brd 3 Essay

CLASSIFICATION OF AIRCRAFT

HELICOPTER is a rotary wing aircraft in which lift is produced by its rotor blades. They can take off and land without the need for runway. They can hover in the air or maneuver in any direction in a 360-degree space. Today, helicopter uses include transportation of people and cargo, military uses, construction, firefighting, search and rescue, tourism, medical transport, law enforcement, agriculture, news and media, and aerial observation.

When the blades rotate relative to the air the special airfoil shape will generate lift force and make them fly.

The blades derive rotation from an engine more specifically a turbo shaft engine. The compressor sucks the air in and pressurizes it fuel is burned in this pressurized and hot air. The hot exhaust leaves the combustion chamber passes through a series of turbine stages and make them turn. There are two Sets of turbines one turbine set turns the compressor and the other set turns the helicopters rotor shaft.

Jet Engines of Airplanes are used to generate thrust force however the primary function of the helicopters jet engine is to turn the rotor shaft.

When the helicopter is at an angle the Force produced by the blade is not vertical. The horizontal component of this Force will make the helicopter move in the desired Direction. The vertical component of the Blade Force will Balance the gravitational force.

The lift produced by an airfoil varies with the angle of attack. Generally, the greater the angle of attack the more the lift.

The lift forces acting on the blades will be different in this case. The variations in the lift forces will result in a torque that can turn the helicopter. Thus, the blades must keep on changing angle of attack so that at one particular location the angle of attack is always the same. Such complex of the blades is achieved by a swash plate mechanism.

The bottom Swash plate does not spin, but it can move and tilt. A top swash plate is fitted on the bottom swash plate Via a bearing. So, the top Swash plate can inherit all the motion of Bottom Swash plate while at the same time it can rotate independently. Top swash Plate is attached to the rotor Shaft with the help of a driver. So, the top swash plate will always move with the blades.

The blades are connected to the top swashplate with the help of control Rods. The interesting thing about this arrangement is that just by tilting the bottom swashplate we will be able to achieve the varying Angle Criterion of the blades.

That means with this swashplate tilt we will always be able to maintain a positive angle of attack at the rear and a negative angle at the front portion of the rotor disk.

In short Swashplate tilting backwards produces a torque. This kind of control is known as cyclic pitch.

What happens in reality is the helicopter will turn sideward. By applying torque in one direction to a rotating object the object turns in different direction. This effect is known as gyroscopic precession.

If we just lift the bottom swashplate without tilting it, the angle of attack of all three blades will vary by the same amount. This means that the helicopter lift Force will be the same in all three blades and the helicopter can move up or down without any tilt. Such blade control is known as collective pitch.

Helicopter needs tail rotor for effective operation. Without the tail rotor the helicopter fuselage would have spun. This is due to a consequence of Newton’s third law of motion.

The rotor gets the force of rotation via a bevel gear connected to the engine. Bevel gear Transmits Force to the rotor bevel gear however according to Newton’s third law of motion, the Rotor bevel gear should Transmit an equal and opposite Force to the engine bevel gear. This reaction Force will make the whole helicopter turn opposite to the blade rotation along the helicopter centre of gravity.

The function of the tail rotor is to prevent such helicopter rotation by producing a force at the tail. By properly adjusting pitch angle of the tail rotor Blades the Pilot can easily manipulate the tail rotor force. With the help of the tail rotor Yaw motion of the helicopter can also be achieved.

LOOMING BAY

It is a bay in which all helicopter wires or we can say loom (bunch of wires) are repaired. When the helicopters come for the servicing or overhauling all the looms are detached from the helicopter and send to the looming bay. Here first the aircraft comes to the aircraft division and here the helicopter is disassembled, and the respective parts are sent to their division for repairing or overhauling. So, in the looming bay all looms are repaired like the insulation of wire is checked, if the insulation of wires are less than 20 mega oms then the wires are replaced, But if the insulation of the wire is more than 20 mega oms then they are repaired. For example, sealing material are inserted, they are properly insulated, they are made fireproof. These checks are performed with the help of following things: –

Circuit Diagram

Fireproof material fluoroplastics is used it can withstand up to 400 degree Celsius.

Sealing material Vgo-I is used

Automatic harner loom testing machine (it checks the isolation).

So, as we know that near engine the temperature is very high and the wires near the engine needs to be high temperature resistance so shielding wire PTFE (polytetrafluoroethylene) is used. These wires can resist high temperature as well as low temperatures (-60 to 200 degree Celsius).

