How to make your own hovercraft

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
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.
F ÷ A
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.
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 = M x
Force
G
Mass
Gravity
(which is 9.81 m/s2)
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
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
Component
Total Mass
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.
kg
Each circular
hole has a 10 cm
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.
Q = ½ x P x V2
Q
Dynamic pressure, which
is measured in pascals
P
Fluid density in kilograms per metres cubed
(kg/m3), 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