Powertrain for aircraft in runways

The algebraic sign of the moment, based on the datum location and whether weight is being installed or removed, would be as follows:

• Weight being added aft of the datum produces a positive moment (+ weight, + arm).
• Weight being added forward of the datum produces a negative moment (+ weight, − arm).
• Weight being removed aft of the datum produces a negative moment (− weight, + arm).
• Weight being removed forward of the datum produces a positive moment (− weight, − arm)

CENTRE OF GRAVITY:

                                  The center of gravity (CG) of an aircraft is a point about which the nose heavy and tail heavy moments are exactly equal in magnitude. It is the balance point for the aircraft. An aircraft suspended from this point would have no tendency to rotate in either a nose-up or nose-down attitude. It is the point about which the weight of an airplane or any object is concentrated. A first class lever with the pivot point (fulcrum) located at the center of gravity for the lever. Even though the weights on either side of the fulcrum are not equal, and the distances from each weight to the fulcrum are not equal, the product of the weights and arms (moments) are equal, and that is what produces a balanced condition.

MAXIMUM WEIGHT:

                               The maximum weight is the maximum authorized weight of the aircraft and its contents, and is indicated in the Aircraft Specifications or Type Certificate Data Sheet. For many aircraft, there are variations to the maximum allowable weight, depending on the purpose and conditions under which the aircraft is to be flown. For example, a certain aircraft may be allowed a maximum gross weight of 2,750 lb when flown in the normal category, but when flown in the utility category, which allows for limited aerobatics, the same aircraft’s maximum allowable gross weight might only be 2,175 lb. There are other variations when dealing with the concept of maximum weight.

 

                                         The heaviest weight to which an aircraft can be loaded while it is sitting on the ground. This is sometimes referred to as the maximum taxi weight. 

 

                                               The heaviest weight an aircraft can have when it starts the takeoff roll. The difference between this weight and the maximum ramp weight would equal the weight of the fuel that would be consumed prior to takeoff.    

 

                                               The heaviest weight an aircraft can have when it lands. For large wide body commercial airplanes, it can be 100,000 lb less than maximum takeoff weight, or even more.

MAXIMUM ZERO FUEL WEIGHT:

                                                The heaviest weight an aircraft can be loaded to without having any usable fuel in the fuel tanks. Any weight loaded above this value must be in the form of fuel.

EMPTY WEIGHT:

                         The empty weight of an aircraft includes all operating equipment that has a fixed location and is actually installed in the aircraft. It includes the weight of the airframe, powerplant, required equipment, optional or special equipment, fixed ballast, hydraulic fluid, and residual fuel and oil. Residual fuel and oil are the fluids that will not normally drain out because they are trapped in the fuel lines, oil lines, and tanks. They must be included in the aircraft’s empty weight. For most aircraft certified after 1978, the full capacity of the engine oil system is also included in the empty weight. Information regarding residual fluids in aircraft systems that must be included in the empty weight, and whether or not full oil is included, will be indicated in the Aircraft Specifications or Type Certificate Data Sheet. Other terms that are sometimes used when describing empty weight include basic empty weight, licensed empty weight, and standard empty weight. The term “basic empty weight” typically applies when the full capacity of the engine oil system is included in the value. The term “licensed empty weight” typically applies when only the weight of residual oil is included in the value, so it generally involves only aircraft certified prior to 1978. Standard empty weight would be a value supplied by the aircraft manufacturer, and it would not include any optional equipment that might be installed in a particular aircraft. For most people working in the aviation maintenance field, the basic empty weight of the aircraft is the most important one.

EMPTY WEIGHT OR CENTRE OF GRAVITY:

                                                                 The empty weight center of gravity for an aircraft is the point at which it balances when it is in an empty weight condition. The concepts of empty weight and center of gravity were discussed earlier in this site, and now they are being combined into a single concept. One of the most important reasons for weighing an aircraft is to determine its empty weight center of gravity. All other weight and balance calculations, including loading the aircraft for flight, performing an equipment change calculation, and performing an adverse condition check, begin with knowing the empty weight and empty weight center of gravity. This crucial information is part of what is contained in the aircraft weight and balance report.

USEFUL LOAD:

                      To determine the useful load of an aircraft, subtract the empty weight from the maximum allowable gross weight. For aircraft certificated in both normal and utility categories, there may be two useful loads listed in the aircraft weight and balance records. An aircraft with an empty weight of 900 lb will have a useful load of 850 lb, if the normal category maximum weight is listed as 1,750 lb. When the aircraft is operated in the utility category, the maximum gross weight may be reduced to 1,500 lb, with a corresponding decrease in the useful load to 600 lb. Some aircraft have the same useful load regardless of the category in which they are certificated.

The useful load consists of fuel, any other fluids that are not part of empty weight, passengers, baggage, pilot, copilot, and crewmembers. Whether or not the weight of engine oil is considered to be a part of useful load depends on when the aircraft was certified, and can be determined by looking at the Aircraft Specifications or Type Certificate Data Sheet. The payload of an aircraft is similar to the useful load, except it does not include fuel.

A reduction in the weight of an item, where possible, may be necessary to remain within the maximum weight allowed for the category in which an aircraft is operating. Determining the distribution of these weights is called a weight check.

