Project-1: Powertrain for aircraft in runways

Q1: Search and list out the total weight of various types of aircrafts. 

Ans:-As per federal aviation department,considering aircraft there are different types and different weights are taken to consideration those are explained below

Types Of Weights considered in aircraft:

Aircraft Gross Weight:- As per federal aviation department, aircraft gross weight is defined as the total weight at any moment during flight or ground operation.

The aircraft gross weight decreases during flight due and oil consumption.In some case gross weight (aircraft) may vary due to drop in payload or inflight refueling,where as on the other hand when the brakes are released the gross weight will be equal to take off weight.

During flight an aircraft gross weight will be refered as the en-route weight or in-flight weight.

Types of aircraft weights are the following:

1)Manufatures empty weight:-It includes the weight of aircraft of the entire flight with its intergal working parts,but excludes baggage ,passenger and fuels.

2)zero fuel weight:-It includes total weight of aeroplanes including unuseable fuels but excludes total weight of useable fuel at board.

3)Payload:It is load carrying capacity of an aircraft which includes passenger ,cargo and fuels,But if it is in the case of cargo flight it determines the total load of logistics weight of the container which it needs to transport.

4)Maximum take off weight:This is the maximum weight at which the aircraft would be made to takeoff .

5)Regulated take off weight:-Depending on different factors (flap setting,altitude,lenght of runway),RTOW varies for each take off,but can never be high for MTOW.

6)Maximum landing weight:-It is maximum weight at which an aircraft is permitted to land.

7)Maximum Ramp weight:-It is the maximum weight used for manuevering (towing) aircraft on the ground.

Types Of Aircraft:

There are a number of ways to identify aircraft by type. The primary distinction is between those that are lighter than air and those that are heavier than air.

 Lighter-than-air:

Aircraft such as ballons nonrigid airships(blimps), and dirigibles are designed to contain within their structure a sufficient volume that, when filled with a gas lighter than air (heated air, hydrogen, or helium), displaces the surrounding ambient air and floats, just as a cork does on the water. Balloons are not steerable and drift with the wind. Nonrigid airships, which have enjoyed a rebirth of use and interest, do not have a rigid structure but have a defined aerodynamic shape, which contains cells filled with the lifting agent. They have a source of propulsion and can be controlled in all three axes of flight Dirigibles are no longer in use, but they were lighter-than-air craft with a rigid internal structure, which was usually very large, and they were capable of relatively high speeds. It proved impossible to construct dirigibles of sufficient strength to withstand routine operation under all weather conditions, and most suffered disaster, either breaking up in a storm, as with the U.S. craft Shenandoah, Akron, and Macon, or through ignition of the hydrogen, as with the Hindenburg in 1937.

                                  AIRSHIP

Heavier Than Air:

This type of aircraft must have a power source to provide the thrust necessary to obtain lift. Simple heavier-than-air craft include kites These are usually a flat-surfaced structure, often with a stabilizing “tail,” attached by a bridle to a string that is held in place on the ground. Lift is provided by the reaction of the string-restrained surface to the wind.

Another type of unmanned aircraft is the unmanned aerial vehicle(UAV), commonly called drones or sometimes remotely piloted vehicles (RPVs). These aircraft are radio-controlled from the air or the ground and are used for scientific and military purposes.

             unmanned aerial vehicle

                     unmanned aerial vehicle

Glider:-

Unpowered manned heavier-than-air vehicles must be launched to obtain lift. These include hang gliders gliders, and sailplanes.

Hang gliders are aircraft of various configurations in which the pilot is suspended beneath the (usually fabric) wing to provide stability and control. They are normally launched from a high point. In the hands of an experienced pilot, hang gliders are capable of soaring (using rising air columns to obtain upward gliding movement).

Weight of Glider planes : 110 kg - 200 kg.

Ultralight Aircraft:-

Ultralights which were originally merely hang gliders adapted for power by the installation of small engines similar to those used in chain saws, have matured into specially designed aircraft of very low weight and power but with flying qualities similar to conventional light aircraft. They are intended primarily for pleasure flying, although advanced models are now used for training, police patrol, and other work, including a proposed use in combat.

Civil aircraft:

All nonmilitary planes are civil aircraft. These include private and business planes and commercial airliners.

Private aircraft are personal planes used for pleasure flying, often single-engine monoplanes with nonretractable landing gear. They can be very sophisticated, however, and may include such variants as: “warbirds,” ex-military planes flown for reasons of nostalgia ranging from primary trainers to large bombers; “homebuilts,” aircraft built from scratch or from kits by the owner and ranging from simple adaptations of Piper Cubs to high-speed, streamlined four-passenger transports; antiques and classics, restored older aircraft flown, like the warbirds, for reasons of affection and nostalgia; and aerobatic planes, designed to be highly maneuverable and to perform in air shows.

                                 Beechcraft Baron

Business aircraft are used to generate revenues for their owners and include everything from small single-engine aircraft used for pilot training or to transport small packages over short distances to four-engine executive jets that can span continents and oceans. Business planes are used by salespeople, prospectors, farmers, doctors, missionaries, and many others. Their primary purpose is to make the best use of top executives’ time by freeing them from airline schedules and airport operations. They also serve as an executive perquisite and as a sophisticated inducement for potential customers. Other business aircraft include those used for agricultural operations, traffic reporting, forest-fire fighting, medical evacuation, pipeline surveillance, freight hauling, and many other applications. One unfortunate but rapidly expanding segment of the business aircraft population is that which employs aircraft illegally for transporting narcotics and other illicit drugs. A wide variety of similar aircraft are used for specialized purposes, like the investigation of thunderstorms, hurricane tracking, aerodynamic research and development, engine testing, high-altitude surveillance, advertising, and police work.

                  Gulfstream G450

Powered Lift :

A powered lift aircraft takes off vertically  under engine power but uses a fixed wing  for horizontal flight. These aircraft do not need a long runway to take off and land, like helicopters , but they have a speed and performance similar to standard fixed wing  aircraft in combat or other situations.

 

 Weight : 160 kgs .

Fighter Aircraft: 

A fighter aircraft, often referred to simply as a fighter, is a military fixed wing aircraft designed primarily for air to air combat against other aircraft. The key performance features of a fighter include not only its firepower but also its high speed and manuverability relative to the target aircraft.

 

Weight : 13500 kgs.

Transport Planes :

Military transport aircraft or military cargo aircraft are used to airlift troops, weapons and other military equipment to support military operations. Transport aircraft can be used for both strategic and tactical missions, and are often diverted to civil emergency relief missions.

Weight : 250,000 kgs.

Aerobatic Planes:

An aerobatic aircraft is an aerodyne (a heavier-than-air aircraft) used in aerobatics, both for flight exhibitions and aerobatic competitions

Weight : 771 kgs.

                   Antonov An-225

                                           Airbus A380-800

                                                  Boeing 747-8F

                                                 Boeing 737-900

Below is the table od weights data of some aircrafts.

Aircraft Type	Empty WEIGHT	Max Fuel Weight	Max Cargo Weight	Gross Weight
Antanov AN-225	285,000 kg	300,000 kg	190,000 kg	640,000
Airbus A-380-800	277,000 kg	254,000 kg	84,000 kg	575,000
Boeing 747-800	220,100 kg	194,000 kg	134,000 kg	447,700
Airbus A340-500	168,000 kg	175,000 kg	54,000 kg	372,000
Boeing 777-300ER	168,000 kg	145,500 kg	67,100 kg	352,000
Boeing 787-10	135,500 kg	101,500 kg	57,300 kg	254,000
Boeing 737-900	24,000 kg	20,000 kg	20,200 kg	85,000
Airbus A320-100	42,600 kg	22,100 kg	20,000 kg	68,000
Embraer 190	28,800 kg	13,000 kg	13,100 kg	48,000
Gulfstream G650	24,000 kg	21,900 kg	3,000 kg	45,200
Bombardier CRJ900	21,850	8,900	2,760	36,500
Bombardier Q400	17,800	5,300	8,500	28,000
Learjet 75	6,300	2,750	1,300	9,700
Cessna Citation CJ4	4,700	2,650	1,000	7,800
Beechcraft King Air B100	3,200	1,450	1,900	5,400
Diamond DA50RG	1,450	155	560	2,000
Beechcraft Bonanza G36	1,150	200	385	1,660
Cessna 206H	990	235	520	1,630
Sirrus SR22	1000	220	430	1,630
Cessna 172R	770	170	255	1,100

 Q2: Is there any difference between ground speed and air speed?

Ans:

Air Speed of an Aircraft is defined as the speed at which the aircraft is moving relative to the air it is flying in. I.E. we can say the speed at which the air is flowing around the aircraft's wings.

Where ground speed on the other hand, is the aircraft’s speed relative to ground, the important thing here is that ground speed is the horizontal speed rather than vertical speed- an aircraft climbing completely vertical would have a ground speed of zero.

Yes there is lot of difference between ground speed and airspeed.

Relation between ground and airspeed:

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 a headwind, and its ground speed is lower than its airspeed.

Q3:Why is it not recommended to use aircraft engine power to move it on the ground at Airport? 

Ans:

Generally most of the airplane can move itself in reverse manner by making use of reverse thrust technology.But in most of the practical it is not possible because when airplanes start using reverse thrust it will consume lot of fuels as well as causes lot of noise and also hazardous for the people working near by.

