The Aviation Science

APU Fire Detection & Extinguishing System 🛩️The APU fire protection system is similar in design to engine fire protection systems, but there are some differences. The APU is often operated with no personnel in the flight deck and; the APU fire protection system can operate in an unattended mode on the ground with the engines not running. 🛩️If there is an APU fire in the unattended mode, the fire extinguisher discharges automatically. The APU operates in the attended mode when at least one engine is running. If there is an APU fire in this mode, the crew discharges the bottle manually. Fire switches are located on the cargo fire/ engine control panel and the service and APU shutdown panel located outside the airplane on the nose landing gear. 🛩️If there is an APU fire, the APU fire detection system gives fire warnings and automatically stops the APU. The APU fire warning light comes on to identify the correct fire switch to use to extinguish the fire. The fire switch sole...

Helicopter Structure 🛩️The major components of a helicopter are the airframe, fuselage, landing gear, powerplant/ transmission, main rotor system, and antitorque system. 🛩️The airframe, or fundamental structure, of a helicopter can be made of either metal or wood composite materials, or some combination of the two. Typically, a composite component consists of many layers of fiber- impregnated resins, bonded to form a smooth panel. Tubular and sheet metal substructures are. 🛩️The major components of a helicopter are the airframe, fuselage, landing gear, powerplant/ transmission, main rotor system, and antitorque system. 🛩️The airframe, or fundamental structure, of a helicopter can be made of either metal or wood composite materials, or some combination of the two. Typically, a composite component consists of many layers of fiber- impregnated resins, bonded to form a smooth panel. Tubular and sheet metal substructures are usually made of aluminum, though stainless steel or...

Helicopter Flight Control System 🛩️helicopter pilot manipulates the helicopter flight controls to achieve and maintain controlled aerodynamic flight. 🛩️Changes to the helicopter flight control system transmit mechanically to the rotor, producing aerodynamic effects on the rotor blades that make the helicopter move in a deliberate way. 🛩️To tilt forward and back (pitch) or sideways (roll), requires that the controls alter the angle of attack of the main rotor blades cyclically during rotation, creating differing amounts of lift(forces) at different points in the cycle. 🛩️To increase or decrease overall lift requires that the controls alter the AoA for all blades collectively by equal amounts at the same time, resulting in ascent, descent, acceleration and deceleration. 🛩️A typical helicopter has three flight control inputs—the cyclic stick, the collective lever, and the anti-torque pedals. 🛩️Depending on the complexity of the helicop...

Transonic Area Rule 🛩️The Transonic area rule, also called the Whitcomb area rule, is a design technique used to reduce an aircraft's drag at transonic and supersonic speeds, particularly between Mach 0.75 and 1.2. 🛩️This is one of the most important operating speed ranges for commercial and military fixed-wing aircraft today, with transonic acceleration being considered an important performance metric for combat aircraft and necessarily dependent upon transonic drag. 🛩️At high-subsonic flight speeds, the local speed of the airflow can reach the speed of sound where the flow accelerates around the aircraft body and wings. The speed at which this development occurs varies from aircraft to aircraft and is known as the critical Mach number. 🛩️The resulting shock waves formed at these points of sonic flow can result in a sudden increase in drag, called wave drag. To reduce the number and power of these shock waves, an a...

Types Shock Waves 🛩️In physics, a shock wave is a type of propagating disturbance that moves faster than the local speed of sound in the medium. A shock wave carries energy and can propagate through a medium but is characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density of the medium. ✈️Normal Shocks 🛫In elementary fluid mechanics utilizing ideal gases, a shock wave is treated as a discontinuity where entropy increases over a nearly infinitesimal region. Since no fluid flow is discontinuous, a control volume is established around the shock wave, with the control surfaces that bound this volume parallel to the shock wave (with one surface on the pre-shock side of the fluid medium and one on the post-shock side). The two surfaces are separated by a very small depth such that the shock itself is entirely contained between them. Taking into account the established assumptions, in a system where the downstrea...

