Aerospace Engineering

BIRD STRIKE EVENTS ON AIRCRAFT

noreply@blogger.com (Anonymous) — Thu, 07 Feb 2013 17:34:00 +0000

Bird-strike events are relatively common, occur most often on the ground or at low altitude, and are usually benign. However, bird strikes can have significant economic and occasional safety consequences for flight operations. Pilots and operators should be knowledgeable about the hazard, and flight crews should use facts, data, and standard operating procedures to reduce the potential for and consequences of a bird strike.

Flight crews can reduce the possibility and effects of a bird strike by increased awareness and by following recommended procedures.

Bird strikes are a lesser hazard to aviation than other well-known hazards such as loss of control in flight, controlled flight into terrain, and runway excursions, but they can and do present risk that needs to be addressed. The first bird strike was recorded by the Wright brothers in 1905, and the aviation wildlife hazard has been a risk to aviation ever since. The January 15, 2009, ditching of US Airways flight 1549 on the Hudson River in Weehawken, New Jersey, was the dramatic result of dual engine thrust loss arising from an airborne encounter with a flock of Canada geese. Although Boeing airplanes meet and exceed the government regulations for bird strikes, accidents and serious incidents can occur. Aviation wildlife hazards encompass birds on the ground and in flight, terrestrial animals (e.g., deer, coyotes, cattle, camels), and even airborne animals such as fruit bats; however, this article focuses on bird strikes in particular. Operators and flight crews should be aware of the risk of bird strikes, prevention strategies, and actions to take following a bird strike.

This article discusses the characteristics of bird strikes, presents practical information for flight crews, highlights the importance of reporting bird strikes, and provides resources for additional bird-strike information.

Characteristics of bird strikes

According to Bird Strike Committee USA, an organization that was formed in 1991 to facilitate the exchange of information and promote the collection and analysis of accurate wildlife strike data, bird and other wildlife strikes cause more than $650 million in damage to U.S. civil and military aviation annually. In addition, bird strikes put the lives of crew members and passengers at risk — more than 200 people have been killed worldwide as a result of wildlife strikes since 1988. The Bird Strike Committee takes a similar data-driven approach to the bird strike issue that organizations such as the Commercial Aviation Safety Team (CAST) takes to reduce commercial aviation fatality risk. (See www.cast-safety.org.)

Experts within the U.S. Federal Aviation Administration (FAA), the U.S. Department of Agriculture, and the U.S. Navy and U.S. Air Force expect the risk, frequency, and potential severity of wildlife-aircraft collisions to grow over the next decade, based on increasing air traffic, bird populations, and the trend to twin-engine aircraft. (Download PDF.)

While bird strikes usually inflict most damage on the engines, all areas of an airplane can be damaged (see figs. 1 and 2). Airplane damage and effect on flight from bird strikes are closely correlated to kinetic energy, derived from the mass (determined by bird species) and the square of the speed of the collision. (A 20 percent increase in speed raises the kinetic energy by 44 percent.)

Figure 1: Example of bird-strike damage

Bird-strike damage can be quite severe and can shut down jet engines.

Figure 2: Locations of bird-strike damage

Three-quarters of bird strikes involve the wing or engines, but they can damage almost any part of an airplane.

Single or multiple large birds, relatively small numbers of medium-size birds, and large flocks of relatively small birds are all problematic and have resulted in accidents. In the United States, a list of birds most hazardous to flight has been identified: large flocking waterfowl (Canada goose); gulls; pigeons and doves; blackbirds, starlings, and sparrows; and raptors (hawks and kestrels). Most bird strikes occur on or near the ground, highlighting the need for wildlife management on airport grounds and in the vicinity. (Download PDF.)

The aviation bird-strike hazard is a global and industrywide issue affecting all aviation stakeholders, including pilots, mechanics, airlines, airport operators, air traffic controllers, wildlife personnel, aviation safety analysts, airplane and engine manufacturers, flight training organizations, and the traveling public. Boeing participates in national and international groups dedicated to exploring and addressing the problem of bird strikes, and Boeing airplanes meet and exceed regulatory bird-strike requirements. Boeing has many design features, including system separation, system redundancy, and structural attributes, to protect against bird strikes beyond the four-pound regulatory general bird-strike FAA requirement (eight pounds for empennage).

Common misconceptions about bird strikes

A number of widespread misconceptions about bird strikes may give pilots a false sense of security and prevent them from reacting appropriately to the threat of a bird strike or an actual event. These misconceptions include:

Birds don’t fly at night.
Birds don’t fly in poor visibility, such as in clouds, fog, rain, or snow.
Birds can detect airplane landing lights and weather radar and avoid the airplane.
Airplane colors and jet engine spinner markings help to repel birds.
Birds seek to avoid airplanes because of aerodynamic and engine noise.
Birds dive to avoid an approaching airplane.

In fact, none of these statements is scientifically proven.

More than 219 people traveling by airplane have been killed worldwide as a result of bird strikes since 1988.
Between 1990 and 2009, bird and other wildlife strikes cost U.S. civil aviation more than $650 million per year.
About 5,000 bird strikes were reported by the U.S. Air Force in 2010.
More than 9,000 bird and other wildlife strikes were reported for U.S. civil aircraft in 2010.
Between 1990 and 2004, U.S. airlines reported 31 incidents in which pilots had to dump fuel to lighten load during a precautionary or emergency landing after striking birds on takeoff or climb. An average of 11,600 gallons of jet fuel was released in each of these dumps.
Waterfowl (31 percent), gulls (25 percent), raptors (18 percent), and pigeons/doves (7 percent) represented 81 percent of the reported bird strikes causing damage to U.S. civil aircraft between 1990 and 2009.
More than 950 civil aircraft collisions with deer and 320 collisions with coyotes were reported in the United States between 1990 and 2009.
About 90 percent of all bird strikes in the United States are by species federally protected under the Migratory Bird Treaty Act.
Between 1990 and 2009, 415 different species of birds and 35 species of terrestrial mammals were involved in strikes with civil aircraft in the United States that were reported to the Federal Aviation Administration.

Source: Bird Strike Committee USA

Preventive Strategies

Airports are responsible for bird control and should provide adequate wildlife control measures. If large birds or flocks of birds are reported or observed near the runway, the flight crew should consider:

Delaying the takeoff or landing when fuel permits. Advise the tower and wait for airport action before continuing.
Take off or land on another runway that is free of bird activity, if available.

To prevent or reduce the consequences of a bird strike, the flight crew should:

Discuss bird strikes during takeoff and approach briefings when operating at airports with known or suspected bird activity.
Be extremely vigilant if birds are reported on final approach. If birds are expected on final approach, plan additional landing distance to account for the possibility of no thrust reverser use if a bird strike occurs.

The Great Lakes cormorant population increased from only about 200 nesting adults in 1970 to more than 260,000 nesting adults in 2006.
In 1890, about 60 European starlings were released in New York City’s Central Park. Starlings are now the second-most abundant bird in North America with a late-summer population of more than 150 million birds. Starlings are considered “feathered bullets,” having a body density 27 percent higher than herring gulls.
The North American nonmigratory Canada goose population increased about fourfold from 1 million birds in 1990 to more than 3.9 million in 2009. About 1,500 Canada geese strikes with civil aircraft were reported in the United States between 1990 and 2009. About 42 percent of these strike events involved multiple birds.
A 12-pound Canada goose struck by a 150-mph airplane at liftoff generates the kinetic energy of a 1,000-pound weight dropped from a height of 10 feet.
The North American population of greater snow geese increased from about 50,000 birds in 1966 to more than 1 million birds in 2009.
The nesting population of bald eagles in the contiguous United States increased from fewer than 400 pairs in 1970 (two years before DDT and similar chlorinated-hydrocarbon insecticides were banned) to more than 13,000 pairs in 2010. Between 1990 and 2009, 125 bald eagle strikes with civil aircraft were reported in the United States. The mean body mass of bald eagles is 9.1 pounds for males and 11.8 pounds for females.

