Project-1: Powertrain for aircraft in runways
ANS 1
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.
AIRCRAFT TOTAL WEIGHT ( TAKE-OFF WEIGHT)
* Average sized airplane. 80,000 kg
eg. Boeing 737-800
* Fighter jet 113,646 kg
eg. Boeing F-18 Hornet
* Cargo airplanes 165,900 kg
eg. Airbus A300 600F
* Military Helicopter 7,791 kg
eg. Boeing RAH-66 Comanche
* Mid-size helicopter 5,080 kg
eg. Bell 212
* Turboprop aircraft 3,994 kg
eg. Grand caravan EX
ANS 2
Difference between ground speed and air speed:
The importance of the relative velocity explains why, even today, airplanes take off and land on different runways on different days. Airplanes always try to take off and land into the wind. This requires a lower ground speed which means the plane can take off or land in the shortest distance travelled along the ground. Since runways have a fixed length, you want to get airborne as fast as possible on take-off and stopped as soon as possible on landing.
Wind Speed : A reference point picked on the ground, the air moves relative to the reference point at wind speed. The wind speed is a vector quentity and has both magnitude and direction. The wind blowing against the motion of aircraft is called head wind. We have defined a positive velocity to be in direction of aircraft motion, head wind is a negative velocity. When the wind blows in the same direction of aircraft motion it is called Tail wind. The sign of wind is now positive.
Ground speed : The speed on which the aircraft moves relative to the point on the ground.Ground speed is a vector quentity.
Air speed: The relative velocity between the object and the air is called air speed. Airspeed cannot be directly measured from a ground position, but must be computed from ground speed and the wind speed.
Air speed is the vector difference between the ground speed and the wind speed.
AIR SPEED GROUND SPEED
* Speed relative to air speed relative to ground
*measured quentity. using pitot tube calculated quentity ( air speed + wind speed).
ANS 3
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 airpart 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 the 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 of fuel. Taxing can save money. Aircraft engine creates a huge noise around which is not good for surroundings around the airport. It will cause various injuries and damage to the near by population and property if a pilot losses control of the airplane traveling on the ground using engine power.
ANS 4
4. How an aircraft is pushed to runway when its ready to take off?
The term that is used when the aircraft is moved from the hanger to the runway is "TAXIING" which is defined as the movement of an aircraft on the ground, under its own power , in contrast to towing or pushback where the aircraft is moved by tug an airplane uses taxiways to taxi from one place on an airport to another. The term 'taxiing' is used for the accelerating run along a runway prior to take off, or the decelerating run immediately after landing which are called the takeoff roll and landing rollout, respectively.
Pushback is when an aircraft is pushed backwards away from the airport gate by vehicles called tugs or tractors. Closer to departure, an aircraft tug will park right in front of the nose wheel. The tug might be directly attached to the planes nose gear with a tow bar or could be a wheel lift tug.These tugs cradle the gear then lift it up before moving plane. That gives the tug driver control over the planes direction during pushback.
ANS 5
5. Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
Take off power
A normal take-off is one in which the airplane is headed into the wind, or the wind is very light.Also, the take off surface is firm and of sufficient length to permit the airplane to gradully accelerate to normal lift-off and climb-out speed and there are no obstruction along the take off path.
There are four forces which helps the aircraft to take off -
Thrust: It is a force that moves an aircraft in the direction of motion.It is created with a propeller, jet engine, or rocket. Air is pulled in and then pushed out in an opposite direction.
Drag:It is the force that acts opposite to the direction of the motion. It tends to slow an object. Drag is caused by friction and difference in air pressure.
Weight: it is the force caused by gravity.
Lift: It is the force that holds an airplane in the air. The wings create most of the lift used by airplanes.
Therefore Take off power = Total force * velocity
ROLLING RESISTANCE:
The friction between aircraft and runway will be proportinal to the normal force exerted by the aircraft on the runway.
F =u (W - L) ....Where u = friction coefficient
The normal force will be differance between weight of aircraft and lift the friction coefficient will be typically of a magnitude.
TYRE DESIGN:
Designing aircraft tires is a very intense undertaking. The tyre is a designed to withstand heavy loads while landing, take off, taxing. parking. the number of wheels required for aircraft increase with the weight of the aircraft, as weight needs to be distribute evenly.
Radial tyre: It has fibre strands of the ply fabric oriented at 90 degree to the direction of rotation and the tyre sidewall. This restricts flexibility bidirectional and the flexibility of the side wall while it strengthens the tyre to carry heavy loads.
Bias ply tyre : It has the fabric bias oriented with and across the direction of rotation and the sidewall. since fabric can stretch on thr bias, the tyre is flexible and can absorb the loads.
TYRE PRESSURE:
Aircraft tyres 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 tyre-related events is to maintain proper line inflation pressure.
following are the three actions is a good way to make the safe operation of your aircraft:
1.Perform daily pressure checks with a calibrated gauge.
2. Target the highest pressure recommended in the AMM or POH (105 percent of operating pressure)
3. Compensate for ambiet temperature changes.
BRAKE FORCE WHEN LANDING:
Stopping a 200 tonne of aircraft landing at 180 kmp requires a lot of braking force. T o do this either hydraulic brakes or electric brakes are used. Hydraulic brakes put on weight of the aircraft. Now a days designers use electric brake system. The aim of brake force when landing is to minimise the distance.
*ANS 6
The given data is taken from the towing truck TMX-150-9 and aircraft airbus A319
*given data-
Mass of the truck= 8300 kg
Mass of the aircraft = 75500 kg
Length of the aircraft = 33.84 m
Velocity of the truck = 25 kmph
Height of the aircraft = 11.76 m
Air density = 1.225 kg/m^3
Drag coefficient (Cd) = 0.75
Rolling resistance coefficient urr = 0.013
*calculation for rolling ressistance(Frr)
Frr = urr*m*g
Gravitational constant(g) = 9.81
m = Mass of the truck + mass of the aircraft
=8300+75000 = 83800 kg
substituting the values
Frr = 0.013*83800*9.8
Frr = 1676.12 Nm
*Calculation for aerodynamic drag(Fad)
Fad = 0.5*rho*Cd*A*V^2
velocity of the truck(m/sec) = 25/3.6 = 6.95 m/sec
Area = legth * height = 33.84 * 11.76
Area = 392.544 m^2
Fad = 0.5*1.225*0.75*392.544*6.95^2
Fad = 8816 N
*Total force required to push/ pull an aircraft by a towing vehicle is
In newton
* Ftotal = Frr + Fad
Ftotal = 19492.8 N
in Power
power = Ftotal * velocity
Power = 135.363 kW
B. Develop the model for the calculated force and power using Simulink.
ANS 7
from above calculations
*Torque required at the wheels(Tw):
Tw = Total force* Tyre radius = 19492* 0.411
Tw = 8011.212 Nm
*Actual power required(Pac):
Pac = (power required)/(ηt*ηm)= 135.363/(0.8*0.92)
Pac = 183.917 KW
It is the motor power rating should be around 190 KW.
* To calculate motor torque(Tm)
Tm = (Tw)/(Gear ratio * ηt) = 8011.212/ (7*0.8)
Tm = 1.430 kNm
* Actual motor torque:
Tmac = (Tm)/(ηm) = 5.6/ 0.92
Tmac = 1.555 kNm
*To calculate battery capacity:
the towing tractor takes 15 minutes for taxing.
15 minutes = 0.016667 hours
Battery capacity = Pac * hours = 183.917 * 0.016667
Battery capacity = 3.067 Kwh
The battery must deliver the power output of 3.067 kwh.
if i use the 210 KW battery i can run the towing tractor easily.
*Duty cycle calculation:
Duty cycle =(power required(Pac))/ Battery capacity = 183.917 / 210
Duty cycle = 0.875
*to run the towing tractor for 15 minutes with speed of 7 m/sec the duty cycle is varies between ( 0 - 0.875)
