Project-1: Powertrain for aircraft in runways
AIM: Part A:
1. Search and list out the total weight of various types of aircrafts.
2. Is there any difference between ground speed and air speed?
3. Why is it not recommended to use aircraft engine power to move it on the ground at Airport?
4. How an aircraft is pushed to runway when its ready to take off?
5. Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
Ans: 1
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 .
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.
|
Type |
MTOW [kg] |
MLW [tons] |
|
640,000 |
591.7 |
|
|
589,670 |
||
|
575,000 |
394 |
|
|
447,700 |
346.091 |
|
|
443,613 |
306.175 |
|
|
412,770 |
295.742 |
|
|
Antonov An-124-100M |
405,060 |
330 |
|
396,900 |
295.742 |
|
|
381,000 |
288.417 |
|
|
377,840 |
285.700 |
|
|
377,840 |
260.320 |
|
|
371,950 |
240 |
|
|
367,400 |
256 |
|
|
347,800 |
260.816 |
|
|
351,800 |
251.29 |
|
|
347,450 |
223.168 |
|
|
340,200 |
265.300 |
|
|
308,000 |
233.5 |
|
|
299,370 |
237.683 |
|
|
297,550 |
213.00 |
|
|
276,700 |
190 |
|
|
273,300 |
185 |
|
|
270,000 |
175 |
|
|
270,000 |
195.04 |
|
|
256,280 |
183 |
|
|
254,000 |
192.777 |
|
|
254,000 |
201.849 |
|
|
253,500 |
181 |
|
|
250,000 |
175 |
|
|
242,000 |
185 |
|
|
242,000 |
180 |
|
|
231,300 |
166.92 |
|
|
228,000 |
172.365 |
|
|
211,400 |
||
|
208,000 |
175 |
|
|
204,000 |
158.758 |
|
|
192,000 |
140 |
|
|
187,000 |
136.08 |
|
|
185,000 |
111.1 |
|
|
163,000 |
138 |
|
|
159,000 |
136.078 |
|
|
157,000 |
124 |
|
|
152,000 |
151.9 |
|
|
151,000 |
97.5 |
Maximum taxi weight (MTW)
The maximum taxi weight (MTW) (also known as the Maximum Ramp Weight (MRW) is the maximum weight authorized for manoeuvre (taxiing or towing) an aircraft on the ground as limited by aircraft strength and airworthiness requirements. It includes the weight of taxi and run-up fuel for the engines and the APU (Auxillary Power Unit).
It is greater than the maximum takeoff weight due to the fuel that will be burned during the taxi and runup operations.
The difference between the maximum taxi/ramp weight and the maximum take-off weight (maximum taxi fuel allowance) depends on the size of the aircraft, the number of engines, APU operation, and engines/APU fuel consumption, and is typically assumed for 10 to 15 minutes allowance of taxi and run-up operations.
Maximum takeoff weight (MTOW)
The maximum takeoff weight (also known as the maximum brake-release weight) is the maximum weight authorised 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 and the APU.
In operation, the maximum weight for takeoff may be limited to values less than the maximum takeoff weight due to aircraft performance, environmental conditions, airfield characteristics (takeoff field length, altitude), maximum tire speed and brake energy, obstacle clearances, and/or en route and landing weight requirements.
Ans-2 Is there any difference between ground speed and air speed?
There is a difference between ground speed and air speed to understand this we should take in to account wind speed too.
Wind Speed :
For a reference point picked on the ground, the air moves relative to the reference point at the wind speed. Notice that the wind speed is a vector quantity and has both a magnitude and a direction. Direction is important. A 20 mph wind from the west is different from a 20 mph wind from the east. The wind has components in all three primary directions (north-south, east-west, and up-down). In this figure, we are considering only velocities along the aircraft's flight path. A positive velocity is defined to be in the direction of the aircraft's motion. We are neglecting cross winds which occur perpendicular to the flight path but parallel to the ground, and updrafts and downdrafts which occur perpendicular to the ground
Ground Speed
For a reference point picked on the ground, the aircraft moves relative to the reference point at the ground speed. Ground speed is also a vector quantity so a comparison of the ground speed to the wind speed must be done according to rules for vector comparisons.
Airspeed
The important quantity in the generation of lift is the relative velocity between the object and the air, which is called the airspeed. 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.
Airspeed = Ground Speed - Wind Speed
On a perfectly still day, the airspeed is equal to the ground speed. But if the wind is blowing in the same direction that the aircraft is moving, the airspeed will be less than the ground speed.
For Example:
Suppose we had an airplane that could take off on a windless day at 100 mph (liftoff airspeed is 100 mph). We are at an airport with an east-west runway that is 1 mile long. The wind is blowing 20 mph towards the west and the airplane takes off going east. The wind is blowing towards the aircraft which we call a headwind. Since we have defined a positive velocity to be in the direction of the aircraft's motion, a headwind is a negative velocity. While the plane is sitting still on the runway, it has a ground speed of 0 and an airspeed of 20 mph:
Airspeed = Ground Speed (0) - Wind Speed (-20) = 20 mph
The airplane starts its take off roll and has a constant acceleration a. From Newton's second law of motion, the ground speed V at any time t is:
V = a * t
and the distance d down the runway at any time is:
d = 1/2 * a * t^2
For a fixed length runway, this specifies the time to be used in the velocity equation. Let's assume that at 5000 feet down the runway, the velocity is 80 mph. Then the airspeed is given by
Airspeed = Ground Speed (80) - Wind Speed (-20) = 100 mph
and the airplane begins to fly. Now another pilot, with exactly the same airplane decides to take off to the west. The wind is now in the same direction as the motion and this is called a tailwind. The sign on the wind speed is now positive, not negative as with the headwind. The acceleration along the ground is the same, so at 5000 feet down the runway, the ground speed is again 80 mph. The airspeed is then given by:
Airspeed = Ground Speed (80) - Wind Speed (20) = 60 mph
Ans-3 Why is it not recommended to use aircraft engine power to move it on the ground at Airport?
Aircraft towing equipment is typically used for the towing and pushback process to avoid some of the significant hazards posed by aircraft engines. When an aircraft's engine is activated, the thrust can create a high-speed wind that can easily cause damage to the airport terminal, surrounding ground vehicles, jetway, baggage and most importantly, ground personnel.
Suppressing the use of engines is especially important when towing a large aircraft, as their more powerful thrust capabilities can become exceedingly dangerous. Engine thrust can easily send any loose items airborne, turn the tiniest grains of dust into hazardous projectiles and create debris that can cause damage to multi-million dollar engines. Additionally, aircraft engines consume a great deal of fuel and generate extreme noise that can be harmful to ground personnel. Using a pushback tug for aircraft is simply a more economical and safer option than running the engines.
The extensive noise arises from the engine power also dangerous for humans and other living things around the vicinity.
Hence for the above reasons it is not recommended to use engine power to move on the ground.
Ans-4 How an aircraft is pushed to runway when its ready to take off?
Airplanes have engines, and they can use them to move forward along the ground. So they push themselves to the runway.
It is true that most of the time, a small vehicle is needed to push the larger commercial airplanes backwards away from the terminal building, because even if a plane can reverse it’s thrust, it’s not always safe to hit the buildings with that reverse thrust. So the little trucks push the bigger planes back away from the buildings, but after that, the planes can apply a small amount of engine power to roll forward just as all airplanes can.
Aircraft push themselves to the runway.
In aviation, pushback is an airport procedure during which an aircraftis pushed backwards away from an airport gate by external power. Pushbacks are carried out by special, low-profile vehicles called pushback tractors or tugs.
Although many aircraft are capable of moving themselves backwards on the ground using reverese thrust (a procedure referred to as a powerback), the resulting jetblast or propwash 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.
Ans-5 Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
Take off power=>
Power Requirement to Keep a Jet Aircraft in the Air
The total energy of an aircraft flying in the atmosphere can be calculated using equation,
E = ½ m v2+ mgh
However, the engines mounted onto the wings of the plane are required to provide additional energy per time, power, in order to keep the aircraft flying at a constant altitude and speed. This extra power needed to overcome the drag acting on the airplane and is calculated using
P = (dh/dt) m g
where (dh/dt) is the decent speed required to keep the plane's speed constant if the engines fail.
Takeoff is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne. For aircraft traveling vertically, this is known as liftoff.
For aircraft that take off 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 costs and reduce noise emissions. In some emergency cases, the power used can then be increased to increase the aircraft's performance. Before takeoff, the engines, particularly piston engines, are routinely run up at high power to check for engine-related problems. The aircraft is permitted to accelerate to rotation speed (often referred to as Vr). The term rotation is used because the aircraft pivots around the axis of its main landing gear while still on the ground, usually because of gentle manipulation of the flight controls to make or facilitate this change in aircraft attitude (once proper air displacement occurs under / over the wings, an aircraft will lift off on its own; controls are to ease that in).
The nose is raised to a nominal 5°–15° nose up pitch attitude to increase lift from the wings and effect liftoff. For most aircraft, attempting a takeoff without a pitch-up would require cruise speeds while still on the runway.
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, 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.
A Boeing 737NG & 737MAX uses 6 wheels, Boeing 787 uses 10 wheels, Boeing 777 uses 14 wheels and Airbus A380 uses 22 wheels. Aircraft tyres work under extreme conditions, carrying up to 340 tons and accelerating at over 250 km/hour at takeoff, in addition to enduring varied environmental stress when in flight and taxiing.
Design and Construction of Aircraft tyre
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 aeroplane.
3. 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.
Some technical aspects of the tyre :
Retreading – Retreading is methods of restoring a worn tyre by renewing the tread area or by renewing the tread area plus one or both sidewalls. Repairs are included in the tyre retreading process.
Load Rating – Load rating is the maximum permissible load at a specified inflation pressure.
Ply Rating – Ply Rating is used to identify the maximum recommended load rating and inflation pressure for a specified tyre. It is an index of tyre strength.
Speed Rating – The speed rating is the maximum takeoff speed to which the tyre has been tested.
Skid Depth – Skid depth is the distance between the tread surface and the deepest groove as measured in the mould.
Aircraft tyres must have an approved speed and load rating and have sufficient clearance when retracted through landing gear to allow for tyre growth. Tyre growth is the increase in the size of the tyre due to centrifugal forces at high speed.
Aircraft tyres may be Tube-type or Tubeless
Tubeless tyres are more advantageous over tube-type. There is no longer the use of tube-type tyre in recent aviation. Nowadays all airliners are using tubeless tyres. Tubeless that are meant to be used without a tube has the word TUBELESS on the sidewall of the tyre.
Aircraft tyres may be Radial or Bias
Almost all airliners are using Radial tyre. Bias is an older design, and it’s mainly used for road vehicles. Radial tyres have the word RADIAL on the sidewall. Radial tires are more expensive than bias-ply tyres. Radial tires are in demand because of their lower life cycle cost and long term value.
Radial tyre construction :
Radial tires are the most modern design of aircraft tyres. It is a design that is similar to that of car tyres. Typically, the radial tyre offers more landings per tread and lighter weight than a bias tyre; though sometimes at the expense of retread lives.
Radial aircraft tyres differ to bias aircraft tyres in that the plies all run radially from bead to bead at approximately 90° to the centre-line of the tyre. Angled belt plies are laid between the tread and the top casing ply, resulting in a flatter tread and adding strength to the tyre.
Bias ply tyre :
A bias-ply tyre 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.
Rolling Resistance :
Rolling resistance is one of the forces that act to oppose the motion of a cyclist. It is caused mainly because of deformation of the tyre and can be understood by thinking about:
1. energy losses due to heat (hysteresis)
2. the forces pushing on the tyre.
Energy is lost as heat
As the tyre comes into contact with the road, it changes shape as it is compressed (pushed in a bit). This compression causes parts of the rubber tube and the casing of the tyre to heat up. It also causes the tread on the outside of the tyre to heat up as it comes into contact with the road. A tyre with knobbly tread will have a lot more rolling resistance than a smooth tyre because there will be more rubber being compressed and so there will be more heat.
The tyre is a bit like a spring or a rubber band. Some of the energy is stored as the tyre becomes compressed (squeezed in). As the tyre comes back off the road, there is not as much of this stored energy returned because some of it has gone towards making the tyre heat up. This loss of available energy due to heating is called hysteresis. This means there will be less energy available to make the bike go faster.
If you feel the temperature of your tyres when you have been biking fast, you will notice this heat. If your tyres are not pumped up hard, there will be even more heat created.
The force of rolling resistance does not change at higher speeds. However, because there is a lot more heat being produced at higher speeds, the cyclist uses more power (energy per second) to work against rolling resistance.
Forces on the front part of the tyre are greater
Tyre pressure =>
An aircraft tire or tyre 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 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.
Inflation :
Each of the twelve Boeing 777-300ER 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.
Aircraft tires generally operate at high pressures, Inflation up to 200 psi (14 bar; 1,400 kPa) for airliners, and even higher for business jets.
Tests of airliner aircraft tires have shown that they are able to sustain pressures of maximum 800 psi (55 bar; 5,500 kPa) before bursting.
