Project-1: Powertrain for aircraft in runways

1.Total weight of various types of aircrafts.

Various types of aircraft and its weights are listed below:

In an aircraft, the centre of gravity (CG) is the point about which the aircraft would balance when it is suspend by that point. As the location of the centre of gravity affects the stability of the aircraft, it must fall within specified limits that are established by the aircraft manufacturer. Both lateral and longitudinal balance are important, but the primary concern is longitudinal balance; that is, the location of the CG along the longitudinal or lengthwise axis.

From “Manufacturing” to “Commissioning” and from “On the Ramp” to “Take-off” there are huge variations in the weight and balance of an aircraft. It varies significantly, so striking a correct balance with all loads on an aircraft is significantly important.

Prerequisites:

• Weight of a male person – 88 kg (avg)
• Weight of a female person – 70 kg (avg)
• Weight of children (2-12) years – 35 kg (avg)
• Weight of cabin crew – 75 kg (including 3kg of crew baggage) (avg)
• Weight of fuel in aircraft can be approximated as approx 12000 kgs for 4000 km by an narrow body aircraft (A-320).
• Payload – Passengers, Cargo, Mail, Baggage. (mainly)

2.Difference between ground speed and air speed

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.

Below, I will explain the two types of speed in more detail, as well as talk about the four types of airspeed that are commonly used.

Airspeed vs. Ground Speed

As mentioned above, 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.

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.

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.

3.Why is it not recommended to use aircraft engine power to move it on the ground at Airport.

Aircraft towing equipment is typically used for the towing and pushback process to avoid some of the significant hazards posed by aircraft engines. When an aircraft's engine is activated, the thrust can create a high-speed wind that can easily cause damage to the airport terminal, surrounding ground vehicles, jetway, baggage and most importantly, ground personnel.

Suppressing the use of engines is especially important when towing a large aircraft, as their more powerful thrust capabilities can become exceedingly dangerous. Engine thrust can easily send any loose items airborne, turn the tiniest grains of dust into hazardous projectiles and create debris that can cause damage to multi-million dollar engines. Additionally, aircraft engines consume a great deal of fuel and generate extreme noise that can be harmful to ground personnel. Using a pushback tug for aircraft is simply a more economical and safer option than running the engines.

Towing and pushback tugs for aircraft are also used to make general maintenance easier for ground personnel. When an aircraft needs to be moved to a hangar for maintenance purposes or is not required for flight, the easiest way is to send an aircraft tug to the tow-in gate for transport. Aircraft towing frees up time for the airline, maintenance team, airport ground controllers and pilots who don't need to waste time getting the engines started. It's also not cost-efficient to start aircraft engines just to reposition an aircraft for maintenance purposes. Typically, ground personnel are trained to only need the aircraft brake system when towing a large aircraft.

Another common reason aircraft towing equipment is used in airports concerns aircraft safety from the taxiway to the tow-in gate. Aircraft towing from the taxiway occurs with significant time constraints, so pilots and ground personnel are under extreme pressure to navigate the aircraft quickly and efficiently. The tight confines of the terminal tow-in gate combined with the restricted view of the pilots generally always require a tow in order to arrive safely and on time.

Even though pilots follow taxi centerlines, aircraft with very large wingspans are often faced with the challenge of having adequate clearance. If an airplane connects with another aircraft or hits a gate terminal, it can cause significant damage, huge expenses and contribute to lost time for extra maintenance repairs.

Aircraft towing can prevent contact with other structures because ground personnel have much better visibility from the airplane tug. With the aid of ground personnel walking with the wings and tail, the airport tug driver can precisely position the aircraft to ensure it will not hit a structure, vehicle, person or another aircraft. In addition to this, the airplane tug driver is in constant communication with the pilots to ensure the aircraft will brake if an emergency occurs.

4.How an aircraft is pushed to runway when its ready to take off

• The take off power required mainly depends upon the kinetic energy of the vehicle and the height i.e, potential energy of the aircraft.

