Project-1: Powertrain for aircraft in runways

Although many aircrafts move in back ward using reverse thrust as a result. The jet blast or prop wash might damage the terminal building and other equipment. Engine close to ground may also damage the engine. This may cause the huge damage to the aircraft. Hats because pushback trucks are provided for the backword movement of crafts in airports. A push back truck lifts the front wheel of the aircraft. Their (push back truck) role is to move the aircraft away from the parking area.

During high power engine running damage can occur itself to the aircraft. It is easier to the truck driver to see the outside and drive the vehicle compared to the pilot. The push back driver knows well about the airport compared to pilot. Another main thing is it saves the huge fuel for such a small thing. These may damage the aircrafts which are next to it in reversing by itself. Huge risk of jet blast and surrounding buildings,

The aircraft is in parking place before it goes to the runway the thing is when it needs to fly it needs to come back to the runway to fly.

The aircraft can itself move backwords although it is risky for the aircraft and the surrounding's it uses the towing system.

The forward movement of an aircraft, usually with engines off, using the power of a specialised ground vehicle attached to or supporting the nose landing gear. It may occur for the movement of both in service and out of service aircraft.

Before the aircraft to be towed is moved, a qualified person must be in the flight deck to operate the brakes in case the tow bar fails or becomes unhooked. The aircraft can then be stopped, preventing possible damage.

Towing aircraft can be a hazardous operation, causing damage to the aircraft and injury to personnel, if done recklessly or carelessly. ... The aircraft can then be stopped, preventing possible damage. Some types of tow bars available for general use can be used for many types of towing operations.

Towing:

In the parking areas, where taxing the aircraft is not practical or is unsafe, such as moving aircraft in and out of maintenance hangars, or moving aircraft that are not under their own power or moving backwards, then towing of aircraft is performed using the power of a specialized ground vehicle attached to or supporting the nose landing gear. The traditional method of allowing the ground vehicle to move an aircraft is to attach it to the aircraft nose landing gear by means of towbar.

As a pilot can’t see what is behind the aircraft, steering is done by pushback tractor driver and 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 towing is completed, the towbar is disconnected and the aircraft can taxi forward under its own power.

Taxiing:

Taxiing is the movement of an aircraft on the ground under its own power while on the surface. The aircraft always moves following the yellow lines, to avoid collision with the surrounding buildings, vehicles or other aircrafts. The taxing motion has a speed limit. Before making a turn, the pilot reduces speed further to prevent the tires skids just like other vehicles. The reason for taxing is to reach the vehicle into the runway or from the runway to the terminal.

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

The amount of power that an engine is allowed to produce for a limited period of time for takeoff. The use of takeoff power is usually limited to 5 min for reciprocating engines and up to 2½ min for gas turbine engines. This may not always be the case. Specifically, with respect to reciprocating engines, it is the brake horsepower developed under standard, sea-level conditions and under the maximum conditions of the crankshaft rotational speed and the engine manifold pressure approved for the normal take-off. It is limited in continuous use to the period of time shown in the approved engine specifications. With respect to gas turbine engines, it is the thrust developed under static conditions at a specified altitude and atmospheric conditions of the rotor shaft rotational speed and gas temperature approved for the normal takeoff. It is limited in continuous use to the period of time shown in the approved engine specifications.

Tyre Design:

The tryes help to absorb the shock of landing and provide cushioning. It also provides the necessary traction for braking and stopping of an aircraft.

An aircraft tyre 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 aeroplane needs to be distributed more evenly.

Design:

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

• They support the weight of an aircraft while it is on the ground.
• It also provides the necessary traction for braking and stopping of an aeroplane.
• 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 tyre, 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.

Aircrafts tyres are manufactured with tread rubber with conducting compounds to permit earthing of static charges.

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 of the wheel, roadbed, etc., is recovered when the pressure is removed. Two forms of this are hysteresis losses, and permanent (plastic) deformation of the object or the surface. Note that the slippage between the wheel and the surface also results in energy dissipation. Although some researchers have included this term in rolling resistance, some suggest that this dissipation term should be treated separately from rolling resistance because it is due to the applied torque to the wheel and the resultant slip between the wheel and ground, which is called slip loss or slip resistance.

Tyre Pressure:

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).

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.

Landing Brake Forces:

On other aircraft types, the brake units are powered by the hydraulics system. An electrical signal is sent from the flight deck to hydraulic actuators near the main landing gear. Here, hydraulic fluid at 3,000 pound per square inch is used to force the brake unit against the wheel, thus slowing it down.

Aircraft braking systems include:

• Aircraft Disc Brake: In the landing gear it is used to brake the wheels while touching the ground.These brakes are operated hydraulically. In most modern aircraft they are activated by the top section of the rudder pedals (“toe brakes''). In some older aircrafts the bottom section is used instead (“hee brakes”). Levers are used in a few aircraft. Most aircraft are capable of differential braking.

• Thrust Reverse: that allows thrust from the engines to be used to slow the aircraft.

• Air Brake: It is a dedicated flight control surface that works by increasing drag.

• Drogue Parachute: It is used by several former and current military and civilian aircraft (examples include the American B-52 and the sovient Tu-134 & 144).

-Take off is the phase of the flight in which an aeroplane leaves ground and becomes airbone.For lighter aircraft full power is given during take off whereas on the other hand large cargo carriers aircraft make use of less power during take-off in order to increase the life span of engine, reduce maintenance cost, reduce engine heat and also for a smooth take off flight.

-The forces involved during take-off are the following:

T=Thrust force pushes the aircraft in forward directions on the runway.

D=Drag force resist the forward motion of the aircraft.

F=Rolling resistance force when wheel comes in contact with the ground during landing and take-off.

-During take-off on the runway the imbalance force will cause an acceleration along the runway and it is given by the formula:

dv/dt=T−D−Fm

-Now when the pilot is ready to take off the aircraft will accelerate to a speed which would be given by aircraft controlling department. Then after take-off the flight will be elevated to a certain angle and hieght.then it will be made to stabilise in an equilibrium manner.

-Here safe speed or rotational speed is defined as Vr which act as a critical factor for determining take off performance. For safety reasons Vr is usually determined as 1.1*Vstall(lowest speed that aircraft can be flown before the air starts to separate from the wings when the angle of attract becomes too great.

-Vstall can be calculated by using a formula given:

*Tyre design of an aircraft:

-An aircraft tyre is designed to withstand extreme heavy loads by absorbing shocks during and there by providing cushioning effect.

-The number of tires required for an aircraft depends on the total weight of aircraft as the weight needs to be distributed evenly.

-Aircraft tyre is designed to facilitate stability in high crosswind condition, to channelize the water away for preventing skidding and helps to give a good braking effect.

-Aircraft tires are usually inflated by nitrogen air in order to reduce expansion and contraction from extreme changes in ambient pressure and tempurature.This type of inert gases will eliminate the possibility of tire explosion.

-Aircraft tire design are set into an aircraft based on its application and also sufficient clearance with the ground for allowing tyre growth which happens when centrifugal force is at high speed.

*Rolling Resistance:

-Rolling resistance or rolling drag is the force resisting the motion when the body rolls on a surface and it is mainly caused by non-elasticity that is not all the energy needed for deformation of wheel is recovered when the pressure is removed.

-The rolling resistance equation can be defined by the following equation:

-Usually aircrafts have a very low rolling resistance coeffiecient of 0.06. Some other examples are as follows:

*Tyre Pressure:

-Aircraft tyres are designed to withstand heavy loads and shocks during landing and take-off and also needs to distribute weight evenly.

-As per research and testing it is found that aircraft tyres are able to sustain pressure up to 800 psi.Generally to note the tyre pressure of an aircraft a special type of sensors are used, its diagram is given below:

-There are 2 primary parameters which is hazardous to the aircraft tires:

I)Deflation:

Here the tire deflates in a controlled manner with minimum direct consequence to other system.

II)Explosive breakup:

In this case the tire deflates or bursts in an uncontrolled manner with a probability of causing damage to other secondary system, which further can cause a major crash-landing incident.

*Brake forces:

-Braking an aircraft is a challenging job for most of the pilots especially during landing in a rainy and cross wind environment.

-In order to encounter these kinds of problem pilots usually make use of spoilers and reverse thrust method in order to have a safe landing so that the energy required to apply brakes on tires can be reduced and henceforth they do not skid.

-Now there is method which determines the brake force for aircrafts and they are as follows:

k=12mv2, where m= mass of aircraft and v=velocity of aircraft. A typical commercial landing speed will range between 150 to 165 MPH. AND for passenger flight it is about 166 to 172mph.

The drag force acting on the tow will be :

The drag force D exerted on a body traveling though a fluid is given by

C is the drag coefficient, which can vary along with the speed of the body. But typical values range from 0.4 to 1.0 for different fluids (such as air and water)

ρ is the density of the fluid through which the body is moving

v is the speed of the body relative to the fluid

Now the tractive force or the pulling force required by the tow will be

Pulling force = Drag force + friction force + Rolling resistance force

Now let us consider aircrafts with the following specifications :

Now as we have seen that various kinds of planes have different weights ,the amount of pulling force also will be different .Therefore we will consider a range of weight :

Range of weight = 200 kgs - 250000 kgs '

The towing speed considered is 5 m/s

Area range : 50 - 100 m^2

Coefficient of rolling resistance : 0.02

Coefficient of friction : 0.01

clc 
clear all 

%Inputs
c=0.002;%Rolling resistance coefficient
m=linspace(200,25000,2000); % Weight
g=9.81; %acceleration of gravity
u=0.6;%friction coefficient
A=linspace(50,100,2000);%area of planes
v=2; % velocity
Cd=0.8; %Drag Coefficient
%Calculations

F1=c*m*g; %Rolling resistance force
F2=u*g*m;%Friction force
F3=0.5*A*1.2*Cd*(v)^2;
Ft=F1+F2+F3;

plot(m,Ft)
title('Tractive Force vs Weight of planes')
xlabel('Weight of planes(kg)')
ylabel('Tractive Force')
axis([0 2000 0 20000])

Part B:

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

To propel any vehicle we need to overcome several opposite forces acting on the same vehicle .

The actual forces acting on the vehicle varies from place to place.

Let us consider the regular runway the opposite forces are acting to propel the vehicle are

Rolling resistance force (Frr)

and aerodynamic drag force. (Fad)

there is no grade so hill climbing force (Fhc)is neglected.

The sum these forces is actual or total force (Fte) to overcome to propel the vehicle.

Frr=m.g.μrr;

Fad=1/2*ρACdv^2;

where,

m-mass of the vehicle(kg)

g-gravitational constant. (kg/m^2)

μrr-rolling resistance

ρ-air density(kg/m^3)

A-frontal area(m^2)

Cd-aero drag coefficient

v-velocity of the vehicle(m/s)

Fte=Rolling resistance force (Frr)+aerodynamic drag force.(Fad)

Fte=mgμrr+1/2*ρACdv^2

assume any vehicle (aircraft):

some of the assumptions are:

mass of the aircraft (ma)=24500kg;

mass of the towing vehicle=10000kg;

gravitational constant(g)=9.81m/s^2;

rolling resistance(μrr)=0.05;

air density(ρ)=1.5kg/m^3;

frontal area (A)=10m^2;

aero drag coefficient (Cd)=0.4+0.2=0.6;

velocity(v)=21.6km/hr=6m/sec

Frr=mgμrr

=(24500+10000) *9.81*0.05

=16922.25N

Fad=1/2*ρACdv^2

=0.5*1.5*10*0.6*6^2

=162N

Fte=mgμrr+1/2*ρACdv^2

=16922.25N+162N

=17084.25N

force required to pull or push the vehicle Fte=7909.9488N

torque at the wheels =force *radius

=17084.25*0.2(tire radius=0.2m)

=3416.85Nm

power required to pull the vehicle;

we know;

power(p) =force *velocity

=Fte*v

=17084.25*6

=102505.5watts

=102.505kw

The power required to propel the vehicle is 102.505kw.

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

With necessary assumptions, calculated the force and power required to push / pull an aircraft by a towing vehicle. Develop the model for the calculated force and power using Simulink. Designed an electric powertrain with type of motor, it’s power rating, and energy requirement to fulfill aircraft towing application in Simulink. Estimated the duty cycle range to control the aircraft speed from zero to highest. plotted necessary required graphs.