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How to make your own hovercraft

Bosch ‘All Around You’ Roadshow

Curriculum links

FORCES - Balanced and unbalanced forces, forces measured in newtonsPRESSURE IN FLUIDS - Atmospheric pressure, upthrust effects, floating and sinking, pressure measured by ratio of force over area – acting normal to any surfaceFORCES AND MOTION - Forces being needed to cause objects to stop or start moving

ALGEBRA - Substitute numerical values into formulae and expressions, including scientific formulaeGEOMETRY AND MEASURES - Areas of circles

SCIENCE

MATHEMATICS

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.

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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.

How it works

Some of the air escapes through six circular

holes cut into the sheet material , which causes the craft to hover above

the floor.

FIGURE 2

The leaf blower’s impeller rotates at high speed,

sucking in air and forcing it downwards into the space

underneath the board

FIGURE 1

Impeller

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).

How to make your own hovercraft

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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.

Hovercrafts help to save lives

Imag

e: R

NLI/C

hris

Jam

eson

Figure 4: The propellers draw air into the space underneath the hovercraft

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.

Propeller

Engine

FIGURE 3

Hovercraft Skirt

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Imag

e: R

NLI/C

hris

Jam

eson

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.

Table 1: Bosch ‘All Around You’ Roadshow hovercraft components

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.

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 (m2).

Under pressure: a scientific guide to making a craft hover

Each circular hole has a 10 cm diameter (0.1 m).

The unit of measurement for pressure can be newtons per square metre (N/m2) or the

pascal (Pa). 1 N/m2 is the same as 1 Pa.

Force

Pressure

Mass

Force

Gravity (which is 9.81 m/s2)

Area

F

P

M

F

=

=

x

÷

G

A

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.

Calculate the force exerted by the Bosch ‘All Around You’ Roadshow hovercraft, and its pilot, on the area directly below it using the formula:

Component Quantity Mass In Kilograms (Kg)

Bosch cordless electric leaf blower 2 3.6Chassis - The structure the leaf blowers are attached to and the pilot kneels on

1 10

Pilot 1 50Total Mass kg

1

2

3

Time to think: 1

How to make your own hovercraft

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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.

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.

Time to think: 2 (stretch and challenge)

Student activity: make your own model hovercraft

Dynamic pressure, which is measured in pascals

Fluid density in kilograms per metres cubed (kg/m3), in this instance the fluid is air

Fluid velocity in metres per second (m/s)

QPV

Q ½= x x V2

The completed model hovercraft before switching the motor on

FIGURE 5The completed model

hovercraft inflated

FIGURE 6

Stretch and challengeOnce 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.

P

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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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Royal Academy of Engineering Prince Philip House, 3 Carlton House Terrace, London SW1Y 5DGTel: +44 (0)20 7766 0600www.raeng.org.ukRegistered charity number 293074

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 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.