MINIMUM FUEL:

                         There are times when an aircraft will have a weight and balance calculation done, known as an extreme condition check. This is a pencil and paper check in which the aircraft is loaded in as nose heavy or tail heavy a condition as possible to see if the center of gravity will be out of limits in that situation. In a forward adverse check, for example, all useful load in front of the forward CG limit is loaded, and all useful load behind this limit is left empty. An exception to leaving it empty is the fuel tank. If the fuel tank is located behind the forward CG limit, it cannot be left empty because the aircraft cannot fly without fuel. In this case, an amount of fuel is accounted for, which is known as minimum fuel. Minimum fuel is typically that amount needed for 30 minutes of flight at cruise power. For a piston engine powered aircraft, minimum fuel is calculated based on the METO (maximum except take-off) horsepower of the engine. For each METO horsepower of the engine, one-half pound of fuel is used. This amount of fuel is based on the assumption that the piston engine in cruise flight will burn 1 lb of fuel per hour for each horsepower, or 1⁄2 lb for 30 minutes. The piston engines currently used in small general aviation aircraft are actually more efficient than that, but the standard for minimum fuel has remained the same.
Minimum fuel is calculated as follows:
Minimum Fuel (pounds) = Engine METO Horsepower ÷ 2
For example, if a forward adverse condition check was being done on a piston engine powered twin, with each engine having a METO horsepower of 500, the minimum fuel would be 250 lb (500 METO Hp ÷ 2).
For turbine engine powered aircraft, minimum fuel is not based on engine horsepower. If an adverse condition check is being performed on a turbine engine powered aircraft, the aircraft manufacturer would need to supply information on minimum fuel.

TARE WEIGHT:

                       When aircraft are placed on scales and weighed, it is sometimes necessary to use support equipment to aid in the weighing process. For example, to weigh a tail dragger airplane, it is necessary to raise the tail in order to get the airplane level. To level the airplane, a jack might be placed on the scale and used to raise the tail. Unfortunately, the scale is now absorbing the weight of the jack in addition to the weight of the airplane. This extra weight is known as tare weight, and must be subtracted from the scale reading. Other examples of tare weight are wheel chocks placed on the scales and ground locks left in place on retractable landing gear.

2) DIFFERENCE BETWEEN GROUND SPEED & AIR SPEED:

                                                                                           The true airspeed is simply the speed at which an aircraft is moving relative to the air it is flying in. As such, it’s also the speed at which the air is flowing around the aircraft’s wings. Ground speed, on the other hand, is the aircraft’s speed relative to the ground. One thing that should be noted here is that it’s its horizontal rather than vertical speed – an aircraft climbing completely vertically would have a ground speed of zero. In other words, while airspeed is what determines whether there is enough airflow around an aircraft to make it fly, ground speed is what determines how fast an aircraft will get to its destination.

WIND'S EFFECT ON GROUND SPEED:

                                                           The relationship between airspeed and ground speed is fairly simple. Ground speed is simply the sum of airspeed and wind speed. If the aircraft is flying in the same direction as the wind is blowing, the aircraft experiences tailwind, and its ground speed is higher than its airspeed. On the other hand, if the wind is blowing against the direction the aircraft is traveling in, the aircraft experiences headwind, and its ground speed is lower than its airspeed.

Imagine an aircraft that cruises at an airspeed of 500 miles per hour that has to cover a ground distance of 2,000 miles. If there is no wind at all, then both the aircraft’s airspeed and ground speed would be the same 500 miles per hour, and the aircraft would reach its destination in four hours. If there was a 100 miles per hour headwind – wind blowing against the aircraft’s direction of travel – the aircraft would still be traveling at an airspeed of 500 miles per hour. However, its ground speed would be just 400 miles per hour (100 miles per hour slower than its airspeed). And as such, it would take the aircraft five hours to reach its destinations. Finally, if there was a 100 miles per hour tailwind – wind blowing in the same direction as the aircraft’s travel – the aircraft would still be traveling at an airspeed of 500 miles per hour, but its ground speed would be 100 miles faster. And, at 600 miles an hour, the aircraft would reach its destination in just three hours and twenty minutes.

Thus the reason why some flights go “out of their way” to avoid headwinds or catch tailwinds. And, why some flights might appear to be traveling at “supersonic speeds,” even though their airspeed – the speed that would actually matter in determining whether or not the flight truly is supersonic – is subsonic.

 TYPES OF AIR SPEED:

INDICATED AIR SPEED:

                                      It's an airspeed that is calculated directly off an aircraft’s pitot-static system. It’s the calculated off the aircraft’s dynamic pressure – the difference between its total pressure and static pressure. The dynamic pressure depends not only on the aircraft’s speed, but also on the density of the air it is flying in. As such, the higher the aircraft flies and the lower the air density as a result the bigger difference between the indicated and true airspeed.

CALIBRATED AIR SPEED:

                                        It's ben adjusted for variety of errors. For an example, one of the things it’s adjusted for is the flap position. The reason for that is that at different flap positions, air flows differently around the pitot-static system and affects the indicated airspeed readings.

TRUE AIR SPEED:

                           It's been mentioned numerous times the actual speed at which an aircraft is moving relative to the air it is traveling in. It’s calibrated airspeed adjusted for the the exact conditions (altitude, air temperature, etc.) that the aircraft is flying in.

