At high altitudes, temperatures can drop below zero degrees Fahrenheit. Combined with seasonally cold temperatures, heating an aircraft’s cabin interior becomes a necessity, not a luxury. Pressurized aircraft use air cycle conditioning systems that mix bleed air from the engines with cold air produced by the air cycle machine expansion turbine to obtain warm air for the cabin. Some turbine-powered aircraft not equipped with air cycle systems still use engine compressor bleed air to heat the cabin, by mixing it with ambient air, or cabin return air, and distributing it back throughout the aircraft via ducting. These bleed air heating systems are simple and function well, as long as the valves, ducting, and controls work well.

 Electric heating systems are another option. Electricity flowing through a heating element makes the element warm, and a fan blows air over the elements and into the cabin to transfer the heat. Other floor or sidewall elements simply radiate heat to warm the cabin. These require a significant amount of the aircraft’s generator output however, and therefore are not very common. They can, however, be used on the ground when powered by a ground electrical source before passengers board.

 Most single-engine light aircraft use exhaust shroud heating systems to heat the cabin. Ambient air is directed into a metal shroud or jacket that encases part of the aircraft’s exhaust system. The air is warmed by the exhaust and directed through a firewall heater valve into the cabin. This requires no electrical or engine power and makes use of heat that is otherwise wasted. The largest concern with exhaust shroud heat systems is the possibility of exhaust gases contaminating the cabin’s air. A crack in the exhaust manifold can send carbon monoxide into the cabin, so strict inspection procedures are mandatory to prevent this from happening.

Combustion heaters are also used on small to medium-sized aircraft. It is a heat source independent from the aircraft’s engines, although it does draw fuel from the main fuel system. Similarly, to exhaust shroud systems, they use ambient air that is heated and sent to the cabin, the source in this case being an independent combustion chamber located inside the cylindrical outer shroud of the heater unit. Fuel and air are ignited inside an airtight chamber (the exhaust of which is funneled overboard), while ambient air is directed between the combustion chamber and the outer shroud. There, it absorbs heat by convection, and is channeled into the cabin.

             



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Resistor networks are networks of… resistors. Obviously. They combine groups of three to over twenty resistors in a single IC-like package. An array is a subset of networks, all of which have the same ohmic value.

Networks are especially useful when the design needs multiple pull-up, line-termination, or gain-setting resistors. One strong case for using a resistor network is the inherent matching it offers in terms of changes in resistance due to things like temperature shifts, a consequence of the common thermal substrate. This is an important consideration for many sensor- and interface-related applications where balanced or ratiometric circuits facilitate cancellation of drift-related errors. While discrete resistors can provide close TCR matching through selection or tight absolute TCR, they can never offer matching of actual element temperatures.

This does not mean that all such networks are prone to large drift; some are able to combine both stability and precision. The QSOP-C and SOIC-C resistor networks, for instance, combine a ceramic substrate, large feature size, and a self-passivating tantalum nitride film technology for an inherently moisture-proof film system. These networks can ease some of the pressure from a project’s error budget.

Resistor networks also have the advantage of saving PC board “real estate” since a multi-resistor package typically takes less space than individual resistors. They can also reduce needed PC traces if some or all of the resistors have a common connection. Networks also support a routing discipline which enables a cleaner, more logical layout arrangement.

In terms of production, using a network results in a shorter Bill of Materials, which means fewer items to order, stock, and risk being unavailable. Networks also simplify the production process as there are fewer reels components to use, and they speed assembly since a single pick-and-place step is needed to put the resistors on the board, rather than multiple steps.

Resistor networks are not always the best way to go, however. Placing all resistors in a single package and location can end up requiring longer PC-board traces, which can lead to board crowding and layout challenges, and increasing noise pickup and affect signal integrity. Custom networks offer the ultimate design flexibility, but arrays are easier to source off of the shelf. All the resistors having the same value can also be a design constraint.

Two other factors to keep in mind are thermal impact and crosstalk. Although the network package may be operating within its dissipation ratings, it does concentrate this dissipation in a small localized area. If this location is in a thermal “shadow” zone with marginal airflow, some resistor-network thermal derating may be needed. Crosstalk can occur since, unlike individual devices, multiple resistors share the common substrate. While this is a potential issue with networks using silicon substrates, ceramic-based substrates feature larger sizes and therefore crosstalk.

               


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Spend enough time reading about machinery of any kind, and you will see repeated references to things like bolts, screws, and studs. But for the uninformed, these labels can seem interchangeable and vague? What differentiates a bolt from a screw from a stud? In this blogpost, we will explore and define these differences.

According to the Machinery’s Handbook, the primary difference between bolts and screws lies in their purpose. While there are of course exceptions, bolts are used to assemble two or more unthreaded components. When used in conjunction with a nut, the bolt will remain secure, holding the components together and fastening them. Screws, on the other hand, are used with threaded components. This does not necessarily mean that the component or components used with screws must be threaded, as the installation of the screw may create the threading. This is a key difference between the two; bolts must be installed in holes that are unthreaded and must be completed with a nut on one end to be secure, while screws are inserted into holes that have an internal thread or create their own threading. Bolts are tightened by winding the nut further down on the bolt’s threaded portion, while screws are tightened by twisting the head with torque.               

Finally, a stud is a metal rod or shaft with threads on both ends. Most studs are long, but the size of course varies depending on the intended purpose and application. Studs do not have a head like a screw or bolt does that can be turned for tightening, and therefore requires a nut at both ends to be fastened.             

Bolts, screws, and studs are made from several different metals, including carbon and stainless steel, brass, nickel alloy, and aluminum alloy. What type of metal is chosen depends on the role the fastener will play, and what stresses it will face, like heat, weight loads, corrosion, exposure to chemicals, etc.



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Bearings are used in many of the machines we use on a daily basis. If bearings didn’t exist, we would constantly be replacing parts, which would inevitably slow down productivity. The bearing was designed with a simple concept in mind— objects can roll better than they can slide. Bearing design is based on the magnitude and direction of the load that they are intended to support.


The beauty in the simplistic design of bearings is something to be admired. The ball bearings are essentially made up of a ball and a dual sided surface for dissipating stress that is applied to it. The ball carries the load of the weight while the force associated is what enables rotation. The method in which the force is absorbed depends on two factors: thrust load and radial load.


Radial loads apply tension to the bearing which causes it to rotate. Thrust loads put stress directly on the bearing from an angled position. A deep groove ball bearing and a tapered roller bearing can facilitate both loads. The load type and capacity to support weight are factors to consider when choosing the proper bearing for a job.


The ball bearing is the most common type on the market and can handle both thrust and radial loads. There are also roller bearings, ball thrust bearings, roller thrust bearings, tapered roller bearings, and magnetic bearings. Each one supports a different function.


Roller bearings are used in objects such as the conveyor belt rollers and are capable of holding heavy radial loads. The roller is constructed as a cylinder meaning the contact between the inner and outer race is a line. Ball thrust bearings are used in instances where low speed is key, and a radial load can’t fully be handled.


Roller thrust bearings are constructed to support large thrust loads. These bearings are commonly found in vehicle transmissions and are used to separate the gears. Tapered roller bearings have the ability to support both large thrust loads and large radial loads. Magnetic bearings contribute to the functionality of high-speed devices. This includes advanced flywheel energy storage systems. Bearings with rollers or balls can’t withstand the high-speed temperatures and would ultimately melt.


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            A constant speed propeller allows a pilot to delegate specific engine speed (RPM) per stage of flight. The ability to maintain “on” speed functioning is due to a component called the aircraft propeller governor— Ello, Guv’nor! It’s the governor's job to maintain a pilot specified RPM when the blades are moving over speed or under speed. Though turbofan and turbojet aircraft require constant speed capabilities as well, the use of a governor to achieve this is most often seen in a turboprop engine.

            A governor system controls RPM by shifting pressurized oil to and from the propeller shaft, where a piston is connected to outer blades. Most constant speed governor systems will include a speeder spring, flyweights, a pilot valve, a gear driven pump, a fine pitch tube, and a coarse pitch tube. Once the governor is set to a definitive RPM, it will adjust the angle and position of the propeller blades whenever necessary during the flight to maintain constant speed. A pilot can usually set takeoff and cruise speed using a propeller control knob or a manual lever near the throttle.

            A governor is shaped like a jack-hammer positioned on top of a gear driven pump. The speeder spring sits at the top, with flyweights attached directly underneath. Both of these components sit above the pilot valve, which is linked to a high-pressure oil tube extending from the engine. In the event of an overspeed propeller condition, the propeller begins to move faster than the selected speed. This causes the engine gear to turn at a faster rate as well, which will rotate the governor components.  If the propeller is spinning too fast, the engine gear will spin faster, and in tandem, it will spin the pilot valve, flyweights, and speeder spring. The centrifugal force will cause the flyweights to push up on the speeder spring, adjusting the pilot valve. Its new raised position allows high pressure oil to flow into the coarse pitch tube and into one side of the piston, causing the piston to adjust, and therefore adjusting the propeller blades to a coarse position.

            When a propeller is underspeed, a governor achieves “on” speed by employing centrifugal force like it does with overspeed, but this time the flyweights will collapse and lower the speeder spring, causing the pilot valve to drop instead of pull up. The governor then allows pressurized oil to flow only into the fine pitch tube, the pressurized oil pushes the piston against existing oil in the cylinder. This oil is then moved by the piston and transferred out through the coarse pitch tube to the engine sump as the propeller blades adjust to a fine position— propeller blades in a fine position raise RPM. Now remember, the propeller speed will adjust the speed of the engine gear as a direct result. As the engine gear speeds up, it creates centrifugal force with the flyweights, and pushes the speeder spring up. The pilot valve is raised again, and hydraulic lock is achieved.  With its ability to customize RPM based on varying conditions, a governor can help a constant speed propeller aircraft to achieve optimized fuel efficiency and performance. 


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           ‘Cost effective’, ‘reliable’, and ‘efficient’— all words we love to hear about an engine, and ones that aptly describe the turboprop design. Not to be confused with turbofan and turbojet aircrafts, a turboprop powered aircraft enters a class all on its own.?

            With an ingenious compact design, a plane equipped with a turboprop engine can land and take off more efficiently than a majority of lighter jets. Perhaps the most warm and fuzzy quality about the turboprop engine— its ability to run off of affordable Jet-A fuel. With fuel prices rising 38% in the last year alone, the cost-effective turboprop engine has gained popularity. At low to mid altitude, these engines allow aircraft to burn less fuel per passenger than both turbofan and turbojet powered birds.

 So, how exactly does the mechanism manage these feats? The basic design concepts follow this formula: air is compressed, combusted, and converted resourcefully in a snake like design. While the combustion and turbine systems generally work the same as turbofan and turbojet engines, a few unique specs allow the turboprop to achieve its superior efficiency.

            This engine design utilizes reverse flow. This process allows air to travel through intakes near the propeller scoop, and backward towards the engine firewall. The air is then directed in reverse towards the compressor where airfoil shaped blades create axial flow to speed up and compress incoming air flow to reach the combustor. The air then makes another turn to redirect air to the relatively standard combustor. This begins spinning the compressor turbine of an aircraft. This is where the turboprop engine works more of its magic.

            While the compressor turbine operates relatively similarly to standard operation, there is one significant difference, it does not spin the aircraft propeller. The turboprop features a secondary engine shaft in front of the turbine. Continuous airflow moves toward the compact power turbines, which then powers the propeller.

            With the resourceful nature of this design, it’s not surprising to see that the aviation industry has taken notice. The most popular turboprop engines include the Pratt and Whitney PT6 and the up and coming General Electric ATP engine. Regional airliners and single pilot crop dusters alike can benefit from the reliability and efficiency of the turboprop engine.


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Abrasives are one of the most common tools in any manufacturing industry. They’re used to buff, sand, grind, and polish surfaces— as long as the abrasive is harder than the material you’re trying to finish, the abrasive will be very effective. Because abrasives are used for so many different applications, there are many different types to choose from.

In general, abrasives consist of minerals that can either be naturally occurring or synthetic. Examples include calcite, emery, pumice, sandstone, garnet, borazon, ceramic, steel, and silicon carbide. Industrial applications like mining, construction, railroad, and wholesale/retail operations all have different requirements, so abrasive usage falls into several different categories, depending on the type and shape of the abrasive— bonded, coated, or other.

Bonded abrasives are generally contained within some sort of material like clay, resin, or rubber. They’re shaped into wheels or blocks and often have two different densities of grit. Common bonded abrasive materials include aluminum oxide, silicon carbide, tungsten carbide, or garnet.

Coated abrasives are generally affixed to a backing material like paper or metal with the help of resin or some other type of adhesive. Sandpaper is the most common coated abrasive, they come in different shapes and sizes and can be used for various different tools.

Other abrasives are various miscellaneous ones like loose metal pellets, sand or glass beads used for sandblasting. Cleaning products are another common miscellaneous abrasive, typically used to clean floors, pots, pans, etc.

Abrasives are also categorized by hardness. Some abrasives are harder than others, like diamond abrasives compared to pumice. The harder the abrasive, the more easily it can affect the material. For example, pumice is sufficient as an abrasive in soaps and cleaning solutions, but it cannot do much to diamonds. On the other hand, diamonds are perfect as an abrasive for other diamonds and gems but is too much for cleaning your bathroom.


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An abrasive is a material used to polish and grind objects. There are many ways to use abrasives, making it a versatile and popular tool. Today we will be discussing various types of abrasives, the difference in roughness, and what their use.

To begin, there are two types of abrasives— coated and bonded abrasives. Coated abrasives have grits and grains which are layered. A good example of this would be sandpaper. This type of abrasive can adhere to sheets, discs, rolls etc. The second type is the bonded abrasive, which is when the grains are attached with a bonding solution to support the surface when it is being cut.

Now we will discuss the common types of grinding wheel abrasives.

 1. The most common type of grinding wheel abrasive is aluminum oxide. This can be used on just about anything from iron, bronze, and alloy steel. And with the many different specifications and kinds of aluminum oxide, you will surely find the best fit for your needs.


  2. A very rough grinding abrasive is zirconia alumina, this is used for the roughest and toughest of cutting. It is created by a mixture of steel and steel alloys which makes a powerful surface.


  3. Silicon carbide is an extremely sharp surface. This surface will cut anything, including rubber, stone, cast iron, and more. This surface needs to be replaced very often due to the brittleness.


  4. Ceramic aluminum oxide is a top of the line grinding surface. This abrasive takes grinding to the next level. A fantastic feature of this is that the grains break down, yet the surface stays quite sharp. It is the best type of abrasive when working with the hardest metals or with precision grinding.


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In the aerospace and aviation industries, every rough surface, sharp edge, or imperfection has the potential to lead to disastrous consequences. Or, at the very least, cost a lot of money as a result of decreased efficiency caused by higher friction and wear-and-tear. As a result, abrasives are an important part of the manufacturing process.

Abrasives are the hard crystals either manufactured or found in nature are materials used to clean, grind, or polish hard surfaces like metals and alloys. They’re also commonly used to work with other materials such as stone, glass, plastic, wood, and rubber. Abrasives work by scratching. The particles will first penetrate the surface and then cause a tearing off of particles. However, it only works if the abrasive is has a higher hardness rating than the abraded material. As a result, the most common abrasives are made of materials like aluminum oxide, silicon carbide, cubic boron nitride, and even diamond, which have Mohs hardness ratings of 9+.

However, for the last 100 years or so, manufactured abrasives have largely begun to replace natural abrasives. Synthetic diamonds and lab-made silicon carbide and aluminum oxides have replaced their natural counterparts. And that’s mostly because manufactured materials are more superior in their uniformity and controllable properties.

In most industries, what kind of abrasive being used will depend on what the application is. Hard and brittle abrasives like silicon carbide and aluminum oxide tend to form sharp edges so they’re best for  precision and finish grinding. On the other hand, tougher abrasives that resist fracture and last longer are used for rough grinding. The application also dictates which of the 3 types of abrasives are used, 1) bonded to form solid tools such as a grinding wheel; 2) coated on backings made of paper or cloth like sandpaper; or 3) loose and held in some liquid or solid carrier such as sandblasting.


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          Aircraft wheel bearings, like all other parts of the aircraft, need proper care and maintenance in order to continue performing at the highest capacity, which means that they need grease. But, they can not just use any grease, and certainly not automotive grease. Your average sedan isn’t going to experience the same stresses and conditions that a commercial jetliner does. Aviation parts need aviation grease specially designed with certain applications in mind. So, with that being said, here are the top 3 aviation greases for the aircraft wheel bearings.

  1. Mobil SHC100 is a performance synthetic grease featuring a unique blend of polyalphaolefin synthetic base fluid and high-quality lithium complex soap thickener. SHC100 is manufactured by Mobil, a highly reliable and reputable brand of oil and gas products. It offers great protection at operating temperatures from -54 to 177 (degree Celsius). Good for high speed, heavy load applications such as wheel bearings and slower speed, high load applications such and landing gear bearings, the SHC100 is a good multipurpose grease.

  2. Royco 22CF MIL-PRF-81322F is a gel-type inorganic grease with additives for oxidation and corrosion stability as well as load-carrying and rust protection. Royco offers protection against friction for a wide operating temperature range. It’s suitable for use in a wide range of applications other than wheel bearings, such as instruments, gearboxes, anti-friction bearings, rotor bearings, actuators, and general airframe applications.

  3. Braycote 622 MIL-PRF-81322G #2 is a synthetic hydrocarbon base, non-soap thickened grease. It is manufactured by Castrol Braycote, a major manufacturer of lubricants and grease. Braycote 622 offers great protection in low and high temperatures of up to 177 degree Celsius, water resistance, and extreme pressure characteristics. The Braycote is another good all-around aviation grease with many applications such as in control systems, high-speed miniature ball bearings, and other bearing applications where fretting, oscillating, and vibrations create problems.


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