Project-1: Powertrain for aircraft in runways
1.
Maximum design taxi weight (MDTW)
It is the maximum weight which is permitted for an aircraft on the ground for taxiing or towing purpose which is being constrained by aircraft’s strength
Maximum design takeoff weight (MDTOW)
It is the maximum weight which is permitted for an aircraft when the brakes are released for takeoff.
Maximum design landing weight (MDLW):
It is the maximum weight which is permitted for an aircraft when the aircraft meets the appropriate landing certification requirements. It depends on landing gear strength and impact loads.
List of various aircrafts along with their weights is attached as 1.xlsx worksheet.
2.Airspeed is defined as the difference of vector between the ground and the wind velocity. When winds are not blowing, or on the still day , the airspeed will be equivalent to the ground speed.
If wind direction is similar to the aircraft dierection, the airspeed will be lesser than the ground speed.
And on the other side if wind direction is opposite, the airspeed will be greater than ground speed.
3. When aircraft is moved under its own power, it is known as taxiing.
When aircraft is pushed backed or towed it is known as towing
The engine and the tyre are having no connection, unlike other ground vehicles. The engines produce thrust in the normal way by sucking in some air from the front and accelerating it backwards either through a jet engine or using a propeller. As a result, the whole aircraft moves forward.They have no additional engines to power the wheels.
By twisting the propeller's blades, it is possible to have them suck air from behind and accelerate it forward. That way, the aircraft can move backwards.
Tug vehicles' are generally used to pushback the plane away from the terminal prior to take-off. These are specialized vehicles with high torque and heavy mass.
The reason for the use of tugs is that the alternative (i.e., pushback using the jet-engine's thrust-reverser) is a highly fuel-consuming and noisy process. It is also potentially hazardous for personnel working near the plane.
4. When we use external power to push an aircraft backwards towards the gate of an airport, this procedure is known as pushback.Special and low profile vehicles known as tugs or pushback tractors are used for carrying out oushback operation .. Thus pushback is the most preferred method for carrying the aircraft away from plane.
Fig 1 Pushback operation
5.
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 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 take-off run the imbalance in these forces will produce an acceleration along the runway.
where dV/dt is the acceleration along the runway and m is the mass of the vehicle.
Take off Power: It will be the product of net force acting on plane and velocity of the aircraft.
Rolling resistance: The friction between aircraft and runway will be proportional to the normal force exerted by the aircraft on the runway
Tyre design: Unlike an automobile or truck tyre, it does not have to carry a load for a long period of continuous operation. However, an aircraft tyre absorbs the high impact loads of landing and also it’s operating at high speeds for a short time when required.
- 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 aeroplane.
- Tyre also helps to absorb the shock of landing and provide cushioning the roughness of takeoff, roll-out, and taxi operations.
Aircraft tires also include fusible plugs , designed to melt at a certain temperature. Tires often overheat if maximum braking is applied during an aborted takeoff . 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.
Different terms for aircraft tyre are shown in the figure below:
Fig 2 Tyre Design
Tyre pressure: Aircraft tires generally operate at high pressures, up to 200 psi (14 bar; 1,400 kPa) for airliners, and even higher for business jet. The main landing gear was typically inflated to 232 psi (16.0 bar), whilst its tail bumper gear tires were as high as 294 psi. Aircrafts main tires is inflated to 220 psi (15 bar).
Brake power: The brake units are powered by the hydraulics system. An electrical signal is sent from the flight deck to hydraulic actuators near the main landing gear. Here, hydraulic fluid at high pressure is used to force the brake unit against the wheel, thus slowing it down.
Modern airplanes use disc brakes. The disc rotates as the turning wheel assembly rotates, but when brakes are applied, a stationary caliper resists the rotation by causing friction against the disc.
Air brakes are also used, which uses the drag force of air to slow down the speed of the aircraft at initial stage.
6.
Free Body diagram for pulling and pusing of an aircraft are given above.
We will use Boeing 737-800 which is an example of an average sized airplane. It has a maximum takeoff weight of about 80,000 kg (weight of plane=41000kg, weight of fuel=39000kg)
Rolling resistance can be assumed to be 0.02
This force can be delivered by a pulling truck or - as occasionally seen - by a number of pulling people. Enough weight for the pullers are required to create friction forces against the tarmac that equals the plane rolling resistance.
Required Mass for Pulling Truck
We will use Boeing 737-800 which is an example of an average sized airplane. It has a maximum takeoff weight of about 80,000 kg (weight of plane=41000kg, weight of fuel=39000kg)
Rolling resistance can be assumed to be 0.02
This force can be delivered by a pulling truck or - as occasionally seen - by a number of pulling people. Enough weight for the pullers are required to create friction forces against the tarmac that equals the plane rolling resistance.
The frictional force for the puller can be calculated as:
Ff = μ W
= μ mg
where
Ff = frictional force (in N)
μ = friction coefficient
W = weight (in N)
Thus frictional force is:
Fr = 0.02 (40000 kg) (9.81 m/s2)
= 7848 N
Required Mass for Pulling Truck
The friction coefficient between a pulling truck rubber wheels and surface is 0.9. Since pulling trucks are connected to air crafts nose wheels we simplify the calculation of required truck mass as:
mf = (7848 N) / (0.9 (9.81 m/s2))
= 889 kg
In aviation, pushback is an airport procedure during which an aircraft is pushed backwards away from an airport gate by external power. Pushbacks are carried out by special, low-profile vehicles called pushback or tugs.
Although many aircraft are capable of moving themselves backwards on the ground using reverse thrust,the 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.
7.
Fig 3 Vehicle blockset
Fig 4 Aircraft Towing vehicle blockset
As seen in the figure above,aircraft towing vehicle blockset include Powercontroller, Motor, battery and an external force for towing an aircraft which is calculated above as
Fr = 0.02 (40000 kg) (9.81 m/s2)
= 7848 N
Table for assumptions used:
1. Mass of an aircraft= 41000kg
2. Rolling resistance of aircraft tire= 0.02
3. Towing vehicle battery voltage= 400 V
4. Towing Vehicle average speed= 4m/s
5. Estimated duty cycle= 65% or 0.65
Power required = Fr * Velocity= 7848 *4= 31.4 KW
Assumed time for towing=10 minutes
Thus Energy(in Kwh)= 31.4*(10/60)= 5.232 Kwh
Thus battery must be used above the calculated value rating i.e above 6 Kwh range.