drag coefficient

The fluid dynamics, the drag coefficient (commonly denoted as: c_d, c_x or c_w) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment such as air or water. It is used in the drag equation  where a lower drag coefficient indicates the object will have less aerodynamic or hydrodynamic drag. The drag coefficient is always associated with a particular surface area.

The drag coefficient of any object comprises the effects of the two basic contributors to fluid dynamic drag: skin friction and from drag. The drag coefficient of a lifting airfoil or hydrofoil also includes the effects of lift induced drag. The drag coefficient of a complete structure such as an aircraft also includes the effects of  interference drag.

spoiler

A spoiler is an  automotive aerodynamic  device whose intended design function is to 'spoil' unfavorable air movement across a body of a vehicle in motion, usually described as turbulence or drag. Spoilers on the front of a vehicle are often called air dams, because in addition to directing air flow they also reduce the amount of air flowing underneath the vehicle which generally reduces aerodynamic lift and drag. Spoilers are often fitted to race and high-performance sporty cars,although they have become common on passenger vehicles as well. Some spoilers are added to cars primarily for styling purposes and have either little aerodynamic benefit or even make the aerodynamics worse.

The term "spoiler" is often mistakenly used interchangeably with "wing". An automotive wing is a special type of spoiler whose intended design is to generate down force as air passes around it, not simply disrupt existing airflow patterns. As such, rather than decreasing drag wings actually increase drag.

Single-grade of oil

A single-grade engine oil, as defined by SAE J300, cannot use a polymeric  viscosity index improver (also referred to as Viscosity Modifier) additive. SAE J300 has established eleven viscosity grades, of which six are considered Winter-grades and given a W designation. The 11 viscosity grades are 0W, 5W, 10W, 15W, 20W, 25W, 20, 30, 40, 50, and 60. These numbers are often referred to as the "weight" of a motor oil, and single-grade motor oils are often called "straight-weight" oils.

For single winter grade oils, the dynamic viscosity is measured at different cold temperatures, specified in J300 depending on the viscosity grade, in units of mPa·s, or the equivalent older non-SI units, centipoise (abbreviated cP), using two different test methods. They are the Cold Cranking Simulator (ASTMD5293) and the Mini-Rotary Viscometer (ASTM D4684). Based on the coldest temperature the oil passes at, that oil is graded as SAE viscosity grade 0W, 5W, 10W, 15W, 20W, or 25W. The lower the viscosity grade, the lower the temperature the oil can pass. For example, if an oil passes at the specifications for 10W and 5W, but fails for 0W, then that oil must be labeled as an SAE 5W. That oil cannot be labeled as either 0W or 10W.

For single non-winter grade oils, the kinematic viscosity is measured at a temperature of 100 °C (212 °F) in units of mm²/s (millimeter squared per second) or the equivalent older non-SI units, centistokes (abbreviated cSt). Based on the range of viscosity the oil falls in at that temperature, the oil is graded as SAE viscosity grade 20, 30, 40, 50, or 60. In addition, for SAE grades 20, 30, and 1000, a minimum viscosity measured at 150 °C (302 °F) and at a high-shear rate is also required. The higher the viscosity, the higher the SAE viscosity grade is.

SAE Motor Oil Viscosity Standard

What is motor oil viscosity? 
Simply put viscosity is a physical property of a fluid or gas that reflects it’s tendency to flow. We commonly refer to high
viscosity fluids as being “thick” and low viscosity fluids as being “thin”. It’s an important property of a motor oil because
changes in viscosity affect the ability of the oil to lubricate and protect the moving parts of an internal combustion engine. If
the oil is too thin the oil pump cannot maintain enough pressure to circulate it and the oil will not withstand the forces that form
between moving parts. The metal parts will rub against each other and wear out or fail prematurely from lack of proper
lubrication. Conversely, if the oil is too thick the oil pump will again have problems circulating the oil and it will be too thick
to penetrate into the tiny openings between moving parts. The result is the same – premature wear and failure. So it’s important
that the viscosity of a motor oil be a proper balance between too thin and too thick.
How is viscosity measured? 
There are two units of measure commonly used for viscosity of fluids. The basic unit is the centipoise (cP or
mPa·s). This unit describes the movement of the different layers of a fluid when subjected to a horizontal force. It
is commonly known as dynamic or simple viscosity. Another unit of viscosity is the centistoke (cSt or mm2
/s).
This unit describes the ease with which a fluid moves under the force of gravity and is the form of viscosity with
which we are most commonly familiar. This form of viscosity is known as kinematic viscosity.

One of the oldest and most common methods for measuring kinematic viscosity is an apparatus called the
capillary viscometer (see picture). This apparatus is a precisely graduated glass tube. A small quantity of the fluid
to be tested is placed into the top of the tube and held there with air pressure. The pressure is then released and the
length of time it takes for the fluid to move to a graduated mark on the other end of the tube is measured. Higher
viscosity fluids move slower, lower viscosity fluids move faster. The viscometer is usually immersed in a
temperature controlled bath during the test so that the measurement is calibrated to a specific fluid temperature.

Function of hydraulic clutch

The hydraulics with the master cylinder (in the picture on the right) and the slave cylinder (on the left) take the place of the Bowden cable. The brake fluid is taken from the reservoir (mounted high enough) of the brake system or from a separate container. This pipe leads to the master cylinder (in the picture, at the top). The amount of fluid sinks as the brake-pads wear down, therefore, in this situation the container should not be filled to the brim.

The pressure is distributed from the master cylinder and stays the same for the respective pedal pressure everywhere. By using various piston diameters, a manufacturer can set a transformation ratio, e.g., by using a smaller master cylinder diameter, the pedal force can be reduced. The spring in the slave cylinder presses the piston through the linkage, even when no activity is taking place, against the release bearing, which then lies on the tongue of the membrane spring and always rotates with it.

Earlier, only the hydraulic clutch operation was self-adjusting, nowadays it is also the standard in cable operated systems.

thermostat (wax-pellet)

The engine temperature is primarily controlled by a wax-pellet type of  thermostat, a valve which opens once the engine has reached its optimum operating temperature.

When the engine is cold, the thermostat is closed except for a small bypass flow so that the thermostat experiences changes to the coolant temperature as the engine warms up. Engine coolant is directed by the thermostat to the inlet of the circulating pump and is returned directly to the engine, bypassing the radiator. Directing water to circulate only through the engine allows the temperature to reach optimum operating temperature as quickly as possible whilst avoiding localised "hot spots." Once the coolant reaches the thermostat's activation temperature, it opens, allowing water to flow through the radiator to prevent the temperature rising higher.

Once at optimum temperature, the thermostat controls the flow of engine coolant to the radiator so that the engine continues to operate at optimum temperature. Under peak load conditions, such as driving slowly up a steep hill whilst heavily laden on a hot day, the thermostat will be approaching fully open because the engine will be producing near to maximum power while the velocity of air flow across the radiator is low. (The velocity of air flow across the radiator has a major effect on its ability to dissipate heat.) Conversely, when cruising fast downhill on a motorway on a cold night on a light throttle, the thermostat will be nearly closed because the engine is producing little power, and the radiator is able to dissipate much more heat than the engine is producing. Allowing too much flow of coolant to the radiator would result in the engine being over cooled and operating at lower than optimum temperature. A side effect of this would be that the passenger compartment heater would not be able to put out enough heat to keep the passengers warm. The fuel efficiency would also suffer.

The thermostat is therefore constantly moving throughout its range, responding to changes in vehicle operating load, speed and external temperature, to keep the engine at its optimum operating temperature.

Radiator construction

Automobile radiators are constructed of a pair of header tanks, linked by a core with many narrow passageways, giving a high surface area relative to volume. This core is usually made of stacked layers of metal sheet, pressed to form channels and soldered or brazed together. For many years radiators were made from brass or copper cores soldered to brass headers. Modern radiators save money and weight by using plastic headers and may use aluminium cores. This construction is less easily repaired than traditional materials.

Honeycomb radiator tubes

An earlier construction method was the honeycomb radiator. Round tubes were swaged into hexagons at their ends, then stacked together and soldered. As they only touched at their ends, this formed what became in effect a solid water tank with many air tubes through it.^[1]

Some vintage cars use radiator cores made from coiled tube, a less efficient but simpler construction.