mechanical presentation 1

8/9/2019 Mechanical Presentation 1

1/30

HOVERCRAFT

Submitted to: Submitted by:

asd fggh


2/30

CONTENTS1. What is hovercraft?

2.Brief history3.Principle of working

4.Types

5.Parts

6.Applications


3/30

It is a craft capable of moving

over water or land on a cushionof air created by jet engines.

WHAT IS

HOVERCRAFT ?


4/30


5/30

The first design was put forward by Swedish designer and

philosopher Emmanuel Swedenborg in 1716.The project was short-lived because it was never built.It was then in 1956 that a brilliant British radio engineerChristopher Cockerell and French engineer John Bertin whoinvented it.

The first working example wasshown in public in June 1959.

It was called the Saunders Roe

Nautical One or SRN1 .

Historyof

hovercraft


6/30

Principleofworking

Lift the craft by a cushion

of air to propel it using

propellers. Large lifting fans suck in air through a port which is

pushed to the under side of craft.

At the point when the pressure equals the weight of

the craft, the craft lifts up and air is escaped aroundthe edges of the skirt.

Therefore a constant feed of air is needed to liftthe craft.

Thus craft is lifted up.


7/30

Once the craft is lifted up, the air from thepropellers are passed over rudders, which are used

to steer the craft similar to an aircraft.Hovercraft is thus propelled and controlled and its

powerful engine makes it to move.


8/30


9/30

Crafttypes

These can be divided into three types:

1.Twin fan

2.Integrated

3.Twin engine


10/30

1.T i f cr ft

It has 2 fans : a small fan and a large fan.

Small fan provides the lift air to the cushion.

Large fan or aircraft propeller providesthrust air, to move in a particular direction.

Powered by single engine.

Are more efficient and quieter thenintegrated craft.


11/30

2.Int r t d

Its design consists of 1 engine and 1 fan.

A single fan lifts the craft and also makes to

move. It is the most simplest craft.

They are cheap and easy to fly.


12/30

3.T in engine

The twin engine is similar to the twin fan .

Each fan has its own engine.

Both fans require separate engine for itsmotion.

The transmission is simpler than the twin fan

type.


13/30

PARTS F CRAFT

Parts

ofCraft

3.Engine

2.Skirt1.Fan


14/30

1. Fans

Fans

Axial

Ducted Propellers

Centrifugal

Types of fans


15/30

a)Axi lf ns

These propel air parallel to their axis.

Ducted fans

utilize several blades that are generally wideat the tip and taper towards the base.

contain 3-12 blades or even more.

generally of a smaller diameter than propellers.


16/30

a)Axialfans(cont)

Propellers

have 2-5 blades that arelonger than those used on

ducted fans.

are generally noisier thanducted fans.

generally more efficient and safe.


17/30

b)Centrifugalfans

propel air perpendicular to their axis.

they draw air in the center and throw it out

to the side (similar to the type used in hairdryers).

generally used as a lift fan.


18/30

Propellersv/sfan

Propellers

More thrust

Less costly Noisy

Rotate fast

Large Diameter

Fans

Less thrust

More costly Quiet

Rotate slow

Smaller diameter


19/30

2.Skirts andits

functi nsGive adequate stability.

Offer little resistance to passage of obstacles

beneath.Have the ability to absorb a large proportion of the

energy.

Contains the cushion of air beneath the craft at

the required hover height.Have the ability to keep loss of cushion air

minimum.

Return to its original shape after having been

deformed.


20/30

Skirt y s

Skirttypes

a)Bag Skirt

b)SegmentedSkirt

c)Juped Skirt


21/30

a)T e Bag Skirt

The bag is inflated which serves to lift thecraft off the ground and to contain the air

cushion.Two methods of inflating the bag skirt are:

Serial Feed: requires that air be directed

from the lift fan through the skirt and thenout into the cushion.

Parallel Feed: requires that a certain amountof air be split off of the lift fan into the

skirt and the rest into the cushion.


22/30

b)T e Segmented Skirt

(fingerskirt)consists of several separate nylon segments

that, when inflated, press together to form

a shape that looks like fingers of a hand.offers much less resistance to obstacles.

are less stable.

ease of repair when damaged since only oneor two damaged fingers need to be replacedinstead of an entire skirt.


23/30

c)The Juped skirt

(cell skirt) consists of several cells that look like cones with

their tops cut off .

have their bases attached to the bottom of thecraft.

When inflated, these cones readily support theweight of the craft upon a stable cushion.

utilizes a minimum of 2 or 3 cells surrounded by alarge jupe & encompasses perimeter of craft.

tend to scoop water in rough conditions and drag ongrass.


24/30

3. ngine

a hovercraft needs

at least one engine.

Larger, commercialcraft may use as many

as 6-8.

Engines types arediesel , gasoline and

jet turbine.


25/30

a)Diesel engine

Have low noise.

Low specific fuel consumption.

Low maintenance.High safety and dependability.

Highly economic.

Have tremendous weight.Power to weight ratio being 0.1.


26/30

b)Gasoline engine

1. Two-cycle gasoline engine

Mostly used by small hovercraft.

Weight to power ratio is high. Have twice the specific fuel consumption as

compared to 4-cycle engine.

Are small and compact. Has ample power over about 2600 fan rpm

to push the fan to full power revolutions.

Power to weight ratio is 0.8 .


27/30

2. Four-cycle gasoline engine

More reliable than 2-cycle engines.

Have low noise and less vibration.Has 4-8 cylinders producing about 250 hp

output.

Power to weight ratio is 0.36 .


28/30

c)Jet engine

(Aircraft engine)Power to weight ratio is 0.5.

Used basically by military commercial craft

put out thousands of horse power .It mainly has more hp than the other two.


29/30

APPLICATI S

Rescue work on swift

water, ice, mud, deserts,

wetlands, marshes, snowand floodwaters.

Finding vast number of

narrow waterways that

cannot be reached by boat.

Border Patrol and

Homeland Security.


30/30

APPLICATI S(cont)

Traveling from land to water where there is noboat dock.

Military services:Assault vehicles

and transporting troops.

Transport in environmentally sensitive areas where

habitat and erosion are a concern.Oil spill clean up.

Cruising purpose.

mechanical presentation 1

Documents