Project-1: Powertrain for aircraft in runways
1.
The "aircraft gross weight"(also know as the all-up weight and abbreviated AUW) is the total aircraft weight at any moment during the flight or ground operation.An aircraft's gross weight will decrease during a flight due to fuel and oil consumption.An aircraft's gross weight may also vary during a flight due to payload dropping or in-flight refuelling.At the moment of releasing its brakes, the gross weight of an aircraft is equal to its takeoff weight. During flight, an aircraft's gross weight is referred to as the en-route weight or in-flight weight.
The following image depicts takeoff weight components:
MTOW-maximum take off weight
MLW-maximum landing weight
| type | MTOW(kg) | MLW(tons) |
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Maximum taxi weight(MTW):
The maximum taxi weight(MTW) also known as the maximum ramp weight is the maximum weight authorized for maneuvering an aircraft on the ground as limited by aircraft strength and aieworthiness 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.
Maximum takeoff weight(MTOW):
The maximum takeoff weight (also known as the maximum brake release weight) is the maximum weight authorised at brake for takeoff, or at the start of the takeoff roll.The maximum takeoff weight is always less than the maximum taxi/ramo weight to allow for fuel burned during taxi by the engines and the APU.
Maximum loading weight:
The maximum weight authorised for normal landing of an aircraft.The MLW must not exceed the MTOW.The operation landung 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.
Maximum zero-fuel weight(MZFW):
The maximum permissible weight of the aircraft less all usable fuel and other specified usable agents (engine injection fuild, and other consumable propulsion agents).it is maximum weight permitted before usable fuel and other specified usable fluids are loaded in specified of the airplane.
2.
There is a difference between ground speed and air speed to understand this we should take in to accound wind speed too.
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.Direction is important.A 20 mph wind from the west is different from a 20 moh wind from the east.The wind has components in all three primary directions.
Ground speed:
For a reference point 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 the ground speed and the wind speed.
Airspeed=ground speed-wind speed
On a perfectly still day, the airspeed is equal to the ground speed. But if the wind is blowing in the same direction that the aircraft is moving, the airspeed will be less than the ground speed.
For example taking wind speed as 20 km/hr and runway is east-west runway the wind blowing towards west and the flight runs at 80 km/hr the wind speed acting in the west and the flight takes off east then the Airspeed=Groundspeed(80)-wind speed(-20)=100 km/hr
If the planes runs towards west along the wind blowing direction then the Airspeed=Groundspeed(80)-wind speed(20)=60 km/hr
HENCE THERE IS A DIFFERENCE BETWEEN GROUND SPEED AND AIR SPEED.
3.
The risks which may arise from engine ground running relate to the potential for loss of control of the aircraft by those persons occupying the pilot seats in the flight deck.Unwanted consequences from such static running are mainly related to those arising from the unintended movement of the aircraft during engine running-effectively a loss of control-especially during high power engine running.Damage can occur to the aircraft itself, other aircraft nearby or to airside structures.In addition, there is a risk of injury to ground support personnel who may be in relatively close proximity to the aircraft.
When modern jet engines are operated at rated thrust levels, the exhaust wake can exceed 375 mi/h immediately after of the engine exhaust nozzle.This exhaust flow field extends aft in a rapidly expanding cone, with portions of the flow field contacting and extending aft along the pavement surface.Exhaust velocity components are attenuated with increasing distance from the engine exhaust nozzle.However, an airflow of 300 mi/h can still be present at the empennage, and significant people and equipment hazards will persist hundreds of feet beyond this area.At full power, the exhaust wake speed can typically be 150 mi/h at 200 ft beyond the airplane and 50 to 100 mi/h well beyond this point.
The extensive noise arises from the engine power also dangerous for humans and other living things around the vicinity.Hence for the above reasons it is not recommended to use engine power to move on the ground.
4.
In aviation, pushback is an airport procedure during which an aircrafts pushed backwards away from an airport gate by external power .Pushbacks are carried out by special,low-profile vehicles called pushback tractors or tugs.
Although many aircraft are capable of moving themselves backwards on the ground using reverese thrust (a procedure referred to as a powerback),the resulting jetblast or propwash might cause damage to the terminal building or equipment. Engines close to the ground may also blow sand and debris forward and then suck them into the engine,causing damage to the engine. A push back is therefore the perferred method to move the aircraft away from the gate.
Pushbacks at busy aerodromes are usually subject to ground control clearance to facilitate ground movement on taxiways.Once clearance is obtained,the pilot will communiocate with the tractor driver to start the pushback.To communicate, a headset may be connected near the nose gear.
Since the pilots cannot see what is behind the aircarft, steering is done by the pushback tractor driver and not by the pilots.Depending on the aircraft type and airline procedure,a bypass pin may be temporarily installed into the nose gear to disconnect it from the aircraft's normal steering mechanism.
Once the pushback is completed, the towbar is disconnected, and any bypass pin removed.The ground handler will show the bypass pin to the pilots to make it clear that it has been removed.The pushback is then complete, and the aircraft can taxi forward under its own power.
5.
Take-off power:
For light aircraft, usually full power is used during takeoff.Large transport category(airliner) aircraft may use a reduced power for takeoff, where less than full power is applied in order to prolong engine life, reduce maintenance costs and reduce noise emissions.In some emergency cases, the power used can then be increased to increase the aircraft's performance.Before takeoff, the engines, particularly piston engines, are routinely run up at high power to check for engine related problems.The aircraft is permitted to accelerate to rotation speed.The term rotation is used because the aircraft pivots around the axis of its main landing gear while still on the ground, usually because of gentle manipulation of the flight controls to make or facilitate this cahnge in aircraft attitude.
The nose is raised to a nominal 5 degrees to 15 degrees nose up pitch attitude to increase lift from the wings and effect liftoff.For most aircraft, attempting a takeoff without a pitch-up would require cruise speeds while still on the runway.
Tyre design:
Based on the type of piles used the tyres can be:
Radial ply tires: These tyres feature a flexible casing which is constructed of rubber-coated ply cards which extend around the beads and are substantially at 90 degrees to the centerline of the tread.The casing is stabilized by an essentially inextensible circumferential belt.
Bias ply tires: These tyres featurea casing which is constructed of alternate layers of rubber-coated ply cords which is extend around the beads and are at alternate angles substantially less than 90 degrees to the center line of the tread
Rolling resistance:
The resistance offered by the tyres against motion of vehicle/aircraft is called as rolling resistance is produced during take off/landing in the runway.
Tyre pressure:
Aircraft tires are usually inflated with nitroge 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, but common compressed air sources ma contain moisture, which increases the expansion rate with temperature.
Brakes forces when landing:
In general, when the wheels touch the ground, a set of spoilers raise up quickly, which kills the lift provided by the wings.while the spoilers provide some drag, their primary ourpose is to stop the plane from actually flying, putting all of the weight on the landing gear and in turn making the brakes that much more effective.Aircraft have highly engineered, multi disc brakes made of a carbon steel material.Manufacturers include honeywall and goodrich, part of collins aerospace.In general, the brakes are composed of discs that rotate with the wheel and seperate discs that are fixed.
6.
The rolling resistance for the air plane can be calculated as
Fr=C*Mr*Ag
where
Fr=rolling resistance(N)
C=rolling resistance coefiicient
Mr=rolling mass(kg)
Ag=acceleration of gravity(9.81 m/s^2)
If the mass of a plane is 40000 kg and the rolling resistance coefficient between aircraft wheel and the runway is 0.02
The force required to overcome the rolling resistance can be calculated as
Fr=0.02*(40000)*(9.81)
=7848 N
The friction for the puller can be calculated tp
Ff=u*W
=u*Mf*Ag
where,
Ff=frictional force(N)
u=friction coefficient
w=weight(N)
Mf=friction mass(kg)
The friction coefficient between a pulling truck rubber wheels and dry runway is 0.9. since pulling trucks are connected to aircrafts bose wheels close to runway we simplify the calculationof required truck mass
Mf=(7848)/(0.9*9.81)
=889 kg
Taking radius of the wheel R is 0.3m
The torque is given by T=F*R
T=2354 N.m
The power for pulling/push the aircraft can be calculated as
P=F*V
V=velocity of pull vehicle taken as 5 km/hr
V=1.388 m/s
P=7848*1.388
=10893 watts
P=10.89 kw
7.
Taking the previous example power value 10 kw for this problem
Power=10 kw
The motor power should be greater than or equal to 10 kw assuming it as 10 kw
The energy required can be calculated as E=P*t
assuming taxi time of 5 mins
E=10*(5*60)Kj
= 3000lj
From power equation:
Vo*Io=n*Vi*Ii
where,
Vo= output voltage
Io=output current
n=power effciency
Vi=input voltage
Ii=input current
consider DC input voltage as 48v and power as 12kw
P=Vi*Ii
12000=48*Ii
Ii=250 A
the efficiency is calculated as
n=10000/12000
n(efficiency)=0.83
From the above power equation
Vo*Io=n*Vi*Ii
Vo*250=0.83*48*250
Vo=40v
The Vout=Vin/(1-D)
40=48/(1-D)
D=0.2 the duty cycle has in the range of (0,0.2)
Block diagram of power train: