General aircraft science deals with various aspects of aircraft construction. It starts with the various components of an aircraft. It then covers the most important on-board systems in small aircraft, the electrical system and the vacuum system. It continues with the structure and function of a simple piston engine, including fuel supply, system circuits and the propeller as well as mixture regulation by the pilot.
This section also deals with various cockpit instruments that are necessary for visual flights.
Fuselage, tail units, supporting structures, control system and landing gear
This initially involves the various components of an aircraft, such as the fuselage, tail units, supporting structures, control system and landing gear. The design must take extreme situations and forces into account, which is why precision and extensive testing are required. Regular inspection and consideration of the limited service life of the parts used are also important.
Various building materials such as wood, metal and composite materials as well as construction methods are described. A distinction is made between primary and secondary structures. Rivets, adhesives and detachable joints are used for connections. Airworthiness is another key topic, with a particular focus on pre-flight checks and maintenance regulations.
The wings, one of the most important elements, are discussed in terms of their structure, arrangement and shape. The tail unit is used to stabilise and control the aircraft. Various control components, such as elevators, ailerons, trim tabs and airbrakes, are explained.
Finally, the loads to which the aircraft structure is exposed are discussed, including the treatment of static and dynamic loads and the load multiple. Various design approaches such as "Safe Life" and "Fail Safe" are presented to ensure the longevity and safety of aircraft structures.
The landing gear is also specifically addressed. There are different landing gear variants, depending on the surface and location of the aircraft. Most general aviation aircraft have three landing gear legs: two main landing gears and a nose or tail landing gear. The main landing gear bears the main load during landing and is mounted close to the aircraft's centre of gravity.
The nose landing gear, usually with one or two wheels, contains the strut and the shock absorber for a soft landing. It is designed for smaller loads and should only touch the ground after the main landing gear. Control on the ground is via the nose wheel. A flutter damper prevents the nose wheel from running unevenly.
A retractable undercarriage is used to reduce drag and thus increase speed and range, but also adds weight. In the event of a system failure, there is the option of manual emergency landing. The landing gear is monitored by indicator lights in the cockpit.
The brakes, usually fitted to the main landing gear, convert kinetic energy into thermal energy and are designed to withstand heat. Most small aircraft use drum or disc brakes that are operated hydraulically or mechanically. The parking brake is used to prevent the aircraft from rolling away unintentionally.
Tyres that are in direct contact with the ground must be checked regularly for tyre pressure and surface condition. They are filled with air or nitrogen and can be with or without an inner tube. It is important that the tyre is firmly seated on the rim and that the carcass is in good condition. The rims, usually made of light alloy, should also be checked for cracks.
On-board systems in small aircraft
This section emphasises the importance of electrical and vacuum systems in modern aircraft, especially sports aircraft. These systems are crucial for supplying power to various technical aids and monitoring instruments.
The electrical system is a key system that supplies a variety of consumers, including radiotelephony and navigation instruments, sometimes also trim rudders and landing flaps. This system consists of a battery and a generator, which together ensure a constant power supply. The pilot must be well informed about the operating mode of the instruments on board in order to be able to react appropriately in the event of problems. If the generator fails, the on-board battery takes over the power supply.
The vacuum system is often used to supply power to gyro instruments. It works by means of a vacuum pump that is connected to the engine speed and maintains a constant vacuum in the system. This system is primarily responsible for the artificial horizon and the heading gyro, while the rate-of-turn indicator is usually operated electrically.
The theory chapter also explains electrical engineering basics such as atomic models, current and voltage, resistance and how DC generators work. The importance of fuses is emphasised as they prevent excessive current flow and therefore eliminate the risk of fire. Different types of fuses, including fuses and circuit breakers, are discussed.
To summarise, this is a comprehensive introduction to the electrical and pneumatic systems of sports aircraft, which are of crucial importance for functionality and safety on board.
Engines and fuel supply, propellers
The working principle of an aircraft engine is described here. The four-stroke petrol engine, which is predominant in small and medium-sized aircraft, functions through the cyclical repetition of four power strokes: Intake, compression, ignition and exhaust. Each of these cycles plays a decisive role in the power development of the engine. One particular challenge is knocking, an uncontrolled combustion that can be caused by the use of low-octane fuels and can lead to damage to the engine. The core components of the engine, such as cylinders, pistons, piston rings, valves and spark plugs, are essential for the proper functioning of the engine.
The cooling system, usually realised by air cooling in sports aircraft engines, uses air currents and cooling fins to dissipate heat. Overheating, often caused by damaged cooling fins, can cause serious damage to the engine and requires constant monitoring of the cylinder head temperature.
The lubricant system has several important tasks such as lubrication, cooling, sealing, cleaning and corrosion protection. A distinction is made between dry and wet sump lubrication systems, with the latter being used more frequently in boxer engines. The choice of the right oil, be it mineral oil or a semi/fully synthetic oil, is crucial for the performance and protection of the engine.
The ignition system in aeroplanes is usually based on a magneto ignition that works independently of the on-board electrical system. Each cylinder is equipped with two independent ignition systems to increase performance and operational safety. The ignition spark, generated by high-voltage sparks from the spark plugs, is essential for the combustion process.
The starter motor, an electric motor connected to the battery, plays an important role in starting and stopping the engine. It should only be switched on briefly. The engine should be switched off by depleting the mixture and not by switching off the ignition in order to avoid glow ignition.
Finally, regular inspection and maintenance of the engine is of crucial importance. This includes checking the ignition system before every flight and regularly checking and changing the oil and oil filters. These measures are crucial to ensure the safety and performance of the aircraft.
The fuel supply is also covered. The power development in the cylinders of aircraft, which serves as the driving force, results from the combustion of an air-fuel mixture. The oxygen content of the air is used to oxidise the fuel. Depending on the aircraft design and engine, there are different methods of feeding the mixture into the cylinder chambers and regulating the mixture of air and fuel. In sports aircraft, the mixture ratio often has to be adjusted manually.
The fuel used for aircraft is specially designed for aircraft engines and differs from conventional automotive fuel. The knock resistance, which is determined by the octane number, is decisive for the suitability of the fuel. The use of an unsuitable fuel can lead to a loss of performance or engine damage.
There are two main systems for the fuel system in sports aircraft: the gravity system and the fuel pump system. In the gravity system, high-wing and shoulder-wing aircraft use gravity, while low-wing and mid-wing aircraft use an engine-driven fuel pump and an additional electric fuel pump (boost pump).
The mixture in the engines is formed either by carburettors or injection systems. Carburettor systems mix fuel and air in the carburettor before the mixture enters the cylinder chamber, while injection systems feed the fuel directly to the cylinders. Injection systems offer advantages such as smoother engine running and lower fuel consumption.
Manual mixture control is necessary to achieve an optimum fuel-to-air ratio, especially at different altitudes. A mixture that is too rich can lead to undesirable deposits and overheating, while a mixture that is too lean can impair engine performance. The setting is made via the mixture control in the cockpit and is monitored by the exhaust gas and cylinder head temperature.
In addition, there are special challenges such as carburettor icing, which can occur at certain temperature ranges and is prevented by carburettor preheating. The correct treatment of the fuel, such as removing water and checking for impurities, is also crucial for safe flight operations.
The function of the propeller is also described. The propeller of a piston engine converts the power generated during the combustion process in the engine into propulsion. The shape of a propeller is similar to that of an aerofoil, with the lift generated acting in the direction of flight. A propeller consists of a hub and several blades, the number and material of which can vary. The hub is covered by a spinner, which is aerodynamically shaped and provides protection.
The rotation of the propeller blades generates lift in the direction of flight. The pitch angle of the blades is crucial here. This angle decreases from the inside to the outside of the blade in order to ensure an even thrust force over the entire blade. This adjustment is known as geometric pitch.
The theoretical distance that a propeller would travel during one revolution in a solid medium is the geometric pitch. The actual distance travelled by the propeller in the air is the aerodynamic pitch. The difference between the two is the slip. The efficiency of a propeller depends on the pitch and the airspeed. With fixed pitch propellers, the best efficiency can only be achieved at a certain speed.
The controllable pitch propeller (constant speed propeller) enables the angle of attack to be adapted to different flight phases, so that a high degree of efficiency is achieved over a wide speed range. The power setting for variable pitch propellers is made via the speed and the boost pressure. The propeller governor controls the adjustment of the propeller hydraulically, electrically, mechanically or pneumatically. If the governor fails, the propeller adjusts itself to the smallest pitch.
The torque effect describes the development of force against the direction of rotation of the propeller, which leads to a yaw tendency. During the climb, the angle of attack can change, which leads to an uneven thrust distribution and also causes yaw tendencies.
In summary, the propeller is an essential component of a piston engine whose design and operation are optimised to convert rotary motion into propulsion. The adjustment of the angle of attack by variable pitch propellers enables efficient power generation across different flight phases.
On-board instruments
The instrumentation of aircraft varies depending on their intended use. Important flight monitoring instruments are the airspeed indicator for measuring speed, the artificial horizon for determining the position, the altimeter for indicating altitude and the gyro for indicating the direction of flight. Ideally, these should be arranged in a "T" layout. Other important instruments are the turn indicator and the variometer, which indicates the rate of climb or descent.
Navigation instruments support navigation, even without outward visibility, while engine monitoring instruments provide information on the condition of the engine. System monitoring instruments monitor electrical, pneumatic and hydraulic systems.
The pressurisation system measures static pressure and dynamic pressure for the instrument display. Static pressure is measured via small openings on the fuselage, total pressure through the pitot tube. Blockages in the pressurisation system can lead to incorrect readings.
The barometric altimeter displays the altitude above a set reference pressure surface, whereby the reference pressure value can be varied using a setting knob. The altitude measurement is based on the decrease in air pressure with increasing altitude. The display is in feet or metres.
The airspeed indicator shows the speed based on a pressure difference measurement between total pressure and static pressure, usually in knots. Coloured markings on the airspeed indicator show important speed ranges or limits.
The variometer displays the vertical speed based on the change in static pressure with height. It measures the vertical speed by means of a diaphragm can, which is directly connected to the static pressure system.
Errors in the printing system, such as blockages, have a considerable influence on the accuracy of these instruments and must therefore be carefully checked.
The gyro instruments used in aviation, such as the heading gyro, the artificial horizon and the turn indicator, utilise the properties of rotating gyroscopes to describe the position of an aircraft in space. Gyroscopes are bodies that can rotate around an axis and whose mass is evenly distributed. They maintain their position in space due to inertia. The plane of rotation is perpendicular to the axis of rotation and the total angular momentum remains constant as long as no external forces are acting. The stability of a gyroscope depends on its mass, the distance to the centre of rotation and the rotational speed. The drive is either pneumatic or electric.
When an external force is applied, the gyroscope reacts with an evasive movement, known as precession, which is perpendicular to the applied force. The amount of precession depends on the force applied and the inertia of the gyroscope. A perfect gyroscope would maintain its position in space, but in reality various causes such as friction on bearings or the rotation of the earth cause the gyroscope to move.
The heading gyro indicates the course being flown and must be readjusted before each flight and regularly during the flight. The artificial horizon indicates the flight attitude around the longitudinal and lateral axes in relation to the earth's surface, which is particularly important for instrument flight. The direction and speed of rotation around the vertical axis and the coordination of the turn can be read off the turn indicator. A spherical level shows whether there is a balance of forces in the turn.
These instruments are susceptible to various errors such as acceleration error, parallax error and gimbal error. They must be regularly checked and correctly adjusted in order to provide accurate information.
The engine monitoring instruments in the cockpit provide the pilot with essential information about the condition of the engine. A thorough familiarisation with these instruments is therefore essential, as the equipment differs depending on the aircraft model. Important standard instruments are the rev counter (possibly with boost pressure indicator), oil pressure and oil temperature indicators, cylinder head temperature and exhaust gas temperature indicators as well as fuel flow and fuel level indicators.
The rev counter displays the revolutions of the crankshaft. There are mechanical local tachometers for single-engine piston aeroplanes and electrical remote tachometers for larger or multi-engine aeroplanes. An operating hours counter is often integrated. However, the tachometer is not an accurate indicator of engine performance, especially at high altitudes.
The manifold pressure gauge is necessary for aircraft with variable pitch propellers and indicates the pressure in the intake manifold. It works according to the barometric principle and is an important indicator of engine performance.
The oil pressure indicator monitors the oil circuit and is particularly important for recognising problems with the engine at an early stage. The minimum and maximum permitted oil pressure are indicated by red lines. The oil temperature display supplements the pressure display and helps to interpret engine problems. Both values should be considered together as they are directly related.
The cylinder head temperature gauge (CHT) measures the temperature at the most critical cylinder and reacts faster to engine temperature changes than the oil temperature.
The exhaust gas temperature indicator (EGT) is relevant for adjusting the mixture and maximising engine performance. It measures the temperature in the exhaust gases and helps to control combustion.
The fuel flow indicator measures the fuel consumption per hour and helps to calculate the remaining flight time. The fuel level indicator shows the available fuel, whereby each tank normally has a separate indicator.
In addition to these main instruments, there are other important displays such as the vacuum gauge for checking the vacuum system and the ammeter, which shows either the battery charging current or the total current consumption.
Coloured markings on the instruments make it possible to quickly identify the operating status: Green indicates normal operation, yellow stands for caution and red indicates a problem.
It is important that pilots familiarise themselves thoroughly with the specific instruments of their aircraft model before each flight.