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Design and Study of Electric Pushback Vehicle for Aircrafts Q1. Search and list out the total weight of various types of aircraft. An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift…
Deepak Gaur
updated on 19 May 2021
Design and Study of Electric Pushback Vehicle for Aircrafts
Q1. Search and list out the total weight of various types of aircraft.
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.
1. Lighter Than Air
Aerostats are lighter than air and use buoyancy to float in the air in much the same way that ships float on the water. They are characterized by one or more large cells or canopies, filled with a relatively low-density gas such as helium, hydrogen, or hot air, which is less dense than the surrounding air. When the weight of this is added to the weight of the aircraft structure, it adds up to the same weight as the air that the craft displaces. Example airships, hot-air balloons, etc.
2. Heavier than air
Aerodynes, such as airplanes, must find some way to push air or gas downwards so that a reaction occurs (by Newton's laws of motion) to push the aircraft upwards. This dynamic movement through the air is the origin of the term aerodyne. There are two ways to produce dynamic upthrust — aerodynamic lift, and powered lift in the form of engine thrust.
a) Fixed Wing-Airplane
The forerunner of the fixed-wing aircraft is the kite. Whereas a fixed-wing aircraft relies on its forward speed to create airflow over the wings, a kite is tethered to the ground and relies on the wind blowing over its wings to provide lift.
b) Rotorcraft
Rotorcraft, or rotary-wing aircraft, use a spinning rotor with aerofoil section blades (a rotary wing) to provide lift. Helicopters have a rotor turned by an engine-driven shaft. The rotor pushes air downward to create lift. By tilting the rotor forward, the downward flow is tilted backward, producing thrust for forwarding flight.
c) Glider Aircraft
A glider is a fixed-wing aircraft that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose free flight does not depend on an engine. Most gliders do not have an engine, although motor-gliders have small engines for extending their flight when necessary.
The 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 or in-flight refueling.
Various weighing terminologies used for aircraft weight
1. Maximum taxi weight (MTW)
The maximum taxi weight (MTW) (also known as the maximum ramp weight (MRW) is the maximum weight authorized for maneuvering (taxiing or towing) an aircraft on the ground as limited by aircraft strength and airworthiness requirements.
2. Maximum takeoff weight (MTOW)
The maximum takeoff weight (also known as the maximum brake-release 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/ramp weight to allow for fuel burned during taxi by the engines.
3. Maximum landing weight (MLW)
The maximum weight authorized for the normal landing of an aircraft. The maximum landing weight(MLW) must not exceed the maximum takeoff weight (MTOW). The operation landing weight may be limited to a weight lower than the Maximum Landing Weight.
4. Maximum zero-fuel weight (MZFW)
The maximum permissible weight of the aircraft less all usable fuel and other specified usable agents (engine injection fluid, and other consumable propulsion agents). It is the maximum weight permitted before usable fuel and other specified usable fluids are loaded in specified sections of the airplane.
List out the total weight of various types of aircraft
Sl. No. | Aircraft Type | Aircraft Name | MTOW [kg] |
1 | Aircraft | Airbus A380-800 | 575,000 |
2 | Aircraft | Boeing 747-8F | 447,700 |
3 | Aircraft | Antonov An-124-100M | 405,060 |
4 | Aircraft | Boeing 747-400 | 396,900 |
5 | Aircraft | Lockheed C-5 Galaxy | 381,000 |
6 | Aircraft | Boeing 747-200 | 377,840 |
7 | Aircraft | Boeing 747-300 | 377,840 |
8 | Aircraft | Airbus A340-500 | 371,950 |
9 | Aircraft | Airbus A340-600 | 367,400 |
10 | Aircraft | Boeing 777-200ER | 297,550 |
11 | Aircraft | Airbus A340-300 | 276,700 |
12 | Aircraft | McDonnell Douglas MD-11 | 273,300 |
13 | Aircraft | Airbus A350-900 | 270,000 |
14 | Aircraft | Ilyushin Il-96M | 270,000 |
15 | Aircraft | McDonnell Douglas DC-10 | 256,280 |
16 | Aircraft | Ilyushin IL-96-300 | 250,000 |
17 | Aircraft | Airbus A330-300 | 242,000 |
18 | Aircraft | Airbus A330-200 | 242,000 |
19 | Aircraft | Boeing 787-8 | 228,000 |
20 | Aircraft | Airbus A300-600R | 192,000 |
21 | Aircraft | Boeing 767-300ER | 187,000 |
22 | Aircraft | Concorde | 185,000 |
23 | Aircraft | Airbus A300-600 | 163,000 |
24 | Aircraft | Boeing 767-300 | 159,000 |
25 | Aircraft | Airbus A310-300 | 157,000 |
26 | Aircraft | Airbus A310-200 | 142,000 |
27 | Aircraft | Airbus A400M | 141,000 |
28 | Aircraft | Boeing 757-300 | 124,000 |
29 | Aircraft | Boeing 757-200 | 116,000 |
30 | Aircraft | Boeing 737-900 | 85,000 |
31 | Aircraft | Boeing 737-900ER | 85,000 |
32 | Aircraft | Airbus A321-100 | 83,000 |
33 | Aircraft | Boeing 737-800 | 79,000 |
34 | Aircraft | McDonnell-Douglas MD-90-30 | 71,000 |
35 | Aircraft | Boeing 737-700 | 70,000 |
36 | Aircraft | Airbus A320-100 | 68,000 |
37 | Aircraft | Boeing 737-400 | 68,000 |
38 | Aircraft | Boeing 737-600 | 66,000 |
39 | Aircraft | Airbus A220-300 | 65,000 |
40 | Aircraft | Airbus A319 | 64,000 |
41 | Aircraft | Boeing 737-300 | 63,000 |
42 | Aircraft | Boeing 737-500 | 60,000 |
43 | Aircraft | Airbus A220-100 | 59,000 |
44 | Aircraft | Airbus A318 | 59,000 |
45 | Aircraft | Fokker 100 | 46,000 |
46 | Aircraft | Embraer 175 | 37,500 |
47 | Aircraft | Bombardier CRJ900 | 36,500 |
48 | Aircraft | Embraer 170 | 36,000 |
49 | Aircraft | Bombardier CRJ700 | 33,000 |
50 | Aircraft | Bombardier Q400 | 28,000 |
51 | Aircraft | Bombardier CRJ200 | 23,000 |
52 | Aircraft | ATR 72-600 | 22,800 |
53 | Aircraft | Embraer ERJ 145 | 22,000 |
54 | Aircraft | ATR 42-500 | 18,600 |
55 | Aircraft | Saab 340 | 13,150 |
56 | Aircraft | Embraer 120 Brasilia | 11,500 |
57 | Aircraft | BAe Jetstream 41 | 10,890 |
58 | Aircraft | Learjet 75 | 9,752 |
59 | Aircraft | Pilatus PC-24 | 8,300 |
60 | Aircraft | Embraer Phenom 300 | 8,150 |
61 | Aircraft | Beechcraft 1900D | 7,765 |
62 | Aircraft | Cessna Citation CJ4 | 7,761 |
63 | Aircraft | Embraer Phenom 100 | 4,800 |
65 | Helicopter | Mil Mi-12 | 105000 |
66 | Helicopter | Mil Mi-26 | 56000 |
67 | Helicopter | Sikorsky CH-53E | 33300 |
68 | Helicopter | Boeing CH-47D/F Chinook | 22680 |
69 | Helicopter | AgustaWestland AW101 | 14600 |
70 | Helicopter | Sikorsky S-92 | 12020 |
71 | Helicopter | Eurocopter EC225 Super Puma | 11200 |
72 | Helicopter | Boeing Vertol CH-46 Sea Knight | 11000 |
73 | Helicopter | NHIndustries NH90 | 10600 |
74 | Helicopter | Eurocopter AS532 Cougar | 9000 |
75 | Helicopter | Bell 412EP | 5397 |
76 | Helicopter | Eurocopter EC145 C-2 | 3585 |
77 | Helicopter | Eurocopter EC135 P2+/T2+ | 2910 |
78 | Helicopter | Eurocopter EC635 P2 | 2900 |
79 | Helicopter | AeroVelo Atlas (human powered) | 128 |
Q2. Is there any difference between ground speed and airspeed?
Yes, there is a difference between the ground speed and airspeed as the ground speed is relative to the surface whereas the airspeed is relative to air. The ground speed is the vector sum of the true airspeed of the aircraft and wind velocity.
Ground speed is the horizontal speed of an aircraft relative to the Earth’s surface. It is vital for accurate navigation to the destination that the pilot has an estimate of the ground speed that will be achieved during a flight. An aircraft diving vertically would have a ground speed of zero. The information displayed to passengers through the entertainment system of airline aircraft usually gives the aircraft ground speed rather than airspeed.
Q3. Why is it not recommended to use aircraft engine power to move it on the ground at the Airport?
The aircraft engine power is not used to move the plane in the airport environment because of engine thrust hazards. Commercial airplanes are equipped with engines rated from 18,000 to nearly 100,000 lb of thrust, such thrust levels provide for a safe takeoff, flight, and landing over a wide range of temperatures, altitudes, gross weights, and payload conditions. However, the exhaust wake from these engines can pose hazards in commercial airport environments. Operators and airport authorities must carefully consider these hazards and the resulting potential for injury to people and damage to or caused by baggage carts, service vehicles, airport infrastructure, and other airplanes.
Power Hazard Areas
When modern jet engines are operated at rated thrust levels, the exhaust wake can exceed 375 mi/h (325 kn or 603 km/h) immediately aft of the engine exhaust nozzle. This exhaust flow field extends aft in a rapidly expanding cone, with portions of the flow field contacting and extending aft along the pavement surface. Exhaust velocity components are attenuated with increasing distance from the engine exhaust nozzle. However, an airflow of 300 mi/h (260 kn or 483 km/h) can still be present at the empennage, and significant people and equipment hazards will persist hundreds of feet beyond this area. At full power, the exhaust wake speed can typically be 150 mi/h (130 kn or 240 km/h) at 200 ft (61 m) beyond the airplane and 50 to 100 mi/h (43 to 88 kn or 80 to 161 km/h) well beyond this point.
One approach to relating these values to airport operations is to consider the hurricane intensity. A Category 1 hurricane has sustained winds of 74 to 95 mi/h (64 to 82 kn or 119 to 153 km/h). At these velocities, minimal damage to stationary building structures would be anticipated, but more damage to unanchored mobile homes and utility structures would be expected. An idling airplane can produce a compact version of a Category 3 hurricane, introducing an engine wake approaching 120 mi/h (104 kn or 192 km/h) with temperatures of 100°F (38°C). This wake velocity can increase two or three times as the throttles are advanced and the airplane begins to taxi.
Foreign Object Damage
Foreign object damage (FOD) caused by high engine thrust can affect airport operations as it relates to
Q4. How an aircraft is pushed to the runway when it's ready to take off?
Most airplanes can taxi backward by using reverse thrust. This entails directing the thrust produced by the plane’s jet engines forward, rather than backward, the resulting jet blast or prop wash might cause damage to the terminal building or equipment.
This method is often used in jet aircraft to brake as quickly as possible after touchdown. It’s also used when making an emergency stop.
Pushback
Pushback is an airport procedure during which an aircraft is pushed backward away from an airport gate by an external power. Pushbacks are carried out by special, low-profile vehicles called pushback tractors or tugs. A pushback is therefore the preferred method to move the aircraft away from the gate.
Pushback Procedure
Pushbacks at busy aerodromes are usually subject to ground control clearance to facilitate ground movement on taxiways. Once clearance is obtained, the pilot will communicate with the tractor driver (or a ground handler walking alongside the aircraft in some cases) to start the pushback. To communicate, a headset may be connected near the nose gear.
Since the pilots cannot see what is behind the aircraft, steering is done by the pushback tractor driver and not by the pilots. 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 pushback is completed, the towbar is disconnected, and any bypass pin removed. 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.
Pushback Tractors
Large aircraft are pulled using a tractor or tug. Pushback tractors use a low profile design to fit under the aircraft's nose. For sufficient traction, the tractor must be heavy, and most models can have extra ballast added. A typical tractor for large aircraft weighs up to 54 tonnes (119,000 pounds) and has a drawbar pull of 334 kN (75,000 lbf). Often the driver's cabin can be raised for increased visibility when reversing and lowered to fit under aircraft.
There are two types of pushback tractors:-
a) Conventional
b) Towbarless (TBL)
a) Conventional
Conventional tugs use a tow bar to connect the tug to the nose landing gear of the aircraft. The tow bar is fixed laterally at the nose landing gear but may move slightly vertically for height adjustment. At the end that attaches to the tug, the tow bar may pivot freely laterally and vertically. In this manner, the tow bar acts as a large lever to rotate the nose landing gear.
b) Towbarless (TBL)
Towbarless (TBL) tractors do not use a towbar; they scoop up the nose landing gear and lift it off the ground. This avoids the time penalty of connecting/disconnecting a towbar and entirely removes the cost/complexity of maintaining towbars on the ramp. The tug itself does not need to be particularly massive - the aircraft's nosewheel weight provides the necessary downward force. Lastly, a TBL tug is much shorter (compared to a tug+towbar system) and has only a single pivot point instead of one at either end of the towbar, so it has much simpler and precise control of the aircraft. This is very useful in general aviation settings with a wider variety of aircraft in more confined spaces than their airline counterparts.
Electric TBL tugs are gaining popularity among general aviation operators and FBOs as an alternative to gas or diesel-powered conventional tugs. Being electric rather than internal combustion-powered, electric tugs are low-emission which is a major advantage for environmentally-conscious operators; this also enables the tug to be safely operated inside a closed hangar.
Q5. Learn about take-off power, tire design, rolling resistance, tire pressure, brake forces when landing.
Takeoff and landing time is a very short proportion of the total flight time, but it is the accident-prone phase of the mission. Research about the flight characteristic of takeoff and landing is of great importance to the safety of the airplane and can provide some reference for aircraft design. At present, these methods: analytical method, numerical integration, and energy method can be used to calculate takeoff and landing performance.
Take off performance
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 take-off run the imbalance in these forces will produce an acceleration along the runway.
dvdt=T−D−Fm
wheredvdt is the acceleration along the runway and m is the mass of the vehicle.
Rotation Velocity, VR
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 climb lift and it will ascend from the ground. The determination of this safe flying speed or rotation speed, VR, is a critical factor in determining take-off performance.
V1- Abort decision speed. Below this speed, the take-off can be safely aborted. After this, there will not be sufficient runway length to allow the aircraft to decelerate to a stop.
V2 – Safe climb speed. V2 must be no less than 1.2⋅Vstall. Below this speed aircraft cannot attain a sufficient climb rate.
Landing
The landing run can be calculated in a similar fashion to the take-off distance. The aim is again to minimize the distance.
The touch-down velocity should be approximately the stall speed of the aircraft in the landing configuration. This will be achieved by a pitch maneuver during the flare portion of the approach which increases drag and decelerates the aircraft to minimum flying speed.
The deceleration on the landing roll from VTD to V=0 will be accomplished by braking and reverse thrust. This can be solved by the average acceleration approach that was used to estimate the take-off roll.
During the take-off run, the imbalance in these forces will produce an acceleration along the runway.
dvdt=−T−D−Fm
The negative acceleration or deceleration value will be based on the friction coefficient for maximum braking and the value of reverse thrust (if available).
Brake Forces
Stopping a 200-tonne aircraft landing at 180 mph requires a lot of braking force. To do this, one brake unit on each of the eight wheels on the main gear assembly. On different aircraft types, the brake units are powered by the hydraulics system or an electrical system. The hydraulics system is usually heavy hence to reduce weight electrical systems are used. When the pilots press on the brake pedals, an electrical signal is sent to the brake unit on the wheel. Here, electrically powered actuators are used to press the carbon brake disc against the wheel, slowing it down.
Anti-skid protection
When landing on slippery runways, there’s a chance that the wheels may start to skid as the brakes are applied. To stop this from happening and to maintain maximum effective braking, each wheel has anti-skid protection.
In this situation, the anti-skid system automatically reduces the braking on that wheel to a point where the skid stops before reapplying the pressure. All this is done in a fraction of a second.
Autobrake
Pressing on the brakes is pretty straight forward when taxiing in a straight line at low speed. However, when we’re landing in strong winds, it can be a little tricky. We need to use our feet on the rudder pedals to line the nose of the aircraft up with the runway centerline at the last moment. Then, whilst holding that position, slide our feet up to press the toe brakes. Really not very easy when moving at 160 mph.
To help us get the braking underway as soon as we touch down, we have the auto brake system. This provides automatic braking at a preselected rate as soon as the aircraft senses that it is on the ground. It also provides full braking pressure in the case of a rejected takeoff if the speed is above 85 knots (98 mph).
Brake temperature indication
With friction comes heat. As a result, each brake unit displays its temperature on the wheel synoptic page in the flight deck. Here, numerical values relating to brake temperature are shown next to each wheel. A value of 0-4.9 is in the normal range. When a temperature becomes 5.0 or above, an advisory message is displayed to the pilots.
Should the brakes become too hot, there’s a chance that the heat transferred to the wheels could cause the tires to explode. To stop this from happening, when a certain temperature is reached, fuse plugs in the tires melt. This allows the air to be released safely and slowly deflate the tires.
Parking brake
Parking brakes are particularly useful on long taxis to the runway and obviously when parked at the gate. The park brake is set by fully pressing down both toe brakes and pulling the parking brake lever up.
Rolling Resistance
The friction between aircraft and runway will be proportional to the normal force exerted by the aircraft on the runway.
F=μ(W−L)
The normal force will be the difference between the Weight of the aircraft and Lift, the friction coefficient will be typical of a magnitude of 0.02 for a standard tarmac runway.
Due to the quadratic nature of acceleration change, an average value, (dvdt)avg=¯a, can be used for the take-off run. This average acceleration can be found at the point where,
V=VR√2
This average acceleration can be used to simplify calculations and the take-off run can be calculated as an equivalent constant acceleration over the complete period of time (tR) taken to get from 0 to VR. For a constant acceleration take-off calculation,
VR=¯a⋅tR and distance traveled s=12⋅¯a⋅t2R
Tire Design
An aircraft 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 landing. The fuses provide a safer failure mode that prevents tire explosions by deflating in a controlled manner, thus minimizing damage to aircraft and objects in the surrounding environment.
Each of the main tires is inflated to 220 psi (15 bar; 1,500 kPa), weighs 120 kg (260 lb), has a diameter of 134 cm (53 in) and is changed every 300 cycles while the brakes are changed every 2000 cycles. Each tire is worth about $5,000. Aircraft tires generally operate at high pressures, up to 200 psi (14 bar; 1,400 kPa) for airliners. 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).
Tests of airliner aircraft tires have shown that they are able to sustain pressures of a maximum 800 psi (55 bar; 5,500 kPa) before bursting. During the tests, the tires have to be filled with water, to prevent the test room from being blown apart by the energy that would be released by gas when the tire bursts.
Aircraft tires are usually inflated with nitrogen to minimize expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight.
Q6. With necessary assumptions, calculate the force and power required to push/pull an aircraft by a towing vehicle.
Consider a free body diagram of the towing vehicle-aircraft system. Let Mt be the mass of the towing truck and Mac be the mass of the aircraft and the road gradient be θ.
The various forces acting on the given towing vehicle-aircraft system at a slope θ is as follows:-
1. Rolling Resistance Force
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) rolls on a surface.
Force due to rolling resistance is given by the equation
Frr=μrr⋅m⋅g where
μ =coefficient of rolling resistance (0.02 for a standard tarmac runway)
g = acceleration due to gravity (9.81ms−2)
m=(Wt+Wac)⋅cosθ
(Vertical component from the combined weight of Aircraft and Towing Vehicle, Wt=6500 and Wac=50000)
2. Aero Dynamic Drag
Aerodynamic force is due to the friction of the vehicle body moving through the air. It is a function of the frontal area, shape, protrusions such as side mirrors, ducts, and air passages, spoilers, and many other factors.
Force due to aerodynamic drag is given by
Fad=12⋅ρ⋅A⋅Cd⋅v2 where
`rho` is the density of air
`A` is the frontal area of the vehicle (19 m2)
`C_d` is the drag coefficient
`v` is the velocity of the vehicle
3. Force due to Gravity
The weight of the vehicle is defined as the force of gravity on the object and may be calculated as the mass times the acceleration of gravity. Force due to gravity is given by
W=m⋅g⋅cosθ
m is mass of the vehicle in kg
g is the acceleration due to gravity (g =9.81 ms−2)
4. Normal Force
The force that surfaces exerts to prevent solid objects from passing through each other. The normal force is a contact force. It is the force that is perpendicular to the surface that an object contacts.
On a flat surface, the Normal Force= Force due to Gravity and on an inclined plane, it is equal in magnitude and opposite in direction to the vertical component of the force due to gravity that is perpendicular to the inclined surface.
5. Force due to Slope
It is an additional force needed to drive the vehicle up a slope. It is dependent on the slope angle and it is simply the component of the vehicle weight that acts along the slope. The force due to hill climb is given by
Fhc=mgsin(θ) where
`m` is mass of the vehicle in kg
`g` is the acceleration due to gravity (g =9.81 ms−2)
`theta` is slope angle in radians
6. Traction Force
Traction or tractive force is the force used to generate motion between a body and a tangential surface. It is the force generated by the powertrain of the vehicle to overcome all the external and internal forces resisting the motion.
The Traction Force is given by
Fte=Frr+Fad+Fhc+Fla+Fwa where
Frr is the Rolling Resistance Force
Fad is the Aero Dynamic Drag Force
Fhc is Hill Climb Force
Fla is Force required for Linear Acceleration
Fwa is force required to give Angular Acceleration to motor
Linear Acceleration Force
The force required to accelerate the vehicle from a state of motion to another is called the Linear Acceleration Force.
The Linear Acceleration Force is given by
Fla=m⋅a where
`m` is the mass of the vehicle in kg
`a` is the acceleration in ms−2
Angular Acceleration Force
The force exerted by the moment of inertia of the motor is called Angular Acceleration Force. It is not because of its particularly high moment of inertia, but because of the higher angular speeds.
It will quite often turn out that the moment of inertia of the motor I will not be known. In such cases, a reasonable approximation is simply to increase the mass of the vehicle by 5% in the equation Fla=m⋅a and ignore the Fωa term.
The Force due to Angular Acceleration is given by
Fwa=I⋅G2ηg⋅r2⋅a where
`I` is the moment of Intertia in kgm2
`G` is the gear ratio
`eta_g` is the efficiency of gear system
`r` is the radius of tire
`a`G is the linear acceleration required.
Design Calculations
Link for Excel Calculator
Q7. Design an electric powertrain with the type of motor, it’s 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.
Consider a motor driving wheel using a belt drive. Let the gear ratio be , the motor torque be T, the radius of the tire be r, and the tractive effort be Fte.
The motor torque T can be expressed as T=Fte⋅rG and motor speed can w can be expressed as w=G⋅vr where v is linear vehicle speed in m/s. If the efficiency of the transmission system is considered the modified gear ratio can be defined as Gη.
The power rating of the motor can be found using the peak performance tractive torque required by the vehicle.
Power Rating of the motor, Prating=Fpeak⋅w1000 in kilowatt.
Considering the combination of overload factor and losses an additional power of 10-15% is considered thus we consider a motor with a power rating of 300kW.
Energy Requirement
The energy required to move the vehicle for each second of the driving cycle is calculated, and the effects of this energy drain are calculated. The process is repeated until the battery is flat. It is important to remember that if we use time intervals of 1 second, then the power and the energy consumed are equal.
The energy flow from the battery in Electric Vehicle
The inefficiencies of the motor, the controller, and the gear system mean that the motor’s power is not the same as the traction power, and the electrical power required by the motor is greater than the mechanical output power according to the simple equations
Pmot→in=Pmot→outηm and Pmot→out=Pteηg Pmot_in
Pmot→in=Pteηm⋅ηg
We also need to consider the other electrical systems of the vehicle, the lights, indicators, accessories such as the radio, and so on. An average power will need to be found or estimated for these, and added to the motor power, to give the total power required from the battery.
Pbattery=Pmot→in+Paux
Considering auxiliary power consumption be to 30% of the traction power the peak power required from the battery can be given as
Pbattery=1.3⋅Pmot→innm . As ηg is already considered while calculating the vehicle traction power the peak battery power requirement can be expressed as
Pbattery=1.3⋅Pteηm
Let the efficiency of the motor combined with the power convertor be 85%.
Pbattery=1.3⋅264.5050.85=404.059kW
Battery Capacity Calculation
Consider the pushback vehicle works for 6 hours per shift.
The energy required by the pushback vehicle in Watt-Hours =Pbattery∗Hours=404.059∗6=2424.354 kWh
Since watt=amp∗volt dividing the watt-hour by the voltage of the battery to get amp-hour of battery storage.
Let the battery voltage to be 800V, the battery capacity in Ah =2424.354800=3030.4 Ah (Ampere Hour).
Duty cycle calculation
Case-1 Vehicle is accelerating from speed Zero to Highest
Power required for the motor from the battery
Pmot→in=Pteηm=63.2240.85=74.381 kW
Considering the max current rating be 400A, the power rating obtained from the battery will be 320kVA which is equal to 320kW when the power factor is 1.
Duty Cycle=74.381320=23%
Case-2 Vehicle is running at full speed at Zero Gradient
Power required for the motor from the battery
Pmot→in=Pteηm=46.8760.85=55.148 kW
Considering the max current rating be 400A, the power rating obtained from the battery will be 320kVA which is equal to 320kW when the power factor is 1.
Duty Cycle=55.148320=17%
Case-3 Vehicle is running at full speed on a slope of 5°
Power required for the motor from the battery
Pmot→in=Pteηm=248.1570.85=291.949 kW
Considering the max current rating be 400A, the power rating obtained from the battery will be 320kVA which is equal to 320kW when the power factor is 1.
Duty Cycle=291.949320=91%
Assumed Parameters
Block diagram of the powertrain
References
1. https://en.wikipedia.org/wiki/List_of_airliners_by_maximum_takeoff_weight
2. https://en.wikipedia.org/wiki/Aircraft_gross_weight
3. https://en.wikipedia.org/wiki/Ground_speed
4. https://en.wikipedia.org/wiki/Aircraft_gross_weight
5. http://www.boeing.com/commercial/aeromagazine/aero_06/textonly/s02txt.html
6. https://en.wikipedia.org/wiki/Pushback
7. https://aviation.stackexchange.com/questions/12162/what-is-the-minimum-thrust-needed-to-takeoff
8. http://large.stanford.edu/courses/2013/ph240/eller1/
9. http://www.aerodynamics4students.com/aircraft-performance/take-off-and-landing.php
10. https://www.worldscientific.com/doi/pdf/10.1142/S2010194516601745
11. https://en.wikipedia.org/wiki/Aircraft_tire
12. https://www.dunlopaircrafttyres.co.uk/technical
13. https://thepointsguy.com/guide/how-do-aircraft-brakes-work/
15. https://www.powerstream.com/battery-capacity-calculations.htm
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