While ground speed is the airplane’s speed relative to the surface of the Earth, airspeed – at least true airspeed – is its speed relative to the air it is flying in.

3) WHY IS IT NOT RECOMMENDED TO USE AIRCRAFT ENGINE POWER TO MOVE IT ON THE GROUND AT AIRPORT:

                                         The term Aircraft Ground Running is usually used to describe the operation of some or all of the engines of an aircraft, whilst on the ground, for the purpose of functionally checking the operation of either engines or aircraft systems. This usually takes place prior to the release to service of an aircraft from maintenance. Ground running may be carried out either prior to, during or after the rectification of a defect or scheduled work on an engine or an aircraft system, when this requires engines to be operating in order to assess its function. Although the aircraft may need to be taxied or towed to an approved ground running position under a clearance from ATC, most operators and maintenance organisations do not require pilots to be on board because aircraft technicians can be trained and approved for these duties.

The risks which may arise from engine ground running relate to the potential for loss of control of the aircraft by those persons occupying the pilot seats in the flight deck. In most cases, such persons will be maintenance personnel holding specific company-issued approval for the required tasks. The consequences of loss of control during taxi or towing are the same as apply to these operations generally and this article is concerned only with the risks arising from the static running of one or more aircraft engines. Unwanted consequences from such static running are mainly related to those arising from the unintended movement of the aircraft during engine running - effectively a loss of control - especially during high power engine running. Damage can occur to the aircraft itself, other aircraft nearby or to airside structures. In addition, there is a risk of injury to ground support personnel who may be in relatively close proximity to the aircraft.

OVERALL RISK MITIGATION:

                                             The best form of overall mitigation is to ensure that all persons authorised to supervise or directly participate in engine ground running from the flight deck, who are not pilots or flight engineers currently rated on the specific aircraft type, are in receipt of suitable initial training and that there is a proper system for both initial and recurrent qualification for engine ground running duties. Both initial and recurrent qualification must include practical training and assessment of task competence using either a full flight simulator or an aircraft. Between formal competency assessments, a maximum interval between performance of the qualified task should be specified. If that interval is exceeded, the qualification would become void until remedial action has been competed. In this respect, the task of engine ground running should be seen as part of a broader group of aircraft ground movement tasks which can be carried out under the control of flight deck occupants other than type rated flight crew.

Generic and type specific knowledge requirements and practical experience related to ground engine runs defined in regulations (i.e. in Europe EASA Part 66 Appendix I (Basic Training Requirements) and Appendix III (Type Training Requirements), AMC 66 Appendix II (Aircraft type practical experience list of tasks)) have to be met by the license holders. Only certifying staff, whose competency has been assessed by the Quality Department of the Approved Maintenance Organisation (i.e. Part 145 Approved Organisation in Europe), can / should be issued with “certification authorisation” to conduct ground engine runs. Although the regulations do not stipulate, some organisations use simulators for training their engineers whilst others prefer on-the-job training and expect engineers to carry out engine runs under supervision before they are given the authorisation. All certifying staff must follow the up-to-date ground engine run procedures, which are defined in the applicable Aircraft Maintenance Manual as well as the Maintenance Organisation Exposition, which may include additional specific requirements applicable to the organisation. (Ref: AMC.145.A.70)

Key proactive components for safe task completion are clear procedural guidance and a series of checklists for use during each stage of a ground running task. Standard Checklists, which should be specific to the non-airborne limitation and so cannot just be the flight crew versions, should include:

• Pre start
• Starting
• After Start (engine ground idle running only)
• After Start (engine running above ground idle)
• Pre Taxi
• Pre Towing
• Pre Engine Running above Flight Idle (unless this action occurs immediately after engine start.)

In addition, response to potential but unexpected occurrences must be covered by appropriate training and, where a rapid response may be necessary, memory actions.

Finally, engine ground running, especially if engine operation above Ground Idle is to take place, is best carried out with both flight deck pilot seats occupied and with clearly defined roles for the person in charge and their assistant. In particular, this allows checklists to be carried out using the challenge and response method.

4) HOW AN AIRCRAFT IS PUSHED TO RUNWAY WHEN IT'S READY TO TAKE OFF:

                                                  The aircraft is now ready for baggage to be loaded for the next flight. A so-called pushback truck reverses the aircraft into taxiing position, pushing it with a towbar attached to the nose-wheel strut. Or, in the most modern versions, by actually lifting the wheel. That speeds up coupling and decoupling.  In aviation, pushback is an airport procedure during which an aircraft is pushed backwards away from an airport gate by external power. Pushbacks are carried out by special, low-profile vehicles called pushback tractors or tugs. A pushback is therefore the preferred method to move the aircraft away from the gate.

READY TO TAKE-OFF:

• The pilot parks the aircraft in exactly the right place. Usually with the help of an automatic system, but occasionally guided by a marshaller waving two paddles or wands. Dozens of handling personnel are already standing by to perform a whole range of tasks simultaneously.
   
• As soon as the aircraft is stationary and the engines are switched off, the first priority is to disembark the passengers as quickly as possible. The apron handler places chocks in front of the wheels and connects the ground power. Meanwhile, the passenger bridge manoeuvres up to the door and a belt loader rolls up to the cargo hold. Luggage is unloaded and transferred to the terminal on baggage carts.
   
• Refuelling begins, usually from a hydrant at the stand. A hose is attached to this from a special vehicle called a dispenser, with the other side connected to the fuel tank in the wing. Read more about refuelling here.
   
• Now it is time to service the aircraft. The caterer loads new meals and takes away the food waste and used cutlery and crockery. Other activities include draining the lavatories, replacing the headrest covers, removing rubbish and distributing fresh blankets and in-flight magazine.
   
• A specialist team – or sometimes the crew themselves – cleans the cabin so that the new passengers board a pristine aircraft.
   
• Meanwhile, specialists from the airline conduct a technical check to make sure that the engines, wings, control surfaces, landing gear, instruments, doors and other equipment are in full working order.
   
• The aircraft is now ready for baggage to be loaded for the next flight. This is a quick process, on average taking only 10-15 minutes. A little later the passengers start boarding. As soon as they are all in their seats, the door is closed and the pilot informs air-traffic control that the flight is ready for departure.
   
• The apron handler removes the chocks. A so-called pushback truck reverses the aircraft into taxiing position, pushing it with a towbar attached to the nose-wheel strut. Or, in the most modern versions, by actually lifting the wheel. That speeds up coupling and decoupling.
   
• The aircraft taxis to the runway to depart at the agreed time.
   
• The pilot waits for permission to take off from air-traffic control. This is possible once the departure route is clear. As soon as the go-ahead is received, the plane takes to the air at full power.

5) LEARN ABOUT TAKE-OFF POWER, TYRE DESIGN, ROLLING RESISTANCE, TYRE PRESSURE, BRAKE FORCES WHEN LANDING:

TAKE-OFF POWER:

                             A power take-off (PTO) is any of several methods for taking power from a power source, such as a running engine, and transmitting it to an application such as an attached implement or separate machine. Most commonly, it is a splined drive shaft installed on a tractor or truck allowing implements with mating fittings to be powered directly by the engine. Semi-permanently mounted power take-offs can also be found on industrial and marine engines. These applications typically use a drive shaft and bolted joint to transmit power to a secondary implement or accessory. In the case of a marine application, such shafts may be used to power fire pumps. In aircraft applications, such an accessory drive may be used in conjunction with a constant speed drive. Jet aircraft have four types of PTO units: internal gearbox, external gearbox, radial drive shaft, and bleed air, which are used to power engine accessories. In some cases, aircraft power take-off systems also provide for putting power into the engine during engine start.

TYRE DESIGN:

                      An aircraft tire or tyre is designed to withstand extremely heavy loads for short durations. The number of tires required for aircraft increases with the weight of the aircraft, as the weight of the airplane needs to be distributed more evenly. Aircraft tire tread patterns are designed to facilitate stability in high crosswind conditions, to channel water away to prevent hydroplaning, and for braking effect. Aircraft tires also inclu (which are assembled on the inside of the wheels), designed to melt at a certain temperature. Tires often overheat if maximum braking is applied during an aborted takeoff or an emergrncy. The fuses provide a safer failure mode that prevents tire explosions by deflating in a controlled manner, thus minimizing damage to aircraft and objects in the surrounding environment.

ROLLING RESISTANCE:

                                     Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire or wheel) rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy needed for deformation (or movement) of the wheel, roadbed, etc., is recovered when the pressure is removed. Two forms of this are hysterisis losses and permanent plastic deformation of the object or the surface (e.g. soil). Another cause of rolling resistance lies in the slippage between the wheel and the surface, which dissipates energy. Note that only the last of these effects involves friction therefore the name "rolling friction" is to an extent a misnomer. In analogy with sliding friction rolling resistance is often expressed as a coefficient times the normal force. This coefficient of rolling resistance is generally much smaller than the coefficient of sliding friction. Any coasting wheeled vehicle will gradually slow down due to rolling resistance including that of the bearings, but a train car with steel wheels running on steel rails will roll farther than a bus of the same mass with rubber tires running on tarmac. Factors that contribute to rolling resistance are the (amount of) deformation of the wheels, the deformation of the roadbed surface, and movement below the surface. Additional contributing factors include wheel diameter, load on wheel, surface adhesion, sliding, and relative micro-sliding between the surfaces of contact. The losses due to hysterisis also depend strongly on the material properties of the wheel or tire and the surface. For example, a rubber tire will have higher rolling resistance on a paved road than a steel railroad wheel on a steel rail. Also, sand on the ground will give more rolling resistance than concrete. Sole rolling resistance factor is not dependent on speed.

TYRE PRESSURE:

Each of the twelve Boeing-777-300ER main tires is inflated to 220 psi (15 bar; 1,500 kPa), weighs 120 kg (260 lb), has a diameter of 134 cm (53 in) and is changed every 300 cycles while the brakes are changed every 2000 cycles. Each tire is worth about $5,000. Aircraft tires generally operate at high pressures, up to 200 psi (14 bar; 1,400 KPa) for airliners, and even higher for business jets. The main landing gear on the concorde was typically inflated to 232 psi (16.0 bar), whilst its tail bumper gear tires were as high as 294 psi (20.3 bar). The high pressure and weight load on the Concorde tyres were a significant factor in the loss of AIr France Flight 4590 Tests of airliner aircraft tires have shown that they are able to sustain pressures of maximum 800 psi (55 bar; 5,500 kPa) before bursting. During the tests the tires have to be filled with water, to prevent the test room being blown apart by the energy that would be released by a gas when the tire bursts. Aircraft tires are usually inflated with nitrogen to minimize expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight. Dry nitrogen expands at the same rate as other dry atmospheric gases (normal air is about 80% nitrogen), but common compressed air sources may contain moisture, which increases the expansion rate with temperature. The requirement that an inert gas, such as nitrogen, be used instead of air for inflation of tires on certain transport category airplanes was prompted by at least three cases in which the oxygen in air-filled tires had combined with volatile gases given off by a severely overheated tire and exploded upon reaching autoignition temperature. The use of an inert gas for tire inflation eliminates the possibility of tire explosion.

The aircraft tire manufacturing industry is dominated by a four firm oligopoly that controls 85% of market share.

The four major manufacturers in aircraft tire manufacturing are

• Goodyear (United States)
• Michelin (France)
• Dunlop Aircraft tyres (United Kingdom)
• Bridgestone (Japan)

These firms control approximately 85% of the manufacturing market and account for most of the retreads. Dunlop is the smallest player among the major firms with revenue reported at £40m in a 2015 media report.

BRAKE FORCES WHEN LANDING:

                                                    Aircraft brakes stop a moving aircraft by converting its kinetic energy to heat energy by means of friction between rotating and stationary discs located in brake assemblies in the wheels. Brakes provide this critical stopping function during landings to enable airplanes to stop within the length of the runway. They also stop aircraft during rejected takeoff events, in which an attempted takeoff is canceled as the airplane is rolling down the runway before it lifts off from the ground due to engine failure, tire blowout, other system failure or direction from air traffic control. Aircraft brakes also prevent motion of the aircraft when it is parked, limit its speed during taxiing and can even help steer the aircraft on the ground by applying different levels of braking force to the left- and right-side brakes. Aircraft brakes work in conjunction with other brake mechanisms such as thrust reversers, air brakes and spoilers. Thrust reversers are surfaces that are deployed into the path of the jet blast from the engines to redirect propulsive thrust in a direction that opposes the motion of the aircraft. Air brakes and spoilers are flight control surfaces that create additional aerodynamic drag when deployed into the path of air flowing around the aircraft.

HOW AIRCRAFT BRAKES WORK:

                                                 The most common type of brake used on aircraft is the disc brake. Disc brakes function by exploiting friction between rotating and stationary discs inside the brake. Upon receiving a command signal to brake — from the pilot depressing a foot pedal or from the autobrake system — actuators in the brake move a piston to squeeze the discs together, generating a frictional force that slows the rotation of the wheel. The friction between the discs generates heat as the aircraft’s kinetic energy is converted to heat energy. In this function, the brakes act as a heat sink, absorbing tremendous amounts of heat as the aircraft sheds kinetic energy. During RTO stops, the temperature of carbon disc brakes can exceed 1,800° C.Gulfstream G450 main landing gear brake assembly. Source: G450 Maintenance Manual via Code 7700

The discs are mounted on a carrier assembly consisting of a torque tube, which resists and transmits brake torque to the landing gear structure. Sandwiched together between the carrier assembly housing and a backing plate, the discs are arranged in an alternating pattern of rotors and stators. Notch and groove geometry around the circumference of each rotor fits into corresponding geometry in the wheel, keying the rotors to the wheel so that they rotate with it. The stators are keyed to the torque tube and are thus held stationary since the torque tube is connected to the axle and landing gear structure.

Cylindrical spaces within the carrier assembly hold actuator pistons. Braking occurs as piston force squeezes the discs together.

During each application of the brakes, disc material is worn away by frictional forces. A wear indicator in the form of a pin that protrudes out of the carrier assembly indicates the thickness of the stack of discs. Over hundreds of brake applications, material wears away and discs become thinner, requiring replacement following periodic maintenance intervals.

BRAKE DESIGN:

The primary design considerations for aircraft brakes include the number of discs, the diameter of the discs and the material of the discs.

A major design point around which aircraft brakes are designed is the worst-case scenario of rejected takeoff (RTO) at the maximum rolling speed V₁, known as the decision speed. Above V₁, a takeoff could not be safely aborted without serious risk of the airplane failing to stop before the end of the runway. In this situation, the brakes need to absorb more energy than any other scenario.

An A380’s brakes exhibit a red-hot glow during a rejected take off (RTO) test on the runway at ISTRES AFB in the south of France. Source: Airbus (Click image to enlarge)

To illustrate how much energy this is, consider an Airbus A380 — the world’s biggest passenger airplane — performing an RTO at V₁. The maximum take-off weight of an A380 is 575,000 kg (1,267,658 lb) and its maximum V₁ is around 170 knots (about 195 mph or 87 m/s). A rough estimate for the maximum energy that the A380’s 16 brakes need to dissipate during RTO can be obtained by calculating the kinetic energy of the aircraft (neglecting the effects of thrust reversers, air brakes, tailwinds, headwinds and runway slope).

Since kinetic energy (KE) is a function of mass (m) and velocity (v) according to the equation:

KE = ½mv²

The kinetic energy of the A380 during RTO is calculated as follows:

KE = 0.5 * 575,000 kg * (87.4556 m/s)² = 2.2 x 10⁹ J = 2.2 GJ

2.2 GJ (gigajoules) is about the amount of energy an average cloud-to-ground lightning strike dissipates. It is also enough energy to power an 8 W LED light bulb (with light output equivalent to a 60 W light bulb) continuously for 8 years and 10 months

To generate the necessary frictional forces and to handle this much energy within the length of a runway, large commercial transport aircraft typically require multiple discs per brake assembly and brakes on most, if not all, of their wheels. For example, an A380 has 22 wheels distributed on five landing gear legs to support its massive weight: two nose wheels on a leg beneath the nose of the aircraft, eight wing wheels split between two legs that fold out from under the fuselage to support the left and right wings, and 12 body wheels split between two inboard landing gear legs under the fuselage. Sixteen of these wheels have brakes (four aft body wheels and the nose wheels are not braked). The A380 uses Honey well's Carbenix brakes. Each of the aircraft’s 16 brake assemblies has five rotors made of Carbenix 4000 carbon-carbon composite. The brake assemblies are located within wheels made of 2014-T6 aluminum alloy and attached to the axle and landing gear structure, which is comprised of 300 M high-strength alloy steel, titanium and aluminum components.

 

BRAKE MATERIALS:

                                The most common aircraft brake disc material until around 1963 was steel. The introduction of beryllium as a disc material provided improved thermal properties at the cost of material handling difficulties due to the toxic nature of beryllium oxide.

Carbon brakes became widely available for commercial airplanes starting in the 1980s. Carbon brakes — made of, for example, carbon fibers in a graphite matrix — are lighter, more durable, less thermally sensitive and have higher energy absorption and faster cooling rates compared to steel brakes. Compared to steel, carbon’s higher specific heat — the amount of heat that a unit mass of carbon absorbs to raise its temperature by one unit — enables reduced brake weight. Carbon’s higher thermal conductivity allows faster heat transfer and uniform heat distribution through the disc. Carbon also has lower thermal expansion, higher thermal shock resistance and a higher temperature limit than steel. The specific strength of carbon is relatively constant over a very wide range of temperatures, unlike steel and beryllium, which both exhibit steep declines in specific strength at high temperatures, dropping below carbon around 650° C (1,200° F).

Safran Landing Systems claims its Sepcarb III oxidation-resistant carbon brakes used on Boeing 787s are four times lighter, have three times higher endurance and have two to three times higher absorption capacity than steel brakes. UTC Aerospace Systems said its Duracarb carbon disk technology results in a weight-savings of 700 lbs (318 kg) per airplane for Boeing 737NGs compared to steel brakes. Other brake materials are available as well, such as Honeywell’s Cerametalix, a sintered combination of powdered metals and ceramics.

BRAKE ACTUATOR TYPE:

                                       Brake actuators perform the critical task of squeezing discs together to generate the frictional forces that convert the aircraft’s kinetic energy of motion into heat to stop the aircraft. Most brake actuators on commercial aircraft are hydraulic, although electrically powered electromechanical actuators have entered service as well; the brakes on both the Airbus A220 (formerly known as the Bombardier C-series) and the 787 are electromechanically actuated. Hydraulic brakes are powered by the aircraft’s hydraulic system. A servo valve modulates the flow of hydraulic fluid to the hydraulic actuator to control the amount of braking force — the force with which the hydraulic cylinder presses the discs together. Electric brakes are powered by the aircraft’s electric system. Electricity is converted to mechanical power in the brake’s electromechanical actuators. In these actuators, an electric motor drives gears to turn a ball screw and nut to apply force to press the brake discs together. Redundancy is a necessary attribute built into aircraft braking systems due to the critical safety function that brakes provide. For example, the A380’s hydraulic brake system is powered by multiple separate 5,000 psi hydraulic systems. The set of brakes on the wing wheels and the set of brakes on the body wheels are attached to two separate hydraulic systems. The brake system is also supplied by a backup hydraulic system called the local electrohydraulic generation supply (LEHGS), which provides an alternate source of hydraulic power in the event of primary hydraulic system failure. The LEHGS generates hydraulic pressure with an electric motor-driven pump supplied by the aircraft’s electrical system. The design for the 787’s electric brakes also features redundancy. With four independent electromechanical actuators per wheel, operation of the 787 is permissible with 100% braking function available even if one of the electric brake actuators (EBAs) fails. The modular nature of the EBAs enables easy, in-situ maintenance during which a failed EBA can be quickly swapped out for a new one.

BRAKE COOLING:

                           The large amount of heat generated during aircraft braking is dissipated by means of passive or active cooling. Passive cooling occurs due to natural conduction of heat through the disc material and to surrounding components, radiation of heat off the brake and wheel assembly, and convection as air flows past and through the brake assembly. Active cooling is achieved by using fans that force air through the brakes. Fans are either built into the wheel or part of the external ground support equipment that is positioned against the wheel and removed once sufficient temperature drop has occurred.

  The GS100 aircraft brake cooler has a gas or diesel engine-powered fan that provides suction cooling for fast turnaround times.