The another for not using reverse thrust is that the jet blast can cause damage to terminal buildings or its equipments.Since the engine is also close to the ground it will blow off the sand and debreis forward and sucks it to the engine and causes damage to it.

To solve this kind of issue we use a towing vehicle which helps to tow the vehicle in reverse dierection and it eill be tugged until it reaches a safe place and from there onwards airplane will move by itself for further take off.

 

Q4: How an aircraft is pushed to runway when its ready to take off? 

 Ans:

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. ... The aircraft taxis to the runway to depart at the agreed time.

Pushback:- Pushback is when an aircraft is pushed backwards away from the airport gate by vehicles called tugs or tractors.Closer to departure, an aircraft tug will park right in front of the nose wheel.The tug might be directly attached to the plane's nose gear with a tow bar, or could be a "wheel-lift" tug. These tugs cradle the nose gear, then lift it up before moving the plane. That gives the tug driver control over the plane's direction during pushback.New taxi technologies are appearing, like pilot-controlled tugs, and electric motors mounted to the plane's landing gear. Both promise to save fuel, and reduce airport noise.

Towing of Aircraft :- Movement of large aircraft about the airport, flight line, and hangar is usually accomplished by towing with a tow tractor (sometimes called a “tug”).In the case of small aircraft, some moving is accomplished by hand pushing on the correct areas of the aircraft. Aircraft may also be taxied about the flight line but usually only by certain qualified personnel.Towing aircraft can be a hazardous operation, causing damage to the aircraft and injury to personnel, if done recklessly or carelessly. This article outline the general procedure for towing aircraft. However, specific instructions for each model of aircraft are detailed in the manufacturer’s maintenance instructions and are to be followed in all instances. 

Taxiing

Taxiing is the controlled movement of the airplane under its own power while on the surface. Since an airplane is moved under its own power between a parking area and the runway, the pilot must thoroughly understand and be proficient in taxi procedures.

Taxiing (rarely spelled taxying) is the movement of an aircraft on the ground, under its own power, in contrast to towing or pushback where the aircraft is moved by a tug. ... An airplane uses taxiways to taxi from one place on an airport to another; for example, when moving from a hangar to the runway.

 Q5: Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.

Ans:

Take off Power:-

Take off is the phase of the flight where the airplane leaves the ground and becomes airborne. For aircrafts travelling vertically, this is known as liftoff. For light weight aircraft, usually full power is used for take off. For heavies aircrafts like passenger planes, full engine power is not used for take off, This will increase the life of engine, reduce maintanence cost and decreases the noise. In some emergency cases, the power used can then be increased to increase the aircraft's performance.

For aircraft that take off horizontally, this usually involves starting with a transition from moving along the ground on a runway For ballons, helicopters and some specialized fixed-wing aircraft (VTOL aircraft such as the Harrier), no runway is needed.

The forces involved during take off are the following:

T=Thrust force pushes the aircraft in forward dierection on the runway.

D=Drag force resist the forward motion of the aircraft.

F=Rolling resistance force when wheel comes in contact with the gorund during landing and take off.

m = mass of the aircraft.

• During take off on the runway the imbalance force will cause an acceleration along the runway and it is given by the formula:

Contents

1)Horizontal Take Off

1.1)Power setting 

For light aircraft, usually full power is used during takeoff. Large transport category (airliner) aircraft may use a reduced power for takeoff, where less than full power is applied in order to prolong engine life, reduce maintenance costs and reduce noise emissions. In some emergency cases, the power used can then be increased to increase the aircraft's performance. Before takeoff, the engines, particularly piston engines are routinely run up at high power to check for engine-related problems. The aircraft is permitted to accelerate to rotation speed (often referred to as V_r). The term rotation is used because the aircraft pivots around the axis of its main landing gear while still on the ground, usually because of gentle manipulation of the flight controls to make or facilitate this change in aircraft attitude (once proper air displacement occurs under / over the wings, an aircraft will lift off on its own; controls are to ease that in).

The nose is raised to a nominal 5°–15° nose up pitch attitude to increase lift from the wings and effect liftoff. For most aircraft, attempting a takeoff without a pitch-up would require cruise speeds while still on the runway.

Three airliners taking off simultaneously (note similar pitch attitudes)

Fixed-wing aircraft designed for high-speed operation (such as commercial jet aircraft) have difficulty generating enough lift at the low speeds encountered during takeoff. These are therefore fitted with high lift devices, often including slats and usually flaps which increase the camber and often area of the wing, making it more effective at low speed, thus creating more lift. These are deployed from the wing before takeoff, and retracted during the climb. They can also be deployed at other times, such as before landing.

