Project-1: Powertrain for aircraft in runways

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

Maximum taxi weight (MTW)

The maximum taxi weight is the maximum weight authorized for maneuvering (taxiing or towing) an aircraft on the ground as limited by aircraft strength and airworthiness requirements. It includes the weight of taxi and run-up fuel for the engines and the APU.

Maximum takeoff weight (MTOW)

The maximum takeoff weight is the maximum weight authorized at brake release for takeoff, or at the start of the takeoff roll.

The maximum takeoff weight is always less than the maximum taxi weight as the fuel burned during taxi by the engines and the APU are reduced.

Maximum landing weight (MLW)

The maximum weight authorized for the normal landing of an aircraft. The MLW must not exceed the MTOW. The fuel load of the plane is reduced during the journey.

Maximum zero-fuel weight (MZFW)

The maximum permissible weight of the aircraft less all usable fuel and other specified usable agents. It is the maximum weight permitted before usable fuel and other specified usable fluids are loaded in specified sections of the airplane.

Takeoff Run (TOR)

The length of the runway declared available and suitable for the ground run of an airplane taking off.

Landing Run (LR)

The length of the runway that is declared available and suitable for the ground run of an airplane landing.

MTOW = Maximum take-off weight, MLW = Maximum landing weight, TOR = Take-off run , LR = Landing run.

2. Difference between ground speed and airspeed? 

Airspeed - It is the speed of the airplane relative to wind surrounding the plane. It is measured using the pitot tube mounted on the nose or wings of the airplane. It is the measured quantity. 

Ground speed - It is the horizontal speed of an aircraft relative to the ground. An aircraft heading vertically would have a ground speed of zero. Ground speed can be determined by the vector sum of the aircraft's true airspeed and the current wind speed and direction.

V_P/G - Velocity of ground with respect to the ground.

V_P/W  - Velocity of the air.

V_W/G  - Velocity of the wind.

The velocity of the wind acts in two ways i) towards & against the direction of the plane.

                                                            ii) Perpendicular to the direction of the plane.

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

Jet blast is the phenomenon of rapid air movement produced by the jet engines of aircraft particularly on or before takeoff. A large jet-engined aircraft can produce winds of up to 100 knots (190 km/h; 120 mph)  as far away as 60 meters behind it at 40% maximum rated power. Jet blast can be a hazard to people or other unsecured objects behind the aircraft and is capable of flattening buildings and destroying vehicles.

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

The aircraft is pushed to the runway using a taxing vehicle. 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. 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.

5. Takeoff power

Takeoff is the phase of flight in which an aircraft goes through a transition from moving along the ground (taxiing) to flying in the air and during this phase the engines are run at full power during takeoff. Aircraft employ the concept of the takeoff V-Speeds, V1 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. 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, Then, V2 (the safe takeoff speed) is called. This speed must be maintained after an engine failure to meet performance targets for the rate of climb and angle of climb. The power required to achieve the takeoff speed is Takeoff power. 

Tyre Design

Tires are used to absorb the shock of landing and provide cushioning. It is made up of three components steel, rubber & fabric. It also provides the necessary traction for braking and stopping of an aircraft. An aircraft tire 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 airplane needs to be distributed more evenly.

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.

Rolling Resistance

6. Calculate the force and power required to push/pull an aircraft by a towing vehicle.                                                  

The two forces which are acting on the vehicle are drag force & rolling resistance force since the vehicle moves on the plane & the parameters for it are assumed.

Thrust

The thrust of the gas turbines or turbofan engines will be relatively constant during take-off. A good assumption is to use the manufacturer's values for maximum static thrust for take-off calculations.

The thrust of a propeller-driven aircraft can be found from the given shaft horsepower data for the engine and the use of the equations using propeller efficiency given in the previous section.

It is critical to correctly estimate the propeller efficiency for the particular aircraft velocity along the runway. At V=0 the efficiency is 0 so the above equation makes no sense. At V=V_R the efficiency will be in the range 50% to 80% depending on the type of propeller system used and the thrust value at this point will be easy to obtain. In practice, the thrust obtained throughout the take-off roll is roughly constant so this endpoint value is a good approximation from V=0 to V=V_R

Drag

The resistance to motion due to the air viscosity will give a drag resistance

where,

F_ad  = 0.5*ρ* C_d * A*V²

F_ad - Drag force (N)

ρ - Density (kg/m3)

C_d - drag coefficient

A - Frontal Area (m2)

V - Velocity (m/s)

Rolling Resistance

The friction between aircraft and runway will be proportional to the normal force exerted by the aircraft on the runway.

     
Average acceleration and distance to the rotation

The rate of change of velocity can be predicted at any point on the take-off roll by substituting results for T, D and F into the initial equation for dV/dt. The subsequent velocity at any point can be found by integrating this resulting equation and the distance traveled found by then integrating the velocity.

The force to move an airplane on an absolute flat runway with no wind at constant low speed is equal to the rolling resistance between the plane and the surface.

F_r = c * m_r * a_g                                  

where

F_r = rolling resistance (N)

c = rolling resistance coefficient

m_r = rolling mass (kg)

a_g = acceleration of gravity (9.81 m/s²)

The normal force will be the difference between Weight of aircraft and Lift, the friction coefficient will be typical of the magnitude of 0.02 for a standard tarmac runway.

Consider the Boeing 737 flight parameters for our calculation

Matlab Code

% Boeing 737 flight
% Power required for the towing vehicle

clear all
close all
clc

% Input parameters 
rho = 1.225;  % Density
Cd = 0.25;    % Drag coefficient
A = 2.5;      % Frontal area
V = 11.11;    % Velocity of vehicle
Cr = 0.02;    % Rolling resistance coefficient
g = 9.81;     % Acceleration due to gravity
Ma = 80000;   % Mass of aircraft
Mv = 4205;    % Mass of the towing vehicle

% Rolling resistance force
Fr= Cr*(Ma+Mv)*g;
fprintf('Rolling resistance force = %0.2f in N',Fr)

% Drag force 
Fad = 0.5*rho*Cd*A*V^2;
fprintf ('\nDrag force = %0.2f in N',Fad)

% Power calculation
P = (Fr+Fad)*V/1000;
fprintf ('\nTowing vehicle power = %0.2f in kW\n',P)

Results

7. a) Motor Type

The Induction motor is preferred over BLDC motor for high kW range due to its operating range and cost. 

b) Power rating 

The power required by the motor is 184 kW since the motor has an efficiency of 90% & the motor is designed to run at 80% of the full capacity for the safe operations in the motor. The 250kW power motor is chosen for our application.

Power rating - 250kW.

c) The energy required for aircraft

The mass of the vehicle of 84205 kg.

Energy = P*T

P - Motor power (kW).

T - Taxing time (s).

The average taxing time for an aircraft is 10mins (i.e) 600 seconds.

E = 184.28*600.

   = 110.57 MJ.

The energy required for the vehicle is 110.57MJ.

d) Duty Cycle range

The 250kW motor has a full load current of 420A & a full voltage of 400V.

Pin = Iin * Vin.

Vin = 250/420.

Pout = Iout * Vout.

The current at the input and output are the same. So the ratio power at input & output is equal to voltage ratio.

Pout / Pin = Vout / Vin.

184.25/250 = 0.737.

The duty cycle range is from 0 to 73.7%.

e) Block diagram