Also, some red tapes are used to repair the wires, these tapes have a property that they stick to itself only and does not stick to any other material.

Figure 1 wire looms

STRUCTURAL REPAIR BAY

BLADES

Helicopter blades are of two types one is main rotor blade and second one is tail rotor blade. Blades plays an important role in producing the lift and carrying the whole weight of the helicopter so, blades should be strong enough to take the load of the aircraft and bear all stresses which act over it that is why the main rotor blade are made by joining small-small blades together. All these small blades are having honeycomb structure from inside so that load can be distributed, and the weight of the blade does not exceed. The main advantage of this type of blade is that they can be repaired easily. If there is some crack or deformation over the blade, then we don’t have to change the whole blade just we have to change the small blade which got damaged. So, this save time and money both.

Whereas tail rotor blades come in the set of three and we cannot repair the blade if, one blade got damaged and cannot be repaired then we have to change the whole set of blades, this we can say the disadvantages of the tail rotor blade. Also, one important feature is added to the blade is that a light is fitted at the ends of both blades so that during night flight the area can be visible that is covered by the blades while rotating.

Another feature is added that a metal strip is joined in front of the blade so that ice formation can be prevented when the helicopter is flying at an area where temperature is low with the help of electrical supply on these metal strips.

Figure 1 main rotor blades

TAIL ROTOR ASSEMBLY

Tail rotor assembly is a place where tail rotor is repaired. It got fully dissembled here and then checked for damages and areas for improvement and then they are fixed. On MI 17 helicopters the tail rotor has 3 blades and all three blades have marking and you have to follow it like first blade has red colour marking similarly second blade has green and third one has blue colour marking and these blades should be fitted in their exact positions. You cannot fit red marking blade in second or third position you have to place it in first position.

Some more precautions are taken for a safety these are: –

The difference between the height of blades should not be exceed by ±5 millimetre.

Difference in blade angle (both minimum and maximum) should not be more than 10’ (1/6 degree).

In general MI 17 tail rotor assembly takes 500-man hours to complete the task or 33 days.

FIRE PROTECTION SYSTEM

Fire protection system is very crucial system for an aircraft. It needs to be active all time and in case of fire it should work. This type of system can help to safe in emergency situations.

The fire protection system used in MI 17 helicopters has an operating voltage of 24 to 36 milli volts.

This system is fitted in different places and monitors the temperature, if the temperature rises from the limited value then it indicates in the cockpit with red light and some sound. This system consists of 6 plates which monitors temperature up to 150 degree Celsius and 1 more plate up to 200 degree Celsius. And in this Freon gas is used as fire extinguisher. Also, hand co2 extinguishers are also used in case there is some system failure or small fire is taken place. This system measures every 2-degree Celsius rise in temperature.

INSPECTION AND REPAIRING METHOD

BRINELL HARDNESS TEST

This method is generally used for measuring the hardness of a metal or alloy. In this method a ball shape indenter is pressed under a load into the specimen. Due to the load the material deforms, and this deformation is measured, and hardness of the material is determined. Now a days this is done digitally means you don’t have to observe or measure the deformation with the help of computers it is shown on screen digitally.

Figure 2 Brinell hardness test

SAND BLASTING

Sand blasting is a technique to make the material surface rough before it is sent for casting. This method helps to coat the material easily over it. In sand blasting method a mixture of sand and metal is used. The material is kept inside the chamber and the machine is started, inside the chamber a turbulence is created due to which the sand and metal particles bombard to the material surface which makes it rough.

Figure 3 Sand blasting machine

THERMAL SPRAY MACHINE

This machine is used for the coating of the materials. In this process temperature can reach up to 3000? F. in this process acetylene and oxygen gas is used and imparted on the material. This technique is mainly used for the rotable parts. When the desire temperature is reached over the material then an alloy rod is inserted from the back and it gets sucked inside and gets coated over the material.

Figure 4 Thermal spray unit

ROBOTIC PLASMA SPRAY

As we know that plasma spray is the technique in which the hot spray is sprayed over the material which softens the material and the powder is sprayed with which gets coated over the material. The similar process is done in the robotic plasma method, but the only difference is that it is done with the help of robotic arm. And it is done in a closed room because the temperature reaches very high and some amount of radiation is also there. Everything is done with the help of computers. This method is very effective now a days and saves lots of time. The specimen is placed at the table as shown in the figure and everything is done by robotic arm.

