Powertrain for aircraft in runways - HEV
Project-1: Powertrain for aircraft in runways
Objective:
- To search and list out the total weight of various types of aircrafts.
- To brief differences between ground speed and air speed.
- Why is it not recommended to use aircraft engine power to move it on the ground at Airport?
- How an aircraft is pushed to runway when its ready to take off?
- Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
- To calculate the force and power required to push / pull an aircraft by a towing vehicle.
- Design an electric powertrain with 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.
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1. Total weight of various types of aircrafts.
Manufacturer's empty weight (MEW)
Also called Manufacturer's Weight Empty (MWE) or Licensed Empty Weight
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.
Zero-fuel weight (ZFW)
This is the total weight of the airplane and all its contents (including unusable fuel), but excluding the total weight of the usable fuel on board.
As a flight progresses and fuel is consumed, the total weight of the airplane reduces, but the ZFW remains constant.
Maximum zero fuel weight (MZFW) is the maximum weight allowed before usable fuel and other specified usable agents (engine injection fluid, and other consumable propulsion agents) are loaded.
Operating empty weight (OEW) (Roughly equivalent to basic empty weight on light aircraft)
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.
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.
Maximum takeoff weight (MTOW)
This is the maximum weight at which the pilot of the aircraft is allowed to attempt to take off.
Regulated takeoff weight (RTOW)
Depending on different factors (e.g. flap setting, altitude, air temperature, length of runway), RTOW or maximum permissible takeoff weight varies for each takeoff. It can never be higher than MTOW.
Maximum landing weight (MLW)
This maximum weight at which an aircraft is permitted to land.
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2. To brief differences between ground speed and air speed.
Ground speed is the airplane’s speed relative to the surface of the Earth, airspeed – at least true airspeed – is its speed relative to the air it is flying in.
True airspeed is simply the speed at which an aircraft is moving relative to the air it is flying in. As such, it’s also the speed at which the air is flowing around the aircraft’s wings.
Ground speed, on the other hand, is the aircraft’s speed relative to the ground. One thing that should be noted here is that it’s its horizontal rather than vertical speed – an aircraft climbing completely vertically would have a ground speed of zero.
The relationship between airspeed and ground speed is fairly simple. Ground speed is simply the sum of airspeed and wind speed.
If the aircraft is flying in the same direction as the wind is blowing, the aircraft experiences tailwind, and its ground speed is higher than its airspeed. On the other hand, if the wind is blowing against the direction the aircraft is traveling in, the aircraft experiences headwind, and its ground speed is lower than its airspeed.
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3. Why is it not recommended to use aircraft engine power to move it on the ground at Airport?
Taxiing is the movement of an aircraft on the ground, under its own power, in contrast to towing or pushback where the aircraft is moved by a tug. The aircraft usually moves on wheels, but the term also includes aircraft with skis or floats (for water-based travel).
An airplane uses taxiways to taxi from one place on an airport to another; for example, when moving from a hangar to the runway. The term "taxiing" is not used for the accelerating run along a runway prior to takeoff, or the decelerating run immediately after landing, which are called the takeoff roll and landing rollout, respectively.
Generally aircrafts move with the help of Engine power on the ground at airport. The difference being that the engine power is not used at its full performance as obtained during the flight of the aircraft. The engine is operated under throttle 1 condition which uses engine power to obtain less speed. Sometimes it is not recommended to use the engine power to move the aircraft on the ground at Airport. There are multiple reasons for this one of which is that there are a lot of things as well as airport crew members surrounding the aircraft. If the aircraft uses its engine power in such an environment, the engine turbine or fan may suck or throw the surrounding objects, trash or even human beings which are accidental.
he air intake of a jet engine is powerful enough to suck in a human body. Even at a distance, the jet engine suction is strong enough to devour loose debris e.g., rags, bolts, paper, stones, catering foils, plastic cups and bags. All these will damage the jet engine. In case of Jet exhaust, the temperatures of the exhaust can severely burn the skin of a person standing too close. The jet blast or prop wash can exceed 100 mph and is capable of moving or toppling heavy persons or equipment. Other reasons being the noise of the engine which are at very high decibels as well as the fumes emitted by the burning of the fuel, the fuel consumption of an aircraft and also the risk of damage to the engine due to foreign objects.
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4. How an aircraft is pushed to runway when its ready to take off?
There are two ways through which an aircraft is pushed to the runway on Airport.
Pushback – In aviation, pushback is an airport procedure during which an aircraft is 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 reverse thrust (a procedure referred to as a power back), the resulting jet blast or prop wash 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. 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. When the aircraft is stopped, the brakes of the towing vehicle alone should not be relied upon to stop the aircraft. The man in the cockpit should coordinate the use of the aircraft brakes with those of the towing vehicle.
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 for water-based travel. An airplane uses taxiways to taxi from one place on an airport to another; for example, when moving from a hangar to the runway. The term taxiing is not used for the accelerating run along a runway prior to take-off, or the decelerating run immediately after landing, which is called the take-off roll and landing rollout, respectively. When taxiing, aircraft travel slowly. This ensures that they can be stopped quickly and do not risk wheel damage on larger aircraft if they accidentally turn off the paved surface. Taxi speeds are typically 30 to 35 km/h.
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5. Take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
Take-Off Power : Take-off is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne. 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 take-off. Large transport category aircraft may use a reduced power for take-off, where less than full power is applied in order to prolong engine life, reduce maintenance costs and reduce noise emissions. The aircraft is permitted to accelerate to rotation speed. 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 and once proper air displacement occurs under or over the wings, an aircraft will lift off on its own.
Generally, the T-O phase is split into the segments shown in the figure below. The ground roll is the distance from brake release to the initiation of the rotation, when the pilot pulls the control wheel (or stick or yoke) backward in order to raise the nose of the aircraft. This maneuver is required to increase the area of attack of the airplane to help it become airborne. The aircraft typically remains in this attitude for some 1-3 seconds, depending on aircraft size, before the tires lose contact with the ground. This segment is called the rotation. The rotation phase concludes as the aircraft lifts off the ground and begins the transition and subsequent climb phase.
Here V is the instantaneous airspeed of the aircraft, V is the ground run speed, V is the lift off for rotation speed, V is the climb speed and V is the stalling speed in the T-O configuration. This means that if the airplane features high-lift devices, V refers to the stalling speed with flaps deployed. The important point is that the airplane must accelerate from standstill to a given airspeed, called the lift-off speed, before it can, well, lift off. Generally the take of speed or the climb speed of the aircraft (V2) is calculated as,
Tyre Design – An aircraft must withstand a wide range of operational conditions. When on the ground, it must support the weight of the aircraft, during taxied it must provide cushioned ride. At take off the tire structure must be able endure forces generated at higher angular velocities. Landing requires the tire to absorb impact shocks. These extreme demands require a tire which is highly engineered and precisely manufactured. For these tires are made of various rubber, fabric and steed material. To meet the aircraft demands tire are manufactured in two distinct categories Bias tire and radial tire.
Bias Tyre construction – these types of tire consist casing plies which is running diagonally at approximate right angle to one another. The number of plies and the angles at which they are laid decide strength and load capacity.
Radial Tyre construction – these are the most modern design of aircraft tyres.in radial tires each carcass ply is laid at right angle. The radial tire offers more landings per thread and lighter weight than a bias tire.
Tyre Pressure : Aircraft tires generally operate at high pressures, 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. During the tests the tires have to be filled with water, to prevent the test room being blown apart by the energy that would be released by a 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. Dry nitrogen expands at the same rate as other dry atmospheric gases (normal air is about 80% nitrogen), but common compressed air sources may contain moisture, which increases the expansion rate with temperature. The requirement that an inert gas, such as nitrogen, be used instead of air for inflation of tires on certain transport category airplanes was prompted by at least three cases in which the oxygen in air-filled tires had combined with volatile gases given off by a severely overheated tire and exploded upon reaching auto ignition temperature. The use of an inert gas for tire inflation eliminates the possibility of tire explosion.
Rolling resistance – when a tire rolls on the road, mechanical energy is converted to heat as a result of phenomenon referred to as rolling resistance. The term rolling resistance is often mistaken as a measure of the force opposing tire rotation, when instead is actually a measure of rolling energy loss.i in another terms we can say rolling resistance is the effort required to keep a given tire rolling. Its magnitude depends on the tire used, roughness of road, inflation pressure, load and speed. Generally rolling resistance is given by following formula –
F = Cr ⋅ R
F = Rolling resistance force Cr = rolling resistance coefficient
R = Normal force between surface and tire
Brake forces when landing : One of the effective parameters in fluencing landing run is the brake force, while it is ineffective during take-off operation.
The airspeed during approach is decreased by increasing the angle of attack, but airspeed during ground roll is decreased by applying brakes. The mechanical brakes present at the wheels are of two common kinds; drum brakes and disc brakes. Drum brakes usually reside inside the wheel, which reduces their frontal area and, if mounted on retractable landing gear, makes them a possible solution for space-claim issues in thin wings. Disc brakes have superior performance, are lighter, and easier to maintain. The brake force is sometimes reinforced with other means such as parachute, engine thrust reversal, hook and string, and spoiler. These factors will reduce the landing run. The maximum aircraft angle of attack during landing is often 2°–4° less than the maximum aircraft angle of attack during take-off (e.g., 10°–15°). To compensate for this angle of attack reduction, a higher flap detection is employed. In most cases, flap de tection during landing is between 30° and 60°, while during take-off it is between 5° and 30°.
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6. To calculate the force and power required to push / pull an aircraft by a towing vehicle.
The possible forces acting on the vehicle are
- Rolling resistance force
- Air drag force
- Hill climb force
- Neglecting all the losses
Assumptions
- Mass of the aircraft: m = 75,000 Kg
- Rolling ground friction coefficient of wheels for Dry concrete or asphalt road: μ = 0.03
- Acceleration due to gravity: g = 9.81ms^2
- Frontal area of an aircraft: A = 100m^2
- Final Velocity of an aircraft: v = 5m/s
- Initial Velocity of an aircraft: u = 0
- Coefficient of drag of an aircraft: Cd = 0.015
- Density of air: ρ = 1.225kgm^3
- Acceleration time of aircraft: t = 10s
Calculation EXCEL
Based on assumed condition, Total Towing Power required is 200Kw
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7. Design an electric powertrain with 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
Consider the results and assumptions from previous case,
Motor data sheet
An AC Induction Motor based on online searches is selected
Power, Duty Cycle & Energy
Block Diagram of Powertrain
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