Lecture 2: Composition of Aircraft Weight

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1 Lecture 2: Composition of Aircraft Weight
AIRCRAFT (MASS) WEIGHT & PERFORMANCE

2 Introduction All aircraft have a specified maximum mass.
This limit must be respected, whether the aircraft is a micro-light or a Boeing 747. Attempting to fly an overloaded/overweight aircraft can cause various effects.

3 Introduction To ensure aircraft can fly safely with best performance, limitation are set by engineer. Maximum Take-Off Weight (MTOW): The maximum permissible weight to conduct a takeoff. Maximum Landing Weight (MLW): The maximum permissible weight to conduct a landing. Maximum Zero Fuel Weight (MZFW): The maximum weight of an aircraft which its structural limits would allow.

4 Maximum Takeoff Weight (MTOW)
MTOW of an aircraft is the maximum weight at which the pilot of the aircraft is allowed to attempt to take off. It is the heaviest weight which should be limited in order to ensure the aircraft can fly safely during take-off. At its MTOW an aircraft complies with all the structural and performance requirements. The MTOW of an aircraft is fixed. It does not vary with altitude or air temperature or the length of the runway to be used for takeoff or landing. MTOW is usually specified in units of kilograms or pounds.

5 Maximum Landing Weight (MLW)
The maximum permissible weight to conduct a landing.

6 Maximum Zero-Fuel Weight (MZFW)
The Zero Fuel Weight (ZFW) of an airplane is the total weight of the airplane and all its contents, minus the total weight of the fuel on board. When an airplane is being loaded with crew, passengers, baggage and freight it is most important to ensure that the Zero Fuel Weight does not exceed the Maximum Zero Fuel Weight. Designers of airplanes can optimize the MTOW and prevent overloading in the fuselage by specifying a MZFW. This is usually done for large airplanes. Most small airplanes do not have a MZFW specified among their limitations. Maximum Zero-Fuel Weight The Zero Fuel Weight (ZFW) of an airplane is the total weight of the airplane and all its contents, minus the total weight of the fuel on board. For example, if an airplane is flying at a weight of 5,000 lb and the weight of fuel on board is 500 lb, the Zero Fuel Weight is 4,500 lb. Some time later, after 100 lb of fuel has been consumed by the engines, the total weight of the airplane is 4,900 lb and the weight of fuel is 400 lb. The Zero Fuel Weight is still 4,500 lb. Note that, as a flight progresses and fuel is consumed, the total weight of the airplane reduces, but the Zero Fuel Weight remains constant (unless some part of the load, such as parachutists or stores, is jettisoned in flight). For many types of airplane, the airworthiness limitations include a Maximum Zero Fuel Weight. Maximum Zero Fuel Weight in airplane operations When an airplane is being loaded with crew, passengers, baggage and freight it is most important to ensure that the Zero Fuel Weight does not exceed the Maximum Zero Fuel Weight. When an airplane is being loaded with fuel it is most important to ensure that the Takeoff Weight will not exceed the maximum permissible takeoff weight. MZFW : The maximum weight of an aircraft prior to fuel being loaded. :ZFW + FOB = TOW For any aircraft with a defined Maximum Zero Fuel Weight, the maximum payload can be calculated as the MZFW minus the OEW (Operational Empty Weight) :Max Payload = MZFW - OEW Wing bending relief In an airplane, fuel is usually carried in the wings. Weight in the wings does not contribute as significantly to the bending moment in the wing as does weight in the fuselage. This is because the air loads on the wing, and the weight of the fuselage, bend the wing tips upwards and the wing roots downwards; but the weight of the wing, including the weight of fuel in the wing, bend the wing tips downwards, providing relief to the bending effect on the wing. When an airplane is being loaded the capacity for extra weight in the wing is greater than the capacity for extra weight in the fuselage. Designers of airplanes can optimise the Maximum Takeoff Weight and prevent overloading in the fuselage by specifying a Maximum Zero Fuel Weight. This is usually done for large airplanes. Most small airplanes do not have a Maximum Zero Fuel Weight specified among their limitations. For these airplanes, the loading case that must be considered when determining the Maximum Takeoff Weight is the airplane with zero fuel and all disposable load in the fuselage. With zero fuel in the wing the only wing bending relief is due to the weight of the wing.

7 The Importance to set up weight limitations (MTOW, MLW, MZFW)
To avoid over-stressing of aircraft structures. To ensure the aircraft structure is capable of withstanding all the loads likely to be imposed on it during maneuvering by the pilot, and gusts experienced in turbulent atmospheric conditions. To ensure the aircraft is capable of climbing at an adequate gradient with all its engines operating; and also with one engine inoperative.

8 For Landing: AUW/LW ≤ MLW
All Up Weight (AUW) All Up Weight (AUW): The total weight of the aircraft including of all items at any specific time. During take off All up weight (AUW) must not exceed the Maximum Take Off Weight (MTOW) For Take-Off: AUW/TOW ≤ MTOW During landing All up weight (AUW) must not exceed the Maximum Landing Weight (MLW) For Landing: AUW/LW ≤ MLW Total ZFW also must not exceed the Maximum Zero Fuel Weight (MZFW). ZFW ≤ MZFW

9 All Up Weight (AUW) Where, DOW = Dry Operating Weight PAYLOAD = Passengers & Cargo FUEL = Flight Fuel + Reserve Fuel

10 Dry Operating Weight (DOW)
Also known as Aircraft Prepared for Service (APS). It is the basic weight plus crew plus crew’s baggage's. Basic Weight It consists of Empty Weight plus Basic Equipment Weight. Empty Weight Weight of airframe, engines and standard structures. Basic Equipment Weight Weight of common installations inside the airplane. These items are standard: Fuel that cannot be used, Engine oil, oxygen,Miscellaneous equipment, galley structures and fixed inserts. These items are operational: crew and crew baggage, passenger service equipment, catering allowance, potable water, waste tank disinfectant, Items for sale if applicable, emergency equipment.

11 Flight Fuel = Fuel Flow × Flight Time
Payload The weight of all persons and items of load carried in an aircraft for which a fare or charge is being paid. PAYLOAD = Passengers & Cargo Fuel FUEL = Flight Fuel + Reserve Fuel Flight Fuel = It is the weight of the fuel required for and burnt during a flight. With the given flight distance and mean airspeed , Flight Fuel can be calculated as follows: Flight Fuel = Fuel Flow × Flight Time Where, Flight time= Distance / Mean Airspeed

12 All Up Weight (AUW) However, AUW is not same during Take-off and landing During TAKE-OFF: AUW during Take-Off=DOW + PAYLOAD + (Flight Fuel + Reserve Fuel) During LANDING: AUW during Landing =DOW + PAYLOAD + Reserve Fuel Note that, as a flight progresses , flight fuel is consumed and finished.

13 Calculation Normally, there are only one way on how to ensure aircraft total weight (AUW) either at take-off or landing is within limitations. The only way is to reduce the number of passengers, the amount of baggage or cargo (PAYLOAD) or the fuel load.

14 Payload Calculation Based on above equation, to ensure AUW ≤ MTOW, MLW,MZFW Take-off consideration : replace AUW as MTOW, and re-arrange equation as: Payload = MTOW-DOW- (Flight Fuel+ Reserve Fuel) Landing consideration : replace AUW as MLW, and re-arrange equation as: Payload = MLW-DOW- Reserve Fuel Zero Fuel consideration : replace AUW as MZFW, and re-arrange equation as: Payload = MZFW-DOW Based on the calculation, the lowest result is the maximum payload that the aircraft is able to carry for a flight.

15 Example 1 Aircraft fly from M to N, given: MTOW = 6180kg MLW = 5740kg MZFW = 5395kg DOW=4400kg Flight Fuel = 767kg Reserve Fuel=250kg Calculate maximum payload that the aircraft is able to carry. Answer: 961kg

16 Example 2 Aircraft fly from A to B, given:
MTOW = 41,300kg, MLW = 32,250kg DOW = 23,000kg Fuel Flow= 2000kg/hr, Mean Speed=455knots, Flight Distance=2150nm Reserve Fuel=2500kg Calculate maximum payload that the aircraft is able to carry. (**Assume MZFW is not specified) Solution: Step 1: Calculate Flight time & Flight Fuel Step 2: Find the maximum payload by ensuring total weight ≤ MTOW, MLW Answer: 6350kg

17 Effects Of overloaded airplane

18 Introduction Aircraft’s manufacturers attempt to make the airplane as light as possible together with higher strength and enough safety. Either flight operators or pilot of an airplane should always be aware of the consequences of overloading. An overloaded airplane MAY NOT BE ABLE TO LEAVE THE GROUND, or if it does become airborne, IT MAY FACE UNEXPECTED OR POOR PERFORMANCE DURING FLIGHT. The initial indication of poor performance usually takes place during takeoff. Any item aboard the airplane which increases the total weight significantly is undesirable as far as performance is concerned.

19 MK Airlines Flight 1602, a F, crashed while attempting to take off from Halifax Stanfield International Airport on 14 October The aircraft's take-off weight had been incorrectly calculated, and the plane was only briefly airborne before impacting an Earth berm at the end of the runway. The seven-member crew was killed. It concludes that the crew carelessly transferred and used weight data from the aircraft’s previous flight while calculating performance criteria for the next take-off. The obsolete data misled the crew to derive incorrect thrust settings and critical speeds for take-off. About two-thirds of the way along Halifax’s runway 24, the aircraft rotated, but failed to become airborne. Its tail struck the ground twice, the second time with just 130m (420ft) of the 2,682m runway remaining. The jet overran the runway by 250m and briefly lifted off for a distance of 100m before it struck an earth berm, the impact severing the tail section and causing the 747 to crash 370m beyond. All seven crew members on board were killed.

20 Reduced Climb Performance 4. Lower maximum altitude (ceiling). 5.
EFFECTS OF OVERLOADED AIRCRAFT ON PERFORMANCE 1. Higher Takeoff Speed. 2. Longer Takeoff Run 3. Reduced Climb Performance 4. Lower maximum altitude (ceiling). 5. Lower Cruising Speeds 6.Shorter Range 7.Less Maneuver 8. Reduced Landing Performance 9. Aircraft Structure Damage EFFECT OF OVERLOADED AIRPLANE Increased Takeoff Speed—because more lift is necessary to counter the additional weight, higher speed is necessary to create sufficient lift to attain flight. Longer Takeoff Roll—the increase in necessary speed for takeoff and slower acceleration due to increased weight translates to more runway required to accelerate the airplane to takeoff speed. It is possible to overload an airplane to a point where no amount of runway is sufficient to reach takeoff speed. Were it not for forces such as aerodynamic drag and friction of the landing gear against the runway, this would not be true, but these forces are present and limit the performance of the airplane. Reduced Climb Angle—increases in weight must be countered by additional lift. Lift that is otherwise available for climb performance now must support the additional weight. The airplane's capability to out climb obstructions near the airport may be compromised. Reduced Rate of Climb—for the same reason that the angle at which the airplane can climb is reduced, the rate at which it can climb is also reduced. This means more problems if an engine fails during or shortly after takeoff. Lower Ceilings—because air density normally decreases as you go up in the atmosphere, there is an altitude at which an airplane climbs no more. This is known as the absolute ceiling of the airplane, and it occurs where the maximum indicated airspeed in level flight is just above stall speed. As the weight of the airplane is increased, the stall speed increases. Accordingly, an increase in weight results in a reduction in absolute ceiling and, in severe situations where there is high terrain, it may be impossible for the airplane to climb above the terrain. Lower Cruising Speeds—production of additional lift to counteract greater weight results in an increase in drag. This increased drag reduces the speed at which the airplane travels, thereby exacerbating the problem of the increased stall speed. Shorter Range —because cruising speeds are reduced by overloading the airplane, the range of the airplane is also reduced. On a trip that calls for most of the airplane's normal range, the destination may prove to be unreachable. Less Maneuverability—the heavier the airplane is, the less maneuverable it becomes. This is so because the force necessary to change the speed or direction of an object in motion increases with the mass of the object. Higher Landing Speeds—because stall speed is higher when the airplane is overloaded, higher approach and landing speeds are necessary. Greater Landing Distance—increases in touchdown speed increase roll out distance exponentially. Therefore, an increase in weight that requires touchdown at a speed that is only five percent greater than normal may have a significant impact on the required runway length. Aircraft Structure Overload—although the primary concern of an overloaded airplane is its effect on aerodynamic performance, a secondary concern is its effect on structural components, such as landing gears.

21 Effects Of overloaded airplane
1. Increased Take-off Speed Because more lift is necessary to counter the additional weight, higher speed is necessary to create sufficient lift to attain flight. 2. Longer Take-off Run The increase in necessary speed for takeoff and slower acceleration due to increased weight translates to more runway required to accelerate the airplane to takeoff speed. Climb angle: Rate of Climb: Ceilings: Range: Maneuverability:

22 Effects Of overloaded airplane
3. Reduced Climb Angle Increases in weight must be countered by additional lift. Lift that is otherwise available for climb performance now must support the additional weight. The airplane's capability to out climb obstructions near the airport may be compromised. 4. Lower Ceilings (ceiling=maximum altitude can reach by aircraft) An increase in weight results in a reduction in absolute ceiling and, in severe situations where there is high terrain, it may be impossible for the airplane to climb above the terrain.

23 Effects Of overloaded airplane
5. Lower Cruising Speeds Production of additional lift to counteract greater weight results in an increase in drag. This increased drag reduces the speed at which the airplane travels. 6. Shorter Range Because cruising speeds are reduced by overloading the airplane, the range of the airplane is also reduced. On a trip that calls for most of the airplane's normal range, the destination may prove to be unreachable.

24 Effects Of overloaded airplane
7.Less Maneuverability The heavier the airplane is, the less maneuverable it becomes. This is so because the force necessary to change the speed or direction of an object in motion increases with the mass of the object. Maneuverability = aircraft ability to turn away from its previous path.

25 Effects Of overloaded airplane
8. Reduced Landing Performance Overloaded can cause higher approach and landing speeds are necessary. Higher landing speed thus lead to greater landing distance. 9. Aircraft Structure Damage Although the primary concern of an overloaded airplane is its effect on aerodynamic performance, a secondary concern is its effect on structural components, such as landing gears.