Project-1: Powertrain for aircraft in runways

Part A:

Aim1: Search and list out the total weight of various types of aircrafts.

The aircraft gross weight 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 n aircraft is equal to its takeoff weight. During flight, an aircraft’s gross weight is referred to as the en-route or in-flight weight.

Maximum design taxi weight (MDTM)

The maximum design taxi weight also known as maximum ramp weight is the maximum weight certificated for aircraft maneuvering on the ground as limited by aircraft strength and airworthiness requirements.

Maximum design take-off weight (MDTOW)

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 the landing impact loads on certain parts of the wing structure. The MDLW does not exceed the MDTOW. 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. 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 worthiness requirements. At this weight the subsequent addition of fuel will not result in the aircraft design strength being exceeded. The weight different between the MDTOW and the MDZFW may be utilized only for the addition of fuel.

Minimum flight weight (MFW)

Minimum certificated weight for flight as limited by aircraft strength and airworthiness requirements.

Types of aircraft

There are number of ways to identify aircraft by type. The primary distinction is between those that are lighter than air and those that are heavier than air.

Lighter-than-air

Aircraft such as balloons, nonrigid airships, and dirigibles are designed to contain within their structure volume that, when filled with a gas lighter than air (heated air, hydrogen or helium) displaces the surrounding ambient air floats and floats, just as a cork does on the water. Balloons are not steerable and drift with the wind. Nonrigid airships, which have enjoyed a rebirth of use and interest, do not have a rigid structure but have a defined aerodynamic shape, which contains cells filled with the lifting agent. They have a source of propulsion and can be controlled in all three axes of flight. Dirigibles are no longer in use, but they were lighter-than-air craft with a rigid internal structure, which was usually very large, and they were capable of relatively high speeds. It proved impossible to construct dirigibles of sufficient strength to withstand routine operation under all whether conditions, and most suffered disaster, either breaking up in storm, as with the U.S. craft Shenandoah Akron and Macon or though ignition of the hydrogen, as with the German in 1937.

Heavier than air

This type of aircraft must have a power source to provide the thrust necessary to obtain lift. Simple heavier-than-air craft include kites. These are usually a flat-surfaced structure, often with a stabilizing ‘tail’, attached by a bridle to a string that is held in place on the ground. Lift is provided by the reaction of the string-restrained surface to the wind.

Another type of unmanned aircraft is the unmanned aerial vehicle (UAV), commonly called drones or sometimes remotely piloted vehicles (RPVs). These aircraft are radio-controlled from the air or the ground are used for scientific and military purpose.

Hang gliders are aircraft of various configurations in which the pilot is suspended beneath the wing to provide stability and control. They are normally launched from the high point. In the hands of an experienced pilot, hang gliders are capable of soaring

Civil Aircraft

All nonmilitary planes are civil aircraft. These include private and business planes and commercial airlines. Private aircraft are personal planes used for pleasure flying, often single-engine monoplanes with nonretractable landing gear. They can be very sophisticated, however, and may include such variants as: ’warbirds’, ex-military planes flown for reasons of, ranging from primary trainers to large bomber, ’homebuilt’, aircraft built from scratch or from kits by the owner and ranging from simpler of Piper Cubs to high-speed, streamlined four-planes, designed to be highly maneuverable and to perform in air shows.

 

Aleksander Markin (CC BY-SA 2.0) B      

Business aircraft are used to generate revenues for their owners and include everything from small single-engine aircraft used for pilot training or to transport small packages over short distances to four-engine executive jets that can span continents and oceans. Business planes are used by salespeople, prospectors, farmers, doctors, missionaries, and many others. Their primary purpose is to make the best use of top executive’s time by freeing them from airline schedules and airport operations. They also serve as an executive perquisite and as a sophisticated inducement for potential customers. Other business aircraft include those used for agricultural operations, traffic reporting, forest-fire fighting, medical evacuation, pipeline surveillance, freight hauling, and many other applications. One unfortunate but rapidly expanding segment of the business aircraft population is that which employs aircraft illegally transporting narcotics and other illicit drugs. A wide variety of similar aircraft are used for specialized purposes, like the investigation of thunderstorms, hurricane tracking, aerodynamic research and development, engine testing, high-altitude surveillance, advertising and police work.

 

Aircraft configurations:

Aircraft can be categorized by their configurations. One measure is the number of wings, and the style include monoplanes, with a single wing (that is, on either of the fuselage); biplanes, with two wings, and even though rarely, triplanes and quadplanes. A tandem-wing craft has two wings, one placed forward of the other.

The wing platform is the shape it forms when seen from above. Delta wings are formed in the shape of the Greek letter delta (Δ) they are triangular wings lying at roughly a right angle to the fuslrage. The supersonic Concord featured delta wings.

 

Aim2: Is there any difference between ground speed and air speed?

One of the most confusing concepts for young scientists is the relative velocity between objects. Aerodynamic are generated by an object moving through a fluid. A fixed object in a static fluid does not generate aerodynamic forces. Hot air balloons ‘lift’ because of buoyancy forces and some aircraft like the Harrier use thrust to ‘lift’ the vehicle, but these are not examples of aerodynamic lift. To generate lift an object must move through the air, or air must move past the object. Aerodynamic lift depends on the square of the velocity between the object and the air. Now things get confusing because not only can the object be moved through the air, but the air itself can move. To properly define the relative velocity, it is necessary to pick a fixed reference point and measure velocities relative to the fixed point. In this slide, the reference point is fixed to the ground but it could just as easily be fixed to the aircraft itself. It is important to understand the relationship of wind speed to ground speed and air speed.

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 20mph wind from west is different from a 20mph 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 aircrafts flight path. A positive velocity is defined to be in the direction of the aircrafts motion. We are neglecting cross wind, 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 lifts is the relative velocity between the object and the air, which is called the airspeed. Air speed cannot be directly measured from a ground position, but must be computed from the ground speed and the wind speed. Air speed is the vector difference between the ground speed and the wind speed.

Airspeed = Ground speed – Wind speed

Aim3: Why is it not recommended to use aircraft engine power to move it on the ground at Airport?

Unless an aircraft is in a location where it is unwise to taxi under aircraft power and necessitating a tow by a large tractor, the aircraft’s engine is how the craft moves. Obviously, it is prudent to use only the amount of power to get the airplane moving and then reduce the power for taxing to avoid high volumes of air spreading debris or damaging other aircraft or ground vehicles.

Aim4: 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 the most of the time, a small vehicle is needed to push the airplane backwards away from the terminal building, because if a plane can reverse its thrust, its not always safe to hit the buildings with a jet blast. So the little trucks push the jets back away from the buildings, but after that, the plane can apply small amount of engine power to roll forward. They push themselves to the runway.

Aim5:  Learn about take-off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.    

The amount of power that an engine is allowed to produce for a limited period of time during takeoff. The use of take off power is usually limited to 5 min for reciprocating engines up to 2 and half for gas turbine engines. This may not always be the case. Specifically, with respect to the reciprocating engines, it is the brake horsepower developed under standard, sea-level conditions and under the maximum conditions of the crankshaft rotational speed and the engine manifold pressure approved for the normal take-off. It is limited in continuous use to the period of time shown in the approved engine specifications. With respect to gas turbine engines, it is the thrust developed under the static conditions at a specified altitude and atmospheric conditions of the rotor shaft rotational speed and gas temperature approved for the normal takeoff. It is limited in continuous use to the period of time shown in the approved engine specifications.

 Design and construction of Aircraft tyre

Carcass piles are used to form the tire. They are sometimes called piles. 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.

What is tire rolling resistance?

When you press down the accelerator in your vehicle, you are essentially transferring energy – in the form of gas or electricity, depending on your automobile, through the engine and other system in your vehicle. That results in your tires turning and enough momentum being built up to move your automobile. To accomplish this, though, your vehicle must overcome a lot of different factors that can make it resistant to forward movement. One of those factors is the tires rolling resistance.

Tire rolling resistance is the energy that your vehicle needs to send to your tires to maintain movement at a consistent speed over a surface. In other words, it is the effort required to keep the tire rolling. The main contributor to the rolling resistance is the process known as hysteresis. Hysteresis is essentially the energy loss that occurs as a tire-rolls through its footprint. The energy loss must be overcome by the vehicle’s engine, which results in wasted fuel.

Tyre pressure

Tyre as the only part of the vehicle that is in the contact with the ground perform a very important function of carrying the load. Compressed air fills the tyre and carries the overall vehicle weight. Therefore, it is very important to maintain correct tyre pressure. Tyres are porous and naturally lose air even when they are not being used. Tyres should be neither underinflated nor overinflated but inflated to manufacturers recommended pressure.

In addition to wing spoilers, airplanes use disc brakes. Airplane disc brakes are similar to the braking system in automobiles. They consist of a pair of a caliper that, when engaged, squeeze pads against the rotors of an airplanes landing gear.

