Airframe 1 (done)

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Task-1a (P1)

Three purposes of pneumatic systems are given below: 1. Pneumatic systems are used in air-conditioning system and pressurization system of

aircraft.

2. For aircraft anti-icing and deicing systems pneumatic systems are used.

3. It can be used for engine starting system and gas turbine compressor.

The functions of piston engine, air compressor and receiver are describes below:

(a) Function of piston engine:

The Otto cycle is the ideal air standard cycle for the spark ignition piston engine. In this cycle it

is assumed that the working fluid, air, behaves as a perfect gas and that there is no change in

the composition of the air during the complete cycle. Heat transfer occurs at constant volume

and there is reversible adiabatic compression and expansion. This piston cycle differs from the

practical engine cycle in that the same quantity of working fluid is used repeatedly and so an

induction and exhaust stroke are unnecessary. The thermodynamic processes making up a

complete piston engine Otto cycle are detailed below:

Figure: Working cycle of piston engine

MD. FARHAN RAHMAN AOYON ID NO: 04 BATCH: 09

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1–2 Adiabatic compression takes place. No heat transfer takes place, temperature and pressure

increase and the volume decrease to the clearance volume.

2–3 Reversible constant volume heating, temperature and pressure increase.

3–4 Adiabatic expansion (through swept volume) takes place. Air expands and does work on

the piston. Pressure and temperature fall. No heat transfer takes place, during the process.

4–1 Reversible constant volume heat rejection (cooling). Pressure and temperature fall to

original values.

During the compression and expansion of the working fluid, the ideal Otto cycle assumes that

no heat is transferred to or from the working fluid during the process.

(b) Function of air compressor:

An air compressor is a machine that uses an electric motor or gas engine to power a device that

sucks in successive volumes of air from the atmosphere, compresses (squeezes) each volume

of air in a confined place to increase its pressure by making the volume smaller, and then

transfers the high-pressure air to a receiver tank.

(c) Function of air r eceiver :

The receiver usually stores enough compressed air for several applications. From the air

compressor this high pressure air is then stored in the air receiver until it is needed. The Air

receiver is basically a metal bottle. The high-pressure air is drawn off from the receiver tank to

power equipment. Such as:

A high pressure air line connects the bottle to an air valve which controls operation of the

emergency brakes. If the normal brake system fails, place the control handle for the air valve in

the "on" position. The valve then directs high-pressure air into lines leading to the brake

assemblies. But before air enters the brake assemblies, it must first flow through a shuttle valve.


P a g e | 3

Task-1b (P2)

How bleed air is supplied to the system pre-cooler from turbine engine is describes below:

On most jetliners, air is supplied to the ECS by being "bleed" from a compressor stage of

each gas turbine engine, upstream of the combustor. The temperature and pressure of this

"bleed air" varies widely depending upon which compressor stage and the RPM of the engine.

Figure: Bleed air supplied to system pre-cooler from engine

A "Manifold Pressure Regulating Shut-Off Valve" (MPRSOV) restricts the flow as necessary to

maintain the desired pressure for downstream systems. This flow restriction results in efficiency

losses. To reduce the amount of restriction required, and thereby increase efficiency, air is

commonly drawn from two bleed ports.

When the engine is at low thrust, the air is drawn from the "High Pressure Bleed Port." As thrust

is increased, the pressure from this port rises until "crossover," where the "High Pressure Shut-

Off Valve" (HPSOV) closes and air is thereafter drawn from the "Low Pressure Bleed Port."

To achieve the desired temperature, the bleed-air is passed through a heat exchanger called a

"pre-cooler." Air from the jet engine fan is blown across the pre-cooler, which is located in the

engine strut. A "Fan Air Modulating Valve" (FAMV) varies the cooling airflow, and thereby

controls the final air temperature of the bleed air.


http://en.wikipedia.org/wiki/Strut

http://en.wikipedia.org/wiki/Heat_exchanger

http://en.wikipedia.org/wiki/Bleed_air

http://en.wikipedia.org/wiki/Pressure

http://en.wikipedia.org/wiki/Temperature

http://en.wikipedia.org/wiki/Combustor

http://en.wikipedia.org/wiki/Gas_turbine_engine

http://en.wikipedia.org/wiki/Gas_compressor

http://en.wikipedia.org/wiki/Bleed_air

http://en.wikipedia.org/wiki/Jetliners

P a g e | 4

Task-1c (P3)

