Derived from the term “thermally sensitive resistor,” thermistors are accurate and cost-effective sensors for measuring temperatures. Thermistors are available as negative temperature coefficient (NTC), and positive temperature coefficient (PTC), with NTC thermistors being the more commonly-used. NTC thermistors have their resistance decrease as their temperature increases, while PTC thermistors’ resistance increases as their temperature increases.
Thermistors are made from metallic oxides, binders, and stabilizers, pressed into wafers and cut into chip size, left in disc form, or made into another shape. The precise ratio of these materials governs their resistance/temperature “curve.” This is closely controlled, as this determines how the thermistor will function.
Thermistors are comprised of materials with a known resistance. As the temperature increases, an NTC thermistor’s resistance will increase in a non-linear fashion, following a particular curve. The shape of this resistance vs. temperature curve is determined by the properties of the materials that make up the thermistor.
Thermistors are available with a variety of base temperatures and resistance vs. temperature curves. Low-temperature applications generally use lower-resistance thermistors, while higher temperature applications use higher-resistance thermistors. Thermistors must be accurate, durable, long-lasting, and inexpensive. They are often chosen for applications where ruggedness, reliability, and stability are important, where environmental conditions are extreme, and where electronic noise is present. Thermistors with epoxy coatings are used in lower temperature applications (-50 to 150 degrees Celsius), while glass-coated thermistors are used in higher temperature applications (-50 to 300 degrees Celsius).
Thermistors are available in several configurations. The three most commonly-used are hermetically-sealed flexible (HSTH) thermistors, bolt-on/washer, and self-adhesive surface-mounting. HSTH thermistors are sealed within PFA (plastic polymer) jackets to protect the sensing element from moisture and corrosion. They are used to measure temperatures of liquids like oils, chemicals, and food. Thermistors with bolt or washer-mounted sensors are installed to standard-sized threaded holes or openings. Lastly, surface-mounted thermistors have adhesive exteriors and can be stuck in place on flat or curved surfaces, and can be removed and re-mounted at will to serve their various commercial and industrial applications.
What goes up must inevitably come back down. An aircraft’s landing gear ensures that the “coming back down” part ends safely and allows the aircraft to maneuver safely on the ground. Landing gear on aircraft comes in several different types and configurations, which this blog will explore.
What are the types of landing gear?
The first type of widely used landing gear is tailwheel-type landing gear, also called conventional gear because so many early aircraft used it. Tailwheel fitting actuator landing gear places the center of gravity behind the main wheels, causing the tail to require support from a third wheel assembly. A few early aircraft designs used a skid rather than a wheel, but improvements to landing runways and wheel durability negated the need for them. A tailwheel configuration causes the aircraft’s nose to angle upwards when on the ground, which elevates the engine and allows a larger propeller to be installed, which compensates for older, unpowered engines. This greater clearance also allows the aircraft to operate in and out of unpaved runways, and in the wilderness for bush flying. For these reasons, and for the fact that a light tail assembly saves weight, tailwheel aircraft are still made to this day.
However, tricycle-type landing gear is the most frequently used type in modern aircraft. In a tricycle aircraft, the center of gravity is in front of the main gear, requiring a wheel in the nose to support the aircraft’s weight and balance it on the ground. Tricycle landing gear have several advantages: they allow for more forceful application of the brakes without nosing over when braking, they provide better visibility from the cockpit during landing and ground maneuvering, and they prevent ground-looping on the aircraft since forces affecting the aircraft’s center of gravity push it forward rather than causing it to loop. Most aircraft have steerable nose gear, either attached via mechanical linkage to the rudder panels, or by hydraulic power linked to an independent tiller in the cockpit.
How does aircraft landing gear work?
Main landing gear are attached to a reinforced wing or fuselage structure and will often have two or more wheels to spread the aircraft’s propellers weight over a larger area and provide a safety margin should one tire fail. When more than two wheels are attached to a landing gear strut, it is called a bogie. The number of wheels on a bogie is a function of the gross weight of the aircraft, and the surface type the aircraft is intended to land on. The Boeing 777, for instance, uses a triple bogie main gear featuring six wheels.
Alternative landing gear types do exist. Tandem landing gear sets, featuring a main and tail gear aligned on the longitudinal axis of the aircraft, are used by sailplanes, several military bombers like the B-47 and B-52, and the VTOL Harrier jet. Helicopters use landing skids, and seaplanes will mount floats rather than wheels to be able to take off and land on water.
The increasing complexity of aircraft engine systems has facilitated more requirements of proper lubrication. Aircraft engines require lubrication to prevent friction from reducing the engines’ efficiency; oil is the lifeblood of the engine. If the oil flow to the bearings stops, the lubricating films break down and cause degradation, wear and tear, and burning between moving parts. Fortunately, the engine fuel pump and oil system are very reliable. Like the circulatory system of the human body, they quietly perform their functions.
The central purpose of lubricant is to reduce friction caused by metal foil resistors. Lubricating oils provide a film that permits surfaces to glide over one another with less friction. Therefore, lubrication is essential to prevent wear in mechanical devices where surfaces rub together repeatedly. The selection of the proper lubricant depends on the design of the equipment and the operating conditions. Maintenance instruction manuals or maintenance requirements cards list the type of lubricant required for specific aircraft. With an understanding of the different types of lubricants, their characteristics, and purposes, you will know why we must utilize the proper lubricant. Using the wrong type of lubricant, mixing different types, or lubricating improperly can cause extra unnecessary maintenance and part failures.
Lubricants are classified according to their source—petroleum, mineral, or synthetic. Mineral-base lubricants are usually divided into three groups: solids, semisolids, and liquids. Petroleum-based oils were used in early aircraft engines. This oil was distributed in two grades—1010 for normal use and 1005 for extremely low temperatures. A MIL-PRF 6081 grade 1010 is still used as reserve oil in fuel systems. As the power output of jet engines increased, aircraft were able to fly higher. The operation of jet engines at these higher, colder altitudes and higher engine temperatures created greater demands on lubricating oils. This, in turn, required the development of synthetic lubricants that could withstand these higher bearing temperatures.
Engine lubrication is one of the primary functions oil provide. Oils should have the following characteristics to lubricate properly:
Lubricating oil must cool moving parts by carrying heat away from gears and bearings. This is a vital process considering the numerous parts located next to burners or turbine wheels, where temperatures can reach over 1700°F. Liquid lubricants cool by pumping or spraying oil on/around bearings or gears. The oil absorbs the heat and dissipates it through oil coolers.
Another function of lubricating oil is cleaning. Oil carries dirt, small carbon and metal particles, gum, and varnish to filters. This has become increasingly important with the higher compression ratios, engine speeds, operating temperatures, and closer tolerances between parts in newer engines.
Within each flight cycle, an aircraft fuel system must deliver clean fuel to the engine at a proper flow rate to sustain flight— regardless of the operating conditions. A fuel system is composed of boost pumps, tanks, strainers, selector valves, pressure gauges, engine-driven pumps, and more.
Typically, there are several tanks to store the required amount of fuel. The location of these depends on the system design and structure of the aircraft. In a standard assembly, a line leads to the selector valve from each one of these tanks, which is operated from the cockpit. The aircraft fuel pump boosts then forces fuel through the selector valve to the main line strainer. The strainer acts as a filtering unit, which removes water and dirt from the fuel. It then travels through a bypass in the engine-driven pump, causing it to rotate. Once it is operating at an adequate speed, it delivers fuel to the metering device to measure, allowing the aircraft to start up. These aircraft fuel systems can be categorized into two variations: a gravity feed system or a pump feed system.
It is not uncommon for aircraft to come equipped with a fuel tank in each wing. In this design, gravity is used to deliver the fuel to the engine; hence, a gravity feed system. The area above the fuel is vented to sustain atmospheric pressure on the fuel as the tank is emptied. The tanks are also vented to each other to maintain equal pressure between the two of them. An outlet on each tank feeds lines that connect to a fuel shutoff valve or multi position selector valve. As the fuel travels it passes through a main system strainer which removes sediment and/or water. It then flows to the carburetor or the primer pump for engine starting and operating. The gravity feed system doesn’t require a fuel pump and is simplistic in design.
Pump feed systems involve one or more pumps that are used to move fuel from the fuel tanks to the engine. Each fuel tank has a line from the outlet to a selector valve. In this system, fuel cannot be drawn from both tanks simultaneously. If the fuel in one tank is depleted, the pump would draw air. This negates the need to connect the tank vent spaces together. The fuel then passes through the selector valve, making its way through the main strainer, where it can then supply the engine primer. It then travels downward to the fuel pumps; one electric pump and one engine-driven fuel pump are arranged next to each other. These draw fuel from the tank and transport it to the carburetor. The two pumps facilitate each other as the engine-driven pump is the primary operator while the electric pump provides a supportive option.
Some high-performance aircraft are equipped with a fuel system that features fuel injection as opposed to a carburetor. This design combines gravity flow with the use of a fuel pump, operating in unison; but we’ll save that for next time.
In order to ensure optimal performance of your drone, it is important to consider battery care. Most drones run off of a rechargeable lithium-ion battery or lithium-polymer battery. There are a few common tips that manufacturers recommend preserving a battery’s power capacity. Take note of the following suggestions to ensure battery efficiency and longevity.
Pay Attention to Your “Low Battery” Alert
In taking care of your drone battery, you’ll want to make sure to avoid a common mistake— depleting your battery completely. Doing this not only increases the length needed to recharge, but also causes the battery to deteriorate quicker over time and it shortens the flight cycle durations. Most drones have a low battery alert that operates cohesively with smart return, which directs the drone back to its designated home location. It is important to utilize this automatic control or direct your drone to land as soon as the low battery alert is given.
Overcharging a battery can reduce its lifespan and weaken its power capacity, meaning your drone won’t perform with the same power efficiency and you’ll have to replace your battery more frequently. To prevent this, charge your battery 24 hours before your intended flight.
Keep Temperature In Mind
Drastic temperatures alter the way a battery will charge. Hot and cold temperatures provide challenges. Ideally, you should charge your battery in a cool, dry environment between 60 and 75 ?. A battery achieves its most optimal charging rate between this temperature range.
Remove Your Battery After Flight
When your drone is not in use, remove the battery. Leaving it attached to your drone depletes the battery faster. As with overcharging, leaving a battery attached to your drone for extended periods reduces the battery’s power capacity.
And there you have it, the 4 key suggestions to keep in mind for drone battery parts & their care. Keep these in mind to preserve your battery and keep it operating at its best. Happy flying!
Aircraft are under a constant state of stress when logging flight hours. Boeing aircraft, for example, have the ability to fly upwards of 14 hours non-stop and their lifetime can extend anywhere from 20 - 27 years in operation. In this time, an aircraft will experience about 35,000 pressurization cycles and will undergo the associated, and often expected, degradation and parts fatigue. So, how do modern aircraft maintain their reliability and safety over time?
Beginning at the production level, an aircraft undergoes FAA regulated inspections and checks to ensure quality control and safety. Manufacturers of commercial airliners usually resort to a non-destructive evaluation (NDE) when an aircraft is on the production line. This program is structured to ensure that components are free of defects before they even see a buyer. Companies that consult these large-scale evaluations include the likes of Boeing and Airbus, among many others.
Maintenance checks are regulated by the FAA and scheduled over the life cycle of an aircraft. Standard parameters set forth by manufacturers by these regulations will include the following: line maintenance, A checks, C checks, and D checks. B checks have actually been absorbed into the A category, as B checks have become obsolete or covered by the A category with the advancement of aviation technology.
Line maintenance of an aircraft often involves up to 12 hours of inspection per week. System checks include some of the elements you may have seen in standard automotive servicing. The assessment will survey the brakes, wheels, fluid levels and landing gear of an aircraft. Any necessary repairs are also attended to during this phase of maintenance.
Proceeding through the life cycle of the aircraft, the next inspection it will encounter is the A-check. These checks are required after every 100 flight hours. Processing of the inspection takes longer than line maintenance, often totaling over 12 hours. Under this careful examination, lubrication and oil are changed, and systems and functional checks should be performed.
Defined as a heavy maintenance check, a C-check is completed between 18 months and 2 years, 1800 flight hours, or 2,000 pressurized cycles. It is typically a 3-week process in which airlines might make changes to interior cabin design or amenities.
Lastly, a D-check is performed after the aircraft has been in service for about 6 years, or after it has received a total of four C-checks. This assessment is broken up into a series of steps, often referred to as C4 or C8 checks. During this inspection, the aircraft is dismantled including the cabin, landing gear, and any applicable accessories. The airframe is then removed, and the engine/s undergo routine maintenance checks.
Despite inspection during and post production, it is crucial to stay up to speed on the durability limits specified by a parts manufacturer. Each aircraft will encounter different levels of pressurization and degradation, and each part’s component will have its own established flight cycle limit. With proper care, following manufacturer and FAA parameters will promote the longevity of the aircraft.
Despite the millions of dollars it costs to fly and maintain, aircraft have a surprisingly short lifespan with an average of around 30 years. Once the aircraft has to be retired, they go to boneyards— large plots of land where airplanes are parked until further notice. It’s interesting to learn about what happens at the world's largest boneyard— how aircraft life is determined and how retired planes are salvaged for parts.
Retired American planes all end up at boneyards located in California, Arizona, New Mexico, and Texas, where the dry and arid climate is perfect for decelerating rust. So, it makes sense that the world’s largest boneyard is the 209th Aerospace Maintenance and Regeneration Group (AMARG) in Tucson Arizona. AMARG’s large lot currently holds more than $32 billion of retired airplanes, with a total of 4,400 parked planes.
The operational life an airplane is not determined by years, but by the number of pressurization cycles. It is estimated that an aircraft can make up to 35,000 pressurization cycles, which is around 135,000 to 165,000 flight hours before metal fatigue sets in and the FAA deems it unsafe to fly. In years, it is estimated to be 25 to 30 years depending on the destination and if the aircraft is used for domestic or international flights.
Once an aircraft is retired or decommissioned, it’s stripped and sold for parts. Aircraft parts are huge commodities because while the lifespan of the aircraft as a whole is over, the parts still have a lot of life left in them due to the regular maintenance and repair. Parts are often salvaged and sold for other aircraft still in operation because used parts are cheaper than new ones. Just the scraps of a single aircraft can be sold for up to $55,000.
When preparing for a flight, there are many things to worry about and consider like packing luggage, arriving at the airport on time, fitting the carry-ons in the overhead compartment, and so on. The one thing no one really thinks about and often does automatically, that’s boarding. And no matter if it’s the massive Airbus A380 or the luxurious Embraer Lineage 1000E, when we board a plane, we board on the left side. But most of us can’t even begin to explain why.
Boarding from the left stems from two major reasons: traditional nautical custom and the pilot’s field of view. In nautical tradition ships are docked portside (on the left) because of the tiller, what is controlled by the ship’s wheel and resultingly turns the ship, being starboard (on the right). Many historians believe that planes follow the same marine convention out of habit.
The other reason is that back when planes had to taxi in front of the terminal to discharge passengers, pilots had to be on the left side to more accurately judge the wingspan of the plane and dock in the terminal. As a result, it was easier to have passengers embark and disembark on the left and have all the servicing of the plane done on the right.
Servicing a plane can involve anything from unloading and loading cargo, restocking the food carts, refueling, or hooking up the plane to the auxiliary power unit. With how complex planes are and how many different tools and aviation parts can be required to service them, servicing on the right and away from passengers is safer too.
The efficiency of a gas turbine cycle rises as the turbine entry temperature is increased. Because of this, the hotter the combustion gases that go in to the first turbine stage, the more particular power the jet engine can create. In a modern engine, about twenty percent of compressed air bleeds off for cooling and sealing purposes. This is mostly for guide vanes and turbine blades. The stators and the outer wall of a turbine’s flow passage utilize cooling air moving from the compressor between the combustor and casing of the outer engine.
The turbine rotor blades, disks, and inner walls of a turbine flow passage uses the air that bleeds from the compressor though inner passageways. Because the stators materialize before the first row of rotating blades, it is expected that the first stage of stators are uncovered to very high temperatures. This includes local hot-spots from the combustor close by. The temperature at this first stage is slightly lowered by dilution of the gases with cooling air, along with the relative velocity effecting and powering extraction from the turbine.
The laws of thermodynamics demand that because of combustion inefficiencies, there be a pressure loss inside the combustor. This means that the mainstream pressure at the first row of stators in the turbine located after the combustor is lower than on the way out of the last stage of the compressor. This difference in pressure is used to guide the cooling air through the internal passageways and into the stators and blades.
ASAP Parts Online follows ASAP Semiconductors tradition of creating websites and applications built upon the requirements and recommendations of customers. With the ability to supply jet engine parts, jet engine aircraft parts, turbine engine cooling parts and more, ASAP Parts Online is an excellent source for customers to fulfill their requirements. With the fastest load time, ASAP Parts Online boasts a customized database that allows for user to purchase parts ranging from components to national stock number parts on one single website. With over 85,000 manufacturers in the system, customers can expect fast quotes and excellent service for every experience.
Earlier in the year, The Boeing Company finished up the flight tests for the newest model of the KC-46 Pegasus wide-body, a plane used to re-fuel other squad member’s during flight. Now they are waiting on word from the FAA to see if their new tankers can fly legally. More certifications are needed on this aircraft than normal because it is classified as a tanker, meaning it may take longer for the tanker to become airworthy.
This new model is based off a classic Boeing 767 with some modifications to allow for refueling multiple planes. The tanker can also be re-fueled itself by other planes, which required a few tweaks to the previous model. The new tanker model is being built in Boeings private Everett location, just north of Seattle, Washington, and testing is taking place in Seattle proper.
The draw of building a new tanker, like the KC-46A, is the fact that it’s a multitasking dream. Not only can it re-fuel other planes in its squadron but it can also handle a load of cargo, quite a few passengers, and if needed, individuals who need medical attention.
The KC-46 has successful flown with seven different types of aircrafts and logged over 2,000 miles in flight. Even though the delivery, and implementation, of the KC-46 line is still some ways out, the fact that they successfully passed flight tests means its one huge step closer to being air worthy.
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