Landing brakes

Disc brakes are designed to remain static all the time. In other words, they don’t rotate with the wheels of an airplane landing gear. As the wheels turn, the disc brake will remain static and stationary. They are a vital component of an airplane braking system because they are designed to apply pressure to the airplane wheels. Disc brakes will squeeze the wheels, thereby slowing down the speed at which they spin. In turn, this reduces the speed of the airplane so that it can come to a complete stop on the runway.

 

Part2:

Aim1: With necessary assumptions calculate the force and power required to push/pull an aircraft by a towing vehicle

Mass of aircraft = 183500 kg

Mass of towing machine = 30000 kg

Coefficient of rolling resistance of aircraft (μ₁) = 0.005

Coefficient of rolling resistance of towing vehicle (μ₂) = 0.002

Drag coefficient of aircraft (Cd₁) = 0.12

Drag coefficient of towing (Cd₂) = 0.6

Frontal area of aircraft (A1) = 320 m²

Frontal area of towing (A2) = 42 m²

Towing speed (V) = 3m/s

Air density = 1.25 kg/m³

g = 9.81 m/s²

Solution:

Rolling resistance,

Fr = μ_rr * m * g

Rolling resistance for aircraft

Fr₁ = μ₁ * m1 * g = 0.005 * 183500 * 9.81 = 9000.675 ≈ 9 kN

Rolling resistance for towing

Fr₂ = μ₂ * m2 * g = 0.002 * 30000 * 9.81 ≈ 589 N

For drag force

F_d = (1/2) ρAV²Cd

For Aircraft

F_d1 = (1/2) ρ A₁ V₁² Cd = (1/2) 1.25 * 320 * 0.12 * 3² = 216 N

For towing

F_d2 = (1/2) ρ A₂ V₂² Cd = (1/2) 1.25 * 42 * 0.6 * 3² = 141.75 N

Total force (F) = Fr₁ + Fr₂ + Fd₁ + Fd₂

F = 9000 + 589 + 216 + 141.75

F = 9946.75 N

Power required to push/pull the aircraft

P = F * V

P = 9946.75 * 3

P = 29.84 kW

Aim2: Develop a model for the calculated force and power using SIMULINK

 

Aim3: Design an electric powertrain with type of motor, its power rating, and energy requirement to fulfil 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. 

Solution:

The 200HP DC motor is separately excited with a constant 150 V DC field voltage source. The armature voltage is provided by an IGBT converter controlled by two PI regulators. The converter is fed by a 515 V DC bus obtained by rectification of a 380V AC 50Hz voltage source. In order to limit the DC bus voltage during dynamic braking mode, a braking chopper has been added between the diode rectifier and the DC7 block.

The first regulator is a speed regulator, followed by a current regulator. The speed regulators outputs the armature current reference used by the current controller in order to obtain the electromagnetic torque needed to reach the desired speed. The speed reference change rate follows acceleration and deceleration ramps in order to avoid sudden reference                changes that could cause armature over-current and destabilize the system. The current regulator controls the armature current by computing the appropriate duty ratios of the 5kHz pulses of the four IGBT devices. For proper system behavior the instantaneous pulse values of IGBT devices 1 and 4 are opposite to those of IGBT devices 2 and 3. This generates the average armature voltage needed to obtain the desired armature current. In order to limit the amplitude of the current oscillations a smoothing inductance is placed in series with the armature circuit.

Output:

Simulation

Before starting the simulation, set the initial bus voltage to 515 V via the GUI block. Start the simulation. We can observe the motor armature voltage and current, the four IGBT pulses and the motor speed on the scope. The current and speed references are also shown. The motor is coupled to a linear load, which means that the mechanical torque of the load is proportional to the speed. The speed reference is set at 500 rpm at t = 0s. Observe that the motor speed follows the reference ramp accurately and reaches steady state around t = 1.3 s

The armature current follows the current reference very well, with fast response time and small ripples. Notice that the current ripple frequency is 5 kHz. At t = 2s, speed reference drops to -1148 rpm. the current reference decreases to reduce the electromagnetic torque and causes the motor to decelerate with the help of the load torque. At t = 2.2 s the current reverses in order to produce a braking electromagnetic torque. This causes the DC bus voltage to increase. At t = 3.25 s, the motor reaches 0 rpm and load torque reverses and become negative. The negative current now produces an accelerating electromagnetic torque to allow the motor follow the negative ramp (-400rpm/s). At t = 6.3 s, the speed reaches -1184 rpm and stabilizes around its reference.

Also Design the parameters in excel sheet