The purposes of the given aircraft pneumatic supply systems are state below:

Cabin air conditioning system:

The function of an air conditioning system is to maintain a comfortable air temperature within the

aircraft fuselage. The system will increase or decrease the temperature of the air as needed to

obtain the desired value. Most systems are capable of producing an air temperature of 700 to

800 F. with normally anticipated outside air temperatures. This temperature-conditioned air is

then distributed so that there is a minimum of stratification (hot and cold layers). The system, in

addition, must provide for the control of humidity, it must prevent the fogging of windows, and it

must maintain the temperature of wall panels and floors at a comfortable level.

Cabin pressurization system:

When an aircraft is flown at a high altitude, it burns less fuel for a given airspeed than it does for

the same speed at a lower altitude. In other words, the airplane is more efficient at a high

altitude. In addition, bad weather and turbulence can be avoided by flying in the relatively

smooth air above the storms. Aircraft which do not have pressurization and air conditioning

systems are usually limited to the lower altitudes.

A cabin pressurization system must accomplish several functions if it is to assure adequate

passenger comfort and safety. It must be capable of maintaining a cabin pressure altitude of

approximately 8,000 ft. at the maximum designed cruising altitude of the aircraft. The system

must also be designed to prevent rapid changes of cabin altitude which may be uncomfortable

or injurious to passengers and crew. In addition, the pressurization system should permit a

reasonably fast exchange of air from inside to outside the cabin. This is necessary to eliminate

odors and to remove stale air.

The functions of the given things of aircraft pneumatic supply system are given below:

Ram air:


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It is more of ventilation system rather than cooling or conditioning system. Ram air taken from

atmosphere is made to pass over engine exhaust air outlet pipes which assist in raising the

temperature. Heated air can now be mixed with cold ram air to obtain desired level on

temperature and same can be introduced in cockpit.

Bleed air:

In bleed air system compressed air is taken from two stages of compressor to meet the

adequate flow requirements with varying compressor RPM or thrust settings. In order to prevent

air flow from high pressure to low pressure duct, non return valve is fitted to low pressure duct.

A high pressure shutoff valve is fitted to the high pressure duct in order to modulate/stop the

flow of air from high pressure stage incase aircraft is flying at sufficiently higher speeds. Once

the flow from both the stages is merge, a valve to govern the amount of flow entering main

system is added to main line namely Bleed Air Valve.

In order to reduce and distribute the workload, the bleed air requirement by the system is

distributed to both the engines (for multi engine) of aircraft. Should there be any lag in air supply

by one engine due failure or other problem, the isolation valve can be opened so that live

engine can assist the system functioning

Air cycle unit:

An air cycle cooling system consists of an expansion turbine (cooling turbine), an air-to-air heat

exchanger, and various valves which control airflow through the system. The expansion turbine

incorporates an impeller and a turbine on a common shaft. High-pressure air from the cabin

compressor is routed through the turbine section. As the air passes through the turbine, it

rotates the turbine and the impeller. When the compressed air performs the work of turning the

turbine, it undergoes a pressure and temperature drop. It is this temperature drop which

produces the cold air used for air conditioning.

Humidifier:

When aircraft is flying at very high altitudes like 30,000ft or so, the moisture content in ambient

air is almost negligible. In order to aid comfortable respiration, some moisture can be added to

air. Drinking water stored in the pressurized tank is splashed in downstream of air flow from

water separator or air cycle unit and any excess moisture is absorbed by fabric covered spill


P a g e | 6

vanes fitted in path of air flow. The amount of moisture added by humidifier can be controlled by

pilot with the data given by humidity sensor fitted at outlet of humidifier.

