Project-1: Powertrain for aircraft in runways

AIM: 1) To list out the total weight of various types of aircraft.

2) To distinguish between ground speed and airspeed.

3) To learn about towing vehicles (tug) and to calculate the force and power requires for pulling the aircraft.

4) To design electric powertrain for towing vehicles.

QUESTIONS:-

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

Below are the different maximum take-off weights for aircraft.

Aircraft Types	Maximum Take-Off Weight (kg) MTOW
Antonov An-225	640,000
Airbus A380-800	575,000
Boeing 747-8F	447,700
Boeing 747-400	396,900
Airbus A340-500	371,950
McDonnell Douglas MD-11	273,300
Boeing 787-10	254,000
Airbus A340-200	253,500
Ilyushin IL-96-300	250,000

Q. 2) Difference between airspeed and ground 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 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.

Wind’s Effect on Ground Speed:

The relationship between airspeed and ground speed is fairly simple. Ground speed is simply the sum of airspeed and wind speed.

If the aircraft is flying in the same direction as the wind is blowing, the aircraft experiences tailwind, and its ground speed is higher than its airspeed. On the other hand, if the wind is blowing against the direction the aircraft is traveling in, the aircraft experiences headwind, and its ground speed is lower than its airspeed.

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.

Finally, if there was a 100 miles per hour tailwind – wind blowing in the same direction as the aircraft’s travel – the aircraft would still be traveling at an airspeed of 500 miles per hour, but its ground speed would be 100 miles faster. And, at 600 miles an hour, the aircraft would reach its destination in just three hours and twenty minutes.

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

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

Although many aircraft are capable of moving themselves backward on the ground using reverse thrust (a procedure referred to as a power back), the resulting jet prop 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. Using the aircraft engine power causes a lot of noise. Also, Towing and Pushback reduce fuel consumption on a large scale.

Pilots have a very limited view of their surroundings and may fail to notice a ground vehicle or even another airplane. The tug operator can see everything.

Below is the image of the towing vehicle for pulling.

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

Taxiing refers to the movement of an aircraft on the ground, under its own power. The aircraft moves on wheels. An airplane uses taxiways to taxi from one place on an airport to another; for example, when moving from a terminal to the runway. The aircraft always moves on the ground following the yellow lines, to avoid any collision with the surrounding buildings, vehicles, or other aircraft. The taxiing motion has a speed limit. Before making a turn, the pilot reduces the speed further to prevent tire skids. Just like cars, there is a certain list of priorities during taxiing.

The aircraft that are landing or taking off have higher priority. The other aircraft have to wait for these aircraft before they start or continue taxiing. The thrust to propel the aircraft forward comes from its propellers or jet engines. Steering is achieved by turning a nose wheel or tail wheel/rudder; the pilot controlling the direction traveled with their feet. The use of engine thrust near terminals is restricted due to the possibility of jet blast damage. This is why the aircraft is pushed back from the buildings by a vehicle before they can start their own engines for taxiing.

The Towing vehicle follows a printed yellow line for pulling the airplane for the right path.

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

Take-off power:

Take off is the phase of flight in which aircraft go through a transition from moving along the ground to flying in the air, usually on a runway, and power used in this phase called take-off power. Usually, the engines are run at full power during take-off, but large transport category aircraft may use reduced power for take-off to reduce maintenance cost, reduce noise emission and prolong engine life.

Tire Design:

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

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

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

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

3. 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 tire, 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.

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

Below are the tire building terminologies.

Rolling Resistance:

The Rolling resistance force is mainly Experienced by the Tyre when the vehicle moves over any surface. The rolling resistance force is given by the expression,

`Frr = murr * m*g`

Where,

`m`= mass (kg)

g = gravity ( 9.81 `m/s^2`

`murr` = coefficient of rolling resistance.

The coefficient of rolling resistance (`murr`) depends on many factors like the Tyre Pressure,Tyre Temperature, Material of the Tyre, Thread pattern of the Tyre, and also the Road Roughness and Liquids on the Road. These factors determine the rolling resistance force.

Tire Pressure:

A Boeing 777 uses 14 tires, Airbus' A380 carries 22, and the enormous Antonov An-225 demands 32. The key to their remarkable durability is maximizing the air pressure. The high-flying rubber is typically inflated to 200 psi, roughly six times what you put in an automobile tire, and the tires on an F-16 fighter are pumped
to 320 psi. It's really pressurized air that's so strong.
Like everything in aviation, tires must meet specific and demanding rules—for example, a tire must withstand four times its rated pressure for at least three seconds.

Brake Forces when landing:

Aircraft brakes stop a moving aircraft by converting its kinetic energy to heat energy by means of friction between rotating and stationary discs located in brake assemblies in the wheels.

Brakes provide this critical stopping function during landings to enable airplanes to stop within the length of the runway. They also stop aircraft during rejected takeoff events, in which an attempted takeoff is canceled as the airplane is rolling down the runway before it lifts off from the ground due to engine failure, tire blowout, other system failure or direction from air traffic control.

Aircraft brakes work in conjunction with other brake mechanisms such as thrust reversers, air brakes and spoilers. Thrust reversers are surfaces that are deployed into the path of the jet blast from the engines to redirect propulsive thrust in a direction that opposes the motion of the aircraft. Air brakes and spoilers are flight control surfaces that create additional aerodynamic drag when deployed into the path of air flowing around the aircraft.

Above is the Landing gear and brakes on an Airbus A319-114

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

1) Forces acting on the Aircraft and Tug (Towing vehicle):-

There are mainly two forces acting in the Towing condition;

A) Rolling resistance force:

The Rolling resistance force is experienced by the tyres of the vehicle.

The rolling resistance force is given by the expression,

`Frr = murr * m*g`

Where,

`m`= mass of the vehicle (kg)

`g`= gravity ( 9.81 `m/s^2`)

`murr`= coefficient of rolling resistance.

Calculations:

1) For Aircraft:

Let us assume,

Weight of the Aircraft = 500000 Kg

Coefficient Rolling Resistance for an Aircraft (`murr`) = 0.004

Hence,

Rolling resistance Force of Aircraft = `murr*m*g` = `0.004 * (500000)*(9.81)`

= `19.620` kN

2) For Towing vehicle :

Let us assume,

Weight of the Towing tractor = 50000 kg

Coefficient of Rolling Resistance of Towing vehicle (`mu_(rr)`) = 0.001

Hence,

Rolling resistance force of towing vehicle = `murr*m*g` = `0.001 * (50000)*(9.81)`

Rolling resistance force of towing vehicle = `0.49` KN

Now,

Total Rolling Resistance Force = Rolling Resistance Force of aircraft + Rolling Resistance Force Towing tractor

= `19.620 + 0.49`

Total Rolling Resistance Force = `20.11` kN

B) Air Drag Force:-

The air drag force is the force experienced by the vehicle due to the air striking when moving.

The Air Drag Force is given by;

`Fad = 1/2*rho*A*v^2*C_d`

Where,

`rho` = density of air

`A`= frontal area of the vehicle on which the air strikes

`v`= velocity of the vehicle

`C_d`= Drag Coefficient

Calculations:

Here,

Density of Air (rho) = 1.25 kg/m^3

Let us assume maximum speed,

The velocity of the Aircraft while Towing = 10 km/h = 2.77 m/s ( Towing speed is in between 5 km/h to 10 km/h and it does not exceed 10 km/h in any case )

1) For Aircraft:

Assume,

The frontal area of the Aircraft = 20 `m^2`

The coefficient of Drag of the Aircraft = 0.2

`therefore`Air drag force = `1/2* rho * A * v^2 * C_d`

= 0.5 * 1.25 * 20 * (`2.77^2`) * 0.2

= 0.019 kN

2) For Towing Vehicle:

Assume,

The frontal area of the Towing vehicle = 2 `m^2`

The coefficient of Drag of the Towing vehicle = 1.1

`therefore`Air drag force = `1/2* rho * A * v^2 * C_d`

= 0.5 * 1.25 * 2 * (`2.77^2`) * 1.1

= 0.011kN

`therefore` The total Air Drag force = Air Drag force of the aircraft + Air Drag force of the towing vehicle

= 0.019 + 0.011 = 0.03 kN

Hence,

The Total Force that the towing vehicle needs to overcome in order to pull the Aircraft = Total Rolling Resistance Force + The total Air Drag force

= 20.11 + 0.03 = 20.14 kN

`therefore` Total Force reqiured is 20.14 kN.

2) Power Required:-

The maximum speed of Pull = 10 km/h = 2.77 m/s

Power required by the towing vehicle = Total Forces * Velocity = 20.14 kN * 2.77 m/s

Power required by the Towing vehicle = 55.78 kW.

Q. 7) Design an electric powertrain with the type of motor, it’s power rating, and energy required to fulfill 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.

With these assumed parameters we have calculated the power required for towing. Hence, Power = 55.78 kW.

Energy Required:

Required Energy(E) for towing application based on the assumed time,

Energy =`P * t`

= 55.78 * 0.5

= 27.89 kWh

Hence we will use a battery that stores more than 27.89 kWh energy.

We are using 'NetGain HyPer9 HV' AC Motor

Its maximum power is 88 kW

Let's assume continuous power is 80 kW

Hence,

Duty cycle =`(55.78/80)*100` = 80 %

80% will be used for a half-hour to complete the task in one cycle from zero to high.

Block diagram for the electric towing vehicle.

CONCLUSION:-

Weights of different aircraft are enlisted. The difference between airspeed and ground speed is explained. The reasons for not recommending the use of aircraft engine power is elaborated well. The force and power requirement is calculated for towing vehicles for pull purposes. And also electric drivetrain is designed for towing purposes.