Project-1: Powertrain for aircraft in runways
Part A:-
Objective:-
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.
- Study 1:-
Objective 1:- Search and list out the total weight of various types of aircrafts.
The different terms represent different weights or masses. For each flight, the weights are taken into account for several reasons.
- Manufactre'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) :- The zero-fuel weight (ZFW) of an aircraft is the total weight of the airplane and all its contents, minus the total weight of the usable fuel on board. Unusable fuel is included in ZFW.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) :- Operational empty weight (OEW) is the basic empty weight or fleet empty weight plus operational items. The operator has two choices for maintaining OEW. The loading schedule may be utilized to compute the operational weight and balance of an individual aircraft, or the operator may choose to establish fleet empty weights for a fleet or group of aircraft.
- 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. The following image depicts takeoff weight components.
- Maximum Ramp Weight (MRW) :- Also called maximum taxi weight (MTW). It is the maximum weight authorized for maneuvering (taxiing or towing) an aircraft on the ground.
- Aircraft Gross Weight :- It is the total aircraft weight at any moment during the flight or ground operation. This decreases during flight due to fuel and oil consumption.
Types of aircraft :-
Objective 2 :- Is there any difference between ground speed and air speed?
Ground speed :-It is when you are measuring the horizontal velocity of the plane relative to the ground. It’s the speed that is shown on the speedometer of a car. If your car suddenly started levitating for God knows what reason, the speedometer reading would not take into account your vertical velocity, so a plane could be moving vertically but still have zero ground speed. It is the velocity you have in any direction perpendicular to the vertical axis.
Air speed :- Is the velocity of the plane relative to the winds around it. It is like having two cars, one travelling at 100 km/h and the other at 60 km/h, both towards the right. These speeds are the ground speeds of the car. The air speed is wanting to know the difference in velocity between the two cars, which is 40 km/h, or -40 km/h depending on which car you are looking at. If the 100 km/h car represents the plane, and the 60 one the winds, then the difference is 40km/h. So you are essentially measuring how fast the plane is compared to the winds. And in the example above, if the car was travelling at 60 km/h to the left instead, the speed difference would be 160 km/h. It is the same thing for planes: when winds blow towards the plane, the plane’s air speed is bigger than the ground speed, because you are adding to the ground speed, and when winds blow in the same direction as the plane, the air speed is less than the ground speed.
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.
From the above two figures indicates that relative velocity with respect to the aircraft reference and ground reference.
The aircraft usually operate on land as well as in air and so we need to study their speed difference in ground and in air.
The ground speed and he airspeed usually chnge based on the wind component.
If we consider that there is no wind component then, ground speed = airspeed Speed.
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 mojor role in increasing the aircraft's speed whileit is descending.
Here wind speed is the vector difference between ground andairspeed. On a perticular day, the wind speed may be zero ad it is equal to the ground speed.
If the measured airspeed is greater than the observed groundspeed the wind speed become positive.
Objective 3 :- Why is it not recommended to use aircraft engine power to move it on the ground at Airport?
Although most aircraft are capable of moving themselves on the ground, it is not typically done due to the following reasons,
- The jet blast from the engines can damage the terminal building and nearby equipment. It can even throw away people standing nearby.
- Engines can blow sand and debris.
- Engines can suck in sand and debris which can cause serious damage to the engine.
- It is easier for the truck driver to see the surroundings better than the pilot sitting in the cockpit with limited windows.
- The pushback truck driver knows the airport better than the pilot.
- The plane engines are very loud. This noise can add up substantially when multiple planes are moving around the airport. It won't be a pleasant experience for people sitting inside the terminal, as most people don't even like the sound of powerful motor-bikes.
- It saves fuel.
- Modern planes are huge. It is difficult to navigate such gigantic structures through limited space. An A380 is eight stories high. The pilots won't be able to see anything directly in-front of them or anything behind the wings.
Actually Pushback is for moving the aircraft backwards from the gate, and towing or taxing is the procedure to move the aircraft. These machineries are called as aircraft tugs. Aircraft tugs are real modern marvels, moving aircraft weight hundreds of tons all day, every day. A true pushback tug aims to allow the operator to have excellent visibility of the attaching mechanism between airplane and tug.
While moving the aircraft in the reverse direction by applying the forward thrust, care msut be taen because reverse thrust is unsafe when stopped or at low speed. This is because the nose may lift, dropping the tail on to the tarmac. The cause is the engines being at some considerable height from the ground and the aircraft centre of gravity being just ahead of the main (rear) wheel set. Additionally, once moving backwards, if the aircraft’s own brakes are used, the same can happen, i.e., the plane can sit on its tail.