1.2)Speed required

The speeds needed for takeoff are relative to the motion of the air (indicated air speed). A head wind will reduce the ground speed needed for takeoff, as there is a greater flow of air over the wings. Typical takeoff air speeds for jetliners are in the range of 240–285 Km/h (130–154 Kn; 149–177 mph). Light aircraft, such as a Cessna 150, take off at around 100 Km/h (54 Kn; 62 mph). Ultralights have even lower takeoff speeds. For a given aircraft, the takeoff speed is usually dependent on the aircraft weight; the heavier the weight, the greater the speed needed.Some aircraft are specifically designed for short takeoff and landing(STOL, which they achieve by becoming airborne at very low speeds.

The takeoff speed required varies with aircraft weight and aircraft configuration (flap or slat position, as applicable), and is provided to the flight crew as indicated airspeed

Operations with transport category aircraft employ the concept of the takeoff V- speeds V₁, V_R and V₂. These speeds are determined not only by the above factors affecting takeoff performance, but also by the length and slope of the runway and any peculiar conditions, such as obstacles off the end of the runway. Below V₁, in case of critical failures, the takeoff should be aborted; above V₁ the pilot continues the takeoff and returns for landing. After the co-pilot calls V₁, they will call V_R or "rotate," marking speed at which to rotate the aircraft. The V_R for transport category aircraft is calculated such as to allow the aircraft to reach the regulatory screen height at V₂ with one engine failed. Then, V₂ (the safe takeoff speed) is called. This speed must be maintained after an engine failure to meet performance targets for rate of climb and angle of climb.

In a single-engine or light twin-engine aircraft, the pilot calculates the length of runway required to take off and clear any obstacles, to ensure sufficient runway to use for takeoff. A safety margin can be added to provide the option to stop on the runway in case of a rejected takeoff In most such aircraft, any engine failure results in a rejected takeoff as a matter of course, since even overrunning the end of the runway is preferable to lifting off with insufficient power to maintain flight.

If an obstacle needs to be cleared, the pilot climbs at the speed for maximum climb angle (V_x), which results in the greatest altitude gain per unit of horizontal distance travelled. If no obstacle needs to be cleared, or after an obstacle is cleared, the pilot can accelerate to the best rate of climb speed (V_y), where the aircraft will gain the most altitude in the least amount of time. Generally speaking, V_x is a lower speed than V_y, and requires a higher pitch attitude to achieve.

1.3)Assisted take off is any system for helping aircraft into the air (as opposed to strictly under its own power). The reason it might be needed is due to the aircraft's weight exceeding the normal maximum takeoff weight insufficient power, or the available runway length may be insufficient, or a hot and high airfield, or a combination of all four factors. Assisted takeoff is also required for gliders which do not have an engine and so are unable to take off by themselves.

2)Vertical takeoff refers to aircraft or rockets that take off in a vertical trajectory. Vertical takeoff eliminates the need for airfields. Most vertical take off aircraft are also able to land horizontally, but there were certain rocket powered aircraft of the Luftwaffe that only took off vertically, landing in other ways. 

2.1)Vertical take-off and landing (VTOL) aircraft include fixed wing aircraft that can hover, takeoff and land vertically as well as helicopters and other aircraft with powered rotors, such as tiltrotors. Some VTOL aircraft can operate in other modes as well, such as CTOL (conventional take-off and landing), STOL (short take-off and landing), and/or STOVL (short take-off and vertical landing). Others, such as some helicopters, can only operate by VTOL, due to the aircraft lacking landing gear that can handle horizontal motion. VTOL is a subset of V/STOL (vertical and/or short take-off and landing).

2.2)Rocket Launch

 The takeoff phase of the flight of a rocket is called "rocket launch". Launches for orbital space flights, or launches into interplanetary space, are usually from a fixed location on the ground, but may also be from a floating platform such as the San Marco Platform, or the Sea Launch vessel.

Aircraft Tyre Design and Construction :-

Many aviation technicians are not aware of the critical design factors of aircraft tyre in use today. I will discuss step by step, but first, I would like to ask the importance of tyre in aircraft.

Why are tyres important in Aircraft?

When it comes to safety, tyres are one of the most important components of aircraft. They help to absorb the shock of landing and provide cushioning. It also provides the necessary traction for braking and stopping of an aircraft.

An aircraft tyre is designed to withstand extremely heavy loads while landing, take off, taxing, and parking. The number of wheels required for aircraft increases with the weight of the aircraft, as the weight of the aeroplane needs to be distributed more evenly.

A Boeing 737NG & 737MAX uses 6 wheels, Boeing 787 uses 10 wheels, Boeing 777 uses 14 wheels and Airbus A380 uses 22 wheels. Aircraft tyres work under extreme conditions, carrying up to 340 tons and accelerating at over 250 km/hour at takeoff, in addition to enduring varied environmental stress when in flight and taxiing.

Design and Construction of Aircraft tyre

Carcass plies are used to form the tire. They are sometimes called casing plies. An aircraft tyre is constructed for the purpose it serves.

