Project-1: Powertrain for aircraft in runways
AIM:
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 it's ready to take off?
5. Learn about take-off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
6. With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.
7. Design an electric powertrain with type of motor, its power rating, and energy requirement to fulfil 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 powertrain.
STUDY I:
List out the total weight of various types of aircrafts.
Weight is a major factor in airoplane 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 80,000kg
Eg: Boeing 737-800
- Fighter jet 113,646kg
Eg: Boeing F-18 Hornet
- Cargo airplanes 165,900kg
Eg: Airbus A300 600F
- Military Helicopter 7,791kg
Eg: Boeing RAH-66 Comanche
Mid-size Helicopter 5,080kg
Eg: Bell 212
- Turboprop aircraft 3,994kg
Eg: Grand Caravan EX
STUDY 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. In the old days, a large "wind sock" was hung near the runway for pilots to see which way the wind was blowing to adjust their take-off and landing directions. Now mechanical or electronic devices provide the information that is radioed to the cockpit. It is important to understand the relationships of wind speed to ground speed and airspeed.
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 quantity 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 the 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 quantity.
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 the ground speed and the wind speed. Airspeed 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 quantity. Using Pitot tube. Calculated quantity. (Air speed + Wind velocity)
To visualize these speed an animation by NASA is attached below.
mpszl lwww.grc.nasa.govlwwwlk-lZZairplanelAnimation!airrellanrelwhtml
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. Taxing can save money.
During high power engine running damage occure itself to aircraft,then its easier to driver see outside and drive better that pilot,also push back driver better know about airport roads than pilots.as well as another benefits is save the fuel of pilot ,because pilot run this avg distance required more fuel.
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When an aircraft is parked at the gate, it draws its power from the ground power units. It also takes at least 3 - 5 minutes to power up the engines. That is a lot of time in an over crowded airport like Mumbai — which has only one functional ru An aircraft engine has multiple functions.
How an aircraft is pushed to runway when it’s ready to take off?
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 plane's nose gear with a tow bar, or could be a "wheel-lift" tug. These tugs cradle the nose gear, then lift it up before moving the plane. That gives the tug driver control over the plane's direction during pushback. New taxi technologies are appearing, like pilot-controlled tugs, and electric motors mounted to the plane's landing gear. Both promise to save fuel, and reduce airport noise.
Ready for take-off in ten steps…
- The pilot parks the aircraft in exactly the right place. Usually with the help of an automatic system, but occasionally guided by a marshaller waving two paddles or wands. Dozens of handling personnel are already standing by to perform a whole range of tasks simultaneously.
- As soon as the aircraft is stationary and the engines are switched off, the first priority is to disembark the passengers as quickly as possible. The apron handler places chocks in front of the wheels and connects the ground power. Meanwhile, the passenger bridge manoeuvres up to the door and a belt loader rolls up to the cargo hold. Luggage is unloaded and transferred to the terminal on baggage carts.
- Refuelling begins, usually from a hydrant at the stand. A hose is attached to this from a special vehicle called a dispenser, with the other side connected to the fuel tank in the wing. Read more about refuelling here.
- Now it is time to service the aircraft. The caterer loads new meals and takes away the food waste and used cutlery and crockery. Other activities include draining the lavatories, replacing the headrest covers, removing rubbish and distributing fresh blankets and in-flight magazine.
- A specialist team – or sometimes the crew themselves – cleans the cabin so that the new passengers board a pristine aircraft.
- Meanwhile, specialists from the airline conduct a technical check to make sure that the engines, wings, control surfaces, landing gear, instruments, doors and other equipment are in full working order.
- The aircraft is now ready for baggage to be loaded for the next flight. This is a quick process, on average taking only 10-15 minutes. A little later the passengers start boarding. As soon as they are all in their seats, the door is closed and the pilot informs air-traffic control that the flight is ready for departure.
- The apron handler removes the chocks. A so-called pushback truck reverses the aircraft into taxiing position, pushing it with a towbar attached to the nose-wheel strut. Or, in the most modern versions, by actually lifting the wheel. That speeds up coupling and decoupling.
- The aircraft taxis to the runway to depart at the agreed time.
- The pilot waits for permission to take off from air-traffic control. This is possible once the departure route is clear. As soon as the go-ahead is received, the plane takes to the air at full power
Take google reference about this queation and got information below:-
If you are driving on the road within the speed limit towards a car which is parked, will you crash into it at some point? If your answer to this question is yes, then the answer to your question is also a yes.
The speed v1">v1v1 by definition is the highest speed at which the pilot must act on to stop the aircraft in a failure event. Depending on the situation the aircraft may run out of the runway, if the stop is attempted after v1">v1v1. It is always easier to explain how v1">v1v1 works by using the balanced field graph which is shown below. The graph shows two curves. One is the Take off distance required (TODR) in green and the other is the Accelerated stop distance required (ASDR). The y-axis is the runway distance and the x-axis the range of v1">v1v1 speeds possible.
The TODR decreases with an increase in v1">v1v1 speed because the later the engine fails in the take off run the more time aircraft is with two engines operative which gives it more acceleration. The ASDR increases with an increase in v1">v1v1 because an aircraft with a higher speed has more momentum and requires more runway length to stop the aircraft.
If you look at the graph, you can see that I have marked two speeds. One is 140 knots and the other is 135 knots. Here I assumed a case where the v1">v1v1 of the aircraft is 140 knots, but for some reason we do not accelerate beyond 135 knots. According to the markings if the pilot tries to stop the aircraft at 140 knots, it will take 6200 ft of runway to come to a halt. And if we assume that the aircraft is stuck 135 knots, it will take 5800 ft to stop the aircraft. So, even if the aircraft is not accelerated to the v1">v1v1 there will be a point where the aircraft will run out of runway. If we consider our case here, if the pilot does not want to run out of runway at 135 knots, he/ she should attempt to stop the aircraft with 5800 ft remaining on the runway.
STUDY 5:
Learn about take—off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.
Take-offPower:
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 gradually accelerate to normal lift—off and climb—out speed, and there are no obstructions along the take—off path. There are four forces which helps the aircraft to take off: Wings keep an airplane up in the air, but the four forces are what make this happen. They push a plane up, down, forward, or slow it down.
Thrust:-It is a force that moves on aircraft in the direction of the motion. It is created with a propeller, jet engine, or rocket. Air is pulled in and then pushed out in an opposite direction. One example is a household fan.
T = (Pshaft * Efficiency)/V
Drag: It is the force that acts opposite to the direction of motion. It tends to slow an object. Drag is caused by friction and differences in air pressure. An example is putting your hand out of a moving car window and feeling it pull back.
D=Cd*0.5*Air dencity*V^2*S
Weight: It is the force caused by gravity.
W = mg
Lift: It is the force that holds an airplane in the air. The wings create most of the lift used by airplanes.
L=Cd*0.5*Air dencity*V^2*S
Therefore Take—off power= Total force*Velocity
For smaller aircrafts like turboprop we use full power for take-off. Because they don’t have take-off power settings. But in aircrafts like Jet plane they have take—off power settings so they don't have to take the full power.
Rolling Resistance:
The friction between aircraft and runway will be proportional to the normal force exerted by the aircraft on the runway.
F = MW - L
The normal force will be the difference between Weight (W) of aircraft and Lift (L), the friction coefficient (p) will be typically of a
magnitude of 0.02 for a standard tarmac runway.
Tyre Design:
Designing aircraft tires is a very intense undertaking. The tyre 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 aeroplane needs to be distributed more evenly. Aircraft tyre generates more heat during landing. Aircraft drags the wheel until they match the rotational velocity of wheels. Due to this heat generates. However, each tyre is built to operate within a given temperature. This is known as vulcanization temperature. During the course of its use, if the tire is heated past the vulcanization temperature, it begins to wear gradually.
Two types of tires are used in aircraft applications: bias—ply tires and radial tires.
Radial Tyre:- It has fibre strands of the ply fabric oriented at 90° to the direction of rotation and the tyre sidewall. This restricts flexibility bidirectional and the flexibility of the sidewall while it strengthens the tyre to carry heavy loads. Due to their unique construction most radial tyres are resistant to penetration ad cuts. Due to stiffer tread they distribute weight evenly. Thus provide greater traction. Radial tyres have an advantage in term of reducing the heat better.
Bias- ply Tyre:- It has the fabric bias oriented with and across the direction of rotation and the sidewall. Since fabric can stretch on the bias, the tyre is flexible and can absorb loads. Tyre strength is obtained by adding plies. It is cut resistant is sidewall area. These tyres do not offer as much smoothness in terms of riding quality.
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 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:
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 ambient temperature changes.
Brake forces when landing:
Stopping a 200-tonne aircraft landing at 180 mph requires a lot of braking force. To 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.
The touch down velocity should be approximately the stall speed of the aircraft in landing configuration. This will be achieved by increasing the drag and decelerate the aircraft to minimum flying speed. The deceleration on the landing roll from to will be accomplished by braking and reverse thrust. This can be solved by the average acceleration approach that was used to estimate the take—off roll.
dv/dt=(-T-M-F/m)
Where,
T — Thrust of propulsion system pushing aircraft along 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.
m - Mass
So the brake force: Mass * Deceleration.
STUDY 6:
Calculate the force and power required to push / pull an aircraft by a towing vehicle.
To propell any vehicle we need to overcome several opposite forces acting on the same vehicle . The actual forces acting on the vehicle varies from place to place. let us consider the regular runway the oposite forces ore acting to propel the vehicle are Rolling resistance force (Frr) and aerodynamic drag force.(Fad) there is no grade so hill climbing force (Fhc)is neglected. The sum these forces is actual or total force (Fte) to overcome to propel the vehicle.
Frr=mgµrr
Fad=1/2*pACdV^2;
Where,
p=Air dencity
A=frontal area
Cd-aero drag coefficient
v-velocity of the vehicle(m/s)
Fte=Rolling resistance force (Frr)+aerodynamic dragforce(Fad)
Fte=mgµrr+1/2*pACdV^2
assume any vehicle(aircraft ):
some of the asumptions are :
mass of the aircraft (ma)=24500kg;
mass of the towing vehicle=l0000kg;
gravitational constont(g)=9.81m/ s^2;
rolling resistonce(µrr)=0.05;
air density(V)=1.5kg/m^3;
frontalarea (A)=l0m^2;
aero drag coefficient(Cd)=0.4+0.2=0.6;
velocity(v)=21.6km/hr=6m/sec
Frr=mm1rr
=(24500+10000)*9.81*0.05
=16922.25N
Fod=1/ 2*pACdvl^2
=0.5*1.5*1080.s*s^2
=162N
Fte=mgµrr+1/2*pACdvl^2
=16922.25N+162N
=17084.25N
force required to pull or pushthe vehicle Fte=7909.9488N
torque at the wheels =force *radius
=17084.25°0.2(tlre radlus=0.2m)
=3416.85Nm
Power Required to pull the vehicle=Force * velocity
=Fte*v (Kw)
6b)The model for calculated force and power using Simulink :
The following are the equations modeled in simulink
Frr=mgµrr;
Fad=1/2* pACdv^2;
Fte=mgµrr+1/2*pACdv^2
power(p) =force *velocity
The simulink is one of the best tool for doing mathamatical model calculations .
"The model consists of differnet blocks like constant ,gain ,product,squre ,dispaly blocks."
Constant block :-This block is used to declare the diffrent input like
1)m-mass of the vehicle(kg)
2)µrr-rolling resistance
3)p-air density(kg/m^3)
4)A-frontal area(m^2)
5)v-velocity of the vehicle(m/s)
Gain block: This block is multiply the input withthe gainvalue. This block is used for
g-gravitational constant.(kg/m^2)
Cd-aero drag coefficient
Display :-which results the output of the equations ie,forces and power.
Tags :-Used to tag the data between the blocks.(goto &from)
"power rating,and energy requirement to fulfill aircraft towing application:"
From the forces acting on the vehicle we calculated the power required the vehicle.
The power required to propell the vehicle is 102.505kw. This power is the output power of the motor. In order to select the power rating of the machine we need to consider the efficiency accepct .
Because the machine consists of different types of losses . we know that
input power =outpower +losses in machine
efficiency (TJ)= outpower/inputpower let us assume the machine efficiency is 85% then the input power is calculated as
inputpower =outpower/efficiency (TJ)
=102.505kw/0.85
=120.59kw
From this we can select a 120kw de motor is sufficient for the powertrain.
If we consider the particular motor to operate for a 1hr then the energy for the machine is given by
energy =power *time =120.59°3600
=434.124kwh or 434124wh
Duty cycle range to control the aircraft speed from zero to highest Block diagram of powertrain :
To operate the machine at high speed the it needs max power the duty cycle will be
duty cycle=outpower /input power
=102.505/120 .59
=0.85%
Block diagram of powertrain:
Assumed parameters :
Here i assumed the rafale fighter aircraft ;
parameter
mass of the aircraft (ma)=24500kg
mass of the towing vehicle=10000kg
rolling resistance(µrr)=0.05
air density(p)=1.5kg/m^3
frontal area (A)= 10m^2
aero drag coefficient(Cd)=0.6
velocity(v)=21.6km/hr=6m/sec
assumption=
gravitational constant(g)= 9.8lm/s^2
power train model designed In slmulink :
The below model represents the simple powertrain model for aircraft on the runway. In general the power train consists of the battery (source), motor ,motor controller ,This model consists of battery,four quadrant chopper de drive (DC) The main purpose of the de drive is it consist tho controller also.
Q7)DC 7 example:-
Excel sheet calculation data :-
References:-