           

Example of brake temperature over time after three takeoff and landing cycles. Toward the end of a busy day full of short flights, it may be necessary to mandate a cooling period for hot brakes, during which the aircraft remains on the ground, to allow the brakes to cool so that they will not exceed the acceptable operating temperature range during RTO or landing.          

AUTOBRAKES & SKID CONTROL:

                                                    Modern commercial aircraft are equipped with an autobrake system that controls the deceleration of the aircraft by automatically optimizing the application of brake force independent of pilot operation of the brake pedals to minimize stopping distance, reduce pilot workload and smooth braking action.

Another common feature of aircraft brake systems is a skid control function. Similar to anti-lock brakes on an automobile, skid control systems prevent wheel lockup. They minimize stopping distance and prevent the negative effects of skidding on tires such as unnecessary tire wear and blowout. Skid control is accomplished by applying an optimal brake force that maximizes the coefficient of friction and remains just below the amount of force that would cause skidding. In one implementation, the proper force is arrived at by continuously sensing wheel speed and comparing it to a calculated aircraft velocity. The difference between the two values represents wheel slip and brake force is reduced if it rises above a specified value.

6) WITH NECESSARY ASSUMPTIONS, CALCULATE THE FORCE & POWER REQUIRED TO PUSH/PULL AN AIRCRAFT BY A TOWING VEHICLE:

Forces acting on rolling resistance:

Frr = Urr*(m.g)

where;

m.g - Weight in Newton(N)

Urr - Co-efficient of rolling resistance

CALCULATION:

                       Weight of Airbus A-380 = 575000 Kg

                      Rolling resistance(Urr) = 0.004

                      Weight of towing tractor = 50000 Kg

                      Rolling resistance of towing vehicle = 0.001

                      Rolling resistance of towing tractor = Urr*(m.g)

                                                                         = 0.001*(5000*9.81)

                                                                         = 0.49 KN

                      Rolling resistance of aircraft = Urr*(m.g)

                                                                = 0.004*(575000*9.81)

                                                                = 22.56 KN

                    Total rolling resistance force = Rolling resistance of air craft + Towing factor

                                                                             = 0.49+22.56

                                                                             = 23.05 KN

ii) Air Drag Force:

                             Aerodynamic drag force 

                             `Fad = 1/2 *rho*A8V^2*C_d`

                    where;

                             Rho = Density of air medium

                             A = Frontal area of vehicle which strikes the air

                             V = Velocity with which vehicle moves

                            C_d = Co-efficient of drag which varies for different shapes of the frontal area

CALCUATION: 

                     Velocity of aircraft while towing = 30KMPH

                                                                   = 8.3 m/sec

                     Density of air medium (rho) = 1.225

                     Frontal area of the aircraft = 20 m^2

                     Co-efficient of drag of the aircraft = 0.025

                     Air drag force = `1/2 *rho*A8V^2*C_d`

                                         = `0.5*1.225*20*8.33^2*0.025`

                                         = 0.022 KN

                   Force =  Rolling resistance force + Air drag force 

                           = 23.05 + 0.022

                           = 23.07 KN

Power required:

                         Average speed of push/pull = 20 KMPH

                                                                = 5.5 m/sec

                        P = Total forces*velocity

                           = 23.07*5.5

                           = 126.8 Kw

                       `Fte = T*G/r`

                        Fte - Total tractive force(rolling resistance force + air drag force)

                        T - Torque output

                        r - radius of tire

                       G - Gear ratio

For heavy duty towing tractor

                       G = 11

                        r = 25 inches 

                          = 0.635 m

                       `T = F_te*r/G`

                            = `23000*0.635/11`

                            = 1.327 KN-m

7) DESIGN AN ELECTRIC POWERTRAIN WITH TYPE OF MOTOR IT'S POWER RATING & ENERGY REQUIREMENT TO FULLFILL AIRCRAFT TOWING APPLICATION, ESTIMATE THE DUTY CYCLE RANGE TO CONTROL THE AIRCRAFT SPEED FROM ZERO TO HIGHEST MAKE ALL REQUIRED ASSUMPTIONS, PREPARED A TABLE OF ASSUMED PARAMETERS, DRAW A BLOCK DIAGRAM OF POWERTRAIN: 

To design the vehicle the parameters are assumed;

1) Weight of the aircraft = 575000 Kg

2) Weight of the towing tractor = 50000 Kg

3) Rolling resistance co-efficient of aircraft = 0.004

4) Rolling resistance co-efficient of towing tractor = 0.001

5) Velocity of the aircraft while towing = 8.33 m/sec

6) Density of air medium(rho) = 1.225 kg/m^3

7) Frontal area of the aircraft = 20m^2

8) Co-efficient of drag of the aircraft = 0.026

9) Towing tractor gear ratio = 11

10) Towing tractor tire radius = 0.635 m

11) Operational time of the towing for one vehicle = 0.33hour

12) Battery Armature Voltage = 350 V

13) Battery Armature Current = 350 A

14) Motor terminal voltage for full power output = 630 V

15) Power converters used Bi-directional DC-DC Boost converter 

16) Maximum duty ratio for achieving full power = 70%

17) Assuming the operational time of the towering truck around 20minutes for one cycle

       20 minutes = 0.33 hour

      Energy(Kwh) = power(Kw) 8 Time(h)

                          = 162.8*0.33

      Energy(Kwh) = 41.8 Kwh 

Motor Selection:

                          We have choosen BLDC Motor type and it's power rating is 126.8 Kw with gear ratio & transmission should able to deliver 1.32 KNm of torque.

POWER CONVERTER:

                                 A converter is an electrical circuit which accepts a DC input and generates a DC output of a different voltage, usually achieved by high frequency switching action employing inductive and capacitive filter elements. A power converter is an electrical circuit that changes the electric energy from one form into the desired form optimized for the specific load. A converter may do one or more functions and give an output that differs from the input. It is used to increase or decrease the magnitude of the input voltage, invert polarity, or produce several output voltages of either the same polarity with the input, different polarity, or mixed polarities such as in the computer power supply unit.

The DC to DC converters are used in a wide range of applications including computer power supplies, board level power conversion and regulation, dc motor control circuits and much more. The converter acts as the link or the transforming stage between the power source and the power supply output. There are several kings of converters based on the source input voltage and the output voltage and these falls into four categories namely the AC to DC converter known as the rectifier, the AC to AC clycloconverter or frequency changer, the DC to DC voltage or current converter, and the DC to AC inverter.

SPEED CONTROL OF THE VEHICLE:

                                                       Drivers need to constantly estimate their speed and driving to determine a safe speed for the current road conditions, other vehicles, pedestrians, and any of a thousand other things that can happen at any moment. Choosing the best speed has become more difficult as cars have become quieter and smoother, and cruising speeds have increased. This has thrown driving safety into the limelight.

Most new safety features are factory installed, but older cars require aftermarket solutions and devices. There is a wide range of speed control devices, like top speed limiters, automatic speed limiters, on-board monitoring devices, and crash recorders. Limiting the top speed of your vehicle is usually done either through engine management systems or through a device that controls the throttle or the fuel injectors directly. Cruise control systems can also be classified as a kind of speed-limiting system for vehicles. They are handy to maintain a minimum speed but do not control the behavior of the driver since they simply maintain whatever speed the driver sets them to.

So what is needed in the modern traffic environment is an AUTOMATIC VEHICLE SPEED CONTROL SYSTEM that will effectively influence driving speeds, and encourage drivers to obey the speed limits, significantly increasing safety. The functionality of such a system would vary depending on the size of the vehicle (car or truck) and is based on controlling the vehicle speed using a microcontroller. The system features could include:

• Real-time information about the vehicle location and speed (usually GPS-based)
• Real-time information about existing speed limits and possible danger areas
• Real-time, in-vehicle feedback on overspeeding
• Remote control features
• Anytime, anywhere access via smartphone or tablet

Car speed control devices that can read data from the car are usually plugged into the vehicle's onboard diagnostic port (OBD-II port) located near the steering column. Finally, you need special software to process the car data and warn the driver about potentially dangerous situations and speeding violations.

For example, ARCHER'S SOFT PORTFOLLIO includes a driving behaviour monitoring & safety managent solution for tracking vehicles and analyzing and improving driver performance. The key features of this solution are:

• Real-time, in-vehicle feedback on aggressive driving and speeding
• Real-time vehicle tracking Idling and speed management
• Configurable dashboards and reports
• Real-time alerts
• Anytime, anywhere access via smartphone or tablet

POWER TRAIN:

                       Powertrain test rigs can now be built to be capable of using either the engine as the prime mover, or an electric motor simulating the engine. The evolution of such cells has been made possible by the comparatively recent development of permanent magnet motors (PMMs) and their associated controls in the automotive power ranges. These units are capable of engine simulation including that of most driveline dynamics and combustion pulses.The same motor technology has produced dynamometers having low inertia yet capable of absorbing high torque at low speeds, thus providing road wheel load simulation that, with customized controllers, includes tire-stiffness and wheel-slip simulation. An important logistical justification for such “all-electric” powertrain cells, besides not having to install and maintain all the cell services required by running an IC engine, is that the required engine may not be available at the time of the transmission test. One cost-effective arrangement that suffers from similar logistical problems of unit availability but which overcomes several rig design problems, where a complete (dummy or modified production) vehicle is mounted within either a two-wheel or “four-square” powertrain test tig.

It should be noted that, in spite of advances in motor and drive technology, flywheels still have a valuable part to play in transmission and powertrain testing and are often fitted to the free end of “wheel” dynamometers, a position that allows various flywheel masses to be fitted according to the demands of the test and UUT (see Chapter 11 for a discussion of flywheels). Powertrain rigs have to be designed to be able to take up different configurations on a large bedplate, as required by the UUT layout. A large tee-slotted test floor, made up of sections of cast-iron bedplates bolted together and mounted on “air springs” is the usual way to enable the various drive-motor or dynamometer units to be moved and aligned in typical powertrain configurations. However, a cheaper alternative for multiconfiguration transmission test rigs, which usually experience lower vibration levels than engine rigs, where steel slideways set into the concrete floor allow relative movement, albeit restricted, of the major dynamometer frames. To allow fast transition times the various test units should be pallet mounted in a system that presents a common height and alignment to the cell interface points.

BLOCK DIAGRAM: 

RESULTS:

               1) The force and power required to push / pull an aircraft by a towing vehicle is 1.327 KN-m