Aircraft tires are usually inflated with nitrogen to minimize expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight.
Brake forces when landing :
Bringing at aircraft down to the runway from 37,000 feet is only part of the challenge. It’s not over until the aircraft is safely parked at its gate. In order to do this, pilots have a number of systems available to slow the aircraft down, even in a blizzard on a snowcovered runway.
The 787 braking system:
Stopping a 200-tonne aircraft landing at 180 mph requires a lot of braking force. To do this, the 787 has one brake unit on each of the eight wheels on the main gear assembly.
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.
That’s the case on the 787 Dreamliner. Designers did away with the use of the hydraulic system and all its associated architecture and instead used electricity to power the brakes. 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.
Electric brakes
The brake system on the 787 Dreamliner is controlled by the pilots pressing the tops of the rudder pedals under their feet, demanding the rate of braking which they require. This sends an electronic signal to the Left and Right Brake System Control Units (BSCUs).
These then send signals to the four Electronic Brake Actuator Controllers (EBAC) which control the rate of braking on the wheels. Each wheel has four Electric Brake Actuators (EBA), a kind of piston which presses against the carbon brake discs.
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Part B
6. A. With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.
Since the surface is flat so We will consider two forces Rolling resistance and aerodynamic drag force
The main two forces acting while pushing or pulling an aircraft by using towing vehicle
will be aerodynamic drag and rolling resistance force.
Rolling Resistance can be calculated as;
F=Crr*N,
where N is the normal force acting perpendicular to the surface on which wheel is
rolling.
N = m*g, where m is the mass and g is the acceleration due to gravity.
We are taking the typical value for Crr Coefficient of Rolling resistance , i.e, 0.02.
Aerodynamic drag force can be calculated as;
Fad = 0.5* air density * A*Cd*v²
where A is the frontal area and v is velocity.
Assumptions:
- Velocity or speed of vehicle in m/s = 8m/s.
- Mass of towing vehicle = 35000 kg.
- Mass of aircraft = 140000 kg
- Total mass, m = 140000+35000 = 175000 kg
Frontal area, A = 20 m². - Drag coefficient, Cd = 0.5
- Coefficient of Rolling resistance, Crr = 0.02
- Air density = 1.25 kg/m³
- acceleration due to gravity = 9.8 m/s²
- Calculating, Rolling resistance force, F = Crr*m*g = 0.02*175000*9.8 = 34300 N.
Calculating aerodynamic drag, Fad = 0.5*air density * A*Cd*v²=0.5*1.25*20*0.5*8² = 400
N.
Total force required to push / pull an aircraft by a towing vehicle = Rolling resistanceforce+aerodynamic drag = Frr +Fad = 34300 N+400 N = 34700 N.
Total power required to push / pull an aircraft by a towing vehicle, P = Force *velocity
=34700*8= 277600 W = 277.6 KW.
B. Develop the model for the calculated force and power using Simulink.
7. A
We are considering the total power and force calculated in the above section 6.A.
Total force required to push / pull an aircraft by a towing vehicle, Ft= 34700 N
Total power required to push / pull an aircraft by a towing vehicle, P = 277.6 KW
Now we need to assume the values of Gear ratio, Transmission efficiency, Motor efficiency,
Radius of tyre,r and the time taken for towing, battery capacity used by towing vehicle.
Assumptions:
Gear ratio 7
Transmission efficiency 85%
Motor efficiency 95%
Tyre radius, r 15 inches = 0.381m
Battery capacity 400 KW / 1290.3 Ah
Time taken for towing 10 mins = 0.16 hrs
Wheel torque, Tw = Force * Radius = 34700 * 0.381= 13220.7 Nm
Motor torque,Tm = Tw/(G*transmission efficiency) = 13220.7/(7*0.85)= 2221.96 Nm
Required motor torque with motor efficiency of 95% = 2221.96/0.95 = 2338.905 Nm
Considering all efficiencies, total Power, P = 277.6 /(0.85*0.95) = 343.77 KW.
Total energy consumed for 10 minutes = 343.77 *0.16 =55 KWh.
Duty cycle, D = Required power/Rated power = 343.77 /400 = 0.85 ≈
85% duty cycle.
As my motor Nominal voltage is 310 and Total power calculate is 343 so my motor HP rating will be above 300 Horse powers.
Due to higher weight of load we require higher HP motor which is not given in simulink model . These is the rating which i got from the calculations . According to this we can design the motor .
b.
