Project-1: Powertrain for aircraft in runways

 AIM:- Powertrain for aircraft in runways

 

OBJECTIVE:-

1. Search and list out the total weight of various types of aircraft. 
2. Is there any difference between ground speed and airspeed? 

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

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

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

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

    7. Design an electric powertrain with a type of motor, its power rating, and energy requirement 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. 

 

OBJECTIVE:-1

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

The different terms represent different weights or masses.

For each flight, the weights are taken into account for several reasons.

 

Manufacturing empty weight (MEW)

Also called Manufacturer's Weight Empty (MWE) or Licensed Empty Weight.

It is the weight of the aircraft "as-built" and includes the weight of the structure, power plant, furnishings, installations, systems, and other equipment that are considered an integral part of an aircraft.

This excludes any baggage, passengers, or usable fuel.

 

Zero fuel weight:-

This is the total weight of the airplane and all its contents (including unusable fuel), but excluding the total weight of the usable fuel on board.

As a flight progresses and fuel is consumed, the total weight of the airplane reduces, but the ZFW remains constant.

Maximum zero fuel weight (MZFW) is the maximum weight allowed before usable fuel and other specified usable agents (engine injection fluid, and other consumable propulsion agents) are loaded.

Operating Empty Weight  (OEW)

 Roughly equivalent to basic empty weight on light aircraft

It is the basic weight of an aircraft including the crew, all fluids necessary for operation such as engine oil, engine coolant, water, unusable fuel, and all operator items and equipment required for flight but excluding usable fuel and the payload.

Read this from left to right, from detailed to generalized. Boxes on the right sum up the separate items which they run across.

 

Basic Empty Weight (BEW) 

 The weight of the aircraft "as-built" and includes the weight of the structure, power plant, furnishings, installations, systems, and other equipment that are considered an integral part of an aircraft before additional operator items are added for operation.

• Dry Operating Weight (DOW) BEW + Weight of Crew (Pilot + Cabin including their bags) + Pantry

• Operating Weight (OW) DOW + Takeoff fuel (i.e. Ramp Fuel - Taxi fuel)

• Maximum Zero Fuel Weight (MZFW) DOW + Payload (anything put on the aircraft that generates revenue to the company, e.g. passenger, baggage, cargo, mail and fret)

• Maximum Taxi Weight (MTW) MZFW + Ramp fuel

      . Maximum Takeoff Weight (MTOW) MZFW + Takeoff fuel, or MTW - Taxi fuel

      . Maximum Landing Weight (MLW) MTOW - Trip Fuel

 

OBJECTIVE:-2)

Is there any difference between ground speed and airspeed?

 

Airspeed is the vector difference between the ground speed and the wind speed. On a perfectly still day, the airspeed is equal to the ground speed.

But if the wind is blowing in the same direction that the aircraft is moving, the airspeed will be less than the ground speed.

 

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). 

 

Ground speed:-

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 is the vector difference between the ground speed and the wind speed.

Airspeed = Ground Speed - Wind Speed

On a perfectly still day, the airspeed is equal to the ground speed.

But if the wind is blowing in the same direction that the aircraft is moving, the airspeed will be less than the ground speed.

 

OBJECTIVE:-3)

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

For movement on the ground, the aircraft uses its own engine power, which is called taxiing.

Engine power is used all the time to move aircraft on the ground. 

 engine power is used all the time in the ramp.

They do get pushed back because the only aircraft with engines on the tail can power-back due to FOD.

Taxiing (rarely spelled taxying) is the movement of an aircraft on the ground, under its own power, in contrast to towing or pushback where the aircraft is moved by a tug.

Taxiing (rarely spelled taxying) is the movement of an aircraft on the ground, under its own power, in contrast to ... At low power settings, combustion aircraft engines operate at lower efficiency ... Skid-equipped helicopters and other VTOL (Vertical Take-Off and Landing) aircraft conduct hover taxiing to move in ground effect.

An airspeed indicates the aircraft's speed relative to the air mass.

The air mass may be moving over the ground due to wind, and therefore some additional means to provide position over the ground is required.

An airplane uses a taxiway to taxi from one place onto another; for example, when moving from a hanger to the runway.

The term "taxing" is not used for the accelerating run along a runway prior to takeoff, or the decelerating run immediately after landing, which is called the takeoff roll and landing rollout, respectively.

 

OBJECTIVE:-4)

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

The pilot releases the brakes and pushes the throttle to maximum takeoff power, and the airplane accelerates down the runway.

At some distance from its starting point, the airplane lifts into the air.

The Distance the airplane cover along the runway before it lifts into the air is called the ground roll (sg).

In aviation, pushback is an airport procedure during which an aircraft is pushed backward away from an airport gate by an external power. ...

The ground handler will show the bypass pin to the pilots to make it clear that it has been removed.

