Aeroplane Propulsion Systems(Mechanical project)

introduction
A heavier than air flying machine, supported by aerofoils, designed to obtain, when driven through the air at an angle inclined to the direction of motion, a reaction from the air approximately at right angle to their surfaces is known as aeroplane. The various forces which acts on the aeroplane when it travels through the air are lift force, drag force, thrust force and its own weight. For steady condition the weight should be balanced by the lift and drag by thrust. The lift is obtained due to the special shape of wings and thrust is obtained by propulsion systems.

INTRODUCTION

What is an air craft?

"All man made contrivances which fly, that is to say which are kept in the air by forces produced by the air are called aircraft".

Eg: balloons, kites, aeroplanes etc.

There are two kinds of air crafts, those which are lighter than air and those which heavier than air. The lighter than means their weight by volume is less than that of air. Heavier than means the weight by volume is heavier than that of air. The former includes balloons, airships etc. and the later comprises kites and aero planes.

AEROPLANE BASICS

Definition

"A heavier than air flying machine supported by airfoils , designed to obtain, when driven through the air at an angle inclined to the direction of motion, a reaction from the air approximately at right angles to their surfaces".

Four forces on an aeroplane

Weight

Weight is a force that is always directed toward the center of the earth. The magnitude of this force depends on the mass of all of the parts of the airplane itself, plus the amount of fuel, plus any payload on board (people, baggage, freight, ...).The weight is distributed throughout the airplane. But we can often think of it as collected and acting through a single point called the center of gravity. In flight, the airplane rotates about the center of gravity, but the direction of the weight force always remains toward the center of the earth. During a flight, the airplane's weight constantly changes as the aircraft consumes fuel.

Lift

To make an airplane fly, we must generate a force to overcome the weight. This force is called the lift and is generated by the motion of the airplane through the air. Lift is an aerodynamic force ("aero" stands for the air, and "dynamic" denotes motion). Lift is directed perpendicular (at right angle) to the flight direction. As with weight, each part of the aircraft contributes to a single aircraft lift force. But most aircraft lift is generated by the wings. Aircraft lift acts through a single point called the center of pressure. The center of pressure is defined just like the center of gravity, but using the pressure distribution around the body instead of the weight distribution.

Drag

As the airplane moves through the air, there is another aerodynamic force present. The air resists the motion of the aircraft; this resistance force is called the drag of the airplane. Like lift, there are many factors that affect the magnitude of the drag force including:

" shape of the airplane
" "stickiness" of the air
" speed of the aircraft

Infrared Curing and Convection Curing(mechanical project)

INTRODUCTION

The coatings and paint industries strive to provide high technology coatings while reducing volatile organic compounds and energy consumption to produce a finished coating. Conventionally Convection ovens are used to cure the coatings. But this process which uses electric heaters is not an optimal process and is associated with various disadvantages. Improved technologies are available today, which can either replace or improve the convection curing process. Infrared Curing is such a technology which uses Infrared rays emitted by an Infrared emitter to provide the required cure. Infrared curing applies light energy to the part surface by direct transmission from an emitter. Some of the energy emitted will be reflected off the surface, some is absorbed into the polymer and some is transmitted into the substrate. This direct transfer of energy creates an immediate reaction in the polymer and cross linking begins quickly once the surface is exposed to the emitter. Infrared emitters are often custom manufactured to suit the production demand. The various aspects of Infrared curing and convection curing and the possibility of combining these two technologies into a singe system will be discussed in this seminar.

CURING

Curing is a process of baking surface coatings so as to dry them up quickly. Curing is a broad term which means all the techniques employed for the finishing operations incurred during part production. Curing essentially involves either the melting of the coating or evaporation of volatile fluids present in the coating by the application of heat energy.

Curing is given to a wide range of materials both organic and inorganic .Usually curing is given to materials like ,

" Paints
" Enamel
" Laquer
" Powder coatings
" Varnishes
" Epoxy coatings
" Acrylic coatings
" Primers Etc

Curing is also given to Rubber and Latex .The principle used for curing can also be used for drying rice and grains.

CONVECTION CURING

Convection ovens are usually used for curing purposes. Traditional convection ovens use heated forced air to provide the necessary cure. Convection ovens consist of a chamber lined on the inside with Electric heaters. The shape of the chamber will be in accordance to the shape or geometry of the part being cured. A series of blowers circulate the heated air around providing the required cure. This process depends on convection to transfer heat from hot air to body surface and conduction to transfer heat to the interior of the surface. The air being delivered is held at temperature using closed-loop control, which provides predictable, repeatable results. Typically a temperature of around 250-500 degree farenheit is required for paint or powder. Though convection ovens are widely used today they have certain disadvantages, which chokes the overall productivity of a company

Disadvantages of convection ovens :

" Fairly long heating times:-
Convection is a slow process. It takes a considerable amount of time for the heaters to heat up and raise the temperature of air to the required level. This causes a lag in the process and hence the curing time increases. Longer curing time spells reduced assembly line movement. This in turn reduces productivity.

" High energy consumption:-
A convection column dryer uses around 2000 BTU(British Thermal Unit) of energy to remove 1 pound of moisture. They use around 7.7 KW of electrical energy to dry a ton of rice. These are significantly larger figures for any company trying to bring energy consumption under control. The additional use of blowers and compressors further increases energy consumption.

" Large floor area required:-
Convection ovens are bulky in nature. Due to the presence of compressors and blowers, additional space is needed, which in turn increases the floor area requirement.

" Air circulation is required:-
Convection heating requires a medium for transmission of heat. Hence blowers are employed for good circulation of heated air. This increases the overall cost of the equipment.

Hovercraft

INTRODUCTION

A Hovercraft is a vehicle that flies like a plane but can float like a boat, can drive like a car but will traverse ditches and gullies as it is a flat terrain. A Hovercraft also sometimes called an air cushion vehicle because it can hover over or move across land or water surfaces while being held off from the surfaces by a cushion of air. A Hovercraft can travel over all types of surfaces including grass, mud, muskeg, sand, quicksand, water and ice .Hovercraft prefer gentle terrain although they are capable of climbing slopes up to 20%, depending upon surface characteristics. Modern Hovercrafts are used for many applications where people and equipment need to travel at speed over water but be able load and unload on land. For example they are used as passenger or freight carriers, as recreational machines and even use as warships. Hovercrafts are very exciting to fly and feeling of effortlessly traveling from land to water and back again is unique.

HISTORY

In the beginning……

Hovercraft as we know them today started life as an experimental design to reduce the drag that was placed on boats and ships as they ploughed through water. The first recorded design for an air cushion vehicle was put forwarded by Swedish designer and philosopher Emmanuel Swedenborg in 1716. The craft resembled an upturned dinghy with a cockpit in the centre.

Apertures on either side of this allowed the operator to raise or lower a pair of oar-like air scoops, which on downward strokes would force compressed air beneath the hull, thus raising it above the surface. The project was short-lived because it was never built, for soon Swedenborg soon realized that to operate such a machine required a source of energy far greater than that could be supplied by single human equipment. Not until the early20th century was a Hovercraft practically possible, because only the internal combustion engine had the very high power to weight ratio suitable for Hover flight.

In the mid 1950s Christopher Cockrell, a brilliant British radio engineer and French engineer John Bertin, worked along with similar line of research, although they used different approaches to the problem of maintaining the air cushion. Cockrell while running a small boatyard in Norfolk Boards in the early 1950s began by exploring the use of air lubrication to reduce the hydrodynamic drag, first by employing a punt, then a 20 knot ex-naval launch as a test craft.

PRINCIPLE OF WORKING

The principle of working of a Hovercraft is to lift the craft by a cushion of air to propel it using propellers. The idea of supporting the vehicle on a cushion of air developed from the idea to increase the speed of boat by feeding air beneath them. The air beneath the hull would lubricate the surface and reduce the water drag on boat and so increasing its speed through water.

The air sucked in through a port by large lifting fans which are fitted to the primary structure of the craft. They are powered by gas turbine or diesel engine. The air is pushed to the under side of the craft. On the way apportion of air from the lift fan is used to inflate the skirt and rest is ducted down under the craft to fill area enclosed by the skirt.
At the point when the pressure equals the weight of the craft, the craft lifts up and air is escaped around the edges of the skirt. So a constant feed of air is needed to lift the craft and compensate for the losses.

Thus craft is lifted up. After the propulsion is provided by the propellers mounted on the Hovercraft. The airs from the propellers 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 fly.

The Development of Mind By A. J. P. Kenny, H. C. Longuet-Higgins, C. H. Waddington

The experimental and highly regarded Gifford Lectures atEdinburgh University was endowed in the late nineteenthcentury. Over the years, participants have including manyleading representatives of religion, science, and philosophy.This series has as its subject, The Development of Mind. Firstpublished in 1972, the series continues to attract widespreadinterest. In this volume, contributors argue about the mindfrom diverse analytical standpoints.The focus of the series remains the relationship betweenreligion, science, and philosophy. This volumeattempts to achieve a comprehensive view of the subjectof mind. The mental development of children in the lightof modern psychology is discussed, and the distinctionbetween "how" and "why" questions is put forward withclarity. The development of mind is further contrastedwith the evolution of embryos in the young. The mind isconsidered as a capacity for intellectual activity, and asa multi-purpose program. Goal-directed behavior andlanguage development are given importance, and issuesof cosmic purpose, and the how and why of evolution, arenever far from the surface of the argument.The lecturers know their opposition and their positions,and the cut-and-thrust of the discussion has muchacumen and wit to it. Issues ranging from the impact ofmind on theories of religion, causation, and rational willare examined in an informal, yet compelling, manner.