They support the weight of an aircraft while it is on the ground.

It also provides the necessary traction for braking and stopping of an aeroplane.

Tyre also helps to absorb the shock of landing and provide cushioning the roughness of takeoff, roll-out, and taxi operations.

Unlike an automobile or truck tyre, it does not have to carry a load for a long period of continuous operation. However, an aircraft tyre absorbs the high impact loads of landing, and also it’s operating at high speeds for a short time when required.

 

Let’s go through some technical aspects of the tyre.

Retreading – Retreading is methods of restoring a worn tyre by renewing the tread area or by renewing the tread area plus one or both sidewalls. Repairs are included in the tyre retreading process.

Load Rating – Load rating is the maximum permissible load at a specified inflation pressure.

Ply Rating – Ply Rating is used to identify the maximum recommended load rating and inflation pressure for a specified tyre. It is an index of tyre strength.

Speed Rating – The speed rating is the maximum takeoff speed to which the tyre has been tested.

Skid Depth – Skid depth is the distance between the tread surface and the deepest groove as measured in the mould.

Aircraft tyres must have an approved speed and load rating and have sufficient clearance when retracted through landing gear to allow for tyre growth. Tyre growth is the increase in the size of the tyre due to centrifugal forces at high speed.

Aircraft tyres may be Tube-type or Tubeless

Tubeless tyres are more advantageous over tube-type. There is no longer the use of tube-type tyre in recent aviation. Nowadays all airliners are using tubeless tyres. Tubeless that are meant to be used without a tube has the word TUBELESS on the sidewall of the tyre.

Aircraft tyres may be Radial or Bias

Almost all airliners are using Radial tyre. Bias is an older design, and it’s mainly used for road vehicles. Radial tyres have the word RADIAL on the sidewall. Radial tires are more expensive than bias-ply tyres. Radial tires are in demand because of their lower life cycle cost and long term value.

Are aviation tyres are conductive?

Yes, Today’s tyres are conductive. Aircraft tyres are manufactured with tread rubber with conducting compounds to permit earthing of static charges.

In early days when tyres were not sufficiently conductive, aircraft used to have a conductive strip hanging down from the axle of the landing gear. Upon landing, this strip would be the first part of the aircraft to touch the earth. This discharges any static electricity accumulated on the outer surfaces of the aircraft. Now you don’t see them anymore.

What is the purpose of Chines in aviation tyre

 

Chines are also called deflectors. Chine tyre used on the nose wheel of aircraft, specially fuselage-mounted jet engines. It diverts runway water away from the engine inlets.

Chines are circumferential protrusions that are moulded into the sidewall of nose tyres that deflect water sideways to help reduce excess water ingestion into the engines. Tyres may have chines on one or both sides, depending on the number of nose tyres on the aircraft.

Aircraft Tyre Standards

Each tyre manufacturer produces their own designs of the tyre with different tread patterns, wear patterns, wear limits etc, and in some cases, different names for the same part of the tyre. But all tyres must meet the approved standards before being accepted by the FAA or CAA.

All commercial aircraft tyres approved under FAA Requirement Technical Standard Order (TSO) C62. A TSO is a minimum performance standard for specified materials, parts, and appliances used on civil aircraft. 

ROLLING RESISTANCE:

Rolling resistance force (Frr)

                       Frr = µrr * mg

Here µrr is the rolling resistance coefficient, m is mass of the vehicle & g is gravitational force. µrr depends on the road material, vehicle tyre material, vehicle tyre pattern, liquids on the road, tyre pressure & tyre temperature etc.,

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 hysteresis losses (see below), 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.^[1]

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,^[2] load on wheel, surface adhesion, sliding, and relative micro-sliding between the surfaces of contact. The losses due to hysteresis 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:

Inflation Tyre Pressure Checking

It is essential that aircraft tyres be maintained at the correct inflation pressure. Any deviation from specified operational inflation pressures will affect both the performance and safe operation of the tyre.

Under-inflation will increase tyre deflection resulting in excessive heat generation and over-stressing of the carcass leading to either ply or tread separation.

Over-inflation will accelerate wear in the tread crown area and render the tyre more susceptible to foreign object damage (FOD). Therefore it is essential that tyre inflation pressures are checked and adjusted on a regular basis, at least every 24 hours or preferably at each pre-flight inspection.

Tyres on multi-bogie gears can not be visually inspected for equal deflection, because if one tyre is under-inflated then the companion will take the load of both tyres and will, therefore, appear at equal deflection, in any case, visual inspection is totally unsatisfactory and dangerous.

All inflation pressures in rating tables are usually for unloaded tyres ambient temperature (cold). A two hour cooling time should be allowed after landing before checking inflation pressure.

