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 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 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 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. 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 Image: RNLI/Chris Jameson Try to solve thisproblem yourself. If you get stuck,there are somesteps below to helpyou. You’ Roadshow hovercraft? How muchpressure dotheBoschleafblowers needto create inorder to lifttheBosch‘All Around 3 2 1 making acraftmaking hover pressure:Under Pressure Time toTime 1 think: the following formula. Pressure equals theweight of thecraft, itwillstartto hover. hover. Aswe learnedabove, whentheforce created by theairpressure below acraft Pressure P expressed in metres squared (m there are six circular holes andyou willneedto make sure your final answer is You willneedto usePi(π)to calculate thearea of thesecircular holes. Remember, which anopposite andequalforce hasto actinorder to liftthehovercraft anditspilot. You mustnow calculate thetotal area of thesesixholes, asthisisthearea upon material underneath thecraft (seeFigure 2). air that leaves the‘cushion’ through thesixcircular holesthat are cutfrom thesheet As explained above, theBosch‘All Around You’ Roadshow hovercraft hovers onthe will helpyou to calculate this. calculate theforce itexerts. Table 1 and itspilot before you can Roadshow hovercraft components of theBosch‘All Around You’ need to know thecombined mass In order to complete step 1,you on thearea directly below itusingtheformula: Around You’ Roadshow hovercraft, and its pilot, Calculate the = canbedescribedastheratio of force to area anditcanbecalculated using isthekey scientific concept that helpsengineers to create machinesthat can Force force F exerted by theBosch‘All ÷ Area 2 A ). Table 1: Total Mass Pilot are attached to andthepilot kneelson Chassis -Thestructure theleafblowers Bosch cordless electricleafblower a scientific to guide

Bosch‘All Around You’ Roadshow hovercraft components Component be newtons persquare metre (N/m The unitof measurement for pressure can Force pascal (Pa). 1N/m F = 2 isthesameas1Pa. Mass M Quantity 2 1 1 x How to make your own hovercraft 2 (which is 9.81 m/s 9.81 is (which ) orthe diameter (0.1m). hole hasa10cm Gravity Each circular Kilograms G kg Mass In 3.6 50 10

2 (Kg) ) 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

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