Purchasing Efficiency Blog

Bearings are used in many of the machines we use on a daily basis. If bearings didn’t exist, we would be constantly replacing parts, which would inevitably slow down productivity. The bearing parts were 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. 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 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 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.

Bevel gears are gears where the axes of two shafts intersect, and the tooth-bearing faces of the gears themselves are conically shaped. Bevel gears are typically mounted on shafts that are 90 degrees apart but can be designed to function at other angles as well. One of the most common use of bevel gears is in the differential of a vehicle, where it transmits power generated by the power engine to the vehicle’s wheels.
 
The two most important concepts in gearing are pitch surface and pitch angle. The pitch surface of a gear is the imaginary toothless surface that one would have by averaging out the peaks and valleys of the individual teeth. The pitch surface of an ordinary gear is in the shape of a cylinder. The pitch angle of a gear is the angle between the face of the pitch surface and the axis. Most kinds of bevel gears have pitch angles of less than 90 degrees and are therefore cone shaped. These are called external bevel gears, because their gear teeth point outwards. Internal bevel gears, meanwhile, have pitch angles of greater than ninety degrees, and have teeth that point inward. Bevel gears with pitch angles of exactly 90 degrees are known as crown gears.
 
Bevel gears can be classified into several different types, based on their geometry. Straight bevel gears have a conical pitch surface and teeth that are straight and tapering towards the apex. Straight bevel gears have a conical pitch surface and teeth that are straight and taper towards the apex. Spiral bevel gears have teeth that curve at an angle, which allows contact to be gradual and smooth. Zerol bevel gears are technically spiral bevel gears but have a spiral angle of zero at the middle of the face width, effectively combining the strengths of both straight and spiral bevel gears. Lastly, hypoid bevel gears are similar to spiral level, but the pitch surfaces are hyperbolic and not conical. A hypoid pinion is also larger in diameter than an equivalent bevel pinion. Lastly, mitre gears are a type of bevel gear with equal numbers of teeth and are primarily used to transmit rotational motion at a 1:1 ratio.

To understand how an airplane’s wings keep it in the sky, we first have to understand the forces influencing all aircraft - thrust, drag, lift, and weight. Thrust is the force that propels the aircraft forward provided by its engines, both piston and jet turbine. Drag is the force trying to pull the aircraft back, generated as the aircraft displaces the air in front and around it. Lift is the force generated by the airplane’s wings and the flow of air over and below them, while finally weight is the force of the Earth’s gravity trying to pull the plane back to the ground. 
               
 An airplane’s wings generate lift as they move through the air, but how exactly? They do so for two reasons: Bernoulli’s principle, and the shape of the wing itself, also known as the airfoil.  Bernoulli’s principle, named after the Swiss mathematician that discovered and described the phenomenon in 1738, states that as air speeds up, its pressure drops. An aircraft airfoil is shaped deliberately so that air going over the wing will be going faster than the air going under it. This means that the faster air going over the airfoil exerts less pressure than the high-pressure, slower-moving air going underneath it.  This results in lift that pushes the airfoil, and the rest of the airplane, up. 
               
Typically, a plane’s airfoil will be designed to provide enough lift to keep the plane level while flying at its cruising speed. But what about when a plane is taking off and landing? In those situations, the plane’s flaps and slats come into play to alter its airfoil and generate more lift.  
               
During takeoff and landing, the flaps located on the back of the wing extend downward from the trailing edge, altering the shape of the wing’s airfoil and generating more lift. This altered shape also generates more drag; this is useful for slowing down during landing, but it also means takeoff requires more thrust than normal. Slats also work on the same principle of altering the wing’s shape but are located on the leading edge of the aircraft. They are also used during takeoff and landing.

Vehicles go, but how do they stop? What components are involved in bringing a moving object to a halt? The answer lies within the aircraft braking system, specifically, brake calipers. Brake calipers play a crucial role in allowing your vehicle to stop and contribute to the overall safety of its operation. Understanding how they function can be essential in comprehending how the differing systems of your car.
 
Brake calipers are designed to fit over the brake rotor, with the brake pads being attached to the inside of the caliper. When the brake pedal is activated, brake fluid from the master cylinder creates hydraulic pressure that pushes the pistons in the brake caliper. The brake pads clamp down on the brake rotor to slow the car down or bring it to a complete stop. Because the rotor is attached to the wheels, they all slow down together.
 
There are two different types of calipers: fixed and floating. Fixed calipers are solidly mounted to a bracket, or spindle, with no sliding pins or bushings in its mount. The bracket is fastened to the rotor and typically consist of 2, 4, 6, or 8 pistons. There are an equal number of pistons on both the inboard and outboard halves of the caliper. When you apply pressure to the brakes, the pistons on both sides function in tandem and squeeze the pads against the side of the rotor. Fixed calipers provide a smoother braking feeling for the driver, which is why this type of caliper is found in performance and luxury vehicles. 
 
Floating calipers have the ability to move. However, this movement is in and out, and is relative to the rotor. It consists of pistons on one side and slides back and forth on bushing, or pins, acting as a clamp. When the brakes are applied, the piston pushes the brake pad on the inward side against the rotor. The caliper then slides on the bushings and squeezes the outward pad against the rotor. This forces the caliper to clamp the rotor between the brake pads. Since the pistons are located on the inward side of the caliper, it provides better clearance to the wheel, as opposed to a fixed mount caliper. Floating calipers are generally cheaper in cost as they only use a single piston.
 
Brake calipers deteriorate over time, limiting their functionality as they age. Heat generated from the braking system inevitably wears them down which is why routine maintenance is vital. You should have your brakes checked if you experience one of the following:

Helicopters typically have a 14- or 28-volt direct current electrical system. A volt is a unit of measurement that expresses the capability of the force that pushes electrical energy. Amperes are the unit of measurement for a current and describe the measure of an electrical quantity that is available in the system. Small piston-powered helicopters use an engine driven alternator because they are light, low maintenance, and produce a uniform electric output— even at low RPMs. In a turbine powered helicopter, starter/ generator systems are used. Once the engine is started, the battery powers the starter, which turns the engine. After this initial jump, the generator is powered by the engine.
 
A voltage regulator is used to distribute the electrical supply; it prevents excessive voltage, which can cause damage to various electrical components. After the electricity is passed through the voltage regulator, it goes to a bus bar, which then distributes the current to different electrical components. The battery is mostly used to start the engine, but also powers a few things when the engine isn’t running— such as radios and lights— and is a good emergency electrical power source. An ammeter is used to monitor the electrical current flowing to and from the battery. An ammeter that is charging represents the fact that the battery is charging while a discharging ammeter indicates that the electrical load is exceeding the output of the alternator or the starter generator of a helicopter.
 
Electrical components can be selected through electrical switches. If the capacity of the switch is exceeded, a solid state relay may be used. When an electrical component is overloaded, a circuit breaker will pop out. A fuse will burn out when it’s overloaded and can be easily replaced. Caution lights may also be utilized to display when there is an electrical component malfunctioning.

Helicopters fly using the same aerodynamic concepts that airplanes use; they use an airfoil to generate lift. The difference is that helicopters generate vertical thrust while aircraft generate horizontal thrust. When an airplane moves forward, the air flows across the wing and produces downwash which creates lift; the airplane has to gain enough speed for this force to overcome weight. When helicopter blades, or airfoils, begin spinning, it produces downwash which then creates lift. Speed is an important factor in generating enough force to overcome the weight in a helicopter as well. Vertical thrust allows a helicopter to take off vertically and hover.

Most helicopters use gas turbine engines over piston engines (reciprocating engines), but most modern helicopters use turboshaft engines. Turboshaft engines differ from turbojet engines in that they do not utilize exhaust to create thrust. Their main function is to generate shaft power which is used to run the rotor. Shaft power is transferred from the turbine blades. High pressure gas created in the combustion chamber is the force that rotates the turbine blades.

 The upper swashplate and the rotor blade system is attached to the rotor shaft, or mast, and they all begin rotating at the same time. A helicopter is controlled by the pilot with a collective, cyclic, two pedals, and the throttle. The collective is used to control the swashplate, which adjusts the blade pitch equally. A swashplate has two plates: one rotates with the rotor and one is fixed. A bearing is between the two plates. The upper plate is connected to the blades with a pitch change arm. The lower plate is connected to hydraulic servos which can raise, lower, or tilt the plate. Once this occurs, the pitch of the blades shift.

