Project-1: Powertrain for aircraft in runways

AIM :

Part A:

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

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

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

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

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

Part B:

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

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

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.

(Hint :DC7 Block)

B. Also, Design the parameters in excel sheet.

PART - A :

1. Total Weight of Various Aircraft :

Various types of aircraft weights are as follows,

1. Maximum Design Taxi Weight (MDTW) :

The MDTW is the maximum weight certified for aircraft manoevring on the ground as limited by aircraft strength and airworthiness requirments.

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 aircraf meets the appropriate landing requirements. It generally depends upon landing gear strength or the landing impact loads on 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 min) 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 usuable fuel and other specified usable agent (engine injection fluid, and other consumable propulsion agents). It is the maximum weight permitted before usuble fuel and other specified usable fuel are loaded in specified section

List of Aircrafts with their weight :

​

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[1][2][3]	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[4][5][6]	381,000	288.417	2530	1494	Heavy	Heavy
Boeing 747-200[7]	377,840	285.700	3338	2109	Heavy	Heavy
Boeing 747-300[7]	377,840	260.320	3222	1905	Heavy	Heavy
Airbus A340-500[8]	371,950	240	3050	2010	Heavy	Heavy
Airbus A340-600[8]	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[7]	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[8][9]	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[10]	254,000	192.777	2900		Heavy	Heavy
Boeing 787-10[10]	254,000	201.849			Heavy	Heavy
Airbus A340-200[8][11]	253,500	181	2990		Heavy	Heavy
Ilyushin IL-96-300	250,000	175	2600	1980	Heavy	Heavy
Airbus A330-300[12][13]	242,000	185	2500	1750	Heavy	Heavy
Airbus A330-200[12][13]	242,000	180	2220	1750	Heavy	Heavy
Lockheed L-1011-500	231,300	166.92	2636		Heavy	Heavy
Boeing 787-8[10]	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[14]	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[14]	163,000	138	2324	1536	Heavy	Heavy
Boeing 767-300	159,000	136.078	2713	1676	Heavy	Heavy
Airbus A310-300[14]	157,000	124	2290	1490	Heavy	Heavy
Vickers VC10	152,000	151.9			Heavy	Heavy
Boeing 707-320B[15]	151,000	97.5			Heavy	Heavy
Boeing 707-320C[15]	151,000	112.1			Heavy	Heavy
Douglas DC-8-61	147,000				Heavy	Heavy
Airbus A310-200[14]	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[15]	117,000	86.3			Medium	Large
Boeing 757-200	116,000	89.9	2347	1555	Medium	Large
Boeing 720B[16]	106,000	79.5			Medium	Large
Boeing 720[16]	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[17]	84,000	70.1			Medium	Large
Airbus A321-100[18]	83,000	77.8	2200	1540	Medium	Large
Boeing 737-800	79,000	65.32	2308	1634	Medium	Large
Boeing 727-200[17]	78,000	68.1			Medium	Large
McDonnell-Douglas MD-83	73,000	63.28			Medium	Large
Boeing 727-100[17]	72,500	62.4			Medium	Large
Boeing 727-100C[17]	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[18]	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[18]	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[18]	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[19]	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[20]	37,500	32.8	2244	1304	Medium	Large
Bombardier CRJ900[21]	36,500	33.345	1778	1596	Medium	Large
Embraer 170[22]	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[23]	9,752	8.709	1353	811	Medium	Small
Pilatus PC-24[24]	8,300	7.665	893	724	Medium	Small
Embraer Phenom 300[25]	8,150	7.65	956	677	Medium	Small
Beechcraft 1900D	7,765	7.605	1036	853	Medium	Small
Cessna Citation CJ4[26]	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

2. Difference between Air speed and ground speed of aircraft.

Airspeed is more than simply reading off your airspeed indicator. Here are the 4 types of airspeed, and what each means for your flying...