• The total energy of an aircraft flying in the atmosphere can be calculated from the below energy equation:

E = ½ m v² + mgh

here m = total mass of the aircraft

v = velocity with which air craft is moving.

g = acceleration due to gravity

h = height at which aircraft is moving

• A Boeing 737-300 has a maximum takeoff weight of 5.65 × 10⁴ kg, a cruise altitude of h = 10,195 m, and cruise speed of 221 m/sec. Inserting these numbers into the above equation, we obtain 7.03 GJ for the energy at cruise conditions. [3] However, the engines mounted onto the wings of the plane are required to provide additional energy per time, power, in order to keep the aircraft flying at a constant altitude and speed.
• The extra power needed to overcome the drag acting on the airplane can be given by the following equation :

P = (dh/dt) m g

Here dh/dt = the decent speed required to keep the plane's speed constant if the engines fail.

m = mass of the aircraft

g = acceleration due to gravity

Tyre Design :

Aircraft tires can easily be taken for granted. Their simplistic appearance may lead some to a false feeling of complacency. Many technicians are not aware of the critical design factors that go into every aircraft tire in use today. Seemingly minor flaws can lead to disastrous results, and inadequate maintenance practices can cause shortened tire life and even cause unsafe operating conditions.
When one considers the forces that aircraft tires endure, it seems amazing that engineers were ever able to develop these special products. Some tires are subjected to speeds as fast as a race car while at the same time supporting more weight than the largest land moving machines. They go through cyclic exposure to varying temperatures and pressures. These factors make aircraft tire design a critical process and tire maintenance an ever important step in safe aircraft operation.

Designing aircraft tires is a very intense undertaking. Once an aircraft manufacturer goes to the tire manufacturer with the size and weight requirements, the tire manufacturer begins the process of designing a tire that meets the needs of the aircraft manufacturer as well as all regulatory requirements — including foreign regulations in many cases.
Engineers are challenged with designing tires with cool running, heat-resistant materials while simultaneously exceeding tire service requirements. Tire prototypes are put through rigorous tests that simulate cycles of landings, take-offs, and taxi operations. It is only after the tires pass all mandatory tests and meet the requirements of the aircraft manufacturer and airworthiness authorities that the tires are put into production.
Two types of tires are used in aircraft applications — bias-ply tires and radial tires. Although both types of tires share some similarities in design, there are differences that need to be noted.

Bias-ply tire construction :

A cutaway of a typical bias-ply tire is shown in Figure 1. Bias-ply tires are popular choices for aircraft tires because of their durability and retreadability. The tire construction consists of the following components:
Tread: The tread is made of rubber mixed with other additives to obtain the desired level of toughness, durability, and resistance to wear. The tread pattern is designed to aircraft operational requirements, with the ribbed tread design used widely due to its good traction under varying runway conditions.
Sidewall: The sidewall is a protective layer of rubber that covers the outer casing ply. It extends from the tread edge to the bead area.
Tread Reinforcing Ply: One or more layers of fabric that strengthens and stabilizes the tread area for high-speed operation. It also serves as a reference for the buffing process when tires are retreaded.
Buff Line Cushion: The buff line cushion is made of rubber compound to enhance the adhesion between the tread reinforcing ply and the breakers or casing plies. It is of sufficient thickness to allow for the removal of the old tread when the tire is retreaded.
Breakers: Breakers are reinforcing plies of rubber-coated fabric placed under the buff line cushion to protect casing plies and strengthen and stabilize the tread area. They are considered an integral part of the casing construction.
Casing Plies: Alternate layers of rubber-coated fabric (running at opposite angles to one another) provide the strength of the tire.
Wire Beads: Hoops of high tensile strength steel wire that anchor the casing plies and provide a firm mounting surface on the wheel. The outer edge of the bead that fits against the wheel flange is called the bead heel. The inner bead edge is called the bead toe.
Apex Strip: A wedge of rubber affixed to the top of the bead bundle.
Flippers: Layers of rubberized fabric that help anchor the bead wires to the casing and improve the durability of the tire.
Ply Turnups: The casing plies are anchored by wrapping them around the wire beads, thus forming the ply turnups.
Chafer: A protective layer of rubber and/or fabric located between the casing plies and wheel to minimize chafing.
Liner: In tubeless tires, the liner is a layer of low permeability rubber that acts as a built-in tube and restricts gas from diffusing into the casing plies. In tube-type tires, a thinner liner is used to prevent tube chafing against the inside ply.

Radial-ply tire construction :

With their rigid belt, they provide increased landings and reduced rolling resistance. They have fewer components in their construction and are lighter than similarly sized bias ply tires. Components that differ from bias-ply construction as follows:
Overlay: A layer of reinforcing rubber coated fabric placed on top of the belts to aid in high speed operation.
Belt Plies: A composite structure that stiffens the tread area for increased landings. The belt plies increase the tire strength in the tread area.
Casing Plies: As in bias-ply tires, the casing plies are layers of rubber-coated fabric. However, unlike those in bias plies that run at opposite angles to one another, radial plies run radially from bead to bead.
Chippers: The chippers are layers of rubber-coated fabric applied at diagonal angles that improve the durability of the tire in the bead area.

Tire inspection :

In order to ensure safety and increase tire life, systematic inspections of mounted tires should be performed. A word of warning — Never probe cracks, cuts, or embedded foreign objects while the tire is inflated! Serious injuries could result. In addition, defects such as cuts, cracks, and bulges should be marked with a crayon or chalk prior to deflation since the defects may disappear when the tire is deflated. The following should be checked:
Tread wear: Treads should be visually inspected for wear. The tire should be replaced when tread has worn to the base of any groove at any spot or to a minimum depth specified in the aircraft maintenance manual. Tread wear can also be an indication of improper tire inflation. Refer to Figure 3 for tread wear indications.
Tread cuts: The tire should be inspected for cuts and other foreign damage. Follow the criteria from the applicable aircraft maintenance manual. If no specific criteria is outlined in the manual, the following can be used for guidance in determining tread cuts.

A-Normal
Even tread wear on this tire indicates that it has been properly maintained and run at correct inflation pressure.

B-Excessive
Worn to the breaker/casing plies, the tire should not be left in service or retreaded.

C-Overinflation
Continuous overinflation accelerates center tread wear. It reduces traction while making tread more susceptible to cutting.

D-Underinflation
Excessive tread shoulder wear results from chronic underinflation. It increases the chance of damaging shoulders and sidewalls which shortens tire life because of excessive flex heating.

• Any cut that extends into the casing plies on bias tires.
• Any cut into the belt on radial tires.
• Any cut that extends across one or more rubber tread ribs to the fabric.
• Rib undercutting at the base of any
cut or tread splice warrants replacement.
Sidewall damage: Tires should be replaced if weatherchecking, cracking, cuts, or snags extend down to the casing ply in the sidewall and bead areas.
Bulges: Bulges in any part of the tire tread, sidewall, or bead area are indicative of a separation or damaged tire. The area should be marked and the tire should be removed from service immediately.
Fabric fraying/groove cracking: Tires should be removed from service if groove cracking exposes any fabric or if cracking undercuts the tread ribs.
Flat spots: Flat spots can be caused by braking during touchdown or hydroplaning skids. Tires with flat spots don’t necessarily need to be removed from service unless fabric is exposed. However, if there is an objectionable unbalance issue, the tire assembly can be re-balanced or removed from service.
Radial tire sidewall indentation: Remove tire from service with 3mm or greater sidewall indentation.
Beads: The tire bead areas should be inspected next to the wheel flanges for heat-induced damage, especially if brake drag or severe braking was experienced.
Tire clearance: The tires should be inspected for marks that might indicate rubbing the wheel area due to inadequate clearance.
Wheel assemblies: The wheel assemblies should be inspected for damage. Wheels that are cracked or damaged should be taken out of service for repair or replacement.

Tire inflation
Tire inflation is the most critical issue when inspecting installed tires. Although overinflation can damage the tires by causing uneven tread wear, reduced traction, increased susceptibility to cutting, and increased stress on the wheel assemblies, underinflation is by far more damaging. Underinflation produces uneven tread wear and shortens tire life due to excessive flex heating. The bead area of an underinflated tire can be 50 percent hotter than that of a properly inflated one. Heat is damaging to tire rubber compounds and fabrics. It contributes to tread and carcass separations and bead failures.
Ideally, tire pressure should be checked with a calibrated gauge prior to each flight. At a minimum, they should be checked daily. Do not make the mistake of relying on your "calibrated eye" to determine tire inflation. Tire inflation is difficult to determine visually, especially in tandem configurations. Always use a gauge to check inflation. If servicing is required, dry nitrogen should be used due to its inability to sustain combustion. Also, degradation of the casing plies and liner due to oxidation occurs if regular shop air is used. Nitrogen also helps to deter corrosion on the wheel assembly.
It is a good practice to establish a method of recording tire servicing actions. This aids in identifying chronic leakage problems.

