AIM

To understand powertrain for aircraft in runways.

PROBLEM SPECIFICATION AND SOLVING:

PROBLEM STATEMENT I:

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

EXPLANATION AND OBSERVATION:

• [1] There are many factors that lead to efficient and safe operation of aircraft. Among these vital factors are proper weights and balance control.
• MAXIMUM ALLOWABLE WEIGHT: The maximum allowable weight for an aircraft is determined by design considerations. The manufacturer provides the aircraft operator with the empty weight of the aircraft and the location of its empty weight center of gravity (EWCG) at the time the certified aircraft leaves the factory.
• However, the maximum operational weight may be less than the maximum allowable weight due to such considerations as high-density altitude or high-drag field conditions caused by wet grass or water on the runway. The maximum operational weight may also be limited by the departure or arrival airport’s runway length.
• The maximum allowable weight for an aircraft is determined by design considerations by the aircraft’s manufacturer.
• However, the maximum operational weight may be less than the maximum allowable weight due to such considerations as high-density altitude or high-drag field conditions caused by wet grass or water on the runway.
• The maximum operational weight may also be limited by the departure or arrival airport’s runway length.
• The structural weight limits are based on aircraft maximum structural capability and define the envelope for the CG charts. Aircraft structural weight capability is established during aircraft design and certification.
• MAXIMUM DESIGN TAXI WEIGHT(MDTW or MTW): The maximum design taxi weight or maximum design ramp weight (MDRW) is the maximum certificated design weight for aircraft ground maneuvers as limited by aircraft strength and airworthiness requirements.
• The difference between the maximum taxi/ramp weight and the maximum take-off weight (maximum taxi fuel allowance) depends on the size of the aircraft, the number of engines, APU operation, and engines/APU fuel consumption, and is typically assumed for 10 to 15 minutes allowance of taxi and run-up operations.
• MAXIMUM DESIGN TAKEOFF WEIGHT (MDTOW OR MTOW): The maximum design takeoff weight is the maximum certificated design weight for takeoff run as limited by aircraft strength and airworthiness requirements.
• MAXIMUM DESIGN LANDING WEIGHT (MDLW OR MLW): The Maximum design landing weight is the maximum certificated design weight for landing limited by aircraft strength and airworthiness requirements. It generally depends on the landing gear strength or the landing impact loads on certain parts of the wing structure.
• It should be noted that:

MDLW < MDTOW < MDTW

• MAXIMUM DESIGN ZERO-FUEL WEIGHT (MDZFW): The maximum design zero-fuel weight is the maximum certificated design weight of the aircraft less all usable fuel and other specified usable agents as limited by aircraft strength and airworthiness requirements.
• It is the maximum weight permitted before usable fuel and other specified usable fluids are loaded in specified sections of the airplane.
• The weight difference between the MDTOW and the MDZFW may be utilized only for the addition of fuel.
• It should be noted that:

Maximum payload = MDZFW – OEW

• MINIMUM FLIGHT WEIGHT (MFW): Minimum certificated weight for flight as limited by aircraft strength and airworthiness requirements.
• AIRCRAFT GROSS WEIGHT: The aircraft gross weight is the total aircraft weight at any moment during the flight or ground operation.
• The aircraft gross weight decreases during flight due to fuel and oil consumption. The aircraft gross weight may also vary during flight due to payload dropping or in-flight refueling.
• MANUFACTURER’S EMPTY WEIGHT (MEW): The following list constitutes the MEW and is tabulated below:

MEW	Not MEW
Airframe structure with all moving mechanical parts (fuselage, wings, flaps, gear, rudder, nacelle …)	Fuel
Power generation system (APU, main engines, power plant…)	Oil, potable water
Systems (electrical, hydraulics, pneumatic, fuel flow system, instrument, navigation, air conditioning, anti-ice, fixed furnishing)	Payload (Cargo, passenger, luggage)
Fixed equipment and services considered an integral part of the aircraft	Removable equipment
Fixed ballast	Customer specific installations or operator items
Closed system fluids	Fuel
Unused fuel only for small aircraft	Oil, potable water

Table 1. Weights that constitute MEW and which does not.

 

• OPERATIONAL EMPTY WEIGHT (OEW): The MEW and the operator’s items are summed up to the Operational Empty Weight (OEW). The OEW is usually fixed for a specific aircraft and only gets changed during maintenance or operational changes.
• OEW is the empty weight that is used in the flight simulator or the usual planning software. The list of items constituting the OEW is tabulated below:

 

S.No	Operator’s weight
1	fluids necessary for aircraft operation (engine oil and coolant, water, unusable fuel)
2	the water for galleys and lavatories
3	aircraft documentation
4	passenger seats (and the life vests)
5	galley structure
6	catering emergency equipment
7	aircraft crew and their luggage.
8	standard items necessary for full operation

Table 2. List constituting OEW.

 

• ACTUAL ZERO FUEL WEIGHT(AZFW): If we add the payload to the empty plane weight, we get the Actual Zero Fuel Weight.
• The payload includes: the passengers weight (the standard weights used defined by ICAO respectively) , the passengers luggage’s weight, the cargo weight.
• ACTUAL GROSS WEIGHT(AGW): In addition to the actual zero fuel weight, we add the fuel required for the flight and we get the Actual Gross Weight.
• TAKE-OFF WEIGHT: Fuel burn during taxi operation to the departure runway reduces the gross weight. At the holding point, we have the Actual Take-off Weight (ATOW) which is used for take-off performance calculation.
• The gross weight varies during flight. Fuel and oil consumption reduces the gross weight. Additionally it may vary during flight due to inflight refueling or payload dropping.
• MAXIMUM DESIGN TAKEOFF WEIGHT (MDTOW): The maximum takeoff weight (also known as the maximum brake-release weight) is the maximum weight authorized at brake release for takeoff, or at the start of the takeoff roll.
• The maximum takeoff weight is always less than the maximum taxi/ramp weight to allow for fuel burned during taxi by the engines and the APU.
• In operation, the maximum weight for takeoff may be limited to values less than the maximum takeoff weight due to aircraft performance, environmental conditions, airfield characteristics (takeoff field length, altitude), maximum tire speed and brake
• At this weight, the subsequent addition of fuel will not result in the aircraft design strength being exceeded. The weight difference between the MTOW and the MZFW may be utilized only for the addition of fuel.
• LANDING WEIGHT: With the calculation of fuel consumption during flight, we can calculate the Estimated Landing Weight (ELW) which is used for landing performance calculation at the destination.
• Approaching your destination you use your current gross weight to determine the final approach speed. The gross weight now is the Actual Landing Weight (ALW).
• [2] The list of total weight of various types of aircraft is tabulated below:

Type	MTOW [kg]	MLW [tonnes]	TOR [m]	LR [m]	ICAO category	FAA category
Antonov An-225	640,000	591.7	3500		Heavy	Super
Scaled Composites Model 351 Stratolaunch	589,670		3660		Heavy	Super
Airbus A380-800	575,000	394	3100	1930	Super	Super
Boeing 747-8F	447,700	346.091	3100	1800	Heavy	Heavy
Boeing 747-8	443,613	306.175	3100		Heavy	Heavy
Boeing 747-400ER	412,770	295.742	3090		Heavy	Heavy
Antonov An-124-100M	405,060	330	2520	900	Heavy	Heavy
Boeing 747-400	396,900	295.742	3018	2179	Heavy	Heavy
Lockheed C-5 Galaxy	381,000	288.417	2530	1494	Heavy	Heavy
Boeing 747-200	377,840	285.700	3338	2109	Heavy	Heavy
Boeing 747-300	377,840	260.320	3222	1905	Heavy	Heavy
Airbus A340-500	371,950	240	3050	2010	Heavy	Heavy
Airbus A340-600	367,400	256	3100	2100	Heavy	Heavy
Boeing 777F	347,800	260.816	2830		Heavy	Heavy
Airbus A330-900	352,000	251.5	3100		Heavy	Heavy
Boeing 777-300ER	351,800	251.29	3100		Heavy	Heavy
Boeing 777-200LR	347,450	223.168	3000		Heavy	Heavy
Boeing 747-100	340,200	265.300			Heavy	Heavy
Airbus A350-1000	308,000	233.5			Heavy	Heavy
Boeing 777-300	299,370	237.683	3380		Heavy	Heavy
Boeing 777-200ER	297,550	213.00	3380	1550	Heavy	Heavy
Airbus A340-300	276,700	190	3000	1926	Heavy	Heavy
McDonnell Douglas MD-11	273,300	185	2990	1890	Heavy	Heavy
Airbus A350-900	270,000	175	2670	1860	Heavy	Heavy
Ilyushin Il-96M	270,000	195.04	3115	2118	Heavy	Heavy
McDonnell Douglas DC-10	256,280	183	2990	1890	Heavy	Heavy
Boeing 787-9	254,000	192.777	2900		Heavy	Heavy
Boeing 787-10	254,000	201.849			Heavy	Heavy
Airbus A340-200	253,500	181	2990		Heavy	Heavy
Ilyushin IL-96-300	250,000	175	2600	1980	Heavy	Heavy
Airbus A330-300	242,000	185	2500	1750	Heavy	Heavy
Airbus A330-200	242,000	180	2220	1750	Heavy	Heavy
Lockheed L-1011-500	231,300	166.92	2636		Heavy	Heavy
Boeing 787-8	228,000	172.365	3300	1695	Heavy	Heavy
Lockheed L-1011-200	211,400				Heavy	Heavy
Ilyushin IL-86	208,000	175			Heavy	Heavy
Boeing 767-400ER	204,000	158.758	3414		Heavy	Heavy
Airbus A300-600R	192,000	140	2385	1555	Heavy	Heavy
Boeing 767-300ER	187,000	136.08	2713	1676	Heavy	Heavy
Concorde	185,000	111.1	3440	2220	Heavy	Heavy
Airbus A300-600	163,000	138	2324	1536	Heavy	Heavy
Boeing 767-300	159,000	136.078	2713	1676	Heavy	Heavy
Airbus A310-300	157,000	124	2290	1490	Heavy	Heavy
Vickers VC10	152,000	151.9			Heavy	Heavy
Boeing 707-320B	151,000	97.5			Heavy	Heavy
Boeing 707-320C	151,000	112.1			Heavy	Heavy
Douglas DC-8-61	147,000				Heavy	Heavy
Airbus A310-200	142,000	123	1860	1480	Heavy	Heavy
Airbus A400M	141,000	122	980	770	Heavy	Heavy
Douglas DC-8-32	140,000				Heavy	Heavy
Douglas DC-8-51	125,000				Medium	Large
Boeing 757-300	124,000	101.6	2550	1750	Medium	Large
Boeing 707-120B	117,000	86.3			Medium	Large
Boeing 757-200	116,000	89.9	2347	1555	Medium	Large
Boeing 720B	106,000	79.5			Medium	Large
Boeing 720	104,000	79.5			Medium	Large
Tupolev Tu-154M	104,000	80			Medium	Large
Tupolev Tu-204SM	104,000	87.5	2250		Medium	Large
Convair 880	87,500				Medium	Large
Boeing 737-900	85,000	66.36	2500	1704	Medium	Large
Boeing 737-900ER	85,000	71.35	2804	1829	Medium	Large
Boeing 727-200 Advanced	84,000	70.1			Medium	Large
Airbus A321-100	83,000	77.8	2200	1540	Medium	Large
Boeing 737-800	79,000	65.32	2308	1634	Medium	Large
Boeing 727-200	78,000	68.1			Medium	Large
McDonnell-Douglas MD-83	73,000	63.28			Medium	Large
Boeing 727-100	72,500	62.4			Medium	Large
Boeing 727-100C	72,500	62.4			Medium	Large
McDonnell-Douglas MD-90-30	71,000	64.41	2165	1520	Medium	Large
de Havilland Comet 4	70,700				Medium	Large
Boeing 737-700	70,000	58.06	1921	1415	Medium	Large
Airbus A320-100	68,000	66	1955	1490	Medium	Large
Boeing 737-400	68,000	54.9	2540	1540	Medium	Large
de Havilland Comet 3	68,000				Medium	Large
Boeing 377	67,000				Medium	Large
Boeing 737-600	66,000	54.66	1796	1340	Medium	Large
Airbus A220-300	65,000	57.61	1890	1494	Medium	Large
Hawker Siddeley Trident 2E	65,000				Medium	Large
Airbus A319	64,000	62.5	1850	1470	Medium	Large
Boeing 737-300	63,000	51.7	1939	1396	Medium	Large
Boeing 737-500	60,000	49.9	1832	1360	Medium	Large
Airbus A220-100	59,000	50.80	1463	1356	Medium	Large
Airbus A318	59,000	57.5	1375	1340	Medium	Large
Boeing 717-200HGW	55,000	47.174	1950		Medium	Large
Douglas DC-7	55,000				Medium	Large
de Havilland Comet 2	54,000				Medium	Large
Boeing 717-200BGW	50,000	46.265	1950		Medium	Large
de Havilland Comet 1	50,000				Medium	Large
Douglas DC-6A	48,600				Medium	Large
Douglas DC-6B	48,500				Medium	Large
Embraer 190	48,000	43	2056	1323	Medium	Large
Caravelle III	46,000				Medium	Large
Fokker 100	46,000	39.95	1621	1350	Medium	Large
Douglas DC-6	44,000				Medium	Large
Avro RJ-85	42,000	36.74			Medium	Large
Handley Page Hermes	39,000				Medium	Large
Embraer 175	37,500	32.8	2244	1304	Medium	Large
Bombardier CRJ900	36,500	33.345	1778	1596	Medium	Large
Embraer 170	36,000	32.8	1644	1274	Medium	Large
Bombardier CRJ700	33,000	30.39	1564	1478	Medium	Large
Douglas DC-4	33,000				Medium	Large
Vickers Viscount 800	30,400				Medium	Large
Bombardier Q400	28,000	28.01	1219	1295	Medium	Large
Bombardier CRJ200	23,000	21.319	1918	1479	Medium	Large
ATR 72-600	22,800	22.35	1333	914	Medium	Large
Saab 2000	22,800	21.5	1300		Medium	Large
Embraer ERJ 145	22,000	19.3	2270	1380	Medium	Large
ATR 42-500	18,600	18.3	1165	1126	Medium	Small
Saab 340	13,150	12.930	1300	1030	Medium	Small
Embraer 120 Brasilia	11,500	11.25	1560	1380	Medium	Small
BAe Jetstream 41	10,890	10.570	1493	826	Medium	Small
Learjet 75	9,752	8.709	1353	811	Medium	Small
Pilatus PC-24	8,300	7.665	893	724	Medium	Small
Embraer Phenom 300	8,150	7.65	956	677	Medium	Small
Beechcraft 1900D	7,765	7.605	1036	853	Medium	Small
Cessna Citation CJ4	7,761	7.103	1039	896	Medium	Small
de Havilland Hercules	7,000				Medium	Small
Embraer Phenom 100	4,800	4.43	975	741	Light	Small

Table 3. List of the aircraft sorted by maximum takeoff weight.

PROBLEM STATEMENT II:

Is there any difference between ground speed and air speed?

EXPLANATION AND OBSERVATION:

• [3] WIND SPEED: For a reference point picked on the ground, the air moves relative to the reference point at the wind speed. It can be noticed that the wind speed is a vector quantity and has both a magnitude and a direction. Direction is important. A 20-mph wind from the west is different from a 20-mph wind from the east. The wind has components in all three primary directions (north-south, east-west, and up-down). In this figure, only the velocities along the aircraft's flight path are considered. A positive velocity is defined to be in the direction of the aircraft's motion. The cross winds, which occur perpendicular to the flight path but parallel to the ground, and updrafts and downdrafts, which occur perpendicular to the ground are neglected.
• GROUND SPEED: Groundspeed is the speed of the aircraft directly over the ground. It is a vector quantity. Higher the ground speed the faster you reach your destination. 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 therefore, the comparison of the ground speed to the wind speed must be done according to rules for vector comparisons.

 

Figure 1. Relative Velocities.

 

• AIR SPEED: Airspeed is the speed of the aircraft relative to the speed of surrounding air in which the aircraft is flying. 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.

 

Airspeed = Ground Speed - Wind Speed

 

• On a perfectly still day, the airspeed is equal to the ground speed. But if the wind is blowing in the same direction that the aircraft is moving, the airspeed will be less than the ground speed. [3]

 

PROBLEM STATEMENT III:

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

EXPLANATION AND OBSERVATION:

• [4] Taxiing (rarely spelled taxying)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).
• 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.

 

Figure 2. Jet airliners taxiing.

• During taxiing, the aircraft generates a large amount of emissions and is exposed to damage due to Foreign Object Damage (FOD). This results in large fuel consumption, wear and tear on the engine which later effects the efficiency of the aircraft, unnecessary jet blast and noise.
• The airports house large amounts of burnt fuel emissions and noise pollution. IN addition to these, if engine power is used to move on the ground, it results in release of debris along with significant amounts of heat.
• [5] Not only pollution being the issue, using engine power on the ground results to potential loss of control of the aircraft by the pilot. Unintended movement of the aircraft during the engine running results in effective loss of control especially when the power developed exceed by a fraction over the threshold value.
• Damage to the aircraft, the structures nearby, the passengers and the crew is imminent under such circumstances. [5]
• Therefore, this results in being taxed for operational and maintenance along with being taxed for excessive emissions.
• Therefore, aircrafts avoid using the engine power in the runways.

PROBLEM STATEMENT IV:

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

EXPLANATION AND OBSERVATION:

• [6] In aviation, pushback is an airport procedure during which an aircraft is pushed backwards away from its parking position, usually at 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.
• IATA defines aircraft pushback as "rearward moving of an aircraft from a parking position to a taxi position by use of specialized ground support equipment.

 

PROCEDURE:

• 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.

 

Figure 3. Figure showing pushback truck pushing the aircraft.

 

EQUIPMENT USED FOR PUSHBACK:

• Moving light aircraft: Very small airplanes may be moved by human power alone. The airplane may be pushed or pulled by landing gear or wing struts since they are known to be strong enough to drag the airplane through the air. To allow for turns, a person may either pick up or push down on the tail to raise either the nose wheel or tail wheel off the ground, then rotate the airplane by hand. A less cumbersome method involves attaching a short tow bar to either the nose wheel or tail wheel, which provides a solid handhold and leverage to steer with, as well as eliminates the danger of handling the propeller. These tow bars are usually a lightweight aluminum alloy construction which allows them to be carried on board the airplane. Other small tow bars have a powered wheel to help move the airplane, with power sources as diverse as lawnmower engines or battery-operated electric drills. However, powered tow bars are usually too large and heavy to be practically carried on small airplanes.
• Tractors and Towbars: Large aircraft cannot be moved by hand and must have a tractor or tug. Pushback tractors use a low-profile design to fit under the aircraft nose. For sufficient traction, the tractor must be heavy, and most models can have extra ballast added. Often the driver's cabin can be raised for increased visibility when reversing and lowered to fit under aircraft. There are two types of pushback tractors: conventional and towbarless (TBL).
  • Conventional tugs use a tow bar to connect the tug to the nose landing gear of the aircraft. The tow bar is fixed laterally at the nose landing gear, but may move slightly vertically for height adjustment. At the end that attaches to the tug, the tow bar may pivot freely laterally and vertically. In this manner the tow bar acts as a large lever to rotate the nose landing gear. Each aircraft type has a unique tow fitting so the towbar also acts as an adapter between the standard-sized tow pin on the tug and the type-specific fitting on the aircraft's landing gear. The tow bar must be long enough to place the tug far away enough to avoid hitting the aircraft and to provide sufficient leverage to facilitate turns.

 

Figure 4. Light aircraft can usually be moved by human power alone. Here, this Aerotechnik EV-97A Eurostar is being pulled into position for refueling.

 

• Towbarless (TBL) tractors do not use a towbar; they scoop up the nose landing gear and lift it off the ground. This avoids the time penalty of connecting/disconnecting a towbar, and entirely removes the cost/complexity of maintaining towbars on the ramp. The tug itself does not need to be particularly massive - the aircraft's nosewheel weight provides the necessary downward force. Lastly, a TBL tug is much shorter (compared to a tug and towbar system) and has one only a single pivot point instead of one at either end of the towbar, so it has much simpler and precise control of the aircraft. This is very useful in general aviation settings with a wider variety of aircraft in more confined spaces than their airline counterparts.

 

Figure 5. A conventional tractor hooked up to a United Airlines Boeing 777-200ER at Denver International Airport.

 

Figure 6. Towbars are used to connect the tractor to the aircraft..

 

Figure 7. A towbarless tug at Frankfurt Airport transporting a Lufthansa Airbus A340-300.

 

• Robotic Tractor: The Lahav Division of Israel Aerospace Industries has developed a semi-robotic towbarless tractor it calls Taxibot that can tow an aircraft from the terminal gate to the take-off point (taxi-out phase) and return it to the gate after landing (taxi-in phase). The Taxibot eliminates the use of airplane engines during taxi-in and until immediately prior to take-off during taxi-out potentially saving airlines billions of dollars in fuel that is used. The Taxibot is controlled by the pilot from the cockpit using the regular pilot controls.

 

PROBLEM STATEMENT V:

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

EXPLANATION AND OBSERVATION:

• TAKE-OFF POWER: [7] An airplane, by definition, is a fixed wing aircraft. Its wings can produce lift only when there is a relative velocity between the airplane and the air. In order to be airborne, the lift produced by the airplane must be at least equal to the weight of the airplane. This happens when the velocity of the airplane is equal to or greater than its stalling speed. To achieve this velocity called ‘Take-off velocity(VTO)’ the airplane accelerates along the runway. Thus, an airplane covers a certain distance before it can take-off. The horizontal distance covered along the ground, from the start of takeoff till the airplane is airborne is called the take-off run. However, to decide the length of the runway required for an airplane, it is important to ensure that the airplane is above a certain height before it leaves the airport environment. This height is called ‘Screen height’ and is equal to 15 m (sometimes 10 m), which is above the height of common obstacles like trees and electricity poles. The takeoff distance is defined as the horizontal distance covered by an airplane from the start of the run till it climbs to a height equal to the screen height. It is assumed that the weight of the airplane during take-off is the gross weight for which it is designed, and that the take-off takes place in still air.

The take-off flight is generally divided into three phases namely: ground run, transition(or flare) and climb.[7]

 

Figure 8. Phases of Take-Off flight.

From the point of view of performance analysis, the following two quantities are of interest.

(i) The take-off distance (s) (ii) The time (t) taken for it.

The equations of motion for the aircraft under consideration are as follows:

Where, T is the thrust force, D is the drag force, R is the reaction force and W is the weight of the aircraft. Using equilibrium conditions, the reaction force R is calculated as:

Where L si the lift force.

The take off power can be calculated using the thrust component of force which is rewritten as:

The forces acting on the airplane are shown in Figure 8. It is observed that the ground reaction (R) and the rolling friction, μ R, are the two additional forces along with the lift, the drag, the weight and thrust ; μ is the coefficient of rolling friction between the runway and the landing gear wheels. The value of µ depends on the type of surface. The angle of attack and hence, the lift coefficient (C_L ) and the drag coefficient (C_D ) can be assumed to remain constant during the take-off run.

The equation for the ground run (s1) is given as:

  

The time taken for the ground run (s1) is given as:

[8] 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.

[9] The amount of power that an engine is allowed to produce for a limited period of time for takeoff is called Take-Off Power. The use of takeoff power is usually limited to 5 min for reciprocating engines and up to 2½ min for gas turbine engines. This may not always be the case. Specifically, with respect to 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 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.

•  TYRE DESIGN: [10] Carcass plies are used to form the tire. They are sometimes called casing plies. An aircraft tyre is constructed for the purpose it serves. They support the weight of an aircraft while it is on the ground. It also provides the necessary traction for braking and stopping of an airplane. Tyre also helps to absorb the shock of landing and provide cushioning the roughness of takeoff, roll-out, and taxi operations. Unlike an automobile or truck tyre, it does not have to carry a load for a long period of continuous operation. However, an aircraft tyre absorbs the high impact loads of landing, and also, it’s operating at high speeds for a short time when required.

Figure 9. Description of an aircraft tyre.

The technical aspects of the tyre are as follows:

1. Retreading: Retreading is methods of restoring a worn tyre by renewing the tread area or by renewing the tread area plus one or both sidewalls. Repairs are included in the tyre retreading process.
2. Load Rating: Load rating is the maximum permissible load at a specified inflation pressure.
3. Ply Rating: Ply Rating is used to identify the maximum recommended load rating and inflation pressure for a specified tyre. It is an index of tyre strength.
4. Speed Rating: The speed rating is the maximum takeoff speed to which the tyre has been tested.
5. Skid Depth: Skid depth is the distance between the tread surface and the deepest groove as measured in the mould.

Aircraft tyres must have an approved speed and load rating and have sufficient clearance when retracted through landing gear to allow for tyre growth. Tyre growth is the increase in the size of the tyre due to centrifugal forces at high speed. Tubeless tyres are more advantageous over tube-type. There is no longer the use of tube-type tyre in recent aviation. Nowadays all airliners are using tubeless tyres. Tubeless that are meant to be used without a tube has the word TUBELESS on the sidewall of the tyre. Almost all airliners are using Radial tyre. Bias is an older design, and it’s mainly used for road vehicles. Radial tyres have the word RADIAL on the sidewall. Radial tires are more expensive than bias-ply tyres. Radial tires are in demand because of their lower life cycle cost and long-term value.

Aircraft tyres are manufactured with tread rubber with conducting compounds to permit earthing of static charges. In early days, when tyres were not sufficiently conductive, aircraft used to have a conductive strip hanging down from the axle of the landing gear. Upon landing, this strip would be the first part of the aircraft to touch the earth. This discharges any static electricity accumulated on the outer surfaces of the aircraft, which is not the case anymore.

Chines are also called deflectors. Chine tyre used on the nose wheel of aircraft, specially fuselage-mounted jet engines. It diverts runway water away from the engine inlets. Chines are circumferential protrusions that are moulded into the sidewall of nose tyres that deflect water sideways to help reduce excess water ingestion into the engines. Tyres may have chines on one or both sides, depending on the number of nose tyres on the aircraft.

Figure 10. Tyre showcasing chine.

[11] An aircraft tire or tyre is designed to withstand extremely heavy loads for short durations. The number of tires required for aircraft increases with the weight of the aircraft, as the weight of the airplane needs to be distributed more evenly. Aircraft tire tread patterns are designed to facilitate stability in high crosswind conditions, to channel water away to prevent hydroplaning, and for braking effect. Aircraft tires also include fusible plugs (which are assembled on the inside of the wheels), designed to melt at a certain temperature. Tires often overheat if maximum braking is applied during an aborted takeoff or an emergency landing. The fuses provide a safer failure mode that prevents tire explosions by deflating in a controlled manner, thus minimizing damage to aircraft and objects in the surrounding environment.

• ROLLING RESISTANCE: [12] Airfield performance of an airplane plays an important role in the analysis of takeoff and landing and determines, among others, ground roll distances. Forces and moments that act on aircraft landing gear wheels are effects of gravitational acceleration, as well as surface reactions. These reactions are easily obtainable on paved runways, but difficulties arise when an airplane operates on unpaved, grassy, or gravel surfaces. Rolling resistance is a property of the tire–surface system and depends on many factors. In automotive technology, rolling resistance is determined for a tire rolling on a drum test stand and its coefficient takes essentially constant values, on the order of 0.010–0.012. In the case of a tire of the aircraft interacting with a deformable surface, such as grassy surface, rolling resistance is difficult to determine, mainly due to the changing conditions of the surface, which was mentioned in the introduction. In addition, the values of the rolling resistance coefficient of the tire–grass surface system can vary by as much as an order of magnitude, considering, for example, changes in soil moisture. The presence of vegetation (grass, roots), as well as the size and mass of green parts of vegetation, are also significant. The rolling resistance coefficient, k_RR, is defined as the ratio of horizontal force during free turning to vertical force.

The following result is obtained in the field experiments which include courses of wheel forces and moments acting on the left wheel of the Wilga airplane. Figure 11(a,b) shows an example of horizontal force, F_X, which is input data for calculations (upper graph) and the rolling resistance coefficient, k_RR (lower graph), value determined using equation of the rolling resistance mentioned above. Average values are marked on the graphs (F_X = 1719 N and k_RR = 0.275). When determining the k_RR coefficient, it is important to correctly select a portion of the F_X force waveform. Namely, it is a fragment where the waveform is determined (in Figure 11(a,b), up, this fragment begins after the first second of the wave).

 

Figure 11 (a) Sample courses of the measured horizontal force, F_X, and calculated rolling resistance coefficient, k_RR.

Figure 11 (b) Calculated rolling resistance coefficient, k_RR.

 

• TYRE PRESSURE: [13] Aircraft tires are not the same as passenger car or truck tires. As a result, their care and service requirements differ. Although the tires are dimensionally similar, they differ significantly in rated inflation pressure, load, and speed.

Figure 12. below compares key parameters between a passenger car tire and two aircraft tires of about the same dimensions.

Additionally, the passenger car and truck tires are able to operate continuously because they reach thermal equilibrium while aircraft tires do not. An aircraft tire which taxis continuously at rated load and 40 mph will continue to heat up until the tire fails. The failure to reach thermal equilibrium is a consequence of the high deflections (the difference between the unloaded and loaded tire section height) at which aircraft tires operate. High inflation pressure and high deflection rates – 2.5 times greater than a car tire – allow relatively small tires to support the high loads of an aircraft.

Because aircraft tires operate at such high extremes of pressure, load, and speed, their care and service is critically important. The most important action an operator can take to prevent tire-related events is to maintain proper tire inflation pressure. Failure to keep aircraft tires properly inflated can lead to very serious consequences. The most serious of these is the structural failure of the tire. If the tire operates underinflated or over-deflected/over-loaded, the nylon cords which form the structure of the tire go in and out of compression as the tire rotates. This weakens the cords – much like a paperclip which is bent back and forth – until eventually the cords break. If enough cords break, the entire structure will eventually fail.

 

Figure 13. Compressive break in an interior ply.

This particular break damaged the inner liner, allowing air to migrate through the tire to the atmosphere. Another serious consequence of under-inflation is the thrown tread.  Over-deflection increases shear between components in the tire as it rolls in and out of contact and deforms. This results in a more rapid build‐up of heat within the tire than would be evident if the tire were properly inflated. At some point the excessive heat will cause the rubber to revert, or reverse cure. This reverted rubber is like grease with no strength or adhesion to contain the structure. This can allow the tire to decompose, throwing the entire tread or pieces of it.  In addition to destroying the tire, thrown treads often result in expensive aircraft damage. 

  

Figure 14.  Example of reversion.

Aircraft tires are designed and tested to “rated” conditions. These rated conditions are specified by industry standard’s bodies like The Tire and Rim Association (T&RA) and The European Tyre and Rim Technical Organization (ETRTO). However, most aircraft are not operated at the rated limits.This means that an operator must consult the aircraft’s Aircraft Maintenance Manual (AMM) or Pilot Operating Handbook (POH) to find out the recommended operating pressure range.

In order to ensure that an aircraft’s tires are properly inflated, Michelin recommends checking the inflation pressure, with a calibrated gauge, before the first flight of the day or before each flight if not flown daily. Because of the high pressures and extreme temperatures at which aircraft tires operate, they do not hold air perfectly. In fact, an aircraft tire can lose up to 5 percent of its pressure in 24 hours and still be perfectly serviceable.

It’s important to check tire pressures when they are cold if at all possible. Michelin recommends checking a tire’s pressure no sooner than three hours after it has last rolled. Tires that have rolled under load recently heat up, making it very difficult to determine what the proper pressure should be. Pilots and mechanics One may think that they can identify under-inflated tires by looking at them, hitting them with a bat, or looking at the wing height. In fact, it is impossible to look at tires and tell if they’re underinflated because, on a two-wheel gear, the properly inflated tire assumes more of the load than the under-inflated tire and both tires deflect the same amount.

Because the consequences of having improperly inflated tires can be so severe, the acceptable limits of operation are narrow. The chart in Figure 15 shows Michelin’s recommended actions when checking air pressures. The target pressure range is between 100 and 105 percent of the AMM-defined operating pressure. Michelin recommends always servicing the tires to the top of that range – 105 percent. If the pressure is found to be between 95 and 100 percent of operating pressure, service the tire to 105 percent; this is considered normal pressure loss. If it is between 90 and 95 percent, the pressure loss is no longer normal. Service the tire to 105 percent, make a log book entry, and recheck in 24 hours. If the pressure is again found to be in the 90 to 95 percent range, remove the tire and troubleshoot the reason for the pressure loss. If the tire has operated at less than 90 percent of the targeted operating pressure, it is no longer serviceable and must be removed. Tires that have operated under these conditions have been over-deflected to the point where the structure of the tire may be compromised. Finally, if a tire has operated at less than 80 percent of the operating pressure, it must be removed from service and so must its mate (on dual-wheel gears). In this case, the mate is most likely damaged as well.

 

Figure 15.  Pressure Monitoring Action Chart.

Finally, when servicing tires, it is important to think about ambient temperature change. For every 5 F (3 C) change in temperature, there is a corresponding 1 percent change in tire pressure. If, for example, a tire is serviced in Miami where it is 85 F and the plane flies to Minneapolis where it is 25 F, a tire which was serviced to 100% of operating pressure, will be at 88 percent in Minneapolis (after cooling for three hours). If a mechanic checks the pressure in Minneapolis before the plane returns to Miami, the tire will be unserviceable and need to be changed.

This is another reason Michelin recommends servicing the tires to the top of the acceptable range (105 percent of operating pressure). If this same tire had been serviced to 105 percent in Miami, it would have been at 93 percent in Minneapolis and still serviceable. Improper tire pressure maintenance can have serious consequences for aircraft safety. One relatively easy way to help avoid those consequences is to check tire pressures regularly and service them, as necessary.  Following these three actions is a good way to make sure you get the most value out of your tires and contribute to the safe operation of your aircraft:

•  Perform daily pressure checks with a calibrated gauge.
• Target the highest pressure recommended in the AMM or POH (105 percent of operating pressure).
• Compensate for ambient temperature changes.

 

• BRAKE FORCES WHILE LANDING: [7] When an airplane comes in to land, the lift produced must be nearly equal to the landing weight. Hence, the airplane has a velocity, called ‘Touch down speed (VTD)’, when it touches the ground. It then covers a certain distance before coming to halt. [14] A short landing run requirement for an aircraft is important from economic, operational, and strategic considerations. Too strong a braking produces skid, which is an undesirable condition, while weak breaking results in a long landing run. The shortest possible (optimal) landing run without any skidding requires a variable braking force to match the frictional force at all times. The maximum allowable braking force at any instant is a random variable as the ground-induced excitation and the frictional force between the wheel and the tyre are random in nature.

 [15] 787 braking system:

Stopping a 200-tonne aircraft landing at 180 mph requires a lot of braking force. To do this, the 787 has one brake unit on each of the eight wheels on the main gear assembly. On other aircraft types, the brake units are powered by the hydraulics system. An electrical signal is sent from the flight deck to hydraulic actuators near the main landing gear. Here, hydraulic fluid at 3,000 pound per square inch is used to force the brake unit against the wheel, thus slowing it down. This system works fine, but the pipes and actuators that form this part of the hydraulic system come at a considerable weight cost. Extra weight means more fuel burn, which in turn increases costs and carbon emissions. Hence, a more effective braking system is needed. Therefore, the use of the hydraulic system and all its associated architecture was replaced by the use  of electricity to power the brakes.

When the pilots press on the brake pedals, an electrical signal is sent to the brake unit on the wheel. The electrically powered actuators are used to press the carbon brake disc against the wheel, thereby slowing it down. By changing to electric brakes, a 787-8 saves 141 pounds per aircraft and a 787-9 saves 245 pounds. The brakes are also known as “plug and play” because electrical wiring replaces the traditional hydraulics and it’s much easier and quicker to change the brake units when needed. Smart features also allow engineers to monitor the brake performance more closely, giving a real-time measurement of wear on the carbon disks.

 

Figure 16. 787 Dreamliner.

Electric braking system:

The brake system on the 787 Dreamliner is controlled by the pilots pressing the tops of the rudder pedals under their feet, demanding the rate of braking which they require. This sends an electronic signal to the Left and Right Brake System Control Units (BSCUs). These then send signals to the four Electronic Brake Actuator Controllers (EBAC) which control the rate of braking on the wheels. Each wheel has four Electric Brake Actuators (EBA), a kind of piston which presses against the carbon brake discs. The brake disks are made up of two parts. They have rotors. These rotors are connected to the wheel by drive tabs. As these drive tabs are in contact with the inside of the wheel, they spin at the same speed. Depending on the brake manufacturer, there are either four or five of these rotors on each brake assembly. The second part of the disks are the stators. These sit around each rotor and are fixed in place and thus are stationary. As the wheel turns, the rotors spin round inside the stators.  When the brakes are applied, the four EBAs apply pressure to the first stator. This in turn squeezes the stationary stators up against the spinning rotors and it’s this friction which slows the wheel down.

 

Antiskid Protection:

When landing on slippery runways, there’s a chance that the wheels may start to skid as the brakes are applied. To stop this from happening and to maintain maximum effective braking, each wheel has anti-skid protection. Using a variety of sources to determine the aircraft speed, the brake units know how fast the wheels should be spinning. If that speed drops significantly, it’s because the current brake pressure on that wheel is too great and the wheel is just skidding over the surface. In this situation, the anti-skid system automatically reduces the braking on that wheel to a point where the skid stops before reapplying the pressure. All this is done in a fraction of a second.

 

Autobrake:

Pressing on the brakes is pretty straight forward when taxiing in a straight line at low speed. However, when  landing in strong winds, it can be a little tricky. It is needed to use our feet on the rudder pedals to line the nose of the aircraft up with the runway centerline at the last moment. Then, whilst holding that position, slide our feet up to press the toe brakes which is not easy when moving at 160 mph. To help the aircraft get the braking underway as soon as touch down, autobrake system is used. This provides automatic braking at a preselected rate as soon as the aircraft senses that it is on the ground. It also provides full braking pressure in the case of a rejected takeoff if the speed is above 85 knots (98 mph).

 

Brake temperature indication:

With friction comes heat. As a result, each brake unit displays its temperature on the wheel synoptic page in the flight deck. The numerical values relating to brake temperature are shown next to each wheel. A value of 0-4.9 is in the normal range. When a temperature becomes 5.0 or above, an advisory message is displayed to the pilots. Should the brakes become too hot, there’s a chance that the heat transferred to the wheels could cause the tires to explode. To stop this from happening, when a certain temperature is reached, fuse plugs in the tires melt. This allows the air to be released safely and slowly deflate the tires.

 

Parking brake:

Very often it is needed to engage the brakes and keep them on. This is particularly useful on long taxis to the runway and obviously when parked at the gate. The park brake is set by fully pressing down both toe brakes and pulling the parking brake lever up. With this set, we can then release the pressure from the pedals. To release, we just press the brake pedals again.

 

In addition to the brakes, there are two other systems which help slow the aircraft down on landing. The spoilers and the reverse thrust.

 

Spoilers:

The large panels at the top of the wings which raise up on touch down are the called the spoilers as they literally spoil the airflow over the wing. This dumps any remaining lift the wings are generating, allowing the wheels to take all the weight and achieve maximum efficiency from the brakes.

 

Reverse thrust:

The final part of the braking process comes from reverse thrust. Just after the touched down, two levers are pulled on top of the thrust levers to engage the reverse thrust, a sort of “reverse gear” for jet engines. This causes blockers inside the engine to deploy and a door in the side of the engine to slide backward. The air which normally leaves the engine out the back is deflected forward by the blockers and out through the door.

PROBLEM STATEMENT VI:

With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle and develop the model for the calculated force and power using Simulink.

EXPLANATION AND OBSERVATION:

The following values are assumed to calculate the force and power required to push/pull the aircraft by a towing vehicle. The aircraft under consideration is Boeing 747-200. The maximum take-off weight of the given aircraft is 3,77,840 kg. But the aircraft authority doesn’t fill the aircraft to that weight abiding safety protocols. A wavier is applied to the weight as some percentage of the maximum take-off weight. Following are the assumptions made to calculate the force and power required to push/pull the aircraft by towing vehicle:

Let the of the aircraft i.e. Boeing 747-200 W_A= 636klbs [16] = 288484.747  kg

Rolling resistance coefficient for the aircraft tyre  i.e.,

Let the weight of the towing vehicle be W_TV = 30000 kg

Rolling resistance coefficient for the towing vehicle tyre  i.e.,

We know, the value of acceleration due to gravity i.e. g = 9.806 m/s²

Let the aircraft velocity while towing be V = 20 kmph = 5.556 m/s

Let the towing vehicle velocity while towing be V_T = 6 m/s

Let the air density ρ = 1.1839 kg/m³ (at 25 ^oC)

Let the frontal area of the aircraft be A = 18 m²

Assuming the coefficient of the drag as C_D = 0.0088 [16].

Let the overall diameter of the tyre of the towing vehicle having a tyre size of 10.00-22 [17] = 1130 mm = 1.13m

Therefore, the radius of the towing vehicle tyre is R = 0.565 m.

CALCULATING THE FORCES:

Rolling resistance due to aircraft (RR_A ):

Rolling resistance due to towing vehicle (RR_TV ):

The total Rolling resistance is given as (RR):

The drag force exerted while taxiing the aircraft:

Therefore, to obtain the total force required to pushback the aircraft, it is required to consider the effect of rolling resistance due to aircraft and the towing vehicle along with the drag force exerted while taxiing the aircraft. It is mathematically expressed as:

The torque required by the towing vehicle to perform the operation of push/pull on the aircraft is given by:

The power required by the towing vehicle to perform the operation of push/pull on the aircraft is given by:

The above calculation can be performed in SIMULINK as follows:

Figure 17. Layout of the SIMULINK model of Calculation of the force and power required to push/pull the aircraft by a towing vehicle.

 

• This SIMULINK model uses lots of constant blocks to input the values required to perform the calculations. No arrays are used.
• To multiply the constants, the product block is used. And to add the constants, Add block is used.
• Power block is used to calculate the square of the velocity. The parameter in power block is changed to square and the output of the velocity block is given to it.
• The values of the total force, torque developed, and the power required are obtained in the display blocks individually.

 

PROBLEM STATEMENT VII:

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. (Hint :DC7 Block)

EXPLANATION AND OBSERVATION:

• Earlier, in the problem statement VI, towing vehicle with IC engine is considered. But the current problem statement requires the usage of an EV to fulfil the task of the IC engine driven towing vehicle to puh/pull the aircraft. Therefore, it is required to design an EV that has a capacity to support the aircraft under similar conditions as presented in the problem statement VI.
• All the assumptions made in the problem statement VI are also valid in the current problem evaluation.
• To calculate the energy required to push/pull the aircraft under consideration, it is assumed that the time taken for towing is i.e.., t_W = 10 min. Therefore, the energy required is calculated as follows:

 In terms of kWhr,

 

 

• To design the EV, it is required to design the battery such that it is capable of storing 17.27kWhr of energy. It is expected to deliver the same amount of energy, instantly to contribute to the push/pull of the aircraft. For this heavy-duty performance, batteries with parallel connected ultracapacitors (for high capacitance) can be used. For the given condition, battery design is not considered. The battery voltage is altered to suit the needs of the application.
• The motor in the powertrain should be considered such that it can develop the torque of 9757.4 Nm instantly with the power rating as close to 103.6 kW as possible.
• To suit the power of 103.6 kW application requires a 139 HP motor. And to attend this high-power demand, a 150 HP.
• Therefore, a Simulink model using two quadrant chopper is used for the required application as follows:

Figure 18. Layout of two-Quadrant chopper in Simulink.

 

• Although the powertrain model in the Figure 18 is incomplete, the required output parameters are plotted in the scope. The values help in the calculation of the power developed by the vehicle and the duty cycle.
• The layout of the Two-Quadrant chopper is taken from the Figure 33. In this, Two IGBT blocks and two diode blocks are considered. A DC machine is employed to impart the inductance required by the chopper circuit. An external DC voltage source of 240 V is supplied. A separate excited field voltage of 300V is given to the F terminal of the DC machine.
• The load torque (T_L) input is given by using a step block. For simulation time (1 sec) greater than or equal to the Step time (1 sec), the output is the Final value parameter value.
• The initial value is set to 1000 and final value is set to 100 in the step function generator. The sample time is kept at 0.
• The initial default parameters set to IGBT links is defined in the table given below:

Parameter	Value/Specification
Resistance Ron	0.001 ohms
Forward Voltage Vf	1 V
Snubber resistance Rs	1e5 ohms
Snubber capacitance Cs	Inf F

Table 4. Predefined parameters for IGBT.

• The IGBT blocks are assumed to take the same values. The IGBTs are named as Q1 and Q2. The ‘m’ ports of the IGBTs i.e., Q1 and Q2 are connected to GoTo blocks named Q1 and Q2, respectively.
• Since both Q1 and Q2 are to be connected in series, the ‘E’ port of Q1 is connected to the ‘E’ port of Q2. The ‘C’ port of Q1 is connected to the positive terminal of the DC Voltage supply of 240 V and the ‘E’ port of the Q2 is connected to the negative terminal of the DC Voltage supply.
• The ‘g’ port of the IGBT takes the input as gate pulses. Therefore, pulse generator block is connected to both the ‘g’ ports of the IGBTs, and the following gives the details of the parameters given to the pulse generator:

Parameter	Value/Specification
Pulse type	Time based
Time (t)	Simulation time
Amplitude	1
Period	0.002 seconds
Pulse width (% of period)	75
Phase delay	0

Table 5. Predefined parameters for Pulse generator block.

• The diodes are connected in parallel to the IGBTs. The diode parallel to Q2 is called Free Wheeling diode. The ‘m’ ports of the Diodes i.e., D1 and D2 are connected to GoTo blocks named D1 and D2, respectively.
• The ‘a’ port of the diode D1 is connected to the ‘k’ port of the Free-Wheeling Diode i.e., D2.
• The ‘k’ port of the diode D1 is connected to the positive terminal of the DC Voltage Supply of 240 V and the ‘a’ port of the Diode D2 is connected to the negative terminal of the DC Voltage supply.
• The initial default parameters set to Diode links is defined in the table 13 as given below.

Parameter	Value/Specification
Resistance Ron	0.001 ohms
Forward Voltage Vf	0.8 V
Snubber resistance Rs	inf ohms
Snubber capacitance Cs	0       F

Table 6. Predefined parameters for Diode.

• The left armature port ‘A’ of the DC machine is connected to the mid connections of Q1 and Q2 along with the mid connections of the diodes D1 and D2. The right side ‘A’ port of the DC Machine is connected to the negative terminal of the DC voltage source.
• The T_L port of the DC machine is connected to the step block. The ‘m’ port of the DC Machine is connected to the scope to give the pictographic representation of the variation of armature current, field current, angular velocity and electromechanical torque in the scope through the bus selector.
• The input value to the T_L port and the electromechanical torque is connected to the scope along with the electromechanical torque obtained from the ‘m’ port of the DC Machine.
• The inputs of as obtained from the DC Machine block parameters is as follows:

Parameter	Value/Specification
Model	17: 150HP 500V 1750RPM Field:300V
Mechanical Input	Torque TL
Initial Speed	0.001 rad/sec
Sample time(-1 for inherited)	-1

Table 7. Parameters that are predefined for the DC Machine.

• The GoTo blocks from both IGBT and Diode blocks through their ‘m’ ports will each give two outputs namely Voltage and Current. As a result, there are four current values, and four voltage values as follows:

Q1 current, Q2 current, D1 current, D2 current; Q1 voltage, Q2 voltage, D1 voltage, D2 voltage.

• Each block’s (IGBT and Diode) value of voltage and current is available in the subsystem named as ‘Data’.
• Different subsystems are created to understand the variations of voltages and currents of different blocks with respect to one another.
• The total simulation time is set to 1 sec and the different voltages and currents are evaluated and the simulation is performed resulting in appropriate pictographic solutions in scope.

 

RESULTS

• There are many factors that lead to efficient and safe operation of aircraft. Among these vital factors are proper weights and balance control. The list of weights of different aircraft are tabulated.
• Groundspeed is the speed of the aircraft directly over the ground. It is a vector quantity. Higher the ground speed the faster you reach your destination. This can be measured from the ground. The important quantity in the generation of lift is the relative velocity between the object and the air, which is called the airspeed and it is not directly measured from the ground. Air speed is the difference between the ground speed and the windspeed.
• Aircraft does not use its engine power on the ground as it results in large fuel consumption, wear and tear on the engine which later effects the efficiency of the aircraft, unnecessary jet blast and noise. This also may lead to unnecessary and unintended movement of the aircraft which may result in the damage of the aircraft, the structural entities in the surrounding and may result in hurting the crew, passengers, and pilots.
• Pushback is when an aircraft is pushed backwards away from the airport gate by vehicles called tugs or tractors. 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.
• The amount of power that an engine is allowed to produce for a limited period of time for takeoff is called Take-Off Power .The use of takeoff power is usually limited to 5 min for reciprocating engines and up to 2½ min for gas turbine engines. An aircraft tire or tyre is designed to withstand extremely heavy loads for short durations. The fuses provide a safer failure mode that prevents tire explosions by deflating in a controlled manner, thus minimizing damage to aircraft and objects in the surrounding environment. Rolling resistance is a property of the tire–surface system and depends on many factors. This can be defined as the product of rolling resistance coefficient and the normal force. Because aircraft tires operate at such high extremes of pressure, load, and speed, their care and service is critically important. The most important action an operator can take to prevent tire-related events is to maintain proper tire inflation pressure. The target pressure range is between 100 and 105 percent of the AMM-defined operating pressure. A braking system with less weight, less occupancy, quick feedback response time along with other factors result in a good braking.
• The manually calculated force and power required to push / pull an aircraft by a towing vehicle are 17270.35 N and 1036221 W respectively and the values developed by the Simulink model are 17270.36 N and 103622.18 W respectively. The torques developed by manual and Simulink calculations are 9757.74 Nm and 9757.76 Nm respectively.
• The following graph plots different parameters of the DC motor under consideration:

 

Results of DC motor under consideration. The green plot indicates electromechanical torque, and the red curve indicates the angular velocity. The yellow curve indicates the armature current, and the blue curve indicates the field current.

The output of the Simulink model gives the maximum value of electromechanical torque as 1300 Nm. Where as the value of the corresponding angular velocity is 81.68 rad/sec. We know that the power developed is given by the following formula:

  

 

Therefore, the total power developed at maximum torque condition is 106.184 kW which is achieved at 0.077 seconds from the start of the EV. The value of the power developed is slightly greater than the power required to tow the aircraft as the power rating required was of 139 HP but the vehicle under consideration has 150 HP motor. The difference in power required and developed is obvious.

To estimate the duty cycle:

 

Input power is the power developed by the EV which is 106.184 kW and the output power is the power required to tow the aircraft which is 103.6221 kW.

Therefore, the duty cycle is calculated as follows:

 

The duty cycle ratio obtained is 97.58% which effectively high. This might not be the case in the practical applications.

BIBLIOGRAPHY

1. https://mediawiki.ivao.aero/index.php?title=Standard_aircraft_weight
2. https://en.wikipedia.org/wiki/List_of_airliners_by_maximum_takeoff_weight
3. https://www.grc.nasa.gov/www/k-12/airplane/move.html
4. https://en.wikipedia.org/wiki/Taxiing
5. https://www.skybrary.aero/index.php/Aircraft_Ground_Running
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7. https://nptel.ac.in/content/storage2/courses/101106041/Chapter%2010%20Lecture%2032%2022-12-2011.pdf
8. https://en.wikipedia.org/wiki/Takeoff
9. An Illustrated Dictionary of Aviation. S.v. "takeoff power." Retrieved May 12 2021 from https://encyclopedia2.thefreedictionary.com/takeoff+power
10. https://www.aviationhunt.com/aircraft-tyre-construction/
11. https://en.wikipedia.org/wiki/Aircraft_tire
12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6983224/
13. https://www.aviationpros.com/engines-components/aircraft-airframe-accessories/article/12029645/how-does-tire-pressure-maintenance-impact-aircraft-safety
14. Yadav, C.V.K. Singh, “Landing response of aircraft with optimal anti-skid braking”, Journal of Sound and Vibration, Volume 181, Issue 3, 1995, Pages 401-416, ISSN 0022-460X, https://doi.org/10.1006/jsvi.1995.0148.
15. https://thepointsguy.com/guide/how-do-aircraft-brakes-work/#:~:text=On%20other%20aircraft%20types%2C%20the,wheel%2C%20thus%20slowing%20it%20down.
16. http://www.dept.aoe.vt.edu/~mason/Mason_f/B747PresS07.pdf?q=747
17. https://www.mrftyres.com/downloads/heavydutytrucks.pdf