How conditioned air is supplied from intercooler to the aircraft cabin is describes below:

Air conditioning prepares engine bleed air to pressurize the aircraft cabin. The temperature and

quantity of the air must be controlled to maintain a comfortable cabin environment at all altitudes

and on the ground. The air cycle system is often called the air conditioning package or pack. It

is usually located in the lower half of the fuselage or in the tail section of turbine-powered

aircraft.

Figure: Air conditioning system

Even with the frigid temperatures experienced at high altitudes, bleed air is too hot to be used in

the cabin without being cooled. It is let into the air cycle system and routed through a heat

exchanger where ram air cools the bleed air. This cooled bleed air is directed into an air cycle

machine. There, it is compressed before flowing through a secondary heat exchange that cools

the air again with ram air. The bleed air then flows back into the air cycle machine where it

drives an expansion turbine and cools even further. Water is then removed and the air is mixed


P a g e | 7

with bypassed bleed air for final temperature adjustment. It is sent to the cabin through the air

distribution system. By examining the operation of each component in the air cycle process, a

better understanding can be developed of how bleed air is conditioned for cabin use.

Task - 1d (P10)

Job title:

Replace the check valve of engine bleed air system.

Safety equipments:

Safety goggles.

Gloves.

Safety Shoes

Apron

Face Mask

Helmet and etc.

Tools Needed:

Cutter

22 mm ring spanner.

19 mm open end spanner.

Nose Pliers.

Locking wire

Cleaning rag.

Disassemble procedure:

1. First I cut off the wire locks using cutter.

2. Removed the check valve nuts on each side opening nuts on opposite sides.


P a g e | 8

3. Then I removed the bigger nuts under check valve nuts by using 22mm ring spanner.

4. Removed circlip using nose pliers.

5. Then I serially took out the body, spool, spring, valve, fittings and nut.

Replace procedure:

1. Firstly, serially put on the body, spool, spring, valve, fittings and nut.

2. Then I put on the circlip using nose pliers.

3. Then used 22 mm ring spanner to fit the bigger nut beneath the check valve nut.

4. Then by using 19mm spanner we fitted the check valve nuts on each side.

5. Then again fitted the locking wire.

6. At last we settled the check valve into the system.

Safety precaution:

Proper tools should be used

After the re-installing it should wire lock.

Pliers gripe should not be moveable.

Fuel system should be depressurized

To stop fuel supply, reservoir should be empty

Put tag on cockpit to avoid other people using this system

When I took the tools needed, I have registered the tools before taking them out of the

workshop.


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Task – 1e (P11)

I.

Job title:

Replace bleed air wing isolation valve.

Safety equipments:

Safety goggles.

Gloves.

Safety Shoes

Apron

Face Mask

Helmet

All kinds of safety equipments.

Required Tools:

Open ended ring spanner (size 8 mm).

Cutter.

Pliers.


At first I cut the wire locking by using cutter.

Then I removed the nuts and bolt of wing isolation valve by using open ended spanner

(size 8mm)


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After that I remove the cover plate of the wing isolation valve.

Then clean it with the cleaning rag.

Replace procedure:

I fitted cover plate back of the wing isolation valve.

Then I tightened nuts and bolts with hand.

After that I tightened by using spanner.

At last wire lock the wing isolation valve.

Safety precaution:

Proper tool should be used.

Tools should be lubricant and oil free.

Tag should be place in starter switch in cockpit

Completely drain the fuel tanks before work


workshop.


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II.

Job title:

Replace cabin safety valve.

Safety equipments:

Safety goggles.

Gloves.

Safety Shoes

Apron

Face Mask

Helmet

All kinds of safety equipments.

Tools Needed:

27 mm ring spanner

Wire locking

Cutter

Phillip Screw driver


At first cut off the wire locking.

Unscrew the screw with Phillip screw driver

Using 27mm ring spanner, remove nuts

Take out the spring carefully.

After that take out the safety valve.


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Replace procedure:

At first put the safety valve.

Then put the spring.

And then tighten the union by using spanner.

Then fit the cabin safety valve into the system.

Safety precaution:


workshop.

System should be depressurized during operation.

Tag should be place on cockpit to avoid people using of system

Proper tools should be used for avoiding damage to parts.


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Task – 1f (M1)

Pneumatic supply system of piston engine and gas turbine engine are explained below:

Pneumatic supply system of piston engine:

Many aircraft equipped with reciprocating or piston engines obtain a supply of low-pressure air

from vane-type pumps. These pumps are driven by electric motors or by the aircraft engine.

Pump compresses air tat raising air pressure to above ambient pressure for use in pneumatic

systems. Then one-way valve allows pressurized air to enter the pneumatic system, but

prevents backflow of air toward the Compressor when Compressor is stopped (prevent loss of

pressure. Accumulator then Stores compressed air, Prevents surges in pressure Prevents

constant Compressor operation (“duty cycles” of Compressor). Directional valve Controls

pressurized air flow from Accumulator (source to user equipment via selected port some valves

are one way shut tight Some valves are two way, allowing free exhaust from the port not

selected valves can be actuated manually or electrically. Then actuator converts energy stored

in compressed air into mechanical motion. Thus, the pump delivers to the pneumatic system a

continuous supply of compressed air from 1 to 10 psi. Low-pressure systems are used for wing

deicing boot systems.

Pneumatic supply system of gas turbine engine:

The turbine engine is a generator of high-speed gas aimed to provide thrust for the aircraft.

Before entering the combustion chamber and being mixed with atomized fuel, the external air is

processed by a multi-stage axial compressor, driven by the turbine. From one or more stages of

the compressor, a limited volume of air can be bled without significant degradation of the engine

performances.

Air is commonly bled at two different stages of the compressor: a low pressure port at an

intermediate stage (around 7TH stage) and a high pressure port at a final stage (around 15TH

stage). A check valve is necessary to prevent air flowing from high to low pressure bleeding

ports. The low pressure bleeding port is normally open, but can be excluded with the shut-off

valve if the engine is in critical conditions; the high pressure port is open when the pressure

coming from the intermediate stage is not adequate, or a considerable amount of air is

necessary, and anyway the engine must be in operating conditions that cannot be deteriorated


P a g e | 14

by intensive air bleeding: typically this bleeding is operated during taxiing or descent, with the

engine near idle.

Figure: Pneumatic system of gas turbine engine

A low flow rate can be extracted from the engine, between 2 and 8% of the total flow rate

processed, but a significant amount of energy content. The same amount of energy is obtained

by compressed air extracted from the APU, but the bleeding rate is here around 70-80% of the

total flow rate, because the APU is not finalized to generate thrust with the exhaust gases. This

allows operation of all pneumatic uses when the aircraft is on ground with engines off, in

particular the environmental control system and engine starting. Bleed air conditions from the

compressor stages range, for a modern turbofan, from 0.2 to more than 1 MPa in pressure and

from 180 to more than 350 °C in temperature, depending on altitude and engine speed.

Because the generated air is at a temperature higher than that requested by the uses, and may

be too hot to be canalised safely to other regions of the aircraft, it is cooled through a heat

exchanger with fresh external air before going to the pneumatic system delivery (see again fig.

5.1). By metering the fresh cooling air with a flow rate regulator, the compressed air temperature

is controlled, usually for a final temperature around 175 °C. Moreover a regulator on the

compressed air line keeps the pressure to system at about 0.3 MPa.


P a g e | 15

Differences between pneumatic supply systems of gas turbine powered aircraft and piston engine powered aircraft:

Gas turbine pneumatic supply system Piston engine pneumatic supply system

Pneumatic supply system in gas

turbine engine aircraft is more efficient.

Pneumatic supply system in piston

engine aircraft is less efficient.


turbine engine aircraft is effective.


engine aircraft is cost expensive.

The repairing is difficult of Pneumatic

supply system in gas turbine engine

aircraft.

The repairing is easy of Pneumatic

supply system in piston engine aircraft.


turbine engine aircraft, consumes less

fuel.


engine aircraft, consumes more fuel.

The use of pneumatic supply system in

gas turbine engine aircraft, are

available even in some modern

aircrafts.

The use of pneumatic supply system in

piston engine aircraft, are now nearly

extinct and very rare to find.

The manufacturing process is difficult

of pneumatic supply system which to

be installed in piston engine aircraft.

The manufacturing process is easy of

pneumatic supply system which to be

installed in piston engine aircraft.

The installation of pneumatic supply

system which to be installed in gas

engine aircraft, is easy.

The installation of pneumatic supply

system which to be installed in piston

engine aircraft, is difficult.

The future of using pneumatic supply

system in gas turbine aircrafts is way

better than piston engine aircraft.

The future of using of pneumatic

supply system in piston engine aircrafts

is under threat as it’s usage has

already become nearly extinct.


P a g e | 16

Task – 1g (M2)

The function of the given components of air conditioning system is given below:

Sensors:

Cabin temperature pickup units and duct temperature sensors used in the temperature control

system are thermistors. Their resistance changes as temperature changes. The temperature

selector is a rheostat that varies its resistance as the knob is turned. In the temperature

controller, resistances are compared in a bridge circuit. The bridge output feeds a temperature

regulating function. An electric signal output is prepared and sent to the valve that mixes hot

and cold air. On large aircraft with separate temperature zones, trim air modulating valves for

each zone are used. The valves modulate to provide the correct mix required to match the

selected temperature. Cabin, flight deck, and duct temperature sensors are strategically located

to provide useful information to control cabin temperature.

Duct stats:

Ducts having circular or rectangular cross sections are most frequently used in air distribution

systems. Circular ducts are used wherever possible. Rectangular ducts are generally used

where circular ducts cannot be used because of installation or space limitations. Rectangular

ducts may be used in the cabin where a more pleasing appearance is desired. Distribution ducts

for various cabin zones, individual air outlets for passengers, and window demisters can have

various shapes. Cabin air supply ducts are usually made from aluminium alloys, stainless steel,

or plastic. Main ducts for air temperatures over 2000 C. are made from stainless steel.

Motor operated valve:

The use of electric motors to operate air conditioning system valves is common on large aircraft

due to the remote location from the cockpit of air system components. The types of valves used

are basically the same as the manually operated valves, but electric motors are used to actuate

the units. The two most common electric motor operated air valves are the gate valve and the

plug-type valve. The motor-operated gate valve uses a geared, reversible electric motor to turn

the actuating arm of the valve that moves the fuel gate into or out of the path of the air. As with

the manually operated gate valve, the gate or blade is sealed. A manual override lever allows


P a g e | 17

the technician to observe the position of the valve or manually position it. Regardless of the type

of valve used, large aircraft air conditioning systems.

How cabin temperature is controlled by using sensors, duct stats and motor operated valves are explained below:

Most cabin temperature control systems operate in a similar manner. Temperature is monitored

in the cabin, cockpit, conditioned air ducts, and distribution air ducts. These values are input into

a temperature controller, or temperature control regulator, normally located in the electronics

bay. A temperature selector in the cockpit can be adjusted to input the desired temperature. The

temperature controller compares the actual temperature signals received from the various

sensors with the desired temperature input. Circuit logic for the selected mode processes these

input signals. An output signal is sent to a valve in the air cycle air conditioning system. This

valve has different names depending on the aircraft manufacturer and design of the

environmental control systems. It mixes warm bleed air that bypassed the air cycle cooling

process with the cold air produced by it. By modulating the valve in response to the signal from

the temperature controller, air of the selected temperature is sent to the cabin through the air

distribution system.


P a g e | 18

Figure: Cabin Temperature Control System

Cabin temperature pickup units and duct temperature sensors used in the temperature control

system are thermistors. Their resistance changes as temperature changes. The temperature

selector is a rheostat that varies its resistance as the knob is turned. In the temperature

controller, resistances are compared in a bridge circuit. The bridge output feeds a temperature

regulating function. An electric signal output is prepared and sent to the valve that mixes hot

and cold air. On large aircraft with separate temperature zones, trim air modulating valves for

each zone are used. The valves modulate to provide the correct mix required to match the

selected temperature. Cabin, flight deck, and duct temperature sensors are strategically located

to provide useful information to control cabin temperature.

Task – 1h (D11)

I. The normal operation of cabin pressurization system with given steps are explained

below:

Before takeoff:

Turn the rate knob to the desire rate.