Objective 4 :-How an aircraft is pushed to runway when its ready to take off ?
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.
Objective 5 :-Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
Take off :- is the phase of flight in which an aircraft goes through a transition from moving along the ground (taxiing) to flying in the air, usually starting on a runway.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 :-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.
During 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 climb lift and it will ascend from the ground. The determination of this safe flying speed or rotation speed, `V_R` is a critical factor in determining take-off performance. Take-off rules vary slightly depending on the aircraft category.
Take off Field Length :- The required length of runway will be the sum of the distance required to get to rotation speed and the extra length required to clear a 50ft obstacle or the extra length required to allow for rapid braking if the pilot decides to abort take-off at the decision speed.
This length will typically be considerably longer than the distance required to achieve rotation (flying) speed. A rough approximation is that runway total length is around (2.S1)2⋅S1">
Therefore, Takeoff power = force * displacement =
Rolling Resistance :- The landing run can be calculated in a similar fashion to the take off distance. The aim is again 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 a pitch manoeuvre during the flare portion of the approach which which increase drag an decelerate the aircraft to minimum flying speed. The deceleration on the landing roll from VTD to V0 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.
The negative acceleration or deceleration value will be based on friction coefficient for maximum braking and the value of reverse thrust (if available).
Aircraft Tyre design :- Aircraft wheels are an important component of a landing gear system. With tires mounted upon them, they support the entire weight of the aircraft during taxi, tkeoff, and landing. The typical aircraft wheel is lightweight, strong, and made from aluminium alloy. Some magnesium alloy wheels also exist. Early aircraft wheels were of single piece construction, much the same as the modern automobile wheel.
As aircraft tires were improved for the purpose they serve, they were made stiffer to better absorb the forces of landing without blowing out or separating from the rim. Stretching such a tire over a single piece wheel rim was not possible. A two-piece wheel was developed.
Early two piece aircraft wheels were essentially one-piece wheels wth a removable rim to allow mounting access for the tire.These are still found on older aircraft. Later, wheels with two nearly symmetrical halves were developed. Nearly all modern aircraft wheels are of this two piece construction
two piece aircraft wheel found on modern airliner :- The typical modern two piece aircraft wheel is cast or forged from aluminium or magnesium alloy. The halves are bolted together and contain a groove at the mating surface for an o-ring, which seals the rim sice most modern aircraft utilize tubeless tires. The bead seat area of a wheel is where the tire actually contacts the wheel. It is the critical area that accepts the significat tensile loads from the tire during landing. To strengthen this area during manufacturing, the bead seat area is typically rooled to pre stress it with a compressive stres load. Modern tyres are much more rigid, due to the load bearing requirements, which results in the wheels having to be of two piece construction.
Aircraft Tyre Pressure :- Aircraft tires generally operate at high pressures, up to 200 psi (14 bar or 1,400 kPa) for airliners, and even higher for business jets. The main landing gear was typically inflated to 232 psi (16.0 bar), whilst its tail bumper gear tires were as high as 294 psi (20.3 bar). The high pressure and weight load tyres were a significant factor.
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 autoignition temperature. The use of an inert gas for tire inflation eliminates the possibility of tire explosion.
Brake when landing :-
The brakes used in the aircraft while landing are as follows:
1. Aircraft Disc Brakes:- It is used to brake the wheels while touching the ground. These brakes are operated hydraulically or pneumatically. In most modern aircraft they are activated by the top section of the rudder pedals(toe brakes). In some older aircraft the bottom section is used instaed(heel brakes). Levers are used in a few aircraft. Most aircraft are capable of differential braking.
2. Thrust Reversers: It is used on a jet aircraft to provide a significant way of increasing the rate of deacceleration during the initial stages of both a landing roll or a rejected takeoff from a high speed. Use of reverse thrust on low wing aircraft with mounted engines should be limited to the time when the aircraft is on an active runway.
3. Air Brakes: Air brakes or speed brakes are used to cause the aircraft to slow more rapidly when they were deployed. They produce a drag which required a high power setting, these settings are much more responsive and rapid thus making power and glide slope corrections on approach more rapidly with speed brakes deployed.
4. Large Drogue Parachutes: It is a parachute designed for deployment from a rapidly moving object. It is used for various purposes such as to decrease the speed, to provide control and stability, or as a pilot parachute to deploy a larger parachute.
Objective 6 :-With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle?.
- Rolling Resistance Force: As discussed earlier, it is the force which is responsible for resisting the motion of the body such as ball, tire or wheel, when its starts to roll on the surface. The governing equation of this force is given by:-
Frr=Crr*m*g
where, Crr = Rolling Resistance Co-efficient(dimensionless)
m = mass of the body under consideration
g = acceleration due to gravity.
- Aerodynamic Drag Force: Drag is the aerodynamic force which opposes the motion of the body. It is actually the resistance offered by the air to the movement of the body. So when a car is moving it is actually displaces the air which in turn affects the car's speed and its performance. Manufacturers always try to keep the Aerodynamic Drag to the minimum possible value. It is due to the fact that this force has a negative impact on the vehicle's performance and the efficiency. The upright stance of some vehicles gives it a drag co-efficient of 1.30 while a randrop design has the least amount of drag. The governing equation of these force is given as follows:-
where, A = It is the reference area(frontal area of the car)
V = It is the velocity/flow velocity relative to the object(speed)
ρ">ρ = Air Density
Cd = It is the Drag Coefficient which is dimensionless related
to the object's geometry and take into account both skin friction and form drag.
The Drag Co-efficient for various objects is shown below:
Calculation :-
Towing Vehicle Mass(kg) - 40000 kg
Mass of the aircraft which act as a payload to the Towing Vehicle(kg) - 150000 kg
Therefore, Total Mass of the towing vehicle(m)=150000+40000 = 190000 kg.
Frontal Area of the vehicle(A) = 18m^2
Speed of the vehicle(v) = 20kmph.
In m/sec;
Speed of the vehicle(v) = 20*5/18 = 5.556m/sec
Rolling Resistance Co-efficient(Crr">Crr) = 0.01
Now, Rolling Resistance Force, Frr=Crr*m*g
= (0.01)*190000*9.8
= 18,620N
Similarly,for Aerodynamic Drag:-
Now, Aerodynamic Drag (Fad) = 0.5*(Cd*v+Cd*a)*V^2* ρ">ρ*A
= 0.5*(0.608+0.15)*5.5562">5.55625.5562*1.225*18
= 257.97 N
Therefore, Total Force Required to Push/Pull the aircraft by the Towing Vehicle is:-
= Frr +Fad
= 18620 + 257.97
Total Force = 18,877.97N
Power calculation:-
= Total force *V
= 18877.97 *5.556
= 104886.993 W
= 104.9 KW.
- Rolling Resistence Force Calculation
- Aerodynamic Drag Calculation
- Power Calculation
Objective 7 :- 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.
Figure shows the Towing Vehicle Application
| Assumation for Powertrain Design | |
| Parameter | Value |
| Aircraft Mass | 150000 Kg |
| Towing Vehicle Mass | 40000 Kg |
| Rolling Resistance Co-efficient | 0.01 |
| Air Density | 1.225 Kg/m^3 |
| Towing Vehicle Drag Co-efficient | 0.608 |
| Aircraft Drag Co-efficient | 0.15 |
| Frontal Area | 18 m^2 |
| Inclination Angle | 0 rad |
| Tyre Pressure | 196 PSI/13.51 bar |
| Towing Velocity(V) | 10 Km/hr = 2.778 m/s |
| Towing Time(t) | 2 min |
| Radius of the Towing Vehicle Wheel | 0.4 m |
Now from the above calculation we get the Total Force acting on the Vehicle as:-
Total Traction Force(F) = 18877.9706 N
Power Required (P) = 104.886kW
Now, The Torque required by the vehicle to move is given by:-
Torque = Force(F)*Radius of Wheel (R)
therefore, T = 18877.9706*0.4
T = 7551.1882 Nm
The Energy required by the vehicle for Towing application is given by:-
Energy(E) = Power(P)*Towing Time
= 104.886*2/60
= 3.496kWh
For this application an electric motor which can be either a BLDC motor or an Induction Motor is choosen for the above power specs is given below:-
Here in the above figure, the Peak Motor Output Power given in the Motor Parameters in the input to the Towing Vehicle:-
So therefore, Input Power to the Towing Vehicle(kW):- 120kw
Output Power of the Towing Vehicle(kw) - 104.886
- Duty Cycle = Output power/Input Power
= 104.886/120
= 0.87
Therfore Duty Cycle is = 87%
- Simulink Diagram of powertrain:-
Output:-
B. Designing the parameters in excel sheet:-
Reference: -
1) NASA Wikipedia.