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PART-A 1. Manufacturer's Empty Weight(MEW): It is the weight…
Appala Pavansai
updated on 27 Apr 2021
PART-A
1.
Manufacturer's Empty Weight(MEW):
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(ZFW):
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.
Payload:
It is the carrying capacity of an aircraft. It includes cargo, people, extra fuel. In the case of a commercial airliner, it may refer only to revenue-generating cargo or paying passengers.
Maximum Take-off Weight(MTW):
This is the maximum weight at which the pilot of the aircraft is allowed to attempt to take off.
Regulated Take-off Weight(RTW):
Depending on different factors (e.g. flap setting, altitude, air temperature, length of runway), RTOW or maximum permissible take-off weight varies for each takeoff. It can never be higher than MTOW.
Maximum Landing Weight(MLW):
This maximum weight at which an aircraft is permitted to land. The following image depicts takeoff weight components:
Maximum Ramp/Taxi Weight(MRW/MTW):
It is the maximum weight authorized for maneuvering (taxiing or towing) an aircraft on the ground.
Aircraft Gross-Weight:
It is the total aircraft weight at any moment during the flight or ground operation. This decreases during the flight due to fuel and oil consumption.
The above figure is a rough estimation of weight parameters for different aircraft.
Now we will see the gross weights of different Aircrafts available:
(a) Airbus [A 300,318,319,320,321,330,340,350,380] ---- (500000 - 600000kg)
(b) Boeing [B 747-8F,737,747,757,767,777,787] ---- [200000 - 447700kg]
(c) Single engine-piston ---- (< 5700kg)
(d) Business Jets ---- [7000 - 15000kg]
(e) Tricycle gear ---- [5000 - 10000kg]
(f) Taildraggers ---- [5000-10000kg]
(g) Light sport Craft ---- [5000 - 10000kg]
(h) Biplanes ---- [80000kg(41000 plane, 18000 fuel)]
(I) Sea planes ---- [5000-10000 kg]
(j) Turboprops
(k) Helicopters ---- [5000-22000kg]
(l) Tilt rotor planes ---- [max11000kg]
(l) Airship ---- [5000-10000kg]
(m) Convair 880 ---- 87500kg
(n) de Havilland Comet 4 ---- 70700kg
(o) HS -121 Trident ---- 65000kg
(p) Embraer 190 ---- 48000kg
(q) Home builts
2.
Ground speed is the horizontal speed of an aircraft relative to the Earth's surface. ... An airspeed indicator indicates the aircraft's speed relative to the air mass.
Airspeed is the speed of an aircraft relative to the air through which it is moving.
In simple words, we can imagine Ground speed is how fast an airplane's shadow would move across the land. If there's a strong wind pushing an aircraft, that's reflected in the ground speed.
Airspeed, in contrast, is how fast an airplane is really flying strictly under its own power, which is calculated by subtracting the wind speed from the ground speed
The above is an example that represents the speed of an aircraft that cruises at an airspeed of 500 miles per hour that has to cover a ground distance of 2,000 miles.
This is a relative velocity of an aircraft defined by NASA.
It is like a vectorial representation of the aircraft's speed when it is in the air.
This is the mere explanation of ground and true air/wind speed.
3.
In airports, aircraft usually do not use their main engines to travel from shed's to runway i.e., when on the ground because of the following reasons:
• Modern planes are huge. It is difficult to navigate such gigantic structures through limited space. An A380 is eight stories high. The pilots won't be able to see anything directly in front of them or anything behind the wings.
The plane engines are very loud. This noise can add up substantially when multiple planes are moving around the airport. It won't be a pleasant experience for people sitting inside the terminal, as most people don't even like the sound of powerful motor-bikes. . It saves fuel.
The vehicles used for this towing or moving from terminal to runway are called Taxiing. Here the fuel cost is also reduced to a great extent. And nowadays electric taxiing is becoming more economical and efficient way.
