The Aviation Science

Empennage 🛩️The empennage of an aircraft is also known as the tail section. Most empennage designs consist of a tail cone, fixed aerodynamic surfaces or stabilizers, and movable aerodynamic surfaces. 🛩️The tail cone serves to close and streamline the aft end of most fuselages. The cone is made up of structural members like those of the fuselage; however, cones are usually of lighter construction since they receive less stress than the fuselage. 🛩️The other components of the typical empennage are of heavier construction than the tail cone. These members include fixed surfaces that help stabilize the aircraft and movable surfaces that help to direct an aircraft during flight. The fixed surfaces are the horizontal stabilizer and vertical stabilizer. The movable surfaces are usually a rudder located at the aft edge of the vertical stabilizer and an elevator located at the aft edge the horizontal stabilizer. 🛩️The structure of the stabilizers is very similar to that which ...

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...

Five Major Stresses 🛩️Aircraft structural members are designed to carry a load or to resist stress. Aircraft parts must be planned to carry the load to be imposed upon it. 🛩️The term stress is often used interchangeably with the word “strain.” They are not the same thing. External loads or forces cause stress. Stress is a material’s internal resistance, or counterforce, that opposes deformation. The degree of deformation of a material is strain. When a material is subjected to a load or force, that material is deformed, regardless of how strong the material is or how light the load is. 🛩️Here 5 major stresses to which aircraft is subjected ✳️Tension ✳️Compression ✳️Torsion ✳️Shear ✳️Bending ✈️Tension is the stress that resists a force that tends to pull something apart. The engine pulls the aircraft forward, but air resistance tries to hold it back. The result is tension, which stretches the aircraft. The tensile strength of a material is measured in pounds per square inc...

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 can be...

Basic Clouds 🛩️Cloud type is determined by its height, shape, & characteristics. They are classified according to the height of their bases as low, middle, or high clouds, as well as clouds with vertical development. 🛩️Low clouds are those that form near the Earth’s surface and extend up to about 6,500 feet AGL. They are made of water droplets but can include supercooled water droplets that induce hazardous aircraft icing. Typical low clouds are stratus, stratocumulus, nimbostratus. Fog is also low cloud formation. This Clouds create low ceilings, hamper visibility, & can change rapidly. They influence flight planning & can make visual flight rules (VFR) flight impossible. 🛩️Middle clouds form around 6,500 feet AGL & extend up to 20,000 feet AGL. They are composed of water, ice crystals, & supercooled water droplets. Typical middle-level clouds include altostratus & altocumulus. These types of clouds are encountered on cross-country flights at highe...

Lateral and Longitudinal Balance 🛩️Balance refers to the location of the CG of an aircraft, and is important to stability and safety in flight. The CG is a point at which the aircraft would balance if it were suspended at that point. 🛩️The primary concern in balancing an aircraft is the fore and aft location of the CG along the longitudinal axis. The CG is not necessarily a fixed point; its location depends on the distribution of weight in the aircraft. 🛩️As variable load items are shifted or expended, there is a resultant shift in CG location. The distance between the forward and back limits for the position of the center for gravity or CG range is certified for an aircraft by the manufacturer. 🛩️The pilot should realize that if the CG is displaced too far forward on the longitudinal axis, a nose-heavy condition will result. Conversely, if the CG is displaced too far aft on the longitudinal axis, a tail heavy condition results. It is possible that the pilot could not c...

Forces in Turn 🛩️If an aircraft were viewed in straight & level flight from the front & if the forces acting on the aircraft could be seen, lift & weight would be apparent: two forces.If the aircraft were in a bank it would be apparent that lift did not act directly opposite to the weight, rather it now acts in the direction of the bank. When the aircraft banks, lift acts inward toward the center of the turn, perpendicular to the lateral axis as well as upward. 🛩️An increase in airspeed results in an increase of the turn radius, & centrifugal force is directly proportional to the radius of the turn. In a correctly executed turn, the horizontal component of lift must be exactly equal & opposite to the centrifugal force. As the airspeed is increased in a constant-rate level turn, the radius of the turn increases. This increase in the radius of turn causes an increase in the centrifugal force, which must be balanced by an increase in the horizontal compo...

Vortex Devices 🛩️Vortex devices maintain airflow at low speeds and delay the stall, by creating a vortex which re-energises the boundary layer close to the wing . 🛩️Vortex generator: small triangular protrusion on the upper leading wing surface; usually, several are spaced along the span of the wing. Vortex generators create additional drag at all speeds . 🛩️Vortilon: a flat plate attached to the underside of the wing near its outer leading edge, roughly parallel to normal airflow. At low speeds, tip effects cause a local spanwise flow which is deflected by the vortilon to form a vortex passing up and over the wing . 🛩️Leading-edge root extension (LERX): generates a strong vortex over the wing at high angles of attack, but unlike vortex generators it can also increase lift at such high angles, while creating minimal drag in level flight. ➡️Subscribe us for more aircraft knowledge and aircraft fact⬅️ ➡️Do Share with your Friends⬅️

Drag Reduction Devices 🛩️Anti-shock body: a streamlined pod shape added to the leading or trailing edge of an aerodynamic surface, to delay the onset of shock stall and reduce transonic wave drag. Sometimes called a Küchemann carrot . 🛩️Fillet: a small curved infill at the junction of two surfaces, such as a wing and fuselage, blending them smoothly together to reduce drag . 🛩️Fairings of various kinds, such as blisters, pylons and wingtip pods, containing equipment which cannot fit inside the wing, and whose only aerodynamic purpose is to reduce the drag created by the equipment ➡️Subscribe us for more aircraft knowledge and aircraft fact⬅️ ➡️Do Share with your Friends⬅️

High Lifting Devices 🛩️The most common types of High-lift devices are fixed slots, movable slats, leading edge flaps, and cuffs. 🛩️Fixed slots direct airflow to the upper wing surface and delay airflow separation at higher angles of attack. 🛩️The slot does not increase the wing camber, but allows a higher maximum CL because the stall is delayed until the wing reaches a greater AoA. 🛩️Movable slats consist of leading edge segments that move on tracks, At low AoA, each slat is held flush against the wing’s leading edge by the high pressure that forms at the wing’s leading edge. 🛩️As the AoA increases, the high pressure area moves aft below the lower surface of the wing, allowing the slats to move forward. 🛩️Some slats, however, are pilot operated and can be deployed at any AoA. Opening a slat allows the air below the wing to flow over the wing’s upper surface, delaying airflow separation. 🛩️Leading edge flaps and Leading edge cuffs , like trailing edge flaps, are ...

Bleed Air from Engine 🛩️When air enters a turbine engine, it goes through a series of compressors, which significantly increase the air temperature and pressure before mixing that air with fuel and igniting it. A small portion of that compressed air, however, does not enter the combustion chamber and instead is redirected from the engine via valves, ducting and manifolds to various other areas of the aircraft. 🛩️Bleed air is extracted from the compressor of the engine or APU. 🛩️The specific stage of the compressor from which the air is bled varies by engine type. 🛩️In some engines, air may be taken from more than one location for different uses as the temperature and pressure of the air is variable dependant upon the compressor stage at which it is extracted. 🛩️Bleed air from that system can be utilized for internal cooling of the engine, cross-starting another engine, engine and airframe anti-icing, cabin pressurization, pneumatic actuators, air-driv...

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...

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...

Precision Approach Path Indicator 🛩️ A precision approach path indicator (PAPI) is a visual aid that provides guidance information to help a pilot acquire and maintain the correct approach (in the vertical plane) to an airport or an aerodrome. 🛩️It is generally located on the left-hand side of the runway approximately 300 meters beyond the landing threshold of the runway. 🛩️The ratio of white to red lights seen is dependent on the angle of approach to the runway. 🛩️Above the designated glide slope a pilot will observe more white lights than red. 🛩️At approaches below the ideal angle more red lights than white will be seen. 🛩️For the optimum approach angle the ratio of white to red lights will remain equal throughout, for most aircraft, the exceptions being the Boeing 747 and now retired Concorde. 🛩️With the 747, because the cockpit is approximately 20 feet behind the nose and much higher than other aircraft, the fl...

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...