The pushback is then complete, and the aircraft can taxi forward under its own power.

 

Ready for take-off in steps

 

The pilot parks the aircraft in exactly the right place. Usually with the help of an automatic system, but occasionally guided by a marshaller waving two paddles or wands.

Dozens of handling personnel are already standing by to perform a whole range of tasks simultaneously.

As soon as the aircraft is stationary and the engines are switched off, the first priority is to disembark the passengers as quickly as possible.

Refueling begins, usually from a hydrant at the stand.

A hose is attached to this from a special vehicle called a dispenser, with the other side connected to the fuel tank in the wing.

Now it is time to service the aircraft.

The caterer loads new meals and takes away the food waste and used cutlery and crockery.

Other activities include draining the lavatories, replacing the headrest covers, removing rubbish, and distributing fresh blankets and in-flight magazines.

Take-off performance can be predicted using a simple measure of the acceleration of the aircraft along the runway based on force equilibrium.

The forces involved will be,

T – Thrust of propulsion system pushing aircraft along the runway.

D – Aerodynamic Drag of vehicle resisting the aircraft motion.

F – Rolling resistance friction due to the contact of wheels or skids on the ground.

During the take-off runs, the imbalance in these forces will produce an acceleration along the runway.

dV

dt

=

T−D−F

m

where dV/dt is the acceleration along the runway and m is the mass of the vehicle.

The procedure for take-off will be that the vehicle will accelerate until it reaches a safe initial flying speed.

The procedure for take-off will be that the vehicle will accelerate until it reaches a safe initial flying speed.

The pilot can then rotate the vehicle to an attitude to produce a climb lift and it will ascend from the ground.

The determination of this safe flying speed or rotation speed, V_R, is a critical factor in determining take-off performance.

Take-off rules vary slightly depending on the aircraft category.

Small commuter aircraft should be considered as meeting FAR 23 rules, transport category aircraft should comply with FAR 25 rules.

 

 

 

OBJECTIVE:-5)

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

Friction is a crucial factor affecting air accident occurrence on landing or taking off.
Tire–runway friction directly contributes to aircraft stability on land.

The aircraft taxiing on runways relies on the friction generated by the tires and the runway surface, which enables the aircraft to safely accelerate, turn, taxi, and eventually stop the aircraft from moving.

Airfield performance of an airplane plays an important role in the analysis of takeoff and landing and determines, among others, ground roll distances.

Forces and moments that act on aircraft landing gear wheels are effects of gravitational acceleration, as well as surface reactions.

These reactions are easily obtainable on paved runways, but difficulties arise when an airplane operates on unpaved, grassy, or gravel surfaces.

The model will respect non-linear, dynamic effects such as hyper-elastic tire deflection, rheological soil response to high rate deformation, and effects of grass and roots.

 

 

Tire design:-

An aircraft tire or tire 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 crosswind conditions, to channel water away to prevent hydroplaning, and for the 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.

 

 

Tire pressure

Tests of airliner aircraft tires have shown that they are able to sustain pressures of a maximum of 800 psi (55 bar; 5,500 kPa) before bursting

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.

The requirement that an inert gas, such as nitrogen, be used instead of air for inflation of tires on certain transport category airplanes was prompted by at least three cases in which the oxygen in air-filled tires had combined with volatile gases given off by a severely overheated tire and exploded upon reaching autoignition temperature

 

 

Brake forces when landing

The most common type of brake used on aircraft is the disc brake. 

Disc Brake functions by exploiting friction between rotating and stationary discs inside the brake.

Upon receiving a command signal to brake — from the pilot depressing a foot pedal or from the auto brake system — actuators in the brake move a piston to squeeze the discs together, generating a frictional force that slows the rotation of the wheel.

In this function, the brakes act as a heat sink, absorbing tremendous amounts of heat as the aircraft sheds kinetic energy.

During RTO stops, the temperature of carbon disc brakes can exceed 1,800° C.

 

The maximum take-off weight of an A380 is 575,000 kg (1,267,658 lb) and its maximum V₁ is around 170 knots (about 195 mph or 87 m/s).

A rough estimate for the maximum energy that the A380’s 16 brakes need to dissipate during RTO can be obtained by calculating the kinetic energy of the aircraft (neglecting the effects of thrust reversers, air brakes, tailwinds, headwinds, and runway slope).

KE = ½mv²

^{E = 0.5 * 575,000 kg * (87.4556 m/s)2 = 2.2 x 109 J = 2.2 GJ}

Rolling Resistance:-

The rolling resistance of an aircraft rolling along with a snow runway

Drolling = Dr + Dc + Dd

Dr = is the rolling resistance on a dry hard surface.

Dc and Dd are for single tires.

The aircraft has at least 3 tires.

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

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 tarmac.

