Project-1: Powertrain for aircraft in runways
- Search and list out the total weight of various types of aircrafts.
some of the types of Engines or propeller in aircrafts are:
1) Reciprocating engines - Reciprocating engines in in aircraft have three main variants, radial,inline and flat or horizontally opposed. The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel and was commonly used for aircraft engines before gas turbine engines became predominant. An inline engine is a reciprocating engine with banks of cylinders, one behind another, rather than rows of cylinders, with each bank having any number of cylinders, but rarely more than six, and may be water-cooled. A flat engine is an internal combustion engine with horizontally-opposed cylinders.
2) Gas turbine - A turboprop gas turbine engine consists of an intake, compressor, combustor, turbine, and a propelling nozzle, which provide power from a shaft through a reduction gearing to the propeller. The propelling nozzle provides a relatively small proportion of the thrust generated by a turboprop.
3) Electric motor - An electric air craft runs on electric motors rather than internal combustion engine, with electricity coming from fuel cells, solar cells, ultracapacitor, power beaming, or batteries. Currently, flying electric aircraft are mostly experimental prototypes, including manned and unmanned areal vehile, but there are some production models on the market already.
4) Jet - Jet aircraft are propelled by jet engine which are used because the aerodynamic limitations of propellers do not apply to jet propulsion. These engines are much more powerful than a reciprocating engine for a given size or weight and are comparatively quiet and work well at higher altitude.
PROCEDURE - For the first part - 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.
The weights are classified as following:
Maximum design taxi weight (MDTW) - The maximum design taxi weight (also known as the maximum design ramp weight (MDRW)) is the maximum weight certificated for aircraft manoeuvring on the ground (taxiing or towing) as limited by aircraft strength and airworthiness requirements.
Maximum design takeoff weight (MDTOW) - It is the maximum certificated design weight when the brakes are released for takeoff and is the greatest weight for which compliance with the relevant structural and engineering requirements has been demonstrated by the manufacturer.
Maximum design landing weight (MDLW) - The maximum certificated design weight at which the aircraft meets the appropriate landing certification requirements. It generally depends on the landing gear strength or the landing impact loads on certain parts of the wing structure. The maximum landing weight is typically designed for 10 feet per second (600 feet per minute) sink rate at touch down with no structural damage.
Maximum design zero fuel weight (MDZFW) - The maximum certificated design 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. The MDZFW is limited by strength and airworthiness requirements. At this weight, the subsequent addition of fuel will not result in the aircraft design strength being exceeded.
Manufacuturer'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.
Pay load - 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.
Operating empty weight (OEW) - 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.
In the above fig. Boxes on the right sum up the separate items which they run across. To simply this :
Dry Operating Wieght (DOW) OEW + 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
The total weights of various types of aircraft are shown below:
Airbus A330-800F – 1,117,882 pounds (507,063 kg)
Boeing 747-400 – 875,014 pounds (396,900 kg)
Lockheed C-5 Galaxy – 839,961 pounds (381,000 kg)
McDonnel Douglas MD-11 – 602,523 pounds (273,300 kg)
Boeing 767-400ER – 449,743 pounds (204,000 kg)
Concorde – 407,855 pounds (185,000 kg)
Boeing 727-100 – 159,835 pounds (72,500 kg)
- Is there any difference between ground speed and air speed?
The importance of the relative velocity explains why, even today, airplanes take off and land on different runways on different days. Airplanes always try to take off and land into the wind. This requires a lower ground speed, which means the plane can take off or land in the shortest distance travelled along the ground. Since runways have a fixed length, you want to get airborne as fast as possible on take-off and stopped as soon as possible on landing. In the old days, a large "wind sock" was hung near the runway for pilots to see which way the wind was blowing to adjust their take-off and landing directions. Now mechanical or electronic devices provide the information that is radioed to the cockpit. It is important to understand the relationships of wind speed to ground speed and airspeed.
Wind Speed: A reference point picked on the ground, the air moves relative to the reference point at wind speed. The wind speed is a vector quantity and has both magnitude and direction. The wind blowing against the motion of aircraft is called Head wind. We have defined a positive velocity to be in direction of the aircraft motion, head wind is a negative velocity. When the wind blows in the same direction of aircraft motion it is called Tail wind. The sign of wind is now positive.
Ground Speed: The speed on which the aircraft moves relative to the point on the ground. Ground speed is a vector quantity.
Air Speed: The relative velocity between the object and the air is called air speed. 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.
AIR SPEED
Speed relative to air.
Speed relative to ground.
GROUND SPEED
Measured quantity. Using Pitot tube.
Calculated quantity. (Air speed + Wind velocity)
- Why is it not recommended to use aircraft engine power to move it on the ground at Airport?
Aircraft can move using their own engine power all the time on the airport apron and taxiways under their own power to go towards runways and after landing taxi to their assigned gate. But the thrust produced resulting jet blast might cause damage to 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 therefore the preferred method to move the aircraft away from the gate. And also, it can reduce the cost for fuel. Taxing can save money.
- How an aircraft is pushed to runway when its ready to take off?
How an aircraft is pushed to runway when it’s ready to take off?
Pushback is when an aircraft is pushed backwards away from the airport gate by vehicles called tugs or tractors. Closer to departure, an aircraft tug will park right in front of the nose wheel. The tug might be directly attached to the plane's nose gear with a tow bar, or could be a "wheel-lift" tug. These tugs cradle the nose gear, then lift it up before moving the plane. That gives the tug driver control over the plane's direction during pushback. New taxi technologies are appearing, like pilot-controlled tugs, and electric motors mounted to the plane's landing gear. Both promise to save fuel, and reduce airport noise.
- Learn about take-off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
Take-off Power:
A normal take-off is one in which the airplane is headed into the wind, or the wind is very light. Also, the take-off surface is firm and of sufficient length to permit the airplane to gradually accelerate to normal lift-off and climb-out speed, and there are no obstructions along the take-off path.
There are four forces which helps the aircraft to take off:
Wings keep an airplane up in the air, but the four forces are what make this happen. They push a plane up, down, forward, or slow it down.
Thrust: It is a force that moves an aircraft in the direction of the motion. It is created with a propeller, jet engine, or rocket. Air is pulled in and then pushed out in an opposite direction. One example is a household fan.
T=Pshaft⋅ηV
Drag: It is the force that acts opposite to the direction of motion. It tends to slow an object. Drag is caused by friction and differences in air pressure. An example is putting your hand out of a moving car window and feeling it pull back.
D=CD⋅0.5⋅ρ⋅V2⋅S
Weight: It is the force caused by gravity.
W=mg
Lift: It is the force that holds an airplane in the air. The wings create most of the lift used by airplanes.
L=CL⋅0.5⋅ρ⋅V2⋅S
Therefore Take-off power= Total force*Velocity
For smaller aircrafts like turboprop we use full power for take-off. Because they don’t have take-off power settings. But in aircrafts like Jet plane they have take-off power settings so they don’t have to take the full power.
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 Weight (W) of aircraft and Lift (L), the friction coefficient (μ) will be typically of a magnitude of 0.02 for a standard tarmac runway.
Tyre Design:
Designing aircraft tires is a very intense undertaking. The tyre is designed to withstand 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. Aircraft tyre generates more heat during landing. Aircraft drags the wheel until they match the rotational velocity of wheels. Due to this heat generates. However, each tyre is built to operate within a given temperature. This is known as vulcanization temperature. During the course of its use, if the tire is heated past the vulcanization temperature, it begins to wear gradually.
Two types of tires are used in aircraft applications: bias-ply tires and radial tires.
Radial Tyre: It has fibre strands of the ply fabric oriented at 90° to the direction of rotation and the tyre sidewall. This restricts flexibility bidirectional and the flexibility of the sidewall while it strengthens the tyre to carry heavy loads. Due to their unique construction most radial tyres are resistant to penetration ad cuts. Due to stiffer tread they distribute weight evenly. Thus provide greater traction. Radial tyres have an advantage in term of reducing the heat better.
Bias- ply Tyre: It has the fabric bias oriented with and across the direction of rotation and the sidewall. Since fabric can stretch on the bias, the tyre is flexible and can absorb loads. Tyre strength is obtained by adding plies. It is cut resistant is sidewall area. These tyres do not offer as much smoothness in terms of riding quality.
Tyre Pressure:
Aircraft tyres operate at such high extremes of pressure, load, and speed, their care and service is critically important. The most important action an operator can take to prevent tyre-related events is to maintain proper tire inflation pressure. Failure to keep aircraft tires properly inflated can lead to very serious consequences. One relatively easy way to help avoid those consequences is to check tire pressures regularly and service them as necessary. Following these three actions is a good way to make sure you get the most value out of your tires and contribute to the safe operation of your aircraft:
Perform daily pressure checks with a calibrated gauge.
Target the highest pressure recommended in the AMM or POH (105 percent of operating pressure).
Compensate for ambient temperature changes.
Brake forces when landing:
Stopping a 200-tonne aircraft landing at 180 mph requires a lot of braking force. To do this either hydraulic brakes or electric brakes are used. Hydraulic brakes put on weight of the aircraft. Now a days designers use electric brake system. The aim of brake force when landing is to minimise the distance.
The touch down velocity should be approximately the stall speed of the aircraft in landing configuration. This will be achieved by increasing the drag and decelerate the aircraft to minimum flying speed. The deceleration on the landing roll from to 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.
dvdt=−T−D−Fm
Where,
T – Thrust of propulsion system pushing aircraft along 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.
m – Mass
So the brake force= Mass * Deceleration
- A. With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.
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 rolling resistance for the air plane can be calculated as
F
r
=
C
⋅
m
r
⋅
a
g
(1)
Where,
F
r
= rolling resistance (N, lbf)
C = rolling resistance coefficient
mr= rolling mass (kg, lbm)
ag= acceleration of gravity (9.81 m/s2)
EXAMPLE - FORCE REQUIRED TO PULL AN AIRPLANE AT CONSTANT LOW SPEED ON TARMAC
If the mass of a plane is 40000 kg and the rolling coefficient between the aircraft wheel and the tarmac is 0.02
The force required to overcome the rolling resistance can be calculated as:
Fr = 0.02 (40000 kg) (9.81 m/s2)
= 7848 N
This force can be delivered by a pulling truck. Enough weight of truck 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
Ff=μW
=μ⋅mf⋅ag
(2)
Where,
Ff = frictional force (N, lb)
μ = friction coefficient
W = weight (N, lbf)
mf= friction mass (kg)
Required Mass for Pulling Truck:
The friction coefficient between a pulling truck rubber wheels and dry tarmac is 0.9.
Since pulling trucks are connected to air crafts nose wheels close to tarmac we simplify the calculation of required truck mass to:
Mf = (7848 N) / (0.9 (9.81 m/s2))
= 889 kg
Power required for pulling truck with a velocity of 5m/s:
P= F*V
Where,
F = total force acting on truck (N)
V = velocity of truck (m/s)
P = 7848* 5= 39.24 kW
- 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.
Power train - The power tarin provides power to vehicle. Power train refers to the set of components that generate the power required to move the vehicle and deliver it to the wheels.
An electric powertrain has 60% fewer components than the powertrain of the IC engine vehicle. The components that forms an electric power train are
1) Battery - The battery is a component which will give power to the electric motor. The batteries generally used in electic vehicles are Lithium ion type. Battery also stores the energy.
2) power electronics converter - Power electronic technology deals with processing and controlling the flow of electrical energy in order to supply voltages and currents in a form that optimally suited for end user’s requirements. A power electronic converter uses power electronic components such as SCRs, TRIACs, IGBTs, etc. to control and convert the electric power. The main aim of the converter is to produce conditioning power with respect to a certain application.
The types of power converters used in electic vehicles are :
AC to DC converter - converts AC input signal into DC.
DC to DC converter - converts DC input siganl into DC. Also called chopper beacuse the output we get here is chopped.
DC to AC converter - converts DC iinput signal into AC.
3) Electric motor - The electric motor converts electrical energy into mechanical that is delivered to the wheels via transmission system.
4) Motor controller - Motor controller is used to control the output of the motor as per the drivers requirement.
5) Transmission system - Transmission system is a system consisting of gears which will transmit the power to the wheels.
Here for designing the elecric power train i have assumed that my towing vehicle is going to pull an 'Airbus A319' so here again i will calculate all the forces that will be exerted on both the vehicle and aircraft.
Here i am neglecting the aceleration forces because there is no change in speed of the vehicle and aircraft as it moving with a constant speed. Also iam neglecting the hill climbing force because the vehicle is moving on a flat surface.
so two forces will be acting on both vehicle and aircraft. The first is the Rolling resistance force and second is the Aerodynamic drag force.
The parameters i have assumed for calculations are shown below in table:
S.NO PARAMETERS VALUES
1 Weight of Towing vehicle 40000 kg
2 Weight of Airbus A319 64000kg
3 Coefficient of Rolling resistance (Towing vehicle) 0.06
4 Coefficient of Rolling resistance (Airbus A319) 0.08
5 Fontal area (Towing vehicle) 15
m
2
6 Frontal area (Airbus A319) 32
m
2
7 Coefficient of drag(Towing vehicle) 0.3
8 Coefficient of drag(Airbus A319) 0.1
9 Density of air 1.25
k
g
m
3
10 speed 5 m/s
11 Motor efficiency 0.90
12 Transmission efficiency 0.80
13 Gear ratio 5
14 Tyre radius of towing vehicle 20 inches
First calculating the rolling resistance force by formulae Fr =
c
r
r
⋅
m
⋅
g
Rolling resistance force (fr1) for vehicle =
0.06
⋅
9.81
⋅
40000
= 23544 N or 23.544 KN
Rolling resistance force(fr2) for aircraft =
0.08
⋅
9.81
⋅
64000
= 50227 N or 50.227 KN
Total rolling resistance force (fr1 + fr2) = 73771 N or 73.771 KN
Now calculating drag force by the formulae Fd =
1
2
⋅
e
⋅
c
d
⋅
A
⋅
v
2
Drag force (fd1) for Towing vehicle =
1
2
⋅
1.25
⋅
0.3
⋅
15
⋅
5
2
= 70.132 N
Drag force (fd2) for aircraft =
1
2
⋅
1.25
⋅
32
⋅
0.1
⋅
5
2
= 50 N
Total drag force (fd1 + fd2) = 120.132 N
Total force ( total rolling resistance + total drag force) = (73771 + 120.132) = 73891.132 N or 73.891 KN
Total power required = (Total force * velocity)
Total power required in KW = (73891.132⋅(5) = 369.455 KW
Here i have assumed the gear ratio (G) as 5 and efficiency of gear system i have assumed is 0.8, and motor efficiency i have assumed is 0.9
so calculating the actual power considering all the efficiencies
power required (KW) =
369.455 (0.8)⋅(0.9)= 513.13 KW
Tyre radius for the towing vehicle i have assumed here is 20 inches or 0.508 m
Now i will calculate the Torque required at the wheels by the Torque formuale wich is given by the product of Total force and tyre radius
(Torque) = (Total force)*(Tyre radius)
(Torque) = (73891.132)*(0.508)
(Torque) = 37.536 KN m
Now i will calculate the motor torque by the following formulae
Motor torque = (T)wheelG⋅n
Here T is the wheel torque
G is the gear ratio
n is the efficiency of the gear system
Motor Torque = 37.5365⋅0.8
Motor Torque = 9.384 KN m
Now considering the motor efficiency is well so actual Motor torque will be
(T)motor =
9.384
0.9
= 10.426 KN m
Now i am assuming that the towing time is 20 minutes meaning the towing vehicle is taking 20 minutes to pull the aircraft from the hanger to the runway.
Actual power required is 513.13 KW
Total energy consumed in that process is given by
converting 20 minutes in hours that is 0.33 hours
Total energy = 513.13*0.33 = 169.33
Total energy consumed is 169.33 KWh
so a battery of higher capacity than 169.33 KWh should be selected to perform the operation.
So if i use a battery capacity of 180 KWh which if runs for 20 mins will produce 545.45 or approx 546 KW power which is higher than my actual power so it will be able to run my towing vehicle.
For duty cycle range lets see first what is duty cycle
Duty cycle - Duty cycle is a parameter that is measured in percentage which shows the amount of time the switch is on.
Duty cycle = (Time)/Total time
Total time = (Time)on + (Time)off
Duty cycle basically controls the output voltage.
Duty cycle =
513
546
= 0.93
this means that if i want to my towing vehicle for 20 minutes with a speed of 5 m/s i have to set the duty cycle range as (0 to 0.93)
0 shows the starting condition that the vehicle is starting and 0.93 shows that vehicle has reached the highest speed which in my case is 5m/s.
The above fig shows the block diagram for the electric power train of towing vehicle. here you can see that all the components are connected in series the power train starts with battery which will give power to the electric motor through power converter. The electric motor is further connected with motor controller to control the output as per drivers requirement and finally the motor controller is connected to transmission system which will transmit the power to the wheels.
RESULT - 1) The total weight of various aircarft was menioned in the above section.
2) The difference between the ground speed and air speed was mentioned in the above section
3) The reason for not using aircraft engine power to move it on the ground was also mentioned in the above section.
4) The description of how an aircraft is pushed to runway when it is ready to take off was mentioned in the above section.
6) The force required in my case with my assumed values to push/pull an aircraft by towing vehicle was found out as 580.18 KN
The power required in my case with my assumed values to push/pull an aircraft by towing vehicle was found out as 14520.46 KW
7) For electric power train for Towing vehicle following ratings of the components should be used:
The battery capacity should be above 169.33 KWh so as to run the vehicle for 20 minutes at 5m/s speed.
The motor should be selected which is capable of producing power over 513 Kw
The duty cycle range if I select battery capacity of 180 KWh was found out as ( 0 to 0.93)
CONCLUSION - The designing of electric power train for aircraft in runways has been completed successfully and the results are shown above.