Project-1: Powertrain for aircraft in runways

Part A :

1) Search and list out the total weight of various types of aircrafts.

• The aircraft gross weight (also known as the all up weight and abbreviated AUW) is the total aircraft weight at any moment during a flight or ground operation. An aircrafts gross weight will decrease during a flight due to fuel and oil consumption.
• An aircrafts gross weight may also vary during a flight due to payload dropping or inflight fueling. At the moment of releasing its brakes the gross weight of an aircraft is equal to its takeoff weight. During flight an aircrafts gross weight is referred to as the en-route weight or in flight weight.
• An aircrafts structural weight capability is typically a function of when the aircraft was manufactured, and in some cases old aircraft can have their structural weight capability increased by structural modifications.

1) Maximum design taxi weight (MDTW)

The maximum design taxi weight (also know as the maximum design ramp weight (MDRW) is the maximum weight certified for aircraft manuoeuvring on the ground (taxing or towing) as limited by aircraft strength and airworthiness requirements.

2) Maximum design takeoff weight (MDTOW)

It is the maximum certified 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.

3) Maximum design landing weight (MDLW)

The maximum certified design weight at which the aircraft meets the appropriate landing certification requirements. It generally depends on the landing gear strength or the landing impact loads on the certain parts of the wing structure. The MDLW must 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.

4) Maximum design zero fuel weight (MDZFW)

The maximum certified design weight of the aircraft less all usable fuel and other specified usable agents (engine injection fluid, and other consumable proplusion agents). It is the maximum weight permitted before usable fluids are loaded in specified sections of the airplane. The MDZFW is limited by strength and airworthiness requirements. At the weight the subsequent addition of fuel will not result in the aircraft design strength being exceeded. The weight difference between the MDTOW and the MDZFW may be utilised only for the addition of fuel.

5) Minimum flight weight (MFW)

Minimum certified weight for flight as limited by aircraft strength and airworthiness requirements. In order to design an electric towing tractors we need to know their load operating conditions, so the weights of various types of aircrafts is shown. The total weight of an aircraft includes the aircrafts empty weight + payload.

Aircraft's empty weight - The aircrafts weight with leftover fuel in the tank + engine oil + other operating fluids.

Payload - The fuel weight + passenger weight + luggage weight.

2) Is there any difference between ground speed and air speed ?

GROUND SPEED :

• They are the airplane speed which is related to the ground.
• They are the speed which determines how fast the airplane will reach the destination.
• They are calculated by summing up the airspeed and windspeed.

Air speed :

• It refers to the speed which is relative to air it is flying in.
• They determine whether there is enough airflow around an aircraft to make it lift.
• They are independent of ground speed.

• The above two diagram relative velocity with respect to aircraft reference and ground reference.
• If the measured air speed is greater than the observed ground speed the wind speed becomes positive.
• The wind speed is the vector difference between ground and air speed. On a perfect still day the wind speed is zero and it is equal to the ground speed.

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

• It is not recommended to use aircraft engine power to move it on the ground at airport because there are certain extreme cautios for everything around us.
• Applying thrust can create a blast behind each engine. People, equipment and anything else in the way can be injured or damaged from the jet blast.
• Before applying power to engines the areas in front of each engine are like super critical factors that must me carefully negotiated.
• The immediate area in front of the jet engine creates an area where people and equipment can be sucked into the engine if anything is too close to the intake.
• To avoid extreme cautions its not recommended to use aircraft engine power to move it on the ground at the airport.
• Taxiing is the movement of the aircraft on the ground under its own power in contrast to towing or push back where the aircraft is moving by a tug. (water based travel)
• An airplane uses taxiways to taxi from one place of an airport to another. Ex when moving from hanger to runway. The term taxiing isn't used for accelerating run along a runway prior to take-off the decelerating run immediately run after landing, which are called take-off roll and landing roll out respectively.

4) How an aircraft is pushed to runway when its ready to take off ?

• Taxiing refers to movement of an aircraft on the ground, under its own power. The aircraft moves on wheels. An airplane uses taxiways to taxi from one place on an airport to another. like moving from terminal to the runway.
• When aircraft is ready with all the passesngers and luggages the aviation is an airport procedure during which an aircraft is pushed backwards away from an airport gate by external power.
• The aircraft always moves on the ground following the yellow lines, to avoid any collision with the surrounding buildings, vehicles or other aircrafts. The taxiing motion has a speed limit. Before making a turn the pilot reduces the speed further to prevent tire skids.
• The thrust to propel the aircraft forward comes from its propellers or jet engines. Steering is achieved by turning a nose wheel or tail wheel/rudder.
• The use of engine thrust near terminals is restricted due to the possibility of jet blast damage. This is why the aircrafts are pushed back from the buildings by a vehicle before they can start their own engines for taxxing.

• Pushbacks are carried out by special, low profile vehicles called pushback tractors or tugs.
• These are heavy weighing low profile vehicles with enourmous torque to do the job of pushing/pulling the large aircraft from the terminals to the runway.
• The tractors are designed with extra weight purposely to offer them enough traction to push/pull heavy aircraft.

5) Learn about 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 transistion from moving along the ground on a runway.
• The take off speed required varies with air density, aircraft gross weight and aircraft configuration. The power from the engine of the aircraft used to achieve the flight is called take off power.
• For light aircraft usually full power is used during take off. Large transport category (airliner) aircraft may use a reduced power for take off where less than full power is applied in order to prolong engine life, reduced maintenance costs and reduced noise emissions.

TYRE DESIGN :

• The aircraft tyre is usually specially designed as the tyre has to withstant more load and also higher speed at the same time. The number of tyres required for any aircraft increases with aircraft's weight, as the weight of the aircraft needs to be distributed more evenly.
• Aircraft's tread pattern are designed to facilate stability in high crosswind conditions, to channel water away to de prevent hydroplanning and for braking effect. Some of the tyre design is given below.

BIAS PLY TYRE :

• The bias ply tyre consists of casing plies running diagonally at approximate right angles to one another. The number of plies and angles at which they are laid dictate strength and load capacity.
• High performance bias aircraft tyres feature inter-tread reinforcing fabric (ITF). This provides additional high speed stability, reduces tread distortion under load, protects the casing plies from damage and can act as wear indicators on retreadable tyres.

RADIAL TYRE :

• Radial tired 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 degree to the center line of the tyre. Angled belt plies are laid between the tread and top casing ply, resulting in a flatter tread and adding strength to the tyre.

ROLLING RESISTANCE :

• The rolling resistance force is mainly experienced by the tyre when the vehicle moves over any surface. The rolling resistance force is given by the expression.

Frr = urr * (m.g)

where,

(m.g) = weight in newton.

(urr) = coefficient of rolling resistance.

• The coefficient of rolling resistance (urr) depends on many factors like the, tyre pressure, tyre temperature, material of the tyre, thread pattern of the tyre and also the road roughness and liquids on the road. These factors determine the rolling resistance force.

TYRE PRESSURE :

• The pressure generally is very high in an aircraft tire to reduce the rolling resistance and to withstand the weight. Usually it will be around 200 to 300psi of pressure and they change based on the type of the aircraft.
• Tests of airliner aircraft tyres have shown that they are able to sustain pressures of maximum 800 psi. Aircraft tyres are usually inflated with nitrogen to minimise expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight.

BRAKE FORCE WHILE LANDING :

The brake force while landing is done by three different process they are.

• Aircraft disc brakes - Aircraft has disc rotors in the landing gear used to brake the wheels while touching the ground. These brakes are operated hydraulically or pneumatically.
• Thrust reversers - It allows thrust from the engines to be used to slow the aircraft. This is also very effective in bringing down the speed of the aircraft. by using a negative angle plane, we are turning the wind that is coming into the propeller to flow in the opposite direction.
• Air brake - It is dedicated flight control surface that work by increasing the drag force, air brakes are designed to increase drag while making little change to lift resulting in a higher stall speed. These are some of the tyres of braking methods used to bring down the aircrafts speed while landing the flight.

Part B :

6) A. With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.

Here the pushback trucks experience two kinds of forces acting on them when they try to push/pull the aircraft.

• Rolling resistance.
• Aerodynamic drag force.

Rolling resistance force

• The formula used for the rolling resistance is Frr = u*m*g

where,

U = coefficient of rolling resistance,

m = mass,

g = acceleration due to gravity.

• The rolling resistance force acts on both the pushback truck and the aircraft. So considering the aircraft,

u = 0.02, m = 40,000kg

Frr (aircraft) = 0.02*40000*9.81 = 7848 N

considering pushback

u = 0.09, m = 1000kg

Frr (pushback truck) = 0.09*1000*9.81 = 883 N

• The total resistance will be the sum of the aircraft and pushback truck rolling resistance = 7848 + 883 = 8731 N

Aerodynamic force

• The aerodynamic force to move an airplane on a absolute flat runway with no wind at constant low speed is usually very negligible. Fd = 1/2.p.A.Cd.v^2

where,

p = ai density kg/m^3,

A = front area in m^2,

Cd = drag coefficient

V = velocity is m/s.

• Since the aerodynamic force is very negligible the net force acting on the pushback truck during the push/pull of an aircraft

Fnet = Frr (pushback truck) + Frr(aircraft)

= 8731 N

The power required is

P = F * V

P = 8731 * 9.72

P = 84.86 KW.

B. Develop the model for the calculated force and power using Simulink.

• Constant blocks are used to feed the parameters such as mass, rolling resistance, drag coefficient, front area, Air density and velocity.
• Product blocks are used to calculate the resistive forces.
• Sum block is used to get the total resistive forces.
• The display blocks are used to get the output.

Link : https://drive.google.com/file/d/1i302fIHwoanP9Jp3o0N9KqPsFSapjHGq/view?usp=sharing

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.

• The aircrafts use electric drives for ground operations (Taxxing and push back), in order to save the jet fuel consumptions.
• The type of motor to be used for aircraft towing applications. There are two types of alternatives. One is PMDC (Permanent magnet DC motor) and the BLDC (Brushless DC motor). We can select PMDC motor because it is widely used in electric vehicles.
• To calculate the power rating of the DC motor chosed. The power required for towing an aircraft is about 84.86KW. This will be our motor rating.
• To calculate the energy required for towing.

Energy for towing = (power required for towing) * (time required for towing)

Let the time be 15 mins for towing = 900 seconds.

It should be calculated in KW-h

E = 84.86*(900/1200) = 63.645 Kw-h.

This is the energy required for towing.

• Now to calculate the duty cycle for the towing operation. we can use a standard lithium ion battery pack for this operation. Assuming the input voltage needed to be 200V and the current required to be 400A.

Power input = V*I = 200*400 = 80000W = 80KW

• We have calculated the power output to be 63.645 Kw-h
• Duty cycle = power output/power input = 63.645/80 = 0.7955.
• Duty cycle for this towing operation is 79%

Paramters that have been assumed in this calculation :

Aircraft weight = 41000Kgs.

Rolling resistance (runway) = 0.02

Rolling resistance (Push back) = 0.10

Pushback vehicle weight = 2000kgs

Pushback velocity = 5.55m/s

Towing operation time = 15mins

Battery voltage = 200V

Current required = 400A

The aerodynamic drag is not considered because it is negligible in the ground.

B. Also, Design the parameters in excel sheet.

Link https://drive.google.com/file/d/1hL7gW_CrRlIWLTkarXqnzh-ou3gWsAX2/view?usp=sharing