The force that resists the motion of a body rolling on a surface is called the rolling resistance or the rolling friction.

 

Force required to pull an airplane at constant low speed on tarmac

If the mass of a plane is 40000 kg and the rolling resistance between the aircraft wheel and the tarmac is 0.02 - the force required to overcome the rolling resistance can be calculated as

F_r = 0.02 (40000 kg) (9.81 m/s²)

   = 7848 N  

This force can be delivered by a pulling truck or - as occasionally seen - by a number of pulling people. Enough weight for the pullers is required to create friction forces against the tarmac that equals the plane rolling resistance.

The friction force for the puller can be calculated to

F_f = μ W

   = μ mf a_g                      

where

F_f = frictional force (N, lb)

μ = friction coefficient

W = weight(N, lb_f)

m_f = friction mass (kg)

 

Air Craft Pulled by People

When persons participate in aircraft pulling there is normally an offset between the rope connected to the aircraft nose wheel and the tarmac. It is common for persons to bend over with the rope over the shoulder or holding it in the hands.

The horizontal friction force between the person's shoes and the tarmac must be equal to or larger than the airplane rolling resistance. 

The minimum required vertical force - or a minimum weight of the people - depends on the bending angle as illustrated in the vector diagram below.

 

 

If they bend over 45^o - the vertical force or weight equals the horizontal force.

 

 

 

QUESTION - 6
Solution:-
Assumed values are given below:-
mass of aircraft(m1) = 40000kg
mass of the Towing machine(m2) = 30000kg
Coefficient of rolling resistance of aircraft (u) = 0.004
Coefficient of Rolling Resistance of towing vehicle (u) = 0.002
Drag coefficient of aircraft [cd1] = 0.11
Drag coefficient thug  [cd2] =  0.6
The frontal area of aircraft (A1) = 300m^2
The frontal area of towing (A2) = 40m^2
Towing speed (v) = 3m/s
Air density  = 1.25
Gravity Acceleration (g) = 9.81m/s^2
Calculation:-
we know that
Rolling Resistance force = fr = umg
where m = mass of aircraft towing and mass
u = coefficient of Rolling Resistance (m/s^2)
g = acceleration due to gravity(m/s^2)
Drag force
Fd = 1/2*density *A*cd*v^2
Rolling Resistance force of Aircraft
Fr1  = u1*m1*g = 0.005*4000*9.81
Fr1 = 1962
Rolling Resistance force of towing.
Fr2  = u2*m2*g = 0.002*30000*9.81
Fr2 =589N
Now to calculate Drag force.
we know that
Fd1 = 1/2*density*area*cd*v^2
216
Fd2 = 1/2*density*A2*twoning*v^2
Fd2 =141.75N
Total force(F) = Fr1+Fr2+Fd1+Fd2
Total Required to push-pull the aircraft
Power = (total force)*(velocity)^2
2908.75
2908.75*3^2
2617.75

 

clear all
close all
clc
%mass of the Aircraft
mass = 70000;

%Acceleration OF THE Aircraft
g = 9.81;

%cofficient rolling resistance
ur = linspace(0.006, 0.008,3);
%Density of Air
 rho=  1.25;
 %Frontal Aera of Aircraft
 Area = 340;
% coefficient of drag
c_d = 0.17;
%speed of towing vehicle
 v =3;
 slope = 0.035;
 Ft = [];
 
 for i = 1:length(ur)
     Fr = ur(i)*mass*g;
     Fd = 0.5*rho*Area*c_d*(v^2);
     Fh = mass*g*sin(slope);
     Ft(i) = Fr + Fd + Fh;
 end
 power =(Ft*v)/1000
 %plot
 plot(power,ur)
 xlabel ('Tractive ,power(kw)')
 ylabel('coefficient of Rolling Resistance ur')
 title('variation of tractive power with ur')
 

Result:-

 

OBJECTIVE:-7

Design an electric powertrain with the type of motor, its power rating, and energy requirement 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. 

Solution:

-From the above calculation we came to know that the Force required to push or pull the aircraft which is around 5.911KN and the power required is around 26.178 KW.

-Now we need to find out the torque required at the thug's wheel, motor torque and its efficiency, and also its duty cycle.

 

 

 

 

 

 

 

 

 

Result:

• The reference Aircraft Taken here is the Heavy Aircraft build and so our designed towing tractor is a heavy-duty operational vehicle.
• The power requirements are calculated for the particular load to be pushed/pulled and to achieve this power at the motor output, the motor type and its voltage at the terminals are discussed
• Then the power converters are used to upscale the battery armature voltage to the desired high voltage value so that the motor may spin full power and the required torque can be achieved using a Bidirectional DC-DC Converter.
• Finally, the speed control of the vehicle is done with Switching techniques where the duty cycle adjustment can change the motor speed from minimum to maximum.