Aircraft characteristics

Aircraft characteristics are of prime importance to the airport planner and designer. The following characteristics need to be studied

1. Type of propulsion

2. Size of aircraft

3. Minimum turning radius

4. Minimum circling radius

5. Speed of aircraft

6. Capacity of aircraft

7. Aircraft weight and wheel configuration

8. Jet blast

9. Fuel spillage

10. Noise

Type of propulsion

The size of aircraft, its circling radius, speed characteristics, weight carrying capacity, noise nuisance etc,. depends upon the type of propulsion of the aircraft. The performance characteristics of aircrafts, which determine the basic runway length, also depends upon the type of propulsion

Size of Aircraft

The size of aircraft involves following important dimensions:

1. Wing span

2. Fuselage length

3. Height

4. Distance between main gear

The wing span decides the width of taxiway, separation clearance between two parallel traffic ways, size of apron and hangers, width of hanger gates.

The length of the aircraft decides the widening of taxiways on curves, size of apron hanger etc.

The height of the aircraft decides the height of the hangar gate.

Wheel base affect the minimum turning radius of the aircraft.

Minimum circling radius

In order to decide the radius of taxiway, the position of aircraft in loading apron and hangars and to establish the path of the movement of aircraft, it is very essential to study the geometry of the turning movement of aircrafts.

Minimum circling radius

There is certain minimum radius with which the aircraft can take turn in space. This radius depends upon the type of aircraft, air traffic volume and weather conditions. The radii recommended for different types of aircrafts are as follows.

1. Small general aviation aircrafts = 1.6 km

2. Bigger aircrafts say two piston = 3.2 km

3. Piston engine aircraft under IFR =13 km

4. Jet enginer aircrafts under IFR = 80 km

IFR= Instrument Flight rules

Speed of aircrafts

The speed of aircraft can be defined in two ways viz., crusing speed and air speed. Crusing speed is the speed of aircraft with respect to the ground when the aircraft is flying in air its maximum speed. Air speed is the speed of aircraft relative to wind.

Aircraft capacity

The number of passengers, baggage, cargo and fuel that can be accommodated in the aircrafts depend upon the capacity of the aircraft. The capacity of aircraft using an airport have an important effect on the capacity of runway system as well as that of the passenger processing terminal facilities.

Weight of aircraft and wheel configuration

Weight of the aircraft directly influence the length of the runway as well as the structural requirements. i.e, the thickness of the runway, taxiway, apron and hangers. It depends not only on the weight of the passenger baggage, cargo and fuel it is carrying and its structural weight, but also the fuel which is continuously decreasing during the course of the flight.

Jet Blast

At relatively high velocities, the aircrafts eject hot exhaust gases. The velocity of jet blast may be as high as 300 Kmph. This high velocity causes inconvenience to the passengers travelling in the aircraft. several types of blast fences or jet blast deflector are available to serve as an effective measure for diverting the smoke ejected by the engine to avoid the inconvenience to the passengers. Since, the bituminous pavements are affected by the jet blast, therefore, it is desirable to provide cement concrete pavement at least at the touch down portion to resist the effect of blast in preference to the bituminous pavements.

Fuel spillage

At loading apron and hangars, it is difficult to avoid spillage completely, but effort should be made to bring it within minimum limit. The bituminous pavements are seriously affected by the fuel spillage and therefore, it is essential that the areas of bituminous pavements under fueling inlets,

Noise

Noise generated by aircraft create problems in making decision on layout and capacity. The correct assessment of future noise patterns to minimize the effect on surrounding communities

Correlation between aircraft characteristics and airport planning

Sl.No

Aircraft Characteristics

Impacted Airport Design element

1

Wing Span

Width of taxiway, clearance between parallel taxiways, size of apron, Hanger

2

Height of aircraft

Height of hanger gate

3

Wheel Base

Turning Radius of taxi ways

4

Aircraft capacity

Capacity of runway system and terminal facilities

5

Wheel configurations

Length of runway

6

Aircraft Velocity

Bituminous pavements are affected by jet balst. Cement concrete pavements are required. Therefore, effect of jet blast decides position, size and location of gates

7

Noise

Optimal layout of runway to minimize effect on surrounding communities

Airport layout

Airport layout components

The main components of an airport layout are:

1. Airport consists of following

a. Landing strip, consisting of a runway, shoulder and stop ways

b. Taxiways

c. Apron

2. Terminal area, consisting of the following

a. Gates

b. Terminal building

c. Aircraft service facilities

3. Flight support area, consisting of structures and facilities for air traffic control, navigation aids, fuelling the aircraft

The runway is a strip provided specifically for landing and take-off. It is generally paved. Shoulders are provided on either side of the runway to serve as safety zones should an aircraft go off the runway sideways during landing or take off. They are generally unpaced.

Stopways are provided at the ends of a runway, again for safety, to accommodate an aircraft that overshoots or undershoots a runway during landing or has an aborted takeoff

A taxiway is a strip connecting runways with one another and with the aircraft parking apron

The apron is the hard standing area where aircraft are parked. Passengers emplane/ deplane here and cargo is loaded/unloaded here without interference to aircraft operation. Fuelling and other servicing is also carried out here. The aprons are subjected to higher stresses than a runway due to slow moving or stationary position of aircrafts. Apron in airport are synonymous with platforms in railway stations, jetties in harbour and ports. The size of the apron depends on

1. Type of airports

2. Number and type of aircrafts using the airports

3. Basic configuration of aircrafts

A holding apron is the portion provided near the end of a runway for engine run-up and for hatching or unhatching vehicles towing the aircraft. They also serve as the area for aircraft waiting for take-off

The gate is the opening in the terminal building though which passengers enter/ leave the terminal building on arrival/ departure from an aircraft parked in the apron.

Terminal building: Primary function of an airport building is to accommodate terminal and operations activities like control towers, weather bureau, and administrative block and passenger facilities. Location of building with respect to runway and taxiway should provide space for future expansion terminal building should be set back by 150 m and 75 m for instrumental and non-instrumental landing systems respectively.

Hangers refered to large sheds where repair, renovation, servicing and fuelling of aircrafts are undertaken. Hangers are usually steel framed structures with ventilation as essential requirement. Machine shops and spare parts stores are provided within hangears. Size and number of hangers depend upon the demand .

Flight support area consists of a number of structures and facilities for air traffic control navigation aids and fuelling the aircraft

Regional planning

The planning of an airport should be done considering the air traffic needs of the nation as a whole rather than an individual locality. Airport planning including the airport administration, if not done on regional basis, would seriously impair the effective air traffic services of the country. It may further result in surplus or shortage of airport facilities on regional basis. Improper location of the airport in relation to the area served would result in unrealistic planning and undesirable air space conflicts.

Airport planning on regional basis avoids the creation of separate airports by individual jurisdiction.

The regional plan usually provides the following information:

1. Approximate location of airports in national map

2. Classification of airport

3. Location of air strips

4. Routes of air travel

The following data needs to be collected for a scientific and sound planning on regional basis

1. Population

2. Topographical and geographical features

3. Existing airports in the vicinity

4. Air traffic characterisitics

Population

The population growth of an area to be served and the character of population based on the income groups and activities should be determined. The trend and needs of the people towards saving of travel time should also be studied.

Topographical and geographical features

Sometimes because of the topography, air service is the only accessible mode of transportation. The geographical location of the area to be served is also equally important.

Existing airports in the vicinity

Distance, population and economic charater of the adjoining areas having air service should be studied. Two nearby airports should be located sufficiently apart so that the encircling radii of two aircraft landing simultaneously do not overlap

Air traffic characteristics

Various existing modes of transport, with their merits and demerits in the area to be served, should be carefully studied. The future expected volume of air traffic in terms of passengers, cargo, mail etc., and the number of aircraft movements required for the above should also be determined.

Airport site selection

The selection of a suitable site for an airport depends upon the class of airport under consideration. However, if such factors as required for the selection of the largest facility are considered, the development of airport by stages will be made easier and economical. The factors listed below are for the selection of a suitable site for a major airport installation:

1. Regional plan

2. Airport use

3. Proximity of other airports

4. Ground accessibility

5. Topography

6. Obstructions

7. Visibility

8. Wind

9. Noise nuisance

10. Grading, drainage and soil characteristics

11. Future development

12. Availability of utilities from town

13. Economic considerations

Regional plan

The site selected should fit well into the regional plan, therby forming it an integral part of the national network of airport

Airport use

The selection of site depends upon the use of an airport i.e. weather for civil or for military operations. However, during the emergency, civilian airports are taken over by the defence. Therefore, the airport site selected should be such that it provides natural protection to area from air raids.

Proximity to other airports

The site should be selected at a considerable distance from the existing airports so that the aircrafts landing in one airport does not interfere with the movement of aircraft at other airport. The required separation between the airports mainly depend upon the volume of air traffic, the type of aircraft and the air traffic control,.i.e. weather the airports are equipped with instrumental landing facilities or not.

Ground accessibility

The site should be so selected that it is readily accessible to the users. The airline passenger is more concerned with the door-to-door time rather than the actual time in air travel. The time to reach the airport is, therefore, an important consideration specillay for short haul operations. The time required to reach an airport in a passenger car, from the business or residential centres should normally not exceed 30 min. the best location is a site adjacent to the main highway.

Topography

This includes natural features like ground contors, trees, streams etc. a raised ground e.g. a hill top os usually considered to be an ideal site for an airport. The reasons are.

1. Less obstruction in approach zones and turning zones

2. Natural drainage, low land may result in flooding

3. More uniform wind

4. Better visibility due to less fog

Obstructions

When aircraft is landing or taking off, it loses or gains altitude very slowly as compared to the forward speed. For this reason, long clearance areas are provided on either side of the runway known as approach areas over which the aircraft can safely gain or lose altitude. The areas should be kept free of obstructions. Obstruction may be consists of fences, tress, pole lines, building and other natural or man made objects, sometimes the ground itself may slope upwards from the end of the runways to such an extent that it forms an obstruction to the aircraft operation. If the obstruction exists around a site over which an airport is to be built, the removal is imperative at any cost.

Visibility

Poor visibility lowers the traffic capacity of the airport. The site selected should therefore be free from visibility reducing conditions, such as fog, smock and haze. Fog generally settles in the area where windblown is minimum. E.g. in a valley areas.

Wind

Runway is so oriented that landing and takeoff is done by heading into the wind. Wind data .i.e., direction, duration and intensity of wind should be collected over a minimum period of about five years. This helps in proper orientation of runway and influence the shape of the site needed for the development of the airport.the site should be located to the windward direction of the city, so that a minimum smoke from the city is blow over the site.

Noise nuisance

The extent of noise nuisance depends upon the limb out path of aircraft, type of engine propulsion and the cross weight of aircrafts. Therefore, the site should be so selected that the landing and take-off paths of the aircrafts pass over the land which is free from residential or industrial development. Sometime buffer zone may have to be provided between the take off end of a runway and a nearby residential area. If buffer zone cannot be provided, some acoustical barrier may have to be installed. Federal Aviation Agency (FAA) recommends that to minimise community disturbance due to noise, the area nearby to the airports should be kept free from the residential development and places of public assembly.

Grading, Drainage and soil Characteristics

Grading and drainage plays an important role in the construction and maintenance of airport which in turn influences the site selection. The original ground profile of a site together with any grading operations, determines the shape of the airport area and the general pattern of the drainage system. Possibility of floods at the valley site should be investigated.

Future development

Considering than the air traffic volume will continue to increase in future, more number of runways may have to be provided for an increased traffic, similarly, more facilities may be required for processing of passengers, baggage and shelter of aircraft.

Availability of utilities from town

An airport has to be provided with facilities like water supply, sewer, telephones, electricity etc. in the selection of site, the availability of these utilities from the town should be given due consideration.

Wind rose diagram

A wind rose is a graphic tool used by meteorologists to give a succinct view of how wind speed and direction are typically distributed at a particular location.

Steps involved in windrose analysis

Step I: Analysis for Wind Direction

Group all winds of a given direction together

Step II: Determination of Frequency of Wind in Wind Direction

Find the number of readings in each directional category and the total number of readings. Then find the percentage that each of the 16 wind directions occurs.

Step III: Analysis for Wind Speed

For each wind direction, group the readings into wind speed categories. For example, use ranges of 3 miles/hour , i.e. calm, 1-3 mph, 4-6 mph, 7-10 mph etc.

For each wind direction, find the percentage of readings in each speed range.

Step IV: Preparation of Polar Diagram

On polar coordinate paper, label each of the 16 wind directions

Plot each wind direction percentage from Step II making the length of each line proportional to its corresponding percentage.

Step V:Result

From the graph obtained in the step 4, use the direction which has the maximum wind frequency as the direction of landing and takeoff for aircrafts.

Windrose type 2

The wind data as in the previous type is used for this case. Each circle represents the wind intensity to some scale. The values entered in each segment represent the percentage of time in a year during which the wind having a particular intensity blows from the respective direction. The procedure for determining the orientation of runway from this type of wind rose is described below.Draw three equi-spaced parallel lines on a transparent paper strip in such a way that the distance between the two nearby parallel lines is equal to the permissible cross wind component. This distance is measured with the same scale with which the wind rose diagram is drawn the permissible cross wind component is 25kph. Place the transparent paper strip over the wind rose diagram in such a way that the central line passes through the centre of the diagram. With the centre of wind rose rotate the tracing paper and place it in such a position that the sum of all the values indicating the duration of wind within the two outer parallel lines is the maximum. The runway should be thus oriented along the direction indicated by the central line. The wind coverage can be calculated by summing up all the percentages.