TOWING VEHICLE IN AIRPORT
This became revolutionary in the aircraft industry, Which nearly saves an average annual savings of US$250,000 per aircraft, with some airlines seeing savings of as much as US$500,000 per aircraft along with a reduction of their environmental footprint.
4.
SMALL TOW BAR
Powered TOW BAR
5.
In order to understand the part this 35 feet screen height plays in the takeoff, we first need to look at the various distances that affect the take-off performance of an aircraft.
(a) Take-Off Run Available(TORA) -- the distance from the point at which the aircraft can start its takeoff run to the point at which the surface can no longer bear its weight.
(b) The clearway -- area at the end of the TORA that is free from any obstructions exceeding 0.9 meters in height like buildings or trees. The aircraft can use this area in order to achieve the 35 feet screen height.
(c) Takeoff Distance Available(TODA) -- The TODA is the total distance that the aircraft has to start its takeoff run and climb to the 35 feet screen height. On a runway without a Clearway, the TODA will equal the TORA.
(d) Accelerate Stop Distance Available(ASDA) -- The distance of weight-bearing surface available to the aircraft to accelerate and then come to a safe stop in the case of a rejected takeoff.
Now to analyze the take-off power of an aircraft we should consider the parameters like
D= drag force
F = rolling resistance
T = thrust of the propulsion
During take-off: m*dv/dt = T -F -D, where m=mass of aircraft; dv/dt is the acceleration
Now the vehicle will reach its safe flying speed. The safe flying speed is represented by 'Vr'
Vr = 1.1*Vstall
where Vstall = √(2*(G/S)/(ρ*Clmax))
G = aircraft weight; S = aircraft wing area; Clmax = lift co-efficient; ρ = density of air
here we consider the displacement as 2*S
Takeoff power = force*displacement = (m*dv/dt)*2*S = (T -F -D)*S
Tyre Design:
The material used to manufacture the tire is Carcass plies. They are sometimes called casing plies. An aircraft tire is constructed for the purpose it serves.
Wheel construction:
The typical modern two-piece aircraft wheel is cast or forged from aluminum or magnesium alloy. The halves are bolted together and contain a groove at the mating surface for an o-ring, which seals the rim since most modern aircraft utilize tubeless tires. The bead seat area of a wheel is where the tire actually contacts the wheel. It is the critical area that accepts the significant tensile loads from the tire during landing. To strengthen this area during manufacturing, the bead seat area is typically rolled to prestress it with a compressive stress load.
Need of aircraft tire:
Aircraft wheels are an important component of a landing gear system. With tires mounted upon them, they support the entire weight of the aircraft during taxi, takeoff, and landing. The typical aircraft wheel is lightweight, strong, and made from aluminium alloy. Some magnesium alloy wheels also exist. Early aircraft wheels were of single-piece construction, much the same as the modern automobile wheel. As aircraft tires were improved for the purpose they serve, they were made stiffer to better absorb the forces of landing without blowing out or separating from the rim. Stretching such a tire over a single-piece wheel rim was not possible. A two-piece wheel was developed.
This is designed for thermal stress it experiences during flight take-off and landing.
Below the figure is the entire components-wise integration inside an aircraft tire.
Technical aspects of the tire are:
Nowadays only tubeless tires are being used in aviation construction.
The above are the variations available in tires, however now all the aviation companies are using radial type.
All the aircraft tires should meet the approved standards before being accepted by the FAA or CAA.
All commercial aircraft tires approved under FAA Requirement Technical Standard Order (TSO) C62. A TSO is a minimum performance standard for specified materials, parts, and appliances used on civil aircraft.
rolling resistance:
Rolling resistance sometimes called rolling friction/ drag, is the force resisting the motion when a body rolls on a surface. Its mainly caused by non-elastic effects that are, not all the energy needed for deformation (or movement) of the wheel, roadbed, etc., is recovered when the pressure is removed.
Now, to calculate the rolling resistance of an aircraft tire, the coefficient of rolling resistance
Crr = √(z/d); where z = sinkage depth
d = diameter of rigid wheel
F = Crr*N; where F = rolling resistance force, N = normal force
Usually friction coefficient will be around 0.02 for a standard runway.
Tire 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).
The different layers in a tire are shown above which reflects the tough protection provided for an aircraft tire.
This is the tire pressure and maintenance values for a usual domestic aircraft.
Brake Forces:
There are two kinds of brakes in an airplane: air brakes and landing brakes. Just like the brakes on a vehicle, the wheels of most airplanes also have brakes. But those can only be used when the plane touches the ground.
Forces acting on an aircraft after landing are rolling friction force(Froll), drag force(Fd), braking force(Fb), normal reaction of nose gear(Nng), normal reaction of main-gears(Nmg)
The forces acting on a wheel while landing on a runway.
The above figure is the calculation of the coefficient of forces acting on aircraft when it is landing.
PART-B
6.(A)
To tow the aircraft we need to overcome 2 forces mainly, they are: (a)Rolling resistance force (b) Aerodynamical force
(c) Inertial force
The towing vehicles of different manufacturers are available in the market. The towing is done from terminal to runway.
For calculation of force and power required for towing, we are considering Airbus A320 specifications & Mototok Twin 6500 AC-AD
Ramp weight | 50000 kg |
wingspan area | 122.6 sq.m |
Assumptions: | |
Coefficient of rolling resistance | 0.01 |
Air Density | 1.225 kg/m^3 |
Coefficient of Drag | 0.025 |
Towing time | 18 sec |
AIRBUS A320
Weight | 1180kg |
Frontal Area | 0.70657m^2 |
Tow speed | 1.6667m/s |
Assumptions: | |
Coefficient of rolling resistance | 0.01 |
Air Density | 1.225 kg/m^3 |
Coefficient of Drag | 1.25 |
Towing time | 18sec |
MOTOTOK TWIN 6500 AC-AD
(a)Rolling resistance force
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.
Fr = c*Mr*g
where Fr = rolling resistance(N);c = rolling resistance coefficient;Mr = rolling mass(kg); g= acceleration due to gravity
For A320:
Consider an example for towing, take c = 0.01,Mr = 50000kg, g = 9.81m/s^2
=>Fr = 0.01*50000*9.81 = 4905N
=> Fr = 4905N =4.9kN
Now friction force for puller
Ff = μ*W = μ*Mf*g
where Ff = frictional force; Mf = friction mass;μ = coefficient of friction
Consider μ = 0.75
Mf = Ff/(μ*g) = 4905N/(0.75*9.81)
= 666.666kg
For TWIN 6500:
consider c = 0.01, Mr = 1180kg, g = 9.81m/s^2
Fr = 0.01*1180*9.81
=> Fr = 115.78N = 0.115kN
Mf = Ff/(μ*g) = 115.78/(0.75*9.81)
= 15.736kg
(b) Aerodynamic Force:
This force is acted on the vehicle because the body needs to move through the air. And it depends on frontal area, aerodynamic structure, spoilers, ducts, etc.,
For A320:
Fad = (1/2)*(ρ*A*Cd*V^2)
where ρ = density of air; A = frontal area; Cd = coefficient of drag; V = velocity of vehicle
consider ρ = 1.225kg/m^3; A = 100.5211m^2; Cd = 0.025; V = 1.6667m/s
Fad = 5.131N =0.005131kN
For TWIN 6500:
consider ρ = 1.225kg/m^3; A = 0.70657m^2; Cd = 0.025; V = 1.667m/s
Fad = 0.0360N = 0.000036kN
(c) Inertial Force:
F = m(v/t)
where F = force required, m= mass of vehicle, v = velocity of vehicle, t= towing time
For A320:
F = 50000*(1.667/18) = 4630.55N
= 4.63kN
For TWIN 6500:
F = 1180*(1.667/18) = 109.281N
= 0.109kN
Now total Force applied by a towing vehicle Ft = Fr + Fad + F
Ft = (4.9+0.005131+4.63+(0.115+0.000036+0.109))
= 9.7591kN
Total Traction Power = 9.7591*1.667 = 16.26kW
6. (B)
Here I simulated a model to display the traction effort required for towing by connecting simple math blocks(i.e., Constant, product, divide, square, add blocks).
The blue rounded value and red rounded values are the Total Traction force and Total Traction power respectively required to tow an aircraft of 50tonne weight with TWIN 6500.
The .slx file for the above model has been attached below for reference.
https://drive.google.com/file/d/1ZFGoVcitc5tgWBhjqjwDOG-R-xqoKUa-/view?usp=sharing
7.(A)
Here I considered Aircraft with mass of 50000kg and towing vehicle(TWIN 6500) of 1180kg for pull/tow of aircraft
Here by we utilised DC7 chopper block in order to produce the required torque for towing puprose.
The battery parameters given for the chopper to drive is taken from
Here the towing vehicle 4 batteries are arranged in series combination as we are using for high torque application.
So the overall voltage & current will be V = 48v and I = 880Ah respectively.
Now the RPM of the motor is defined by considering its wheel radius and the max towing speed of the vehicle i.e.,
N = 6kmph= 1.667m/s
Rpm of vehicle = N/ r; where N = speed of vehicle, r = radius of vehicle
Rpm = 1.667/0.127m = 125.29=> ω = 125.29rpm.
Radius of the tyre = height of towing vehicle - ground clearance = 344 - 88.5 = 258.5 mm(diameter)
= 0.129m (radius)
Now to calculate the armature resistance of motor we opt
=> battery 'V' / battery resistance'r' = 48v/4*(3.5ohm) = 3.428A
Armature resistance = V/I = 48v/3.428
= 14.4ohm
Required torque (T) = F.r / G.η ;
F = force at wheels, r = radius of wheel, G = gear ratio=10, η = efficiency
T = (9.7591kN)*(0.127m)/(10*0.87)
= 142.4Nm
Here we consider the motor power of 18kW to meet our load torque for towing operation.
Now the duty cycle by above data is 'Duty Cycle' = Po/Pi ; Po =output power, Pi = input power
'Duty Cycle' (D) = 16.26kW/18kW = 0.9033 = 90.33%
We used Li-ion battery connected to DC7 chopper with necessary parameter changes for towing, and we observed the output waveforms of Ia, V, Vdc, duty cycle of IGBT's, speed of motor.
Here we can notice the armature current it is drawing at 480A which represents the high torque application and with a low speed nearly 150rpm.
Now to accomplish this towing we assumed some parameters. They are:
Efficiency(η) = 87%
Gear ratio(G) = 10
co- efficient of friction = 0.75
Mass of aircraft = 50ton (50000kg)
rolling resistance quotient (c) = 0.01
Air density(ρ) = 1.225kg/m^2
Drag coefficient(Cd) = 0.025
Frontal area of aircraft (A) = 100.5211m^2
Towing time = 18sec
Velocity of Towing vehicle = Velocity of aircraft
By considering all these parameters and the name plate parameters of MOTOTOK TWIN 6500 we are able to tow the vehicle.
NOTE: Here we are unable to connect this chopper to a real-time load of aircraft body because of simscape and simulnk conversion in the blocks we use for towing and aircraft respectively.
The towing model of aircraft wad attached below for reference
https://drive.google.com/file/d/1gxBR0-vwncRJarNTfcE0ruIdlFZtIA7r/view?usp=sharing
7.(B)
Here i created a excel sheet with the necessary parameters required and assumed in towing a vehicle
https://drive.google.com/file/d/1T1zXQeF4EZZm9GTkb4-YA5TTjE35RyIs/view?usp=sharing
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