Figure 5 Robotic plasma spray

NDT TECHNIQUES

RED DYE INSPECTION METHOD

As the name suggest that a red dye is used to inspect the cracks or defects. This technique is used for no ferrous materials.

FLUORESCENT PARTICLE INSPECTION

This technique is also used for the nonferrous materials to detect the defects and cracks.

MAGNETIC PARTICLE TESTING (MPT)

This technique is used for the ferrous materials. This technique is used for crack detection. The following steps are followed in this technique: –

First the material is magnetized with the help of magnets.

Due to the magnetization magnetic particles are deposited over the crack (if there) and if there is no crack then no particle will be deposited.

Now a magnetic ink is sprayed over the material.

At last UV rays are put over the material and if the cracks are their then they will glow. And we can say that crack is there.

Figure 6 Magnetic particle testing

RED DYE INSPECTION METHOD

As the name suggest that a red dye is used to inspect the cracks or defects. This technique is used for no ferrous materials.

FLUORESCENT PARTICLE INSPECTION

This technique is also used for the nonferrous materials to detect the defects and cracks.

ENGINE DIVISION

In the engine division we were glad to see three main engine of different aircrafts first is MI-8 helicopter second is MI-17 helicopter and the third one is An-32 aircraft.

These all three have different engine fitted inside them.

MI-8 Helicopter —– TV-2 engine

MI-17 Helicopter —– TV-3 engine

AN-32 aircraft —– AI-20 engine

Different engines have different specifications given below: –

TV-2 ENGINE

Its weight is 332.5±2% (in kgs)

It has a 10-stage axial compressor

Turbine– 2 stage compressor turbine and 2 stage free turbine

TV-3 ENGINE

Its weight is 285±5.7 (in kgs)

It has 12 stage axial compressor.

Turbine– 2 stage compressor turbine and 2 stage free turbine.

AI-20 ENGINE

Its weight is 1040±2 (in kgs)

It has a 10-stage axial compressor

Combustion chamber annular type

Turbine—3 stage reaction turbine

Also, in AN-32 aircraft TG-16M (auxiliary power unit) is used. It is a gas turbine APU. It is used for the starting of AN-32 aircraft. It provides 20-60 volts variable DC at 1000 amps.

Its maximum use height is 3.5 kms.

ENGINE OVERHAULING PROCESS

SELF SEALING TANKS

In MI-17 helicopters some special types of fuel tanks are used, these have a property that they seal itself when there is some damage or hole in the tanks. These tanks are especially made so that during war condition if any bullet hits the tank then instead of leaking of fuel or burning of fuel it will seal the hole or damage and no such incidence will take place.

These tanks are made with the help of following items: –

Cotton canvas

They initially cover the tank

Cellous rubber

This rubber has a property to heal itself. After cotton canvas 2 layers of cellous rubber is used to make it safer.

Glass cloth

After this a layer of glass cloth is used. It has a property that it is fireproof so, in case of leakage of fuel it will not catch fire ever in contact with sparks or fire.

Fireproof paint

At the last 2 layers of fireproof paint is done so that there are no chances of damage even when the spark is initiated due to bullets or some artillery damage.

Figure SEQ Figure * ARABIC 7 Self-sealing tank

HYDRAULIC OIL AND ITS COOLING

In MI-17 helicopters there is a hydraulic tank of 15 liters which carries the hydraulic oil so that the hydraulic system will work properly. There is also a drainage tank of 3 liters so that the fuel which gets wasted will deposited in the drainage tank. The hydraulic oil which is used for MI-17 helicopters is OM-15. This hydraulic oil can be used up to 110 degrees Celsius, after that temperature the oil starts losing its properties.

For the cooling of the hydraulic oil radiator is used. When the temperature of the hydraulic oil reaches the 65 degrees Celsius then the oil start flowing through the radiator. The process of oil flowing through the radiator has a different mechanism, the mechanism is given below:-

When the oil temperature reaches 65 degrees Celsius a valve will expand.

Now this expanded valve stops the direct flow of the oil and the oil passes through the radiator.

The valve which get closed is due to the expansion of the spring which is fitted beside the valve, when the temperature reaches 65 degrees Celsius the spring got thermal expansion and the valve get closed. The maximum expansion in the spring is 5mili meters.

Now the oil will pass through the radiator and get cooled and will reach to the desire system

CORDINATE MEASURING MACHINE (CMM)