Tyre Pressure – Loaded vs Unloaded Condition

Most tyres are put into service at loads less than the rated load. In order to maintain the design operating conditions of the tyre, the operating inflation pressure is adjusted accordingly. This adjustment is in direct proportion to the rated load of pressure.

Many inflation checks are made while the tyre is mounted on the aircraft. Under loaded conditions, the measured pressure of the tyre will be a value 4% greater than the unloaded pressure due to the weight of an aircraft.

Tyre Pressure vs Temperature Relationship

The relationship between tyre temperature and tyre pressure is proportional. As the temperature of the tyre increases, so the pressure will also increase. The inverse is also true. When the tyre temperature is reduced, the pressure will also reduce.The manufacturer has found that as a general rule, a temperature change of 3°C will result in a tyre pressure change of approximately 1%.

BRAKE FORCES:

The 787 braking system

Stopping a 200-tonne aircraft landing at 180 mph requires a lot of braking force. To do this, the 787 has one brake unit on each of the eight wheels on the main gear assembly. On other aircraft types, the brake units are powered by the hydraulics system. An electrical signal is sent from the flight deck to hydraulic actuators near the main landing gear. Here, hydraulic fluid at 3,000 pound per square inch is used to force the brake unit against the wheel, thus slowing it down.

This system works fine, but the pipes and actuators that form this part of the hydraulic system come at a considerable weight cost. Extra weight means more fuel burn, which in turn increases costs and carbon emissions. What if the brakes could be powered a different way?

The brakes on the 787 Dreamliner work differently to those on other types. 

Thats the case on the 787 Dreamliner Designers did away with the use of the hydraulic system and all its associated architecture and instead used electricity to power the brakes. When the pilots press on the brake pedals, an electrical signal is sent to the brake unit on the wheel. Here, electrically powered actuators are used to press the carbon brake disc against the wheel, slowing it down.

By changing to electric brakes, a 787-8 saves 141 pounds per aircraft and a 787-9 saves 245 pounds. The brakes are also known as “plug and play” because electrical wiring replaces the traditional hydraulics and it’s much easier and quicker to change the brake units when needed. Smart features also allow engineers to monitor the brake performance more closely, giving a real-time measurement of wear on the carbon disks.

Electric brakes

The brake system on the 787 Dreamliner is controlled by the pilots pressing the tops of the rudder pedals under their feet, demanding the rate of braking which they require. This sends an electronic signal to the Left and Right Brake System Control Units (BSCUs).

These then send signals to the four Electronic Brake Actuator Controllers (EBAC) which control the rate of braking on the wheels. Each wheel has four Electric Brake Actuators (EBA), a kind of piston which presses against the carbon brake discs.

 

An Electric Brake Actuator (EBA) pressing against the brake disc. (Photo by Charlie Page/The Points Guy).

The brake disks themselves are made up of two parts. Firstly, there are the rotors. These are connected to the wheel by drive tabs (in the video below they are the black rectangles on the rotor disks). As these drive tabs are in contact with the inside of the wheel, they spin at the same speed. Depending on the brake manufacturer, there are either four or five of these rotors on each brake assembly.

The second part of the disks are the stators. These sit around each rotor and are fixed in place and thus don’t move. As the wheel turns, the rotors spin round inside the stators.

When the brakes are applied, the four EBAs apply pressure to the first stator. This in turn squeezes the stationary stators up against the spinning rotors and it’s this friction which slows the wheel down. 

Anti-skid protection

When landing on slippery runways, there’s a chance that the wheels may start to skid as the brakes are applied. To stop this from happening and to maintain maximum effective braking, each wheel has anti-skid protection.

Using a variety of sources to determine the aircraft speed, the brake units know how fast the wheels should be spinning. If that speed drops significantly, it’s because the current brake pressure on that wheel is too great and the wheel is just skidding over the surface.

In this situation, the anti-skid system automatically reduces the braking on that wheel to a point where the skid stops before reapplying the pressure. All this is done in a fraction of a second.

Autobrake

Pressing on the brakes is pretty straight forward when taxiing in a straight line at low speed. However, when we’re landing in strong winds, it can be a little tricky. We need to use our feet on the rudder pedals to line the nose of the aircraft up with the runway centerline at the last moment. Then, whilst holding that position, slide our feet up to press the toe brakes. Really not very easy when moving at 160 mph.

To help us get the braking underway as soon as we touch down, we have the autobrake system.This provides automatic braking at a preselected rate as soon as the aircraft senses that it is on the ground. It also provides full braking pressure in the case of a rejected takeoff if the speed is above 85 knots (98 mph).

Brake temperature indication

With friction comes heat. As a result, each brake unit displays its temperature on the wheel synoptic page in the flight deck. Here, numerical values relating to brake temperature are shown next to each wheel. A value of 0-4.9 is in the normal range. When a temperature becomes 5.0 or above, an advisory message is displayed to the pilots.