Source: Bird Strike Committee USA

Additional Resources

Additional information is available online through a number of industry groups. Information includes significant strike events, key issues to reduce strikes, risk assessment, system information, papers and newsletters, and discussion forums.

Bird Strike Committee USA.
International Bird Strike Committee.
International Civil Aviation Organization (ICAO).
Embry-Riddle Aeronautical University.
National Bird Strike Committees or Aviation Wildlife Hazard Groups.

The importance of reporting bird strikes

Flight crews and maintenance and line personnel are encouraged to report all bird strikes because data are essential to quantify and manage the hazard. Reporting bird strikes enables aviation authorities to monitor the risk to aviation and the effectiveness of wildlife hazard mitigation measures. Bird-strike data, together with knowledge of the operational environment, are utilized by Boeing as a basis of many airplane design features beyond regulatory requirements. Bird-strike data also help researchers understand the nature of strikes and develop a scientific approach to reduce the cost and safety consequences of bird strikes.

Aviation stakeholders should report all known or suspected bird strikes to their national or recognized wildlife strike data repository (e.g., the FAA National Wildlife Strike Database in the United States) and share the strike information with the airport operator, the airline safety department, and the aircraft and engine manufacturers. Each of these individual reports will be combined into a single composite data record. Reporters should provide as much information as possible, including:

Airplane model and series designation (e.g., 777-300).
Airplane serial number or registration.
Phase of flight.
Speed and altitude of the airplane.
Geographical location of the airplane.
Date and time of day.
Origin and destination airport.
Number and species of bird observed and struck.
Impact locations of strikes and damage on airplane.
Effect on flight (e.g., rejected takeoff, air turnback, diversion).

If bird remains are available, trained personnel should identify the species involved, or the bird remains should be collected using the correct procedure (as outlined here) and bird-strike collection kit and shipped to a qualified laboratory. It is crucial to determine the species of the bird or birds involved in a bird strike and the location of the strike, so that wildlife management can take appropriate actions. Effective wildlife management involves controlling attractants, often species-specific, including food, foraging, roosting, and nesting opportunities. Managing the environment may be necessary, even to the extent of grass type and height, insects, rodents, and invertebrates, along with water sources and land use, such as agriculture.

In the event of a bird strike, maintenance personnel should follow the appropriate maintenance procedures for bird strike inspection in the Airplane Maintenance Manual. Maintenance personnel must be cognizant of the possibility that the bird remains can contain infectious material. The bird strike should be reported by the flight crew in the pilot’s log or by the maintenance crew in the maintenance log. After a bird strike, the airplane should be inspected for possible damage to airplane structure and airplane systems.

In the United States and Canada, bird-strike information can be reported online or via FAA form 5200-7 Bird/Other Wildlife Strike Report.

How airlines can get involved

Airlines and other stakeholders can help address the ongoing problem of bird strikes by participating in local, regional, national, or international aviation wildlife hazard activities, such as bird-strike committees or equivalent groups.

Airlines can also form their own internal aviation wildlife hazard group and designate a single point of contact for coordinating all aviation wildlife hazard activity, both internally and externally.

Although it is not possible to avoid all bird strikes, flight crews can take steps to reduce the chance of a bird-strike event. If a bird strike does occur, the appropriate action can improve the flight crew’s ability to maintain control of the airplane and land safely.

This information from the Boeing Flight Crew Training Manual provides flight crews and flight operations personnel with practical information about preventing and managing bird-strike events.

Prevention strategies

Pilots should not rely on onboard weather radar, landing lights, airplane markings, time of day, or visibility to prevent bird strikes.
Flight operations may need to be modified in the presence of known or anticipated bird activity.
Delay takeoff or landing in the presence of bird activity.
Below 10,000 feet, keep speed below 250 knots if operationally possible.
Below 2,000 feet, climb at the maximum rate to reduce the flight time exposure to a strike hazard.
Descend with idle power and avoid extended low-altitude level flight, particularly over water courses, nature reserves, or other areas of known or expected bird activity.
When landing is assured, consider landing through birds versus a missed approach to avoid birds. This reduces the energy of the collision, the potential for increased damage associated with engines at a high power level, and the potential for multiple engine ingestions at low airplane energy states and low altitude.
Avoid or minimize maneuvering at low altitude to avoid birds.

Bird strikes during takeoff roll

If a bird strike occurs during takeoff, the decision to continue or reject the takeoff is made using the criteria found in the Rejected Takeoff maneuver of the QRH. If a bird strike occurs above 80 knots and prior to V1, and there is no immediate evidence of engine failure (e.g., failure, fire, power loss, or surge/stall), the preferred option is to continue with the takeoff followed by an immediate return, if required.

Detecting a bird strike while in flight

Visual: Birds seen in close proximity to the airplane or colliding with the airplane, bird remains on windshield, cracked windshield.
Tactile: Vibration of airframe or engine, thrust loss, asymmetric thrust, increased drag, abnormal airplane handling characteristics.
Auditory: Noise of strike or noise attributed to resulting damage: engine surging, compressor stalls, aerodynamic noise from damaged radome, loss of pressurization from pressure vessel penetration.
Olfactory: Smoke, odor, or cooked bird smell.
Engine indications: Reduction or fluctuation in primary power parameter (e.g., engine pressure ratio, fan speed, or equivalent), abnormal fuel flow, abnormal engine vibration monitoring (e.g., error vector magnitude or equivalent), engine failure, engine exceedances.
Flight instruments: Loss of data or erroneous indications arising from damage to air data sensors or angle-of-attack sensors.
Other airplane systems or structure affected directly by a strike: Damaged communications or navigation antennas, damage to exposed electrical wiring or hydraulic lines, damaged radome or weather radar, broken landing lights, or cascading and multiple effects from sensor damage or engine damage.

Responses to a known or suspected bird strike

Immediate action

Fly the airplane and maintain flight path control.
Monitor flight and engine instruments.

Multiple engine failure or thrust loss

Attempt to restart engine(s).

Severe engine damage

Shut down engine according to procedure.

Strong engine vibration

Reduce thrust, which will often reduce vibration.
Shut down engine per flight crew operations manuals guidance.

Multiple engine ingestion and abnormal engine indications

Air turnback or diversion to nearest suitable airport.

Known or suspected multiple engine ingestion, with normal engine indications

Consider air turnback or diversion to nearest suitable airport.
Reevaluate decision to continue with extended-range twin-engine operational performance standards, extended range operations, or overwater flight because engine damage or performance degradation may manifest later in the flight.

Known or suspected strikes with large flocking birds, such as Canada geese

Consider air turnback or diversion to nearest suitable airport, because damage may affect aerodynamic lift and drag, subsequent fuel burn, and ability to complete the flight safely.

Known or suspected airframe damage or engine damage

Maintain or reduce speed — do not accelerate unless necessary for safety of flight or to maintain flight path control.

Damaged windshield or depressurization

Below 10,000 feet, discontinue climb and level off.
Above 10,000 feet, descend to 10,000 feet or the minimum safe altitude.

Known or suspected strike with landing gear extended or in takeoff or landing configuration with high lift deployed

Use available system information to assess possible damage to flight controls and high lift devices, and make minimal and prudent changes in airplane configuration in accordance with the flight phase.
Use available system information to assess possible damage to landing gear and associated systems, including exposed electrical, pneumatic, and hydraulic systems, and potential effects on the ability to steer and stop on the runway.

Known or suspected strikes to air data and angle-of-attack sensors

Be aware that this may affect other airplane systems and have cascading effects.
Be aware of the potential for loss or erroneous air data and degraded flight control modes, including loss of envelope protection or limiting, unreliable airspeed, propulsion systems in alternate mode.

Bird strikes during approach or landing

If the landing is assured, continuing the approach to landing is the preferred option. If more birds are encountered, fly through the bird flock and land.
Maintain as low a thrust setting as possible.
If engine ingestion is suspected, limit reverse thrust on landing to the amount needed to stop on the runway. Reverse thrust may increase engine damage, especially when engine vibration or high exhaust gas temperature is indicated.

Postflight actions following a known or suspected bird strike

Report all known or suspected bird strikes or bird activity on or in the vicinity of the airport via established procedures. Ideally this information reaches all stakeholders, including air traffic control, the airport operator, the airline, airplane and engine manufacturers (particularly the local representative), the national regulatory authority, and the appropriate national bird-strike committee or aviation wildlife hazard group.

Summary

Bird strikes have always been a part of aviation. While they usually cause no more than minor damage, they can pose a threat to air safety. By being aware of the ongoing possibility of bird strikes and by following recommended procedures, flight crews can reduce the possibility and effects of a bird strike.

Aircraft Brakes

noreply@blogger.com (Anonymous) — Fri, 01 Feb 2013 05:32:00 +0000

Wheel brakes are normally used to slow the aircraft down during landing roll on the runway and to aid in directional control during ground handling operations as taxi and parking.In small GA aircraft the brakes are connected to the main landing gear only and are operated independently from each other.The brake systems are operated by hydraulic pressure and the rudder pedals have the brakes installed on top and are toe operated. Some aircraft use heel brakes or even with separate levers in the cockpit operated by hand (e.g. DynAero MCR and Tecnam).

With larger aircraft the weight increases but the force pilots can apply will usually about the same for every human being.It is therefore important that the pilot gets help in the form of brake boosters or power assisted brakes.

The wheel brakes are usually made of the disc type, but on some exotic aircraft the drum type with two brake shoes inside is still being used.

Drum type

With this model the two brake shoes are operated by either pneumatic (air) or hydraulic (oil) pressure or maybe even manually with a cable (very rare). You won't see these on modern aircraft anymore. Inside there are a couple of springs attached to the shoes to make sure that the brake contacts the drum evenly as friction will try to move them slightly. The springs also make sure that the shoes retracts when brake pressure is released.

Disc brakes

Very popular as they are lightweight and the disc sits between the braking pads clamping them when brake pressure is applied. For heavier aircraft multiple brake calipers and or multiple discs can be used.The brake disc is made from steel and bolted onto the wheel and rotates. The clamping part, caliper, contains two brake pads and is self centering. When brakes are applied the pressure moves a piston cylinder arrangement inside the caliper and the pads will clamp the disc. With even pressure on both sides.

Brake system

Most light aircraft have two independent brake systems on the upper part of the rudder pedal. This part is hinged and connected to a master cylinder. High pressure tubing is used to connect the master cylinder to the brake cylinder in the caliper. Special hydraulic fluid (DOT4, AeroShell Fluid 41) is used to transmit the brake pressure. Careful: this fluid will eat away paint.Make sure that at the start of the take-off run you place your feet low enough as not to ride the brakes as this would result in a sluggish take-off roll.As the aircraft has two separate brake systems the pilot can use differential braking to help steer the aircraft, some aircraft (Pelican PL, Cessna) have their nose wheel steering connected to the brake system where the first 10° left or right the nose wheel moves and with further rudder movement the main gear will help steer the aircraft, helpful during taxi and parking.

Parking brake

Some aircraft have a sort of ratchet type system where they keep the brake pressure in the system, holding the aircraft in its place. Others use a hydraulic valve and after pressing the toe brakes they close the parking valve, thereby locking the hydraulic pressure. Check the POH to see which type of system is installed.

Power Assist

The simplest system is the boosted brake. In this systems main hydraulic pressure is used progressively through a valve to help the pilot applying the brakes.With power assisted brakes the brake system is fed by the main hydraulic system with a much higher pressure than the pilot can apply. Brake pressure regulates main hydraulic pressure to the wheel and caliper.These power assisted brake systems usually have a backup in case the main hydraulic pressure fails so the aircraft can still be stopped by using the brakes.

AIRCRAFT HYDRAULIC SYSTEM

noreply@blogger.com (Anonymous) — Fri, 25 Jan 2013 07:49:00 +0000

ABSTRACT :

Hydraulic systems provide a means of remotely controlling a wide range of components by transmitting a force through a confined fluid.Because hydraulics can transmit high forces rapidly and accurately along lightweight pipes of any size, shape and length, they are the prime source of power in aircraft systems such as flying controls, flaps, retractable undercarriages and wheel brakes.
Modern aircrafts include many different types of subsystems. These subsystems are very closely interlinked to each other. One of these subsystems is hydraulic subsystem, which is usually used for actuating most of the mechanical subsystems, such as landing gear, flight control surfaces, weapons system etc. Thus the hydraulic system is a very essential part of the aircraft and its reliability and functionality are very essential to the flight worthiness of the whole aircraft.

INTRODUCTION

Hydraulics is based on a very simple fact of nature - you cannot compress a liquid. You can compress a gas (think about putting more and more air into a tire, the more you put in, the higher the pressure). If you're really strong you can compress a solid mass as well. But no matter how much pressure you apply onto a liquid, it isn't possible to compress it. Now if you put that liquid into a sealed system and push on it at one end, that pressure is transmitted through the liquid to the other end of the system. The pressure is not diminished.

Aircraft Hydraulics Definition

It is a system where liquid under pressure is used to transmit this energy. Hydraulic systems take engine power and convert it to hydraulic power by means of a hydraulic pump. This power can be distributed throughout the airplane by means of tubing that runs through the aircraft. Hydraulic power may be reconverted to mechanical power by means of an actuating cylinder, or turbine.
(1) - A hydraulic pump converts mechanical power to hydraulic power
(2) - An actuating cylinder converts hydraulic power to mechanical power
(3) - Landing Gear
(4) - Engine power (mechanical HP)
If an electrical system were used instead of a hydraulic system, a generator would take the place of the pump and a motor would take the place of the actuating cylinder

Some Hydraulic Systems in Aircrafts

1. Primary control boosters
2. Retraction and extension of landing gear
3. Sweep back and forth of wings
4. Opening and closing doors and hatchways
5. Automatic pilot and gun turrets
6. Shock absorption systems and valve lifter systems
7. Dive, landing, speed and flap brakes
8. Pitch changing mechanism, spoilers on flaps
9. Bomb bay doors and bomb displacement gears

Principles of Operation

Part of the hydraulic system is the actuating cylinder whose main function is to change hydraulic (fluid) power to mechanical (shaft) power. Inside the actuating cylinder is a piston whose motion is regulated by oil under pressure. The oil is in contact with both sides of the piston head but at different pressures. High pressure oil may be pumped into either side of the piston head.
The selector valve determines to which side of the actuating cylinder the high pressure oil is sent. The piston rod of the actuating cylinder is connected to the control surface.
As the piston moves out, the elevator moves down. As the piston moves in, the elevator moves up. The selector valve directs the high pressure oil to the appropriate side of the piston head causing movement of the piston in the actuating cylinder. As the piston moves, the oil on the low pressure side returns to the reservoir since return lines have no pressure!
The differential in oil pressure causes movement of the piston. The force generated by this pressure difference can be sufficient to move the necessary loads. Each cylinder in
the plane, boat, etc., is designed for what it must do. It can deliver the potential it was made for; no more, no less. Air loads generally determine the force needed in aircraft applications.

Hydraulic System

A hydraulic system transmits power by means of fluid flow under pressure. The rate of flow of the oil through the system into the actuating cylinder will determine the speed with which the piston rod in the actuating cylinder extends or retracts. When the cylinder is installed on the aircraft, it is already filled with oil. This insures that no air bubbles are introduced into the hydraulic system, which can adversely affect the operation of the system.
Pascalâ„¢s Theory
In a confined stationary liquid, neglecting the effect of gravity, pressure is distributed equally and undiminished in all directions; it acts perpendicular to the surface it touches. Because the actuating cylinder is not vented, the force delivered through the piston to the surface of the fluid is translated into a pressure on the surface of the fluid.
The pressure (p) acting on the incompressible oil does work [(pressure) x (Area of piston) x (piston's stroke) = Work].

Hydraulic Pressure Regulated Power System

The system in drawing below represents a pressure regulated power system comprised of two parts:
1) the power system, and
2) the actuating system part of the overall hydraulic system.
Parts of the Power System
1. Reservoir -- holds an extra supply of fluid for system from which oil was drawn when needed, or oil was returned to it when not needed.
2. Accumulator -- absorbs pulsation within the hydraulic system and helps reduce "linehammer effects" (pulses that feel and sound like a hammer has hit the hydraulic tubes). It is an emergency source of power and it acts as another reservoir.
3. Filter -- removes impurities in the hydraulic system and in the reservoir. The reservoir has one big filter inside the tank.
4. Power Pump -- it changes mechanical horsepower (HP) to hydraulic HP.
5. System Relief Valve -- relieves pressure on system as a safety.measure and takes over as a pressure regulator when pressure regulator fails.
6. Pressure Regulator -- as the name implies, regulates the pressure in the hydraulic system. When it senses a built-up in pressure in the lines to the selector valves, it acts so that the system automatically goes to bypass.

Aircraft Hydraulic System Reservoir

Functions of the Reservoir
1. Provides air space for expansion of the oil due to temperature changes
2. Holds a reserve supply of oil to account for
a. thermal contraction of oil.
b. normal leakage - oil is used to lubricate piston rods and cylinder seals. When the piston rod moves, it is scraped to remove impurities that might collect on the rod when returning into actuating cylinders. If many actuating cylinders are operating at the same time, then the amount of oil lost is greater.
c. emergency supply of oil - this case occurs only when the hand pump is used.
d. volume changes due to operational requirements - oil needed on side 2 of piston head is less than that needed on side 1 of cylinder piston (which occurs during actuation).

3. Provides a place to remove air or foam from liquid.
4. Provide a pressure head on the pump, that is, a pressure head due to gravity and depends upon the distance of the reservoir above the power pump.
The best shape is a domed cylindrical shape. Not only can it be mounted easily, but it can be made to order.

5.Aircraft Hydraulic System Power Pumps

Function:
1. The function of the hydraulic system power pump is to change mechanical horsepower to hydraulic horsepower.
Types of Power Pumps
There are two types of power pumps, a gear pump and a piston pump.
1. Gear pumps have efficiencies that average about 70-80% overall efficiency, where overall efficiency is defined as:
overall efficiency = (mechanical efficiency)*(volumetric efficiency)
Gear pumps move fluid based upon the number of gear teeth and the volume spacing between gear teeth.
2. Piston pumps move fluid by pushing it through the motion of the pistons within the pump. They can generate overall efficiencies in the 90-95% range.

Principles of Operation:

Gear type pumps are ideal when working with pressures up to 1500 lb./sq.in. As mentioned previously, the volumetric efficiency of gear pumps depends upon the number of teeth, the engine speed and the tooth area.
As the liquid comes from the reservoir, it is pushed between the gear teeth. The oil is moved around to the other side by the action of the drive gear itself and sent through the pressure line. What makes the oil squeeze in between the gear teeth? gravity and the pressure head. To prevent leakage of oil from the high to the low pressure side from occurring, you can make the gears fit better.
You might want to increase the pressure used to move the fluid along. However, the higher the pressure, the higher the friction loading on the teeth. Friction will develop heat which will expand the gears and cause the pump to seize (parts will weld together and gears will stop rotating). In order to stop this, you can have the pump case, the gears, and the bearings made out of different materials, (e.g., steel gears [1-1/2 inch thick], bronze bearings, aluminum casing). Normally, the gear speed is higher than the engine speed (normally 1.4 times the engine speed).
Oil can leak over and under the gears. To prevent leakage, you can press the bearings up against the gears. This decreases seepage but this decreases the mechanical efficiency when friction increases. Even though oil acts as lubricant, seizing can occur when oil is drained from the hydraulic system.
As mentioned previously, we can push the bearings up against the gears to decrease leakage. As F increases, M decreases, thus, the gears and bushing increase in friction and mechanical efficiency decreases. When you increase the pressure on the inlet side of the pump, leakage will increase around the gears. To reduce the leakage, you must push the bearings and gears closer, causing an increase in friction. That is why inlet pressures over 1500 lb/sq in, are not used.

Principle of the Shear Shaft

Gear pumps are built using a shear shaft principle. That is, if the pump fails, the shear shaft breaks and this allows each of the gears to rotate in its own part of the system
(pump side or engine side) and nothing else will happen to the system. This phenomenon is similar to a fuse in an electrical system. When the electrical system overloads, the fuse breaks, causing the circuit to break without damaging the rest of the electrical circuit.
Principle of the Reciprocating Piston Pump
These kind of pumps attain volumetric efficiencies of up to 98% and they can maintain pressures from 1500 to 6000 psi. They can achieve overall efficiencies of up to 92% and can move fluid volumes up to 35 gallons per minute.
As the cylinder block rotates, space between the block and the pistons increase, letting in more oil. As the block rotates from bottom dead center, the reverse occurs and the pistons push oil out through the outlet. When the pistons move down, the suction caused by the vacuum from the space, created by the movement of the piston, pulls in oil. Changing the angle between the swash plate and the cylinder block gives a longer pumping action and causes more fluid to be pulled in. As the cylinder block rotates, the piston cylinder openings over the inlet and the outlet vary. When cylinders 4-6 take in hydraulic fluid and act as the inlet to the pump, then cylinders 1-3 push the hydraulic fluid out and act as outlet to the pump.

As the shaft and swash plate rotate, the piston will suck oil into the cylinder block and as the shaft and swash plate keep on rotating, the piston pushes oil out through the outlet. Pumps can be made to move more or less oil volume.
6.Hydraulic System Check Valves
Function of Check Valves
Check Valves are hydraulic devices which permit flow of fluid in one direction only.

Check Valve Used In Aircrafts

Poppet type valve is the preferred type that is used in hydraulics now. The front of the poppet (left side of the picture above) sits snugly on the hard seat (darker shaded areas on the left side). The poppet works on the following principle. When high pressure fluid (with pressure P1 ) comes in on the left, it forces the poppet open. Since P1>P2 , the force on the left side of the poppet (F1) is greater than the force due to the spring (F2 ) and is just enough to open the poppet. But, when flow stops, or there is a high pressure flow from the right side of the poppet, then P2>P1 and the pressure forces the poppet against the valve seat, closing off the opening. Thus the fluid is allowed to flow through in one direction only.
Check valves are designed so as not to tolerate leakage. The purpose of the light spring is only to keep the poppet on the seat.
Most manufacturers use sharp-edged, very hard seats and soft, maybe plastic, poppets. Parallel seats are very good except that they are too prone to trapping contaminants between the seat and the poppet.

Pressure Control

(Pressure limiting device-relief valves)
Function
To limit the pressure of some section of the hydraulic system when the pressure has reached a predetermined level. That pressure level may be considered dangerous and, therefore, must be limited.
Principle of Operation
The adjustment screw at the top of the pressure relief valve is set for a certain pressure value, let us call it P2. In general, even with a pressure of P1, the poppet would lift up, except that the spring is strong and has downward force forcing the poppet closed. Poppet will not move until a pressure greater than that required is felt by the system (i.e., P1>P2). When the pressure increases, the poppet will move up, forcing the excess
liquid to move through opening at high velocity. On other side of seat, pressure is zero because the back side of the relief valve is connected to the return line. When the
pressure in the system decreases below maximum, poppet will return to its seated position, sealing the orifice and allowing the fluid to follow its normal path. These type of pressure relief valves are only made to be used intermittently.
Circuits Using Pressuring Limiting Devices (PLDs)
1. The power system where the system relief valve is used to back up the regulator is an example of a use of the PLD. In such a system, the pressure setting, P2, is set 125% above the system pressure. Rate of flow is dependent upon engine speed.
2. Thermal relief valves are set at 150% of system pressure. When the temperature (T) changes, the liquid expands more than the expansion of the hydraulic tubing. Since T increases, the pressure (P) increases. Thus, the tubing will burst unless there are thermal relief valves in the system. Set at one pressure, the thermal relief valves are connected to the return lines because the pressure there is close to nil. This only works when the selector valve is set in the neutral position.
3. Force Limiting Device (FLD). Suppose that we want 1000 pounds of force to move a certain control surface. But our system can deliver 3000 pounds per square inch. If that pressure can be delivered on a 2 square inch piston head that moves the control surface, we would be= 6000 lb, a much higher force than is needed. We can put a force limiting relief valve (FLD) which would limit the force to 1000 lb by adjusting the FLD to act when the pressure reaches 500 psi (1000 lb/ 2 square inches).
5. Blow up devices. When a plane is coming in for landing on a carrier deck, the brakes are set and the selector valve is put at neutral. If the plane is waved off on its landing attempt, the brakes must retract quickly so that the plane does not stall. Therefore, when the pilot is waved off, he will push the throttle to get more speed to get away from carrier. In doing so, the air pressure force acting on the brakes, F, is so great that it moves the brake. In doing so, the piston moves to right, causing fluid to flow and to push on the relief valve. This action allows more oil into the other line which in turn pushes on the piston and repeats the process. After the pilot reacts to this situation, he will change the selector valve position (if he has to change it), to move the b

Hydraulic System Accumulator

Principle of Operation

At the bottom of the accumulator is a gas valve. Compressed gas at about one half the system pressure is let into the accumulator through the gas valve. This forces the diaphragm that separates the oil side from the gas side to "pop" up towards the oil side. Then oil is sent through the system. When the system pressure reaches a point when it
is greater than the pressure of the accumulator, the diaphragm will deploy (inflate). Using Boyleâ„¢s Law, the compressed gas will increase in pressure as its volume decreases. The diaphragm will move up or down, depending on system pressure.
When the diaphragm is at half way, the gas volume will be Ã‚Â½ as much as it was initially, while the accumulator pressure will be twice as much as its pre-load pressure (i.e., 1/2 system pressure). Therefore when the accumulator is at half volume of gas, it will be charged at full system pressure.
Uses of an Accumulator
1. Absorbs the shocks due to rapid pressure variations in a hydraulic system
2. Helps maintain a constant pressure within the hydraulic system
3. Helps the hydraulic pump under peak pressure loads
4. It is an emergency source of power (the braking system has its own accumulator)
The preload is checked every day. Nitrogen and helium are preferred to compressed air. Oxygen leaks into the oil will cause spontaneous combustion and that is why it is not used in the accumulator. Carbon dioxide (CO2 ) is not used because it
liquefies at 800 or 900 psi (which is considered low pressure compared to the pressure requirements of the system).
The accumulator has to withstand about 450,000 lb of force. The spherical shape is used because a monocoque (single shell) body is the strongest and can withstand high pressures before failing.

Pressure Regulation in

Hydraulic Systems

If a system relief valve (SRV) were used to regulate pressure, it would have to be replaced in a very short time. This would be due to the overuse of the SRV and the failure of the spring's elasticity. If the SRV were used, the oil pushing on the spring-ball combination would cause tremendous vibrations and heat would be dissipated by the oil under high pressure attempting to push the ball away from the seat to get to the low pressure side.
Douglass Pressure Regulator
When an actuating cylinder finishes its motion and stops, a high pressure will be felt through the system. If so, this high pressure oil coming from the power pump (right side of diagram) will keep check valve C open and also act on piston A. In its
movement, piston A pushes Ball B off seat D. The oil, taking the passage of least resistance, goes through passage D into the center chamber back to the reservoir. The pressure on the right side of check valve C will drop and will be less than the pressure on the left side of C, therefore, causing the ball to seat itself in check valve C. When the
hydraulic system pressure drops, the pressure on piston A decreases, causing a decrease in pressure on B as well. The path of least resistance through D will close and the oil will move in the direction towards check valve C. Now, because the pressure on the right side of C is greater than on the left of C, the check valve will be forced open and the oil will move toward the selector valve side of the system (left side of diagram).
The range of operation of the pressure regulator is defined by the difference in force required for bypass and the force required at actuation.

Electrol Pressure Regulator

The dual purpose of a pressure regulator is to reduce the load on the hydraulic pump when not needed and to keep the hydraulic pressure within the operating range of the hydraulic system.
When the hydraulic pump is charging the system, balls 1 and 2 are seated on their seats but ball 3 is letting oil pass through to the actuating cylinders. When actuation stops, the pressure in the system builds to maximum. The spring holding ball 1 onto the lower seat is designed to withstand the force produced by the maximum pressure of the hydraulic system. As maximum pressure is reached, ball 1 is made to move to the upper seat, thereby letting high pressure oil reach the A side of piston. But, ball 3 has already moved to its seat due to the higher pressure felt on side C than on side D. Therefore, oil coming from the hydraulic pump is at a charging pressure less than the maximum pressure of side A of the piston, causing the piston to move down, in turn pushing ball 2 down. Oil, wanting to take the path of least resistance, goes by ball 2 to the return line.
If actuation restarts, then pressures at C side of ball 3, at A side of piston and at F side of ball 1 decreases. Ball 1 falls onto the lower seat, since the spring force is greater than
the force generated by the hydraulic system's oil pressure. Piston A will then move up due to the pressure drop on side A, causing ball 2 to close the orifice to the return line. The oil being pumped from the hydraulic pump now has greater pressure on side D of ball 3, causing the ball to move to the left and the hydraulic system oil goes in the direction of the actuating cylinder.
The range of operation depends on ball 1. As you can see, if the force of the spring holding ball 1 is to be overcome, a certain pressure (equal to the spring force divided by the opening's cross-sectional area) at the lower seat would be needed. If the ball were to move upward to the upper seat, the exposed surface area of the ball on which the pressure acts would increase (while the spring force would essentially remain the same) thereby causing the pressure in the system to decrease. Ball 1 would then move from the lower seat to the upper seat very quickly as more surface area is exposed, causing the pressure required to move the ball to drop. When the pressure delivered is much higher than the pressure required to move the ball, then the ball will move quickly and bang shut against the upper seat. The opposite reaction occurs when the pressure in the system is lowered to within operational limits.

Hydraulic System Hand Pumps

Functions

1. Hydraulic system hand pumps are used to test the hydraulic system when the plane is on the ground; and,
2. acts as an Emergency system of power
Principles of Operation
The hand pump converts the power of a human being to hydraulic horsepower. For this reason, such pumps are used in older model aircraft.

Types

There are several types of handpumps.
1. Single action - single impulse (S.A.S.I.)
2. Double action - double impulse (D.A.D.I.)
Analysis of a S.A.S.I. Pump
The pump works on the principle of mechanical advantage.
When pilot moves the handle away to L (see diagram below), a low pressure is caused to form in the chamber of the pump, Z. Since the reservoir liquid pressure is greater than the pressure in Z, liquid is forced around the check valve from the reservoir line. When the pump handle is moved to R, a positive pressure will form in Z, causing the check valve to the reservoir side to close. Since the hydraulic system liquid is incompressible, it is forced out through the bottom check valve to the system line.
Suppose the force delivered by the pilot was F1 = 100 lb, at a distance D1 = 20 inches from the pump handle pivot, and suppose that D2 = 1 inch from the pivot to the pump piston. Then by moment equilibrium (F1D1=F2D2), the force acting on the piston would

be F2 = 2000 lb. If the piston area on which the oil acts is A = 2 square inches, then the pressure developed is The volumetric output . In this case, . But a manâ„¢s average output is about 50 lb for F1. Therefore, the piston area must be made half its present size (if the pressure is to remain constant). Thus, volumetric output will then decrease to 1 cu. in., since .

Analysis of a D.A.D.I. Pump

The DADI pump works in the same way that the SASI pump works, except that while chamber A is filling up from the reservoir, chamber B is pumping oil to the system.
11.Flow Control
Selector Valves
Selector valves are used as (1) directional control devices to insure the movement of the hydraulic fluid flow in the proper direction, and (2) as stop-locks to lock the selector switch in a certain position.

