TABLE OF CONTENT:

1) PROBLEM STATEMENT2) HOVER THEORY3) ELEMENTS OF A HOVERCRAFT4) DESIGN CONSEDERATIONS5) ELECTRONIC EQUIPMENT5) ELECTRONIC EQUIPMENT6) HOVERCRAFT BUILD 7) TROUBLESHOOTING

1) PROBLEM STATEMENT :

v To design a remote controlled hovercraft or ACV(air cushion vehicle) that will be tested for speed, maneuverability and handling on various terrains like sand, mud, water, gravel, concrete. sand, mud, water, gravel, concrete.

v Further details are provided on the website www.technozion.org

2) HOVER THEORY :

� WHAT IS A HOVERCRAFT WHAT IS A HOVERCRAFT WHAT IS A HOVERCRAFT WHAT IS A HOVERCRAFT ? ü A hovercraft is an amphibious vehicle that can move with equal ease on both land and water or any other terrain. It is also known as an “ACV” (air cushion vehicle).

v How does a hovercraft work How does a hovercraft work How does a hovercraft work How does a hovercraft work ? ü A hovercraft works on the air cushioning effect of air trapped at high pressure underneath the hull which seeps slowly through a flexible surface known as “skirt” .The pressure due to this trapped air is responsible for lifting the craft a few inches above the ground.

3) ELEMENTS OF A HOVERCRAFT :

�MAIN PARTS OF A RC HOVERCRAFT :

ü HULL It is the main body of the craft which acts as a base for attaching other acts as a base for attaching other parts of the hovercraft

� LIFT SYSTEMü The lift system consists of a fan or propeller

attached to a motor or an engine ,which provides air for filling the cavity underneath the craft (called as plenum chamber) and also for filling the skirts.

� THRUST SYSTEM� THRUST SYSTEMü It is the same as the lift system with a

difference that it propels the craft forward by the virtue of reaction force applied by the air.

ü The propeller used for generating thrust is generally provided with a duct to increase the velocity of air and hence to increase the thrust.

LIFT FAN

THRUST FAN

SKIRT

� SKIRTü It is the flexible wall that is attached all around the periphery at the bottom of the craft .The skirt prevents the pressurized air from escaping from the plenum chamber .

� CONTROL SYSTEMü This consists of a set of rudders that steer the craft by directing the air from the thrust system toward either left or right which consequently steers the craft.

RUDDERS

4) DESIGN CONSIDERATIONS :

� WEIGHT ü Light weight materials must be used for construction ,but at the same time

the model must have good strength.� PRESSURE IN PLENUM CHAMBERü Lift force= pressure x area of the craftü Sufficient pressure must be generated so that

lift force > weight of the craft� MOMENTSü As rotating parts are involved .the unbalanced moments particularly due

to the lift fan must be balanced to avoid spinning of the craft� POWER SYSTEMü For lift fan generally motor- propeller system having static thrust > ü For lift fan generally motor- propeller system having static thrust >

0.4x(weight of the hovercraft) will generate hover , provided skirts are properly attached.

� SKIRT DESIGNü a bag skirt is generally preferred as it is easy to build and

gives good performance

� DUCT DESIGNü The duct although do not have much effect on thrust due to

propellers ,they must be used for safety from propeller blades.ü In design a duct should have a decreasing area towards exit, such

that velocity of air ,leaving the duct increases and hence thrust increases

5) ELECTRONIC EQUIPMENT:

� MOTORS;ü DC motors used for rc models are categorized as§ BRUSHED DC MOTORS

§ BRUSHLESS DC MOTORS

ü Of these two motors brushless motors are generally preferred because of

§ High power to weight ratio§ Low maintenance

� ELECTRONIC SPEED CONTROLLERS (ESC)ü These are used for controlling the speed of the

motor. They are generally classified on the amount of current they can handle eg. A 30 amp esc can handle 30 amperes of current draw and will burn if current exceeds this value.

ü So while choosing an esc for brushless motor the max. current draw of motor should not exceed the rated value of esc used.

� BATTERIES:ü Li-po or lithium polymer batteries are used because of§ High discharge rates§ Light weight§ High charge retaining capacity

ü Li-po batteries are rated by the amount of charge they can store and the discharge rate and the voltage

ü eg. A 11.1v ,2000mAh ,20C battery can provide 2 amperes of current for two hours at 11.1 volts and the maximum current can be

C rating x mAh ratingi.e. 20 x 2amp= 40 amp

� RECEIVER/TRANSMITTER :

ü Receiver and transmitter are used to control the electronic equipments on the model.

ü A receiver or transmitter is categorized by no, of channels and frequency of operation.

ü The no. of channels define how many equipments can be controlled through the transmitter

ü A three channel radio is suitable for running a hovercraft

� SERVOü A servo is a kind of electronic actuator that rotates

by only a fixed angle ,like 45 degrees, from the neutral position. It can hold it’s position at an angle and is used in rudder mechanism for the model

ü A 9gram servo is ideal for rudder mechanism

ü BRUSLESS MOTOR SETUP:§ choosing the right motor § Lift motor- a high kv motor is generally used with a 6”-7”

propeller.§ Thrust motor-a low kv motor is generally used with a 9”-11”

inch propeller.

Suggested motor setupsSuggested motor setupsSuggested motor setupsSuggested motor setups:Lift motor § EMAX CF2812 +18 amp esc +7”x6” propeller§ EMAX CF2812 +18 amp esc +7”x6” propeller§ EMAX BL2210/25+ 20amp esc+8”x4” propeller § Turnigy 2730 1500kv + 10 amp esc + 7”x3.5” propellerThrust motor§ Turnigy 2830 100kv + 20 amp esc +10”x 4.7” propeller§ Hobbyking 800kv +12 amp esc +10”x6” propeller§ Turnigy 2217 860kv+20 amp esc +11”x4.7” propellerBatteries• 11.1v batteries with rating from 1800mAh to 2700mAh and a

discharge rate of 25-30C I recommended.

ü A 3mm prop saver or prop adapter should be used for attaching the propeller to the motor shaft

Prop adapter

6) HOVERCRAFT BUILD

� MODEL – UH10FUH10FUH10FUH10Fü Materials used:§ Plywood ;thickness -2mm§ Thermocol§ Aluminium plate§ Glue gun or fevitite§ Polythene Garbage bags (black coloured)

� Building the hull:The hull is built by sandwiching thermocol sheet in between ü The hull is built by sandwiching thermocol sheet in between two plywood sheets using fevicol.

ü The duct (hole ) at the front is for the lift fan

ü MOTOR MOUNT :

§ Aluminium plate is used;

DRILL HOLES FOR SCREW

MOUNT SECTIONS ATTACHED

ü Now the parts of the mount are joined using nuts and motor is mounted

ü Motor mount for the lift motor is also made using aluminium plate

lift fan motor mount

Hull with the motors attached

ü BUILDING THE DUCT :

§ Thermocol is used for making the duct. A 9” thick block of thermocol is formed into the required shape by sanding using a sand paper.

§ The thermocol duct is reinforcrd by wrapping thin cotton cloth dipped in diluted fevicol tightly around the duct.

REINFORCED THERMOCOL DUCT THRUST

MOTOR AND PROPELLER

ü RUDDERS :

§ rudders are made using coro sheets and cycle spokes

Corosheet

Passing a spoke through the coro

Hinge for rudder

Four bar mechanism for synchronizing rudder movement

ü Completed rudder

• ATTACHING THE SERVO :• ATTACHING THE SERVO :

SPOKE SERVOCLEVIS

RUDDER

CONTROL HORN

ü SKIRT :

• The skirt is a bag type bag type bag type bag type skirt made using garbage bag as an alternate any thin airtight material can be used

• The skirt is basically a round balloon typestructure that gets inflated when lift motor is switched on.

• For inflating the skirt a fraction of air from the lift fan should be directed into the skirt

SKIRT (inflated)

://www.john-tom.com/hovhttper/MiscHoverPhoto/skirt.swf

• For step by step skirt construction refer the following link

SKIRT CUTOUT

Join at bottom of the craft

SKIRT COMPLETED

Join at the top of the craft

ü ATTACHING THE SKIRT AND DUCT :

• Glue gun is used for attaching the skirt and duct to the hull ,alternately fevitite or any epoxy based glue can be used. skirt is attached using transparent tape.

BATTERY CASE

DUCT

SKIRTPROPELLERPLENUM

CHAMBER

AIR FLOW FOR INLATING THE SKIRT

AIR FLOW FOR LIFT

ü THIS COMPLETES THE BUILD

7) TROUBLESHOOTING :

� CENTRE OF PRESSURE AND CENTRE OF GRAVITY :ü The centre of pressure is basically the geometric centre

of the plenum chamber .But the lift is in general contributed both by thrust due to motor and the pressure force,such that the point where total lift force acts gets shifted towards the lift motor.

ü The centre of pressure and the point of action of lift force must coincide for leveled hovering

ü The line of action of lift force is fixed for a model, the C.G. can be adjusted by moving the battery.C.G. can be adjusted by moving the battery.

� INSUFFICIENT TURNING:ü Increase the rudder area or the servo throw.throw.throw.throw.� NO HOVER:ü Check if the skirts are fully inflatedü The skirt should allow a minimum amount of air leak

from the plenum chamber. check for any rapid air leaks ü Insufficient power of the lift motor� UNCONTROLLED SPIN:ü Provide a slight rudder trim rudder trim rudder trim rudder trim in direction opposite to spin

ü WHERE TO BUY:§ RC stuff is available at following sites which

deliver in 3-4 days

vwww.rcelectro.comvwww.rcdhamaka.comvwww.rcdhamaka.comvwww.rchobbyaddict.comvwww.rcforall.comvwww.rcbazaar.com

§ alternate building materialvDepron foam (BIOFOAM)- available at some stationery shops around ramkote crossroad ,HyderabadvCoroplast (sunpak or sunboard) üSOME USEFUL LINKS:§www.john-tom.com§www.rchovercraft.com§www.gohover.com§www.model-hovercraft.com

v For any queries contact-RAHUL RATHOREemail : rathorerahul345@gmail.comPh. : 9466862434

There is nothing that cannot be achieved by firm imagination