Temperature changes
Another thing to remember pertaining to tire inflation is the change in pressure with temperature changes. For every five degrees Fahrenheit change in temperature, there is approximately a one-percent pressure change in the same direction. This should be taken into consideration if the aircraft is going to be subjected to extreme ground temperature changes. In that case, the tires should be inflated to ensure the minimum required pressure is maintained for the cooler climate. Remember to always check tire pressures when they are at ambient temperature. Checking pressures on hot tires could mask an underinflation condition.
One thing that needs to be noted on newly installed tires is that the tire pressure will drop initially due to tire expansion. The tire pressure should be checked closely until it stabilizes — usually after about 12 hours at rated inflation. If it still exhibits a significant pressure drop after that, the tire should be inspected for possible leaks and corrective action taken.

Protecting tires
Tires should be kept clean and free from oil, hydraulic fluids, grease, tar, and solvents. All of these chemicals have a deteriorating effect on the rubber in the tires. Any contaminant should be wiped off with denatured alcohol followed by a soap and water wash.
Aircraft tires are affected by sunlight and weather extremes. Installation of protective covers can help protect tires on aircraft that are tied down outside.

Operational considerations
Whenever taxiing or towing aircraft, the aircraft manufacturer’s recommended operational procedures should always be followed. It is always prudent to use large radius turns and low speeds to prevent shoulder damage, tread scrubbing, and overheating. Care should also be taken to avoid running over hazardous areas. Tire damage can result from potholes, cracks in the pavement, or stepoffs from pavement to ground.
The areas where the aircraft will be operated should be kept free from debris. In addition to the damage potential FOD (Foreign Object Debris) poses to engines, it can cause considerable damage to tires if it becomes embedded in the tire tread.
This article has briefly discussed some basics on tire composition as well as some inspection and preventive maintenance techniques. Always refer to the applicable aircraft maintenance manual when working with aircraft tires. In addition, the FAA requires tire manufacturers to provide a care and maintenance manual for their products. This is an additional resource that is available to assist in tire maintenance and inspection procedures. With proper attention during inspection and good preventive maintenance practices, your aircraft tires should provide trouble-free service for many landings.

Tube-Type or Tubeless

ROLLING RESISTANCE IN AIRCRAFT :

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 hysterises 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.

The rolling resistance force will be given by the equation as :

F = μ*mg

here :

μ = rolling resistance coefficient

m = total mass of aircraft

g = acceleration due to gravity

But when we consider the extreme condition the surace when considered with a snow we take many considerations into account :

When taking off from a runway covered with slush, standing water or snow, the required take-off ground-run distance will be longer than on a dry runway. This is the result of the fact thatslush, standing water and snow on the runway will generate a rolling resistance that increasesthe total resistance on the aircraft during the ground-run.

Snow is a porous, permeable aggregate of ice grains, which can be single crystals, or closegroupings of several crystals. Air and water vapor surround the crystals. Snow is a complicatedmaterial because of the variety of forms it can take and because it is thermodynamicallyunstable, which means that the physical properties of the snow can change with time (known assnow metamorphism). A large number of different types of snow are known. A possibleclassification of these types including typical densities, is given as follows:

•New snow (50-200 kg/m3)

•Powder snow (200-450 kg/m3)

•Compacted snow (450-700 kg/m3)

•Wet snow (300-700 kg/m3)

All these types of snow are compressible. This means that the volume changes when the snow isloaded. This volume change becomes evident as surface compaction. Density is probably themost useful single parameter of snow properties because e.g. structural characteristics showsome correlation with density. The compression strength of snow, and thus its bearing capacity,also appears to be strongly influenced by its density. Below a density of 400 kg/m3 the bearingcapacity of snow is usually very low resulting in large volume changes of the snow when it isloaded. At higher densities higher loads are required to compress the snow. Whenever snow issubjected to loads e.g. by moving the snow with a bulldozer or running a tire over it, the snowbecomes stronger than natural snow of the same density. This is a result of bond growthbetween the ice crystals. As already pointed out, snow is metamorphic. Environmentalinfluences like wind, temperature fluctuations, and rain can change the characteristics of snowwithin days and even within hours.

The total rolling resistance of an aircraft rolling along a snow-covered runway is given by:

Drolling = Dr+Dc+Dd

In which Dr is the rolling resistance on a dry hard surface. The equations presented in this paperfor Dc and Dd are for single tires. A complete aircraft has at least 3 tires, one on each mainlanding gear and one on the nose landing gear. To obtain the total aircraft rolling resistance dueto snow, the resistance Dc and Dd for each single tire have to be calculated and summed.

TYRE PRESSURE :

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 crosswood conditions, to channel water away to prevent hydroplaning, and for braking effect.

Aircraft tires also include fusible plugs (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 emergency landing. 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.

BRAKES FORCES WHILE LANDING :

Early aircraft had a single braking system with no backup or redundancy. This was seen as impractical by the operators and unacceptable by the regulating authorities so manufacturers were soon incorporating more robust braking systems into their designs. Some of the earlier solutions simply addressed the loss of the primary hydraulic pump and incorporated hand pumps or electrically driven hydraulic pumps to provide an alternate source of hydraulic pressure. These solutions did not address failures due to loss of fluid and were deemed inadequate. To overcome this, some manufacturers such as Convair incorporated a compressed air system into their designs for emergency braking. While it achieved the requirement of providing an independent means of activating the brakes, it was limited in that it did not allow for differential braking and in that the tank contained a finite amount of compressed air. Braking redundancy in most large passenger aircraft today is achieved by multiple, independent hydraulic systems backed up by accumulators. These systems allow for several layers of failure without resulting in total loss of braking capability.

Anti-skid System

The anti-skid system, through various mechanisms, compares the speed of the aircraft with the rotational speed of each main wheel. If the speed of any wheel is too slow for the existing aircraft speed, the brake on that wheel (or wheels) is released momentarily to allow the wheel speed to increase and prevent the wheel from skidding. The system is fully automatic and is active from immediately after initial wheel spin up on landing (during which time brake activation might (or might not) be inhibited) down to a design limited minimum speed; usually about 15 knots. Anti-skid systems are designed to minimise aquaplanning and the potential tyre damage which can occur when a wheel is locked or rotating at a speed which does not correspond to the speed of the aircraft. Anti-skid removes the possibility of reverted rubber skids caused by locked wheels. An anti-skid system also greatly improves stopping distance on substandard surfaces such as gravel or grass and is particularly effective on surfaces contaminated with frozen contaminants such as ice or slush by ensuring maximum effective breaking.

PART - B

6.Force and power required to push / pull an aircraft by a towing vehicle:

Force and Power required to pull / push an aircraft by a towing vehicle is calculated here

Formula for rolling resistance force :

• Frr = Urr*M*g

1. Urr - Coefficient of rolling resistance
2. M - Total mass in kg
3. g - Gravity

Formula for air drag force :

• Fad = 0.5*Cd*rho*A*v^2

1. Cd - Coefficient of air drag
2. rho - Air density in (kg/m^3)
3. A - Frontal area in (m^2)
4. V - Velocity in (m/s)

Assumptions :

Towing vehicle weight (m1) in kgs = 35000 kg

Air craft weight (m2) in kgs = 100000 kg

Gravity (g) = 9.81

Co-efficient of rolling resistance (Urr) = 0.02

Air density rho (kg/m^3) = 1.25 kg/m^3

Width (m) = 2.15 m

Height (m) = 1.16 m

Drag coefficient = 0.6

Velocity (m/s) = 8 m/s

Frontal area (m^2) = 2.49 m^2

Formula for total force required to pull / push an aircraft by a towing vehicle :

• Total tractive force = Frr + Fad

Formula for total power required to pull / push an aircraft by a towing vehicle :

• Total power = Total tractive force*Velocity

B. Calculated force and power using Simulink :

Contant block is used.

Add block is used for addition.

Product block is used for multiplication.

Math opperation block is used for square.

Display block is used to display the values.

Simulink model :

7. 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.

Assumption:

Total tractive force (Fv) in N = 26546.86

Total power (Pv) in KW = 212.37

Motor efficiency (Nm) in % = 93 = 93/100 = 0.93

Transmission efficiency (Nt) in % = 83 = 83/100 = 0.83

Gear ratio = 6

Battery capacity in KW = 280

Time taken for towing (t) (mins-hrs) = 12 = 0.2

Tyre radius,(Tr) in inchs - m = 16 = 0.4

Formula used for Wheel torque :

• (Tw) = Fv*Tr in Nm

Formula used for Motor torque :

• (Tm) = Tw/(G * Nt) in Nm

Req motor torque with motor efficiency of 93%

• Tm/Nm

Formula used for Tota motorl Power :

• (Pm) = Pv/(Nt*Nm) in KW

Total energy consumed for 12 minutes:

• (Pm*t) in KWh

Formula used for Duty cycle:

• D = Pm/Pr

Calculation of excell file is attached here:

Duty cycle is 98%

Aircraft towing application in Simulink:

• Feeded the same parameters

Graph outputs:

Output of battery

Output of Speed and Torque

Output of Motor

B. Also, Design the parameters in excel sheet: