Project-1: Powertrain for aircraft in runways
Part A:
1. Search and list out the total weight of various types of aircrafts.
Aircraft gross weight(also known as the all-up weight and abbreviated AUW) is the total aircraft weight at any moment during the flight or ground operation.
An aircraft's gross weight will decrease during a flight due to fuel and oil consumption. An aircraft's gross weight may also vary during a flight due to payload dropping.
At the moment of releasing its brakes, the gross weight of an aircraft is equal to its takeoff weight. during flight an aircraft's gross weight is referred to as the en-route weight or in-flight weight.
Weight of various types of aircraft weight :
1.Glider
Glider is a fixed wing plane that is supported in flight by the dynamic reaction of the air against its lifting surface , and whose free weight does not depend on an engine. most gliders do not have an engine , although motor glider have small engines for extending their flight when necessary by sustaining the altitude ( normally a saiplane is on a continuously descending slope) with some being powerful enough to take off self launch.
Weight of glider plane : 110 kg -200 kg.
2.Powered lift
A powered lift aircraft takes off vertically under engine power but uses a fixed wing for horizondal flight. these aircraft do not need a long runway to take off and land,like helicopters,but they have a speed and performance similar to standard fixed wing aircraft in combat or other situations.
Weight:180 kgs
3.fighter aircraft
Fighter aircraft is fixed wing military aircraft desing primarily for air combat against other aircraft. the key performance features of a fighter include not only its firepower but also its high speed and manuverability relative to the target aircraft.
weight : 13500 kgs
4. Transport planes :
Military transport aircraft or military cargo aircraft are used to airlift troops, weapons and other military equipment to support military operations. Transport aircraft can be used for both strategic and tactical missions, and are often diverted to civil emergency relief missions.
weight : 250,000 kgs.
5. Aerobatic planes.
An aerobatic aircraft is an aerodyne (a heavier-than-air aircraft) used in aerobatics, both for flight exhibitions and aerobatic competitions.
weight : 771 kgs.
2. Is there any difference between ground speed and air speed?
Ground speed is the airplane's speed relative to the surface of the earth.
Airspeed is the speed relative to the air it is flying in.
Ground speed is what determine how fast an aircraft will get to its destination.
Airspeed is what determine whether there is enough airflow around an aircraft to make it fly.
Ground speed is simple the sum of airspeed and wind speed. It is independent of ground speed.
3. Why is it not recommended to use aircraft engine power to move it on the ground at Airport?
Towing is coupling two or more objects together so that they maybe pulled by a designated power source or sources. the towing source maybe a motorized land vehicle,vessel,animal, or human, and the load being anything that can be pulled.
Although many aircraft are capable of moving themselves backwards on the ground using reverse thrust ( a procedure referred to as a powerback), the resulting jet prop might cause damage on 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 therfore the preferred method to move the aircraft away from the gate.
Although most aircraft are capable of moving themselves backwards on the ground using reverse thrust, a procedure called as a powerback, it is not typically done due to the following reasons:
1. The jet blast from the engines can damage the terminal building and nearby equipment. It can even throw away people standing nearby.
2. Engine can blow sand and debris.
3. Engine can suck in sand and debris which can cause serious damage to the engine.
4. It is easiar for the truck driver to see the surrounding better than the pilot sitting in the cockpit with limited windows.
5. The pushback truck drive knows the airport better than the pilot.
6. The plane engines are very loud. this noise can add up substantially when multiple planes are moving around the airport. It won't ba a pleasant, experience for people sitting inside the terminal,as mostpeople don't even like the sound of powerful motor-bikes.
7. It saves fuel. virgin atlantic had proposed a new system in which the pushback trucks will push the plane all the way to the runway to save fuel and reduce impact on nearby environment.
4. How an aircraft is pushed to runway when its ready to take off?
Taxiing is the movement of an aircraft on the ground, under its own power, in contrast to towiing or push-back where the aircraft is moved by a tug. The aircraft usually moves on wheels , but the term also includes aircraft with skis or floats (for water -based travel).
The power for taxiing comes from the engine itself. If it is a propeller powered aircraft,the propeller provides thrust and pulls the aircraft ,like it would in air. If it is a jet engine, the exhaust air that come out of the engine creates a forward foece due to newton's third law and moves the airplane.
Aieliners have nose wheel steering, Controlled by a cockpit control called a tiller allows nose wheel to rotate at quite extreme angles making tighter turns possible. It also reduce the fuel consumption as you do not need much engine power during taxiing. If rudders were used, the power has to be increased to make sure sufficient air flows over the rudder surface to make it effective.
Once on the take off roll and the airplane gains sufficient speed. i.e. enough air flows over the rudders,pilots go back to using the rudder pedals to maintain the centre line.
Some large airplane with multi wheel main gears have a tendency to scrub the tyre on the tarmac when nose wheel is steered. To counter this problem , an automatic main gear steering is inbuilt in the aircraft. This makes the ,main gears turn the opposite direction to that of the nose wheel, greatly decreasing the wear on the tyres.
Small general aviation aircraft uses the rudder for turns during taxi. They don't have a separate control ffor nose wheel. In such airplane to make tighter turns you could use differential braking. That is ,if you want to make a tight turn for example to the left rudder pedal which would apply left braking. This allows the airplane to make a sharper turn to the left.
5. Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
a.take off power :
takeoff is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne.For aircraft travelling vertically, this is known as liftoff. For aircraft that takeoff horizontally,this usually involves starting with a transition from moving along the ground on a runway. for light aircraft, usually full power is used during takeoff. large transport category(airliner) aircraft may use a reduced power for takeoff, where less than full power is applied in order to prolong engine life, reduce maintenance cost and reduce noise emissions.
After taxiing onto the runway, the airplane should be carefully aligned with the intended takeoff direction, and the nose wheel positioned straight, or centered. After releasing the brakes, the throttle should be advanced smoothly and continuously to takeoff power. An abrupt application of power may cause the airplane to yaw sharply to the left because of the torque effects of the engine and propeller. This will be most apparent in high horsepower engines. As the airplane start to roll forward the pilot should assure both feet are on the rudder pedals so that the toes or balls of the feet are on the rudder portions, not on the brake portions.
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 runways.
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 take-off run the imbalance along the runways.
dv/dt = (T-D-F)/m
Where dv/dt is the accelerating along the runways and m is the mass of the vehicle.
b. Tyre design :
When it comes to safety, Tyres are one of the most important components of aircraft. They 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, taxiing, and parking. the number of wheels required for aircraft increases with the weight of the aircraft, as the weight of the aero plane needs to be distributed more evenly.
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 aero plane.
3. Tyre also help 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 its operating at high speed for a short time when required.
C. Rolling resistance :
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) roll 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 hysteresis losses ( see below),and permanent (plastic) deformation of the object or the surface (e.g.,soil).
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 the ground , which is called slip loss or slip resistance . In addition , only the so called slip resistance involves friction, therefore the name "rolling friction" is to n extent a misnomer.
The "rolling resistance coefficient" is defined by the following equation:
F = Crr N
where ;
F = rolling resistance force
Crr = dimensionless rolling resistance coefficient or coefficient of rolling friction (CRF).
N = normal force, the force perpendicular to the surface on which the wheel is rolling.
D. Tyre pressure :
The typical airline tire can handle a 38-ton load. It can meet the ground 500 times before needing a re-tread,a refresh it can take on seven times in its life.
Aircraft tires generally operate at high pressure ,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), while its tail bumper gear tires were as high as 294 psi(20.3 bar).
E. Brake forces:
In 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.
Part B:
6. A. With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.
The force required to push / pull an aircraft by a towing are rolling resistance force and aerodynamic drag force.
1. Rolling resistance force :
As we have discussed in part-A 5c. It is the force resisting the motion when a body (such as a ball,tire, or wheel) rolls on a surface. Its governing equation is given as
F = Crr N
F = Crr*m*g
Where,
Crr = rolling resistance coefficient
m = mass of the body
g = acceleration due to gravity
2. Aerodynamic drag force:
It is the force opposing the motion of the body. the drag coefficient is a common measure in automotive design as it pertains to aerodynamics. Drag is a force that acts parallel to and in the same direction as the airflow. The drag coefficient of an automobile measures the way the automobile passes through the surrounding air. When automobile companies design a new vehicle, they take into consideration the automobile drag coefficient in addition to the other performance characteristics.
Aerodynamic drag increases with the square of speed; therefore, it becomes critically important at higher speeds. reducing the drag coefficient in an automobile improves the performance of the vehicle as it pertains to speed and fuel efficiency. the governing equation of these force is given as following:
Fd = (1/2) ρν^2 Cd A
Where ,
Fd = drag force
ρ = mass density of the air
ν = flow velocity relative to the object
Cd = drag coefficient
A= reference area
Calculation:-
Let us assume that,
mass of towing vehicle = 40,000 kg
mass of aircraft = 155,000 kg
Total mass (m)= 40,000+155,000 = 195,000 kg
Frontal area of the aircraft (A) = 18 m^2
speed of the vehicle ( V) = 25kmph
converting it into m/sec
v = 25*(1000/3600)=6.9445m/sec
Drag coefficient (Cd) = 0.75
Air density (ρ) 1.225 kg/m^3
calculation rolling resistance force (Frr)=Crr*m*g
=0.01 *195,000*9.8
= 19,110N
calculation Aerodynamic drag force (Fd) = (1/2) *ρ*ν^2 *Cd* A
= 0.5*1.225*0.75*18*(6.9445)^2
= 398.769N
Therefore the total force required to push/pull the aircraft by the towing vehicle (F) = Frr+Fd
= 19,110 + 398.769
= 19,508.769 N
Calculation the power (P)= force *velocity
= 19508.769 * 6.9445
=135.478kw
B. Develop the model for the calculated force and power using Simulink.
blocks used :-
1. Constant
2. Sum
3. Product
4. Square
5. Display
Simulink model:
Explaination:-
In order to understand the above simulink model we do reverse engineering.
1. For calculating power we have to multiply both total force(F) and velocity in m/sec for this we have used 'product' block (P=F*V).
2. For calculating the total force(F) we have added both Frr and Fd by using 'sum' block as shown in the above figure.
3. To find the value of rolling resistance (Frr) we used product to multiply the values Crr, total mass(m) and gravity (g) which are to be entered in the 'constant' block.
4. Similarly for calculating drag force(Fd) we have to multiply the velocity in m/sec, drag coefficient ,frontal area of aircraft(A) and a constant value 0.5 which are to be entered in 'constant' block.
5. In order to convert velocity in kmph to m/sec we have multiplied it with 5/18.
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.
Block diagram of powertrain :-
Based on the calculation done in 6A.
Force required to push/pull the aircraft = 19.508 KN
Power required = 135.478 Kw
Let us assume,
the radius of the tyre for the tug = 25inches = 0.635m
Gear ratio = 8
Transmission Efficiency (ηt)=87%
Motor Efficiency ( ηm)=95%
then,
Torque required for the wheels (TW)= Total force*Radius in meters
= 19.508*0.635
= 12.387 KNm
Motor Torque=Wheel torque / (Gear ratio*ηt)
= 12.387/(8*0.87)
= 1.778 kNm
For ηm = 95% The required motor torque(Tm)=1.778/0.95=1.871 KNm
Similary the total power required by the motor considering all the efficiencies(pt)=135.478/(0.87*0.95)=163.917Kw
Let us assume the towing operation was done for a 15 minutes (0.25 Hrs) duration.
Then ,total energy consumed = 163.917*0.25
= 40.98KWh
If we consider the battery capacity = 220Kw is used by the towing vehicle then, the duty cycle range to control the speed from 0 to 75% in order to control the towing speed.
therefore the controller will be able to provide a duty cycle ranging from 0 to 75% in order to control the towing speed.
Simulink diagram of powertrain:-
Inputs:-
Scope-1: Signal builder
Scope-2:- Battery
Output:-
Scope-3:- DC Drive output
Excel calculation:-