Set the cabin altitude knob to the desire cabin altitude.

Never set cabin altitude than failed pressure altitude.

Set the air conditioning master switch to “air conditioning auto press”.

After takeoff climb:

Set the rate knob to the desire rate.

Adjust the rate setting as required during climb so that the cabin reaches the selected

altitude at the same time the aircraft reaches cruise altitude.

Thus, the rate pressure change is held to a minimum.


P a g e | 19

The rate of cabin pressure change is held constant only up to pressure controller

differential limit.

Monitor cabin altitude against aircraft altitude to make sure that cabin altitude stays

within the isobaric range.

Cruise:

During pressurized flight, monitor the cabin differential pressure and cabin altitude.

Do not allow the cabin differential pressure to exceed the maximum allowable for the

aircraft.

Descent:

Set the cabin altitude knob to the desire cabin altitude.

Set the rate knob to the desire rate.

Before landing:

Check the cabin differential pressure before landing.

If more than 1.5 inches of mercury indicated, the cabin altitude selector and the rate

knob should be adjusted to the higher setting to increase the rate of depressurization.

Cabin differential pressure will be zero for landing.

If less than 0.5 inches of mercury indicated, no discomfort will be experienced. If the air

conditioning master switch is turned to a non-pressure position.


P a g e | 20

II. The emergency operation of cabin pressurization system on ground is explained

below:

An emergency depressurization door, located in the center escape hatch, is released by pulling

the emergency depressurization handle on the overhead control panel directly above the pilot.

The handle is connected by a cable to the release mechanism of the door which is restrained

from consequential loss by two shock cords. After depressurization is accomplished, the door

can be replaced and the release mechanism reset manually.

Figure: Emergency depressurization handle


P a g e | 21

References:-

Unit – 82, Airframe systems

C-130 Maintenance manual (Section 4 - Auxiliary equipments)

Class note

Class lecture

Aviation maintenance technician handbook (Airframe, Volume-2)

Aviation maintenance technician handbook (Power-plant, Volume-2)

http://uk.answers.yahoo.com/question/index?qid=20120425100301AA3b98p

Aircraft engineering principle by Mike Tooley

http://en.wikipedia.org/wiki/Environmental_control_system_%28aircraft%29

http://www.google.com.bd/url?

sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0CEEQFjAG&url=http

%3A%2F%2Fwww.aero.polimi.it%2F~l050263%2Fbacheca%2FDispense_EN%2F05w-

PneuSyst.pdf&ei=cRQrU7G-OqSL0AX-_YHAAQ&usg=AFQjCNFenXJCdevbdGWEzx-

Okibgkah8vQ&bvm=bv.62922401,d.d2k

http://www.google.com.bd/url?

sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCgQFjAA&url=http

%3A%2F%2Fwww.instruction.greenriver.edu%2Faviation%2Fdownloads

%2Favia112_files%2Fpneumatics.pdf&ei=6horU-

fZM4ua0QXY14GgCw&usg=AFQjCNFVyw1euNiqZr7sVbtnu6IdqnoEPA&bvm=bv.62922

401,d.d2k


http://www.google.com.bd/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCgQFjAA&url=http%3A%2F%2Fwww.instruction.greenriver.edu%2Faviation%2Fdownloads%2Favia112_files%2Fpneumatics.pdf&ei=6horU-fZM4ua0QXY14GgCw&usg=AFQjCNFVyw1euNiqZr7sVbtnu6IdqnoEPA&bvm=bv.62922401,d.d2k



http://www.google.com.bd/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0CEEQFjAG&url=http%3A%2F%2Fwww.aero.polimi.it%2F~l050263%2Fbacheca%2FDispense_EN%2F05w-PneuSyst.pdf&ei=cRQrU7G-OqSL0AX-_YHAAQ&usg=AFQjCNFenXJCdevbdGWEzx-Okibgkah8vQ&bvm=bv.62922401,d.d2k



http://en.wikipedia.org/wiki/Environmental_control_system_(aircraft)

http://uk.answers.yahoo.com/question/index?qid=20120425100301AA3b98p

Airframe 1 (done)

Education