Project-1: Powertrain for aircraft in runways
1. Search and list out the total weight of various types of aircrafts.
Weight plays a crucial role in aircraft design and operation, requiring careful attention from both pilots and maintenance personnel. Excessive weight can diminish the aircraft's efficiency and safety margin during emergency situations. The maximum take-off weight, also known as the total weight, represents the highest permissible mass at which the aircraft is certified for take-off, constrained by structural and other considerations.
MTOW = Maximum take-off weight, MLW = Maximum landing weight, TOR = Take-off run, LR Landing run
Maximum Takeoff Weight:
The maximum weight limits for an aircraft to begin its takeo roll is called the max takeoff weight.
Maximum Landing Weight:
The maximum landing weight is, as you might imagine, the maximum aircraft weight limit approved for an aircraft to land. Landing weight can cause structural damage.
Type MTOW [kg]
Antonov An-225 640,000
Scaled Composites Model 351 Stratolaunch 589,670
Airbus A380-800 575,000
Boeing 747-8F 447,700
Boeing 747-8 443,613
Boeing 747-400ER 412,770
Douglas DC-8-32 140,000
Tupolev Tu-154M 104,000
Bombardier Q400 28,000
ATR 42-500 18,600
BAe Jetstream 41 10,890
Learjet 75 9,752
Cessna Citation CJ4 7,761
MTOW[kg]: Maximum Take off weight in kg
2. Is there any difference between ground speed and air speed?
Ground speed
Ground speed is the horizontal speed of an aircraft relative to the ground. An aircraft heading vertically would have a ground speed of zero.
Ground speed can be determined by the vector sum of the aircraft's true airspeed and the current wind speed and direction; a headwind subtracts from the ground speed, while a tailwind adds to it. Winds at other angles to the heading will have components of either headwind or tailwind as well as a crosswind component.
Wind Speed
For a reference point picked on the ground, the air moves relative to the reference point at the wind speed. 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.
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
The aircraft usually operates on land as well as in air and so we need to study their speed differences in-ground and in air
The ground speed and the airspeed usually change based on the wind component.
If we consider that there is no wind component then, ground speed = airspeed
If the wind is blowing in the tail direction of the aircraft then, (airspeed > ground speed) so, airspeed = ground speed+ wind component.
If the wind is blowing in the head direction of the aircraft then, (airspeed < ground speed)so, airspeed ground speed - wind component.
Also, gravity plays a major role in increasing the aircraft's speed while it is descending.
Here wind speed is the vector difference between ground and airspeed. On a particular day, the wind speed may be zero and it is equal to the ground speed.
If the measured airspeed is greater than the observed ground speed the wind speed becomes positive.
For Visualisation purporse by NASA:
https://www.grc.nasa.gov/www/k-12/airplane/Animation/airrel/anrelg.html
3. 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. Taxiing can save money.
Effectively a loss of control can happen, especially during high power engine running. Damage can occur to the aircraft itself, other aircraft nearby or to airsidestructures.
There is a risk of injury to ground support personnel who may be in relatively close proximity to the aircraft.
It is easier for truck driver to see the surroundings better than the pilot sitting in the cockpit with limited window. The pushback driver knows the airport better than the pilot.
It also saves fuel virgin Atlantic hadproposed a new system in which pushback truck will move the aircraft all the way to runway to save fuel and reduce impact of environment.
The plane engines are very loud. When more than one plane will add up their sound, than it will not be pleasent for passangers and others near airport.
4. How an aircraft is pushed to runway when its ready to take off?
Taxiing
Taxiing is the movement of an aircraft on the ground, under its own power, in contrast to towing or push-back where the aircraft is moved by a tug. The aircraft usually moves on wheels, but the term also includes aircraft with skis or floats . An airplane uses taxiways to taxi from one place on an airport to another; for example, when moving from a hangar to the runway.
