## Pitot Static System…Airspeed Calculation

Pitot Static System…Airspeed Calculation

A.  Airspeed Calculation:

Airspeed is calculated as a function of the difference between Pitot Pressure and Static Pressure as follows:

Calculated or Indicated airspeed is indicated airspeed corrected for instrument errors, position error (due to incorrect pressure at the static port) and installation errors.

Calibrated airspeed values less than the speed of sound at standard sea level (661.4788 knots) are calculated as follows:

minus position and installation error correction.

Where

is the calibrated airspeed,

is the impact pressure (inches Hg) sensed by the pitot tube,

is 29.92126 inches Hg; static air pressure at standard sea level,

is 661.4788 knots:, speed of sound at standard sea level

Units other than knots and inches of mercury can be used, if used consistently.

This expression is based on the form of Bernoulli’s equation applicable to a perfect, incompressible gas. The values forand   are consistent with the ISA i.e. the conditions under which airspeed indicators are calibrated.

Keep in mind that this is for your basic vanilla airspeed indicator and does not include calculations for TRUE Airspeed for which you must include the variables of True Temperature and True Altitude.

Stay tuned for upcoming Blogs

## Pitot Static System…. Inside & Out

Pitot Static System ….Inside & Out

A. Pitot Pressure:
Pronounced: PEE-TOE, it is a French word

Pitot pressure is the measurement of the air forced into the Pitot Tube by the movement of the aircraft through the air. Pitot tubes are mounted on the aircraft facing forward so that air is forced into them. Most small aircraft have only one tube, larger aircraft have a redundant system and will have two tubes. The most common manufacturer of these tubes is Rosemont Corp. which is a division of BF Goodrich. Also on larger aircraft, those that fly at higher altitudes, the Pitot Tube is heated in order to prevent icing, smaller aircraft typically do not have this function.

The Pitot Tube is connected directly to the back of the airspeed indicator (the Pitot input) and if the aircraft is so equipped also to the Air Data Computer via a hose which is typically either plastic or rubber

B. Static Pressure:

Static pressure is the measurement of the ambient barometric pressure at the aircraft’s CURRENT location AND CURRENT Altitude.
The Static Port is located in a position on the aircraft that will not be affected by air flow as the aircraft moves through the air. This is typically on the side of the fuselage but can also be on the back side of the Pitot Tube or any other number of locations, it varies by the aircraft. Again smaller aircraft will typically have one Static Port, larger aircraft with redundant systems will have two.

The Static Port is connected directly to the following equipment, depending on aircraft configuration: The Airspeed Indicator (Static Input), the Altimeter, the Vertical Speed Indicator, the Altitude Encoder, the Air Data Computer. Again connection is typically made via a hose either rubber or plastic.

C.  Airspeed Calculation:

Airspeed is calculated as a function of the difference between Pitot Pressure and Static Pressure as follows:

Calculated or Indicated airspeed is indicated airspeed corrected for instrument errors, position error (due to incorrect pressure at the static port) and installation errors.

Calibrated airspeed values less than the speed of sound at standard sea level (661.4788 knots) are calculated as follows:

minus position and installation error correction.

Stay tuned for upcoming Blogs

## All About Altimeters

General Information

The altimeter provides the basic function of indicating to the pilot the altitude of the aircraft above mean (average) sea level (MSL).  The indicator is normally a 31/8” size dial face with multiple pointers or a combination of pointers and counter drum. Location of this indicator is typically in the top row of instruments near the center of the instrument panel. In a standard “T” configuration panel the altimeter is just to the right of the attitude gyroscope.

Types of Altimeters

The various types of altimeters include:

1. Three pointer altimeter
2. Counter Drum Altimeter
3. Encoding Altimeter

Typical altimeter ranges are:

1. –1000 Ft. to +20,000 Ft.
2. –1000 Ft. to +35,000 Ft.
3. –1000 Ft. to +50,000 Ft.
4. –1000 Ft. to +80,000 Ft.

Most general aviation altimeters will fall into the first two ranges. Ranges above 35,000 Ft. are typically corporate jets, commercial aircraft, and military aircraft.

Three Pointer Altimeter

The three-pointer altimeter is the most common type of instrument used in general aviation. It is named as such because it utilizes three pointers in order to display the current altitude. One pointer is used to display 100 Ft. increments. A second pointer is used to display 1000 Ft. increments and the third pointer displays 10,000 Ft. increments. The Technical Information Section of this document provides instructions on how to properly read a three-pointer altimeter.

Counter Drum Altimeter

The counter-drum altimeter is named as such because it displays altitude utilizing a single pointer and a rotating drum that displays digits. The drum displays ten thousand and one thousand foot increments. The pointer displays from 0 to 999 feet.

Encoding Altimeter

An encoding altimeter can be of either the three-pointer or counter drum type of altimeter with an encoding module built into it. The encoding module takes the altitude information and converts that data into a digital code. This code is then sent via a set of wires to the aircraft transponder. A transponder is a radio device that reports the aircraft altitude to ground control radar.

Blind Encoder

The blind encoder is a very special type of altimeter. This unit has no dial or read out that is visible to the user. It has only an electronic output to the aircraft transponder. The use of a standard altimeter in conjunction with a blind encoder is often more economical than purchasing an encoding altimeter.