Hovercrafts
A hovercraft is a vessel that is capable of hovering over virtually any terrain, hence the name hovercraft. Although it may seem
straightforward, the physics involved make this simple concept much more complicated. The basic parts of a hovercraft are a given
(i.e. body, engine, etc.), but the unique components are what separate this vehicle from everything else.
The blueprints for a hovercraft call for several elements that are not traditionally used in vehicles. The craft must have an open
design in order to have a constant supply of air allowing it to maintain its hover and propel itself. The physics concepts for a
hovercraft involve air pressure, lift, propulsion, volume, and friction. Categorizing these into upward lift and forward thrust is much
easier; pressure, lift and volume relate to upward lift while friction and propulsion relate to forward movement.
The lifting of a hovercraft is the hardest part. Many factors have to be taken into account in order to successfully lift the vessel
several inches off the ground (check outhttp://www.rqriley.com/hc-calc.html to find out exact calculations). Movement starts by
directing airflow underneath the craft which inflates a skirt, or air cushion. A ‘skirt’ is a flexible curtain attached to the outside
perimeter of the craft. Once the air cushion is formed, the air escapes out of multiple holes at the bottom of the skirt. As excess air is
pushed out from under the skirt, the downward force of the air produces an upward reaction on the craft, causing lift. The air
pressure needed to lift the craft is different depending on the weight and area of each specific craft.
In order to find the air pressure needed, one can use the formula:
P = F/A with the values P, F, and A being the pressure of air cushion, the weight onboard the vessel (mass * gravity), and
the area of the vessel, respectively. Then once this is calculated, one can find the volumetric flow rate as well as the lift power
needed:
VFR = A*υ with the values VFR, A, and υ being volumetric flow rate, area of the vessel, and velocity of air discharge,
respectively.
PL = P*VFR with the values PL, P, and VFR being lift power, pressure of air cushion, and volumetric flow rate,
respectively. (More equations @http://www.arsp.sojo-u.ac.jp/acv/acv/design/lift.html)
It is important to know the air pressure needed for the lift of the craft. If too much pressure is applied, more lift will occur, causing the
craft to tip. If not enough pressure is applied, the craft will not lift at all, defeating the purpose.
Once the upward lift is in effect, how will the craft move?! Well, because the craft is just floating over a surface and not actually in
contact with it, there is practically no force of friction acting on the craft to hinder movement. With the elimination of friction, a second
set of propellers, used for motion, will be sufficient to push the craft across surfaces. Devices such as turbines or blades provide the
backward push on air to create the forward movement of the craft. In order to steer the vehicle, rudders are used to direct the
airflow. Using kinematics equations, distance, velocity, and acceleration can all be determined. Equations from the upward lift
section can also be used to find air pressure, volumetric flow rate, and power.
The hovercraft is a very fascinating vehicle with a peculiar foundation. The first commercial hovercraft was created by the inventor
Sir Christopher Cockrell. By using two different sized cans, an industrial strength air blower and a pair of kitchen scales, Cockrell
assembled his hovercraft. He placed the smaller can inside the larger can and used the hairdryer to blow air into the cans. The
downward thrust produced was greatly increased when one can was inside the other rather than air just being blown into one can.
He then designed and created a vehicle capable of hovering on a cushion of air. The first working example of a Hovercraft, known
as the Saunders Roe Nautical, was shown to the public in June, 1959.
In the present day, hovercrafts have evolved into a large range of uses and activities. Mainly, hovercrafts are used for transportation
in cases where traditional vehicles are insufficient. They can replace boats because they are safer to use when navigating choppy
waters and just faster in general. They can be used as ferries to transport people across bodies of water as well. Oil field companies
use hovercrafts to transport equipment over mud and swamps that are too dangerous to cross otherwise saving time and money.
Sometimes golf clubs even use hovercrafts to avoid the damage that ground cars make on their courses. Another use for a
hovercraft is military and rescue missions. The coast guards for many countries use hovercrafts because they are quicker and safer
than boats and can navigate any terrain, traveling from open water, to ice, to rough rapids, to pavement without difficulty in one easy
step. The United States Navy uses hovercrafts as patrolling vehicles for land and water, which are fully armored and equipped with
weapons. There are even entire fleets of tremendous hovercrafts holding several tanks and that are used in massive military
operations, just recently as in Iraq in 2003. But that is not all, for the hovercraft can even be a recreational tool. Hovercrafts which
hold one to two passengers are used for thrill and amusement rides across large fields or lakes. Yacht owners can use hovercrafts
to transport people from their ship to the shore with ease. They can be used as scuba diving platforms that are more stable with
their flat bottoms and they don’t require a dock or a boat slip. Hovercrafts can be used as a racing vehicle, and there are many
competitions throughout the world. With hovercrafts becoming increasingly safer, quieter, and easier to use, the possibilities for this
great invention seem endless.
Grade sheet for Hover craft project
Design works, creativity, and safe to operate
20 Points
Design works and is safe to operate during testing – 10 points
Creativity in Design and use of materials – 10 points
Testing
250 Points
The hover craft must carry two people. Two trials minimum, 3 trials maximum, No repeats of
1 person: 1 foot = .5 point
2 people: 1 foot = 1 points
3 people: 1 foot = 2 points
4 people: 1 foot = 3 points
Deliverables met
80 Points
Check Sheet turned in on time to Mrs. Whitecotton
10 Points
Blue Prints Signed by Mrs. Whitecotton
25 Points
Materials list and cost list must be included
Force Diagram
25 Points
Air Flow Diagram
20 Points
Presentation
Concepts explained and discussed
50 Points
20 Points
Newton’s 3 laws and Bernoulli’s Equation
Design used and problems occurred while prototyping
10 Points
Results of changes and final design explained
10 Points
Results from testing and conclusion
10 Points
Total Points for Project
400 Points
Grade sheet for Hover craft project
Design works, creativity, and safe to operate
20 Points
Design works and is safe to operate during testing
____________/10
Creativity in Design and use of materials
____________/10
Testing
250 Points
The hover craft must carry two people. Two trials minimum, 3 trials maximum, No repeats of
1 person: 1 foot = .5 point
___________
2 people: 1 foot = 1 points
___________
3 people: 1 foot = 2 points
___________
4 people: 1 foot = 3 points
___________
Deliverables met
80 Points
Check Sheet turned in on time to Mrs. Whitecotton
___________/10
Blue Prints Signed by Mrs. Whitecotton
___________/25
Materials list and cost list must be included
Force Diagram
___________/25
Air Flow Diagram
___________/20
Presentation
Concepts explained and discussed
50 Points
___________/20
Newton’s 3 laws and Bernoulli’s Equation
Design used and problems occurred while prototyping
___________/10
Results of changes and final design explained
___________/10
Results from testing and conclusion
___________/10
Total Points for Project
Total Points accumulated
400 Points
_____________/400 = ________________
Deliverables Schedule and Check Sheet
Group Members:
______________________________________________________________________
______________________________________________________________________
Deliverables met
80 Points
Check Sheet turned in on time to Mrs. Whitecotton
10 Points
Due 12/4
Blue Prints Signed by Mrs. Whitecotton
25 Points
Due 12/11
25 Points
Due 12/20
Materials list and cost list must be included
Force Diagram
*Include the weights of each team member along with total weight. You might want to include who is going to
ride the craft and with what trial.
*Calculate the area of the craft.
*Label all forces acting on the system
Air Flow Diagram
20 Points
*Include the power output capabilities of the blower(s).
*Draw where the air comes in and out of the system.
Due 112/20