Towing
Movement of large aircraft about the airport, flight line, and hangar is usually accomplished by towing with a tow tractor. In the case of small aircraft, some moving is accomplished by hand pushing on the correct areas of the aircraft. Aircraft may also be taxied about the flight line but usually only by certain qualified personnel.
Towing aircraft can be a hazardous operation, causing damage to the aircraft and injury to personnel, if done recklessly or carelessly. This article outline the general procedure for towing aircraft. However, specific instructions for each model of aircraft are detailed in the manufacturer's maintenance instructions and are to be followed in all instances.
5. Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
Take off power:
Take off power 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 is Thrust of propulsion system pushing aircraft along the runway.
D is Aerodynamic Drag of vehicle resisting the aircraft motion.
F is Rolling resistance friction due to the contact of wheels or skids on the ground.
During the take-off run, the imbalance in these forces will produce an acceleration along the runway.
m*(dv/dt)=T-D-F
where, dv/dt is the acceleration along the runway and m is the mass of the vehicle.
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 a climb lift and it will ascend from the ground. The determination of this safe flying speed or rotation speed. V, is a critical factor in determining take-off performance. Take-off rules vary slightly depending on the aircraft category.
For Small commuter aircraft
V= 1.1*VSTALL
or
V=1.05*V Control
where S-Runway length
Take Off power = force*displacement
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. Aircraft's tread pattern is designed to facilitate stability in high crosswind conditions, to channel water away to prevent hydroplaning and for braking effect.
Radial Tyre: Radial tyres feature ply fabric with fibre strands oriented at a 90° angle to the direction of rotation and the sidewall. This construction limits bidirectional flexibility and sidewall flexibility while enhancing the tyre's ability to handle heavy loads. Their unique design makes them resistant to penetration and cuts, with the stiffer tread distributing weight evenly for greater traction. Radial tyres also excel in dissipating heat efficiently.
Bias-ply Tyre: Bias-ply tyres have fabric plies oriented both with and across the direction of rotation and the sidewall. The bias orientation allows the tyre to be flexible and absorb loads, with tyre strength achieved through additional plies. These tyres offer cut resistance in the sidewall area but may not provide as smooth a riding experience compared to radial tyres.
Tyre Pressure:
Given the extreme conditions of pressure, load, and speed experienced by aircraft tyres, their maintenance and servicing are of paramount importance. Proper tyre inflation pressure is crucial in preventing tyre-related incidents, as failure to maintain adequate inflation can have serious consequences. Regularly checking and servicing tyre pressures is a relatively simple yet effective measure to mitigate risks and ensure optimal tyre performance.
Aircraft tyres are typically inflated with nitrogen to minimize expansion and contraction caused by fluctuations in ambient temperature and pressure during flight. Unlike compressed air, which may contain moisture, nitrogen expands at a consistent rate, as it behaves similarly to other atmospheric gases. Additionally, using an inert gas for tyre inflation eliminates the risk of tyre explosion.
Relation to Rolling Resistance and Tire Pressure:
Braking Forces During Landing:
The following braking devices are used to decelerate the aircraft -
1. Spoilers.
2. Wheel Brakes (Including Anti-Skid systems & Auto-Brake systems).
3. Reverse Thrust
Spoilers:
The mechanical deflection of parts of the wing upper surface by increasing aerodynamic drag on the moving aircraft. This can be achieved by raising upper wing surface panels called ground spoilers or by operation of a tail cone 'clamshell' type air brake and also by increasing the effective downward load on the landing gear and thereby increasing the efficiency of wheel braking.
Wheel Brakes:
To be effective, braking action at any speed depends upon sufficient friction existing between the tires and the runway surface achieved through freely rotating wheels.
Anti skid system:
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.
Using a variety of sources to determine the aircraft speed, the brake units know how fast the wheels should be spinning. If that speed drops significantly, it's because the current brake pressure on that wheel is too great and the wheel is just skidding over the surface.
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.
Reverse Thrust:
Thrust reversers provide a deceleration force that is independent of runway condition. Thrust reverser efficiency is higher at high airspeed therefore. Treversers must be selected as early as possible after touchdown.
