Project-1: Powertrain for aircraft in runways

STUDY 1:  Weight of Various Types of Aircrafts

An aircraft's gross weight will decrease during a flight when fuel and oil are being consumed.Gross weight may also vary during a flight due to payload dropping or in-flight refueling .At the time of releasing its brakes, the gross weight of an aircraft is equal to its takeoff weight. During flight, an it's gross weight is referred to as the en-route weight or in-flight weight

An aircraft's gross weight is limited by several weight restriction. To avoid overloading its structure or to avoid unacceptable performance or handling qualities while in operation aircraft gross weight limits are established during an aircraft's design and certification period . 

There are different types of aircrafts, those are elaborated below-     

1. AEROPLANE>> An airplane or aeroplane (informally plane) is a powered, fixed-wing aircraft that is propelled forward by thrust from a jet engine or propeller or by rocket engine. Aeroplanes come in a variety of sizes, shapes, and wing configuration. The broad spectrum of uses for airplanes includes recreation, transpora

2. HELICOPTER>> A helicopter, sometimes referred to in slang as a "chopper" or "helo" is a type of rotorcraft in which lift and thrust are supplied by horizontally-spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward, and laterally.

3. AIRSHIP>> An airship or dirigible balloon is a type of aerostat or lighter-than-air aircraft that can navigate through the air under its own power. Aerostats gain their lift from a lifting gas that is less dense than the surrounding air. Airships were the first aircraft capable of controlled powered flight, and were most commonly used before the 1940s; their use decreased as their capabilities were surpassed by those of aeroplanes.

 GLIDER>> A glider is a fixed wing aircraft that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose free flight does not depend on an engine. Most gliders do not have an engine, although motor glider have small engines for extending their flight when necessary by sustaining the altitude (normally a sailplane is on a continuously descending slope) with some being powerful enough to take off self-launch.

5. CONVERTIPLANE>> A convertiplane is defined by the Fédération Aéronautique Internationale (FAI or World Air Sports Federation) as an aircraft which uses rotor power for vertical takeoff and landing (VTOL) and converts to fixed-wing lift in normal flight. In the US it is further classified as a sub-type of powered lift.

STUDY 2: Difference Between Ground Speed and Air Speed

Ground Speed>> The ground speed is how fast an airplane is traveling, relative to a fixed point on the ground. It is the speed of how fast an airplane's shadow would move across the land. If there's a strong wind pushing an aircraft, that's reflected in the ground speed.

Air Speed>> Airspeed is how fast an airplane is really flying strictly under its own power, which is the actual velocity of the aircraft.

GROUND SPEED	AIR SPEED
1. Ground speed is the speed of the aeroplane relative to the earth surface.	1. Air speed is the speed of aeroplane relative to the air it is flying in.
2. Ground speed determines how  fast an aircraft will get to its destination.	2. Air speed determines whether  there is enough airflow around an aircraft to make it fly.
3. Ground speed is the sum of  air speed and wind speed.	3. Air speed is independent of ground speed

Ground speed = airspeed+wind speed

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

The risks which may arise from engine ground running relate to the potential for loss of control of the aircraft by those persons occupying the pilot seats in the flight deck. Unwanted consequences from such static running are mainly related to those arising from the unintended movement of the aircraft during engine running - effectively a loss of control - especially during high power engine running. Damage can occur to the aircraft itself, other aircraft nearby or to airside structures. In addition, there is a risk of injury to ground support personnel who may be in relatively close proximity to the aircraft.

When modern jet engines are operated at rated thrust levels, the exhaust wake can exceed 375 mi/h (325 kn or 603 km/h) immediately aft of the engine exhaust nozzle. This exhaust flow field extends aft in a rapidly expanding cone, with portions of the flow field contacting and extending aft along the pavement surface (fig. 1). Exhaust velocity components are attenuated with increasing distance from the engine exhaust nozzle. However, an airflow of 300 mi/h (260 kn or 483 km/h) can still be present at the empennage, and significant people and equipment hazards will persist hundreds of feet beyond this area. At full power, the exhaust wake speed can typically be 150 mi/h (130 kn or 240 km/h) at 200 ft (61 m) beyond the airplane and 50 to 100 mi/h (43 to 88 kn or 80 to 161 km/h) well beyond this point.

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

In aviation, pushback is an airport procedure during which an aircraftis 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 reverese thrust (a procedure referred to as a powerback), the resulting jetblast or propwash 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.

Pushbacks at busy aerodromes are usually subject to ground control clearance to facilitate ground movement on taxiways. Once clearance is obtained, the pilot will communicate with the tractor driver (or a ground handler walking alongside the aircraft in some cases) to start the pushback. To communicate, a headset may be connected near the nose gear.

Since the pilots cannot see what is behind the aircraft, steering is done by the pushback tractor driver and not by the pilots. Depending on the aircraft type and airline procedure, a bypass pin may be temporarily installed into the nose gear to disconnect it from the aircraft's normal steering mechanism.

Once the pushback is completed, the towbar is disconnected, and any bypass pin removed. The ground handler will show the bypass pin to the pilots to make it clear that it has been removed. The pushback is then complete, and the aircraft can taxi forward under its own power.

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

Take-Off Power:

For light aircraft, usually full power is used during takeoff. Large transport category (airliner) aircraft may use a reduced power for takeoff, where less than full power is applied in order to prolong engine life, reduce maintenance costs and reduce noise emissions. In some emergency cases, the power used can then be increased to increase the aircraft's performance. Before takeoff, the engines, particularly piston engines, are routinely run up at high power to check for engine-related problems. The aircraft is permitted to accelerate to rotation speed (often referred to as V_r). 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 (once proper air displacement occurs under / over the wings, an aircraft will lift off on its own; controls are to ease that in).

The nose is raised to a nominal 5°–15° nose up pitch attitude to increase lift from the wings and effect liftoff. For most aircraft, attempting a takeoff without a pitch-up would require cruise speeds while still on the runway.

Tyre Design:

Based on the type of plies used the tyres can be:

Radial ply tires - these tyres feature a flexible casing which is constructed of rubber-coated ply cords which extend around the beads and are substantially at 90° to the centerline of the tread. The casing is stabilized by an essentially inextensible circumferential belt.

Bias ply tires - these tyres feature a casing which is constructed of alternate layers of rubber-coated ply cords which extend around the beads and are at alternate angles substantially less than 90° to the center line of the tread.

Based on the method for containing the inflation gas the tyres can be:

• Tube-type tyres - these require tubes for inflation retention.
• Tubeless tyres - these do not require tubes. They are constructed with an innerliner (integral rubber lining that is engineered to prevent the diffusion of the inflation gas into the casing.).

Rolling Resistance:

The resistance offered by the tyres against motion of vehicle/aircraft is called as rolling resistance, the rolling resistance is produced during take off/landing in the runway.

Tyre Pressure:

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.

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.

The main landing gear on the Concorde 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 on the Concorde tyres were a significant factor in the loss of Air France flight 4590

Brakes Forces When Landing:

In general, when the wheels touch the ground, a set of spoilers raise up quickly, which kills the lift provided by the wings. (There are two sets seen in the image below: ground spoilers that only deploy on landing, and spoilers that are used in flight as speed brakes as well as on landing.) While the spoilers provide some drag, their primary purpose is to stop the plane from actually flying, putting all of the weight on the landing gear and in turn making the brakes that much more effective.

Aircraft have highly-engineered, multi-disc brakes made of a carbon-steel material. Manufacturers include Honeywell and Goodrich, part of Collins Aerospace. In general, the brakes are composed of discs that rotate with the wheel and separate discs that are fixed. When pressure is applied—and below you see pressure applied from the right fixed disc on all of the discs—the entire assembly compresses to create the braking action. Carbon brakes are standard today; they cool faster than steel brakes (their predecessor) and can weigh up to 700 pounds less. That represents a significant weight saving for airlines.

Auto Brakes:

Wheel brakes are usually selected to engage automatically after landing. These are called “autobrakes”.that all airliners have several levels of autobrake “severity”. The crew will decide which is the most appropriate to use for every landing depending upon factors like the length of runway, if it is wet or dry, or if the pilots want to exit the runway at a particular point. “For a short wet runway you might select autobrake 3, or MED on the Airbus. For a long dry runway you might select autobrake 1 or LOW on the Airbus".

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

The rolling resistance  for the air plane can be calculated as

F_r = c m_r a_g    

where

F_r = rolling resistance (N)

c = rolling resistance coefficient

m_r = rolling mass (kg)

a_g = acceleration of gravity (9.81 m/s²)

If the mass of a plane is 40000 kg and the rolling resistance co-efficient between the aircraft wheel and the runway is 0.02 

The force required to overcome the rolling resistance can be calculated as

F_r = 0.02 * (40000 kg) *(9.81 m/s²)

 = 7848 N  

The friction for the puller can be calculated to

F_f = μ W

   = μ m_f a_g

where

F_f = frictional force (N)

μ = friction coefficient

W = Weight (N)

m_f = friction mass (kg)

The friction coefficient between a pulling truck rubber wheels and dry runway is 0.9. Since pulling trucks are connected to air crafts nose wheels close to runway we simplify the calculation of required truck mass 

m_f = (7848 N) / (0.9 (9.81 m/s²))

     = 889 kg

Taking radius of the wheel R as 0.3m 

The torque is given by T=F*R

T= 7848 * 0.3

= 2354 N.m

The power for pulling/push the aircraft can be calculated as 

P=F*V

V= velocity of pull vehicle taken as 5 km/hr

V=1.388 m/s

P=7848*1.388

=10893 W

=10.89 kW

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. Make all            required assumptions. Prepare a table of assumed parameters. Draw a block diagram of powertrain. 

 Taking the prevoius example power value  10 kW for this problem

Power =10 kW 

The motor power should be greater than or equal to 10kW assuming it as 10 kW.

The energy required can be calculated as E=P*t

assuming taxi time of 5 mins.

E=10*(5*60) kJ

 = 3000kJ

From power equation

Vo*Io=ηVi*Ii

where,

V_o is the output voltage

I_o is the output current

η is the power efficiency (ranging from 0 to 1)

V_i is the input voltage

I_i is the input current

Consider DC input voltage as 48V and Power as 12kW

P= Vi*Ii

12000=48*Ii

Ii=250A

The efficiency is calculated as

η=10000/12000
=0.83

From the above power equation
Vo*Io=ηVi*Ii
Vo*250=0.83*48*250
Vo=40V

The Vout =Vin/1-D

40=48/(1-D)

D= 0.2 the duty cycle has in the range of (0,0.2)

Block Diagram of Power Train