Project-1: Powertrain for aircraft in runways

Aim: To design a Powertrain for aircraft in runways.

1. Search and list out the total weight of various types of aircraft. 

The aircraft gross weight (also known as the all-up weight and abbreviated AUW) is the total aircraft weight at any moment during the flight or ground operation.

An aircraft's gross weight will decrease during a flight due to fuel and oil consumption. An aircraft's gross weight may also vary during a flight due to payload dropping or in-flight refuelling.

2. Is there any difference between ground speed and airspeed? 

- To properly define the relative velocity, it is necessary to pick a fixed reference point and measure velocities relative to the fixed point. In this slide, the reference point is fixed to the ground, but it could just as easily be fixed to the aircraft itself. It is important to understand the relationships of wind speed to ground speed and airspeed.

- Wind Speed: 
-For a reference point picked on the ground, the air moves relative to the reference point at the wind speed. Notice that the wind speed is a vector quantity and has both a magnitude and a direction. The direction is important. A 20 mph wind from the west is different from a 20 mph wind from the east. The wind has components in all three primary directions (north-south, east-west, and up-down). In this figure, we are considering only velocities along the aircraft's flight path. A positive velocity is defined to be in the direction of the aircraft's motion.

For a reference point picked on the ground, the aircraft moves relative to the reference point at the ground speed. Ground speed is also a vector quantity. So a comparison of the ground speed to the wind speed must be done according to rules for vector comparison.

- Airspeed:

- The important quantity in the generation of lift is the relative velocity between the object and the air, which is called the airspeed. Airspeed cannot be directly measured from a ground position but must be computed from the ground speed and the wind speed.

Airspeed = Ground Speed - Wind Speed

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

- 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.

- The exhaust wake from these engines can pose hazards in commercial airport environments. Operators and airport authorities must carefully consider these hazards and the resulting potential for injury to people and damage to or caused by baggage carts, service vehicles, airport infrastructure, and other aeroplanes. High engine thrust during maintenance activity can cause considerable damage to airplanes and other elements in the airport environment.

4. How an aircraft is pushed to the runway when it's ready to take off.

- In aviation, pushback is an airport procedure during which an aircraft is pushed backwards away from an airport gate by an external power. Pushbacks are carried out by special, low-profile vehicles called pushback tractors or tugs.

- Although many aircraft are capable of moving themselves backwards on the ground using reverse thrust(a procedure referred to as a powerback), the resulting jet blast or prop wash might cause damage to the terminal building or equipment. Engines close to the ground may also blow sand and debris forward and then suck them into the engine, causing damage to the engine. A pushback is therefore the preferred method to move the aircraft away from the gate.

- Since the pilots cannot see what is behind the aircraft, steering is done by the pushback tractor driver and not by the pilots. Depending on the aircraft type and airline procedure, a bypass pin may be temporarily installed into the nose gear to disconnect it from the aircraft's normal steering mechanism. Once the pushback is completed, the towbar is disconnected, and any bypass pin removed. 

- Large aircraft cannot be moved by hand and must have a tractor or tug. Pushback tractors use a low profile design to fit under the aircraft nose. For sufficient traction, the tractor must be heavy, and most models can have extra ballast added. A typical tractor for large aircraft weighs up to 54 tonnes (59.5 short tons; 53.1 long tons; 119,000 pounds) and has a drawbar pull of 334 kN (75,000 lbf). Often the driver's cabin can be raised for increased visibility when reversing and lowered to fit under aircraft. There are two types of pushback tractors: conventional and towbarless(TBL).

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

Take-off power:

- Takeoff is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne. For aircraft that take off horizontally, this usually involves starting with a transition from moving along the ground on a runway.

- 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).

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.

- 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.

- Bias-ply tires are popular choices for aircraft tires because of their durability and retreadability.

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 Turnips: 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 tyre:

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.

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 aeroplane 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 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.

- 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 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

Brake forces:

Aircraft disc brakes in the landing gear used to brake the wheels while touching the ground. These brakes are operated hydraulically or pneumatically. In most modern aircraft they are activated by the top section of the rubber pedals. In some older aircraft, the bottom section is used instead. Levers are used in a few aircraft. Most aircraft are capable of differential braking.

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.

- 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.

Rolling resistance:

- Rolling resistance, sometimes called rolling friction or rolling drag is the force resisting the motion when a body 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. 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.

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

Aircraft weight airbus A310 gvw = 150000Kg / 5 = 30000Kg 1/5th mass is taken

Gear ratio of tractor = 23:92

Dia of tractor wheel 822mm, radius 411mm, 0.4m

Drag force of aircraft = `0.5*rho*A*V^2*Cd` = 0.5*1.225*219*2.77^2*0.025 = 25.73 KN

Rolling resistance of aircraft = `Urr*m*g` = 0.03*30000*9.81 = 8.83 KN

Drag force of tractor = 0.9*rho*A_vehicle*V_vehicle^2*Cd_vehicle = 0.9*1.225*24*2.27^2*0.025= 2.28KN

Rolling resistance of tractor =  Urr*m*g = 0.9*8291*9.81 = 73.20KN

Total rolling resistance = 82.03 KN

Total force = Total rolling resistance + Drag force of aircraft + Drag force of vehicle   = 82.03 + 25.73 + 2.28= 110.4

Power = Total forc * velocity = 110.4 * 2.77 = 305.80 Kw

T for tractor = F.r/G = 110.4*0.41/0.25 = 181.5 KNm

Simulink model for the entire force calculation of force and power	- Drag force and rolling resistance of the aircraft has been calculated.
Drag force of the vehicle and final torque calculation has been done.	Rolling resistance of the vehicle has been calculated along with inputs from the aircraft subsystem.
A = 219; % aircraft frontle area V = 2.77; % velocity while moving Cd = 0.025; % drag coefficient of aircraft M = 30000; % in kg, 1/5 mass is taken which will be acting on the tractor Urr = 0.03; %rolling resistance coef of aircraft Urr_trac = 0.9; M_tract = 8291; % in kg mass of tractor A_vehicle = 24; % m^2 area of vehicle Cd_vehicle = 0.025; % same as aircraft V_vehicle = 2.77; % m/s velocity of vehicle R_vehicle = 0.41; % in meters gear_ratio = 0.25; %planetory gear ration 23:92 All the necessary values are given in the matlab script and have been called in simulink.

7. Design an electric powertrain with the type of motor, it’s power rating, and energy required to fulfil aircraft towing application. 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 the powertrain. 

- From the above block diagram it can be seen that the basic flow is given. Here a feedback path is given where the output is compared with the reference value and in order to match the reference value proper steps has been taken. All the necessary blocks like motor, controller, converter and PWM are already in built in a DC7 drive block. 

- For modelling, a power train lets say the motor is 80% efficient. Then the rated power is 300kw.

- The battery pack has an overall voltage of 400v.

- Then I = 300000/400 = 750amp

- The DC drive has an internal motor, controller, converter as well as PWM.

- The torque speed relation can be given as

`T = 24.7 + 0.0051*w^2`

The above power train model is roughly made and is only for understanding purpose.

Reference:

http://www.pages.drexel.edu/~oio22/Aircraft.pdf

https://www.aerospecialties.com/product-category/tow-tugs-pushback-tractors/large-20000-dbp/

https://www.aerospecialties.com/aviation-ground-support-equipment-gse-products/tld-ground-support-equipment/tld-tmx-150-9121516-pushback-tow-tractor/

http://www.b757.info/boeing-757-200-specifications/

https://www.grc.nasa.gov/www/k-12/airplane/move.html#:~:text=Airspeed%20is%20the%20vector%20difference,speed%20and%20the%20wind%20speed.&text=On%20a%20perfectly%20still%20day,less%20than%20the%20ground%20speed.

http://www.boeing.com/commercial/aeromagazine/aero_06/textonly/s02txt.html