Automatic Direction Finder 🛩️ADF (Automatic Direction Finder) is the radio signals in the low to medium frequency band of 190 Khz. to 1750 Khz. 🛩️It has the major advantage over VOR navigation in the reception is not limited to line of sight distance. 🛩️The ADF signals follow the curvature of the earth. 🛩️The maximum of distance is depend on the power of the beacon. 🛩️The ADF can receives on both AM radio station and NDB (Non-Directional Beacon). 🛩️Commercial AM radio stations broadcast on 540 to 1620 Khz. Non-Directional Beacon operate in the frequency band of 190 to 535 Khz. ✈️ADF COMPONENTS ✈️ADF Receiver: pilot can tune the station desired and to select the mode of operation. The signal is received, amplified, and converted to audible voice or morse code transmission and powers the bearing indicator. ✈️Control Box (Digital Readout Type) : Most modern aircraft has this type of control in the cockpit. In this equipment the frequency tuned is displayed as digital...

Non Directional Beacon 🛩️A Non-Directional Beacon is a ground-based, low frequency radio transmitter used as an instrument approach for airports and offshore platforms. 🛩️The NDB transmits an omni-directional signal that is received by the Automatic Direction Finder, a standard instrument onboard aircraft. 🛩️The pilot uses the ADF to determine the direction to the NDB relative to the aircraft. 🛩️To navigate using the ADF, the pilot enters the frequency of the NDB and the compass card (or arrow) on the ADF will indicate the heading to the station. 🛩️The signal is transmitted on an uninterrupted 24/7 basis. 🛩️An audible Morse Code call sign of one or more letters or numbers is used to identify the NDB being received. 🛩️NDB’s used for aviation are standardized by ICAO, Annex 10 which specifies that NDB be operated on a frequency between 190 to 1800 kHz. 🛩️In North America, the frequency range is typically from 190 to 625 kHz, for offshore operation...

Runway Designation 🛩️Since aircraft are affected by the wind during takeoffs and landings, runways are laid out according to the local prevailing winds. 🛩️Runways are numbered (designated) to the nearest 10° in relation to magnetic north based on approach direction. ✈️Example: 084° is marked 08 ✈️Example: 085° is marked 08 or 09 ✈️Example: 086° is marked 09 🛩️This number becomes the runway's name, and is how it is referenced by Air Traffic Control (ATC)and other pilots. 🛩️The opposite end of the runway is then marked with the reciprocal heading. 🛩️Reciprocal heading is determined by adding or subtracting 180° from the runway heading. 🛩️You must therefore add 180 to any runway 180 or below, and subtract 180 to anything 180 or above. ✈️Example: (using runway 26) 260° - 180° = 080° ✈️Example: (using runway 08) 080° + 180° = 260° 🛩️If your answer comes out to be greater than 360, or negative, then you added when you should have subtrac...

Microwave Landing System 🛩️The microwave landing system (MLS) is an all-weather, precision radio guidance system intended to be installed at large airports to assist aircraft in landing, including 'blind landings'. 🛩️MLS enables an approaching aircraft to determine when it's aligned with the destination runway and on the correct glidepath for a safe landing. 🛩️MLS has a number of operational advantages over ILS, including a wider selection of channels to avoid interference with nearby installations, excellent performance in all weather, a small "footprint" at the airports, and wide vertical and horizontal "capture" angles that allowed approaches from wider areas around the airport. 🛩️MLS employs 5 GHz transmitters at the landing place which use passive electronically scanned arrays to send scanning beams towards approaching aircraft. 🛩️An aircraft that enters the scanned volume uses a special receiver that calculates its positi...

Instrument Landing System 🛩️An Instrument Landing System (ILS) enables pilots to conduct an instrument approach to landing if they are unable to establish visual contact with the runway. 🛩️It is defined by the International Telecommunication Union as a service provided by a station. 🛩️The ILS works using two components, a localizer and a glideslope. 🛩️The frequencies for the localizer are between 108.1-111.95 MHz and the glide slope between 329.15-335.0 MHz. 🛩️These frequencies are the carrier waves that the modulation takes place. 🛩️A pilot is only concerned with the localizer frequency as the navigation equipment knows the paired glideslope frequency for any given localizer frequency. 🛩️The localizer antenna broadcasts two lobes down the length of the runway for a few miles (typically 18 nm). 🛩️The glideslope antenna sits around the 1000 ft touchdown zone markers on the runway, offset a little bit from the runway. 🛩️It broadc...

PAPI & VASI 🛩️ The visual approach slope indicator (VASI) is a system of lights on the side of an airport runway threshold that provides visual descent guidance information during approach. 🛩️These lights may be visible from up to 8 kilometres (5.0 mi) during the day and up to 32 kilometres (20 mi) or more at night. 🛩️Basic visual approach slope indicators consist of one set of lights set up some 7 metres (23 ft) from the start of the runway. 🛩️Each light is designed so that it appears as either white or red, depending on the angle at which it is viewed. 🛩️When the pilot is approaching the lights at the proper angle, meaning the pilot is on the glide slope, the first set of lights appears white and the second set appears red. 🛩️When both sets appear white, the aircraft is too high, and when both appear red it is too low. 🛩️This used to be the most common type of visual approach slope indicator s...

Primary Flight Display 🛩️A Primary Flight Display or PFD, found in an aircraft equipped with an Electronic Flight Instrument System is the pilot's primary reference for flight information. 🛩️The unit combines the information traditionally displayed on several electromechanical instruments onto a single electronic display reducing pilot workload and enhancing Situational Awareness. 🛩️The layout and information displayed on the PFD varies depending upon manufacturer and installation. 🛩️However, most Primary Flight Displays are configured with a central attitude indicator (AI) and flight director surrounded by other flight parameters. 🛩️Convention normally places the airspeed tape on the left side of the AI and the altitude and vertical speed references on the right. 🛩️Vertical deviation for ILS glideslope or VNAV (vertical navigation) is displayed to the right of the AI while lateral deviation from the ILS, VOR or FMS track is displayed below...

Hydraulic System 🛩️There are multiple applications for hydraulic use in aircraft depending on the complexity of the aircraft. For example, a hydraulic system is often used on small airplanes to operate wheel brakes, retractable landing gear, and some constant speed propellers 🛩️On large airplanes, a hydraulic system is used for flight control surfaces, wing flaps, spoilers, and  other systems 🛩️A basic hydraulic system consists of a reservoir, pump (either hand, electric or engine-driven), a filter to keep the fluid clean, a selector valve to control the direction of flow, a relief valve to relieve excess pressure, and an actuator 🛩️The hydraulic fluid is pumped through the system to an actuator or servo. A servo is a cylinder with a piston inside that turns fluid power into work and creates the power needed to move an aircraft system or flight control. Servos can be either single-acting or double-acting, based on the needs of the system. This means that the fluid ...

🛩️Krueger flaps are lift enhancement devices that are fitted to the leading edge of an aircraft wing. 🛩️Unlike slats or drooped leading edges, the main wing upper surface and its nose is not changed. Instead, a portion of the lower wing is rotated out in front of the main wing leading edge. 🛩️Current Boeing aircraft, and many others, use this design between the fuselage and closest engine, where the wing is thickest. Outboard of the engine, slat flaps are used on the leading edge. The Boeing 727 also used a mix of inboard Krueger flaps and outboard slats, although it had no engine between them. 🛩️Most early jet airliners, such as the Boeing 707 and Boeing 747, used Krueger flaps only. 🛩️The aerodynamic effect of Krueger flaps may be similar to that of slats or slots (in those cases where there is a gap or slot between the flap trailing edge and wing leading edge), they are deployed differently. 🛩️Krueger flaps, hinged at their foremost position that...

🛩️A combustor is a component or area of a gas turbine, ramjet, or scramjet engine where combustion takes place. It is also known as a burner, combustion chamber or flame holder. In a gas turbine engine, combustion chamber is fed high pressure air by the compression system. 🛩️The combustor then heats this air at constant pressure. After heating, air passes from the combustor through the nozzle guide vanes to the turbine. In the case of a ramjet or scramjet engines, the air is directly fed to the nozzle. 𝐀𝐧𝐧𝐮𝐥𝐚𝐫 𝐓𝐲𝐩𝐞 ✈️The most commonly used type of combustor is the fully annular combustor. Annular combustors do away with the separate combustion zones and simply have a continuous liner and casing in a ring. There are many advantages to annular combustors, including more uniform combustion, shorter size, lighter, and less surface area. Annular combustors tend to have very uniform exit temperatures. They also have the lowest pressure drop of the three...