Turbofan airliners Turboprop airliners Business jets Business turboprops Turbine helicopters Light aircraft 50 75 30 80 3 75 5 8 3 8 nm. For shorter stages the coefficient will be less and the reserves smaller. These ratios can be assumed to be similar to aircraft of the same type and size if the absolute mass is difficult to determine. Example To illustrate the use of the initial estimation method described above, consider the design of a medium size seats , medium range nm aircraft. Assumed cruise speed is kt
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Turbofan airliners Turboprop airliners Business jets Business turboprops Turbine helicopters Light aircraft 50 75 30 80 3 75 5 8 3 8 nm. For shorter stages the coefficient will be less and the reserves smaller.
These ratios can be assumed to be similar to aircraft of the same type and size if the absolute mass is difficult to determine. Example To illustrate the use of the initial estimation method described above, consider the design of a medium size seats , medium range nm aircraft.
Assumed cruise speed is kt Because of this sensitivity the initial estimation must be checked against more detailed methods as soon as the aircraft layout is defined in more detail. Detailed mass estimation As more details of the aircraft become known it is possible to use more accurate methods to predict component masses. Ultimately, when the detail drawings of all the components are available, more accurate estimates can be made by calculating the volume of each part and multiplying by the density of the material.
In the project design stages we are unlikely to know the size of individual aircraft components to this level of detail but it is possible to use prediction methods that progressively become more accurate as the aircraft geometry is developed.
Most aircraft design textbooks3 contain such methods. A set of equations using some of the aircraft geometrical data is presented below. Operationally the aircraft will have various take-off masses depending on the stage length and payload. This will give confidence to the prediction and guard against inappropriate use of formulae. When it is impossible to determine the absolute mass of a component perhaps because insufficient details are available it is acceptable to use a standardised mass ratio, i.
This procedure is often used in the early stages of project design. The component mass estimating methods presented below are derived from statistical data of existing aircraft. In general, the aircraft on which the data is based will be of conventional layout with a semi-monocoque aluminium alloy structural framework.
For designs not of this layout or manufactured from other materials the estimates will need to be suitably adjusted. Detail mass formulae will vary for different types of aircraft e. The formulae quoted in the sections below are taken from detailed mass statements of existing civil transport aircraft. Each of the component mass groups in the mass list above will now be considered separately.
Wing group Mw The wing group is assumed to comprise all the structural items on the wing including surface controls ailerons, flaps, lift dumpers, etc. As the design unfolds and more detailed geometric data are known it is possible to use formulae which include specific wing parameters. The expression shown below has been developed for conventional aircraft wing geometry made from aluminium alloy.
It accounts for different materials used in the structural framework. The method is long and complex and should therefore be used when the aircraft configuration is frozen i. Wing flaps, etc. For initial stages of the design process when details of the flaps, etc. Other factors. For aircraft with rear fuselage mounted engines the wing mass M w will be increased due to the lack of inertia relief on the wing structure cf. Tail group M x Although tail mass is not a large fraction of MTOM9 it is necessary to evaluate it accurately because it is positioned well aft of the aircraft centre of gravity.
The tail mass will therefore affect the overall balance of the aircraft. For tail configurations with higher than normal span and for large areas, the higher values should be substituted. When more details are known an analysis similar to the main wing mass estimation can be used.
The above analysis is based on conventional aluminium structures. Body fuselage mass M B The mass of the body is obviously dependent on the size of the fuselage, the aircraft layout e.
Nacelle mass M N Mass items to be attributed to the nacelle group are difficult to specify since some of the structure may be regarded as part of the wing, body, propulsion, or undercarriage groups. Care must be taken when assigning detailed estimates to avoid double accounting of mass items with other component mass groups. The nacelle mass is proportional to the size of the engine and the type of cowling specified short, three-quarter, or full.
In the initial design stages an estimate of the installed required thrust will have been made but the engine configuration may not be known. Details of the nacelle mass for some existing aircraft are shown in Fig. Landing gear mass M u c The mass of the undercarriage will depend on the specified maximum landing mass and the rough field landing capability of the aircraft.
In the initial design stages decisions will not have been taken on the landing mass specification. To avoid the need for fuel dumping many aircraft are now designed for a landing weight close to the maximum take-off weight. When no other information is available use the aircraft MTOM value as used in the expression below. As most airlines are operated from good quality paved runways the main variation lies in the degree of complication, and the degree of compactness necessary i.
Figure 7. For a new aircraft design the landing gear is expected to weigh less than given by the above expression assume 4. Of course this saving will be associated with a slight cost increase for the landing gear.
Aircraft configuration will affect the design of the undercarriage and therefore its weight. Multiply the estimated weight by 1.
Note, care must be taken when comparing landing gear mass from different aircraft as some manufacturers install gear that will be suitable for future larger Landing gear group mass kg 4.
This avoids some of the undercarriage design and certification costs for the development aircraft. For aircraft balance assume the main units are Surface controls M s c The surface controls include all the movable surfaces on the wing that have not been included in the flap mass calculation.
The group includes all the internal wing controls and the controls for external leading edge devices e. If more complex or extensive leading edge flap system or lift dumpers are specified the value should be increased. For simple control systems e.
As a general guide in the early less detailed project phase it is acceptable to assume the structure mass to be about one third aircraft take-off mass i. E Total propulsion group mass M PROP In the early parts of the design process details of all the components in this mass group are unknown. It is therefore necessary to base estimates on the bare engines mass. For current large turbofan engines the specific mass is a function of bypass ratio as shown below.
The relationship in Fig. The increase in mass over the bare engine value is difficult to assess in general terms as it is associated with the operational specification of the engine e. X-Existing aircraft Dry engine mass kg Fig. Items in this mass group are very variable in type e. The items to be included depend textbooks and aircraft group for a variety of be specified the value operation: on operational practices and aircraft specification.
Various manuals list the actual masses for components in this mass different aircraft. Advances in computer and control systems technology will change the size and mass of systems considerably. You are advised to consider this mass group in detail as soon as the aircraft system information and specification is known so that a check can be made on the value assumed from the ratio above. S Operational items mass M OP Some of the operational items are specific to the type of aircraft and other operational practices and must be assessed individually.
Allow 10 kg total although with the introduction of on-line computer stored data this could be reduced e. Minimum numbers are set by the airworthiness authorities. For a conventional aircraft a minimum of two flight crew will be necessary but this must be increased for long-haul duration flights to allow the pilots rest periods. The number of cabin staff will be a function of the seating layout and the emergency evacuation process.
For normal scheduled services allow one attendant for economy-class seats, one for business-class seats, and one for each first-class passengers.
Allow 93 kg for each flight crew member and 63 kg for each of the cabin staff presumably they are usually much slimmer! The number of passengers to be carried in each class and the extra cargo will form part of the design brief. The range over which this load is to be flown is also likely to be specified. This range will need to be related to a fuel load, taking into account reserve fuel and contingencies.
Some items may be particular to the type of aircraft and its operation. This dictates the space required in the cargo holds for passenger luggage but extra volume will be required for the specified freight load. Reserve and contingency allowances will be added to the fuel needed to fly the operation, to allow for any flight diversions and hold and to provide for adverse weather or for other extra fuel use.
The total maximum fuel will be limited by the size of the available fuel tanks. The density of fuel used in aircraft engines varies according to the type. Specific gravity will be between 0. With an assumed density and a calculated amount of fuel required a check must be made on the volume required and this compared to the available space in the wings etc.
SS Aircraft maximum takeoff mass MTOM The maximum take-off mass for the aircraft will be equal to the sum of the aircraft empty mass, operational items mass, payload and the fuel mass. The MTOM will assume a combination of payload and fuel load appropriate to the design specification.
The aircraft will be designed to fly safely at this value of MTOM and the Certificate of Airworthiness will permit operation of the aircraft up to but not beyond this limit. The MTOM is therefore one of the most significant parameters of the design. Aircraft mass statement It has become normal practice in aircraft design to list the various components of aircraft mass in a standard format. The components are grouped in convenient sub-sections as shown below. Auxiliary power unit Flight control systems sometimes included in MSTR Instruments and navigation equipment Hydraulic systems Electrical systems Avionics systems Furnishing Air conditioning and anti-icing Oxygen system Miscellaneous e.
Crew provisions manuals, maps Passenger cabin supplies passenger seats are sometimes included Water and toilet chemicals Safety equipment e. Flight crew 2. Passengers and baggage 2. Weight at the start of take-off will vary depending on the payload and fuel required to fly the range. These are operational considerations relating to the service to be flown.
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