Project-1: Powertrain for aircraft in runways

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

The different terms represent different weights or masses. For each flight, the weights are taken into account for several reasons.

A brief description of these is below:

Design weight limits (Structural design weights):

An aircraft's gross weight is limited by several weight restrictions to avoid overloading its structure or to avoid unacceptable performance or handling qualities while in operation.

Aircraft gross weight limits are established during an aircraft's design and certification period and are laid down in the aircraft's type certificate and manufacturer specification documents.

The absolute maximum weight capabilities of a given aircraft are referred to as the structural weight limits. The structural weight limits are based on aircraft maximum structural capability and define the envelope for the CG charts (both maximum weight and CG limits).

An aircraft's structural weight capability is typically a function of when the aircraft was manufactured, and in some cases, old aircraft can have their structural weight capability increased by structural modifications.

Maximum design taxi weight(MDTW):

The maximum design taxi weight (also known as the maximum design ramp weight (MDRW)) is the maximum weight certification for aircraft maneuvering on the ground (taxiing or towing) as limited by aircraft strength and airworthiness requirements.

Maximum design take-off weight(MDTOW):

Is the maximum certificated design weight when the brakes are released for takeoff and are the greatest weight for which compliance with the relevant structural and engineering requirements has been demonstrated by the manufacturer.

Maximum design Landing weight(MDLW):

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

The MDLW must not exceed the MDTOW.

The maximum landing weight is typically designed for 10 feet per second (600 feet per minute) sink rate at touch down with no structural damage.

Maximum design zero-fuel weight(MDZFW):

The maximum certificated design 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. The MDZFW is limited by strength and airworthiness requirements. At this weight, the subsequent addition of fuel will not result in the aircraft design strength being exceeded. The weight difference between the MDTOW and the MDZFW may be utilized only for the addition of fuel.

Minimum flight weight(MFW):

Minimum certificated weight for flight as limited by aircraft strength and airworthiness requirements

Authorized Weight limits (AWL):

Aircraft authorized gross weight limits (also referred to as certified weight limits) are laid down in the aircraft flight manuals(AFM) and/or associated certificate of airworthiness (C of A). The authorized or permitted limits may be equal to or lower than the structural design weight limits.

The authorized weight limits that can legally be used by an operator or airline are those listed in the AFM and the weight and balance manual.

The authorized (or certified) weight limits are chosen by the customer/airline and they are referred to as the "purchased weights". An operator may purchase a certified weight below the maximum design weights because many of the airport operating fees are based on the aircraft AFM maximum allowable weight values. An aircraft purchase price is, typically, a function of the certified weight purchased.

Maximum weights established, for each aircraft, by design and certification must not be exceeded during aircraft operation (ramp or taxying, takeoff, en-route flight, approach, and landing) and during aircraft loading (zero fuel conditions, the center of gravity position, and weight distribution).

Weights could be restricted on some type of aircraft depending on the aircraft handling requirements; for example, aerobatic aircraft, where certain aerobatic maneuvers can only be executed with a limited gross weight.

Also, the authorized maximum weight limits may be less as limited by the center of gravity, fuel density, and fuel loading limits.

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.

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 authorized at brake release for takeoff or 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 authorized for the 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.

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

One of the most confusing concepts is the relative velocity between objects. Aerodynamic forces are generated by an object moving through a fluid (liquid or gas). A fixed object in a static fluid does not generate aerodynamic forces. Hot air balloons "lift" because of buoyancy forces and some aircraft like the Harrier use thrust to "lift" the vehicle, but these are not examples of aerodynamic lift. To generate lift, an object must move through the air, or air must move past the object. Aerodynamic lift depends on the square of the velocity between the object and the air. Now things get confusing because not only can the object be moved through the air, but the air itself can move. To properly define the relative velocity, it is necessary to pick a fixed reference point and measure velocities relative to the fixed point. The reference point is fixed to the ground, but it could just as easily be fixed to the aircraft itself. It is important to understand the relationships of wind speed to ground speed and airspeed.

Wind Speed

For a reference point picked on the ground, the air moves relative to the reference point at the wind speed. Notice that the wind speed is a vector quantity and has both a magnitude and a direction. The 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). We are considering only velocities along the aircraft's flight path. Positive velocity is defined to be in the direction of the aircraft's motion. We are neglecting crosswinds, which occur perpendicular to the flight path but parallel to the ground, and updrafts and downdrafts, which occur perpendicular to the ground.

Ground Speed

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 so a comparison of the ground speed to the wind speed must be done according to rules for vector comparisons.

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

The risks which may arise from engine ground running relate to the potential for loss of control of the aircraft by those persons occupying the pilot seats in the flight deck. In most cases, such persons will be maintenance personnel holding specific company-issued approval for the required tasks. The consequences of loss of control during taxi or towing are the same as apply to these operations generally and this article is concerned only with the risks arising from the static running of one or more aircraft engines. Unwanted consequences from such static running are mainly related to those arising from the unintended movement of the aircraft during engine running - effectively a loss of control - especially during high power engine running. Damage can occur to the aircraft itself, other aircraft nearby, or airside structures. Also, there is a risk of injury to ground support personnel who may be in relatively proximity to the aircraft.

The aircraft usually does not use its engine powered to reach the runway from the airport terminal. This happens because, when the aircraft engine power is used the propeller blades starts rotating and it eventually pulls the dust and other particles on the ground into the propeller and it can damage the propeller blades. Also, there are other reasons like the propeller will cause a lot of wind disturbances around the aircraft which will be a problem for the nearby buildings and other aircrafts settled nearby. So to avoid all these things towing tractors are introduced for getting the job done.

4. How an aircraft is pushed to the runway when it's ready to take off?

Taxiing is the movement of the aircraft on the ground, under its 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.

The aircraft always moves on the ground following the yellow lines, to avoid any collision with the surrounding buildings, vehicles, or other aircraft. The taxiing motion has a speed limit. Before making a turn, the pilot reduces the speed further to prevent tire skids. Just like cars, there is a certain list of priorities during taxiing. The aircraft that are landing or taking off have higher priority. The other aircraft have to wait for these aircraft before they start or continue taxiing.

The thrust to propel the aircraft forward comes from its propellers or jet engines. Steering is achieved by turning a nose wheel or tail wheel/rudder; the pilot controlling the direction traveled with their feet. The use of engine thrust near terminals is restricted due to the possibility of jet blast damage. This is why the aircraft is pushed back from the buildings by a vehicle before they can start their engines for taxiing.

Takeoff is the phase of flight in which an aircraft goes through a transition from moving along the ground (taxiing) to flying in the air, usually starting on a runway. Usually, the engines are run at full power during takeoff. Following the taxi motion, the aircraft stops at the starting line of the runway. Before takeoff, the engines, particularly piston engines, are routinely run up at high power to check for engine-related problems. This makes considerable noise. When the pilot releases the brakes, the aircraft starts accelerating rapidly until the necessary speed for take-off is achieved.

The takeoff speed required varies with air density, aircraft weight, and aircraft configuration (flap and/or slat position, as applicable). Air density is affected by factors such as field elevation and air temperature.

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

Takeoff performance:

Take off performance 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 – Thrust of propulsion system pushing aircraft along the runway.

D – Aerodynamic Drag of vehicle resisting the aircraft motion.

F – 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.

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

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 climb lift and it will ascend from the ground. The determination of this safe flying speed or rotation speed, V_R, is a critical factor in determining take-off performance.

Take-off rules vary slightly depending on the aircraft category. Small commuter aircraft should be considered as meeting FAR 23 rules, transport category aircraft should comply with FAR 25 rules.

Small commuter aircraft :

For safety reasons, V_R is usually determined as being 1.1 × V_STALL or 1.05 × V_{MIN CONTROL}

whichever is greater. Stall speed, V_STALL, is the lowest speed that the aircraft can be flown before the airflow starts to separate from wings as the angle of attack becomes too great. The wing is assumed in this case to be in take-off configuration or "clean".

It can be calculated based on knowledge of the aircraft take-off configuration and hence the maximum achievable lift coefficient C_L(max). As shown in the previous section, to maintain level flight the lift produced must equal the weight, hence the stall speed can be calculated as,

`V_(stall)= (W/((1/2 )CL(max)ρS))^0.5`

Minimum control speed, V_MC is a more complex calculation and requires knowledge of the stall characteristics of the tailplane and elevator. For conventional aircraft, there is only a small difference between V_R calculations based on stall speed or minimum control speed.

V₁- Abort decision speed. Below this speed, the take-off can be safely aborted. After this, there will not be sufficient runway length to allow the aircraft to decelerate to a stop.V₂ – Safe climb speed. V₂ must be no less than 1.2 * V_stall. Below this speed aircraft cannot attain sufficient climb rate.

Tire design:

Carcass plies are used to form the tire. They are sometimes called casing plies. An aircraft tire 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 tire, it does not have to carry a load for a long period of continuous operation. However, an aircraft tire absorbs the high impact loads of landing, and also it’s operating at high speeds for a short time when required.

some technical aspects of the tire.

Retreading – Retreading is methods of restoring a worn tire by renewing the tread area or by renewing the tread area plus one or both sidewalls. Repairs are included in the tire 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 tire. It is an index of tire strength.

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

Skid Depth – Skid depth is the distance between the tread surface and the deepest groove as measured in the mold.

Aircraft tires must have an approved speed and load rating and have sufficient clearance when retracted through landing gear to allow for tire growth. Tire growth is the increase in the size of the tire due to centrifugal forces at high speed.

• Tubeless tires are more advantageous over tube-type. There is no longer the use of tube-type tire in recent aviation. Nowadays all airliners are using tubeless tires. Tubeless that are meant to be used without a tube has the word TUBELESS on the sidewall of the tire.
• Almost all airliners are using a Radial tire. Bias is an older design, and it’s mainly used for road vehicles. Radial tires have the word RADIAL on the sidewall. Radial tires are more expensive than bias-ply tires. Radial tires are in demand because of their lower life cycle cost and long term value.
• Yes, Today’s tires are conductive. Aircraft tires are manufactured with tread rubber with conducting compounds to permit earthing of static charges.
• In the early days when tires 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 are also called deflectors. Chine tire 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 molded into the sidewall of nose tires that deflect water sideways to help reduce excess water ingestion into the engines. Tires may have chines on one or both sides, depending on the number of nose tires on the aircraft.
• Each tire manufacturer produces their own designs of the tire with different tread patterns, wear patterns, wear limits, etc, and in some cases, different names for the same part of the tire. But all tires must meet the approved standards before being accepted by the FAA or CAA.

All commercial aircraft tires 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.

Rolling resistance:

Rolling ResistanceRolling resistance sometimes called rolling friction or rolling drag, is the force resisting the motion when a body rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy needed for deformation (or movement) of the wheel, roadbed, etc., is recovered when the pressure is removed. The "rolling resistance coefficient" is defined by the following equation:

`F=C_(rr)*N`

where,

F is the rolling resistance force

C_rr is the dimensionless rolling resistance coefficient or the coefficient of rolling friction (CRF), and

N is the normal force, the force perpendicular to the surface on which the wheel is rolling.

C_rr is the force needed to push (or tow) a wheeled vehicle forward (at a constant speed on a level surface, or zero grade, with zero air resistance) per unit force of weight. It is assumed that all wheels are the same and bear the identical weight

Tire pressure:

An aircraft tire 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.

brake forces when landing:

The three primary methods of achieving deceleration on the runway during the landing roll or a rejected take_off are engine power, brakes, and mechanical spoilers. Effective and coordinated use of whichever of these are available will result in a stopping distance appropriate to the available runway ahead, or the desired runway exit point if sooner. The key to success is the properly coordinated use of all the available methods.

engine power:

The most important action to achieve deceleration from a speed at which the engines are still producing forward motion is to select all thrust/power levers to the ground idle position promptly, and if available, continue the action through to the selection of reverse thrust. This is the first action to begin deceleration and must especially be achieved without delay when a high speed rejected take-off is initiated. Thrust reversers and reverse propeller pitch are most effective at high speeds. The selection at these relatively high speeds must be symmetrical because otherwise, directional control may be prejudiced. Once the aircraft groundspeed has reduced sufficiently, thrust/power levers should be returned to the ground idle position to prevent the ingestion of any FOD which could be present, with reversers stowed once at taxi speed.

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.

Fundamental to this are:

• Achieving the maximum possible weight on braked landing gear assemblies

• The condition of the tire tread

• The tire inflation pressure

• The condition of the runway surface

Braking effectiveness will also be affected by the degree of brake wear, which must be within AMM specified limits and the manually or automatically applied brake pressure as modified by system protections. These ensure adequate wheel rotation exists and is maintained before the commanded brake pressure is transmitted to the brake units and takes effect. When brake temperature indication is available on the flight deck, it must be within prescribed limits before a take-off roll is commenced so that effective braking is available if a take-off is rejected. System faults or inappropriate use of brakes during a long taxi out can raise brake temperatures into cautionary ranges where a delay for take-off may be required.

Mechanical spoilers:

The mechanical deflection of parts of the wing upper surfaces and tail cone assembly can assist deceleration in two ways:

• Directly, 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. Both systems can also be used in the air on some aircraft types as in-flight air brakes, but the extent of their operation may be less in the airborne case than in the ground (weight on wheels) case. Extreme care may be needed if it is permissible for a particular aircraft type to carry out a rejected landing after initial touchdown since not all ground settings of deployed spoilers and air brakes necessarily auto retract to the settings needed for a safe initial climb away.

• Indirectly by increasing the effective downward load on the landing gear and thereby increasing the efficiency of wheel braking.

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

The force to move an airplane on an absolute flat runway with no wind at constant low speed is equal to the rolling resistance between the plane and the tarmac.

The rolling resistance for the airplane can be calculated as :

`Fr = c* mr *ag`

where,

Fr = rolling resistance force

c = rolling resistance coefficient

mr = rolling mass

ag = acceleration of gravity (9.81 m/s2)

The friction force for the puller can be calculated to

`Ff = μ *W = μ *mf *ag`

where

Ff = frictional force

μ = friction coefficient

W = weight

mf = friction mass

The drag force acting on the tow will be:

The drag force D exerted on a body traveling through a fluid is given by drag force equation,

`1/2 *C*p*A*V^2`

where,

C is the drag coefficient, which can vary along with the speed of the body. But typical values range from 0.4 to 1.0 for different fluids (such as air and water)

ρ is the density of the fluid through which the body is moving

v is the speed of the body relative to the fluid

Now the tractive force or the pulling force required by the tow will be

Pulling force = Drag force + friction force + Rolling resistance force

Now let us consider aircraft with the following specifications:

Now as we have seen that various kinds of planes have different weights, the amount of pulling force also will be different. Therefore we will consider a range of weight:

The towing speed considered is 5 m/s

friction mass = 889 Kg

Area range: 50 - 100 m^2

Coefficient of rolling resistance: 0.02

Coefficient of friction: 0.01

drag coefficient=0.8

air density = 1.2754 kg/m³

Rolling mass = 40000( aircraft)

Rolling resistance force =Fr= 0.02*40000*9.81= 7848 N --------(1)

Frictional force =0.01*889*9.81 = 87.21 N ----------------(2)

Drag force = 0.5*0.8*1.2754*25*60=765.24 N ------------------(3)

The total pulling force =(1)+(2)+(3)

=8700.45 N

Power = force * velocity

=8700.45*5

= 43.502 Kw.

7. Design an electric powertrain with the type of motor, it’s power rating, and energy requirement to fulfill aircraft towing application. Estimate the duty cycle range to control the aircraft speed from zero to highest. Make all required assumptions. Prepare a table of assumed parameters. Draw a block diagram of the powertrain.

Assumed parameters

S.No.	Assumed parameters	values
1.	weight of aircraft	575000 kg
2.	weight of towing tractor	50000 kg
3.	rolling resistance coefficient of aircraft	0.004
4.	rolling resistance coefficient of towing a tower	0.001
5.	The velocity of aircraft while towing	8.33 m/s
6.	The density of Air medium	1.225 kg/m^3
7.	The frontal area of aircraft	20 m^2
8.	The drag coefficient of aircraft	0.026
9.	Towing tractor gear ratio "G"	11
10.	Towing tractor tire radius "r"	0.635 m
11.	operational time o towing for one cycle	0.33 hour
12.	battery armature voltage	350 V
13.	The battery armature current	350 A
14.	Motor terminal voltage	630V @motor terminals
15.	power converter used	bidirectional DC-DC boost converter
16.	Maximum duty ratio	70%

Assuming the operational time of the towing truck is around 20 minutes for one cycle.

20 minutes = 0.33 hour

energy =power * time =126.8* 0.33

energy= 41.8 KWh

Therefore the battery must be able to store 41.8 kWh and should be able to deliver this energy throughout the run time in order for the motor to produce the 13.2KNm of torque instantaneously.

Motor selection:

Here we have selected a brushless Dc motor type that has a power rating of 126.8 KW and with the gear ratio and the transmission, it should be able to deliver 1.32KN-m of torque instantaneously.

The battery armature voltage = 350 V

The battery armature current = 350 A

Power converters:

Here we use a DC-DC boost converter to upscale the voltage level from the battery to the required level so that when supplied to the motor we can get the desired power output from the motor. The bidirectional DC-DC converters find applications in places where battery charging, regenerative braking, and backup power are required. As a backup power system, the bidirectional DC-DC converter facilitates the safe operation of the vehicle when ICEs or electric drives fail to drive the motor. The boost converter converts the 350V of the armature voltage to a high voltage level of 900 V.

speed control:

The amount of power can be controlled by changing the duty cycle value. Here duty cycle value is 70%.

Motor terminal voltage = Armature voltage * Duty cycle = 900*0.7

With a 70% duty cycle, the voltage at motor terminal is 630V.

Thus by sharing the duty cycle the speed of the vehicle can be controlled.

Block diagram: