you need to know the combined mass of the Bosch All Around You Roadshow hovercraft components and its pilot before you can calculate the force it exerts. Table 1 will help you to calculate this. Table 1: Bosch All Around You Roadshow hovercraft components Component Quantity Mass In Kilograms (Kg) Bosch cordless electric leaf blower 2 3.6 Chassis - The structure the leaf blowers are attached to and the pilot kneels on 1 10 Pilot 1 50 Total Mass kg 3 As explained above, the Bosch All Around You Roadshow hovercraft hovers on the air that leaves the cushion through the six circular holes that are cut from the sheet material underneath the craft (see Figure 2). You must now calculate the total area of these six holes, as this is the area upon which an opposite and equal force has to act in order to lift the hovercraft and its pilot. You will need to use Pi (π) to calculate the area of these circular holes. Remember, there are six circular holes and you will need to make sure your final answer is expressed in metres squared (m 2 ). Each circular hole has a 10 cm diameter (0.1 m). 05
Time to think: 2 (stretch and challenge) How much pressure does the Bosch All Around You Roadshow hovercraft generate? This is a tricky one, as the only data we have for the Bosch cordless lithium ion battery powered leaf blower is the velocity of the air leaving it, which is 210 km/h. You might start to tackle this problem by investigating dynamic pressure, which can be calculated using the following formula. Q = ½ x x V 2 P Q Dynamic pressure, which is measured in pascals P Fluid density in kilograms per metres cubed (kg/m 3 ), in this instance the fluid is air V Fluid velocity in metres per second (m/s) Student activity: make your own model hovercraft A model hovercraft kit is available from www.mindsetsonline.co.uk (search for hovercraft kit ). Follow the instructions provided in the kit to make the model hovercraft shown in Figures 5 and 6. FIGURE 5 The completed model hovercraft before switching the motor on FIGURE 6 The completed model hovercraft inflated Stretch and challenge Once you have made and tested the model hovercraft, you will see that it does not power itself; it needs a gentle push to move it along. Your challenge: Modify the hovercraft model so that it can move in a single direction without being pushed. 06 I Royal Academy of Engineering
Let us know how you got on! Share a photo or video of your hovercraft in action and encourage others to find out more about engineering by posting to the Bosch UK Facebook page www.facebook.com/boschuk 07
Royal Academy of Engineering As the UK s national academy for engineering, we bring together the most successful and talented engineers for a shared purpose: to advance and promote excellence in engineering. We have four strategic challenges: Drive faster and more balanced economic growth To improve the capacity of UK entrepreneurs and enterprises to create innovative products and services, increase wealth and employment and rebalance the economy in favour of productive industry. Foster better education and skills To create a system of engineering education and training that satisfies the aspirations of young people while delivering the high calibre engineers and technicians that businesses need.. Lead the profession To harness the collective expertise, energy and capacity of the engineering profession to enhance the UK s economic and social development. Promote engineering at the heart of society To improve public understanding of engineering, increase awareness of how engineering impacts on lives and increase public recognition for our most talented engineers. Royal Academy of Engineering Prince Philip House, 3 Carlton House Terrace, London SW1Y 5DG Tel: +44 (0)20 7766 0600 www.raeng.org.uk Registered charity number 293074