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 FIGURE 1 is made using two standard Bosch The leaf blower’s impeller cordless leaf blowers powered by rotates at high speed, rechargeable lithium-ion batteries. sucking in air and forcing it downwards into the space It works by blowing air into the space underneath the board underneath the hovercraft on which the operator kneels (see Figure 1). Impeller 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 FIGURE 2 ‘cushion’ of air also reduces the friction between the Some of the air escapes hovercraft and the floor, which makes it easy to move. through six circular holes cut into the sheet The Bosch ‘All Around You’ Roadshow material , which causes hovercraft works like a real hovercraft. the craft to hover above the floor. 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. Hovercraft Skirt 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 Image: RNLI/Chris Jameson to force air against the surface directly below the hovercraft. Propeller 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 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. The unit of measurement for pressure can P = F ÷ A be newtons per square metre (N/m2) or the pascal (Pa). 1 N/m2 is the same as 1 Pa. Pressure Force Area 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. Calculate the force exerted by the Bosch ‘All F = M x G 1 Around You’ Roadshow hovercraft, and its pilot, on the area directly below it using the formula: Force Mass Gravity (which is 9.81 m/s2) In order to complete step 1, you Table 1: Bosch ‘All Around You’ Roadshow hovercraft components need to know the combined mass Mass In of the Bosch ‘All Around You’ Component Quantity 2 Kilograms (Kg) Image: RNLI/Chris Jameson Roadshow hovercraft components Bosch cordless electric leaf blower 2 3.6 and its pilot before you can Chassis - The structure the leaf blowers calculate the force it exerts. Table 1 1 10 are attached to and the pilot kneels on will help you to calculate this. Pilot 1 50 Total Mass kg 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 3 material underneath the craft (see Figure 2). Each circular You must now calculate the total area of these six holes, as this is the area upon hole has a 10 cm which an opposite and equal force has to act in order to lift the hovercraft and its pilot. diameter (0.1 m). 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 (m2). 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. 2 Dynamic pressure, which Q = ½ x P x V Q is measured in pascals Fluid density in kilograms per metres cubed P (kg/m3), in this instance the fluid is air Fluid velocity in metres V 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 FIGURE 6 The completed model hovercraft The completed model before switching the motor on 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 Lead the profession balanced economic growth To harness the collective expertise, To improve the capacity of UK energy and capacity of the engineering entrepreneurs and enterprises to create profession to enhance the UK’s economic innovative products and services, increase and social development. wealth and employment and rebalance the economy in favour of productive industry. Promote engineering at the heart of society Foster better education To improve public understanding of and skills engineering, increase awareness of To create a system of engineering how engineering impacts on lives and education and training that satisfies increase public recognition for our most the aspirations of young people while talented engineers. delivering the high calibre engineers and technicians that businesses need.. 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.