Lecture 2: Composition of Aircraft Weight

AIRCRAFT (MASS) WEIGHT & PERFORMANCE

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.

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.

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.

Maximum Landing Weight (MLW)

• The maximum permissible weight to conduct a landing.

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.

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.

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

All Up Weight (AUW)

Where,

DOW = Dry Operating WeightPAYLOAD = Passengers & CargoFUEL = Flight Fuel + Reserve Fuel

FUELPAYLOADDOWAUW

Dry Operating Weight (DOW)

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.

Baggage &Crew htBasic WeigDOW

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 TimeWhere, Flight time= Distance / Mean Airspeed

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.

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.

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 FuelZero Fuel consideration : replace AUW as MZFW, and re-arrange

equation as:

Payload = MZFW-DOWBased on the calculation, the lowest result is the maximum

payload that the aircraft is able to carry for a flight.

FUELPAYLOADDOWAUW

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

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

EFFECTS OF OVERLOADED AIRPLANE

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.

MK Airlines Flight 1602, a 747-200F, crashed while attempting to take off from Halifax Stanfield

International Airport on 14 October 2004. 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.

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.

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.

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.

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.

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.