The collective control in the cockpit raises and lowers the swashplate and the cyclic control tilts the swashplate. These changes allow the pilot to steer the helicopter. Another rotor is added to a helicopter to counteract torque. This may be a coaxial rotor, which is attached to the same mast as the first rotor, or a tail rotor. The pedals allow the pilot to control the tail rotor. The pedals change the pitch of the tail rotor blades which control the sideways thrust. This allows the pilot to change the direction of the nose of the helicopter. The throttle increases or decreases the engines speed and therefore allows the pilot to control the amount of lift generated. All of these components are used simultaneously to takeoff, hover, change directions, and land.

ATA chapters are highly valuable to aircraft repair stations. Each code is designated to a specific part of the aircraft. These codes were originally made by the Air Transport Association (ATA) in 1956; they have seen been adopted by all major airlines and OEMs. The ATA chapters are designed with 3 sets of two-digit numbers, typically in an AB-CD-EF format. The first two digits are the most important.

Full ATA chapter codes for each part is created by the individual OEM, but they must follow the standard format and traditional number designation of the first two numbers. However, beyond that nothing else is specified by any authority except the OEM. For example, ATA chapter 29 is hydraulics. So, all ATA chapter codes starting with 29 must be hydraulic parts. The remaining four can be anything, which can cause confusion because there can be overlap in ATA chapter codes from one OEM. For example, Satair has 29-10-02 for a solenoid operated 3-way hydraulic directional control valve while Sitec Aerospace has 29-10-02 listed under a 2/2-way manual bleed valve.

 ATA chapters are important because major airlines will designate certain ATA chapters to repair buyers. This process allows each repair buyer to become an expert and specialize with the chapter— knowing anything and everything for that chapter, which is important for building trust and having a go-to person for all those needs. This also solves the issue of accidentally buying the wrong part number, because each repair station will be very knowledgeable of the part and any possible overlaps, streamlining the entire process.
Some examples of what an ATA chapter may consist are:

Aircraft superchargers are an important part of aircraft engines. As an aircraft reaches higher altitudes, there is less air pressure and air density, so a piston engine no longer is enough to power the aircraft. That’s where superchargers come in.
 
Superchargers are engine-driven air pumps or compressors that provide compressed air to the engine, which then provide additional pressure to allow the piston engine to produce more power. A normal piston engine cannot have a manifold pressure higher than atmospheric pressure on its own, but with a supercharger, we can increase the pressure inside manifold by 30 “Hg. This is especially useful to aircraft engines as air density is about 50% that of sea level or less at high altitudes. Superchargers could supply air to the engine at the same density at an altitude of 18,000 ft. as at sea level. The addition of a supercharger to a system doesn’t change much. The supercharger is placed between the fuel metering device and the intake manifold and driven by the engine through a gear train at one, two, or variable speeds. Superchargers also can have one or more stages, each of which provides an increase in pressure. They may be classified by their number of stages and their speeds.  

 
For example, single-stage, single-speed superchargers, also known as sea-level superchargers, use a single gear-driven impeller to increase the power produced by an engine at all altitudes. Single-stage, two-speed superchargers use a single impeller that can operate at two-speed settings, low blower, and high blower. When the aircraft takes off, the aircraft supercharger is in the low blower, but when the aircraft reaches a certain altitude, power is reduced, and the supercharger is switched to the high blower. Then the throttle is reset to the desired manifold pressure, and the flight is maintained. 

Jet Engines revolutionized air travel since their inception the late 1930s. These amazing aircraft engines were so powerful they were capable of outpace, maneuver, and just downright outperform any other plane before it by an extraordinary margin. They completely changed the way wars, travel, and deliveries were handled after their inception. Travelling on jet engine powered planes, we are all familiar with the baggage travelling has, however, before jet engines it took 25 hours to fly from Los Angeles to New York. Today, people save time and even have much interest in what the jet engine made possible they go to air shows showcasing the extraordinary abilities of these aircraft equipped with jet engines. The maneuvers and speeds these aircraft achieve is incredible.

But how do these incredible engines work?  Jet engines get their power from thrust. Thrust is achieved by consuming extraordinary amounts of air that is brought into the engine by aircraft propellers that spin at a very fast rate. In today’s jet engines, the fan alone can produce nearly 90% of the thrust. After the fans get up to speed, the engines compressor compresses the air to make it ready to be introduced to the fuel and be ignited. Once fuel is added to the compressed air, the mixture becomes very unstable and a spark ignites the mixture, then all the air and fire is blown out at extremely high thrust pressures.