Project-1: Powertrain for aircraft in runways

MINIMUM FLIGHT WEIGHT (MFW)

Minimum certificated weight for flight as limited by aircraft strength and airworthiness requirements.

AIRCRAFT GROSS WEIGHT

The aircraft gross weight decreases during flight due to fuel and oil consumption. The aircraft gross weight may also vary during flight due to payload dropping or in-flight refueling.

MANUFACTURER’S EMPTY WEIGHT (MEW)

Let’s start with the aircraft itself. An aircraft “as is” includes:

• Airframe structure with all moving mechanical parts (fuselage, wings, flaps, gear, rudder, nacelle …)
• Power generation system (APU, main engines, power plant…)
• Systems (electrical, hydraulics, pneumatic, fuel flow system, instrument, navigation, air conditioning, anti-ice, fixed furnishing)
• Fixed equipment and services considered an integral part of the aircraft
• Fixed ballast
• Closed system fluids
• Unused fuel only for small aircraft

This weight does not include:

• Fuel
• Oil, potable water
• Payload (Cargo, passenger, luggage)
• Removable equipment
• Customer specific installations or operator items

OPERATIONAL EMPTY WEIGHT (OEW)

TAKE-OFF WEIGHT (TOW)

The gross weight varies during flight. Fuel and oil consumption reduces the gross weight. Additionally it may vary during flight due to inflight refuelling or payload dropping.

MAXIMUM DESIGN TAKEOFF WEIGHT (MDTOW)

• The maximum takeoff weight (also known as the maximum brake-release weight) is the maximum weight authorized at brake release for takeoff, or at the start of the takeoff roll.
• The maximum takeoff weight is always less than the maximum taxi/ramp weight to allow for fuel burned during taxi by the engines and the APU.
• In operation, the maximum weight for takeoff may be limited to values less than the maximum takeoff weight due to aircraft performance, environmental conditions, airfield characteristics (takeoff field length, altitude), maximum tire speed and brake
• At this weight, the subsequent addition of fuel will not result in the aircraft design strength being exceeded. The weight difference between the MTOW and the MZFW may be utilized only for the addition of fuel.

LANDING WEIGHT

With the calculation of fuel consumption during flight, we can calculate the Estimated Landing Weight (ELW) which is used for landing performance calculation at the destination.

Approaching your destination you use your current gross weight to determine the final approach speed. The gross weight now is the Actual Landing Weight (ALW).

Now we will get started and calculate an example (we operate an Airbus A319):

Manufacturer’s Empty Weight (MEW)	36,779 kg
+ Operator’s Items	+ 5,205 kg
= Operational Empty Weight (OEW)	= 41,981 kg
+ Payload	+ 13,529 kg
= Actual Zero Fuel Weight (AZFW)	= 55,510 kg
+ Fuel	+ 13,239 kg
= Actual Gross Weight (AGW)	= 68,749 kg
- Taxi Fuel	- 100 kg
= Actual Take-Off Weight (ATOW)	= 68,649 kg
Fuel consumption	-10,900 kg
= Actual Landing Weight (ALW)	= 57,749 kg

Different types of Aircrafts and their weight.

• Cessna 172 – Used by many as initial training aircraft (27 feet long) – 1450lbs empty weight, 2450lbs max weight
• Citation Jet M2 – (42 feet long) – 6990lbs empty weight, 10,700lbs max weight
• Boeing 767-300 – (185 feet long) – 195,000lbs empty weight, 400,000 max weight
• Boeing 787-800 – (186 feet long) – 264,500lbs empty weight, 502,500lbs max weight
• Boeing 777-300 – (242 feet long) – 354,000lbs empty weight, 660,000lbs max weight
• Boeing 747-400 – (232 feet long) – 407,000lbs empty weight, 910,000lbs max weight
• Airbus A320 – (123 feet long) – 82,000lbs empty weight, 170,000lbs max weight
• Airbus A330 – (210 feet long) – 274,500lbs empty weight, 507,000lbs max weight

----------------------------------------------------------------------------------------------------------------------------------------------------------

Ground speed (GS): - Ground speed is the airplane’s speed relative to the surface of the Earth.

Ground speed = air speed +wind speed (VECTOR SUM)

ground speed is what determines how fast an aircraft will get to its destination.

Air speed (TAS): - Air speed is the speed of airplane’s speed relative to the wind speed.

airspeed is what determines whether there is enough airflow around an aircraft to make it fly.

Wind’s Effect on Ground Speed

The relationship between airspeed and ground speed is fairly simple. Ground speed is simply the sum of airspeed and wind speed. If the aircraft is flying in the same direction as the wind is blowing, the aircraft experiences tailwind, and its ground speed is higher than its airspeed. On the other hand, if the wind is blowing against the direction the aircraft is traveling in, the aircraft experiences headwind, and its ground speed is lower than its airspeed.

• In case you are still unsure about the difference between airspeed and ground speed, here’s an analogy to bring the concepts “down to earth.”
• Imagine a moving walkway going from point A to point B moving at 3 miles per hour
• And, imagine you are walking on the walkway at a speed of 3 miles per hour relative to the walkway. In other words, you are moving from point A to point B at a speed of 6 miles per hour – the sum of the speed of the walkway and the speed at which you are walking relative to the walkway.

What if, though, you tried to walk on the walkway from point B to point A?

Obviously, if you walked at 3 miles per hour relative to the walkway, you would be standing still. To move, you would have to walk faster than 3 miles per hour relative to the walkway. For example, if you walked at 5 miles per hour relative to the walkway, you would be moving from point B to point A at a speed of 2 miles per hour.

Basically, there are three types of air speed which are explained below: -

Indicated airspeed is an airspeed that is calculated directly off an aircraft’s pitot-static system. It’s the calculated off the aircraft’s dynamic pressure – the difference between its total pressure and static pressure.

The dynamic pressure depends not only on the aircraft’s speed, but also on the density of the air it is flying in. As such, the higher the aircraft flies – and the lower the air density as a result – the bigger the difference between indicated and true airspeed is.

Calibrated airspeed is indicated airspeed adjusted for a variety of errors.

Just as an example, one of the things it’s adjusted for is the flap position. The reason for that is that at different flap positions, air flows differently around the pitot-static system and affects the indicated airspeed readings.

True airspeed is, as has been mentioned numerous times in this article, the actual speed at which an aircraft is moving relative to the air it is traveling in. Its calibrated airspeed adjusted for the exact conditions (altitude, air temperature, etc.) that the aircraft is flying in.

----------------------------------------------------------------------------------------------------------------------------------------------------

If an aircraft is moving by using the power of its engines then that movement is called taxiing, whereas if an aircraft is being moved without any help from its engines, it’s either being towed or pushed back.

How aircraft move on the Ground?

• Tugs
• Towbarless
• Enigine

Engines

• Once the pushback has been completed, the aircraft can move under its own power. Normally, the engines provide the thrust for the aircraft to move around and that is called Taxiing.
• An airplane uses taxiways to taxi from one place on an airport to another; for example, when moving from a hangar to the runways.
• The aircraft’s engines are started either during pushback or after pushback and only after informing the ground crew of the starting sequence.

Why not to use aircraft engine during ground operation : -

• Pilots have to be extra cautious while adding power to get the aircraft to start moving initially. There have been many instances of unsuspecting ground crew and ground equipment being hit by jet blast. In some unfortunate instances, the ground crew have also been ingested into the engine as a result of a communication breakdown between the pilots and ground crew.
• The air intake of a jet engine is powerful enough to suck in a human body. Even at a distance, the jet engine suction is strong enough to devour loose debris e.g., rags, bolts, paper, stones, catering foils, plastic cups and bags.
• Loss of control may happen on aircraft engine as power developed by engine is very very high.

-----------------------------------------------------------------------------------------------------------------------------------------------------------

4. How an aircraft is pushed to runway when its ready to take off?

How aircraft move on the Ground?

Tugs

• Tugs are special, low-profile utility vehicles used to either tow an aircraft or to push them back from the terminal or remote parking stand. Most tugs utilize wide tires to provide excellent grip which is essential during push-back or towing operations. There are two main types of tugs: conventional and towbarless.
• Conventional tugs employ the use of a tow-bar which is attached to the nose wheel of the aircraft before pushback. The tow-bar acts as a giant lever and helps to rotate the nose wheel.

Towbarless

On the other hand, towbarless tugs use a hydraulic lifting mechanism to scoop up the nose wheel of the aircraft and then push it back. Towbarless tugs are preferred due to their simplicity and because they provide more precise control of the aircraft during towing and pushback operations.

Engines

Once the pushback has been completed, the aircraft can move under its own power. Normally, the engines provide the thrust for the aircraft to move around and that is called taxiing. The aircraft’s engines are started either during pushback or after pushback and only after informing the ground crew of the starting sequence.

---------------------------------------------------------------------------------------------------------------------------------------------------------

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

Take off Power

• The takeoff in any aircraft occurs when the airplane leaves the ground and becomes airborne.
• Takeoff is the first critical phase of flight pilots encounter, requiring detailed planning
• The amount of power that an engine is allowed to produce for a limited period of time for takeoff. The use of takeoff power is usually limited to 5 min for reciprocating engines and up to 2½ min for gas turbine engines
• This may not always be the case. Specifically, with respect to reciprocating engines, it is the brake horsepower developed under standard, sealevel conditions and under the maximum conditions of the crankshaft rotational speed and the engine manifold pressure approved for the normal take-off.
• It is limited in continuous use to the period of time.
• With respect to gas turbine engines, it is the thrust developed under static conditions at a specified altitude and atmospheric conditions of the rotor shaft rotational speed and gas temperature approved for the normal takeoff.
• It is limited in continuous use to the period of time shown in the approved engine specifications.

Tyre Design

• An aircraft tire or tyre is designed to withstand extremely heavy loads for short durations.^T he number of tires required for aircraft increases with the weight of the aircraft, as the weight of the airplane needs to be distributed more evenly. Aircraft tire tread patterns are designed to facilitate stability in high crosswind conditions, to channel water away to prevent hydroplaning, and for braking effect.

• Aircraft tires also include fusible plugs (which are assembled on the inside of the wheels), designed to melt at a certain temperature. Tires often overheat if maximum braking is applied during an aborted takeoff or an emergency landing. 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.

• Each of the twelve Boeing 777-300ER main tires is inflated to 220 psi (15 bar; 1,500 kPa), weighs 120 kg (260 lb), has a diameter of 134 cm (53 in) and is changed every 300 cycles while the brakes are changed every 2000 cycles. Each tire is worth about $5,000. Aircraft tires generally operate at high pressures, up to 200 psi (14 bar; 1,400 kPa) for airliners,

• The four major manufacturers in aircraft tire manufacturing are the following according to a report by Pelmar Engineering in 2013:

  • Goodyear (United States)
  • Michelin (France)
  • Dunlop Aircraft Tyres (United Kingdom)
  • Bridgestone (Japan)

• Design and Construction of Aircraft tyre

  Carcass plies are used to form the tire. They are sometimes called casing plies. An aircraft tyre 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 braking and stopping of an aeroplane.
  3. Tyre also helps to absorb the shock of landing and provide cushioning the roughness of takeoff, roll-out, and taxi operations.

  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.

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

• Retreading – Retreading is methods of restoring a worn tyre by renewing the tread area or by renewing the tread area plus one or both sidewalls. Repairs are included in the tyre 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 tyre. It is an index of tyre strength.

• Speed Rating – The speed rating is the maximum takeoff speed to which the tyre has been tested.

• Skid Depth – Skid depth is the distance between the tread surface and the deepest groove as measured in the mould.

• Aircraft tyres must have an approved speed and load rating and have sufficient clearance when retracted through landing gear to allow for tyre growth. Tyre growth is the increase in the size of the tyre due to centrifugal forces at high speed.

• Aircraft tyres may be Radial or Bias

• Almost all airliners are using Radial tyre. Bias is an older design, and it’s mainly used for road vehicles. Radial tyres have the word RADIAL on the sidewall. Radial tires are more expensive than bias-ply tyres. Radial tires are in demand because of their lower life cycle cost and long term value.

Rolling resistance