Project-1: Powertrain for aircraft in runways

Aim -

Part A:

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

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

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

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

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

Part B:

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

B. Develop the model for the calculated force and power using Simulink.

7. A. Design an electric powertrain with the type of motor, its power rating, and energy required to fulfill aircraft towing application in Simulink. 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.

(Hint: DC7 Block)

B. Also, Design the parameters in an excel sheet.

Solution:-

Part A:

Q1. Search and list out the total weight of various types of aircraft.

First lets us understand the different types of weight an aircraft has.

• Standard Empty Weight

The weight of an empty airplane includes unusable fuel, full operating fluids (hydraulic fluids), and full engine oil.

• Basic Empty Weight

Standard Empty Weight plus optional equipment. This is the starting point of weight and balance calculations.

• Useful Load

Useful load is total usable fuel, cargo, passengers, and drainable fuel. Equation: Maximum Ramp Weight - Basic Empty Weight = Useful Load

• Payload

This one is simple. Think of payload as what's "paying" for the flight: passengers, bags, and cargo. It's how much weight you can carry besides basic empty weight and fuel.

• Maximum Ramp Weight (Taxi Weight)

This is the maximum allowable weight mass for ground operations. MRW assures acceptable ground maneuverability and includes fuel for taxi, run-up, and start.

• Maximum Takeoff Weight (MTOW)

Maximum allowable mass for the initiation of a takeoff roll. Depending on how big your airplane is, you may have a variety of MTOWs limited by: structural limitations, runway distance, climb performance, or landing weight limits.

• Minimum Flight Weight (MFW)

Minimum certificated weight for flight as limited by aircraft strength and airworthiness requirements. This weight has a lot to do with the balance of weight considering fuel/payload distribution.

• Maximum Landing Weight (MLW)

Maximum landing weight is usually a structural limit but may include calculations based on missed approach climb performance.

• Zero-fuel weight (ZFW)

This is the total weight of the airplane and all its contents (including unusable fuel), but excluding the total weight of the usable fuel on board.

Different weights of various types of aircraft.

1. Fighter Aircraft

• A fighter aircraft often referred to simply as a fighter, is a military fixed-wing aircraft designed primarily for air to air combat against other aircraft. The key performance features of a fighter include not only its firepower but also its high speed and maneuverability relative to the target aircraft.
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2. Transport Planes

• Military transport aircraft or military cargo aircraft are used to airlift troops, weapons and other military equipment to support military operations. Transport aircraft can be used for both strategic and tactical missions, and are often diverted to civil emergency relief missions.
• Airbus C295 is a transport aircraft of 5-10 tonne capacity with contemporary technology that will replace the ageing Avro transport aircraft of the Indian Air Force.
• EADS CASA C-295 weight is 11,000 KG.
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3. Acrobatic

• Aerobatic flight means an intentional maneuver involving an abrupt change in an aircraft's attitude, an abnormal attitude, or abnormal acceleration, not necessary for normal flight. The overhead maneuver is not considered an aerobatic maneuver.
• Weight is around 600KG.
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4. Glider

• A glider is a fixed-wing plane that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose free weight does not depend on an engine. Most gliders do not have an engine, although motor gliders have small engines for extending their flight when necessary by sustaining the altitude (normally a sailplane is on a continuously descending slope) with some being powerful enough to take off self-launch.
• Weight varies from a range of 61Kg of empty Microlift Glider to max 900Kg Self-Launching.
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Q2. Is there any difference between 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. 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). In this figure, we are considering only velocities along the aircraft's flight path. A 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.

• Air speed

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 -

Suppose we had an airplane that could take off on a windless day at 100 mph (liftoff airspeed is 100 mph). We are at an airport with an east-west runway that is 1 mile long. The wind is blowing 20 mph towards the west and the airplane takes off going east. The wind is blowing towards the aircraft which we call a headwind. Since we have defined a positive velocity to be in the direction of the aircraft's motion, a headwind is a negative velocity. While the plane is sitting still on the runway, it has a ground speed of 0 and an airspeed of 20 mph:

Airspeed = Ground Speed (0) - Wind Speed (-20) = 20 mph

The airplane starts its take-off roll and has a constant acceleration a. From Newton's second law of motion, the ground speed V at any time t is:

V = a * t

and the distance d down the runway at any time is:

d = 1/2 * a * t^2

For a fixed-length runway, this specifies the time to be used in the velocity equation. Let's assume that at 5000 feet down the runway, the velocity is 80 mph. Then the airspeed is given by

Airspeed = Ground Speed (80) - Wind Speed (-20) = 100 mph

and the airplane begins to fly. Now another pilot, with exactly the same airplane decides to take off to the west. The wind is now in the same direction as the motion and this is called a tailwind. The sign on the wind speed is now positive, not negative as with the headwind. The acceleration along the ground is the same, so at 5000 feet down the runway, the ground speed is again 80 mph. The airspeed is then given by:

Airspeed = Ground Speed (80) - Wind Speed (20) = 60 mph

This airplane doesn't have enough airspeed to fly. It runs off the end of the runway!

• So in the below figure, we can see that the airspeed was not that enough to carry out the aircraft's weight. That is why plane number two was unable to fly.

• In this second figure, Ground speed is kept constant so both the planes are at the same speed.

• In this below figure, even though the airspeed is the same but there is a difference of 80 mph in ground speed so aircraft seems to be faster than aircraft two.

Q3. Why is it not recommended to use aircraft engine power to move it on the ground at the Airport?

• Airplanes use their jet engines for taxing just like for flying. And they have no additional engines to power the wheels.
• The wheels of an airplane rotate freely as the plane depends on the thrust from its jet engines to propel it forwards or backward.
• However, despite the engines being capable of powering the airplane's 'pushback' from the terminal/gate, they are rarely used for this purpose.
• '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.
• Once the plane is tugged away to a safe distance from the terminal, the plane begins using its own engine power for the rest of the taxing process.
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Q4. How an aircraft is pushed to the runway when it's ready to take off?

• Large jetliner passenger aircraft are pushed away from the passenger loading gate by a tug. This is a machine with wheels, some form of power such as an internal combustion engine, or a battery. When the large aircraft is being pushed backward, there is someone on each wingtip. They are looking out to make sure nothing will touch the aircraft. The whole idea is to avoid expensive crunching noises.

• The below figure is of the Aircraft being pushed out onto the runway ready for take-off.

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Q5. Learn about take-off power, tire design, rolling resistance, tire pressure, brake forces when landing.

A. Take off power

Forces need to overcome while taking off or to maintain aircraft in the air.

• Thrust is a force that moves an 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.

• Drag 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.

• Weight is the force caused by gravity.

• Lift is the force that holds an airplane in the air. The wings create most of the lift used by airplanes.

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B. Tyre design

• When it comes to safety, tires are one of the most important components of aircraft. They help to absorb the shock of landing and provide cushioning. It also provides the necessary traction for braking and stopping of an aircraft.

• An aircraft tire is designed to withstand extremely 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 airplane needs to be distributed more evenly.

• Carcass plies are used to form the tire. They are sometimes called casing plies. An aircraft tire is constructed for the purpose it serves.

• 1. They support the weight of an aircraft while it is on the ground.

• 2. It also provides the necessary traction for the braking and stopping of an airplane.

• 3. Tyre also helps to absorb the shock of landing and provides cushioning for the roughness of takeoff, roll-out, and taxi operations.

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Let’s go through some technical aspects of the tire.

• Retreading – Retreading is a method 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.

C. Rolling Resistance

• The coefficient is a function of the tire material, tire structure, tire temperature, tire inflation pressure, tread geometry, road roughness, road material, and the presence or absence of liquids on the road.
• The values vary with the speed. Tire pressure increases its value decreases need to carefully choose value as per typical cases under consideration.

Frr = Urr*m*g

Where,

Urr = Rolling resistance coefficient

M = mas of the body/vehicle

G = Gravitational force

D. Tyre pressure

Aircraft tires may be Tube-type or Tubeless:- Tubeless tires are more advantageous than tube-type. There is no longer the use of tube-type tires 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

Tyre pressure varies from plane to plane.

• The tires do not use the typical compressed air we would use from a fuel station supply or a home air compressor.

• Aviation tires are made of a much stronger compound than what we use for the auto industry and in fact, they use nitrogen gas to inflate the tires, as opposed to compressed air.

• This provides additional strength to the tires in general, to support the tremendous weight they carry moving the plane or on take-off and for landing.

• The average pressure they run in the tires is between 200–220 PSI, it again depends on the model aircraft, (Automobiles run 30–40 psi on average)

• Tires are required to replace after every 300 or so cycles. A cycle represents 1 for a Landing and 1 for a lift-off. Every time a plane lands and departs, this is considered 2 cycles.

• The requirement that an inert gas, such as nitrogen, be used instead of air for inflation of tires on certain transport category airplanes was prompted by at least three cases in which the oxygen in air-filled tires had combined with volatile gases given off by a severely overheated tire and exploded upon reaching autoignition temperature. The use of inert gas for tire inflation eliminates the possibility of a tire explosion.

• When the tire pressure becomes too low then values of Rolling resistance increase too much.

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E. Brake forces

We will use Newton’s second law to determine force due to deceleration:

That is Energy required to break Bf = (½)*m*(Vi– Vf)^²

Where,

• Bf = Breaking Energy in Joules
• m = Mass of the aircraft
• Vi = Initial speed of the plane
• Vf = Final speed of the plane

If we want to find the Breaking Power in wattage as we know Power in Watt = Workdone /time

So in order to power in wattage, we have to divide Breaking Energy by time.

• Power = Breaking Energy/time

Here, time is nothing but the time required to reach aircraft from Initial velocity to Final velocity.

Part B:

Q6. A. With necessary assumptions, calculate the force and power required to push/pull an aircraft by a towing vehicle.

B. Develop the model for the calculated force and power using Simulink.

Calculations are done in Matlab Simulink to get Power, Torque, Energy.

In this model, two subsystems are 1. Forces for Aeroplane 2. Forces for Tugs

• 1. Forces for an Aeroplane

• 2. Forces on Tugs.

• For calculation of Power, Torque, Energy

Q7 . A. Design an electric powertrain with the type of motor, its power rating, and energy required to fulfill aircraft towing application in Simulink. 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.

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Block diagram of the powertrain.

Total energy consumed by the tug in 20 min(+ extra 10 min considering free time run of tug) is

Energy consumed = Power of motor * 30/60

= (52.750*1000)*0.5

= 26375wh

= 27Kwh

Now for battery sizing, we choose a battery whose output voltage is around 360v

So, Battery current = Motor power/Voltage = 52750/360 = 146.52 =~ 150 amp approx.

for battery rating = Battery current * run time of tug = 150 * (30/60) = 75 amp-hr

From the above calculation, we can see a 75 Amp-hr battery is required to fulfill our requirements which are providing 650 N-m of instantaneous torque with a motor rating of 53kw and a run time of 30min with a velocity of 5 m/sec.

B . Also, Design the parameters in an excel sheet.

Conclusion -

Therefore all the various studies about the aircraft are analyzed and calculations are performed to find the force and power required to push/pull an aircraft by a towing vehicle and energy requirements to fulfill aircraft towing applications are also determined. The values of the mathematical expressions are -

• Motor Rating - 53Kw
• Battery Rating - 360V, 75Amp-hr
• Energy - 27Kwh