Project-1: Powertrain for aircraft in runways

Reference:

https://pilotteacher.com/how-much-do-airplanes-weigh-with-20-examples/

http://aviationavi.com/all-kinds-of-weight-for-an-aircraft/

2. Is there any 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.

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.

To give you an actual example, imagine an aircraft that cruises at an airspeed of 500 miles per hour that has to cover a ground distance of 2,000 miles.

If there is no wind at all, then both the aircraft’s airspeed and ground speed would be the same 500 miles per hour, and the aircraft would reach its destination in four hours.

If there was a 100 miles per hour headwind – wind blowing against the aircraft’s direction of travel – the aircraft would still be traveling at an airspeed of 500 miles per hour. However, its ground speed would be just 400 miles per hour (100 miles per hour slower than its airspeed). And as such, it would take the aircraft five hours to reach its destinations.

reference:https://www.grc.nasa.gov/www/k-12/airplane/move.html

https://knaviation.net/airspeed-and-ground-speed/

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

Aircraft can move using their own engine power all the time on the airport apron and taxiways under their own power to go towards runways and after landing taxi to their assigned gate. But the thrust produced resulting jet blast 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. And also it can reduce the cost for fuel. Taxiing can save money.

• Effectively a loss of control can happen, especially during high power engine running. Damage can occur to the aircraft itself, other aircraft nearby or to airsidestructures.
• There is a risk of injury to ground support personnel who may be in relatively close proximity to the aircraft.
• It is easier for truck driver to see the surroundings better than the pilot sitting in the cockpit with limited window. The pushback driver knows the airport better than the pilot.
• It also saves fuel virgin Atlantic hadproposed a new system in which pushback truck will move the aircraft all the way to runway to save fuel and reduce impact of environment.
• The plane engines are very loud. When more than one plane will add up their sound, than it will not be pleasent for passangers and others near airport.

The extensive noise arises from the engine power also dangerous for humans and other living things around the vicinity.

Hence for the above reasons it is not recommended to use engine power to move on the ground.

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

Aircrafts are usually ‘pushed’ by ground vehicles known as tow vehicles such as tow trucks. It is used mainly to reverse an airplane from the terminal area, until it is in a position to move by itself. These tow trucks will only help move the aircraft to an area where the pilots can safely switch on the engines, not the runway! (Ground vehicles are rarely allowed to move on a runway (save for emergencies and inspection), and the aircraft is supposed to move to the runway by itself.

Aircrafts don’t have powered wheels, and hence cannot move in reverse (let alone forward by themselves). Imagine a tiny jet strapped to one of your toy cars; that’s essentially how airplanes work on the ground! They go where the engines push them towards. (Note: There is a mechanism known as reverse thrusters, which allow the engine air flow to be pushed towards the front, but that is highly risky maneuver, and is only used to reduce speed immediately after landing.)

Another reason to push back an aircraft to a safe area, is for safety reasons. The engines produce tremendous thrust from the exit, and an immense vacuum from the front; enough to suck in people, small vehicles, ground equipment etc.Hence it is a common procedure to start the engines once it is cleared away from the terminal area and lined up on a taxiway (roads that lead to the runway).

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

ake of power required to keep the aircraft in the air without fail:

• 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 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.

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)

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.

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

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

et us assume that,

Mass of Towing Vehicle= 45,000kg

Mass of aircraft = 155,000kg

Total mass (m)= 45,000+155,000 =200,000kg

Frontal Area of the aircraft (A) =18 m²

Speed of the vehicle (2)=35Kmph

converting it into m/sec=9.72222

Drag coefficient (Cd) =0.75

Air density (P)=1.225Kg/m³

Rolling resistance coefficient Crr=0.01

Calculating Rolling resistance Force (Frr) =Crr*m*g= 19620 N

Calculating Aerodynamic Drag Force (Fd)=0.5*p Cd*A* v^2=781N

Therefore the total Force required to push/pull the aircrcraft by the towing vehicle (F) Frr+Fd

=20401.58N

Calculating the power (p) =Force*Velocity

=198.35kW

**excel calculation file is attched

SIMULINK MODEL FOR CALCULATION OF FORCE AND POWER:

Blocks used are : constant, product, square , sum and display

.slx file is attached with it

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.

(Hint :DC7 Block)

B. Also, Design the parameters in excel sheet.

Now from the above calculation we get the Total Force acting on the Vehicle as:

Total Traction Force(F) - 20401.58N

Power Required (P) - 198.36kW

Now, The Torque required by the vehicle to move is given by:

Torque(T) - Force(F)*Radius of the Wheel(R)

Therefore, T = 20401.58*0.4

= 8160.63Nm

The Energy required by the vehicle for Towing application is given by:

Energy(E) = Power(P)*Towing Time

= 198.36*2/60

= 6.612kWh

For this application an electric motor which can be either a BLDC motor or an Induction Motor is choosen for the above power specs

If we consider the battery capacity=220 kw is used by the towing vehicle then. The duty cycle range to control the speed from O to max speed (3m/s) is given as

Duty Cycle (d)= (Required Power)/ (Rated power)= 198.36/220 =0.90

Therefore the controller will be able to provide a duty cycle ranging from 0 to 90% in order to control the towing speed.