AIM: Powertrain for aircraft in runways

Objectives:

STUDY#1:

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

STUDY#2:

Is there any difference between ground speed and air speed?

STUDY#3:

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

STUDY#4:

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

STUDY#5:

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

STUDY#6:

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

STUDY#7:

1. 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.
2. Also, Design the parameters in excel sheet.

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

Weight is a major factor in airplane construction and operation, and it demands respect from all pilots and particular diligence by all maintenance personnel. Excessive weight reduces the efficiency of an aircraft and the available safety margin if an emergency condition should arise. The total weight is the maximum take-off weight. It is the maximum mass at which the aircraft is certified for take-off due to structural or other limits.

MTOW = Maximum take-off weight, MLW = Maximum landing weight, TOR = Take-off run, LR Landing run Maximum Takeoff Weight:

The maximum weight limits for an aircraft to begin its take roll is called the max takeoff weight. Maximum Landing Weight:

The maximum landing weight is, as you might imagine, the maximum aircraft weight limit approved for an aircraft to land. Landing weight can cause structural damage

MTOW-Maximum Takeoff weight

MLW-Maximum Landing Weight

Type	MTOW [kg]	MLW [tons]
Antonov An-225	640,000	591.7
Scaled Composites Model 351 Stratolaunch	589,670
Airbus A380-800	575,000	394
Boeing 747-8F	447,700	346.091
Boeing 747-8	443,613	306.175
Boeing 747-400ER	412,770	295.742
Antonov An-124-100M	405,060	330
Boeing 747-400	396,900	295.742
Lockheed C-5 Galaxy	381,000	288.417
Boeing 747-200	377,840	285.700
Boeing 747-300	377,840	260.320
Airbus A340-500	371,950	240
Airbus A340-600	367,400	256
Boeing 777F	347,800	260.816
Boeing 777-300ER	351,800	251.29
Boeing 777-200LR	347,450	223.168
Boeing 747-100	340,200	265.300
Airbus A350-1000	308,000	233.5
Boeing 777-300	299,370	237.683
Boeing 777-200ER	297,550	213.00
Airbus A340-300	276,700	190
McDonnell Douglas MD-11	273,300	185
Airbus A350-900	270,000	175
Ilyushin Il-96M	270,000	195.04
McDonnell Douglas DC-10	256,280	183
Boeing 787-9	254,000	192.777
Boeing 787-10	254,000	201.849
Airbus A340-200	253,500	181
Ilyushin IL-96-300	250,000	175
Airbus A330-300	242,000	185
Airbus A330-200	242,000	180
Lockheed L-1011-500	231,300	166.92
Boeing 787-8	228,000	172.365
Lockheed L-1011-200	211,400
Ilyushin IL-86	208,000	175
Boeing 767-400ER	204,000	158.758
Airbus A300-600R	192,000	140
Boeing 767-300ER	187,000	136.08
Concorde	185,000	111.1
Airbus A300-600	163,000	138
Boeing 767-300	159,000	136.078
Airbus A310-300	157,000	124
Vickers VC10	152,000	151.9
Boeing 707-320B	151,000	97.5
Boeing 707-320C	151,000	112.1
Douglas DC-8-61	147,000
Airbus A310-200	142,000	123
Airbus A400M	141,000	122
Douglas DC-8-32	140,000
Douglas DC-8-51	125,000
Boeing 757-300	124,000	101.6
Boeing 707-120B	117,000	86.3
Boeing 757-200	116,000	89.9
Boeing 720B	106,000	79.5
Boeing 720	104,000	79.5
Tupolev Tu-154M	104,000	80
Tupolev Tu-204SM	104,000	87.5
Convair 880	87,500
Boeing 737-900	85,000	66.36
Boeing 737-900ER	85,000	71.35
Boeing 727-200 Advanced	84,000	70.1
Airbus A321-100	83,000	77.8
Boeing 737-800	79,000	65.32
Boeing 727-200	78,000	68.1
McDonnell-Douglas MD-83	73,000	63.28
Boeing 727-100	72,500	62.4
Boeing 727-100C	72,500	62.4
McDonnell-Douglas MD-90-30	71,000	64.41
de Havilland Comet 4	70,700
Boeing 737-700	70,000	58.06
Airbus A320-100	68,000	66
Boeing 737-400	68,000	54.9
de Havilland Comet 3	68,000
Boeing 377	67,000
Boeing 737-600	66,000	54.66
Airbus A220-300	65,000	57.61
Hawker Siddeley Trident 2E	65,000
Airbus A319	64,000	62.5
Boeing 737-300	63,000	51.7
Boeing 737-500	60,000	49.9
Airbus A220-100	59,000	50.80
Airbus A318	59,000	57.5
Boeing 717-200HGW	55,000	47.174
Douglas DC-7	55,000
de Havilland Comet 2	54,000
Boeing 717-200BGW	50,000	46.265
de Havilland Comet 1	50,000
Douglas DC-6A	48,600
Douglas DC-6B	48,500
Embraer 190	48,000	43
Caravelle III	46,000
Fokker 100	46,000	39.95
Douglas DC-6	44,000
Avro RJ-85	42,000	36.74
Handley Page Hermes	39,000
Embraer 175	37,500	32.8
Bombardier CRJ900	36,500	33.345
Embraer 170	36,000	32.8
Bombardier CRJ700	33,000	30.39
Douglas DC-4	33,000
Vickers Viscount 800	30,400
Bombardier Q400	28,000	28.01
Bombardier CRJ200	23,000	21.319
ATR 72-600	22,800	22.35
Saab 2000	22,800	21.5
Embraer ERJ 145	22,000	19.3
ATR 42-500	18,600	18.3
Saab 340	13,150	12.930
Embraer 120 Brasilia	11,500	11.25
BAe Jetstream 41	10,890	10.570
Learjet 75	9,752	8.709
Pilatus PC-24	8,300	7.665
Embraer Phenom 300	8,150	7.65
Beechcraft 1900D	7,765	7.605
Cessna Citation CJ4	7,761	7.103
de Havilland Hercules	7,000
Embraer Phenom 100	4,800	4.43

Maximum taxi weight (MTW)

The maximum taxi weight (MTW) (also known as the Maximum Ramp Weight (MRW) is the maximum weight authorized for maneuvering (taxiing or towing) an aircraft on the ground as limited by aircraft strength and airworthiness requirements. It includes the weight of taxi and run-up fuel for the engines and the APU (Auxillary Power Unit).

It is greater than the maximum takeoff weight due to the fuel that will be burned during the taxi and runup operations.

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 takeoff weight (MTOW)

The maximum takeoff weight (also known as the maximum brake-release weight) is the maximum weight authorised 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 energy, obstacle clearances, and/or en route and landing weight requirements.

Maximum landing weight (MLW)

The maximum weight authorised for normal landing of an aircraft.The MLW must not exceed the MTOW.

The operation landing weight may be limited to a weight lower than the Maximum Landing Weight by the most restrictive of the following requirements:

• Aircraft performance requirements for a given altitude and temperature:landing field length requirements,approach and landing climb requirements

• Noise requirements

If the flight has been of short duration, fuel may have to be jettisoned to reduce the landing weight.

Overweight landings require a structural inspection or evaluation of the touch-down loads before the next aircraft operation.

Maximum zero-fuel weight (MZFW)

The maximum permissible weight of the aircraft less all usable fuel and other specified usable agents (engine injection fluid, and other consumable propulsion agents). It is the maximum weight permitted before usable fuel and other specified usable fluids are loaded in specified sections of the airplane.

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

Ground speed

Ground speed is the horizontal speed of an aircraft relative to the ground. An aircraft heading vertically would have a ground speed of zero.

Ground speed can be determined by the vector sum of the aircraft's true airspeed and the current wind speed and direction; a headwind subtracts from the ground speed, while a tailwind adds to it. Winds at other angles to the heading will have components of either headwind or tailwind as well as a crosswind component.

Wind Speed

For a reference point picked on the ground, the air moves relative to the reference point at the wind speed. A positive velocity is defined to be in the direction of the aircraft's motion. We are neglecting cross winds, which occur perpendicular to the flight path but parallel to the ground, and updrafts and downdrafts, which occur perpendicular to the ground.

Airspeed

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

The aircraft usually operates on land as well as in air and so we need to study their speed differences in-ground and in air

The ground speed and the airspeed usually change based on the wind component. If we consider that there is no wind component then, ground speed = airspeed

If the wind is blowing in the tail direction of the aircraft then, (airspeed > ground speed) so, airspeed = ground speed+ wind component.

If the wind is blowing in the head direction of the aircraft then, (airspeed < ground speed)so, airspeed ground speed

- wind component.

Also, gravity plays a major role in increasing the aircraft's speed while it is descending.

Here wind speed is the vector difference between ground and airspeed. On a particular day, the wind speed may be zero and it is equal to the ground speed.

If the measured airspeed is greater than the observed ground speed the wind speed becomes positive.

For Visualizations purpose by NASA:

https://www.grc.nasa.gov/www/k-12/airplane/Animation/airrel/anrelg.html

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

Aircraft can move using their own engine power all the time on the airport apron and taxiways under their own power to go towards runways and after landing taxi to their assigned gate. But the thrust produced resulting jet blast 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. And also it can reduce the cost for fuel. Taxiing can save money.

Effectively a loss of control can happen, especially during high power engine running. Damage can occur to the aircraft itself, other aircraft nearby or to airsidestructures.

There is a risk of injury to ground support personnel who may be in relatively close proximity to the aircraft.

It is easier for truck driver to see the surroundings better than the pilot sitting in the cockpit with limited window. The pushback driver knows the airport better than the pilot.

It also saves fuel virgin Atlantic had proposed a new system in which pushback truck will move the aircraft all the way to runway to save fuel and reduce impact of environment.

The plane engines are very loud. When more than one plane will add up their sound, than it will not be pleasant for passengers and others near airport.

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

Taxiing is the movement of an aircraft on the ground, under its own power, in contrast to towing or push-back where the aircraft is moved by a tug. The aircraft usually moves on wheels, but the term also includes aircraft with skis or floats. An airplane uses taxiways to taxi from one place on an airport to another; for example, when moving from a hangar to the runway.

Towing:

Movement of large aircraft about the airport, flight line, and hangar is usually accomplished by towing with a tow tractor. In the case of small aircraft, some moving is accomplished by hand pushing on the correct areas of the aircraft. Aircraft may also be taxied about the flight line but usually only by certain qualified personnel.

Towing aircraft can be a hazardous operation, causing damage to the aircraft and injury to personnel, if done recklessly or carelessly. This article outline the general procedure for towing aircraft. However, specific instructions for each model of aircraft are detailed in the manufacturer's maintenance instructions and are to be followed in all instances.

STUDY#5. Learn about takeoff power, tire design, rolling resistance, tire pressure, brake forces when landing. Take off power:

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

The forces involved will be.

T is Thrust of propulsion system pushing aircraft along the runway.

D is Aerodynamic Drag of vehicle resisting the aircraft motion.

F is Rolling resistance friction due to the contact of wheels or skids on the ground.

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

m*(dv/dt) =T-D-F

where, dv/dt is the acceleration along the runway and m is the mass of the vehicle. The procedure for take-off will be that the vehicle will accelerate until it reaches a safe initial flying speed. The pilot can then rotate the vehicle to an attitude to produce a climb lift and it will ascend from the ground. The determination of this safe flying speed or rotation speed. V, is a critical factor in determining take-off performance. Take-off rules vary slightly depending on the aircraft category.

For Small commuter aircraft

V= 1.1*VSTALL ()

V=1.05*V Control

`V_{STALL}-=sqrt (W/(0.5 C_{lmax} rhoS)`

where S-Runway length

Take Off power = force*displacement

`(m*{dv}/dt)*2*S_1 Rightarrow (T-D-F).S_1`

Tire Design:

Designing aircraft tires is a very intense undertaking The tire is designed to withstand 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 aero plane needs to be distributed more evenly. Aircraft tire generates more heat during landing Aircraft drags the wheel until they match the rotational velocity of wheels. Due to this heat generates. Aircraft's tread pattern is designed to facilitate stability in high crosswind conditions, to channel water away to prevent hydroplaning and for braking effect.

Construction of tire:

Radial Tire:

It has fiber strands of the ply fabric oriented at 90° to the direction of rotation and the tire sidewall. This restricts flexibility bidirectional and the flexibility of the sidewall while it strengthens the tire to carry heavy loads. Due to their unique construction most, radial tires are resistant to penetration ad cuts. Due to stiffer tread, they distribute weight evenly. Thus, provide greater traction. Radial tire s has an advantage in term of reducing the heat better.

Bias-ply Tire:

It has the fabric bias oriented with and across the direction of rotation and the sidewall. Since fabric can stretch on the bias, the tire is flexible and can absorb loads. Tire strength is obtained by adding plies. It is cut resistant is sidewall area. These tire s do not offer as much smoothness in terms of riding quality.

Rolling Resistance:

Rolling resistance is the force resisting the motion when a body (such as ball, tire or wheel) rolls on a surface. Rolling resistance can be seen in the aircraft when the aircraft takes-off from the runway & while landing at the runway with the help of their wheels.

Rolling resistance can be expressed as

Where

F_rr is the Rolli resistance(N)

μ_rr is coefficient of rolling resistance. m is mass (kg)

g is acceleration due to gravity =`9.81m/s^2`

Tire pressure:

Aircraft tire s 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. 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.

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.

Also, the use of an inert gas for tire inflation eliminates the possibility of tire explosion.

Relation to Rolling Resistance and Tire Pressure:

Braking Forces During Landing:
Rolling resistance and Tire pressure are inversly proportional.

Following braking devices are used to decelerate the aircraft -

2. Wheel Brakes (Including Anti-Skid systems & Auto-Brake systems).
3. Reverse Thrust

Spoilers:

The mechanical deflection of parts of the wing upper surface by increasing aerodynamic drag on the moving aircraft. This can be achieved by raising upper wing surface panels called ground spoilers or by operation of a tail cone 'clamshell' type air brake and also by increasing the effective downward load on the landing gear and thereby increasing the efficiency of wheel braking

Wheel Brakes:

To be effective, braking action at any speed depends upon sufficient friction existing between the tires and the runway surface achieved through freely rotating wheels.

Anti skid system:

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.

Reverse Thrust:
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.

Thrust reversers provide a deceleration force that is independent of runway condition. Thrust reverser efficiency is higher at high airspeed therefore. Treversers must be selected as early as possible after touchdown.

Thrust reversers should be returned after reverse idle at low airspeed to prevent engine stall or foreign object damage.

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

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

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

Considering:

Total mass of ther aircraft (including payload) for airbus a380 = 575,000kg. Mass of the push back: 1000kg (assumed)

Rolling Resistance (Frr):

Coefficient of rolling resistance (Crr) = 0.002 (on tarmac)

Rolling resistance force is given by

`F_{rr} = C_{rr}*m*g`

For the aircraft:

`F_{rr} = 0.002*575000*9.81 Rightarrow F_{rr} = 11281.5N RightarrowF_{rr} = 11.2815kN`

For the Towing Vehicle :

`F_{rrt} =0.002*1000*9.81 Rightarrow F_{rrt}=19.62 N`

As the towing vehicle resistance is so less compared to the Aircraft because this is a heavy aircraft these can be neglected

Aerodynamic resistance (Far):

Drag coefficient (Cd): 0.025 Air Density (ρ) = `1.125kg/m^3` Frontal Area (A): `150m^2.`

Velocity (v) = `14.5kmph or 4m/s`

`F_{ar}=1/2*C_d*rho*A*v^2`

`F_{ar}=1/2*0.025*1.125*150*4^2 Rightarrow 33.75 N`

As the vehicle and Plane is moving at very low speed Aerodynamic resistance can be neglected

Hill Climb Resistance:

Runways are constructed flat so Gradient resistance/ hill climb force is neglected.

Total Resistance:

`F_{t} = 11.2815 Kn`

Power Required:

`P = Ft ⋅ v ⇒ P = 11.2815 ⋅ 4 ⇒ 45.26kW`

The min power required by the tow vehicle is 45.26kW to taxi a heavy air craft at 4m/s.

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

• constant blocks are used to feed the parameters such as mass, coefficients and other parameters using product block the resistive forces are calculated.
• Using sum block, total resistive forces can be calculated. the outputs are visualised using display blocks.

#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.

1. Also, Design the parameters in excel sheet.
2. 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.

Estimation of Duty Cycle:

Based on the calculation done in study 6

The Power Required for towing of the aircraft is 45.26kW. Motor Considred for the drive train is REB 90

Technical Data:

Type	Voltage	Continuous / Peak power	Working	Max	Weight	Cooling
			rotation	torque

REB	400–800 V	60–70 kW / 80 kW	1 500–4 000	300 Nm	22 000 g	Air /	Hybrid	(air	+
90			rpm			fluid)

Considering 60kW as continuous power, so the voltage will be 400V Battery power is considred to be 550v

Duty cycle is given by `(Vo)/(Vb)`

where Vo is motor required voltage Vb is battery voltage.

`d=400/550Rightarrow0.7272`

As there will be losses due to the resistance of FET and Inductance. Correction factor is considred to be 90%

As there is 10% loss, the voltafge demanded by the motor should be 10% more than required

so the voltage demand should be around 440V from the battery.

Assumed Parameters
Mass of aircraft	575000	kg
Mass of the push back truck	1000	kg
Coefficient of Rolling Resistance	0.002
Drag Coefficient	0.025
Air density	1.125	kg/m^3
Frontal Area	150	m^2
Velocity	4	m/s
Uphill gradient	0	deg
Battery Voltage	550	V
Correction Factor	0.8

Block Diagram:

Simulink Model:

Input:

Output:

From the motor:

From the Battery: