Integrated Static Port

[Ailene Goldhirsh]

Thepitot pressure is obtained from the pitot tube. The pitot pressure is a measure of ram air pressure (the air pressure created by vehicle motion or the air ramming into the tube), which, under ideal conditions, is equal to stagnation pressure, also called total pressure. The pitot tube is most often located on the wing or front section of an aircraft, facing forward, where its opening is exposed to the relative wind.[1] By situating the pitot tube in such a location, the ram air pressure is more accurately measured since it will be less distorted by the aircraft's structure. When airspeed increases, the ram air pressure is increased, which can be translated by the airspeed indicator.[1]

The airspeed indicator is connected to both the pitot and static pressure sources. The difference between the pitot pressure and the static pressure is called dynamic pressure. The greater the dynamic pressure, the higher the airspeed reported. A traditional mechanical airspeed indicator contains a pressure diaphragm that is connected to the pitot tube. The case around the diaphragm is airtight and is vented to the static port. The higher the speed, the higher the ram pressure, the more pressure exerted on the diaphragm, and the larger the needle movement through the mechanical linkage.[4]

The pressure altimeter, also known as the barometric altimeter, is used to determine changes in air pressure that occur as the aircraft's altitude changes.[4] Pressure altimeters must be calibrated prior to flight to register the pressure as an altitude above sea level. The instrument case of the altimeter is airtight and has a vent to the static port. Inside the instrument, there is a sealed aneroid barometer. As pressure in the case decreases, the internal barometer expands, which is mechanically translated into a determination of altitude. The reverse is true when descending from higher to lower altitudes.[4]

Aircraft designed to operate at transonic or supersonic speeds will incorporate a machmeter. The machmeter is used to show the ratio of true airspeed in relation to the speed of sound. Most supersonic aircraft are limited as to the maximum Mach number they can fly, which is known as the "Mach limit". The Mach number is displayed on a machmeter as a decimal fraction.[4]

Inherent errors may fall into several categories, each affecting different instruments. Density errors affect instruments metering airspeed and altitude. This type of error is caused by variations of pressure and temperature in the atmosphere. A compressibility error can arise because the impact pressure will cause the air to compress in the pitot tube. At standard sea level pressure altitude the calibration equation (see calibrated airspeed) correctly accounts for the compression so there is no compressibility error at sea level. At higher altitudes the compression is not correctly accounted for and will cause the instrument to read greater than equivalent airspeed. A correction may be obtained from a chart. Compressibility error becomes significant at altitudes above 10,000 feet (3,000 m) and at airspeeds greater than 200 knots (370 km/h). Hysteresis is an error that is caused by mechanical properties of the aneroid capsules located within the instruments. These capsules, used to determine pressure differences, have physical properties that resist change by retaining a given shape, even though the external forces may have changed. Reversal errors are caused by a false static pressure reading. This false reading may be caused by abnormally large changes in an aircraft's pitch. A large change in pitch will cause a momentary showing of movement in the opposite direction. Reversal errors primarily affect altimeters and vertical speed indicators.[6]

Another class of inherent errors is that of position error. A position error is produced by the aircraft's static pressure being different from the air pressure remote from the aircraft. This error is caused by the air flowing past the static port at a speed different from the aircraft's true airspeed. Position errors may provide positive or negative errors, depending on one of several factors. These factors include airspeed, angle of attack, aircraft weight, acceleration, aircraft configuration, and in the case of helicopters, rotor downwash.[6] There are two categories of position errors, which are "fixed errors" and "variable errors". Fixed errors are defined as errors which are specific to a particular model of aircraft. Variable errors are caused by external factors such as deformed panels obstructing the flow of air, or particular situations which may overstress the aircraft.[6]

Lag errors are caused by the fact that any changes in the static or dynamic pressure outside the aircraft require a finite amount of time to make their way down the tubing and affect the gauges. This type of error depends on the length and diameter of the tubing as well as the volume inside the gauges.[7] Lag error is only significant around the time when the airspeed or altitude are changing. It is not a concern for steady level flight.

The Static Port, a small but crucial opening on an aircraft's fuselage, is instrumental in measuring static air pressure, a key parameter for determining an aircraft's altitude, airspeed, and vertical speed. Located to ensure accurate ambient pressure readings free from the aircraft's aerodynamic effects, the static port's data is vital for the precise operation of flight instruments.

The Static Port is a critical component located on an aircraft's fuselage, designed to measure the static air pressure surrounding the aircraft during flight. This small, strategically placed opening is fundamental to accurately determining altitude, airspeed, and vertical speed, which is vital for safe flight operations. Aircraft instruments can calculate airspeed by comparing the pressure sensed by the static port to the dynamic pressure measured by the pitot tube. In contrast, the static pressure alone is used to determine altitude and vertical speed.

The design and placement of the static port are crucial to its function and accuracy. It is typically located on a smooth surface of the fuselage where it can accurately sense the ambient air pressure without being affected by airflow disruptions caused by the aircraft's movement or configuration changes. Manufacturers carefully select the static port's location to minimize the impact of slipstream and ensure accurate pressure readings under various flight conditions.

Maintaining the integrity and accuracy of the static port is essential for flight safety. Blockages, icing, or damage to the static port can lead to inaccurate altitude and airspeed readings, posing significant risks. Regular inspections and maintenance are crucial to ensure the static port is clear and functioning correctly.

The Static Port is an indispensable component of an aircraft's flight instrumentation system, playing a crucial role in measuring static air pressure for accurate altitude, airspeed, and vertical speed determinations. Its design, placement, and maintenance are vital to the safe operation of aircraft, from light general aviation aircraft to sophisticated commercial jets and high-speed military aircraft. Understanding and maintaining the static port's functionality is paramount for pilots and aviation technicians to ensure the reliability of flight data and overall flight safety.

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This article goes through the different formats that are applicable to SQL 2008 (they are the same for R2 as well). It also touches on two items that are important to understand. 1. Automatic SPN Registration and 2. Client Connections. Here is the excerpt from the above article in regards to Automatic SPN Registration.

When an instance of the SQL Server Database Engine starts, SQL Server tries to register the SPN for the SQL Server service. When the instance is stopped, SQL Server tries to unregister the SPN. For a TCP/IP connection the SPN is registered in the format MSSQLSvc/:.Both named instances and the default instance are registered as MSSQLSvc, relying on the value to differentiate the instances.

What does this mean? It means that if the SQL Service account is using Local System or Network Service as the logon account, we will have the permission necessary to register the SPN against the Domain Machine Account. By default, the machine accounts have permission to modify themselves. If we change this over to a Domain User Account for the SQL Service account, things change a little. By default a Domain User does not have the permission required to create the SPN. So, when you start SQL Server with a Domain User Account, you will see an entry in your ERRORLOG similar to the following:

2010-03-05 09:39:53.20 Server The SQL Server Network Interface library could not register the Service Principal Name (SPN) for the SQL Server service. Error: 0x2098, state: 15. Failure to register an SPN may cause integrated authentication to fall back to NTLM instead of Kerberos. This is an informational message. Further action is only required if Kerberos authentication is required by authentication policies.

Lets look at what the client will do. When I say client, this could mean a lot of different things. Really it means an Application trying to connect to SQL Server by way of a Provider/Driver. NOTE: Specifying the SPN as part of the connection is specific to SQL Native Client 10 and later. It does not apply to SqlClient or the Provider/Driver that ships with Windows.

The way the provider/driver determines which SPN to use is based on the Protocol being used. Of note, starting in SQL 2008 we allowed for Kerberos to be used with Named Pipes. If you have a Named Instance and you are using the Named Pipes protocol, we will look for an SPN with the Named Instance specified. For a Default Instance and Named Pipes, we will just look for the SPN with no port or Named Instance Name specified as shown above.

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