Thrust reversers should be returned after reverse idle at low airspeed to prevent engine stall or foreign object damage.
6. A. With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.
B. Develop the model for the calculated force and power using Simulink.
A. With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.
Total mass of the aircraft (including payload) for Airbus A380 = 575,000 kg.
Mass of the pushback: 1000 kg (assumed)
Rolling Resistance (Frr):
Coefficient of rolling resistance (Crr) = 0.002 (on tarmac)
Rolling resistance force is given by
Frr = Crr * m * g
For the aircraft:
Frr = 0.002 * 575000 * 9.81 ⇒ Frr = 11281.5 N ⇒ Frr = 11.2815 kN
For the Towing Vehicle:
Frrt = 0.002 * 1000 * 9.81 ⇒ Frrt = 19.62 N
As the towing vehicle resistance is so less compared to the aircraft because this is a heavy aircraft, this can be neglected.
Aerodynamic resistance (Far):
Drag coefficient (Cd): 0.025
Air Density (ρ) = 1.125 kg/m^3
Frontal Area (A): 150 m^2
Velocity (v) = 14.5 km/h or 4 m/s
Far = 1/2 * Cd * ρ * A * v^2
Far = 1/2 * 0.025 * 1.125 * 150 * 4^2 ⇒ 33.75 N
As the vehicle and plane are moving at very low speed, aerodynamic resistance can be neglected.
Hill Climb Resistance:
Runways are constructed flat, so gradient resistance/hill climb force is neglected.
Total Resistance:
Ft = 11.2815 kN
Power Required:
P = Ft * v ⇒ P = 11.2815 * 4 ⇒ 45.26 kW
The minimum power required by the tow vehicle is 45.26 kW to taxi a heavy aircraft at 4 m/s.
B. Develop the model for the calculated force and power using Simulink.
- constant blocks are used to feed the parameters such as mass, coefficients and other parameters
- using product block the resistive forces are calculated.
- using sum block, total resistive forces can be calculated.
- the outputs are visualised using display blocks.
7. A. Design an electric powertrain with type of motor, it’s power rating, and energy requirement to fulfill aircraft towing application in Simulink. Estimate the duty cycle range to control the aircraft speed from zero to highest. Make all required assumptions. Prepare a table of assumed parameters. Draw a block diagram of powertrain.
B. Also, Design the parameters in excel sheet.
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.
Estimation of Duty Cycle:
Based on the calculation done in study 6
The Power Required for towing of the aircraft is 45.26kW.
Motor Considred for the drive train is REB 90
Technical Data:
Type: REB 90
Voltage: 400–800 V
Continuous / Peak Power: 60–70 kW / 80 kW
Working Rotation: 1,500–4,000 rpm
Max Torque: 300 Nm
Weight: 22,000 g
Cooling: Air / Hybrid (air + fluid)
Considering 60 kW as continuous power, so the voltage will be 400 V.
Battery power is considered to be 550 V.
The duty cycle is given by Vo / Vb, where Vo is the motor required voltage and Vb is the battery voltage.
d = 400 / 550 ⇒ 0.7272
As there will be losses due to the resistance of FET and inductance, the correction factor is considered to be 90%.
With a 10% loss, the voltage demanded by the motor should be 10% more than required.
d = 0.7272 * (1 + 0.1) = 0.799 ≈ 0.8
So, the voltage demand should be around 440 V from the battery.
Assumed Parameters:
Mass of aircraft: 575,000 kg
Mass of the pushback truck: 1,000 kg
Coefficient of Rolling Resistance: 0.002
Drag Coefficient: 0.025
Air density: 1.125 kg/m^3
Frontal Area: 150 m^2
Velocity: 4 m/s
Uphill gradient: 0 degrees
Battery Voltage: 550 V
Correction Factor: 0.8
Block Diagram:
Simulink Model:
Input:
Output:
From motor-
From battery-