Should the brakes become too hot, there’s a chance that the heat transferred to the wheels could cause the tires to explode. To stop this from happening, when a certain temperature is reached, fuse plugs in the tires melt. This allows the air to be released safely and slowly deflate the tires.

Parking brake

Every so often we need to engage the brakes and keep them on. This is particularly useful on long taxis to the runway and obviously when parked at the gate. The park brake is set by fully pressing down both toe brakes and pulling the parking brake lever up. With this set, we can then release the pressure from the pedals. To release, we just press the brake pedals again.

A helping hand

In addition to the brakes, there are two other systems which help slow the aircraft down on landing. The spoilers and the reverse thrust.

Spoilers

Have you noticed the large panels on the top of the wings raise up on touch down? These are the called the spoilers as they literally spoil the airflow over the wing. This dumps any remaining lift the wings are generating, allowing the wheels to take all the weight and achieve maximum efficiency from the brakes.

Reverse thrust

The final part of the braking process comes from reverse thrust. Just after we have touched down, we pull two levers on top of the thrust levers to engage the reverse thrust, a sort of “reverse gear” for jet engines.

This causes blockers inside the engine to deploy and a door in the side of the engine to slide backward. The air which normally leaves the engine out the back is deflected forward by the blockers and out through the door.

There are two stages of reverse thrust — idle reverse and max reverse. Idle reverse is used on most landings and max reverse is used when the landing performance requires it, normally when the aircraft is landing at hot or high elevation airfields.

This forward directed airflow helps slow the aircraft down but is most efficient at high speeds. If using max reverse, we drop this down to idle reverse at 60 knots (70 mph) and then back to normal thrust as we vacate the runway at around 20 knots (25 mph). 

Q6.A:

With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.  

 Ans:

The various forces acting on the aircraft while pushing and pulling are

1)Rolling resistance force (Frr)

2)Aerodynamic drag force (Fad)

3)Linear acceleration force (Fla)

Methods or Formulas used to obtain the solution :

Vehicle propulsion power or tractive effort power is denoted by (Pte) required to overcome the possible opposing forces when the vehicle is going with a constant speed. So, the possible opposing forces are listed below:

1)Rolling resistance force (Frr)

                       Frr = µrr * mg

Here µrr is the rolling resistance coefficient, m is mass of the vehicle & g is gravitational force. µrr depends on the road material, vehicle tyre material, vehicle tyre pattern, liquids on the road, tyre pressure & tyre temperature etc.,

2)Aerodynamic drag force (Fad)

                           Fad = ½ * ρ * A * Cd * v^2

Here ρ air density kg/m^3

A is frontal area of the vehicle m^2

Cd is air drag coefficient

V is velocity m/s

Generally aerodynamic drag force depends on two components like shape of the drag, skin friction of vehicle.

3)Linear acceleration force (Fla)

Generally acceleration power or the forces required by the vehicle is only for a short duration here in this case we assume the vehicle is going with a constant speed. Therefore no acceleration forces are considered

Total tractive effort force is calculated as

                        Fte = Frr + Fad + 

                             = µrr * mg + ½ * ρ * A * Cd * v^2 

Total tractive effort force or vehicle propulsion power (P) is calculated as

                          P (kw) = Fte * v

Q6.A. Assuming vehicle is running with constant speed and there is no hill climbing situation considering here

Solution: 

Let us consider the pushback tug TMX 150-9 and aircraft Airbus A-319

                       TMX 150-9

                          Airbus A-319

The TMX series aircraft tractors are designed to perform pushback and towing operations on narrow, medium, and widebody aircraft. TLD TMX tractors have the ability to move aircraft up to the Boeing 787 and Airbus A350.

TMX-150-9 specifications:

Given Data:

Mass of the tug: 8300 kg

Mass of the aircraft : 75500 kg

Length of the aircraft: 33.8 m

wing span :35.8 m

Tug velocity (V) : 25 kmph = (25*1000)/3600= 6.95 m/s

Aircraft height : 11.76 m 

Air density : 1.225 kg/m^3

Drag coefficient (Cd) = 0.75

Coefficient of rolling resistance(µrr) = 0.013 

Gravitational constant (g) = 9.8 m/s^2

Step1: calculating Rolling resistance force (Frr):

a)Rolling resistance coefficient (µrr) =0.013

b)Considering the Total mass of the aircraft for the below model  including kerb weight + pay load (m) is

m (kg) = (mass of tug + aircraft mass) = (8300 + 75500) = 83800 kg

 From the formula of rolling resistance force   

                              Frr = µrr * m*g

                                    = 0.013*83800*9.8

                                   = 10676.12 N

Step2: calculating Aerodynamic drag force (Fad):