1. Indicated Airspeed (IAS)

This one's pretty simple. It's read right off your airspeed indicator and is usually what you'll reference in the cockpit for speed changes. The speed limits of the sky, like not exceeding 250 knots below 10,000 feet MSL, are all written as indicated airspeed values.

2. True Airspeed (TAS)

True airspeed is the speed of your aircraft relative to the air it's flying through. As you climb, true airspeed is higher than your indicated airspeed. Pressure decreases with higher altitudes, so for any given true airspeed, as you climb, fewer and fewer air molecules will enter the pitot tube. Because of that, indicated airspeed will be less than true airspeed. In fact, for every thousand feet above sea level, true airspeed is about 2% higher than indicated airspeed. So at 10,000 feet, true airspeed is roughly 20% faster than what you read off your airspeed indicator.

Many aircraft, such as those with gas turbine engines, can reach a higher TAS at higher altitudes because their engines are more efficient at higher altitudes.

3. Ground Airspeed (GAS)

The movement of your airplane relative to the ground is called groundspeed. It's true airspeed corrected for wind. With a true airspeed of 100 knots and a tailwind of 20 knots, you'd be flying a groundspeed of 120 knots.

4. Calibrated Airspeed (CAS)

Calibrated airspeed is indicated airspeed corrected for instrument and positional errors. At certain airspeeds and with certain flap settings, the installation and instrument errors may total several knots. This error is generally greatest at low airspeeds, with nose high pitch attitudes.

When flying at sea level under International Standard Atmosphere (ISA) conditions (15 degrees Celsius, 29.92 inches of mercury, 0% humidity), calibrated airspeed is the same as true airspeed. If there is no wind it is also the same as 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 caution for everything like,

• Applying thrust can create a blast behind each engine.
• People, equipments and anything else in the way can be injured or damaged from the jet blast.
• Before we apply power to the engines the areas in front of each engine are like another super critical factor that must be carefully negotiated.
• The immediate area in front of a jet engine creates an area where people and equipment can be sucked into the engine if anything is too close to the intake.
• So to avoid all such extreme cautions it is not recommended to use aircraft engine power to move it on the airport.

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

Taxiing is the controlled movement of the airplane under its own power while on the surface. Since an airplane is moved under its own power between a parking area and the runway, the pilot must thoroughly understand and be proficient in taxi procedures.

An essential requirement in conducting safe taxi operations is where the pilot maintains situational awareness of the ramp, parking areas, taxiways, runway environment, and the persons, equipment and aircraft at all times. Without such awareness, safety may be compromised. Depending on the airport, parking, ramp, and taxiways may or may not be controlled. As such, it is important that the pilot completely understand the environment in which they are operating. At small, rural airports these areas may be desolate with few aircraft which limits the potential hazards; however, as the complexity of the airport increases so does the potential for hazards. Regardless of the complexity, some generally accepted procedures are appropriate.

• The pilot should make themselves familiar with the parking, ramp, and taxi environment. This can be done by having an airport diagram, if available, out and in view at all times. [Figure 2-13]
• The pilot must be vigilant of the entire area around the airplane to ensure that the airplane clears all obstructions. If, at any time, there is doubt about a safe clearance from an object, the pilot should stop the airplane and check the clearance. It may be necessary to have the airplane towed or physically moved by a ground crew.
• When taxiing, the pilot’s eyes should be looking outside the airplane scanning from side to side while looking both near and far to assess routing and potential conflicts.
• A safe taxiing speed must be maintained. The primary requirements for safe taxiing are positive control, the ability to recognize any potential hazards in time to avoid them, and the ability to stop or turn where and when desired, without undue reliance on the brakes. Pilots should proceed at a cautious speed on congested or busy ramps. Normally, the speed should be at the rate where movement of the airplane is dependent on the throttle. That is, slow enough so when the throttle is closed, the airplane can be stopped promptly.
• The pilot should accurately place the aircraft centered on the taxiway at all times. Some taxiways have above ground taxi lights and signage that could impact the airplane or propellers if the pilot does not exercise accurate control. When yellow taxiway centerline stripes are marked, this is more easily accomplished by the pilot visually placing the centerline stripe so it is under the center of the airplane fuselage.
• When taxiing, the pilot must slow down before attempting a turn. Sharp high-speed turns place undesirable side loads on the landing gear and may result in tire damage or an uncontrollable swerve or a ground loop. Swerves are most likely to occur when turning from a downwind heading toward an upwind heading. In moderate to high-wind conditions, the airplane may weathervane increasing the swerving tendency.

Steering is accomplished with rudder pedals and brakes. To turn the airplane on the ground, the pilot should apply the rudder in the desired direction of turn and use the appropriate power or brake to control the taxi speed. The rudder pedal should be held in the direction of the turn until just short of the point where the turn is to be stopped. Rudder pressure is then released or opposite pressure is applied as needed.

More engine power may be required to start the airplane moving forward, or to start a turn, than is required to keep it moving in any given direction. When using additional power, the throttle should immediately be retarded once the airplane begins moving to prevent excessive acceleration.

The brakes should be tested for proper operation as soon as the airplane is put in motion. Applying power to start the airplane moving forward slowly, then retarding the throttle and simultaneously applying just enough pressure to one side, then the other to confirm proper function and reaction of both brakes. This is best if the airplane has individual left/ right brakes to stop the airplane. If braking performance is unsatisfactory, the engine should be shut down immediately.

When taxiing at appropriate speeds in no-wind conditions, the aileron and elevator control surfaces have little or no effect on directional control of the airplane. These controls should not be considered steering devices and should be held in a neutral position.

The presence of moderate to strong headwinds and/or a strong propeller slipstream makes the use of the elevator necessary to maintain control of the pitch attitude while taxiing. This becomes apparent when considering the lifting action that may be created on the horizontal tail surfaces by either of those two factors. The elevator control in nosewheel-type airplanes should be held in the neutral position, while in tailwheel-type airplanes, it should be held in the full aft position to hold the tail down.

Downwind taxiing usually requires less engine power after the initial ground roll is begun, since the wind is pushing the airplane forward. To avoid overheating the brakes and controlling the airplane’s speed when taxiing downwind, the pilot must keep engine power to a minimum. Rather than continuously riding the brakes to control speed, it is appropriate to apply brakes only occasionally. Other than sharp turns at low speed, the throttle should always be at idle before the brakes are applied. It is a common error to taxi with a power setting that requires controlling taxi speed with the brakes.

When taxiing with a quartering headwind, the wing on the upwind side (the side that the wind is coming from) tends to be lifted by the wind unless the aileron control is held in that direction (upwind aileron UP). Moving the aileron into the UP position reduces the effect of the wind striking that wing, thus reducing the lifting action. This control movement also causes the downwind aileron to be placed in the DOWN position, thus a small amount of lift and drag on the downwind wing, further reducing the tendency of the upwind wing to rise.

When taxiing with a quartering tailwind, the elevator should be held in the DOWN position, and the upwind aileron, DOWN. Since the wind is striking the airplane from behind, these control positions reduce the tendency of the wind to get under the tail and the wing and to nose the airplane over. The application of these crosswind taxi corrections helps to minimize the weathervaning tendency and ultimately results in making the airplane easier to steer.

Normally, all turns should be started using the rudder pedal to steer the nosewheel. To tighten the turn after full pedal deflection is reached, the brake may be applied as needed. When stopping the airplane, it is advisable to always stop with the nosewheel straight ahead to relieve any side load on the nosewheel and to make it easier to start moving ahead.

During crosswind taxiing, even the nosewheel-type airplane has some tendency to weathervane. However, the weathervaning tendency is less than in tailwheel-type airplanes because the main wheels are located behind the airplane’s center of gravity, and the nosewheel’s ground friction helps to resist the tendency. The nosewheel linkage from the rudder pedals provides adequate steering control for safe and efficient ground handling, and normally, only rudder pressure is necessary to correct for a crosswind.

Taxiing checklists are sometimes specified by the AFM/POH, and the pilot must accomplish any items that are required. If there are no specific checklist items, taxiing still provides an opportunity to verify the operation and cross-check of the flight instruments. In general, the flight instruments should indicate properly with the airspeed at or near zero (depending on taxi speed, wind speed and direction, and lower limit sensitivity); the attitude indictor should indicate pitch and roll level (depending on airplane attitude) with no flags; the altimeter should indicate the proper elevation within prescribed limits; the turn indictor should show the correct direction of turn with the ball movement toward the outside of the turn with no flags; the directional gyro should be set and crossed checked to the magnetic compass and verified accurate to the direction of taxi; and the vertical speed indictor (VSI) should read zero. These checks can be accomplished on conventional mechanical instrumented aircraft or glass cockpits.

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

1. Take-off Power :

Take-off power is the phase of flight in which an aircraft leaves the ground and becomes airborn. On take-off, in order to position aircraftto a safe height away from terrain and obstacles, the engine thrust is set to a high 'Take-off power' setting and the aircraft is pitched up to maintain a specific speed to the required takeoff power.

Take off performance can be predicted using a simple measure of the acceleration of the aircraft along the runway based on force equllibrium.

The Forces involved are as follows,

T = Thrust of propulsion system pushing aircraft along runway.

D = Aerodynamic Drag of vehicle resisting the forward motion

F = Rolling resistance due to friction between tires and runway

During take-off run the imbalance in these forces will produce an acceleration along the runway.

A = (T - D - F)/m

where,

A = acceleration along the runway

m = mass of aircraft

Thus the take-off power is,

P = (T - D - F) x V

where,

V = velocity of aircraft

2. Tire Design :

An aircraft tyre is designed to withstand extremely heavy loads while landing, take off, taxing, and parking. The number of wheels required for aircraft increases with the weight of the aircraft, as the weight of the aeroplane needs to be distributed more evenly.

A Boeing 737NG & 737MAX uses 6 wheels, Boeing 787 uses 10 wheels, Boeing 777 uses 14 wheels and Airbus A380 uses 22 wheels. Aircraft tyres work under extreme conditions, carrying up to 340 tons and accelerating at over 250 km/hour at takeoff, in addition to enduring varied environmental stress when in flight and taxiing.

Design and Construction of Aircraft tyre

Carcass plies are used to form the tire. They are sometimes called casing plies. An aircraft tyre is constructed for the purpose it serves.

1. They support the weight of an aircraft while it is on the ground.
2. It also provides the necessary traction for braking and stopping of an aeroplane.
3. 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.

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.

Load Rating – Load rating is the maximum permissible load at a specified inflation pressure.

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.

Speed Rating – The speed rating is the maximum takeoff speed to which the tyre has been tested.

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.

Aircraft tyres may be Tube-type or Tubeless

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.

Aircraft tyres may be Radial or Bias

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.

Conductivity of tires

Today’s tyres are conductive. 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. Now you don’t see them anymore.

Chines in Tyre

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.

Aircraft Tyre Standards

Each tyre manufacturer produces their own designs of the tyre with different tread patterns, wear patterns, wear limits etc, and in some cases, different names for the same part of the tyre. But all tyres must meet the approved standards before being accepted by the FAA or CAA.

All commercial aircraft tyres approved under FAA Requirement Technical Standard Order (TSO) C62. A TSO is a minimum performance standard for specified materials, parts, and appliances used on civil aircraft.

3. Rolling Resistance

Rolling resistance is the force resisting the motion when a body rolls on a surface.

It can be seen in the aircraft when the aircraft takes off from the runway and while landing at the runway with help their wheels.

The rolling resistance can be expressed as,

Fr = c x W

where,

Fr = Rolling friction

c = Rolling resistance coefficient

w = m x g

where,

w = weight of body

m = mass of body

g = acceleration due to gravity

Thus rolling resistance of vehicle can be expressed as,

Fr = c x w/r

where,

r = radius of wheel

The Rolling coefficient for air filled tires on dry roads can be estimated as

c = 0.005 + (1/p)(0.01 + 0.0095(v/100)^2)

where,

p = tyre pressure

4. Tire Pressure

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.

Inflation

Each of the twelve Boeing 777-300ER main tires is inflated to 220 psi (15 bar; 1,500 kPa), weighs 120 kg (260 lb), has a diameter of 134 cm (53 in) and is changed every 300 cycles while the brakes are changed every 2000 cycles.Each tire is worth about $5,000. Aircraft tires generally operate at high pressures, up to 200 psi (14 bar; 1,400 kPa) for airliners, and even higher for business jets. 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.

Tests of airliner aircraft tires have shown that they are able to sustain pressures of maximum 800 psi (55 bar; 5,500 kPa) before bursting. During the tests the tires have to be filled with water, to prevent the test room being blown apart by the energy that would be released by a gas when the tire bursts.

Aircraft tires are usually inflated with nitrogen to minimize expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight.Dry nitrogen expands at the same rate as other dry atmospheric gases (normal air is about 80% nitrogen), but common compressed air sources may contain moisture, which increases the expansion rate with temperature.

The requirement that an inert gas, such as nitrogen, be used instead of air for inflation of tires on certain transport category airplanes was prompted by at least three cases in which the oxygen in air-filled tires had combined with volatile gases given off by a severely overheated tire and exploded upon reaching autoignition temperature. The use of an inert gas for tire inflation eliminates the possibility of tire explosion.

Manufacturers

The aircraft tire manufacturing industry is dominated by a four firm oligopoly that controls 85% of market share.

The four major manufacturers in aircraft tire manufacturing are the following according to a report by Pelmar Engineering in 2013:

• Goodyear (United States)
• Michelin (France)
• Dunlop Aircraft Tyres (United Kingdom)
• Bridgestone (Japan)

These firms control approximately 85% of the manufacturing market and account for most of the retreads. Dunlop is the smallest player among the major firms with revenue reported at £40m in a 2015 media report.

There are several other smaller industry players, particularly in China. Among these producers are Guilin-based Guilin Lanyu Aircraft Tire Development Co., a subsidiary of ChemChina that was founded in 1980; a Yinchuan, Ningxia located aircraft tire plant owned by Singapore-based Giti Tire; and Qingdao, Shandong-based Sentury Tire, which manufactures tires for the Boeing 737.

Weihai, Shandong-based Triangle Group announced in 2012 a collaboration with the Harbin Institute of Technology for designing and manufacturing aircraft tires.

5. Aircraft braking on landing

Aircraft brakes stop a moving aircraft by converting its kinetic energy to heat energy by means of friction between rotating and stationary discs located in brake assemblies in the wheels.

Brakes provide this critical stopping function during landings to enable airplanes to stop within the length of the runway. They also stop aircraft during rejected takeoff events, in which an attempted takeoff is canceled as the airplane is rolling down the runway before it lifts off from the ground due to engine failure, tire blowout, other system failure or direction from air traffic control.

Aircraft brakes also prevent motion of the aircraft when it is parked, limit its speed during taxiing and can even help steer the aircraft on the ground by applying different levels of braking force to the left- and right-side brakes.

Aircraft brakes work in conjunction with other brake mechanisms such as thrust reversers, air brakes and spoilers. Thrust reversers are surfaces that are deployed into the path of the jet blast from the engines to redirect propulsive thrust in a direction that opposes the motion of the aircraft. Air brakes and spoilers are flight control surfaces that create additional aerodynamic drag when deployed into the path of air flowing around the aircraft.

How aircraft brakes work

The most common type of brake used on aircraft is the disc brake. Disc brakes function by exploiting friction between rotating and stationary discs inside the brake.

Upon receiving a command signal to brake — from the pilot depressing a foot pedal or from the autobrake system — actuators in the brake move a piston to squeeze the discs together, generating a frictional force that slows the rotation of the wheel. The friction between the discs generates heat as the aircraft’s kinetic energy is converted to heat energy. In this function, the brakes act as a heat sink, absorbing tremendous amounts of heat as the aircraft sheds kinetic energy. During RTO stops, the temperature of carbon disc brakes can exceed 1,800° C.

The discs are mounted on a carrier assembly consisting of a torque tube, which resists and transmits brake torque to the landing gear structure. Sandwiched together between the carrier assembly housing and a backing plate, the discs are arranged in an alternating pattern of rotors and stators. Notch and groove geometry around the circumference of each rotor fits into corresponding geometry in the wheel, keying the rotors to the wheel so that they rotate with it. The stators are keyed to the torque tube and are thus held stationary since the torque tube is connected to the axle and landing gear structure.

Cylindrical spaces within the carrier assembly hold actuator pistons. Braking occurs as piston force squeezes the discs together.

During each application of the brakes, disc material is worn away by frictional forces. A wear indicator in the form of a pin that protrudes out of the carrier assembly indicates the thickness of the stack of discs. Over hundreds of brake applications, material wears away and discs become thinner, requiring replacement following periodic maintenance intervals.

Brake design

The primary design considerations for aircraft brakes include the number of discs, the diameter of the discs and the material of the discs.

A major design point around which aircraft brakes are designed is the worst-case scenario of rejected takeoff (RTO) at the maximum rolling speed V₁, known as the decision speed. Above V₁, a takeoff could not be safely aborted without serious risk of the airplane failing to stop before the end of the runway. In this situation, the brakes need to absorb more energy than any other scenario.

An A380’s brakes exhibit a red-hot glow during a rejected take off (RTO) test on the runway at ISTRES AFB in the south of France. Source: Airbus (Click image to enlarge)

To illustrate how much energy this is, consider an Airbus A380 — the world’s biggest passenger airplane — performing an RTO at V₁. The maximum take-off weight of an A380 is 575,000 kg (1,267,658 lb) and its maximum V₁ is around 170 knots (about 195 mph or 87 m/s). A rough estimate for the maximum energy that the A380’s 16 brakes need to dissipate during RTO can be obtained by calculating the kinetic energy of the aircraft (neglecting the effects of thrust reversers, air brakes, tailwinds, headwinds and runway slope).

Since kinetic energy (KE) is a function of mass (m) and velocity (v) according to the equation:

KE = ½mv²

The kinetic energy of the A380 during RTO is calculated as follows:

KE = 0.5 * 575,000 kg * (87.4556 m/s)² = 2.2 x 10⁹ J = 2.2 GJ

2.2 GJ (gigajoules) is about the amount of energy an average cloud-to-ground lightning strike dissipates. It is also enough energy to power an 8 W LED light bulb (with light output equivalent to a 60 W light bulb) continuously for 8 years and 10 months.

To generate the necessary frictional forces and to handle this much energy within the length of a runway, large commercial transport aircraft typically require multiple discs per brake assembly and brakes on most, if not all, of their wheels.

For example, an A380 has 22 wheels distributed on five landing gear legs to support its massive weight: two nose wheels on a leg beneath the nose of the aircraft, eight wing wheels split between two legs that fold out from under the fuselage to support the left and right wings, and 12 body wheels split between two inboard landing gear legs under the fuselage. Sixteen of these wheels have brakes (four aft body wheels and the nose wheels are not braked).