Types

There are two types of selector valves. They are piston type and poppet type.
Piston Type
Positions 1, 2 and 3 (shown below) are representative positions for the piston-type selector valve. Position (1) is the position of the selector valve, for example, upon the extension of the landing gear or the lowering of flaps. Position (2) is the position of the selector valve upon retraction of the landing gear or the raising of the flaps. Position (3) is the stop-locking position of this type of valve. This piston type valve uses the Vickers spool mechanism in which the piston "lands" isolate the high pressure oil from the low pressure oil.
Poppet Type - Stacked Poppet
In this type valve, any movement of the handle (at the lower right of the diagram) changes the camshaft and cam settings, thereby opening and closing the poppet valves and letting high and low pressure oil to the proper sides of the actuating cylinder and return line, respectively.
In in-line poppets, the poppet valves are set up along a cam shaft, in the same manner as for the intake and exhaust valves of a car engine. The camshaft is represented by the "sinusoidal" line in the diagram below. However, the motion of the poppets are controlled by the pilot.
These mechanical type selector valves require a fair amount of tubing. In order to reduce the amount of tubing, electric switches have been used to operate solenoids which operate the selector valves. This has the added advantage of reducing the wasteful motions of pilot. This is type of combined electronic circuits and hydraulic system is called electrohydraulics.

Flow Restrictors

Since the speed of the actuating cylinder is determined by the rate of flow of the hydraulic fluid, we may need a device to control the rate of flow. This device is called a flow restrictor. Since none of the selector valves meter the flow, we must use the restrictor.
There are four types of restrictors:
1. one way fixed restrictor
2. one way variable restrictor
3. two way fixed restrictor
4. two way variable restrictor

The One Way Fixed Restrictor

The One Way Fixed Restrictor is not used all the time, but, it is being used more than the other types of restrictors. It is a check valve type restrictor with a drilled hole through the seat to the other side of the check valve. When the flow pressure seats the check valve ball (i.e., flow moving from right to left), some of the fluid can still reach the other side through the drilled hole in the seat. However, since the hole size is fixed, the amount of fluid passing through the passage to the other side is also fixed.

The Two Way Fixed Restrictor

The Two Way Fixed Restrictor is not used because it restricts the flow on the side of the restrictor where we want the flow to occur normally. Because the passage size is fixed, the amount of fluid moving from right to left, or vice versa, is fixed, as well.
The One Way Adjustable Restrictor
The One Way Adjustable Restrictor is being used nowadays. It is the same as the One Way Fixed Restrictor but the amount of fluid passed through the drilled opening in the seat is regulated by means of an adjustment screw.
The Two Way Adjustable Restrictor
The Two Way Adjustable Restrictor is the same as the Two Way Fixed Restrictor, but it also has an adjustable screw that can be used to further restrict the amount of hydraulic fluid passing through the opening.

Synchronizing Circuits

During aircraft turns or maneuvers, if wing air loads on one wing are greater than loads on the other wing, and, we attempt to sweep the wings back or sweep them forward, these motions will occur so unevenly that probable loss of aircraft and pilot will result. Therefore, if we want to synchronize our sweepback motion, we must use devices called flow equalizers.

Another example where flow equalizers are needed is in case of air-to-air missile attack. Suppose our selector valve is set to neutral and we try to get away from a rocket missile by turning right or left. The pressure forces on the wings would be so unequal that the wing actuating cylinder (of the wing undergoing the smaller turn radius) would act as a pump, since its greater pressure loading would cause wing sweepback. The hydraulic fluid would be pushed out of one cylinder and the only path that it could take
would be to the other wing's actuating cylinder, causing that cylinderâ„¢s wing to go in the opposite direction to that of the first wing. This would be catastrophic.
If a downward force is applied to the left piston and the selector valve is closed, the oil is forced into the right cylinder causing the right piston to move up--a motion opposite to what is needed.

Flow Equalizer

A device that may be used as a flow equalizer is a power pump that is run in reverse. If the power pump direction were reversed, the flow would push on the outer teeth of the gear and not on the meshing teeth at the center because the oil canâ„¢t be compressed. Since fluid moves towards the meshed teeth at the center of the pump (A1), as well towards teeth closest to pump casing (A2), and since the fluid pressure acts on twice the teeth area (A2) than at A1, the gear direction reverses, as compared to the direction of operation of a power pump.

Thus the flow equalizer is made up of two power pumps placed side by side in which the drive gears of both pumps are connected (see the side view for the figure below). The main figure shows the two power pumps of the side view, cut along the side view's centerline and opened like a book. When one drive gear turns (2), it causes the other to turn as well (1) through the connection. Since the volumetric output per revolution is the same for both sides, we have found the right device to keep synchronization.

This kind of power pump is set between the two cylinders requiring equalization and would channel the flow to both cylinders (as shown below left). The VICKERS EQUALIZER setup is shown below right, where the VICKERS pumps are connected by a shaft at the center of the diagram. Input is at the top of the pumps and outputs are shown by the arrows.

You should never connect the actuation cylinders of the two wings is series, since this type of circuit, for it to work, would require cylinder (1) to put out twice the fluid pressure, or even more, in order to operate itself and cylinder (2) [see the figure below). The hydraulic fluid in this series type of circuit will burst the hydraulic tubing, due to the fluid pressures required to operate both actuating cylinders, and, because this type of circuit does not compensate for expansion or contraction of the hydraulic fluid. The tubing between cylinders and to the selector valve can transmit high pressure hydraulic fluid as well as return line pressure hydraulic fluid.
Sequencing Circuits
These circuits are used to cause certain operations to occur in a particular sequence. Sequencing circuits have been used, for example, for the complete ejection of a pilot from the plane. The sequencing valve is such that it sends hydraulic fluid through the valve to the other sequencing valves and actuating cylinders. As the piston rod (of the extreme left cylinder) moves upward, it activates the sequencing valve releasing hydraulic fluid to the next cylinder.
Sequencing Valve Operation
As the actuating cylinder piston moves upward, it hits the rod of the sequencing valve (shown in bottom). The rod, in turn, moves up into the sequencing valve pushing the poppet up and releases the hydraulic fluid from the holding side (top) to the releasing side (middle), permitting it to go to the next cylinder and sequencing valve.

Double Sequence

We can design a system so that it can perform a double sequence of actuations. In the diagram below, the system is set so that when the selector valve is open to the "red" side, the sequence of events from left to right is 1,3,4,2 (cylinder numbers in red). When the selector valve is open to the "blue" side, the sequence of events goes from right to left and is 4,3,1,2.
By proper connection of the sequencing valves and actuating cylinders, any sequence of events can be made to occur.

14.Actuation Cylinders

The function of the actuating cylinder is to take the pressure and hydraulic fluid flow and change them into either linear or rotary motion. The ones that have been employed more commonly are the double action actuating cylinders, because they work in both directions.

A. Single Piston, Single Rod

This type of actuating cylinder has one piston connected to one rod. Such a device requires the piston rod to move into the actuating cylinder to cause one motion to occur and to move out of the cylinder to cause the reverse motion to occur.

B. Single Piston, Double Rod

This is an equal displacement cylinder and could be used on an aileron system or an automatic guidance system .
The piston ends can be attached to a pulley system that can pivot a control surface. The motion of the piston to the right, due to high pressure fluid in the left side of the actuating cylinder, can be activate the pulley system and pivot the control surface upward. By reversing the flow, the opposite motion will occur.

C. Double Piston, Double Rod

This type of actuating cylinder would be used on bomb bay doors (figure shown below right). High pressure fluid enters the center section of the cylinder, acting on the two pistons simultaneously. The rods would be extended outward, causing the doors to rotate open. When the high pressure fluid enters the two end sections, this operation is reversed, closing the bomb bay doors.

Single Action Cylinders

Bungee Type- this type of actuating cylinder is used where gravity or weight can act as high pressure oil. Either a rubber mass or a spring loading device counteracts the weight. Its disadvantages include:
1. The decrease in piston stroke on account of weight and size of spring or inserted rubber mass;
2. The fact that oil on the spring side of the piston must move both the piston and the spring;
3. The size and weight of the spring to do the job might be too great.

Locking Cylinder

The locking cylinder is a cylinder which has a locking device attached to it. This cylinder is a "fail-safe" design so that it will not actuate beyond some given point.
Â¢ The locking cylinder is part of the Fail-safe design philosophy: if the cylinder is malfunctioning, it should fail in a position that is safe for the rest of the flight.
Stationary Piston-Moveable Cylinder
Whenever we donâ„¢t want the piston rod to extend into an environment that can damage the rod or contaminate the hydraulic fluid (for example, a stream of sea spray or in the
path of little pebbles when landing or taking off from a rough airstrip), we make the piston cylinder extend instead of the piston rod. The type of cylinder we use is the stationary piston moveable cylinder.

CONCLUSION

Real planes have segments called ailerons inserted in the wings and segments called rudders and elevators inserted respectively in the vertical fin and horizontal stabilizer. The pilot controls their position from the airplane cockpit. When the pilot moves them into the air-stream, they cause the plane to react to air pressure. The pilot uses them to go right or left and also up and down.
Hydraulic systems determine flight worthiness, usability and reliabity
Advantages of Hydraulic Systems Over Other Systems
1. It is lighter in weight than alternate existing systems.
2. It is dead beat, that is, there is an absence of sloppiness in its response to demands placed on the system.
3. It is reliable; either it works or doesn't.
4. It can be easily maintained.
5. It is not a shock hazard; it is not much of a fire hazard.
6. It can develop practically unlimited force or torque.
The actuating cylinder can change hydraulic power to linear or rotating motion. It has a reduction gear in it to reduce rotating motion to that amount which is needed.
Previously, systems used to control motion by using steel cables connected by pulleys between the controlling mechanism (such as the pedals) and the controlled surface (such as the rudder). The cables were affected by expansion rates of the cables due to temperature changes. Hydraulic systems can control motion without worrying about the effect of temperature since it is a closed system (not open to the atmosphere) compared to a cable system. This means better control of the plane and less lag time between the pilot's movement to control the plane and the response by the control surface.
Usually there are 3 sets of hydraulic systems in a commercial aircraft.
SYSTEM A USES [ above 3100 psi]:-
1.PRIMARY FLIGHT CONTROLS [LID][LEFT, INBOARD, DOWN]
2.T/E FLAPS.
3.L/E FLAPS AND SLATS.
4.INBOARD FLIGHT SPOILERS.
5.GROUND SPOILERS.
6.L/G EXTENSION AND RETRACTION.
7.THRUST REVERSER.
8.NOSE WHEEL STEERING.
9.BRAKES [INBOARD].
SYSTEM B USES [below 2800 psi]:-
1.PRIMARY FLIGHT CONTROLS.
2.OUTBOARD FLT SPOILERS.
3.OUTBOARD BRAKES.
STANDBY SYSTEM USES:-
1.STANDBY RUDDER.
2.L/E DEVICES [FLAP + SLAT] EXTENSION OMLY.
3.THRUST REVERSERS.

Hydraulic Fluids

Hydraulic fluids that have been used are of several types: water-based, mineral-based and synthetic type oils. Each has its advantages and disadvantages. Though several types are listed here, newer types of oils are being developed.
A. Water-based MIL-O-7083 type hydraulic fluid has been used in naval aircraft because it is not flammable. However, it is still corrosive. It is a water based lubricant which is chemically treated. Its commerical name is HYDROLUBE
B. Mineral-based petroleum oil MIL-O-5606 has been used by NATO. Old name of this type fluid is AN-VV-O-366. It has a cherry red dye added to it.
C. Synthetic Oils have much appeal. They are non-flammable and work over a wide temperature range. One such synthetic oil is known as Skydroll 500 and it has a purple or green color. It is made from a phosphate-ester base.
BIBLIOGRAPHY

Aircraft Pneumatic System for Beginners

noreply@blogger.com (Anonymous) — Thu, 24 Jan 2013 04:57:00 +0000

Pneumatic systems use compressed air as a working fluid and it acts much like the hydraulic systems we already described previously in our articles. In comparison with hydraulics there are advantages to be found by using air in stead of hydraulic fluid to transmit pressure.The principles (Pascal's law) in using air are the same as for hydraulics but with a remarkable difference. Below we will discuss these and see where they are used in aircraft.Air is pressurized by an engine driven pump (compressor) and stored in bottles. This shows the difference with a hydraulic fluid, air is compressible and this property gives it some unique (dis)advantages.The aircraft pneumatic system provides compressed air for various requirements for an aircraft. It is one of the three power sources, the other two are the electrical power and the hydraulic power.

The uses of the compressed air:

Compressed are is mainly used to pressurize the aircraft. As the modern aircraft can fly to as high as 37,000 feet, the air is too thin at that altitude. As such the aircraft cabin pressure has to be maintained high for the comfort and safety of the passengers.

The function to maintain the pressure and the comfortable air condition is handle in different system. We will briefly discuss the subject here.

Aircondition:

It is a system to maintain the cabin air at a specified temperature and humidity and pressurization is the system to control and maintain the cabin pressure at the predetermined level.

The air that comes from the engines or APU are higher pressure and hotter than the cabin. It has to be cooled down by a series of processes using heat exchanger and expansion process. Smaller aircrafts may use a system similar to the home refrigerator.

The flying aircraft acts like a balloon. In fact it can be shown that the diameter of the aircraft increases as it fly higher into the sky. The pressurization is controlled by controlling the rate of air discharged from the aircraft.

Pneumatic is used to start a jet engine.

Most jet engines are started using a pneumatic starter. Pneumatic starter had a better power to weight ratio.

3. Use for anti-icing anf deicing.These involve 2 functions, deicing is removing the ice after it had already formed. Anti-icing is the action taken to prevent the formation of ice.

The hot air is used to heat up the leading edge of the aircraft’s wing to prevent the formation of the ice.

Sources of the pneumatic

The sources of the compressed air are:

1. The primary source is the engines. As air is being compressed by the engine, it gets hotter and has a higher pressure, two tapping are made, one from low pressure position and the other from a higher pressure area. The outputs are regulated to give the required pressure and temperature. The is done by changing the ratio of high pressure bleed to the low pressure bleed.

2. APU – the auxiliary power unit is a small jet engine designed to provide the compressed air as well as the electrical power. Most aircraft’s APUs are located at the tail.

3. On ground, the aircraft can be connected to a ground power unit.

Control and Indication.

A simple switches and indication lights are provided in the cockpit to control the system. The system also has protection against over temperature.

There are three groups of control and indication. One group for the sources of the pneumatic air. The second is for the users, the air condition, anti-icing and engines starter. The third group is for the pressurization.

System description

In small experimental homebuilt aircraft you will find pneumatic systems in the form of the gyroscopic vacuum system and the tyres the aircraft stands on. Some aircraft engines have an airstart system in where pressurized air in a bottle starts the engine, and as long as the engine runs it keeps the bottle topped up.

Larger aircraft use bleed air from the engines to actuate a number of systems from deicing boots, cabin pressurization, backup and main pneumatic systems. See the image.

Backup systems

Used when, for example, the landing gear hydraulic systems fails for a reason. A backup pneumatic system uses a storage bottle with air and an actuator as an emergency means to extend the gear.

Low pressure systems

These are pressurized up to about 1000 psi and use an engine driven vane type pump and they are used to drive the aircon, door seals, de-icer boots, mainly small low power applications.

High pressure systems

An engine driven compressor feeds air via an unloading valve tot the system keeping the pressure around 3000 psi, but this may vary from aircraft manufacturer to another. There will usually also be a ground valve on the aircraft to enable the system to be pressurized when the main engines are not running.

You will also find a moisture separator, dryer (desiccant) and filter to keep the air clean and free from water before it is stored in the high pressure bottles.

Pressurized air at 3000 psi is reduced before it is routed to valves and actuators, this reduced pressure is monitored by gauges. Actuators can be a single acting device where air moves them one way and a strong spring inside pushes the piston actuator back, or can they be double acting. These are sometimes used with flap extension systems.

Disadvantages

One disadvantage is that air does not transmit pressure as easy as a fluid would do. It is springy in nature and therefore not really suitable for precise control operations. This, however, is an advantage when air is used in tyres and damping in undercarriage to smoothen the ride when taxiing.

It is not suitable for large and heavy mechanical devices. Air must be compressed to a large degree to have enough energy and this would require large air tanks and actuators with very high working pressures.

Advantages of air

In contrary to the disadvantages there are some properties which make the use of compressed air very desirable, they are:

No fire problem - Air won't burn by itself, however, bottles can explode and cause damage
Light weight - Air systems do not need a return line as is the case with hydraulic fluids
Simple - Pneumatic systems are by design very simple
Supply - Air can be pumped in from around us and is unlimited in supply

INCREASE YOUR BRAIN POWER

noreply@blogger.com (Anonymous) — Thu, 17 Jan 2013 16:07:00 +0000

How often do you think about your brain? Do you ever stop to marvel at it’s incredible power and supreme cleverness? Or at least check in and give it a little spring clean and a re-furb from time to time?If you’re like the majority of the population, then your answer will be “no”.

Astoundingly, we only use a mere 10% of our brains, yet seldom do we ever think to invest in a little training every now and then. For a long time, scientists believed that we were stuck with the brain we were born with! Luckily for us, that hypothesis has gone out the window!

Enter neuroplasticity – a new theory that has proven one very incredible fact: Our brains can change

This means that if you’re not very intelligent in one area – that’s OK! You have the option to literally ‘change that area of your brain’ through a little training.

An easy way to think about it is like this:

Your brain is a muscle. You need to exercise it regularly.

The exciting thing is that you don’t have to be a millionaire to increase your brain capacity. All you need to do is invest a little time to regularly train your brain.

So what can you do?

Here are 10 simple ways you can increase your brain power and improve your intelligence!

1. Do something new

When you experience something ‘new’ you actually ‘stimulate’ your brain! Don’t get stuck in a rut doing the same old things – the only way to change the structure of your brain is to do something new. This creates new neural pathways, increasing your intelligence. You could take a new route to work, try a new recipe for dinner, or even a new form of exercise – mix it up!

2. Exercise regularly

It’s been proven that regular exercise helps to increase brain function and enhances neurogenesis. This means that every time you exercise you are creating new brain cells! Get off the couch and get moving! Your brain will thank you for it :)

3. Train your memory

How often do you hear people say “I wish I had a better memory!’ Yet no-one does anything about this! If you discipline yourself to memorise phone numbers and other important numbers (passport, credit card, insurance, driving license) you will start to see a marked improvement in your memory.

4. Be curious

Instead of taking everything at face value, get into the habit of questioning everyday things/products, services that you come into contact with. By being ‘curious’ and questioning everything, you force your brain to innovate & create new ideas. Curiosity may have killed that cat, more importantly it created super important things like electricity and computers!

5. Think positive

Stress & anxiety kill existing brain neurons and also stop new neurons from being created. Research has shown that positive thinking, especially in the future tense, speeds up the creation of cells and dramatically reduces stress & anxiety. Try and get a handle on negative thoughts and make an effort to replace them with positive ones.

6. Eat healthy

Our diets have a HUGE impact on brain function. Our brains consume over 20% of all nutrients & oxygen that we consume – so remember to feed your brain with the good stuff! (i.e. fresh fruit and veg & plenty of OMEGA 3 oils found in oily fish)

7. Read a book

Reading relieves tension & stress (brain-cell killers) because it’s a form of escapism. Research has also shown that using your imagination is a great way to train your brain because you force your mind to ‘picture’ what you are imagining. Reading is a great way to trigger your imagination!

8. Get enough sleep

Sleep is like a mini detox for the brain. This is when your body regenerates cells and removes all the toxins that have built up during the day. Get to bed between the hours of 9pm and midnight to benefit from the most effective hours of sleep!

9. Ditch the GPS

Gone are the days of map reading! Sat Nav may have made our lives easier, it has also made our brains lazier and less efficient at the same time! Go back to the old school and use a map to navigate every now and then (this exercises the part of your brain responsible for understanding spatial relationships).

10. Ban the calculator

Remember back at school when we were taught to use our brains to do simple sums like times tables?! It’s incredible how we now rely on devices like smart-phones and laptops to calculate really simple equations. Resist the urge to work things out using an external device – and use the device you were born with – your brain!

WING VORTEX GENERATORS

noreply@blogger.com (Anonymous) — Wed, 16 Jan 2013 07:28:00 +0000

WING VORTEX GENERATORS

During the early design phase of the 767, more stringent high angle of attack stability requirements were established. Specifically, the new requirements established criteria for acceptable stick force vs. g (load factor) characteristics for pitch maneuvers above the angle of attack for initial buffet. Reduced stick force gradients at angles of attack beyond initial buffet are typical for low tail, swept wing aircraft due to the tendency for the boundary layer air on the outboard wing panel to separate prior to the inboard wing. Although the probability of encountering these characteristics in normal service is very small, history has shown that high speed upsets followed by high load factor recoveries do occur. It was the
Boeing Company's desire that this new requirement be met by aerodynamic means,although a solution by means of a pitch augmentation control system was carefully considered.
This alternative was not desired since it would add cost and complexity to the airplane.Early 767 wind tunnel test results showed, as expected, that the configuration with the best
aerodynamic cruise efficiency displayed predicted stick force per g characteristics similar to previous low tail, swept wing transports and did not meet the more stringent design criteria beyond initial buffet.For optimum efficiency, a wing is designed to achieve an approximate elliptic spanwise lift distribution
at cruise angle of attack as shown in Figure
.

This loading minimizes lift induced drag and thereby maximizes lift to drag ratio. The elliptical lift distribution
is accomplished by proper selection of airfoil camber and twist along the wing span. The resulting sectional lift coefficient variation with span is presented in Figure . On a swept wing planform, the largest increase in section lift coefficient with increasing angle of attack occurs on the utboard region of the span as seen in Figure . This is because wing sweepback causes the outboard wing to operate in a local upwash field created by the inboard wing; therefore, the outboard wing effectively operates at a higher angle of attack than the inboard wing.

Another important factor is the spanwise flow of the low energy boundary layer air which makes the outboard wing more susceptible to initial flow separation. The loss of outboard wing lift at high angles of attack is the direct cause of the reduction in stick force per g for swept wing airplanes.Several candidate design modifications were studied as configuration options for improving the stick force per g characteristics to meet the new design requirements:

· Several T-tail configurations were studied in order to separate the wing flow field from the
horizontal tail

· The wing span loading was modified by retwisting the wing to unload the outboard wing

· The inboard wing airfoils were modified in order to promote initial separation on the inboard wing

Each of the above options resulted in a significantly less efficient airplane. A better solution was desired, and vortex generators provided that solution. A 1/10 scale model of the 767 airplane was built and tested at a high Reynolds number wind tunnel in order to obtain data simulating full scale 767 conditions. Vortex generators were evaluated in detail. The test results were very encouraging
because it was determined that only a few small vortex generators located on the wing just outboard of the nacelle were very effective in improving the wing stall pattern and hence the stick force
characteristics. It remained to be proven on the flight vehicle.
The early flight tests on the 767 airplane without the vortex generators confirmed the initial wind tunnel test results. When vortex generators were added, the stick force characteristics beyond initial buffet met the new Boeing design requirements. The vortex generators also provided increased buffet intensity with increasing load factor thereby contributing additional deterrence to a pilot as he pulled into these conditions. The production vortex generator configuration required only seven 3/4 inch high
vortex generators per wing shown in Figure 5. The effect on weight and drag were negligible.