Fad = 0.5 *  ρ * Cd * V^2

Frontal area of the vehicle = width * height =33.84 * 11.76 = 392.544 m^2

So , Fad = 0.5 * 1.224 * 0.95 * 392.544 * 6.95 ^2

      = 11032.84 N

Step3:

Total tractive effort force is calculated as

                        Fte = Frr + Fad

                             = µrr * mg + ½ * ρ * A * Cd * v^2

                              = 10676.12 N + 11032.84 N 

                              =21708.96  N

Total tractive effort force or vehicle propulsion power (P) required to push / pull an aircraft by a towing vehicle

is calculated as

                 P (kw) = Fte * v

                            =21708.96 * 6.95

                           = 150877.27 W

                           = 150.87 kW.

Q6.B:

 Develop the model for the calculated force and power using Simulink.

Ans:

 

Different Blocks Used are listed Below.

1. Constant 
2. Add
3. Product
4. Math function
5. Gain
6. Display

• The constant blocks are used to input the values for Rolling coefficient, Tug mass, Aircraft mass, Gravity constant, Aircraft length and height, Tug velocity, and Drag coefficient.
• The add block is used to sum up the total mass, and total force
• Gain blocks are used for converting velocity to m/s and  to input the air density
• The math function block is used to find the square of the velocity
• Product block is used for all the  multiplication operations in the formulae

Display blocks are used to read out, Rolling resistance, Total force, Total power, Aerodynamic drag

Q7.A:

Design an electric powertrain with type of motor, it’s power rating, and energy requirement to fulfill aircraft towing application in Simulink. Estimate the duty cycle range to control the aircraft speed from zero to highest. Make all required assumptions. Prepare a table of assumed parameters. Draw a block diagram of powertrain. (Hint: DC7 Block) 

 Ans:

Powertrain:

• The powertrain is the mechanism that transmits the drive from the engine/motor of a vehicle to its axle.
• Power is generated by the engine/motor and transmitted to the driveshaft.
• Other internal parts and components of the engine, differentials, axles, emissions control, exhaust, engine cooling system, etc are also included in the powertrain. An EV powertrain has 60% fewer components than the powertrain of an ICE vehicle

 EV Powertrain block diagram:

Simulink model:

• A battery is used as the power source with nominal voltage as per the DC7 block i.e. 310 V and with rated capacity 165..87622 nearly 166 Ah and the 4 quadrant DC 7 chopper is used as the motor controller.
• The output plots for Duty cycles, SOC%, Voltage, and current are plotted.
• We have the simulation time is set as 7 seconds for plotting

  

Calculation:

Given data and assumptions

Air craft model: Airbus A-319

tug model: TMX-150-9

Tyre specification: 315/70R15

Force required to pull/push the aircraft: 21708.91 N

Power required: : 150.87 kW

Tyre radius , R = 15 inches = 0.381 m

Gear ratio : 8

Transmission efficiency : μt = 80%

Motor efficiency: μm = 92%

Duration of operation: 15 mins = 0.25 hrs

Torque available at wheel, Tw = F * R =>21708.91 * 0.381 = 8271.09 Nm

Actual power required, Pact = Preq/(μt*μm) =

150.87/0.736 = 204.98 kW

Motor torque required, Tm = Tw/(Gear ratio * μt) = 8271.09 /5.6 = 1.47 kNm 

Actual motor torque, Tact = Tm/μm  =1.47/0.92 = 1.59kNm

Battery capacity required = Pact * Duration =

204.98 * 0.25 = 51.24 kWh

Duty cycle = Pact/Input power =204.98/220 = 0.931

Output plots:

Plot for SOC %, Voltage and curent

 

Plot for Duty cycles, armature current and voltage, and motor speed.

Q7.B:

 Also, Design the parameters in excel sheet.

Ans:

Parameters	values
Tug Mass (kg)	8300
Aircraft Mass (kg)	75500
Aircraft Height "h" (m)	11.76
Aircraft Length "l" (m)	33.8
Tug Speed (m/s)	6.95
Coefficient of Rolling Resistance	0.013
Drag Coefficient Cd	0.75
Air Density (kgm^3)	1.225
Towing Duration (Hrs)	0.25
Tyre Radius 'R' (m)	0.381
Gear Ratio	8
Transmission Efficiency	0.8
Motor Efficiency	0.92
Total Force Required for Operation F (N)	21708.91
Power Required Preq (KW)	150.87
Calculation
Frontal Area A m^2	392.544
Total Mass m (kg)	83800
Torque at wheel Tw (N)	8271.09
Actual Power Required Pac (KW)	204.98
Motor Torque Tm (KNm)	1.47
Actual Motor Torque Tact (KNm)	1.59
Required Battery Capacity (KWh)	51.24
Duty Cycle	0.931