The A380 uses Honeywell’s Carbenix brakes. Each of the aircraft’s 16 brake assemblies has five rotors made of Carbenix 4000 carbon-carbon composite. The brake assemblies are located within wheels made of 2014-T6 aluminum alloy and attached to the axle and landing gear structure, which is comprised of 300 M high-strength alloy steel, titanium and aluminum components.

Brake materials

The most common aircraft brake disc material until around 1963 was steel. The introduction of beryllium as a disc material provided improved thermal properties at the cost of material handling difficulties due to the toxic nature of beryllium oxide.

Carbon brakes became widely available for commercial airplanes starting in the 1980s. Carbon brakes — made of, for example, carbon fibers in a graphite matrix — are lighter, more durable, less thermally sensitive and have higher energy absorption and faster cooling rates compared to steel brakes.

Compared to steel, carbon’s higher specific heat — the amount of heat that a unit mass of carbon absorbs to raise its temperature by one unit — enables reduced brake weight. Carbon’s higher thermal conductivity allows faster heat transfer and uniform heat distribution through the disc. Carbon also has lower thermal expansion, higher thermal shock resistance and a higher temperature limit than steel. The specific strength of carbon is relatively constant over a very wide range of temperatures, unlike steel and beryllium, which both exhibit steep declines in specific strength at high temperatures, dropping below carbon around 650° C (1,200° F).

Safran Landing Systems claims its Sepcarb III oxidation-resistant carbon brakes used on Boeing 787s are four times lighter, have three times higher endurance and have two to three times higher absorption capacity than steel brakes. UTC Aerospace Systems said its Duracarb carbon disk technology results in a weight-savings of 700 lbs (318 kg) per airplane for Boeing 737NGs compared to steel brakes.

Other brake materials are available as well, such as Honeywell’s Cerametalix, a sintered combination of powdered metals and ceramics.

Brake actuator type

Brake actuators perform the critical task of squeezing discs together to generate the frictional forces that convert the aircraft’s kinetic energy of motion into heat to stop the aircraft. Most brake actuators on commercial aircraft are hydraulic, although electrically powered electromechanical actuators have entered service as well; the brakes on both the Airbus A220 (formerly known as the Bombardier C-series) and the 787 are electromechanically actuated.

Hydraulic brakes are powered by the aircraft’s hydraulic system. A servo valve modulates the flow of hydraulic fluid to the hydraulic actuator to control the amount of braking force — the force with which the hydraulic cylinder presses the discs together.

Electric brakes are powered by the aircraft’s electric system. Electricity is converted to mechanical power in the brake’s electromechanical actuators. In these actuators, an electric motor drives gears to turn a ball screw and nut to apply force to press the brake discs together.

Redundancy is a necessary attribute built into aircraft braking systems due to the critical safety function that brakes provide. For example, the A380’s hydraulic brake system is powered by multiple separate 5,000 psi hydraulic systems. The set of brakes on the wing wheels and the set of brakes on the body wheels are attached to two separate hydraulic systems. The brake system is also supplied by a backup hydraulic system called the local electrohydraulic generation supply (LEHGS), which provides an alternate source of hydraulic power in the event of primary hydraulic system failure. The LEHGS generates hydraulic pressure with an electric motor-driven pump supplied by the aircraft’s electrical system.

The design for the 787’s electric brakes also features redundancy. With four independent electromechanical actuators per wheel, operation of the 787 is permissible with 100% braking function available even if one of the electric brake actuators (EBAs) fails. The modular nature of the EBAs enables easy, in-situ maintenance during which a failed EBA can be quickly swapped out for a new one.

Brake cooling

The GS100 aircraft brake cooler has a gas or diesel engine-powered fan that provides suction cooling for fast turnaround times. Source: Ground Support Specialists, LLC. (Click image to enlarge)The large amount of heat generated during aircraft braking is dissipated by means of passive or active cooling. Passive cooling occurs due to natural conduction of heat through the disc material and to surrounding components, radiation of heat off the brake and wheel assembly, and convection as air flows past and through the brake assembly. Active cooling is achieved by using fans that force air through the brakes. Fans are either built into the wheel or part of the external ground support equipment that is positioned against the wheel and removed once sufficient temperature drop has occurred.

Example of brake temperature over time after three takeoff and landing cycles. Toward the end of a busy day full of short flights, it may be necessary to mandate a cooling period for hot brakes, during which the aircraft remains on the ground, to allow the brakes to cool so that they will not exceed the acceptable operating temperature range during RTO or landing. Source: Airbus (Click image to enlarge)

Autobrakes and skid control

Modern commercial aircraft are equipped with an autobrake system that controls the deceleration of the aircraft by automatically optimizing the application of brake force independent of pilot operation of the brake pedals to minimize stopping distance, reduce pilot workload and smooth braking action.

Another common feature of aircraft brake systems is a skid control function. Similar to anti-lock brakes on an automobile, skid control systems prevent wheel lockup. They minimize stopping distance and prevent the negative effects of skidding on tires such as unnecessary tire wear and blowout. Skid control is accomplished by applying an optimal brake force that maximizes the coefficient of friction and remains just below the amount of force that would cause skidding. In one implementation, the proper force is arrived at by continuously sensing wheel speed and comparing it to a calculated aircraft velocity. The difference between the two values represents wheel slip and brake force is reduced if it rises above a specified value.

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

Assumptions :

• Mass of airbus A380 (with payload) = Ma = 575000 kg
• Mass of push back = Mt 1000 kg
• Co-efficient of rolling resistance = Cr = 0.002
• Frontal area = A = 100 m^2
• Air density = D = 1.125 kg/m^3
• Drag coefficient = Cd = 0.015
• Velocity = v =4 m/s
• Acceleration due to gravity = g = 9.81 m/s^2

Governing equations :

Rolling resistance

Fr = Cr x M x g

Aerodyanmic Drag force

Fd = 0.5 x D x A x Cd x v^2

Total force

Ft = Fra + Frt + Fd

Power

P = Ft x v

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

Calculation of the Force and power is done using simulink as follows

1. Calculating Rolling resistance of Aircraft

2. Calculating Rolling resistance of Towing vehicle

3. Calculating Aerodynamic for both vehicles

4. Calculating total force and power

Result :

Total Force = 11.314 kN

Power = 45.258 kW

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.

(Hint :DC7 Block)

Estimation of Duty Cycle

Based on the calculation done above

The power required for towing of aircraft is 45.28 kW

Motor selected for this drivetrain is REB 90

Technical Data :

Type	REB 90
Voltage	400-800 V
Continous/Peak power	60-70/80 kW
Working rotation	1500-4000 rpm
Max torque	300 Nm
Weight	2.2 kg
Cooling	Air/Hybrid (Air + fluid)

Considering 60 kW as continous power at 400V

Battery Voltage is considered as 550 V

Thus, the duty cycle will be

d = Vo / Vd

d = 400 / 550

d = 0.7272

As there will be some losses due to resistance of FET and inductance

Correction factor is considered as 90%

As there is 10% loss, the voltage demanded by motor 10% more than rated voltage

d = 0.7272 x (1+0.1) = 0.799 = 0.8

So the voltage required by motor is 440V

Assumed parameters

Mass of aircraft	575000 Kg
Mass of Push back truck	1000 Kg
Coefficient of rolling resistance	0.002
Drag Coefficinent	0.015
Frontal Area	100 m^2
Air Density	1.125 Kg/m^3
Velocity	4 m/s
Uphill gradiant	0
Battery Voltage	550 V
Correction Factor	0.8

Block Diagram

Simulink Model

Input

Output

1. From Motor

2. From Battery

B. Also, Design the parameters in excel sheet.

Link to excel - https://drive.google.com/file/d/1or2pLrUw0KgVeZI5CiW7OBp6L74JkyUZ/view?usp=sharing